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高三宇宙奥秘英语阅读理解30题1<背景文章>Black holes are one of the most fascinating and mysterious phenomena in the universe. A black hole is formed when a massive star collapses at the end of its life. The gravitational pull of a black hole is so strong that nothing, not even light, can escape from it.The formation of a black hole begins with the collapse of a massive star. As the star runs out of fuel, it can no longer support its own weight and begins to collapse. The collapse continues until the star reaches a critical density, at which point it becomes a black hole.Black holes have several unique characteristics. One of the most notable is their event horizon, which is the boundary beyond which nothing can escape. Another characteristic is their intense gravitational field, which can distort the space and time around them.Black holes can have a significant impact on the surrounding celestial bodies. They can attract and swallow nearby stars and planets, and their gravitational pull can also affect the orbits of other celestial bodies.Scientists are still working to understand black holes better. They use a variety of tools and techniques, such as telescopes and computer simulations, to study these mysterious objects. Despite significant progressin recent years, there is still much that we don't know about black holes.1. What is a black hole formed by?A. A small star collapsing.B. A massive star collapsing.C. A planet collapsing.D. A moon collapsing.答案：B。
海王星的光环英语作文In the vast universe, Neptune stands out with its remarkable rings. These enigmatic and beautiful structures add an extra layer of fascination to this distant planet.The rings of Neptune are a sight to behold. They extend out from the planet, creating a delicate and intricate pattern in the darkness of space.Made up of tiny particles and dust, the rings glimmer and shine, catching the light and adding a touch of ethereal beauty to the planet.The origin and composition of Neptune's rings remain subjects of ongoing scientific study. Scientists strive to understand how these rings formed and what they can tell us about the planet's history and evolution.The rings vary in width, thickness, and clarity, each adding to the complexity and allure of this celestial wonder.Some of the rings are easily visible, while others require more detailed observations and analysis to be fully appreciated.Studying the rings of Neptune provides valuable clues about the dynamics and interactions within the solar system. They offer insights into the processes that shape and influence planets beyond our own.The presence of these rings also reminds us of the vastness and intricacy of the universe. There are countless wonders waiting to be discovered and explored.。
介绍银河系的英语演讲稿Ladies and gentlemen,Today, I stand before you to talk about one of the most fascinating and awe-inspiring wonders of the universe –the Milky Way Galaxy.The Milky Way Galaxy, our home within the vastness of space, is an immense and breathtaking sight to behold. It is a spiral galaxy, consisting of billions of stars, planets, dust, and other celestial objects. Spanning approximately 100,000 light-years in diameter, it is gravitationally bound by a supermassive black hole at its center, which exerts its influence on the stars and matter surrounding it.Named after its appearance as a hazy band of light stretching across the night sky, the Milky Way has captivated the imagination of humanity for centuries. Ancient civilizations believed it to be a celestial river, a path for spirits to traverse. It wasn't until the 17th century that the true nature of the Milky Way began to be understood, thanks to the discoveries of astronomers such as Galileo Galilei and Isaac Newton.The Milky Way is home to an estimated 100-400 billion stars, with our own sun being just one among them. Within this vast expanse, thereexists an incredible diversity of stellar systems, from binary star systems to pulsars, supernovae, and even the remnants of exploded stars known as neutron stars. These celestial bodies and phenomena contribute to the vast amount of energy that makes the Milky Way shine so brightly.In addition to stars, the Milky Way also hosts a variety of other celestial objects, such as planets, asteroids, comets, and interstellar clouds. These objects play a crucial role in the study of astrobiology, as scientists search for signs of life beyond our own planet. With the discovery of exoplanets –planets outside our solar system –the possibility of finding habitable worlds within the Milky Way has become even more tantalizing.But perhaps the most intriguing aspect of the Milky Way is its history. It is believed to have formed approximately 13.6 billion years ago, shortly after the Big Bang. Over billions of years, it has experienced numerous mergers and collisions with other galaxies, shaping its spiral structure and giving rise to the vast array of stars and stellar systems that we observe today. Studying the history of the Milky Way helps us gain insights into the formation and evolution of galaxies as a whole, providing clues about the origins and fate of our universe.In conclusion, the Milky Way Galaxy is a testament to the grandeur andcomplexity of the universe in which we live. Its beauty and mysteries continue to inspire scientists and amateurs alike to explore and discover its secrets. As we gaze upon the night sky and see the faint glow of the Milky Way, we are reminded of our place in the cosmos and the infinite possibilities that lie beyond. Thank you.。
英语作文石雷鹏带背Title: Exploring the Mysteries of the Universe。
The universe, with its vast expanse and myriad wonders, has long captured the imagination of humanity. From the twinkling stars in the night sky to the enigmatic black holes lurking in the depths of space, every corner of the cosmos holds secrets waiting to be unraveled. In this essay, we embark on a journey to delve into the mysteries of the universe, exploring its wonders and contemplating the questions that have intrigued mankind for centuries.One of the most fascinating phenomena in the universeis the formation and evolution of galaxies. Galaxies arevast collections of stars, gas, dust, and dark matter bound together by gravity. They come in various shapes and sizes, from the majestic spiral galaxies like the Milky Way to the irregularly shaped galaxies that defy classification. But how do galaxies form, and what processes govern their evolution over billions of years?To understand the formation of galaxies, astronomers study the early universe using powerful telescopes and sophisticated computer simulations. They have discovered that galaxies likely formed from tiny fluctuations in the density of matter in the primordial soup of the early universe. Over time, these fluctuations grew through gravitational attraction, eventually coalescing into the vast structures we see today. Moreover, the interactions between galaxies, such as mergers and collisions, play a crucial role in shaping their evolution, triggering bursts of star formation and fueling the growth of supermassive black holes at their centers.Speaking of black holes, these cosmic behemoths are perhaps the most mysterious objects in the universe. Black holes are regions of space where gravity is so intense that nothing, not even light, can escape their grasp. They come in different sizes, ranging from stellar-mass black holes formed from the collapse of massive stars to supermassive black holes found at the centers of galaxies, weighing millions or even billions of times the mass of the Sun.The study of black holes has challenged our understanding of physics, pushing the boundaries of our knowledge. They serve as cosmic laboratories where the laws of gravity and quantum mechanics collide, offering insights into the fundamental nature of space, time, and matter. Despite their mysterious nature, astronomers have made remarkable progress in observing black holes, thanks to advances in technology such as gravitational wave detectors and telescopes capable of capturing images of these elusive objects.Moreover, black holes are not just celestial curiosities; they play a crucial role in the cosmic ecosystem, influencing the evolution of galaxies and shaping the fabric of the universe itself. Their immense gravitational pull can disrupt the orbits of stars and planets, triggering cataclysmic events such as supernova explosions and gamma-ray bursts. Furthermore, the jets of energy and matter emitted by black holes can profoundly impact their surroundings, sculpting the cosmic landscape on scales both large and small.In addition to galaxies and black holes, the universeis also home to a myriad of other fascinating phenomena, from the violent explosions of supernovae to the delicate dance of planets around their parent stars. Each of these cosmic phenomena offers a glimpse into the intricate workings of the cosmos, inspiring awe and wonder in those who seek to understand them.In conclusion, the universe is a vast and mysterious realm filled with wonders beyond imagination. Through the diligent efforts of scientists and astronomers, we continue to uncover its secrets, peering ever deeper into the cosmic abyss. As we journey further into the unknown, may we remain humble in the face of the universe's grandeur and never cease to marvel at its beauty and complexity.。
