Clumpy photon-dominated regions in Carina. I. [CI] and mid-J CO lines in two 4'x4' fields

a r X i v :0711.1320v 1 [a s t r o -p h ] 8 N o v 2007

Astronomy &Astrophysics manuscript no.7815c

ESO 2008February 2,2008

Clumpy photon-dominated regions in Carina

I.[C i ]and mid-J CO lines in two 4′×4′?elds.

C.Kramer 1,M.Cubick 1,M.R¨o llig 3,K.Sun 1,Y.Yonekura 2,M.Aravena 3,F.Bensch 3,F.Bertoldi 3,

L.Bronfman 4,M.Fujishita 5,Y.Fukui 5,U.U.Graf 1,M.Hitschfeld 1,N.Honingh 1,S.Ito 5,H.Jakob 1,K.Jacobs 1,U.Klein 3,B.-C.Koo 6,J.May 4,https://www.doczj.com/doc/d617370857.html,ler 1,Y.Miyamoto 5,N.Mizuno 5,T.Onishi 5,Y.-S.Park 6,

J.L.Pineda 3,D.Rabanus 1,H.Sasago 5,R.Schieder 1,R.Simon 1,J.Stutzki 1,N.Volgenau 1,and

H.Yamamoto 5

1KOSMA,I.Physikalisches Institut,Universit¨a t zu K¨o ln,Z¨u lpicher Stra?e 77,D-50937K¨o ln,Germany 2Department of Physical Science,Osaka Prefecture University,Osaka 599-8531,Japan 3Argelander-Institut f¨u r Astronomie,Auf dem H¨u gel 71,D-53121Bonn,Germany 4Departamento de Astronom ′?a,Universidad de Chile,Casilla 36-D,Santiago,Chile 5Department of Astrophysics,Nagoya University,Chikusa-ku,Nagoya 464-8602,Japan 6

Seoul National University,Seoul 151-742,Korea

Received /Accepted

ABSTRACT

Context.The Carina region is an excellent astrophysical laboratory for studying the feedback mechanisms of newly born,very massive stars within their natal giant molecular clouds (GMCs)at only 2.35kpc distance.

Aims.We use a clumpy PDR model to analyse the observed intensities of atomic carbon and CO and to derive the excitation conditions of the gas.

Methods.The NANTEN2-4m submillimeter telescope was used to map the [C i ]3P 1?3P 0,3P 2?3P 1and CO 4–3,7–6lines in two 4′×4′regions of Carina where molecular material interfaces with radiation from the massive star clusters.One region is the northern molecular cloud near the compact OB cluster Tr 14,and the second region is in the molecular cloud south of ηCar and Tr 16.These data were combined with 13CO SEST spectra,HIRES/IRAS 60μm and 100μm maps of the FIR continuum,and maps of 8μm IRAC/Spitzer and MSX emission.

Results.We used the HIRES far-infrared dust data to create a map of the FUV ?eld heating the gas.The northern region shows an FUV ?eld of a few 103in Draine units while the ?eld of the southern region is about a factor 10weaker.While the IRAC 8μm emission lights up at the edges of the molecular clouds,CO and also [C i ]appear to trace the H 2gas column density.The northern region shows a complex velocity and spatial structure,while the southern region shows an edge-on PDR with a single Gaussian velocity component.We constructed models consisting of an ensemble of small spherically symmetric PDR clumps within the 38′′beam (0.43pc),which follow canonical power-law mass and mass-size distributions.We ?nd that an average local clump density of 2105cm ?3is needed to reproduce the observed line emission at two selected interface positions.

Conclusions.Stationary,clumpy PDR models reproduce the observed cooling lines of atomic carbon and CO at two positions in the Carina Nebula.

Key words.ISM:clouds,ISM:structure,ISM:individual objects:Carina

1.Introduction

1.1.The importance of atomic carbon

The ?ne structure lines of atomic carbon are strong coolants of the interstellar medium (ISM)throughout the universe:in Galactic clouds (e.g.Jakob et al.2007),in the Milky Way as a whole (Fixsen et al.1999),as well as

in

2Kramer et al.:Clumpy photon-dominated regions in Carina

models of photon-dominated regions(PDRs)predict that atomic carbon is formed in a surface layer by recombi-nation of C+and dissociation of CO.This appears to be in contradiction with atomic carbon emission which is observed even at large distances from UV sources.The dynamics of the ISM may play a decisive role,allowing to explain the distribution of[C i]with time dependent chemical models(Oka et al.2004;St¨o rzer et al.1997).

However,stationary,but clumpy PDR models have been successful in explaining e.g.extended[C i]3P1?3 P0and13CO2?1emission in S140(Spaans1996; Spaans&van Dishoeck1997).Inside a clumpy PDR, the UV radiation can penetrate much deeper than it would be possible in a homogeneous layer(Boiss′e1990). Meixner&Tielens(1993)showed that the line intensi-ties of all lines are enhanced compared to a homogeneous model with the same average density.Juvela et al.(2001) presented a model to apply Monte Carlo radiative transfer calculations to the results of magnetohydrodynamic cal-culations to account for a clumpy and turbulent structure. They also found that local density condensations lead to an increased cooling e?ciency and reduced photon trap-ping.Another approach is to describe both the turbulent velocity?eld and the density structure by their statisti-cal properties.Hegmann et al.(2007)calculate CO cool-ing rates based on a stochastic radiative transfer model, which accounts for density and velocity?uctuations with a?nite correlation length.

Here,we study the distribution of atomic carbon and warm CO in the Carina star forming region and test clumpy models using the KOSMA-τPDR model (St¨o rzer et al.1996;R¨o llig et al.2007)to derive the exci-tation conditions of the gas.Spaans et al.model the inho-mogeneous structure with a Monte-Carlo code,assuming a ?xed clump/interclump density ratio of10.In contrast,we assume that all emission analyzed stems from the clumps. The in?uence of the interclump medium or a halo lead-ing to pre-shielding of CO has been discussed by Bensch (2006)and Bensch et al.(2003),who also used KOSMA-τ, but is not considered here.To describe the clumpy struc-ture,we assume that the clumps are distributed follow-ing the canonical clump mass and mass-size distributions which have been found in molecular clouds.

