Pub Date : 2019-08-27DOI: 10.1146/ANNUREV-ASTRO-091918-104438
S. W. Weaver
The recent advancements in far-infrared (far-IR) astronomy brought about by the Herschel, SOFIA, and ALMA observatories have led to technological advancements in millimeterwave and submillimeterwave laboratory spectroscopy that is used to support molecular observations. This review gives an overview of rotational spectroscopy and its relationship with observational astronomy, as well as an overview of laboratory spectroscopic techniques focusing on both historical approaches and new advancements. Additional topics discussed include production and detection techniques for unstable molecular species of astrochemical interest, data analysis approaches that address spectral complexity and line confusion, and the current state of and limitations to spectral line databases. Potential areas for new developments in this field are also reviewed. To advance the field, the following challenges must be addressed: ▪ Data acquisition speed, spectral sensitivity, and analysis approaches for complex mixtures and broadband spectra are the greatest limitations—and hold the greatest promise for advancement—in this field of research. ▪ Full science return from far-IR observatories cannot be realized until laboratory spectroscopy catches up with the data rate for observations. ▪ New techniques building on those used in the microwave and IR regimes are required to fill the terahertz gap.
{"title":"Millimeterwave and Submillimeterwave Laboratory Spectroscopy in Support of Observational Astronomy","authors":"S. W. Weaver","doi":"10.1146/ANNUREV-ASTRO-091918-104438","DOIUrl":"https://doi.org/10.1146/ANNUREV-ASTRO-091918-104438","url":null,"abstract":"The recent advancements in far-infrared (far-IR) astronomy brought about by the Herschel, SOFIA, and ALMA observatories have led to technological advancements in millimeterwave and submillimeterwave laboratory spectroscopy that is used to support molecular observations. This review gives an overview of rotational spectroscopy and its relationship with observational astronomy, as well as an overview of laboratory spectroscopic techniques focusing on both historical approaches and new advancements. Additional topics discussed include production and detection techniques for unstable molecular species of astrochemical interest, data analysis approaches that address spectral complexity and line confusion, and the current state of and limitations to spectral line databases. Potential areas for new developments in this field are also reviewed. To advance the field, the following challenges must be addressed: ▪ Data acquisition speed, spectral sensitivity, and analysis approaches for complex mixtures and broadband spectra are the greatest limitations—and hold the greatest promise for advancement—in this field of research. ▪ Full science return from far-IR observatories cannot be realized until laboratory spectroscopy catches up with the data rate for observations. ▪ New techniques building on those used in the microwave and IR regimes are required to fill the terahertz gap.","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2019-08-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1146/ANNUREV-ASTRO-091918-104438","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44398452","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-08-18DOI: 10.1146/annurev-astro-081817-051832
L. Kewley, D. Nicholls, R. Sutherland
We review the use of emission lines for understanding galaxy evolution, focusing on excitation source, metallicity, ionization parameter, ISM pressure, and electron density. We discuss the physics, benefits, and caveats of emission line diagnostics, including the effects of theoretical model uncertainties, diffuse ionized gas, and sample selection bias. In anticipation of upcoming telescope facilities, we provide new self-consistent emission line diagnostic calibrations for complete spectral coverage from the UV to the IR. These diagnostics can be used in concert to understand how fundamental galaxy properties have changed across cosmic time. We conclude the following: ▪ The UV, optical, and IR contain complementary diagnostics that can probe the conditions within different nebular ionization zones. ▪ Accounting for complex density gradients and temperature profiles is critical for reliably estimating the fundamental properties of Hii regions and galaxies. ▪ Diffuse ionized gas can raise metallicity estimates, flatten metallicity gradients, and introduce scatter in ionization parameter measurements. ▪ New 3D emission line diagnostics successfully separate the contributions from star formation, AGN, and shocks using integral field spectroscopy. We summarize with a discussion of the challenges and major opportunities for emission line diagnostics in the coming years.