天文学专业词汇CAMC, Carlsberg Automatic Meridian 卡尔斯伯格自动子午环Circlecannibalism 吞食cannibalized galaxy 被吞星系cannibalizing galaxy 吞食星系cannibalizing of galaxies 星系吞食carbon dwarf 碳矮星Cassegrain spectrograph 卡焦摄谱仪Cassini 〈卡西尼〉土星探测器Cat's Eye nebula （ NGC 6543 ）猫眼星云CCD astronomy CCD 天文学CCD camera CCD 照相机CCD photometry CCD 测光CCD spectrograph CCD 摄谱仪CCD spectrum CCD 光谱celestial clock 天体钟celestial mechanician 天体力学家celestial thermal background 天空热背景辐射celestial thermal background radiation 天空热背景辐射central overlap technique 中心重迭法Centaurus arm 半人马臂Cepheid distance 造父距离CFHT, Canada-Franch-Hawaii Telecope 〈CFHT〉望远镜CGRO, Compton Gamma-Ray Observatory 〈康普顿〉γ射线天文台chaos 混沌chaotic dynamics 混沌动力学chaotic layer 混沌层chaotic region 混沌区chemically peculiar star 化学特殊星Christmas Tree cluster （ NGC 2264 ）圣诞树星团chromosphere-corona transition zone 色球-日冕过渡层chromospheric activity 色球活动chromospherically active banary 色球活动双星chromospherically active star 色球活动星chromospheric line 色球谱线chromospheric matirial 色球物质chromospheric spectrum 色球光谱CID, charge injected device CID、电荷注入器件circular solution 圆轨解circumnuclear star-formation 核周产星circumscribed halo 外接日晕circumstellar dust disk 星周尘盘circumstellar material 星周物质circumsystem material 双星周物质classical Algol system 经典大陵双星classical quasar 经典类星体classical R Coronae Borealis star 经典北冕 R 型星classical T Tauri star 经典金牛 T 型星Clementine 〈克莱芒蒂娜〉环月测绘飞行器closure phase imaging 锁相成象cluster centre 团中心cluster galaxy 团星系COBE, Cosmic Background Explorer 宇宙背景探测器coded mask imaging 编码掩模成象coded mask telescope 编码掩模望远镜collapsing cloud 坍缩云cometary burst 彗暴cometary dynamics 彗星动力学cometary flare 彗耀cometary H Ⅱ region 彗状电离氢区cometary outburst 彗爆发cometary proplyd 彗状原行星盘comet shower 彗星雨common proper-motion binary 共自行双星common proper-motion pair 共自行星对compact binary galaxy 致密双重星系天文学专业词汇compact cluster 致密星团; 致密星系团compact flare 致密耀斑composite diagram method 复合图法composite spectrum binary 复谱双星computational astrophysics 计算天体物理computational celestial mechanics 计算天体力学contact copying 接触复制contraction age 收缩年龄convective envelope 对流包层cooling flow 冷却流co-orbital satellite 共轨卫星coplanar orbits 共面轨道Copernicus 〈哥白尼〉卫星coprocessor 协处理器Cordelia 天卫六core-dominated quasar （ CDQ ）核占优类星体coronal abundance 冕区丰度coronal activity 星冕活动、日冕活动coronal dividing line 冕区分界线coronal gas 星冕气体、日冕气体coronal green line 星冕绿线、日冕绿线coronal helmet 冕盔coronal magnetic energy 冕区磁能coronal red line 星冕红线、日冕红线cosmic abundance 宇宙丰度cosmic string 宇宙弦cosmic void 宇宙巨洞COSMOS 〈COSMOS〉底片自动测量仪C-O white dwarf 碳氧白矮星Cowling approximation 柯林近似Cowling mechnism 柯林机制Crescent nebula （ NGC 6888 ）蛾眉月星云Cressida 天卫九critical equipotential lobe 临界等位瓣cross-correlation method 交叉相关法cross-correlation technique 交叉相关法cross disperser prism 横向色散棱镜crustal dynamics 星壳动力学cryogenic camera 致冷照相机cushion distortion 枕形畸变cut-off error 截断误差Cyclops project 〈独眼神〉计划D abundance 氘丰度Dactyl 艾卫dark halo 暗晕data acquisition 数据采集decline phase 下降阶段deep-field observation 深天区观测density arm 密度臂density profile 密度轮廓dereddening 红化改正Desdemona 天卫十destabiliizing effect 去稳效应dew shield 露罩diagonal mirror 对角镜diagnostic diagram 诊断图differential reddening 较差红化diffuse density 漫射密度diffuse dwarf 弥漫矮星系diffuse X-ray 弥漫 X 射线diffusion approximation 扩散近似digital optical sky survey 数字光学巡天digital sky survey 数字巡天disappearance 掩始cisconnection event 断尾事件dish 碟形天线disk globular cluster 盘族球状星团dispersion measure 频散量度dissector 析象管distance estimator 估距关系distribution parameter 分布参数disturbed galaxy 受扰星系disturbing galaxy 扰动星系Dobsonian mounting 多布森装置Dobsonian reflector 多布森反射望远镜Dobsonian telescope 多布森望远镜dominant galaxy 主星系double-mode cepheid 双模造父变星double-mode pulsator 双模脉动星double-mode RR Lyrae star 双模天琴 RR 型星double-ring galaxy 双环星系DQ Herculis star 武仙 DQ 型星dredge-up 上翻drift scanning 漂移扫描driving system 驱动系统dumbbell radio galaxy 哑铃状射电星系Du Pont Telescope 杜邦望远镜dust ring 尘环dwarf carbon star 碳矮星dwarf spheroidal 矮球状星系dwarf spheroidal galaxy 矮球状星系dwarf spiral 矮旋涡星系dwarf spiral galaxy 矮旋涡星系dynamical age 动力学年龄dynamical astronomy 动力天文dynamical evolution 动力学演化。
关于太空宇宙的英语作文三句或四句I. IntroductionThe universe, an immense expanse teeming with celestial wonders, has long captivated human imagination and driven our insatiable quest for knowledge. From the twinkling stars that adorn our night skies to the enigmatic black holes lurking in the darkness, the cosmos is a realm of unfathomable beauty and mystery. This vast, ever-expanding entity, comprised of billions of galaxies, each housing countless stars and their planetary systems, represents the ultimate frontier for scientific inquiry.II. The Observable Universe: A Glimpse into Infinity Our observable universe, extending approximately 93 billion light-years in diameter, is but a tiny fraction of what may lie beyond. It contains a staggering array of celestial bodies, ranging from blazing stars in various stages of life to the ethereal, ghostly remnants of exploded stars known as supernovae. Furthermore, it is threaded by invisible forces, such as gravity and dark matter, which shape the cosmic web and govern the dance of galaxies. The cosmic microwave background radiation, theresidual heat left over from the Big Bang, whispers tales of our universe's fiery birth and subsequent expansion.III. The Search for Extraterrestrial LifeAs we peer deeper into this celestial tapestry, one question looms large: Are we alone in the universe? The discovery of thousands of exoplanets orbiting distant stars has fueled optimism that Earth might not be the sole cradle of life. These alien worlds, some found within the "habitable zones" where liquid water can exist, beckon us to ponder the possibility of extraterrestrial organisms thriving under different conditions. Ongoing missions, such as NASA's James Webb Space Telescope and the search for biosignatures, aim to unveil whether these seemingly habitable planets indeed harbor life, thus rewriting our understanding of our place in the cosmos.IV. Challenges and Future ProspectsExploring the universe is an audacious endeavor fraught with challenges, including the vast distances involved, harsh space environments, and the limitations of current technology. However, advancements in fields like astrophysics, aerospace engineering, and artificial intelligence hold promise for surmounting these obstacles.Space telescopes with unprecedented resolution will enable us to observe the universe in greater detail, while interstellar travel concepts like nuclear fusion propulsion and light sails could potentially revolutionize our ability to traverse the cosmos. Moreover, the pursuit of establishing permanent human settlements on other planets, such as Mars, signifies our aspirations to become a multi-planetary species and secure humanity's future among the stars.In conclusion, the universe, a boundless expanse of celestial marvels and profound mysteries, continues to entice and challenge us. As we delve deeper into its secrets, we not only broaden our understanding of the cosmos but also gain invaluable insights into our own existence. The quest to explore and comprehend this magnificent realm reflects our innate curiosity and unyielding spirit of exploration, promising a future filled with groundbreaking discoveries and paradigm-shifting revelations about the universe we call home.。
高一年级英语天文知识单选题40题1. Which planet is known as the "Red Planet" because of its reddish appearance?A. EarthB. MarsC. JupiterD. Venus答案：B。
解析：在太阳系中，火星（Mars）因为其表面呈现出红色的外观而被称为“Red Planet（ 红色星球）”。