1.2.The Carina nebula

The Carina nebula is a very prominent southern star-forming region at a distance of 2.35kpc(Smith 2006b).This giant molecular cloud was?rst observed by Grabelsky et al.(1988)as part of the Columbia CO1–0 survey of the Milky Way.They derived a total mass of 6.7105M⊙and an e?ective radius of66pc.In total65O-type stars,including6of the11O3-type stars known in the Milky Way(Smith2006a),produce a strong UV?eld and strong stellar winds which interact vigorously with the material in the surrounding molecular clouds.This high concentration of the earliest-type stars is unique in the Galaxy and may serve as a template for more extreme but more distant regions containing stellar super clus-ters like the central regions of NGC253or the Antennae (Bayet et al.2006;Schulz et al.2007).The Carina nebula extends more than4square degrees on the sky.It exhibits a peculiar morphological structure on all scales.Massive stars are being born in several regions within molecu-lar condensations,located mainly to the south-east and north-west of the cluster Trumpler16,which is centered atηCar,a luminous blue variable star.ηCar is embed-ded in the Homunculus nebula(e.g.Smith2006a)and its luminosity has changed drastically and repeatedly in the past centuries,leading to strong variations of the FUV ?eld impinging on the surrounding clouds.Its current lu-minosity of5106L⊙makes it one of the brightest celestial infrared objects(Cox1995).In the northern part of the Carina nebula,the stellar population is dominated by the cluster Tr14.Recently,Oberst et al.(2006)reported the detection of the[N ii]line at205μm at the radio peak of the Carina II H ii region using SPIFI at AST/RO.They compared their data with[C ii]data(Mizutani et al.2004, 2002)and concluded that about a third of the[C ii]emis-sion stems from a low-density ionized medium.For a re-cent overview of the Carina region,see Smith&Brooks (2007).

Carina was mapped at～3′resolution in the CO4–3 and[C i]3P1?3P0lines by Zhang et al.(2001)using the AST/RO1.7m telescope.These AST/RO data show large-scale[C i]emission,coextensive with CO4–3.

Here,we have used the4m NANTEN2telescope to map12CO in the rotational transitions J=4–3,7–6,and [C i]in the?ne structure transitions3P1?3P0,and

3P2?3P1(henceforth1–0and2–1)at sub-arcminute res-olutions in two4′×4′regions of Carina(Fig.1).

One region to the north ofηCar covers the cloud inter-face with Tr14.The second region covers another cloud interface to the south ofηCar and Tr16.

The northern molecular cloud to the west of Tr14 (Fig1)contains several sites of massive star forma-tion.Di?use PAH3.29μm emission has been found by Rathborne et al.(2002)to trace the sharp edge of the cloud.Peak intensities at the edge towards the Car I H ii region are almost10times higher than in the other re-gions of Carina.Car I-E is interacting with the front face of the GMC and creating a PDR seen edge-on(Brooks et al. 2003;Brooks et al.2001).Car I-W manifests a second PDR seen face-on(cf.Fig.2).

The CO2–1map of Cox(1995)shows a sharp rim of gas delineating the southern molecular cloud,lo-cated south ofηCar and the Tr16cluster.Several IRAS sources are located along the edge.A prominent peak in PAH3.29μm emission is the ultra compact H ii region IRAS10430?5931(Rathborne et al.2002).

Kramer et al.:Clumpy photon-dominated regions in Carina

3

Fig.1.Overview of the Carina clouds near ηCar lying at 0/010:45:03.59-59:41:04.3(J2000)at the center of the Tr 16cluster.Left:Estimate of the FUV ?ux χin Draine units at a resolution of ～1′and derived from HIRES/IRAS.Dashed contours range from 400to 800in steps of 200.Solid contours range from 103to 5103in steps of 103.Right:MSX emission at 8μm at a resolution of ～20′′.Contours are 1to 10in steps of 110?5Wm ?2sr ?1(cf.Figs.7,11in Rathborne et al.2002).Note the di?raction artefacts near ηCar.The center position of the OB cluster Tr 14is marked by a triangle.The two 4′×4′regions mapped with NANTEN2are delineated by boxes.Crosses in the left panel mark two cuts discussed in the text.

Table 1.Physical parameters derived from the observed integrated intensities I in K kms ?1and intensity ratios R 74

CO =I (CO 7–6)/I (CO 4–3),R 21C =I ([C i ]2–1)/I ([C i ]1–0),R 14CCO =I ([C i ]1–0)/I (CO 4–3)from Gaussian ?ts to the line pro?les at two interface positions.The calibration error of the integrated intensities is estimated to be 15%.

?α/?δ13

CO CO [C i ]R 74CO R 21C R 14CCO

T ex N (CO)N (C)N (H 2)

M C/CO

(′,′)

2–14–37–61–02–1

K

M ⊙

2.NANTEN2observations

We used the new NANTEN24m telescope situated at 4865m altitude at Pampa La Bola in northern Chile to map two regions in Carina in CO 4–3and 7–6,and in the two ?ne structure transitions of atomic carbon.Observations were conducted in 2006between September 21and October 6with a dual-channel 460/810GHz re-ceiver installed for verifying the telescope submillimeter performance.Double-sideband (DSB)receiver tempera-tures were ～250K in the lower channel and ～750K in the upper one.The intermediate frequencies (IF)are 4GHz and 1.5GHz,respectively.The latter IF allows si-multaneous observations of the CO 7–6line in the lower and the [C i ]2–1line in the upper sideband.These two lines are observed simultaneously with one of the lines in the 460GHz channel.As backends,we used two acousto-optical spectrometers (AOS)with a bandwidth of 1GHz and a channel resolution of 0.37kms ?1at 460GHz and 0.21kms ?1at 806GHz.