{"title":"Understanding Galaxy Evolution Through Emission Lines","authors":"L. Kewley, D. Nicholls, R. Sutherland","doi":"10.1146/annurev-astro-081817-051832","DOIUrl":"https://doi.org/10.1146/annurev-astro-081817-051832","url":null,"abstract":"We review the use of emission lines for understanding galaxy evolution, focusing on excitation source, metallicity, ionization parameter, ISM pressure, and electron density. We discuss the physics, benefits, and caveats of emission line diagnostics, including the effects of theoretical model uncertainties, diffuse ionized gas, and sample selection bias. In anticipation of upcoming telescope facilities, we provide new self-consistent emission line diagnostic calibrations for complete spectral coverage from the UV to the IR. These diagnostics can be used in concert to understand how fundamental galaxy properties have changed across cosmic time. We conclude the following: ▪ The UV, optical, and IR contain complementary diagnostics that can probe the conditions within different nebular ionization zones. ▪ Accounting for complex density gradients and temperature profiles is critical for reliably estimating the fundamental properties of Hii regions and galaxies. ▪ Diffuse ionized gas can raise metallicity estimates, flatten metallicity gradients, and introduce scatter in ionization parameter measurements. ▪ New 3D emission line diagnostics successfully separate the contributions from star formation, AGN, and shocks using integral field spectroscopy. We summarize with a discussion of the challenges and major opportunities for emission line diagnostics in the coming years.","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2019-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1146/annurev-astro-081817-051832","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42634355","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-08-18DOI: 10.1146/annurev-aa-57-072419-100001
S. Faber, E. V. van Dishoeck
{"title":"Introduction","authors":"S. Faber, E. V. van Dishoeck","doi":"10.1146/annurev-aa-57-072419-100001","DOIUrl":"https://doi.org/10.1146/annurev-aa-57-072419-100001","url":null,"abstract":"","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2019-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1146/annurev-aa-57-072419-100001","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48172041","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-08-18DOI: 10.1146/annurev-astro-091918-104446
N. Roman
Dear readers: We are sad to report that, soon after submitting her draft manuscript for this prefatory chapter, Nancy Grace Roman passed away on December 25, 2018. This final version of her memoir has been lightly edited but remains very true to the original. However, an Abstract was missing. Rather than trying to synthesize one in Nancy Grace's inimitable style, we take this opportunity to comment briefly on her life and its significance. Nancy Grace Roman was born in 1925 and came of age scientifically in the United States during the 1940s and 1950s. Together with the equally fascinating prefatory by Vera Rubin ( ARAA, Vol. 49), which we also recommend to you, these two memoirs give us intimate insight into the obstacles faced by women astronomers trying to rise in the field during those years. Roman's memoir is bitingly candid, recounting numerous snubs by teachers, insultingly small salaries, and attempts by her thesis advisor to simultaneously exploit her scientific findings and smother her role in them. Discouragement at every turn from doing forefront research is what drove Roman into government service, where she found a niche and blossomed as one of the visionary founders of the US civilian space program. We do not know what impact Roman might have had as a researcher with access to the world's largest telescopes, but we do know that her influence as an enabler of other people's science was vast. Her sobriquet as the “Mother of Hubble,” bestowed by admirer Ed Weiler, is well deserved. Nancy Grace granted an audio interview to Joss Bland-Hawthorn on August 4, 2018, just a few months before her passing. It captures her persona more vividly than mere words on paper, and we recommend the online recording to you at https://www.annualreviews.org/r/nancy-grace-roman-interview .
亲爱的读者：我们很遗憾地报告，Nancy Grace Roman在提交了这一序言章节的手稿草稿后不久，于2018年12月25日去世。她的回忆录的最后一个版本经过了轻微的编辑，但仍然非常忠于原著。但是，缺少一个摘要。我们没有试图综合南希·格蕾丝无与伦比的的风格，而是借此机会简要评论她的生活及其意义。Nancy Grace Roman出生于1925年，在20世纪40年代和50年代在美国科学地成长。这两本回忆录加上维拉·鲁宾（Vera Rubin）同样引人入胜的序言（ARAA，第49卷），我们也向您推荐，让我们深入了解了那些年来女性天文学家试图在这一领域崛起所面临的障碍。罗曼的回忆录非常坦率，讲述了老师们的多次冷落、令人反感的微薄薪水，以及她的论文顾问试图同时利用她的科学发现并扼杀她在其中的作用。从事前沿研究的每一次挫折都驱使罗曼进入政府服务，在那里她找到了一个利基市场，并成长为美国民用航天计划富有远见的创始人之一。我们不知道罗曼作为一名能够使用世界上最大望远镜的研究人员可能会产生什么影响，但我们知道她作为其他人科学的推动者的影响力是巨大的。她的绰号“哈勃之母”，由崇拜者埃德·威勒授予，是当之无愧的。Nancy Grace于2018年8月4日，也就是她去世前几个月，接受了Joss Bland Hawthorn的音频采访。它比纸上的文字更生动地捕捉到了她的个性，我们建议您在https://www.annualreviews.org/r/nancy-grace-roman-interview。
{"title":"Nancy Grace Roman and the Dawn of Space Astronomy","authors":"N. Roman","doi":"10.1146/annurev-astro-091918-104446","DOIUrl":"https://doi.org/10.1146/annurev-astro-091918-104446","url":null,"abstract":"Dear readers: We are sad to report that, soon after submitting her draft manuscript for this prefatory chapter, Nancy Grace Roman passed away on December 25, 2018. This final version of her memoir has been lightly edited but remains very true to the original. However, an Abstract was missing. Rather than trying to synthesize one in Nancy Grace's inimitable style, we take this opportunity to comment briefly on her life and its significance. Nancy Grace Roman was born in 1925 and came of age scientifically in the United States during the 1940s and 1950s. Together with the equally fascinating prefatory by Vera Rubin ( ARAA, Vol. 49), which we also recommend to you, these two memoirs give us intimate insight into the obstacles faced by women astronomers trying to rise in the field during those years. Roman's memoir is bitingly candid, recounting numerous snubs by teachers, insultingly small salaries, and attempts by her thesis advisor to simultaneously exploit her scientific findings and smother her role in them. Discouragement at every turn from doing forefront research is what drove Roman into government service, where she found a niche and blossomed as one of the visionary founders of the US civilian space program. We do not know what impact Roman might have had as a researcher with access to the world's largest telescopes, but we do know that her influence as an enabler of other people's science was vast. Her sobriquet as the “Mother of Hubble,” bestowed by admirer Ed Weiler, is well deserved. Nancy Grace granted an audio interview to Joss Bland-Hawthorn on August 4, 2018, just a few months before her passing. It captures her persona more vividly than mere words on paper, and we recommend the online recording to you at https://www.annualreviews.org/r/nancy-grace-roman-interview .","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2019-08-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1146/annurev-astro-091918-104446","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49197277","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-08-12DOI: 10.1146/annurev-astro-091918-104409
