Discovery of the Narrow-Line Seyfert 1 galaxy Mkn 335 in an historical low X-ray flux state

a r X i v :a s t r o -p h /0103059v 1 4 M a r 2001Mon.Not.R.Astron.Soc.000,000–000(0000)Printed 1February 2008(MN L A T E X style file v1.4)Stellar populations in the nuclear regions of nearbyradiogalaxiesItziar Aretxaga 1,Elena Terlevich 1⋆,Roberto J.Terlevich 2†,Garret Cotter 3,´Angeles I.D´ıaz 41Instituto Nacional de Astrof´ısica,´Optica y Electr´o nica,Apdo.Postal 25y 216,72000Puebla,Pue.,Mexico 2Institute of Astronomy,Madingley Road,Cambridge CB30HA,U.K.3Cavendish Laboratory,Univ.of Cambridge,Madingley Road,Cambridge CB30HE,U.K.4Dept.F´ısica Te´o rica C-XI,Univ.Aut´o moma de Madrid,Cantoblanco,Madrid,Spain.1February 2008ABSTRACTWe present optical spectra of the nuclei of seven luminous (P 178MHz >∼1025W Hz −1Sr −1)nearby (z <0.08)radiogalaxies,which mostly correspond to the FR II class.In two cases,Hydra A and 3C 285,the Balmer and λ4000˚A break indices constrain the spectral types and luminosity classes of the stars involved,re-vealing that the blue spectra are dominated by blue supergiant and/or giant stars.The ages derived for the last burst of star formation in Hydra A are between 7and 40Myr,and in 3C 285about 10Myr.The rest of the narrow-line radiogalaxies (four)have λ4000˚A break and metallic indices consistent with those of elliptical galaxies.The only broad-line radiogalaxy in our sample,3C 382,has a strong featureless blue continuum and broad emission lines that dilute the underlying blue stellar spectra.We are able to detect the Ca II triplet in absorption in the seven objects,with good quality data for only four of them.The strengths of the absorptions are similar to those found in normal elliptical galaxies,but these values are both consistent with single stellar populations of ages as derived from the Balmer absorption and break strengths,and,also,with mixed young+old populations.Key words:galaxies:active –galaxies:starbursts –galaxies:stellar content1.INTRODUCTIONIn recent years new evidence that star formation plays an important role in Active Galactic Nuclei (AGN)has been gathered:•The presence of strong Ca II λλ8494,8542,8662˚A triplet (CaT)absorptions in a large sample of Seyfert 2nuclei has provided direct evidence for a population of red supergiant stars that dominates the near-IR light (Terlevich,D´ıaz &Terlevich 1990).The values found in Seyfert 1nuclei are also consistent with this idea if the dilution produced by a nuclear non-stellar source is taken into account (Terlevich,D´ıaz &Terlevich 1990,Jim´e nez-Benito et al.2000).The high mass-to-light ratios L (1.6µm)/M inferred in Seyfert 2nuclei also indicate that red supergiants dominate the nuclear light⋆Visiting Fellow at IoA,UK†Visiting Professor at INAOE,Mexico (Oliva et al.1995),but a similar conclusion does not holdfor Seyfert 1nuclei.•The absence of broad emission lines in the direct optical spectra of Seyfert 2nuclei which show broad lines in polar-ized light can be understood only if there is an additional central source of continuum,most probably blue stars (Cid Fernandes &Terlevich 1995,Heckman et al.1995).This con-clusion is further supported by the detection of polarization levels which are lower in the continuum than in the broad lines (Miller &Goodrich 1990,Tran,Miller &Kay 1992).•Hubble Space Telescope imaging of the Seyfert Mrk 447reveals that the central UV light arises in a resolved region of a few hundred pc,in which prominent CaT absorption and broad He II λ4686˚A emission lines reveal the red super-giant and Wolf Rayet stars of a powerful starburst.The stars dominate the UV to near-IR light directly received from the nucleus (Heckman et al.1997).At least 50per cent of the light emitted by the nucleus is stellar,as a conservative es-timate.Mrk 447is not a rare case:a large sample of nearby bright Seyfert 2s and LINERs show similar resolved star-c0000RAS2I.Aretxaga,E.Terlevich,R.Terlevich,G.Cotter,A.I.D´ıazburst nuclei of80to a few hundred pc in size(Colina et al. 1997,Gonz´a lez-Delgado et al.1998,Maoz et al.1995,1998), with some of the Seyfert2containing dominant Wolf-Rayet populations(Kunth&Contini1999,Cid Fernandes et al. 1999).A starburst–AGN connection has been proposed in at least three scenarios:starbursts giving birth to massive black holes(e.g.Scoville&Norman1988);black holes being fed by surrounding stellar clusters(e.g.Perry&Dyson1985,Peter-son1992);and also pure starbursts without black holes(e.g. Terlevich&Melnick1985,Terlevich et al.1992).The evi-dence for starbursts in Seyfert nuclei strongly supports some kind of connection.However,it is still to be demonstrated that starbursts play a key role in all kinds of AGN.One of the most stringent tests to assess if all AGN have associated enhanced nuclear star formation is the case of lobe-dominated radio-sources,whose host galaxies have relatively red colours when compared to other AGN vari-eties.In this paper we address the stellar content associated with the active nuclei of a sample of FR II radiogalaxies, the most luminous class of radiogalaxies(Fanaroff&Ri-ley1974)which possess the most powerful central engines and radio-jets(Rawlings&Saunders1991).The presence of extended collimated radio-jets,which fuel the extended radio structure over>∼108yr,strongly suggests the exis-tence of a supermassive accreting black hole in the nuclei of these radiogalaxies.This test addresses the question of whether AGN that involve conspicuous black holes and ac-cretion processes also contain enhanced star formation.In section2we introduce the sample and detail the data acquisition and reduction processes.In section3we provide continuum and line measurements of the most prominent features of the optical spectra of the radiogalaxies.In sec-tion4we discuss the main stellar populations responsible for the absorption and continuum spectra.In section5we offer notes on individual objects.A sumary of the main con-clussions from this work is presented in section6.2.DATA ACQUISITION AND REDUCTION Our sample of radiogalaxies was extracted from the3CRR catalogue(Laing,Riley and Longair1983)with the only selection criteria being edge-brightened morphology,which defines the FR II class of radiogalaxies(Fanaroff&Ri-ley1974),and redshift z<0.08.This last condition was imposed in order to be able to observe the redshifted CaT at wavelengths shorter thanλ9300˚A,where the atmo-spheric bands are prominent.Six out of a complete sam-ple of ten FR II radiogalaxies that fulfill these require-ments were randomly chosen.In addition to this sub-sample of FR IIs,we observed the unusually luminous FR I ra-diogalaxy Hydra A(3C218).This has a radio luminosity of P178MHz=2.2×1026W Hz−1Sr−1,which is an order of magnitude above the typical FR I/FR II dividing luminos-ity.Spectroscopic observations of a total of seven radio-galaxies,one normal elliptical galaxy to serve as reference andfive K III stars to serve as velocity calibrators were per-formed using the double-arm spectrograph ISIS mounted in the Cassegrain Focus of the4.2m William Herschel Tele-scope‡in La Palma during two observing runs,in1997 November7–8and1998February19–20.Thefirst run was photometric but the second was not,being partially cloudy on the20th.The seeing,as measured from the spatial di-mension of spectrophotometric stars,was between0.7and0.8arcsec throughout the nights.A slit width of1.2arcsec centered on the nucleus of galaxies and stars was used.We oriented the slit along the radio-axis for all radiogalaxies,except for Hydra A,for which the orientation was perpendicular to the radio-axis.An R300B grating centered atλ4500˚A with a2148x4200 pixel EEV CCD and an R316R grating centered atλ8800˚A with a1024x1024pixel TEK CCD were used in the1998 run.The projected area on these chips is0.2arcsec/pixel and0.36arcsec/pixel respectively.This configuration pro-vides the spectral resolution necessary to resolve the Mg b and CaT features and,at the same time,offers a wide spec-tral span:λ3350˚A—λ6000˚A at5.1˚A resolution in the blue andλ7900˚A—λ9400˚A at3.5˚A resolution in the red.In the 1997run,in which we assessed the viability of the project, we used the R600B and R600R gratings instead.This setup covers theλ3810˚A—λ5420˚A andλ8510˚A—λ9320˚A range in the blue and red arm,at2.6and1.7˚A resolution respectively. Just one radiogalaxy(DA240)was observed with this alter-native setup.The dichroics5700and6100were used in1997 November and1998February,and in both runs we used a filter to avoid second order contamination in the spectra.We obtainedflux standards(HZ44and G191-B2B)for the four nights and gratings,except in1998Feb20,when we were unable to acquire the red spectrum of the correspond-ing standard due to a technical failure.One calibration lamp CuAr+CuNe exposure per spectral region and telescope po-sition was also obtained for all objects.The total integration times for the radiogalaxies(from1 to3hr)were split into time intervals of about1200or1800s in order to diminish the effect of cosmic rays on individual frames and allow to take lampflat-fields with the red arm of the spectrograph between science exposures.The TEK CCD has a variable fringing pattern at the wavelengths of interest, such that the variations are correlated with the position at which the telescope is pointing.Sinceflat-fielding is crucial for the reddest wavelengths,where the sky lines are most prominent,after every exposure of20to30min we acquired aflat-field in the same position of the telescope