地球（Earth）是我们居住的蓝色星球；木星（Jupiter）是一个巨大的气态行星，外观不是红色；金星 Venus）表面被浓厚的大气层覆盖，不是以红色外观著称。
2. Which planet has the most moons in the solar system?A. EarthB. MarsC. JupiterD. Mercury答案：C。
解析：木星（Jupiter）是太阳系中拥有最多卫星（moons）的行星。
地球（Earth）只有一颗卫星；火星（Mars）有两颗卫星；水星 Mercury）没有卫星。
3. The planet with the shortest orbit around the Sun is _.A. MercuryB. VenusC. EarthD. Mars答案：A。
解析：水星（Mercury）是距离太阳最近的行星，它的公转轨道是最短的。
金星 Venus）、地球 Earth）、火星 Mars）距离太阳比水星远，它们的公转轨道都比水星长。
4. Which planet has a thick atmosphere mainly composed of carbon dioxide?A. EarthB. MarsC. VenusD. Jupiter答案：C。
解析：金星（Venus）有一层非常厚的大气层，其主要成分是二氧化碳 carbon dioxide）。
地球 Earth）的大气层主要由氮气和氧气等组成；火星（Mars）大气层很稀薄，主要成分虽然有二氧化碳但比例和金星不同；木星（Jupiter）的大气层主要由氢和氦等组成。
天文上的英语名词解释天文学是一个广阔而神秘的领域，充满了许多令人着迷的现象和概念。
在这篇文章中，我们将解释一些关于天文学的英语名词，帮助读者更好地理解这些术语的含义。
1. 星系 (Galaxy)星系是宇宙中巨大的星际系统。
它由恒星、行星、气体、尘埃和暗物质组成。
以下是几个常见类型的星系：- 棒状螺旋星系 (Barred Spiral Galaxy)：中心有一条棒状结构，围绕着中心旋转的螺旋臂。
- 普通螺旋星系 (Normal Spiral Galaxy)：没有明显的棒状结构，呈现出螺旋状的臂。
- 椭球星系 (Elliptical Galaxy)：呈椭球形状，没有螺旋臂。
- 不规则星系 (Irregular Galaxy)：形状不规则，通常是由于与其他星系的相互作用产生的。
2. 星际尘埃 (Interstellar Dust)星际尘埃是分布在星系间空间中的微小颗粒。
这些尘埃颗粒主要由碳、硅等化学元素组成，它们的存在可以通过散射或吸收光线来观测到。
星际尘埃在星系形成和恒星诞生中起着重要的作用。
3. 星云 (Nebula)星云是由气体和尘埃组成的大型云状物体。
星云通常是通过恒星爆发、超新星爆炸或行星系统形成的。
以下是几种常见的星云类型：- 星际云 (Interstellar Cloud)：主要由氢气和尘埃组成的巨大云状结构。
- 行星状星云 (Planetary Nebula)：恒星快速膨胀和放出外层气体时形成的云状结构，通常呈现出球形或圆盘状。
- 火箭座Cephei-A (RCW 120)是一个著名的恒星形成区，位于南天星云复合体的一部分 (Southern Complex of Star Formation)。
4. 恒星 (Star)恒星是宇宙中辐射出巨大光和热能的球状天体。
它们主要由氢和一小部分氦等元素组成。
恒星通常被分为不同的类型，例如：- 主序星 (Main Sequence Star)：通过核聚变反应将氢转化为氦并产生巨大的能量的恒星。
以下是90个超新星纪元的词语以及它们的译文：1.超新星纪元- Supernova Age2.星际物质- Interstellar Matter3.星云- Nebula4.恒星- Star5.黑洞- Black Hole6.脉冲星- Pulsar7.星系- Galaxy8.旋臂- Spiral Arm9.恒星系- Stellar System10.双星- Binary Star11.星团- Star Cluster12.星云团- Nebula Cluster13.星际空间- Interstellar Space14.星尘- Stardust15.星系团- Galaxy Cluster16.超星系团- Supercluster17.宇宙射线- Cosmic Ray18.反物质- Antimatter19.高能射线- High-energy Radiation20.量子力学- Quantum Mechanics21.引力波- Gravitational Wave22.宇宙微波背景辐射- Cosmic Microwave Background Radiation23.暗物质- Dark Matter24.暗能量- Dark Energy25.星系核- Galaxy Core26.黑洞吞噬- Black Hole Accretion27.恒星演化- Stellar Evolution28.核合成- Nucleosynthesis29.星系碰撞- Galaxy Collision30.恒星爆炸- Stellar Explosion31.引力透镜- Gravitational Lensing32.宇宙网- Cosmic Web33.反物质粒子- Antimatter Particles34.高纬宇宙模型- High-dimensional Cosmic Model35.宇宙常数- Cosmological Constant36.宇宙密度- Cosmic Density37.宇宙膨胀- Cosmic Expansion38.宇宙学红移- Cosmological Redshift39.大爆炸理论- Big Bang Theory40.弦理论- String Theory41.相对论- Relativity42.量子力学- Quantum Mechanics43.弦理论- String Theory44.卡鲁扎-克莱因理论- Kaluza-Klein Theory45.高维时空- Higher-dimensional Spacetime46.虚时间- Virtual Time47.宇宙微波背景辐射- Cosmic Microwave Background Radiation48.标准宇宙模型- Standard Cosmological Model49.星系团- Galaxy Cluster50.超星系团- Supercluster51.丝状结构- Filamentary Structure52.大尺度结构- Large-scale Structure53.哈勃常数- Hubble Constant54.引力波- Gravitational Wave55.黑洞信息悖论- Black Hole Information Paradox56.夸克星- Quark Star57.反物质星- Antimatter Star58.原子核- Atomic Nucleus59.量子纠缠- Quantum Entanglement60.高温高压状态方程- High-temperature and high-pressure equation ofstate61.星系演化- Galaxy Evolution62.星系动力学- Galaxy Dynamics63.星际物质循环- Interstellar Matter Cycle64.恒星形成- Star Formation65.分子云- Molecular Cloud66.星际空间气体- Interstellar Gas67.星际尘埃- Interstellar Dust68.星系核活动- Active Galactic Nucleus69.射电星系- Radio Galaxy70.光学星系- Optical Galaxy71.X射线星系- X-ray Galaxy72.恒星团- Star Cluster73.双星系统- Binary Star System74.变星- Variable Star75.新星- Nova76.超新星- Supernova77.中子星- Neutron Star78.脉冲星- Pulsar79.黑洞候选体- Black Hole Candidate80.高光度蓝变星- High-luminosity Blue Variable Star81.超巨星- Supergiant Star82.红巨星- Red Giant Star83.黄矮星- Yellow Dwarf Star84.白矮星- White Dwarf Star85.恒星演化模型- Stellar Evolution Model86.星际物质分布- Interstellar Matter Distribution87.分子光谱学- Molecular Spectroscopy88.高能天体物理学- High-energy Astrophysics89.天体化学- Astrochemistry90.宇宙射线物理学- Cosmic Ray Physics。
了解航天事业获得的最新成就英语作文全文共3篇示例，供读者参考篇1The Sky's No Limit: Exploring the Latest Space TriumphsHi there! My name is Emily, and I'm a huge fan of everything having to do with space. Ever since I was a tiny kid, I've been fascinated by the twinkling stars at night and all the mysteries waiting to be discovered out there in the cosmos. That's why I was over the moon (get it?) when my teacher announced we'd be learning about the latest accomplishments in space exploration.Where do I even begin? There's just so much awesome stuff happening in the world of aerospace right now. I guess I'll start with the Artemis program, which is NASA's daring new quest to land the first woman and next man on the lunar surface. In 2022, an uncrewed mission called Artemis I traveled all the way to the Moon and back on a test flight. It was a big success that paved the way for Artemis II, a crewed flyby of the Moon scheduled for 2024.But the real exciting part is Artemis III, the actual landing mission targeted for 2025 or 2026. Just imagine – after morethan 50 years, new astronaut bootprints will finally grace the dusty lunar soil! This time though, instead of just hanging out for a few days like the Apollo crews did, NASA wants to establish a permanent base on the Moon. From there, we can launch future expeditions deeper into space to explore the wonders awaiting us.Speaking of ambitious exploration plans, let's talk about Mars! Studying the Red Planet has been one of humanity's biggest priorities in space for decades now. In 2021, NASA's Perseverance rover landed in Jezero Crater and quickly got to work analyzing the region for signs of ancient microbial life. It has already beamed back tons of incredible images and rock/soil data.But get this – Perseverance isn't alone on Mars anymore! In 2023, NASA's Mars helicopter Ingenuity was joined by two other rotorcraft drones from competing space agencies. One is called Ingenuity's Russian cousin, and the other goes by the cool codename "Red Furry." These little choppers are scouting potential sites of interest and paving the way for future Mars exploration.There's even been talk of trying to bring samples of Martian rock and soil back to Earth sometime in the 2030s. Can youimagine holding in your hands something that was once part of an alien world? Mind-blowing!Okay, let's leave the inner solar system for a bit and turn our eyes toward some more distant targets. In recent years, we've made amazing progress in studying the outer planets and their many unusual moons.In 2023, the Juno probe went into a special orbit to get an up-close look at some of Jupiter's largest moons like Ganymede and Europa. Scientists are particularly interested in Europa because they think it may have a vast liquid water ocean beneath its icy shell – an ocean that could possibly support life! How crazy is that?Meanwhile, after over 14 years of traveling through space, NASA's New Horizons spacecraft finally flew past a weird little object nicknamed "Arrokoth" in the Kuiper Belt region in 2019. Studying Arrokoth and other Kuiper Belt objects is helping shed light on how planets first started forming billions of years ago when our solar system was just an infant.But space agencies aren't just exploring the depths of space with robotic probes these days – they're also launching record numbers of advanced telescopes to scan the cosmos from right here on Earth. Leading the way is the incredible James WebbSpace Telescope, which has been opening our eyes to parts of the universe we've never seen before since its launch in 2021.Webb's ultra-powerful infrared vision can pierce through billowing clouds of gas and dust to reveal newborn stars and galaxies taking shape nearly 14 billion light years away – that's just a mere 500 million years after the Big Bang! With Webb's help, I've gotten to gaze upon images of some of the oldest, most distant galaxies ever detected. Many of them look like smears and blobs, but they represent pivotal moments when the universe was just a baby.Webb has also captured unprecedented views of nearby exoplanets – planets orbiting other stars light-years away from us. In 2023, it detected clouds of silicate particles swirling around a planet outside our solar system for the very first time. As if that wasn't enough, the telescope even managed to take direct pictures of a saturn-like planet with rings in another star system!Not to be outdone, observatories on Earth's surface like the Extremely Large Telescope built by the European Southern