K. Altwegg, H. Balsiger, S. Fuselier
In situ research of cometary chemistry began when measurements from the Giotto mission at Comet 1P/Halley revealed the presence of complex organics in the coma. New telescopes and space missions have provided detailed remote and in situ measurements of the composition of cometary volatiles. Recently, the Rosetta mission to Comet 67P/Churyumov–Gerasimenko (67P) more than doubled the number of parent species and the number of isotopic ratios known for comets. Forty of the 71 parent species have also been detected in pre- and protostellar clouds. Most isotopic ratios are nonsolar. This diverse origin is in contrast to that of the Sun, which received its material from the bulk of the collapsing cloud. The xenon isotopic ratios measured in 67P can explain the long-standing question about the origin of terrestrial atmospheric xenon. These findings strengthen the notion that comets are indeed an important link between the ISM and today's solar system including life on Earth. ▪ Nonsolar isotopic ratios for species such as Xe, N, S, and Si point to a nonhomogenized protoplanetary disk from which comets received their material. ▪ The similarity of the organic inventories of comets and presolar and protostellar material makes it plausible that this material was accreted almost unaltered by comets from the presolar stage. ▪ Large variations in the deuterium-to-hydrogen ratio in water for comets indicate a large range in the protoplanetary disk from which comets formed. ▪ The amount of organics delivered by comets to Earth may be highly significant.
{"title":"Cometary Chemistry and the Origin of Icy Solar System Bodies: The View After Rosetta","authors":"K. Altwegg, H. Balsiger, S. Fuselier","doi":"10.1146/annurev-astro-091918-104409","DOIUrl":"https://doi.org/10.1146/annurev-astro-091918-104409","url":null,"abstract":"In situ research of cometary chemistry began when measurements from the Giotto mission at Comet 1P/Halley revealed the presence of complex organics in the coma. New telescopes and space missions have provided detailed remote and in situ measurements of the composition of cometary volatiles. Recently, the Rosetta mission to Comet 67P/Churyumov–Gerasimenko (67P) more than doubled the number of parent species and the number of isotopic ratios known for comets. Forty of the 71 parent species have also been detected in pre- and protostellar clouds. Most isotopic ratios are nonsolar. This diverse origin is in contrast to that of the Sun, which received its material from the bulk of the collapsing cloud. The xenon isotopic ratios measured in 67P can explain the long-standing question about the origin of terrestrial atmospheric xenon. These findings strengthen the notion that comets are indeed an important link between the ISM and today's solar system including life on Earth. ▪ Nonsolar isotopic ratios for species such as Xe, N, S, and Si point to a nonhomogenized protoplanetary disk from which comets received their material. ▪ The similarity of the organic inventories of comets and presolar and protostellar material makes it plausible that this material was accreted almost unaltered by comets from the presolar stage. ▪ Large variations in the deuterium-to-hydrogen ratio in water for comets indicate a large range in the protoplanetary disk from which comets formed. ▪ The amount of organics delivered by comets to Earth may be highly significant.","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2019-08-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1146/annurev-astro-091918-104409","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49498628","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-06-13DOI: 10.1146/annurev-astro-091918-104501
J. Cordes, S. Chatterjee
We summarize our understanding of millisecond radio bursts from an extragalactic population of sources. Fast radio bursts (FRBs) occur at an extraordinary rate, thousands per day over the entire sky with radiation energy densities at the source about ten billion times larger than those from Galactic pulsars. We survey FRB phenomenology, source models and host galaxies, coherent radiation models, and the role of plasma propagation effects in burst detection. The FRB field is guaranteed to be exciting: New telescopes will expand the sample from the current ∼80 unique burst sources (and only a few secure localizations and redshifts) to thousands, with burst localizations that enable host-galaxy redshifts emerging directly from interferometric surveys. ▪ FRBs are now established as an extragalactic phenomenon. ▪ Only a few sources are known to repeat. Despite the failure to redetect other FRBs, they are not inconsistent with all being repeaters. ▪ FRB sources may be new, exotic kinds of objects or known types in extreme circumstances. Many inventive models exist, ranging from alien spacecraft to cosmic strings, but those concerning compact objects and supermassive black holes have gained the most attention. A rapidly rotating magnetar is a promising explanation for FRB 121102 along with the persistent source associated with it, but alternative source models are not ruled out for it or other FRBs. ▪ FRBs are powerful tracers of circumsource environments, “missing baryons” in the intergalactic medium (IGM), and dark matter. ▪ The relative contributions of host galaxies and the IGM to propagation effects have yet to be disentangled, so dispersion measure distances have large uncertainties.