as the one for which the galaxies were being observed.We followed this procedure with all galaxies except with DA240.The same procedure was also used in the case of the elliptical galaxy, splitting its total integration time in two.Table1summarizes the journal of observations,where column1gives the name of the object;column2the radio-power at178MHz;column3the redshift;column4the integrated V magnitude of the galaxy;column5identifies whether the object is a radiogalaxy(RG),a normal elliptical (E)or a star(S);column6gives the date of the beginning of the night in which the observations were carried out;col-umn7the position angle(PA)of the slit;column8the total ‡The William Herschel Telescope is operated on the island of La Palma by the Isaac Newton Group in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrof´ısica de Canariasc 0000RAS,MNRAS000,000–000Stellar populations in the nuclear regions of nearby radiogalaxies3exposure time;column9the grating used;and column10 the corresponding linear size to1arcsec at the redshift of the galaxies(for H0=50km s−1Mpc−1).The data for the radiogalaxies were extracted from the3C Atlas(Leahy,Bri-dle&Strom,/atlas/)and for the host galaxy of Hydra A from the3CR Catalogue(de Vaucouleurs et al.1991).The data were reduced using the IRAF software pack-age.The frames werefirst bias subtracted and thenflat-field corrected.In the case of the red arm spectra,the different flats obtained for a single object were combined when no sig-nificant differences were detected between them.However,in several cases the fringing pattern shifted positions that ac-counted for differences of up to20per cent.In these cases we corrected each science frame with theflat-field acquired immediately before and/or afterwards.Close inspection of the faintest levels of theflat-fielded frames showed that the fringing had been successfully eliminated.Wavelength and flux calibration were then performed,and the sky was sub-tracted by using the outermost parts of the slit.The atmospheric bands,mainly water absorption at λ8920˚A—λ9400˚A,affect the redshifted CaT region of sev-eral radiogalaxies.The bands have been extracted using a template constructed from the stellar spectra obtained each night.The template was built averaging the normalizedflux of spectrophotometric and velocity standard stars,once the stellar absorption lines had been removed.The atmospheric bands were eliminated from the spectra of the galaxies di-viding by theflux-scaled template.This reduces the S/N of the region under consideration,especially since the bands are variable in time and one of our observing nights was par-tially cloudy.However,the technique allows the detection of the stellar atmospheric features.The CaT of the elliptical galaxy is not affected by atmospheric absorption.Figure1shows the line spectrum of the sky and,as an example,the atmospheric absorption template of1998 Feb19.Water-band correction proved to be critical for the detection of the CaT lines when the atmospheric conditions were most adverse.Figure2shows extractions of the nuclear2arcsec of the spectra of the galaxies.This corresponds to844to2020pc for the radiogalaxies,and98pc for the normal elliptical galaxy.3.LINE AND CONTINUUMMEASUREMENTS3.1.CaT indexThe CaT was detected in all of the objects,although in three cases(3C285,3C382and4C73.08)it was totally or par-tially affected by residuals left by the atmospheric band cor-rections and the measurement of its strength was thus pre-cluded.For the remaining cases,the strength was measured in the rest-frame of the galaxies against a pseudo-continuum, following the definition of the CaT index of D´ıaz,Ter-levich&Terlevich(1989).In Hydra A,3C285and3C382, the red continuum band is seriously affected by residuals left from the atmospheric absorption removal.We defined two alternative continuum bands,8575˚A<λ<8585˚A and 8730˚A<λ<8740˚A,that substitute the red-most contin-uum window of the CaT index.We checked this new defini-tion against the original one in the elliptical galaxy,which doesn’t have residuals in its continuum bands,and the agree-ment between the two systems was good within5per cent.Velocity dispersions were measured by cross-correlating the galaxy spectra with the stellar spectra obtained with the same setup.The errors in the velocity dispersions calculated in this way were less than10per cent.A high velocity dispersion tends to decrease the mea-sured values of indices based on EW measurements.The CaT index has to be corrected from broadening of the ab-sorption lines by the corresponding velocity dispersion.In order to calculate the correction we convolved stellar pro-files with gaussian functions of increasing width,and mea-sured the CaT index in them.A good description of the cor-rection found for our data is given by the functional form ∆EW(˚A)=(σ(km s−1)−100)/200.The corrections were applied to the values measured in the galaxies,and con-verted into unbroadened indices.The values of velocity dispersions(σ),uncorrected EW (CaT u)and corrected EW(CaT),are listed in Table2. 3.2.λ4000˚A and Balmer Break indicesStellar populations can be dated through the measurement of theλ4000˚A or Balmer breaks.In intermediate to old pop-ulations the discontinuity atλ4000˚A results from a combi-nation of the accumulation of the Balmer lines towards the limit of the Balmer absorption continuum atλ3646˚A(the Balmer break)and the increase in stellar opacity caused by metal lines shortwards ofλ4000˚A.Table3lists the values of theλ4000˚A break index,∆4000˚A,measured in the spectra of the6narrow-line ra-diogalaxies and the elliptical galaxy in our sample.This ex-cludes3C382,which has a spectrum dominated by a strong blue continuum and broad-emission lines,and shows very weak stellar atmospheric features and no break.We adopted the definition given by Hamilton(1985),which quantifies the ratio of the averageflux-level of two broad bands,one cov-ering the break(3750-3950)and one bluewards of the break (4050-4250).Both bands contain strong metallic and Balmer absorption lines in the case of normal galaxies.In active galaxies,the measurement can be contaminated by emission of[Ne III]λ3869˚A,which in our case is weak.The contami-nation by high-order Balmer lines in emission is negligible. The net effect of emission contamination is to decrease the Balmer break index.In the radio-galaxies,we have estimated this effect by interpolating the continuum levels below the [Ne III]emission,and we estimate that the ratio can be af-fected by6per cent at worst,in the case of3C192,and by less than3per cent for the rest of the objects.Table3lists emission-devoid indices.Hydra A and3C285have spectra which are much bluer than those of normal elliptical galaxies.In order to quantify better the strength of the break and the ages of the popula-tions derived,we have performed a bulge subtraction using as template the spectrum of NGC4374,scaled to eliminate the G-band absorption of the radiogalaxies.Since the ve-locity dispersion of the stars in NGC4374and in the ra-diogalaxies are comparable inside the spectral resolution of our data,no further corrections were needed.The G-band absorption is prominent in stars of spectral types later thanc 0000RAS,MNRAS000,000–0004I.Aretxaga,E.Terlevich,R.Terlevich,G.Cotter,A.I.D´ıazF5and it is especially strong in types K.NGC4374is a normal elliptical galaxy,with a spectral shape which com-pares well with those of other normal ellipticals in the spec-trophotometric atlas of galaxies of Kennicutt(1992).Thus, by removing a scaled template of NGC4374,we are isolat-ing the most massive stars(M>∼1M⊙)in the composite stellar population of the radiogalaxies.Figure3shows the bulge subtractions obtained on these two radiogalaxies.We measured on the bulge-subtracted spectra∆4000˚A and also the Balmer break index as defined by the classi-cal Dλ1method of stellar classification designed by Barbier and Chalonge(Barbier1955,Chalonge1956,see Str¨o mgren 1963).The latter quantifies the Balmer discontinuity in terms of the logarithmic difference of the continuum levels (D)and the effective position of the break(λ1).The method places a pseudo-continuum on top of the higher order terms of the Balmer series in order to measure the effective posi-tion of the discontinuity.Figure4shows the placement of continua,pseudo-continua and the measurements of D and λ1for an A2I star from the stellar library of Jacoby,Hunter &Christian(1984).The functional dependences on the ef-fective temperature and gravity of the stars are sufficiently different for D andλ1to satisfy a two-dimensional classifi-cation.The Dλ1method could only be reliably applied in the cases of Hydra A and3C285.For the other radiogalaxies, the bulge-subtractions led to results that did not allow the identification of the absorption features and/or the break in an unambiguous way due to the resulting poor S/N.Fig-ure5shows the Dλ1measurements performed on the bulge-subtracted spectra of Hydra A and3C285.We have placed different continuum levels to estimate the maximum range of acceptable parameters of the stellar populations that are involved.Table3lists theλ4000˚A and Balmer break indices mea-sured in both the bulge-subtracted and the original spectra of the radiogalaxies.3.3.Lick indicesThe presence of prominent Balmer absorption lines,from Hγup to H12λ3750˚A,is one of the most remarkable features of the blue spectra of two of the seven radiogalaxies,while Hβand Hαarefilled up by conspicuous