The pointing was checked regularly on Jupiter,IRC+10216,and IRc2in Orion A.The applied correc-tions were always smaller than 20′′,and usually less than 10′′.The atmospheric transmission was derived by mea-suring the atmospheric emission at the reference position.Carina was observed between ～32?and ～54?elevation.Spectra of the two frequency bands were calibrated sepa-rately,and sideband imbalances were corrected using the atmospheric model atm (Pardo et al.2001).We used a ref-erence position at 10.h 50.m 09.s 3?59.?18.′33.′′

7(J2000),～45′to the north-east of ηCar,which was observed to be free of emission by Yonekura et al.(2005).Observations were conducted on-the-?y (OTF),scanning in right ascension at a speed of 2.5′′/sec and with a sampling interval of 10′′.[C i ]emission of the northern ?eld was also observed scanning in declination.The reference position was ob-served at the beginning of each OTF scanning line,i.e.every 1.6minutes in time.To complete a single scan of the 4′×4′map area took ～1hour of total observing time.ON-source integration times per position on a 10′′grid range

4Kramer et al.:Clumpy photon-dominated regions in Carina

between24sec(for CO4-3&7-6in the northern?eld)

and4sec.The total observing time was10hours.

The half power beamwidths(HPBWs)and main beam

e?ciencies(B e?)were determined from continuum cross scans on Jupiter(Simon et al.2007).For the latter,we

linearly interpolated the Jovian brightness temperatures listed by Gri?n et al.(1986)to the observed frequencies.

The HPBWs deconvolved from the observed full widths

at half maximum(FWHM),are38.′′0and26.′′5,in the lower and upper receiver band,respectively.Beam e?-

ciencies are50%and45%,respectively.The forward e?-

ciency(F e?)was derived from skydips and was found to be86%for both frequency bands.The raw data taken at

the telescope was recalibrated to the T?A antenna temper-ature scale and then multiplied by F e?/B e?to scale to

main beam temperatures.All data presented here are on

the T mb scale.We?tted and subtracted2nd order poly-nomials from all spectra.In a few cases,we subtracted

higher-order polynomials.

During the test campaign in the second half of2006,we

were able to roughly measure the error beam amplitudes of the NANTEN2antenna(Simon et al.2007).Continuum

measurements of the solar and lunar edges allowed to measure the extent and strength of a?rst compact er-

ror beam at810GHz following the method described e.g.

by Greve et al.(1998).We?nd a FWHM of240′′corre-sponding roughly to the average panel size of about0.6m.

Only about10–15%of the power is detected within this

error beam which we attribute to panel misalignment.The power detected within a beam of～30′was derived from

lunar continuum scans using a lunar Rayleigh-Jeans tem-perature of350K for both frequency bands(Pardo et al.

2005;Mangum1993).Moon e?ciencies are～70%at both

frequencies.In total,about36%of the total power is de-tected in at least two error beams at both frequencies.

As the spatial source structure in each velocity channel

is convolved by the antenna diagram during observations,

the error beams lead to pickup of extended emission in Carina.Main beam temperatures presented here are some-

what too high.Line pro?les may be slightly distorted(cf. Bensch et al.2001).However,as the error beams are not

yet completely characterized and may moreover be some-

what time variable,we ignore their in?uence in the fol-lowing.To?rst order,[C i]and CO emission stems from

the same region.Line ratios will therefore be much less

a?ected by the error beam compared to absolute intensi-ties.

https://www.doczj.com/doc/d617370857.html,plementary data

3.1.13CO2–1data

Brooks et al.obtained complementary maps of13CO2–1at the Swedish-ESO Submillimetre Telescope(SEST).

The telescope main beam e?ciency at220GHz was50%

and its HPBW25′′.The northern4′×5′SEST map (Brooks et al.2003)covers the northern NANTEN2?eld.

The southern map(Brooks,Schneider,https://www.doczj.com/doc/d617370857.html,m.)cov-ers the southern NANTEN2?eld.We convolved these data with a Gaussian kernel to a resolution of38′′to allow a comparison with the NANTEN2spectra taken along two cuts through the interface regions.

3.2.Dust and PAHs in Carina

Figure1gives an overview of a25′×25′region surround-ingηCar,showing the Keyhole region in the center,and the northern and southern clouds.The OB stars of Tr14 and Tr16emit far-UV photons which are partly absorbed by the dust grains of the surrounding molecular clouds. The heated dust cools in the far-infrared via dust contin-uum emission.Gas heating is very ine?cient;only a few percent at most of the absorbed energy is transferred to the gas(Hollenbach&Tielens1999),which cools via far-infrared and submillimeter line emission.Since the FUV photons play a decisive role in driving the cloud chemistry, determination of the FUV?eld is important.

To derive a map of the estimated FUV?uxes(Fig.1), we obtained HIRES/IRAS60and100μm images at～1′resolution from the IPAC data center.These images at enhanced resolution were created using a maximum corre-lation method(Aumann et al.1990).The?lter properties of IRAS allow us to combine these two data sets to cre-ate a map of far-infrared intensities I FIR between42.5μm and122.5μm(Helou et al.1988;Nakagawa et al.1998). Assuming that the FUV energy absorbed by the grains is reradiated in the far-infrared,we then estimate the FUV ?uxχ(6eV

χ/χ0=4πI FIR/(erg s?1cm?2sr?1)

withχin units ofχ0=2.710?3erg s?1cm?2(Draine 1978;Draine&Bertoldi1996).Here,we assume that heating by photons with hν<6eV contributes a factor of ～2(Tielens&Hollenbach1985)and that the bolometric dust continuum intensity is a factor of～2larger than I FIR(Dale et al.2001).In this case,the two corrections cancel out.In case the clouds do not?ll the beam,the de-rived estimate of the FUV?eld will only be a lower limit. Obviously,this method fails and the FUV?eld cannot be derived at positions without dusty clouds.

The northern4′×4′region mapped with NANTEN2 shows FUV?eld strengths varying between2103in the north-east and5103in the south-west.The FUV?eld in the southern region is a factor10weaker,varying between 4102in the outskirts and8102near the center.

Brooks et al.(2003)estimate the FUV?eld at the position of peak[C ii]emission in the northern cloud (Figs.1,3)from the spectral types of the13brightest stars dominating the stellar content of Tr14.They derive G0=1.4104in units of the Habing?eld,i.e.χ=8.2103, a factor1.6larger than the peak?ux in the northern re-gion,as derived from HIRES.However,the value derived by Brooks et al.(2003)is a strict upper limit as it is as-sumed that the stars and cloud lie at the same distance

Kramer et al.:Clumpy photon-dominated regions in Carina5 to the observer and attenuation by dust can be neglected.

Moreover,the FUV?eld derived from the stars would be

lowered by smearing to the resolution of the HIRES data.