Observatory have also been making eye-opening discoveries. In 2023, it delivered images of an exoplanet that is spiraling inward toward its host star trapped in a fiery "cosmic dance of death"! Its insights into far-off planetary systems, as well as observationsof objects closer to home like asteroids and comets, are advancing our understanding of the solar system and the broader universe.One of my favorite milestones was when we finally got our first glimpse of the supermassive black hole lurking at the heart of our very own Milky Way galaxy in 2022. It was made possible through the collaborative efforts of observatories across the globe participating in the Event Horizon Telescope project. The image shows the black hole's shadow surrounded by a bright ring of glowing gas being heated up to astronomical temperatures. Eating too much of a cosmic dinner, eh?There's been so much more happening in space that I can't even begin to cover it all. Private companies like SpaceX and Blue Origin are helping make space more accessible for everyone by dramatically reducing launch costs with reusable rockets. China has been making waves with ambitious lunar and Martian exploration programs of its own. Scientists believe they may have detected biosignature gases in the clouds of Venus – a huge hint that some sort of lifeforms could possibly exist there. And don't even get me started on all the movie-like sci-fi innovations being dreamed up, like space tugs that can towwayward asteroids, or gigantic orbital sunshades to help cool the Earth and stop climate change.The cosmos is a place of infinite wonder and possibility, filled with mysteries just waiting to be solved. Though we humans are still in our earliest days of reaching out into the great unknown beyond our planet, our latest adventures into the final frontier are already paying off with discoveries that blow my mind wide open. I can't wait to see where our future journeys out among the stars will take us next!I hope you enjoyed learning more about the latest triumphs in space exploration as much as I enjoyed writing about them. The skies may look calm and peaceful from here on Earth, but out there in the inky blackness, a nonstop cosmic revolution is unfolding before our very eyes. There's a whole new universe waiting to be uncovered, and the latest space age is only just beginning!篇2The Exciting World of Space ExplorationHave you ever looked up at the night sky and wondered what's out there? I sure have! The mysteries of space have fascinated humans for centuries, and in recent years, we've madesome amazing discoveries and achievements that are helping us understand more about our universe than ever before.One of the coolest recent space achievements is the James Webb Space Telescope. This incredible telescope was launched in 2021 and it's the largest and most powerful space telescope ever built! It's so strong that it can see galaxies that formed over 13 billion years ago, just a few hundred million years after the Big Bang. With images and data from the Webb, scientists are learning more about how galaxies formed and evolved over billions of years.Another exciting space accomplishment is the Perseverance rover that landed on Mars in 2021. This car-sized rover is studying the climate and geology of Mars to search for signs of ancient microbial life. It even has a little helicopter drone named Ingenuity that flies around scouting locations for the rover! Perseverance has collected rock and soil samples that will eventually be returned to Earth for deeper study by scientists. Wouldn't it be amazing if we found evidence that life once existed on Mars?NASA also made history in 2022 when the DART spacecraft intentionally crashed into an asteroid as part of a planetary defense test mission. The aim was to see if a spacecraft impactcould successfully change the motion of an asteroid that might someday be headed towards Earth. It worked! After the impact, the orbit of the asteroid Dimorphos was altered, proving this could be an effective way to deflect a dangerous asteroid away from our planet if needed. That's pretty cool to think we now have a way to protect Earth from asteroids!Closer to home, we're learning more than ever before about our own Moon thanks to several recent lunar missions and the Artemis program to return humans to the lunar surface. NASA's Lunar Reconnaissance Orbiter has provided stunninghigh-resolution maps of the Moon's surface over the last decade. And in 2019, the Indian Space Agency's Chandrayaan-2 lander detected gaseous ammonia on the Moon for the first time, which could help reveal how the Moon was formed.Through initiatives like Artemis, NASA aims to establish a long-term human presence on and around the Moon in preparation for future crewed missions to Mars. In late 2022, the uncrewed Artemis I mission took the first step by successfully sending the new Orion crew capsule on a multi-week journey around the Moon and back. In the coming years, Artemis II will fly astronauts on a similar loop around the Moon, leading up to Artemis III when the first woman and next man will land on thelunar surface sometime after 2025. I can't wait to see the first new footprints on the Moon in over 50 years!Have you heard of SpaceX and their amazing reusable rockets? Traditional rockets are single-use and just get discarded after launch. But SpaceX's Falcon 9 rockets are designed to return to Earth and vertically land themselves so the most expensive parts can be reused on future flights. This lowers the cost of getting payloads into space tremendously compared to disposable rockets. Even cooler, SpaceX has developed a massive new reusable rocket called Starship that could one day transport crew and cargo for NASA's deep space exploration goals like landing astronauts on Mars.Another private company called Rocket Lab has pioneered techniques to make smaller, more efficient rockets to affordably launch smaller satellites. Thanks to companies like Rocket Lab, we're seeing a surge of new "cube sats" and other tiny satellites launched to study our planet, test new technologies, and more. With so many affordable satellites going up, space is becoming more accessible than ever to companies, schools, and even individual students to get experiments and projects into orbit!I haven't even mentioned all the incredible images and data we're getting from space telescopes like Hubble and Chandrathat are revealing new details about black holes, dark matter, exploding stars, and the evolution of our universe over 13.8 billion years. Or all the new Earth observation satellites carefully monitoring our planet's climate, weather, vegetation, and more from space. There's just so much happening in space exploration right now that it's hard to keep up!With plans for the first crewed missions to Mars in the 2030s, construction of new space stations orbiting the Moon, ongoing searches for habitable exoplanets, and who knows what other new discoveries, the future of space is brighter than ever. I can't wait to see what new frontiers we'll explore and what we'll learn next about our universe. The space age is only just beginning!