emission lines.A clear exception to the presence of the Balmer series in absorption is the broad-line radiogalaxy3C382.In order to estimate the Balmer strength,crucial to date any young stellar population involved,we use the EW of the H10λ3798˚A line,which appears only weakly contaminated by emission in the radiogalaxies.H10is chosen as a compro-mise of an easily detectable Balmer line that shows both a minimum of emission contamination and clear wings to mea-sure the adjacent continuum.The Balmer lines from Hβto H9λ3836˚A are contaminated by prominent emission,which in Case B recombination comes in decreasing emission ra-tios to Hβof1,0.458,0.251,0.154,0.102,0.0709(Osterbrock 1989);H10has an emission contamination of0.0515×Hβ. At the same time,the absorption strengths are quite similar from Hβto H10,although the EW(H10)is actually sys-tematically smaller than EW(Hβ)in young to intermediate-age populations.Gonz´a lez-Delgado,Leitherer&Heckman (2000)obtain,in their population synthesis models,ratios of EW(Hβ)/EW(H10)between1.3and1.6for bursts with ages0to1Gyr and constant or coeval star formation histo-ries.Lines of order higher than10have decreasing emission contamination,but they also increasingly merge towards the Balmer continuum limit.A caveat in the use of H10as an age calibrator comes from the fact that this line might be contaminated by metal-lic lines in old populations.Although our measurements of H10in NGC4374are around1.5˚A,an inspection of the spec-tra of three elliptical galaxies(NGC584,NC720,NGC821) observed in the same wavelegth range(but with lower S/N) and archived in the Isaac Newton Group database,indicates that a wide range of EW(H10),from2to4˚A,could char-acterize elliptical galaxies,while their Hβindices are in the 1to2˚A regime.If confirmed by better data,these results could indicate that although the upper Balmer series is de-tected in elliptical galaxies,it could indeed be contaminated by the absorptions of other species.Clearly,more work needs to be done in the near-UV spectra of elliptical galaxies be-fore conclusive evidence can be derived for the behaviour of EW(H10)in old stellar systems,and its contamination by metallic lines.In all the radio-galaxies observed in this work,the H10 profile is narrow and reproduces the shape of the wings of the lower-order Balmer absorption lines.Hydra A and3C285 clearly provide the bestfittings.As an illustration,Figure6 shows the estimated absorption line profiles for the Hβ,Hγand Hδlines,assuming a constant ratio between their EWs and that of H10,and also a scaled(×1.4)H10profile for the case of Hβin Hydra A.We also measured indices that are mostly sensitive to the metal content of the stellar populations involved. The Lick indices of Mg and Fe(e.g.Worthey et al.1994) serve this purpose.In order to avoid the contribution of [O III]λ4959˚A to the continuum measurement for the molec-ular index Mg2,we have displaced the lower continuum band of this index to4895.125˚A<λ<4935.625˚A.This redefini-tion does not alter the value of the index in the elliptical galaxy,which shows no[O III]emission.Table4compiles the EW of H10,and the metallic in-dices Mg b,Fe5270,Fe5335,[MgFe],Mg2of the Lick system, measured in the rest-frame of the galaxies in our sample.The atomic indices are affected by broadening,like the CaT in-dex,while Mg2is only affected by lamp contributions in the original IDS Lick system(Worthey et al.1994,Longhetti et al.1998).We have calculated broadening corrections as in section3.1for the atomic lines,and adopted the correc-tions calculated by Longhetti(1998)for the molecular lines. The uncorrected values of these indices are denoted with a subindex u in Table4.The errors of the individual line and molecular indices were estimated adopting continua shifted from the bestfit continua by±1σ.This lead to average er-rors between an8and a10per cent for individual line and molecular indices,and∼6per cent for[MgFe].The agreement between our measurements of Lick in-dices and those carried out by other authors(Gonz´a lez1993, Davies et al.1987,Trager et al.2000a)on our galaxy in com-mon,NGC4374,is better than10per cent.4.DISCUSSIONc 0000RAS,MNRAS000,000–000Stellar populations in the nuclear regions of nearby radiogalaxies5parison with elliptical galaxies andpopulation synthesis modelsThe analysis of the spectral energy distributions and colours of elliptical galaxies suffers from a well known age-metallicity degeneracy(Aaronson et al.1978).However,this is broken down when the strengths of suitable stellar absorption lines are taken into account(e.g.Heckman1980).The plane com-posed by the[Hβ]and[MgFe]indices,in this sense,can dis-criminate the ages and metallicities of stellar systems.It is on the basis of this plot,that a large spread of ages in ellip-tical galaxies has been suggested(Gonz´a lez1993).Bressan, Chiosi&Tantalo(1996)claim,however,that when the UV emission and velocity dispersion of the galaxies are taken into account,the data are only compatible with basically old systems that have experienced different star formation histories(see also Trager et al.2000a,2000b).A recent burst of star formation that involves only a tiny fraction of the whole elliptical mass in stars,would rise the[Hβ]index to values characteristic of single stellar populations which are 1to2Gyr old(Bressan et al.1996).Most likely,the stellar populations of radiogalaxies are also the combination of different generations.Direct sup-port for this interpretation in the case of Hydra A comes from the fact that the stellar populations responsible for the strong Balmer lines are dynamically decoupled from those responsible for the metallic lines(Melnick,Gopal-Krishna& Terlevich1997).This interpretation is also consistent with the modest ∆4000˚A measurements we have obtained.Figure7shows a comparison of the values found in radiogalaxies,with those of normal elliptical,spiral and irregular galaxies,including starbursts,from the atlas of Kennicutt(1992).The radio-galaxies3C98,3C192,4C73.08and DA240have indices of the order of1.9to2.3,which overlap with those of normal E galaxies,∆4000˚A=2.08±0.23.These values correspond to populations dominated by stars of ages1to10Gyr old, if one assumes the coeval population synthesis models of Longhetti et al.(1999).However,Hydra A and3C285have indices in the range1.4to1.6,typical of coeval populations which are200to500Myr old.Once the bulge population is subtracted,the∆4000˚A indices of Hydra A and3C285 decrease to1.2and1.0respectively,which are typical of systems younger than about60Myr.Hamilton(1985)measured the∆4000˚A index in a sam-ple of stars covering a wide range of spectral types and lu-minosity classes.He found a sequence of increasing∆4000˚A from B0to M5stars,with values from1to4mag respec-tively.A comparison with the sequence he found leads us to conclude that the break in the bulge subtracted spectrum of Hydra A is dominated by B or earlier type stars while that of3C285is dominated by A type stars.The index ∆4000˚A does not clearly discriminate luminosity classes for stars with spectral types earlier than G0.The equivalent width of the H10absorption line in these two radiogalaxies give further support to the inter-pretation of the Balmer break as produced by a young stel-lar population.In Hydra A wefind after bulge subtraction EW(H10)≈3.9˚A,which,according to the synthesis models of Gonz´a lez-Delgado et al.(2000)gives ages of7to15Myr for an instantaneous burst of star formation,and40to 60Myr for a continuous star formation mode,in solar metal-licity environments.In the case of3C285,EW(H10)≈6˚A would imply an age older than about25Myr for a single-population burst of solar metallicity.The metallic indices of normal elliptical galaxies range between the values0.56<∼log[MgFe]<∼0.66(Gonz´a lez 1993),which characterizes oversolar metallicites for ages larger than about5Gyr.This is also the typical range of our radiogalaxies,although3C285shows a clear departure with log[MgFe]≈0.4.However,[MgFe]tends to be smaller for populations younger than a few Gyr and similar overso-lar metallic content.Since3C285has a clear burst of recent star-formation,we conclude that its overall abundance is also most probably solar or oversolar.4.2.The blue stellar contentA better estimate of the spectral type and luminosity class of the stars that dominate the break in Hydra A and3C285 comes from the two-dimensional classification of Barbier and Chalonge.In Figure8the solid squares connected by lines represent the maximum range of possible Dλ1values mea-sured in these radiogalaxies.The Balmer break index is sensitive to the position-ing of the pseudo-continuum on top of the higher order Balmer series lines,which in turn is sensitive to the merging of the wings of the lines,enhanced at large velocity dis-persions.In order to assign spectral types and luminosity classes to the stars that dominate the break,therefore,it is not sufficient to compare the values we have obtained with those measured in stellar catalogues.The values mea-sured for the radiogalaxies can be corrected for their in-trinsic velocity dispersions;we have chosen instead to recal-ibrate the index using template stars of different spectral types and luminosity classes convolved with gaussian func-tions,until they reproduce the width of the Balmer lines observed in the radiogalaxies(FWHM≈12.5˚A).We used the B0to A7stars from the stellar library of Jacoby et al. (1984),which were observed with4.5˚A resolution.The val-ues of the Dλ1indices measured in these broadened stars are represented in Figure8by their respective classification. By comparison we also plot the grid traced by the locus of unbroadened stars,as published by Str¨o mgren(1963).The broadening of the lines shifts the original locus of supergiant stars from theλ1<∼3720˚A range(Chalonge1956)to the 3720<∼λ1<∼3740˚A range,occupied by giant stars in the original(unbroadened)classification.Giant stars,in turn, shift to positionsfirst occupied by dwarfs.Most dwarfs have Balmer line widths comparable to those of the radiogalaxies, and thus their locus in the diagram is mostly unchanged.The value of the D index indicates that the recent burst in Hydra A is dominated by B3to B5stars,and the effective position of the Balmer break(λ1)indicates that these are gi-ant or supergiant stars,respectively.These stars have masses of7and20M⊙(Schmidt-Kaler1982).From the stellar evo-lutionary tracks of massive stars with standard mass-loss rate at Z⊙or2Z⊙(Schaller et al.1992,Schaerer et al.1993, Meynet et al.1994)we infer that these stars must have ages between7to8Myr(B3I)and40Myr(B5III).Note that the B4V stars in Figure8,near the location of Hydra A, cannot originate the break and at the same time follow the kinematics of the nucleus(see section5.3).Any dwarf star located in the stellar disk of Hydra A would show absorptionc 0000RAS,MNRAS000,000–000。