Figure1shows contours of the FUV?eld together with

an8μm MSX image.The MSX image shows the emission

from very small grains and PAHs(Smith2006a)excited

by the FUV?eld.Evidence that the PAH emission is stim-

ulated by FUV absorption is re?ected by the good corre-

lation between the FIR continuum and the8μm emission.

Fig.2.Northern?eld:Contours of integrated CO4–3in-

tensities(cf.Fig.3)overlayed on8μm IRAC/Spitzer emis-

sion in units of MJy/sr.Car I-E and Car I-W are two H ii

regions described e.g.by Brooks et al.(2003)(cf.Fig.3

for more details).

4.Results

4.1.Northern region

4.1.1.Maps of integrated intensities

Figure2shows an overlay of integrated CO4–3intensities

on an8μm image taken with the Infrared Array Camera

(IRAC)on the Spitzer space telescope1.The8μm data

reveal the complicated spatial structure of the region,

consisting of several?laments and shell-like structures.

The bright region in the south-west is the ionisation front

Car I-W.Approximately～1′to the east lies Car I-E(cf.

Rathborne et al.2002;Brooks et al.2001).

Maps of integrated CO4–3,7–6,[C i]1–0,and2–

1emission(Fig.3)show the boundary of the north-

ern molecular cloud(orientated north-south)towards the

Tr14cluster and its H ii region.For all four tracers,

the integrated intensities are co-extensive and peak in

the south-west,near?13′/+6.5′,i.e.near the peak of

[C ii]emission studied by Brooks et al.(2003).The south-

eastern interface region exhibits increased CO7–6and

6Kramer et al.:Clumpy photon-dominated regions in

Carina

Fig.4.Velocity structure of the northern?eld:CO4–3velocity channels of1.5kms?1width.Contours range between5and45K kms?1in steps of5K kms?1

.

Fig.5.Spectra along a cut through the northern?eld con-necting Tr14and the[C ii]peak on a40′′grid.All data are at a common resolution of38′′and on the main beam scale. The velocity range is?40to5kms?1.The dashed vertical lines and the arrow mark the position of the?24kms?1 velocity component presented in Table1.

At the interface,all tracers show a strong component at ?24kms?1.Further west,this component shifts to lower velocities and splits up into at least3components.The line centroids of the di?erent tracers match very well.The peak temperatures are40K in CO4–3and10K in[C i] 1–0.Line intensities of CO and[C i]stay constant within a factor of2at the positions within the cloud;they increase slightly at the interface,before dropping rapidly towards the east.A weak component at?15kms?1seen in CO and 13CO peaks to the east of the interface at(?9.′8,7.′7).

To give one typical example,Table1shows the in-tegrated line intensities and derived quantities of the ?24kms?1component at the interface position,after Gaussian?tting.T ex is derived from the12CO4–3peak line temperature assuming optically thick emission and a beam-?lling factor of1.Total CO and C column densi-ties,given in1017cm?2,were derived from13CO2–1and [C i]1–0assuming optically thin emission at T ex,LTE, and a12CO vs.13CO abundance ratio of65.Total H2 column densities,given in1021cm?2,and masses were derived from N(CO)assuming an abundance ratio of 8.510?5(Frerking et al.1982).C/CO is the abundance ratio N(C)/N(CO).Errors given for the column densities were derived by varying T ex and the integrated intensi-ties by±15%.While the12CO4–3and7–6lines show FWHMs of5.4and4.7kms?1,the[C i]1–0and2–1line widths are smaller,3.9and3.1kms?1.13CO2–1shows a still narrower line width of2.9kms?1.We attribute this change of line widths to optical depth e?ects.The?tted line center velocities of all tracers agree within0.5kms?1. Line ratios of CO7–6/4–3and[C i]2–1/1–0are0.4and 0.7,which are typical values for the entire cut.

The peak CO4–3temperature of40K translates, through the Rayleigh-Jeans correction,into a lower limit of the gas kinetic temperature of the emission zone of 50K.Optical depth e?ects or a beam-?lling factor of less than1would imply higher gas kinetic temperatures. Brooks et al.(2003)derived a dust temperature of50K from the60vs.100μm IRAS?ux ratio at the[C ii]posi-tion.

The[C i]2–1/1–0line ratio is a sensitive function of the[C i]excitation temperature.In the optically thin limit and assuming LTE,T ex=38.3K/ln[2.11/R21CI].At the in-terface position,we observed a ratio of0.72±0.15,as-suming a calibration error of the ratio of about20%.This translates into T ex([C i])of only35K(43K

29K

).

The13CO2–1spectra(Brooks et al.2003)peak at 15K.At the interface,the[C i]1–0/13CO2–1ratio is0.8.

To derive a?rst estimate of the total CO column den-sities at the two interface positions(Table1),we used the 13CO2–1integrated intensities assuming optically thin emission,LTE,and a12CO vs.13CO abundance ratio of 65.The abundance ratio is in accordance with the av-erage local ISM12C/13C ratio of68±15recently found by Milam et al.(2005),which is valid also for Carina at about solar galacto centric distance.The inferred total op-tical extinction at the northern interface is28±7mag,us-ing the canonical N(H2)/A v ratio of9.361020cm?2mag?1 (Bohlin et al.1978).The C/CO abundance ratio is0.21.

4.2.Southern region

4.2.1.Maps of integrated intensities

Figure6shows an overlay of integrated CO4–3intensities on an8μm IRAC/Spitzer image of the southern NANTEN ?eld.The8μm emission traces a sharp interface running from north-east to south-west.It brightens at the cloud edge,showing several elongated?laments and knots along the interface.It also shows a bright emission knob in the north-west,which probably corresponds to the IRAS point source10430-5931.The8μm,emission here is weaker than in the northern?eld by about a factor5.The IRAC emis-sion drops rapidly towards the bulk of the cloud in the

Kramer et al.:Clumpy photon-dominated regions in Carina

7

Fig.6.Southern?eld:Contours of integrated CO4–3in-tensities(cf.

Fig.7)overlayed on8μm IRAC/Spitzer emis-sion in units of MJy/sr.