篇3The Exciting World of Space ExplorationHi there! My name is Timmy and I'm a huge fan of everything related to space. From the twinkling stars in the night sky to the incredible rockets that blast off into the unknown, the universe has always fascinated me. Today, I want to share with you some of the awesome new things happening in space exploration. Get ready to have your mind blown!One of the coolest things that has happened recently is the launch of the James Webb Space Telescope. This incredible piece of technology was sent into space in December 2021, and it's already sending back some mind-boggling images! The Webb Telescope is the largest and most powerful space telescope ever built, and it can see farther into the universe than any other telescope before it.Using its powerful infrared cameras, the Webb Telescope has captured breathtaking images of distant galaxies, nebulae (those colorful clouds of gas and dust), and even some of the first galaxies that formed after the Big Bang! Just imagine – we're able to see objects that are billions of light-years away, and learn about the earliest days of the universe. It's like having a time machine that lets us peek into the past!Another exciting development in space exploration is the success of the Mars Perseverance Rover. This awesome little robot has been exploring the Red Planet since February 2021, and it's already made some amazing discoveries. One of its coolest achievements was successfully collecting rock and soil samples from Mars, which will eventually be brought back to Earth for studying.By analyzing these Martian samples, scientists hope to learn more about the planet's geology, climate history, and even whether life ever existed there. The Perseverance Rover has also captured some incredible images of the Martian landscape, including breathtaking panoramas and close-up shots of interesting rock formations.But perhaps the most thrilling recent event in space exploration has been the successful launch and return of the Artemis I mission. Artemis I was an uncrewed test flight of the powerful Space Launch System (SLS) rocket and the Orion spacecraft, which are designed to take humans back to the Moon in the coming years.After launching in November 2022, the Orion capsule traveled over 1.3 million miles, orbiting the Moon and testing out various systems before splashing down safely in the Pacific Ocean. This successful mission paves the way for Artemis II, which will have a crew on board, and eventually Artemis III, which aims to land the first woman and the next man on the lunar surface.Imagine how cool it would be to be one of those astronauts, walking on the Moon for the first time since the last Apollo mission in 1972! And who knows, maybe one day I'll get thechance to be an astronaut myself and explore the wonders of space firsthand.But even if I don't become an astronaut, there are still plenty of exciting things happening in space that I can follow and learn about. For example, private companies like SpaceX and Blue Origin are making huge strides in developing reusable rockets and making space travel more affordable.SpaceX's Starship system, which consists of a massive reusable rocket called Super Heavy and a spacecraft called Starship, is designed to eventually carry crew and cargo to the Moon, Mars, and beyond. And Blue Origin's New Glenn rocket is being developed to launch satellites and future human missions into space.It's amazing to think that we're living in a time when space travel and exploration are becoming more accessible and routine. Who knows what other groundbreaking discoveries and achievements lie ahead in the coming years?Maybe we'll find evidence of life on one of the moons of Jupiter or Saturn. Or perhaps we'll uncover clues about the existence of other Earth-like planets in distant solar systems. Heck, maybe we'll even make contact with an alien civilization!(Okay, that might be a bit of a stretch, but hey, a kid can dream, right?)Whatever happens, one thing is for sure – the future of space exploration is looking brighter and more exciting than ever before. With powerful new telescopes, rovers, rockets, and spacecraft at our disposal, we're unlocking the secrets of the cosmos at an unprecedented rate.And who knows, maybe someday humans will even establish permanent settlements on other planets or moons. Imagine living in a colony on Mars or the Moon, looking up at an alien sky filled with unfamiliar stars and planets. It's the stuff of science fiction, but with the rapid pace of technological progress, it might not be as far-fetched as it sounds.So there you have it, my friends – a glimpse into some of the latest and greatest achievements in space exploration. From the awe-inspiring images of the Webb Telescope to the groundbreaking missions to the Moon and Mars, it's an amazing time to be a space enthusiast like me.And who knows, maybe someday I'll be the one making history by stepping foot on another world or discovering something truly extraordinary in the vast expanse of the universe. For now, I'll just keep dreaming big, learning as much as I can,and marveling at the incredible accomplishments of the brilliant minds who are pushing the boundaries of space exploration.The universe is a vast and wondrous place, full of mysteries waiting to be uncovered. And with each new discovery and achievement, we're one step closer to unlocking its secrets. So buckle up and get ready for an out-of-this-world adventure – the future of space exploration is just getting started!。
a r X i v :a s t r o -p h /0403714v 1 31 M a r 2004Draft version February 2,2008Preprint typeset using L A T E X style emulateapj v.11/12/01CALIBRATING THE GALAXY HALO –BLACK HOLE RELATION BASED ON THECLUSTERING OF QUASARSJ.Stuart B.Wyithe 1and Abraham Loeb 2swyithe@.au;aloeb@Draft version February 2,2008ABSTRACTThe observed number counts of quasars may be explained either by long-lived activity within rare massive hosts,or by short-lived activity within smaller,more common hosts.It has been argued that quasar lifetimes may therefore be inferred from their clustering length,which determines the typical mass of the quasar host.Here we point out that the relationship between the mass of the black-hole and the circular velocity of its host dark-matter halo is more fundamental to the determination of the clustering length.In particular,the clustering length observed in the 2dF quasar redshift survey is consistent with the galactic halo –black-hole relation observed in local galaxies,provided that quasars shine at ∼10–100%of their Eddington luminosity.The slow evolution of the clustering length with redshift inferred in the 2dF quasar survey favors a black-hole mass whose redshift-independent scaling is with halo circular velocity,rather than halo mass.These results are independent from observations of the number counts of bright quasars which may be used to determine the quasar lifetime and its dependence on redshift.We show that if quasar activity results from galaxy mergers,then the number counts of quasars imply an episodic quasar lifetime that is set by the dynamical time of the host galaxy rather than by the Salpeter time.Our results imply that as the redshift increases,the central black-holes comprise a larger fraction of their host galaxy mass and the quasar lifetime gets shorter.Subject headings:cosmology:theory –cosmology:observations –quasars:general1.introductionThe Sloan Digital Sky Survey (York et al.2000)and the 2dF quasar redshift survey (Croom et al.2001a)have measured redshifts for large samples of quasars,and de-termined their luminosity function over a wide range of redshifts (Boyle et al.2000;Fan et al.2001a,b;Fan et al.2003).The 2dF survey has also been used to constrain the clustering properties of quasars (Croom et al.2001b).It has been suggested that quasars have clustering statis-tics similar to optically selected galaxies in the local uni-verse,with a clustering length R 0∼8Mpc.The large sample size of the 2dF quasars also provided clues about the variation of clustering length with redshift (Croom et al.2001b)and apparent magnitude (Croom et al.2002).Quasars appear more clustered at high redshift,although with a relatively mild trend.There is also evidence that more luminous quasars may be more highly clustered.As pointed out by Martini &Weinberg (2001)and Haiman &Hui (2001),the quasar correlation length de-termines the typical mass of the dark matter halo in which the quasar resides.One may therefore derive the quasar duty-cycle by comparing the number density of quasars with the density of host dark matter halos.The quasar lifetime then follows from the product of the duty-cycle and the lifetime of the dark-matter halo in between major mergers,although there is a degeneracy between the lifetime and the quasar occupation fraction or beam-ing.Preliminary results suggested quasar lifetimes of t q ∼106−107years,consistent with the values determined by other methods (see Martini 2003for a review),includ-ing the transverse proximity effect (Jakobsen et al.2003)and counting arguments relative to the local populationof remnant supermassive black holes (SMBHs;see Yu &Tremaine 2002).Kauffmann &Haehnelt (2002)used a de-tailed semi-analytic model (Kauffmann &Haehnelt 2000)to predict the correlation length of quasars and its evolu-tion with redshift.They found that their model reproduces the correct correlation length as well as its redshift evolu-tion for present-day quasar lifetimes of t q ∼107years.In this work we argue that the correlation length of quasars