发现神秘船英语阅读High-tech search vehicles found a famous shipwreck on the ocean floor near Antarctica,an international exploration team announced Wednesday.The famous polar explorer Ernest Shackleton's ship,named Endurance,sank in the dangerous and icy Weddell Sea in 1915.Search teams looked for the Endurance before,but were not able to find it because of the rough conditions.A group organized by the Falklands Maritime Heritage Trust used special cameras and search vehicles to find the Endurance.John Shears of Great Britain led the search team,which operated from a South African ice-breaking ship.He and the crew found the Endurance in good condition on the ocean floor about six kilometers from its last-recordedposition.Mensun Bound is the team's Director of Exploration.He said the team is feeling happy about the discovery."This is by far the finest said.Hecondition"brilliant."Shackleton's story of survival is one of the most famousHis 28-man crew was trying to make a land crossing of the South Pole,but never arrived on land.The crew members escaped the sinking ship and all made it home two years after the wreck.The men rowed over 1,000 kilometers on life boats and survived by eating seals and penguins.They eventually got help from people working in thewhaling industry far off the coast of the southern part of Argentina.The successful expedition to find the ship comes 100 years after Shackleton's death.Dan Snow,a British broadcaster and historian,was aboard the exploration ship.He said the ship itself has only been photographed and nothing was removed,as it is protected by the Antarctic Treaty.The treaty permits only peaceful,scientific observation and exploration of the area.一支国际探险队周三宣布，高科技搜索工具在南极洲附近的海底发现了一艘著名的沉船。

高一自然探索英语阅读理解20题1<背景文章>The tropical rainforest is one of the most fascinating ecosystems on Earth. It is a place of extraordinary beauty and biodiversity. The rainforest is home to a vast array of plant and animal species, many of which are found nowhere else.The canopy of the rainforest is a complex and diverse layer. It is filled with tall trees that reach up to the sky. These trees provide shelter and food for countless animals. Monkeys, birds, and insects are just a few of the creatures that call the canopy home.Underneath the canopy, there is a layer of understory. This area is darker and more humid than the canopy. Here, you can find smaller plants and animals that have adapted to living in the shade. Ferns, mosses, and fungi grow in abundance.The rainforest floor is covered with fallen leaves and branches. This layer is teeming with life as well. Insects, worms, and small mammals scurry about, looking for food and shelter.However, the tropical rainforest is facing many threats. Deforestation is one of the biggest concerns. Logging, mining, and agriculture are all contributing to the destruction of the rainforest. Climate change is alsohaving an impact. Rising temperatures and changing rainfall patterns are affecting the delicate balance of the ecosystem.To protect the tropical rainforest, many measures are being taken. Conservation organizations are working to raise awareness about the importance of the rainforest. Governments are implementing laws and regulations to limit deforestation. And individuals can also make a difference by reducing their consumption of products that contribute to deforestation.1. The tropical rainforest is known for its ___.A. simplicityB. biodiversityC. uniformityD. barrenness答案：B。

高一人类与发现英语阅读理解25题1<背景文章>Since the dawn of human civilization, the vast expanse of space has always been a source of great fascination. Humans have long gazed at the stars, wondering what lies beyond our planet.The journey of human space exploration began in earnest in the 20th century. One of the most significant events was the launch of Sputnik 1 by the Soviet Union in 1957. This small satellite was the first artificial object to orbit the Earth, and it marked the beginning of the Space Age. It was a huge shock to the world and spurred the United States to accelerate its own space program.Then came the Apollo program in the United States. The Apollo 11 mission in 1969 was a milestone in human history. Astronauts Neil Armstrong and Buzz Aldrin became the first humans to set foot on the moon. This event not only demonstrated the great technological capabilities of humanity but also inspired generations to come.However, space exploration has not been without difficulties. The extreme environment of space presents numerous challenges. For example, microgravity can cause various health problems for astronauts, such as muscle atrophy and bone loss. The high - energy radiation in space is alsoa major threat to astronauts' health. In addition, the cost of space exploration is extremely high. Building rockets, developing spacecraft, and conducting research all require a large amount of financial resources.Despite these difficulties, the significance of space exploration for humanity is immeasurable. Firstly, it has greatly expanded our understanding of the universe. Through space exploration, we have learned more about the planets, stars, and galaxies in the universe. Secondly, space exploration has also promoted the development of technology. Many technologies that we use in our daily lives today, such as satellite communication and GPS, are the fruits of space exploration. Finally, space exploration also represents the spirit of human exploration and the pursuit of the unknown. It encourages us to constantly break through boundaries and strive for greater development.1. What was the significance of Sputnik 1?A. It was the first manned spacecraft.B. It was the first artificial object to orbit the Earth.C. It was the first spacecraft to land on the moon.D. It was the first spacecraft to reach Mars.答案：B。

2021 年 6 月大学英语四级考试真题(第 2 套)答案解析Part I Writing (30 minutes)Directions: For this part, you are allowed 30 minutes to write an essay titled “Is technology making people lazy?”The statement given below is for your reference. You should write at least120 words but no more than 180 words.Many studies claim that computers distract people, make them lazy thinkers and evenlower their work efficiency.【参考范文】Is technology making people lazy?No one could deny the fact that we are living in an age where the advancements of technology are continuing to accelerate and changing every aspect of our life. At the same time, there has been widespread public debate over whether technology can make people lazy.On the one hand, some people hold the view that technological advancements have really offered more convenient and effective choices for us to communicate, learn and work. For example, learners are flooded with learning opportunities at their fingertips. But on the other hand, there is a risk that technology can make people lazy. This is due to the fact that modern people nowadays are heavily reliant on technological inventions. For instance, many young people always indulge in online social media platforms or computer games and thus are reluctant to do physical exercise on a regular basis. Besides, some students depend on using a calculator to work out simple math problems.In conclusion, technological advancements can bring us both benefits and problems. In view of the risk mentioned above, I highly suggest that we should avoid relying too much on technology. 【解析】这篇作文需要就题目给出的问题Is technology making people lazy? 发表自己的看法。