Fig.7.Southern4′×4′?eld:Velocity-integrated maps of CO4–3,7–6,[C i]1–0,and2–1at a common angular resolution of38′′,integrated over the full velocity range of emission between?20and?32kms?1.Contours range between10and90%in steps of10%of the peak intensities which are114K kms?1for CO4–3,35K kms?1for CO 7–6,37K kms?1for[C i]1–0,and22K kms?1for[C i]2–1.A cross×marks the position of IRAS10430-5931at 10.h45.m02.s4?59.?47.′10.′′0(J2000).Small crosses+mark positions along a cut through the interface region.The circle marks the resolution and the position analyzed in Table1.

south-east,similar to PAH emission traced by the3.21μm image of Rathborne et al.(2002).

In contrast to the mid-infrared emission,CO4–3and [C i]integrated intensities(Fig.7)peak south of the inter-face deep inside the cloud near(1′,?8′).The CO7–6line peaks near IRAS10430-5931,indicating elevated temper-Fig.8.Spectra along a north-south orientated cut through the southern?eld at?α=0.′8on a40′′grid. All data are at a common resolution of38′′.The velocity range is?43to?13kms?1.Vertical lines mark a velocity of?28kms?1.The arrow marks the position analyzed in Table1.

atures and densities.In contrast,the IRAS source is not prominent in[C i].

4.2.2.Spectra along a cut through the region Spectra taken along a north-south cut through the south-ern?eld show one component near?27kms?1with little variation in velocity(Fig.8).Near the interface,12CO line pro?les are?at-topped indicating high optical depths and self-absorption.Table1lists the results of Gaussian?ts to the spectra at the interface position(0.′8,?7.′3).The?t-ted FWHMs are4.3kms?1(CO4–3),3.9kms?1(CO7–6),3.4kms?1(13CO2–1),2.1kms?1([C i]1–0),2.4kms?1 ([C i]2–1).12CO line widths are a factor～2broader than the[C i]line widths which probably re?ects changes of the optical depths.

Compared to the northern?eld,the12CO and13CO lines are weaker while the[C i]1–0line is stronger.The CO4–3peaks at only～20K.The line ratios of CO 7–6/4–3and[C i]2–1/1–0at the interface position are 0.3±20%and0.6±20%respectively.These ratios are slightly lower than in the northern?eld,suggesting lower temperatures and densities.However,optical depth e?ects and self-absorption may also play a role.The[C i]1–0/CO 4–3ratio is0.34at the interface,a factor2higher than in the northern interface.The large-scale survey of the entire Carina region by Zhang et al.(2001)showed varia-tions between0.14and0.45,similar to the ratios we?nd at angular resolutions which are a factor～5higher.Gas kinetic temperatures must be at least30K to explain the 12CO4–3main beam temperatures.In the southern in-terface,this is consistent with T ex([C i])=30.5K(36K

26K

)de-rived from the[C i]line ratio.

The LTE analysis at the southern position indicates a C/CO abundance ratio of0.26,slightly higher than the abundance ratio in the north.Taking into account the calibration errors,the C/CO abundance ratios lie between ～0.1and～0.4at both positions(Table1).Similar abun-dance ratios have been observed in other Galactic star

8Kramer et al.:Clumpy photon-dominated regions in Carina

forming

regions like Cepheus B or NGC 7023(see refer-ences in Mookerjea et al.2006).

Fig.9.Integrated intensities at the two interface posi-tions in Carina-North and South (Table 1).Filled symbols show the observed 13CO 2–1,[C i ]1–0,2–1,12CO 4–3,and 7–6intensities.Error bars denote the 15%calibra-tion error.Model results of the best ?tting clumpy PDR model (Table 2)are shown by solid (12CO)and dotted lines (13CO),and open symbols.

5.Clumpy interface regions

Figure 9shows the cooling intensities 2observed at the two interface positions (Table 1)along the cuts presented in the previous section.At both positions,the 7-6intensity exceeds the 4-3intensity.As this transition has a criti-cal density of 1.4106cm ?3and an upper-level energy cor-responding to 157K,temperatures and densities are ex-pected to be similarly high.

In the following,we compare the observed emission with the predictions of a clumpy PDR model (Cubick 2005;Cubick et al.2007).We assume that the emis-sion stems from an ensemble of spherically symmetric clumps within the beam.The clumps follow the canon-ical clump mass and mass size distributions:dN/dM ∝M ?αand M ∝R γ.For the clump mass spectrum de-rived from molecular line observations,α～1.8in a large number of Galactic clouds (e.g.Kramer et al.1998;Simon et al.2001).For the power law describing the mass-size distribution,γ～2.3in several Galactic clouds (e.g.Heithausen et al.1998).As a result,the clump density distribution is n ∝M 1?3/γ,i.e.the density increases with decreasing clump mass.For the nearby clouds L 1457and

c 3

T d v [K kms ?1

].

the Polaris Flare presented in the Kramer and Heithausen

papers,the canonical clump mass and mass size distribu-tions continue down to masses of less than 10?3M ⊙and radii of less than 10?2pc.

The emission from a clump of given mass and den-sity is calculated by the KOSMA-τmodel (R¨o llig et al.2006;St¨o rzer et al.1996).The radial density structure n (r )of a model clump with radius R 0is given by n (r )∝n 0(r/R 0)?1.5for 0.2≤r/R 0≤1and n (r )=11.18n 0=const.for r/R 0≤0.2.The clump averaged density n is about twice the density at the clump sur-face,called henceforth surface density n 0: n ～1.91n 0.PDR models of individual clumps were calculated on a grid of FUV ?elds log(χ)=0,0.5,to 6,clump surface densities log(n 0/cm ?3)=2,2.5,to 7,and clump masses log(M cl /M ⊙)=?3,?2.5,to 2.The parameters control-ling the ensemble model are the FUV ?eld,the average ensemble density,the total ensemble mass,and the lower and upper clump mass limits.Here,we assume that all clumps are heated by a constant FUV ?eld,as derived from the HIRES observations presented above.We chose a lower mass cuto?of the ensemble of 10?2M ⊙and an up-per cuto?of 100M ⊙.Below,we show that the exact choice of these limits does however not have a strong impact on the resulting model intensities (cf.Cubick et al.2007).To ?t the observed intensity ratios [C i ]2–1/1–0and CO 7–6/4–3,the only free parameter is then the average density of the clump ensemble n ens .