is fundamentally determined by the relation be-tween the masses of SMBHs and their host galactic halo rather than by the quasar lifetime.We find that the am-plitude of the correlation length depends on the product of the SMBH–halo relation and the typical fraction of the Eddington luminosity at which quasars shine.Moreover,we show that the evolution of the correlation length is sensitive to how the SMBH –halo relation evolves with redshift,and therefore to the physics of SMBH formation and quasar evolution.The paper is organized as follows.In §2and §3we dis-cuss the calculation of the correlation function of quasars with a particular apparent magnitude B ,and the differ-ent scenarios for the evolution of the SMBH –galaxy halo relation.In §4we compare fiducial model correlation functions to the results of the 2dF quasar redshift survey (Croom et al.2001b,c).We find that the shallow evolution of the correlation length implies that SMBH mass has a redshift-independent scaling with the circular velocity of the host dark matter halo rather than with its mass.The ranges of the normalizations in the SMBH –galaxy halo relation and of the fraction of Eddington allowed by ob-servations of the observed quasar correlation function are explored in §5.In §6we examine the quasar lifetime1University of Melbourne,Parkville,Victoria,Australia2Harvard-Smithsonian Center for Astrophysics,60Garden St.,Cambridge,MA 0213812by requiring that observational constraints from both the correlation and luminosity functions be satisfied simulta-neously.Finally,in §8we summarize our results and dis-cuss a very simple,physically motivated model that satis-fies all constraints with no free parameters.Throughout the paper we adopt the set of cosmological parameters de-termined by the Wilkinson Microwave Anisotropy Probe (WMAP,Spergel et al.2003),namely mass density pa-rameters of Ωm =0.27in matter,Ωb =0.044in baryons,ΩΛ=0.73in a cosmological constant,and a Hubble con-stant of H 0=71km s −1Mpc −1.2.the correlation function of quasarsThe mass correlation function between halos of mass M 1and M 2,separated by a co-moving distance R is (see Scannapieco &Barkana 2003and references therein)ξm (M 1,M 2,R )=1kRW (kR 1)W (kR 2),(1)whereR 1,2=3M 1,2δc ,0ν′2+bν′2(1−c )−ν′2c /√ν′2c+b (1−c )(1−c/2),(3)where δc ,0(≈1.69)is the critical overdensity threshold for spherical collapse,δc (z )=δc ,0/D (z ),D (z )is the growth factor at redshift z ,σis the variance on a mass-scale M ,ν≡δ2c (z )/σ2(M ),ν′≡√L B ,⊙=5.73×1012ηM bh3 relation between M bh and the stellar velocity dis-persion does not evolve with redshift.This is ex-pected if the mass of the black-hole is determinedby the depth of the gravitational potential well inwhich it resides,as would be the case if growth isregulated by feedback from quasar outflows(e.g.Silk&Rees1998;Wyithe&Loeb2003).Express-ing the halo circular velocity,v c,in terms of thehalo mass,M,and redshift,z,the redshift depen-dent relation between the SMBH and halo massesmay be written asM bh(M halo,z)=const×v5c=ǫM halo M halo3[ζ(z)]52,(7)whereǫis a constant,ζ(z)is close to unity anddefined asζ≡[(Ωm/Ωz m)(∆c/18π2)],Ωz m≡[1+(ΩΛ/Ωm)(1+z)−3]−1,∆c=18π2+82d−39d2,andd=Ωz m−1(see equations22–25in Barkana&Loeb2001for more details).•Case B:we consider the scenario in which theSMBH mass maintains the same dependence on itshost halo mass at all redshifts,namelyM bh(M halo,z)=const×M5/3halo=ǫM halo M halo3[ζ(0)]5L B,⊙ +5log10 D L4Fig. 1.—Predicted correlation function at various redshifts,in comparison to the2dF data(Croom et al.2001b).The dark lines show the correlation function predictions for quasars of various apparent B-band magnitudes(B).The2dF limit is B∼20.85.The lower right panel shows data from entire2dF sample in comparison to the theoretical prediction at the mean quasar redshift of z =1.5.The B=20.85 prediction at this redshift is also shown by thick gray lines in the other panels to guide the eye.This case assumes M bh∝v5c,normalized to local observations,andη=1(case AI).function of redshift was computed from a sample having B 20.85,drawn from the2dF quasar redshift survey (Croom et al.2001b,c).The gray error bars show the val-ues for R0in different redshift bins,while the correlation length measured for the whole sample(plotted at z=1.5 and B=20.3in the left and right hand panels respec-tively)is shown by the dark error bar.Wefind the predic-tions for R0to be consistent with observations.In partic-ular,both the value of the clustering length and its slow evolution with redshift and apparent magnitude are consis-tent with current data.There is little variation of the clus-tering length with apparent magnitude over the range con-sidered,although there is a tendency for brighter quasars to be more highly clustered,as was noted by Croom et al.(2002).Note that the K-correction assumed in equation(9)is only valid out to z∼3where Lyαabsorption enters into the B-band.As a result the extrapolations of redshift de-pendence to z 3shown in Figures2and3do not include Lyαabsorption in the calculation of the quasar luminos-ity.However,these extrapolations are included to illus-trate the evolution of the clustering length at yet higher redshifts(as measured in bands redward of the redshifted Lyαline).The lower panels of Figure2show the corresponding de-pendence of the clustering length on redshift and apparent magnitude for quasars that shine at Eddington fractionsηlower than unity.Only the cases of B=20.3,correspond-5Fig.2.—The correlation length,R0[defined throughξq(R0)=1]plotted as a function of redshift(left hand panel)and apparent magnitude (right hand panel).The data is from the2dF quasar redshift survey(Croom et al.2001b,c),with the gray error bars showing the correlation length from different sub-samples,and the dark error bar at z=1.5(left hand panels)and B=20.3(right hand panels)showing the correlation length for the full sample.The theoretical model assumes M bh∝v5c.In the upper panelsη=1(case AI),and the curves are shown for different apparent magnitudes(left),and different redshifts(right).In the lower panels we show curves corresponding to different choices forηandǫ,(cases AII and AIII)assuming B=20.3and z=1.5respectively.ing approximately to the median quasar B-magnitude(lefthand panel)and z=1.5(right hand panel)are shown,andthe curve corresponding toη=1(case AI)is reproducedfrom the upper panels for comparison(solid lines).As-suming the local normalizationǫ=ǫSIS and thatηrangesbetween0.01and1with a constant dP obs/d(logη)(caseAII),the typical quasar of apparent magnitude B mustbe powered by a more massive SMBH and hence residein a more massive galaxy than in theη=1case.Thisresults in a larger clustering length for quasars of a givenapparent magnitude B.The resulting evolution,indicatedby the dashed lines,appears to be incompatible with thedata.The increase in R0may be compensated for by anincrease in the normalization of the M BH−M halo rela-tion.The dot-dashed curves show the result of increasingthis normalization relative to local observations by a fac-tor of10(ǫ=10ǫSIS).This factor equals the inverse of themedian of the distribution dP/d(logη)=const.The re-sulting curve(corresponding to case AIII)is very similarto ourfiducial case(η=1).These results demonstrate that while a spread in thevalues ofηfor different quasars results in the correlationfunction being measured over a wider range of halo masses,the correlation length is primarily sensitive to the charac-teristic halo mass,as specified by the characteristic valueofη.Furthermore,the results demonstrate the importantpoint that the correlation length measures the product ofthe normalization in the M bh–M halo relation and the me-dian fraction of the Eddington luminosity at which quasarsshine,ηmed.With respect to the correlation function,thisquantityǫηmed(which is the same in cases AI and AIII)is more fundamental to the correlation function than thequasar lifetime since it predicts the correlation length in-dependent from consideration of quasar number counts.It is important to note that since the normalization of thelocal M BH−M halo relation is estimated(ǫ=ǫSIS,Fer-rarese2002),the value of the quasar correlation lengthat low redshift implies that quasars spend most of theirbright phase shining near their Eddington luminosity.4.2.The correlation function for models withM bh∝M5/3haloWe next examine whether the correlation function ob-served by the2dF survey may be used to constrain theevolution of the M bh–M halo relation.In the previous sub-section,we have considered the case of a SMBH mass thatscales with thefifth power of circular velocity independentof redshift(equation7,case A).The alternative case Bexample postulates that the SMBH mass has a redshiftindependent scaling with the halo mass rather than halocircular velocity(equation8).The upper panels of Fig-ure3plot the correlation length in this case withη=1andǫ=ǫSIS(case BI).Both the evolution of the correlationlength with redshift for different apparent magnitudes(left6Fig. 3.