《海底两万里》读书笔记800字英文回答："20,000 Leagues Under the Sea" is a classic science fiction novel written by Jules Verne. It tells the story of Professor Pierre Aronnax, a French marine biologist, who embarks on a journey aboard the submarine Nautilus, commanded by Captain Nemo. Throughout their underwater adventures, they encounter various marine creatures and explore the wonders of the deep sea.One of the main themes in the book is the exploration and discovery of the unknown. As the characters ventureinto the depths of the ocean, they encounter strange and fascinating creatures, such as giant squids and prehistoric animals. This theme reflects humanity's innate curiosity and desire to uncover the mysteries of the world.Another important aspect of the book is the conflict between nature and technology. Captain Nemo represents thepower of technology, as he controls the advanced submarine and uses it to explore the sea. However, his actions also have negative consequences, as he destroys ships and kills sailors. This raises questions about the ethicalimplications of scientific progress and the potential dangers of unchecked technological advancement.Furthermore, the book explores the theme of isolation and the longing for freedom. The characters are confined to the submarine for extended periods of time, cut off fromthe outside world. This sense of confinement and longingfor freedom is exemplified by the character of Ned Land, a harpooner who constantly dreams of returning to the surface. This theme resonates with readers who may have experienced feelings of isolation or a desire for freedom in their own lives.Overall, "20,000 Leagues Under the Sea" is acaptivating and thought-provoking novel that combines adventure, exploration, and philosophical themes. It not only entertains readers with its thrilling underwater adventures, but also raises important questions abouthumanity's relationship with nature and technology.中文回答：《海底两万里》是由朱尔斯·凡尔纳创作的一部经典科幻小说。

a r X i v :a s t r o -p h /0412513v 1 20 D e c 2004What is the origin of the soft excess in AGN?Małgorzata Sobolewska ∗and Chris Done †∗Copernicus Astronomical Center,Warsaw,Poland †University of Durham,Durham,UK Abstract.We investigate the nature of the soft excess below 1keV observed in AGN.We use the XMM-Newton data of the low redshift,optically bright quasar,PG 1211+143,and we compare it with the Narrow Line Seyfert 1galaxy,1H 0707-495,which has one of the strongest soft excesses seen.We test various ideas for the origin of the soft X-ray excess,including a separate spectral com-ponent (for example a low temperature Comptonized component),a reflection-dominated model,or a complex absorption model.All three can give good fits to the data,and χ2fitting criteria are not sufficient to discriminate among them.Instead,we favor the complex absorption model on the grounds that it is the most physically plausible.INTRODUCTION Several models are considered in the literature to explain the origin of the soft excess below 1keV in AGN,which cannot be explained by either of the two emission com-ponents usually considered in accreting black holes,namely the accretion disk and the high energy power law Comptonized emission.Spectra with a strong soft excess also often show a strong deficit at ∼7keV which again has no obvious identification.Partial covering models allow for a spatially non-uniform cold absorber attenuating only a fraction of intrinsic radiation.They can explain the sharp features around 7keV .However,they require an enormous overabundance of iron (5-30times the Solar value [1];5times the Solar value [2]),and they cannot simultaneously explain the soft X-ray emission.Thus,we do not consider partial covering models in our analysis as they only provide a method to explain the sharp feature around 7keV .The soft excess may originate in a distinct unknown physical process which manifests itself as a separate spectral component (Model 1).It can be modeled e.g.with low temperature Comptonization models [3]).The apparent temperature of this component is rather similar (∼0.1−0.3keV)across a diverse selection of AGN (e.g.[4]).An obvious way to produce a fixed soft excess energy is to relate it to atomic processes rather than continuum emission.In reflection models,the dramatic strength of the soft excess requires that the source is reflection dominated (Model 2).This might happen if the disc fragments at high accretion rates,hiding the hard X-ray source among many clumps.Such models can successfully fit the spectra,but need a large range in ionization states of the reflecting material,and supersolar abundances ([5]).Alternatively,the strong jump in opacity for partially ionized material could result in a soft excess from absorption (Model 3,[6]).The underlying continuum may be modeled by only one component.The soft excess and hardening of the spectrum at high energies would be only artifacts of absorption acting at 1-2keV ,while the H-like iron K alpharesonance absorption from the same material could produce the deficit at∼7keV.RESULTSThe bestfit models(and their components)together with the data to model ratios are shown in Figure1.The models are additionally modified by galactic absorption, cold absorption at the redshift of the source,and one(in1H0707-495)or two(in PG1211+143)warm absorbers modeling the narrow absorption features.Thus,the only thing that differentiates the three models is the description of the origin of the soft excess.FIGURE1.Modeling the soft excess in PG1211+143and1H0707-495.Red:the bestfit spectra.Left: Model1–a low temperature Comptonization(blue),power law(magenta)and ionized reflection(green). In1H0707-495there is no need for the intrinsic power law.Middle:Model2–three reflectors(green, magenta and blue)with different column densities and ionization states,located at different radii.Right: Model3–a power law(blue)and reflection(green)subject to relativistically smeared absorption.TABLE1.Results of spectralfits to the PG1211+143and1H0707-495dataPG1211+143989(939)972(937)998(939)1H0707-495311(288)292(283)318(287)χ2of1.10and1.08,respectively).The bestfit is obtained with the model of complex reflection(with iron abundance set to2times the Solar abundance)with reducedχ2of 1.03.The values ofχ2and number of degrees of freedom infits are presented in Table1.DISCUSSION AND CONCLUSIONSBased only on theχ2criterion it is not possible to uniquely distinguish between the three kinds of models as each of them provides an adequate description.Moreover, many model uncertainties can contribute toχ2,e.g.in both the reflection and absorption scenarios we expect an(unknown!)range of ionization states to be present.Hence direct comparison ofχ2can be misleading when the models are known to be incomplete. Instead,we should be guided as well by physical plausibility.The model with a distinct component involves an emission from an unknown physical process,with unknown processfixing its typical energy,which does not seem to have an analogue in the spectra of galactic black holes(GBHs)[7],and cannot simultaneously explain the7keV feature.By contrast,both reflection and absorption are much more plausible,as they give a physical reasonfixed energy for the soft excess and can reproduce the structure around iron K.However,the reflection models require quite strong supersolar abundances,and there is no evidence for reflection dominated spectra in the GBH systems.The absorption model seems to reproduce the strong soft excesses well with moderate column densities(∼1022−23cm−2)of solar abundance material.Such material would not be seen in the GBHs because it would be completely ionized by the much higher accretion disc temperatures seen in the stellar mass black hole systems.Thus the com-plex absorption model provides an interesting alternative because(1)it does not require a separate soft component in the spectra,(2)the hard radiation slope resulting from the fits is similar to that of GBHs in the high/soft state,(3)it describes the spectra of AGNs in terms of atomic processes,explaining the universal shape of the soft excess.ACKNOWLEDGMENTSThis work was partially supported by the Polish Committee for Scientific Research through grants1P03D01626and2P03D00322.REFERENCES1.Tanaka,Y.,Boller,T.,Gallo,L.,Keil,R.,&Ueda,Y.2004,PASJ,56,L92.Gallo,L.C.,Tanaka,Y.,Boller,T.,et al.,W.N.2004,MNRAS,353,10643.Magdziarz,P.,Blaes,O.M.,Zdziarski,A.A.,Johnson,W.N.,&Smith,D.A.1998,MNRAS,301,1794.Czerny,B.,Nikołajuk,M.,Ró˙z a´n ska,A.,et al.2003,A&A,412,3175.Fabian,A.C.,Ballantyne,D.R.,Merloni,A.,et al.2002,MNRAS,331,L356.Gierli´n ski,M.&Done,C.2004,MNRAS,349,L77.Gierli´n ski,M.&Done,C.2004,MNRAS,347,885。

a journey of discovery课文阅读"A Journey of Discovery" is a text about a person's personal journey of self-discovery and growth. The text highlights the importance of stepping out of one's comfort zone and embracing new experiences to uncover one's true potential.The protagonist of the story is a young woman named Sarah who has always been confined by her fears and insecurities. She lives a monotonous and predictable life, always sticking to familiar routines. However, deep inside her heart, she yearns for something more meaningful and fulfilling.One day, Sarah decides to embark on a journey of self-discovery. She leaves her familiar surroundings behind and ventures into the unknown. At first, she is filled with anxiety and doubt, questioning if she is making the right decision. But as she takes the first step into the unknown, she feels a sense of excitement and anticipation.Throughout her journey, Sarah encounters various challenges and obstacles that test her resilience and determination. She learns to adapt to new environments, meet new people, and try new things. Each experience teaches her valuable lessons about herself and the world around her.As Sarah moves forward on her journey, she begins to shed her insecurities and fears. She starts to embrace her uniqueness and discover her true passions and talents. She realizes that life is a constant journey of growth and transformation, and that the only way to truly live is to step out of her comfort zone and embrace new experiences.By the end of her journey, Sarah has transformed into a confident and self-assured individual. She has gained a renewed sense of purpose and direction in life. She has discovered her true identity and has the courage to pursue her dreams and aspirations.The text concludes by emphasizing the importance of embarking on a journey of self-discovery. It encourages readers to overcome their fears and take risks in order to uncover their true potential. It highlights the transformative power of new experiences and the profound impact they can have on one's life.In summary, "A Journey of Discovery" is a text that explores the transformative power of stepping out of one's comfort zone and embracing new experiences. It tells the story of Sarah's personal journey of self-discovery and growth, highlighting the lessons she learns and the changes she undergoes along the way.。