We adapted the total ensemble mass to ?t the absolute intensities.The best ?tting models and their parameters are shown in Figure 9and in Table 2.Table 3lists the ra-tios of observed over modelled intensities for all 5observed transitions.For a perfectly ?tting model,they would all equal 1±15%,re?ecting the estimated calibration error of the observed data.

Northern interface.An average ensemble density of 2105cm ?3allows us to reproduce the observed 12CO 7–6/4–3and [C i ]2–1/1–0line ratios very well at the north-ern interface position.Lower densities do not reproduce the high CO 7–6/4–3line ratios,but rather lead to a peak of the cooling curve at J ≤5.The absolute intensities of the 12CO and 12C lines can be reproduced to within 20%for an ensemble mass of 400M ⊙.The strongest deviation occurs for 13CO;the observed 13CO 2–1line intensity is only 40%of the modelled intensity.

The geometrical beam-?lling factor of the clump en-semble is de?ned as the ratio of the sum of all clump areas over the beam area,i.e.φA =?ens /?beam ,with ?ens = πR 2cl /d 2at distance d .The beam-?lling factor is 3.9at the northern interface position (Table 2).We as-sume that clumps don’t overlap,i.e.that their emission es-capes without being absorbed by foreground clumps,and there is no interclump medium.Clumps have a constant velocity FWHM of ?v =1.7kms ?1.The clumpy ensem-ble models developed by Cubick et al.(2007)do not yet predict line pro?les.Table 2gives the densities and radii

Kramer et al.:Clumpy photon-dominated regions in Carina9 Table2.Parameters of the clump ensembles at the two positions which?t best the observed intensities.Columns(2)to(6) list the input parameters from which the values given in columns(7)to(11)are derived:χis the FUV?eld in Draine units,

n ens is the average density of the clump ensemble,M min

cl,M max

cl,M tot are the minimum and maximum clump mass,and the total ensemble mass,respectively.n0,min and n0,max are the smallest and largest clump surface densities,R min and R max are the smallest and largest clump radii,andφA is the beam-?lling factor of the clump ensemble.

?α/?δχ n ens M min

cl M max

cl M tot n0,min n0,max R min R maxφA

(′,′)cm?3M⊙M⊙M⊙cm?3cm?3pc pc

(1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)

Table3.Ratios of observed integrated intensities over integrated intensities predicted by the clumpy PDR model.The input parameters used are given in Table2;deviations from this setting are listed in column(7).

?α/?δ13CO CO[C i]

(′,′)2–14–37–61–02–1

(1)(2)(3)(4)(5)(6)(7)

+0.8/?7.20.60.81 1.2 1.2

8ln2≈5000yrs.

The modelled intensities depend only weakly on the lower and upper mass limits of the ensemble as shown in Table3.Varying one of the mass limits by one order of magnitude while keeping all other4input parameters listed in Table2unchanged,the absolute intensities of the 5transitions vary by less than a factor of～2relative to the best?tting solution.This is discussed in more detail in Cubick et al.(2007).

The run of12CO intensities with rotational number J, i.e.the CO cooling curve,predicted by the model(Fig.9) shows a maximum at J=7and a steep drop at higher ro-tational numbers up to J=11by more than a magnitude.

A secondary peak of the cooling curve is seen at J=15;it is almost a factor10weaker than the?rst maximum.The second peak shows up only for FUV?elds above～103 and it stems predominantly from the surface regions of the small,dense clumps.These clumps are large in num-ber,have a large total surface area,which is heated to high temperatures,su?cient to excite these high-J lines. The abundance of CO is increased in the hot gas of the H i/H2surface layer,near the OH density peak,due to secondary production paths which become important at high temperatures(Sternberg&Dalgarno1995):

OH+C+→CO+H+(R13)

OH+C+→CO++H→CO+H+(R125,R126) CO++H2→HCO++H(R127)

HCO++e→CO+H(R129)

We suspect that these reactions lead to the secondary peak of the cooling curve shown in Figure9.

Southern interface.At the southern interface position,the FUV?eld is only102.5χ0.An average ensemble density of2105cm?3reproduces the observed12CO7–6/4–3and [C i]2–1/1–0line ratios.Within40%,the clumpy model is also consistent with the absolute intensities of all5tracers for a total ensemble mass of220M⊙(Fig.9,Tables3,2). Due to the weaker FUV?eld compared to the northern position,the CO cooling curve peaks at slightly lower fre-quencies and a second peak is not visible.Similar to the northern position,the strongest deviation occurs for the 13CO2–1lines.

6.Summary

We have mapped the emission of atomic carbon and CO in two?elds of the GMCs surroundingηhttps://www.doczj.com/doc/d617370857.html,bining CO4–3and[C i]1–0data with CO7–6and[C i]2–1 data allows us to study the excitation conditions of both gas tracers.The northern4′×4′?eld lies adjacent to the compact OB cluster Tr14and is associated with the H ii regions Car I-E and Car I-W.The spectral lines show a

10Kramer et al.:Clumpy photon-dominated regions in Carina

rich kinematical structure,with several velocity compo-

nents along the lines of sight spread between?10and

?30kms?1.The southern4′×4′?eld lies on a molecular ridge south ofηCar.Here,spectral lines show only one

rather narrow Gaussian shaped velocity component.The FUV?eld derived from HIRES/IRAS far-infrared data is χ～102.5,about a factor10weaker than in the north-ern?eld.IRAC/Spitzer maps at8μm show the detailed structure of the FUV illuminated dust.The edge of the southern region is clearly delineated by the8μm emission, while the northern region shows a more complex spatial structure.

In both regions,CO and[C i]emission is co-extensive. Both species appear to trace the bulk of molecular gas, rather than the interface regions.This coincidence has been found in many of the previous large-scale studies of Galactic clouds conducted with the Mt.Fuji,KOSMA,and other telescopes.Papadopoulos et al.(2004)stress the im-portance of cosmic rays in raising the C/CO abundance ratio and argue that dynamic and non-equilibrium chem-istry processes explain the ubiquity of[C i]within molec-ular clouds as well as at PDR interfaces.Here,we argue that steady state,clumpy PDR models provide an alter-native explanation.