—The correlation length,R0as a function of redshift(left hand panel)and apparent B-band magnitude(right hand panel).The data is from the2dF QRS(Croom eta al.2001b,c),with the gray error bars showing the correlation length from different sub-samples,and the dark error bars at z=1.5(left hand panels)and B=20.3(right hand panels)showing the correlation length for the full sample.The model assumes M bh∝M5/3halo.In the upper panelsη=1(case BI),and the curves are shown for different apparent magnitudes(left),and different redshifts(right).In the lower panels we show curves corresponding to different choices forηandǫ(cases BII and BIII),assuming B=20.3and z=1.5respectively.hand panel),and the variation of correlation length with agiven apparent magnitude at various redshifts(right handpanel)are shown.The case B M bh−M halo relation resultsin a correlation length that varies significantly more withredshift than the data requires.The lower panels showexamples with values ofηthat differ from unity.Only thecases of B=20.3(left hand panel)and z=1.5(right handpanel)are shown,and the result assumingη=1(case BI)is reproduced from the upper panels for comparison(solidlines).Ifǫ=ǫSIS,andηranges between0.01and1,withdP obs/dη∝const(case BII),then the typical quasar ofapparent magnitude B must have a larger clustering length(dashed lines).This may be compensated for by increasingthe normalization of the M BH–M halo relation by a factorof10(ǫ=10ǫSIS,case BIII)as considered before(dot-dashed lines).The rapid evolution with redshift that results from acase B M BH–M halo relation could be diminished if the lu-minosities of quasars were a higher fraction of their Ed-dington limit at higher redshift.However we have seenthat the locally observed normalization of the M bh–M halorelation requires most present-day quasars to be shiningnear their Eddington luminosity.Quasars at high redshiftwould therefore have to be super-Eddington,shining at∼η∼(1+z)5/2(η∼30at z∼3)in order to repro-duce the observed slow evolution of the clustering length.This requirement onηmay be somewhat relaxed in modelshavingǫ>ǫSIS,as is discussed in the next section.5.constrainingηandǫusing the quasarcorrelation functionThe M bh–M halo relation for local galaxies requires achoice for the relationship between the circular velocityat the radius probed by observations of galaxies,and thecircular velocity at the virial radius.This relationship de-pends on the dark-matter mass profile and is still uncertaindue to the gravitational interaction between the baryons(which cool and often dominate gravity near the centerof galaxies)and the dark matter.Ferrarese(2002)pre-sented M bh–M halo relations for three different cases,whichmay be summarized in the present notation byǫ=ǫSIS,ǫ=ǫNFW=3.7ǫSIS,andǫ=ǫS02=25ǫSIS.The secondcase corresponds to the universal profile of Navarro,Frenk&White(1996,NFW),and the third to the normalizationderived based on the weak lensing study of Seljak(2002).The results in the preceding sections have been pre-sented forfiducial models with(ǫ,η)=(ǫSIS,1),(ǫSIS,0.1)and(10ǫSIS,0.1).It was demonstrated that the correlationfunction is primarily dependent on the product betweenǫand the median value ofη,namelyǫηmed.This raises thepossibility thatǫηmed could be constrained using correla-tion function data.We have computed the evolution of the7Fig. 4.—The probability P (χ2)of case A and case B models as a function of f ǫηmed .The dark lines correspond to fits to the redshift dependent correlation length R 0(z )measured by the 2dF quasar redshift survey (Croom et al.2001b).The gray lines show results for a hypothetical larger future sample whose errors on R 0are reduced by a factor of√2(light lines).Future surveys will betterconstrain the gradient dR 0/dz ,and help discriminate fur-ther between different models of the M bh –M halo relation.Our discussion so far has been independent of the quasar luminosity function.In the next section we discuss how the luminosity function may be used to determine the redshift evolution of the quasar lifetime.6.the luminosity function and quasar lifetimeIn the previous sections we have demonstrated that the evolution of the M bh –M halo relation with redshift may be constrained directly from the quasar correlation function.We have shown that the critical parameter determining the SMBH mass is the halo circular velocity rather thanthe halo mass.We reiterate that this result does not rely on the luminosity function of quasars.On the other hand,the number counts of quasars are proportional to the quasar lifetime.Therefore,the quasar lifetime and its evolution with redshift may be determined by com-paring the observed quasar number counts to the SMBH mass function.The latter may be obtained from the Press-Schechter (1976)mass-function of dark-matter halos (with the improvement of Sheth &Tormen 1999)combined with the M bh –M halo relation.Theoretical models of the quasar luminosity function often associate quasar activity with major mergers (e.g.Kauffmann &Haehnelt 2000;Wyithe &Loeb 2003).A simple model that attributes quasar activity to ma-jor mergers,assumes a M bh –M halo relation that is de-scribed by equation (7),and sets the quasar lifetime equal to the dynamical time of a galactic disk,accurately re-produces the entire optical and X-ray luminosity func-tions of quasars at redshifts between 2and 6(Wyithe &Loeb 2003).At lower redshifts (z 2),this prescription correctly predicts the luminosity function at luminosities below the characteristic break (Boyle et al.2000).In dif-ference to Wyithe &Loeb (2003)we have assumed the quasar activity to take place in the larger SMBH before coalescence of the SMBH binary formed during the merger (Volonteri et al.2002).Figure 5shows the comparison of this model with observations.Specifically,we show the fiducial case AI (which corresponds to the model pre-sented in Wyithe &Loeb 2003)using equation (7)with ǫ=ǫSIS and η=1(solid curves).We have shown that case AI describes the observed quasar correlation function (see figures 1-2).However as discussed in §5,case-B mod-els for the M bh –M halo relation also provide acceptable fits to R 0(z )so long as ǫ 10ǫSIS and η∼1.Therefore a corresponding luminosity function model was also gener-ated for this case assuming a constant lifetime of t q =107years.We have plotted this model in figure 5(dot-dashed lines).8Fig.5.—Comparison of the model and observed quasar luminosity functions at various redshifts.The data points at z 4are summarized in Pei(1995),while the light lines show the double power-lawfit to the2dF quasar luminosity function(Boyle et al.2000).At z∼4.3and z∼6.0the data is from Fan et al.