海底两万里第1部分1章点评主旨英文回答：The main theme of Part 1, Chapter 1 of "Twenty Thousand Leagues Under the Sea" is the introduction of the protagonist and the setting of the story. In this chapter, the narrator, Professor Pierre Aronnax, introduces himself and his background as a scientist. He also explains how he ended up on the ship, the Abraham Lincoln, which is on a mission to hunt down a mysterious sea creature that has been terrorizing ships.The chapter begins with Professor Aronnax describing his fascination with the ocean and his desire to exploreits depths. He talks about his previous experiences as a naturalist and his interest in marine life. This sets up his character as someone who is knowledgeable and passionate about the sea.The main event of the chapter occurs when the AbrahamLincoln encounters the sea creature. The crew of the ship engages in a battle with the creature, but they are unableto capture or kill it. Professor Aronnax, along with his loyal servant Conseil, and Ned Land, a Canadian harpooner, end up overboard and are eventually rescued by the mysterious creature.Throughout the chapter, the author, Jules Verne, uses vivid descriptions to bring the story to life. For example, when describing the battle with the sea creature, he writes, "The waves were dyed red over a vast space, and our ship floated amidst a blood-red sea." This imagery creates a sense of danger and excitement.The main purpose of this chapter is to set the stagefor the rest of the story. It introduces the maincharacters and their motivations, as well as the central conflict of the sea creature. It also hints at the mysterious nature of the creature and the unknown worldthat lies beneath the surface of the ocean.中文回答：《海底两万里》第一部分第一章的主旨是介绍主人公和故事的背景。

TPO 07 Paragraph 11．The wordin thepassage is closest in meaning to○achievement○requirement○purpose○feature2．Which of the following is NOT mentioned in paragraph 1 as a change that occurred in the fauna of the Mediterranean?○Most invertebrate species disappeared during a wave ofextinctions.○A few hardy species wiped out many of the Mediterranean’sinvertebrates.○Some invertebrates migrated to Atlantic Ocean.○New species of fauna populated the Mediterranean whenThe Geologic History ofthe MediterraneanIn 1970 geologists Kenneth J. Hsu and William B.F. Ryan were collecting research data while aboard the oceanographicresearch vessel Glomar Challenger. An of this particular cruise was to investigate the floor of the Mediterranean and to resolve questions about its geologic history. One question was related to evidence that the invertebrate fauna (animals without spines) of the Mediterranean had changed abruptly about 6 million years ago. Most of the older organisms were nearly wiped out, although a few hardy species survived. A few managed to migrate into the Atlantic. Somewhat later, the1the old migrants returned.Paragraph 33．What does the author imply by○The most obvious explanation for the origin of the pebbles was not migrants returned, bringing new species with them. Why did the near extinction and migrations occur?■Another task for the Glomar Challenge r’s scientists was to try to determine the origin of the domelike masses buried deep beneath the Mediterranean seafloor. ■These structures had been detected years earlier by echo-sounding instruments, but they had never been penetrated in the course of dri lling. ■Were they salt domes such as are common along the United States Gulf Coast, and if so, why should there have been so much solid crystalline salt beneath the floor of the Mediterranean? ■With question such as these clearly before them, the scientists2supported by the evidence.○The geologists did not find as many pebbles as they expected.○The geologists were looking for a particular kind of pebble.○The different pebbles could not have come from only one source.4．Which of the following can be inferred from paragraph 3 about the solid gypsum layer?○It did not contain any marine fossil.○It had formed in open-ocean conditions.○It had once been soft, deep-sea mud.○It contained sediment from nearby deserts.5. Select the TWO answer choice from paragraph 3 that identify materials discovered in the deepest part of the Mediterranean basin. To receive credit aboard the Glomar Challenger processed to the Mediterranean to search for the answers. On August 23, 1970, they recovered a sample. The sample consisted of pebbles of gypsum and fragments of volcanicIn the days following, samples of solid gypsum were repeatedly brought on deck as drilling operations penetrated the seafloor. Furthermore, the gypsum was found to possess peculiarities of composition and structure that suggested it had formed on desert flats. Sediment above and below the gypsum layer contained tiny marine fossils, indicating open-ocean conditions. As they drilled into the central and deepest part of the Mediterranean basin, the3you must select TWO answers.○Volcanic rock fragments.○This silt layers○Soft, deep-sea mud○Crystalline salt6. What is the main purpose of paragraph 3?○To describe the physical evidence collected by Hsu and Ryan.○To explain why some of the questions posed earlier in the passage could not be answered by the findings of the Glomar Challenger.○To evaluate techniques used by Hsu and Ryan to explore the sea floor.○To describe the most difficult problems faced by the GlomarChallenger expedition.Paragraph 47. According to paragraph 4, which of the following was responsible for the evaporation of the Mediterranean’s scientists took solid, shiny, crystalline salt from the core barrel. Interbedded with the salt were thin layers of what appeared to be windblown silt.The time had come to formulate a hypothesis. The4waters?○The movements of Earth’s crust○The accumulation of sediment layers○Changes in the water level of the Atlantic Ocean○Changes in Earth’s temperature8. The word “scores” in the passage is closest in meaning to○members○large numbers○populations○different types9. According to paragraph 4, what caused most invertebrate species in the Mediterranean to become extinct?○The evaporation of chemicals necessary for their survival○Crustal movements that connected the Mediterranean to the investigators theorized that about 20 million years ago, the Mediterranean was a broad seaway linked to the Atlantic by two narrow straits. Crustal movements closed the straits, and the landlocked Mediterranean began to evaporate. Increasing salinity caused by the evaporation resulted in the extermination ofof invertebrate species. Only a few organisms especially tolerant of very salty conditions remained. As evaporation continued, the remaining brine (salt water) became so dense that the calcium sulfate of the hard layer was precipitated. In the central deeper part of the basin, the last of the brine evaporated to precipitate more soluble sodium chloride (salt). Later, under the weight of overlying sediments, this salt flowed plastically upward to5saltier Atlantic○The migration of new species through the narrow straits○Their inability to tolerate the increasing salt content of theMediterranean10. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.○The strait of Gibraltar reopened when the Mediterranean and the Atlantic became connected and the cascades of water from one sea to the other caused crustal adjustments and faulting.○The Mediterranean was dramatically refilled by water from the Atlantic when crustal adjustments and faulting opened the Strait of Gibraltar, the place where the two seas are joined.○The cascades of water from the form salt domes. Before this happened, however, the Mediterranean was a vast desert 3,000 meters deep. Then, about 5.5 million years ago came the deluge.tore into the hardened salt flats, broke them up, and ground them into the pebbles observed in the first sample taken by the Challenger. As the basin was refilled, normal marine organisms returned. Soon layer of oceanic ooze began to accumulate above the old hard layer.The salt and gypsum, the faunal changes, and the unusual gravel provided abundant6Atlantic to the Mediterranean were not as spectacular as the crustal adjustments and faulting that occurred when the Strait of Gibraltar was connected to those seas.○As a result of crustal adjustments and faulting and the creation of the Strait of Gibraltar, the Atlantic and Mediterranean were connected and became a single sea with spectacular cascades of water between them.11. The word “Turbulent” in the passage is closest in meaning to○fresh○deep○violent○temperateParagraph 212. Look at the four squares ■ that indicate where the following sentence could be added to the passage.Thus, scientists had information about the shape of the domes but not evidence that the Mediterranean was once a desert.gypsum: a mineral made of calcium sulfate and water7about their chemical composition and origin.Where would the sentence best fit?13．