The northern and southern Carina regions both show

a slight brightening of the CO7–6and[C i]2–1transitions relative to the4–3and1–0transitions near the interfaces. In the south-east part of the northern region,the upper transitions brighten towards the interface(Fig.3).These transitions also show increased intensities near the embed-ded IRAS point source in the southern region(Fig.7).

We selected two cuts from the cloud cores through

the interface regions,roughly pointing towards the illu-

minating sources.The southern cut lies to the east of IRAS10430-5931,avoiding its complicated structure and additional heating sources.The northern cut runs from the peak of[C ii]emission(Brooks et al.2003)through the H ii regions Car I-W and I-E across the edge-on inter-face towards the center of the Tr14cluster.

The peak12CO line temperatures along the northern

cut indicate kinetic gas temperatures of at least50K,

while a lower limit of30K is found along the southern cut.

We selected two positions at the northern and southern interfaces for a detailed analysis.The12CO7–6/4–3and [C i]2–1/1–0intensity ratios at these positions are0.3–0.4 and0.6–0.7,respectively.We use PDR models to interpret the observed line intensities.Our models assume that all observed emission stems from an ensemble of spherically symmetric PDR clumps and there is no emission from an interclump medium or a di?use halo surrounding the clouds.PDR clumps are modelled using the stationary KOSMA-τcode(R¨o llig et al.2006).The clump distribu-tions follow the canonical mass and radius distributions found for molecular clouds.At the two positions analyzed in detail,we?nd that clumpy PDR models are consis-tent with the observed absolute intensities of the12CO and[C i]lines to within20%,i.e.at about the calibration accuracy.

Since the line ratios observed at the two interface posi-tions are fairly typical for the entire observed regions,we conclude that stationary,clumpy PDR models can simul-taneously reproduce the observed[C i]and CO emission of the lower transitions and the upper CO7–6and[C i] 2–1transitions.

However,the observed13CO2–1intensities are only about half of the modelled intensities at the north-ern and southern positions,respectively.Interestingly, Pineda&Bensch(2007)report a similar?nding.They analyzed12CO and[C i]emission observed in the dark cloud globule B68.This emission can be reproduced us-ing a single KOSMA-τspherically symmetric PDR model, while the observed13CO intensities are a factor～2too low.

To study the gas under a broad range of conditions, we plan to extend the present[C i]and CO maps to fully cover the GMCs surroundingηCar using the SMART 492/810GHz multipixel array receiver at NANTEN2 (Graf et al.2003).Future observations with APEX and Herschel will tell in how far the emission of other species tracing the detailed photo-chemical network is also con-sistent with stationary,clumpy PDR models. Acknowledgements.We thank Kate Brooks and Nicola Schneider for making their partly unpublished SEST13CO2–1 data available to us.We also would like to thank an anonymous referee for insightful comments which helped to improve on our arguments.We made use of the NASA/IPAC/IRAS/HiRES data reduction facilities.Data reduction of the spectral line data was done with the gildas software package supported at IRAM(see http://www.iram.fr/IRAMFR/GILDAS).This re-search has made use of NASA’s Astrophysics Data System Abstract Service.

This work is?nancially supported in part by a Grant-in-Aid for Scienti?c Research from the Ministry of Education, Culture,Sports,Science and Technology of Japan(No. 15071203)and from JSPS(No.14102003and No.18684003), and by the JSPS core-to-core program(No.17004).This work is also?nancially supported in part by the grant SFB494 of the Deutsche Forschungsgemeinschaft,the Ministerium f¨u r Innovation,Wissenschaft,Forschung und Technologie des Landes Nordrhein-Westfalen and through special grants of the Universit¨a t zu K¨o ln and Universit¨a t Bonn.L.B.and J.M.ac-knowledge support from the Chilean Center for Astrophysics FONDAP15010003.

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★名词的复数：一般在词尾直接加s,不规则变化要牢记: fish-----fish mouse------mice 3 Sentences 1.Have you got a pet ? 你有宠物吗？ Yes ,I have. 是的,我有。/No, I haven’t. 不，我没有。 2.What have you got ? 你有什么宠物吗？I’ve got a dog . / A dog. 我有一只狗。 3.What colour is the cat ? 你的猫是什么颜色的？It’s black. 它是黑色的。 What is wizard’s pet? 巫师的宠物是什么？ 4.What is it ? 它是什么? It’s a rabbit .它是只兔子。 5.How many budgies /mice are there? 这里有多少只鹦鹉/老鼠？ There are + 数字budgies/mice. 这里有------只鹦鹉/老鼠。 6.Fly like a budgie. 像鹦鹉一样飞。Run like a rabbit. 像兔子一样跑。 Swim like a fish. 像鱼一样游泳。Eat like a hamster. 像仓鼠一样吃东西。 Sit like a dog. 像狗一样坐。Roar like a tiger. 像老虎一样吼叫。 7.What are in the pictures. 图片里面是什么？Animals. 动物。 8. What animals? 什么动物？ 9.How many pandas (elephants /bears/ giraffes/ monkeys/ budgies) are there?有多少.？ How many + 可数名词的复数形式 Unit 2 The days of the week

外研社剑桥小学英语Join_in四年级上册整体课时教案

外研社剑桥小学英语Join_in四年级上册整体课时教案Starter Unit Let's begin 第一学时: The pupils learn to understand: How are you today? I’m fine/OK. Goodbye. The pupils learn to use: What’s your name? I’m (Alice). How are you? I’m fine. I’m OK. Activities and skills: Decoding meaning from teacher input. Using phrases for interaction in class. Greeting each other. I Introduce oneself. Asking someone’s mane. Teaching process: Step 1: Warm—up. Sing a song. Hello, what’s your name? Step 2: Presentation. 1. What’s your name? I’m…. (1) The teacher introduces herself, saying: Hello, /Good morning, I’m Miss Sun. (2) Asks a volunteer’s name:

What’s your name? The teacher prompt the pupil by whispering, I’m (Alice). (3) Asks all the pupils the same question and help those who need it by whispering I’m…. 2. How are you today? I’m fine. I’m OK. (1) The teacher explains the meaning of How are you today? (2) Tell the class to ask the question all together and introduce two answers, I’m (not very) fine/I’m Ok. (3) Asks all the pupils the same question and make sure that all the students can reply. Step3: Speak English in class. 1. Tells the pupils to open their books at page3, look at the four photographs, and listen to the tape. 2. Asks the pupils to dramatise the situations depicted in the four photographs. A volunteer will play the part of the parts of the other pupils, answering as a group. 第二学时: The pupils learn to use these new words: Sandwich, hamburger, hot dog, puller, cowboy, jeans, cinema, walkman, snack bar, Taxi, clown, superstar.