(2001a;2001b;2003).The gray regions show the1-σrange of logarithmic slope([−2.25,−2.75]at z∼4.3 and[−1.6,−3.1]at z∼6),and the vertical bars show the uncertainty in the normalization.The open circles show data points converted from the X-ray luminosity function(Barger et al.2003)of low luminosity quasars using the median quasar spectral energy distribution(Elvis et al.1994).The model luminosity functions shown correspond to cases AI(solid curves)and a model assuming case B evolution withǫ=ǫS02,η=1and a constant lifetime of t q=107years(dot-dashed curves).The dashed pairs of vertical lines show the range corresponding to apparent B-magnitudes between18.25and20.85.Wefind that ourfiducial model(case AI;solid lines) with a quasar lifetime that equals the dynamical time of a galactic disk,reproduces the observed luminosity function over a wide range of redshifts and luminosities(see Wyithe &Loeb2003).Our second model(case B,ǫ 10ǫSIS,η=1,t q=107;dot-dashed lines)also reproduces the ob-served luminosity function at z 4.5.However at z∼6 this model underestimates the observed number counts by two orders of magnitude.Case B evolution for the M bh–M halo relation is therefore challenged by the existence of the highest redshift quasars,which would imply a quasar lifetime that exceeds the age of the universe at z∼6. Moreover,given the Salpeter(1964)time of∼4×107 years,the SMBHs powering these quasars would grow to 25times their initial mass during their lifetime.Provided that quasar activity is trigged by major mergers,the re-quirement that the M bh–M halo relation reproduce the ob-served evolution in quasar clustering,together with the observed evolution in the number counts of quasars there-fore implies case A evolution,and a quasar lifetime that is set by the dynamical time of the host galaxy.We reinforce the important qualitative result that since the evolution of quasar correlations require SMBHs to take a larger fraction of the halo mass at high redshift(case A,see equation7), the observed evolution in the number counts requires a quasar lifetime that is shorter at higher redshifts,scaling approximately as the dynamical time of a dark matter halo [∝(1+z)−3/2].We point out that the model luminosity functions fail to reproduce the rapid drop in the density of luminous quasars seen at low redshift.This drop is thought to be due to the consumption of cold gas in galaxies by star formation(e.g.Kauffmann&Haehnelt2000)and the in-hibition of accretion onto massive halos at late times(e.g. Scannapieco&Oh2004).However,most of the quasars in the2dF quasar redshift survey have B-magnitudes that lie below the characteristic break in the luminosity func-tion at low redshift(Boyle et al.2000;Croom et al.2001). This can be seen in Figure5where the vertical dashed lines show the luminosities bracketing the apparent mag-nitude range18.25<B<20.85.Since the model correctly predicts the luminosity function within most of this lumi-nosity range at all redshifts,we are justified in deriving combined constraints from the luminosity and correlation9functions of quasars.7.do bright low-redshift quasars shine neartheir eddington luminosity?In§4we demonstrated that the2dF quasar sample has a correlation length that is consistent with the local M bh−M halo relation,and that quasars shine near their Eddington luminosity.In addition it was shown that this consistency extends to both bright and faint subsamples of quasars.The brightest2dF quasars(18.1≤B≤19.9)pre-sented by Croom et al.(2002)are mostly brighter than the characteristic break luminosity in the differential quasar number counts(e.g.Boyle et al.2000).These bright quasars have a lower abundance than expected from merg-ing halos at z 2(seefigure5).Either the lifetime(or occupation fraction)of bright quasars is lower than ex-pected at z 2or else these quasars shine well below their Eddington limit.Figure2indicates that the slow dependence of R0with B reported by Croom et al.(2002) is consistent with the expected trend if all quasars shine near their Eddington luminosity.This consistency sug-gests that bright quasars are under represented at z 2 because of a reduced quasar lifetime(or a reduced occu-pation fraction)rather than a reduced value ofηduring their brightest phase.8.discussionIn this paper we have demonstrated that the relation-ship between the mass of a SMBH and its host dark-matter halo is the fundamental quantity that determines the clus-tering of quasars.In particular the M bh–M halo relation and its evolution with redshift,may be determined directly from the evolution in the correlation length of quasars,in-dependent of consideration of the quasar luminosity func-tion or assumptions about the quasar lifetime.Beginning with the locally observed M bh–M halo relation,we have shown that the observed correlation length of quasars in the2dF quasar redshift survey is consistent with SMBHs that shine at∼10–100%of their Eddington luminosity during their bright quasar episode.Moreover,the evo-lution of the clustering length with redshift is consistent with a SMBH mass whose redshift-independent scaling is with the circular velocity of the host dark matter halo (see equation7).In contrast,it appears that a relation for the SMBH mass whose redshift-independent scaling is with the mass of the host dark matter halo(equation8) would have resulted in too much evolution of the clustering length with redshift.The portion of the2dF quasar survey from which the data used in this study were drawn,contains∼104 quasars.Upon completion,the Sloan Digital Sky Sur-vey will have spectra for ten times this number of quasars, spread over a larger redshift range(York et al.2000).This will allow more accurate determination of the correlation length and its evolution,and hence provide more accu-rate constraints the SMBH population.The selection of quasars for the spectroscopic survey of SDSS at z<3is restricted to i∗<19.Thus,most of the low redshift SDSS quasars will fall at luminosities that are brighter than the characteristic break in the luminosity function(e.g.Boyle et al.2000).These bright quasars have a lower abundance than expected from the number of halos merging at z 2.The reason for this low abundance may be either that the lifetime(or occupation fraction)of bright quasars is lower than expected at z 2,or alternatively that the fraction of the Eddington limit at which the quasars shine is small. The2dF quasar sample straddles the luminosity function break.We have shown that the similarity in the cluster-ing statistics of sub-samples of quasars having different ranges in luminosity suggest that the lifetime(or occupa-tion fraction)of bright quasars is lower than expected at z 2,but that these quasars also shine near their Edding-ton luminosity.Measurements of the correlation length as a function of quasar luminosity in SDSS can help further distinguish between these two possibilities.As we have shown in a previous paper(Wyithe& Loeb2003),feedback–regulated growth of SMBHs during active quasar phases implies M bh∝v5c,consistent with the inferred relation for galactic halos in the local universe (Ferrarese2002).Assumingη=1as suggested by obser-vations of both low and high-redshift quasars(Floyd2003; Willott,McLure&Jarvis2003),we have shown that only ∼7%of the Eddington luminosity output needs to be deposited into the surrounding gas in order to unbind it from the host galaxy over the dynamical time of the sur-rounding galactic disk.The power-law index of5in the M bh–v c relation,is larger than the values of4–4.5inferred from the local relation between M bh and the stellar ve-locity dispersionσ⋆(Merritt&Ferrarese2001;Tremaine et al.2002);the difference originating from the observa-tion that the v c–σ⋆relation is shallower than linear for stellar bulges embedded in cold dark matter halos(Fer-rarese2002).Feedback–regulated growth also implies that the M bh–v c relation should be independent of redshift,as implied by the slow evolution in the clustering length of quasars.A very simple model can therefore be constructed to de-scribe the correlation length of quasars and its evolution in the2dF survey,as well as the number counts of quasars out to very high redshift(z∼6).The model includes four simple assumptions,but no free parameters:(i)the locally observed M bh–M halo relation extends to high red-shifts through equation(7)with the SMBH mass scaling as halo circular velocity to the5-th power;(ii)SMBHs shine near their Eddington luminosity with a universal spectrum (Elvis et al.1994)during luminous quasar episodes;(iii) quasar episodes are associated with major galaxy mergers; and(iv)the quasar lifetime is set by the dynamical time of the host galaxy.The assumption of a SMBH mass that scales with halo circular velocity independently of redshift is supported by the observations of Shields et al.(2003)that there is no evolution in the M bh–σ⋆relation out to z∼3.The as-sumption that quasars shine near their Eddington limit is supported by observations of high and low redshift quasars (Floyd2003;Willott,McLure&Jarvis2003).Overall,the sample of available data on the clustering properties and the number counts of quasars is most readily explained by a quasar lifetime that is set by the dynamical time of the host galaxy rather than by the Salpeter(1964)e-folding time for the growth of its mass.This work was supported in part by NASA grant NAG 5-13292,and by NSF grants AST-0071019,AST-0204514。