An expedition to the Mediterranean answered some long-standing questions about the ocean’s history.●●●Answer choices1. The Glomar Challenger expedition investigated changes in invertebrate fauna and some unusual geologic features.2. Researchers collected fossils to determine which new species migrated from the Atlantic with older species.3. Scientists aboard the Glomar Challenger were the first to discover the existence of domelike masses underneath the seafloor.4. Samples recovered from the■Another task for the Glomar Challenger’s scientists was to try to determine the origin of the domelike masses buried deep beneath the Mediterranean seafloor. ■These structures had been detected years earlier by echo-sounding instruments, but they had never been penetrated in the course of drilling. ■Were they salt domes such as are common along the United States Gulf Coast, and if so, why should there have been so much solid crystalline salt beneath the floor of the Mediterranean? ■8旗开得胜expedition revealed importantdifferences in chemical composition andfossil distribution among the sedimentlayers.5. Evidence collected by the GlomarChallenger supports geologists' beliefsthat the Mediterranean had evaporatedand become a desert, before it refilledwith water.6. Mediterranean salt domes formedafter crustal movements opened thestraits between the Mediterranean andthe Atlantic, and the Mediterraneanrefilled with water.9旗开得胜10Paragraph 11. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.○The regularity and power of stone walls inspired Romans attempting to unify the parts of their realm.○Although the Romans used different types of designs when building their walls, they used regular controls to maintain their realm.○Several types of control united the Roman realm, just as design and cement held Roman walls together.○Romans built walls to unite the various parts of their realm into a single entity, which was controlled by powerful laws.2. According to paragraph 1, all of the following are controls that held together the roman world EXCEPTAncient Rome and GreeceThere is a quality of cohesiveness about the Roman world that applied neither to Greece nor perhaps to any other civilization, ancient or modern. Like the stone of Roman wall, which were held together both by the regularity of the design and by that peculiarly powerful Roman cement, so the various parts of the Roman realm were bonded into a massive, monolithic entity by physical, organizational, and psychological controls. The physical bonds included the network of military garrisons, which were stationed in every province, and the network of stone-built roads that linked the provinces with Rome. The organizational bonds were based on the common principles of law and administration and on the universal army of officials who enforced common standards of conduct. The psychological controls were built on fear and punishment —on the absolute certainty○administrative and legal systems○the presence of the military○a common language○transportation networksParagraph 23.The phrase “obsession with” in the passage is closest in meaning to○thinking about○fixation on○interest in○attitude toward4.According to paragraph 2, which of the following was NOT characteristic of Rome’s early development?○Expansion by sea invasion○T erritorial expansion○Expansion from one original settlement ○Expansion through invading armies5.Why does the author mention “Alexander the Great” in the passage?○T o acknowledge that Greek civilization that anyone or anything that threatened the authority of Rome would be utterly destroyed.The source of Roman obsession with unity and cohesion may well have lain in the pattern of Rome’s early development. Whereas Greece had grown from scores of scattered cities, Rome grew from one single organism. While the Greek world had expanded along the Mediterranean seas lanes, the Roman world was assembled by territorial conquest. Of course, the contrast is not quite so stark: in Alexander the Great the Greeks had found the greatest territorial conqueror of all time; and the Romans, once they moved outside Italy, did not fail to learn the lessons of sea power. Yet the essential difference is undeniable. The Key to the Greek world lay in its high-11also expanded by land conquest○T o comp are Greek leaders to Roman leaders○T o give an example of Greek leader whom Romans studied○T o indicate the superior organization of the Greek militaryParagraph 36.is closest in meaning to○accepted○combined○introduced○encouraged7.Paragraph 3 suggests which of thefollowing about the people of Latium?○Their economy was based on trade relations with other settlements.○They held different values than the people of Rome.○Agriculture played a significant r ole in the society. powered ships; the key to Roman power lay in its marching legions. The Greeks were wedded to the sea; the Romans, to the land. The Greek was a sailor at heart; the Roman, a landsman.Certainly, in trying to explain the Roman phenomenon, one would have to place great emphasis on this almost instinct for the territorial imperative. Roman priorities lay in the organization, exploitation, and defense of their territory. In all probability it was the fertile plain of Latium, where the Latins who founded Rome originated, that created the habits and skills of landed settlement, landed property, landed economy, landed administration, and a12○They possessed unusual knowledge of animal instinctsParagraph 48.Paragraph 4 indicates that somehistorians admire Roman civilization because of○the diversity of cultures within Roman society○its strength○its innovative nature○the large body of literature that it developed9.In paragraph 4, the author develops adescription of Roman civilization by○comparing the opinions of Roman intellectuals to Greek intellectuals○identifying which characteristics of roman civilization were copied from Greece○explaining how the differences between Roman and Greece developed as time passed○contrasting characteristics of Roman land-based society. From this arose the Roman genius for military organization and orderly government. In turn, a deep attachment to the land, and to the stability which rural life engenders,the Roman virtues: gravitas, a sense of responsibility, peitas, a sense of devotion to family and country, and iustitia, a sense of the natural order.Modern attitudes to Roman civilization range from the infinitely impressed to the thorough disgusted. ■As always, there are the power worshippers, especially among historians, who are predisposed to admire whatever is strong, who feel more attracted to the might of Rome than to the subtlety of Greece. ■At the same time, there is a solid body of opinion that dislikes Rome. ■For many, Rome is at best the imitator and the continuator of Greece on a larger scale. ■Greek civilization had quality; Rome,13civilization with characteristics of Greek civilization10.According to paragraph 4, intellectual Romans such as Horace held which of the following opinions about their civilization?○Ancient works of Greece held little value in the Roman world.○The Greek civilization had been surpassed by the Romans.○Roman civilization produced little that was original or memorable.○Romans valued certain types of innovations that had been ignored by ancient Greeks.Paragraph 5mere quantity. Greece was the inventor; Rome, the research and development division. Such indeed was the opinion of some of the more intellectual Romans.” had the Greeks held novelty in such disdain as we,” asked Ho race in his Epistle, “what work of ancient date would now exist?”Rome’s debt to Greece was enormous. The Romans adopted Greek14Paragraph 611.The wordin thepassage is closest in meaning to○abilities○areas○combinations○models12.Which of the following statements about leading Roman soldiers and statesmen is supported by paragraphs 5 and 6?○They could read and write the Greek language.○They frequently wrote poetry and plays.○They focused their writing on military matters.