常用标点符号主要用法

常用标点符号主要用法 问号 1、用在特指问句后。如：(7)你今年多大了？ 2、用在反问句后。如：(8)为什么我们不能刻苦一点呢？ ?提示：反问句若语气缓和，末尾可用句号；若语气重可用感叹号。如：(9)国家 主席可以活活被整死；堂堂大元帅受辱骂；……这哪里还有什么尊重可言！ 3、用在设问句后。如：(10)我们能让你计划实现吗？不会的。 4、用在选择问句中。如：(11)我们是革命呢，还是要现大洋？ ( 12)你到底是去，还是不去？ 5、用在表疑问的独词句后。如：(13)我？不可能吧。 ?提示：若疑问句为倒装句，问号应放在句末。如：(14)到底出了什么问题，你的 车？(若说成：“到底出了什么问题？你的车。”则错误。) ?特别提示： 句号、问号均表示句末停顿。句号用于陈述句末尾，问号用于疑问句末尾。有些句 中虽有疑问词，但全句并不是疑问句，句末只能用句号，不能用问号。 例如：(17)……最后应求出铜块的体积是多少？ (18)面对千姿百态、纷繁芜杂的期刊世界，有哪位期刊编辑不想通过期刊版面设 计为刊物分朱布白、添花增色呢？ (19)关于什么是智力？国内外争论多年也没有定论。 (17) (18) ( 19)三句都是非疑问句，(17) (18)句中问号均应改为句号，(19)句中的问号应改为逗号。 感叹号 ?特别提示： 1、在表感叹或祈使语气的主谓倒装句中，感叹号要放在句末。 如：(20)多么雄伟壮观啊，万里长城！ 2、句前有叹词，后是感叹句，叹号放在句末。 如：(21)啊，这儿多么美丽！ 下面介绍句中点号的用法。句中点号包括逗号、分号、顿号、和冒号四种。 逗号 提示：复句内各分句之间的停顿，除了有时用分号外，都要用逗号。 顿号 用于句中并列的词、词组之间较小的停顿。 如：(22)邓颖超的品德、人格、风范为中华民族树立了一座精神丰碑。 (23)从1918年起，鲁迅陆续发表了《狂人日记》、《药》、《祝福》等短篇小说。 ?特别提示：以下九种情况不用顿号。 1、不定数的两个数字间不用顿号。 如：(24)你的年龄大概是十六七岁。(不能写成“十六、七岁”) ?【注意】相邻的两个数字而非约数之间要用顿号。

剑桥英语JOININ三年级上册知识点(供参考)

Join in三年级上册知识点 1.见面打招呼 Hello! = Hi! 你好 Good morning! 早上好！ Good afternoon! 下午好！ Good evening! 晚上好！ (注意：Good night的意思是“晚安”) 2.询问身体健康状况 How are you? 你好吗？ I’m fine. = I’m OK.我很好。 3.临走分别 Goodbye. = Bye bye. 再见。 See you tomorrow. 明天见。 4.Miss小姐Mr先生 5.询问名字 -What’s your name? 你叫什么名字？ -I’m Toby. = My name is Toby. = Toby.我叫托比。 6.Let’s+动词原形 如Let’s go! 我们走吧！ Let’s begin! 我们开始吧！ 7. Are you ready? 你准备好了吗？ I’m ready. 我准备好了。 8.十二个动词 look看listen听mime比划着表达speak讲read读write写draw画colour涂sing唱think想guess猜play玩9.询问物体 -What’s this? 这是什么？ -It’s my dog. / It’s a dog. / My dog. 这是我的狗。 10.my/your+名词 如my apple我的苹果 your apple你的苹果 11.数字0-10 zero零one一two二three三four四five五six六seven七eight八nine九ten十12.询问电话号码 -What’s your phone number? 你的电话号码是多少？ -It’s . / . 13.guess sth 猜东西 如Guess the number. 猜数字 14. What’s in the box? 盒子里有什么？ 15.询问数量 -How many? 多少？ -Nine. 九个。 16. Here is / are sth. 这是……

公文写作中标点符号的使用规范

公文写作中标点符号的使用规范 《中华人民共和国国家标准》（GB|T15834—1995）中有《标点符号用法》，其中对标点符号的使用作了明确的规定： 标点符号是辅助文字记录语言的符号，是书面语的有机组成部分，用来表示停顿、语气以及词语的性质和作用。 常用的标点符号有16种，分点号和标号两大类。 点号的作用在于点断，主要表示说话时的停顿和语气。点号又分为句末点号和句内点号——句末点号用在句末，有句号、问号、叹号3种，表示句末的停顿，同时表示句子的语气；句内点号用在句内，有逗号、顿号、分号、冒号4种，表示句内的各种不同性质的停顿。 标号的作用在于标明，主要标明语句的性质和作用。常用的标号有9种，即：引号、括号、破折号、省略号、着重号、连接号、间隔号、书名号和专名号。 一、常用标点符号用法简表 名称符号用法说明举例 句号。表示一句话完了之后的停 顿。 中国共产党是全中国人民的领导核心。 逗号，表示一句话中间的停顿。全世界各国人民的正义斗争，都是互相支持的。 顿号、表示句中并列的词或词组 之间的停顿。 能源是发展农业、工业、国防、科学技术和提高人 民生活的重要物质基础。 分号；表示一句话中并列分句之 间的停顿。 不批判唯心论，就不能发展唯物论；不批判形而上 学，就不能发展唯物辩证法。 冒号：用以提示下文。马克思主义哲学告诉我们：正确的认识来源于社会实践。 问号？用在问句之后。是谁创造了人类？是我们劳动群众。 感情号！1.表示强烈的感情。 2.表示感叹句末尾的停 顿。 战无不胜的马克思主义、列宁主义、毛泽东思想万 岁！ 引号“”1.表示引用的部分。毛泽东同志在《论十大关系》一文中说：“我们要

【精品】joinin英语剑桥版五年级(上)单词表

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