○They wrote according to the philosophical laws of the Greeks.Paragraph 413.Look at the four squares ■ that religion and moral philosophy. In literature, Greek writers were consciously used as models by their Latin successors. It was absolutely accepted that an educated Roman should be fluent in Greek. In speculative philosophy and the sciences, the Romans made virtually no advance on early achievements.Yet it would be wrong to suggest that Rome was somehow a junior partner in Greco-Roman civilization. The Roman genius was projected into newespecially into those of law, military organization, administration, and engineering. Moreover, the tensions that arose within the Roman state produced literary and artistic sensibilities of the highest order. It was no accident that many leading Roman soldiers and statesmen were writers of high caliber.15indicate where the following sentence could be added to the passage.They esteem symbols of Roman power, such as the massive Colosseum. Where would the sentence best fit?14.The Roman world drew its strength from several important sources●●●Answer choices1. Numerous controls imposed by Roman rulers held its territory together.2. The Roman military was organized differently from older military organizations.3. Romans valued sea power as did the Latins, the original inhabitants of Rome.4. Roman values were rooted in a strong attachment to the land and the stability of rural life.5. Rome combined aspects of ancient Greek civilization with its own contributions in new areas. civilization range from the infinitely impressed to the thorough disgusted. ■As always, there are the power worshippers, especially among historians, who are predisposed to admire whatever is strong, who feel more attracted to the might of Rome than to the subtlety of Greece. ■At the same time, there is a solid body of opinion that dislikes Rome. ■For many, Rome is at best the imitator and the continuator of Greece on a larger scale. ■Greek civilization had quality; Rome, mere quantity. Greece was the inventor; Rome, the research and development division. Such indeed was the opinion of some of the more intellectual Romans.” had the Greeks held novelty in such166. Educated Romans modeled their own literature and philosophy on the ancient Greeks disdain as we,” asked Horace in his Epistle, “what work of ancient date wo uld now exist?”17Paragraph 11.The wordin thepassage is closest in meaning to○emerged○was understood○spread○developed2.According to paragraph 1, why do researchers doubt that agriculture developed independently in Africa?○African lakes and rivers already provided enough food for people to survive without agriculture.○The earliest examples of cultivated plants discovered in Africa are native to Asia.○Africa’s native plants are very difficult to domesticate.○African co mmunities were not large enough to support agriculture.无老师网站:ibtsat3.In paragraph 1, what does theAgriculture, Iron, andthe Bantu PeoplesThere is evidence of agriculture in Africa prior to 3000 B.C. It may have developed independently, but many scholars believe that the spread of agriculture and iron throughout Africa linked it to the major centers of the Near East and Mediterranean world. The drying up of what is now the Sahara desert had pushed many peoples to the south into sub-Sahara Africa. These peoples settled at first in scattered hunting-and-gathering bands, although in some places near lakes and rivers, people who fished, with a more secure food supply, lived in larger population concentrations. Agriculture seems to have reached these people from the Near East, since the first domesticated crops were millets and sorghums whose18author imply about changes in the African environment during this time period?○The climate was becoming milder, allowing for a greater variety of crops to be grown.○Although periods of drying forced people south, they returned once their food supply was secure.○Population growth along rivers and lakes was dramatically decreasing the availability of fish.○A region that had once supported many people was becoming a desert where few could surviveParagraph 24.According to paragraph 2,camels were important because they ○were the first domesticated animal to be introduced to Africa○allowed the people of the West African savannahs to carve out large empires origins are not African but west Asian. Once the idea of plantingtheir own crops, such as certain varieties of rice, and they demonstrated a continued receptiveness to new imports. The proposed areas of the domestication of African crops lie in a band that extends from Ethiopia across southern Sudan to West Africa. Subsequently, other crops, such as bananas, were introduced from Southeast Asia.Livestock also came from outside Africa. Cattle were introduced from Asia, as probably were domestic sheep and goats.19○helped African peoples defend themselves against Egyptian invaders○made it cheaper and easier to cross the Sahara5.According to paragraph 2, which of the following were subjects of rock paintings in the Sahara?○Horses and chariots○Sheep and goats○Hyksos invaders from Egypt○Camels and cattleParagraph 36.What function does paragraph 3 serve in the organization of the passage as a whole○It contrasts the development of iron technology in West Asia and West Africa. Horses were apparently introduced by the Hyksos invaders of Egypt (1780-1560 B.C.) and then spread across the Sudan to West Africa. Rock paintings in the Sahara indicate that horses and chariots were used to traverse the desert and that by 300-200 B.C., there were trade routes across the Sahara. Horses were adopted by peoples of the West African savannah, and later their powerful cavalry forces allowed them to carve out large empires. Finally, the camel was introduced around the first century A.D. This was an important innovation, because the camel’s abilities to thrive in harsh desert conditions and to carry large loads cheaply made it an effective and efficient means of transportation. The camel transformed the desert from a barrier into a still difficult, but more20○It discusses a non-agricultural contribution to Africa from Asia.○It introduces evidence that a knowledge of copper working reached Africa and Europe at the same time.○It compares the rates at which iron technology developed in different parts of Africa.Paragraph 47.The wordin thepassage is closest in meaning to ○fascinating○far-reaching○necessary○temporary8.Theword in thepassage is closest in meaning to ○military○physical○ceremonial accessible, route of trade and communication.Iron came from West Asia, although its routes of diffusion were somewhat different than those of agriculture. Most of Africa presents a curious case in which societies moved directly from a technology of stone to iron without passing through the intermediate stage of copper or bronze metallurgy, although some early copper-working sites have been found in West Africa. Knowledge of iron making penetrated into the forest and savannahs of West Africa at roughly the same time that iron making was reaching Europe. Evidence of iron making has been found in Nigeria, Ghana, and Mali.This technological shift causein the complexity of African societies. Iron21○permanent9.According to paragraph 4, all of the following were social effects of the new metal technology in Africa EXCEPT: ○Access to metal tools and weapons created greater social equality.○Metal weapons increased the power of warriors.○Iron tools helped increase the food supply.○T echnical knowl edge gave religious power to its holders.Paragraph 510.Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information.○While American iron makers developed the latest furnaces, African iron makers continued using earlier represented power. In West Africa the blacksmith who made tools and functions. Iron hoes, which made the land more productive, and iron weapons, which made the warrior more powerful, had symbolic meaning in a number of West Africa societies. Those who knew the secrets of making ironand sometimes political power.22techniques.○Africans produced iron much earlier than Americans, inventing technologically sophisticated heating systems.○Iron making developed earlier in Africa than in the Americas because of the ready availability of carbon and iron ore.○Both Africa and the Americas developed the capacity for making iron early, but African metallurgy developed at a slower rate.Paragraph 611.The wordin thepassage is closest in meaning to○afraid of○displaced by○running away from○responding to12.Paragraph 6 mentions all of the following as possiblecauses of theright into the Iron Age, taking the basic technology and adapting it to local; conditions and resources.The diffusion of agriculture and later of iron was accompanied by a great movement of people23“Bantu explosion” EXCEPT○superior weapons○better hunting skills○peaceful migra tion○increased populationParagraph 613.Look at the four squares ■ that indicate where the following sentence could be added to the passage.T hese people had a significant linguistic impact on the continent as well.Where would the sentence best fit?14.Agriculture and iron working probably spread to Africa from neighboring regions.●●●Answer choices who may have carried these innovations. These people probably originated in eastern Nigeria. ■Their migration may have been set in motion by an increase in population caused by a movement ofthe desiccation, or drying up, of the Sahara. ■They spoke a language, prior-Bantu (“Bantu” means “the people”), which is the parent tongue of a language of a large number of Bantu languages still spoken throughout sub-Sahara Africa. Why and how these people spread out into central and southern Africa remains a mystery, but archaeologists believe that their iron weapons allowed them to conquer their hunting-gathering opponents, who still used stone implements. ■Still, the process is uncertain, and peaceful migration—or simply rapid241 .Once Africans developed their own crops, they no longer borrowed from other regions.2. The harshness of the African climate meant that agriculture could not develop until after the introduction of iron tools.3. The use of livestock improved transportation and trade and allowed for new forms of political control.4. As the Sahara expanded, the camel gained in importance, eventually coming to have religious significance.5. The spread of iron working had far-reaching effects on social, economic, and political organization in Africa.6. Today's Bantu-speaking peoples are descended from a technologically advanced people who spread throughout Africa. demographic growth—may have also caused the Bantu explosion. ■25。