{"title":"Fast Radio Bursts: An Extragalactic Enigma","authors":"J. Cordes, S. Chatterjee","doi":"10.1146/annurev-astro-091918-104501","DOIUrl":"https://doi.org/10.1146/annurev-astro-091918-104501","url":null,"abstract":"We summarize our understanding of millisecond radio bursts from an extragalactic population of sources. Fast radio bursts (FRBs) occur at an extraordinary rate, thousands per day over the entire sky with radiation energy densities at the source about ten billion times larger than those from Galactic pulsars. We survey FRB phenomenology, source models and host galaxies, coherent radiation models, and the role of plasma propagation effects in burst detection. The FRB field is guaranteed to be exciting: New telescopes will expand the sample from the current ∼80 unique burst sources (and only a few secure localizations and redshifts) to thousands, with burst localizations that enable host-galaxy redshifts emerging directly from interferometric surveys. ▪ FRBs are now established as an extragalactic phenomenon. ▪ Only a few sources are known to repeat. Despite the failure to redetect other FRBs, they are not inconsistent with all being repeaters. ▪ FRB sources may be new, exotic kinds of objects or known types in extreme circumstances. Many inventive models exist, ranging from alien spacecraft to cosmic strings, but those concerning compact objects and supermassive black holes have gained the most attention. A rapidly rotating magnetar is a promising explanation for FRB 121102 along with the persistent source associated with it, but alternative source models are not ruled out for it or other FRBs. ▪ FRBs are powerful tracers of circumsource environments, “missing baryons” in the intergalactic medium (IGM), and dark matter. ▪ The relative contributions of host galaxies and the IGM to propagation effects have yet to be disentangled, so dispersion measure distances have large uncertainties.","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2019-06-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1146/annurev-astro-091918-104501","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43596442","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-04-05DOI: 10.1146/annurev-astro-081817-051846
N. Madhusudhan
Exoplanetary science is on the verge of an unprecedented revolution. The thousands of exoplanets discovered over the past decade have most recently been supplemented by discoveries of potentially habitable planets around nearby low-mass stars. Currently, the field is rapidly progressing toward detailed spectroscopic observations to characterize the atmospheres of these planets. Various surveys from space and the ground are expected to detect numerous more exoplanets orbiting nearby stars that make the planets conducive for atmospheric characterization. The current state of this frontier of exoplanetary atmospheres may be summarized as follows. ▪ We have entered the era of comparative exoplanetology thanks to high-fidelity atmospheric observations now available for tens of exoplanets. ▪ Recent studies reveal a rich diversity of chemical compositions and atmospheric processes hitherto unseen in the Solar System. ▪ Elemental abundances of exoplanetary atmospheres place important constraints on exoplanetary formation and migration histories. ▪ Upcoming observational facilities promise to revolutionize exoplanetary spectroscopy down to rocky exoplanets. ▪ The detection of a biosignature in an exoplanetary atmosphere is conceivable over the next decade. In the present review, we discuss the modern and future landscape of this frontier area of exoplanetary atmospheres. We start with a brief review of the area, emphasising the key insights gained from different observationalmethods and theoretical studies. This is followed by an in-depth discussion of the state of the art, challenges, and future prospects in three forefront branches of the area.
{"title":"Exoplanetary Atmospheres: Key Insights, Challenges, and Prospects","authors":"N. Madhusudhan","doi":"10.1146/annurev-astro-081817-051846","DOIUrl":"https://doi.org/10.1146/annurev-astro-081817-051846","url":null,"abstract":"Exoplanetary science is on the verge of an unprecedented revolution. The thousands of exoplanets discovered over the past decade have most recently been supplemented by discoveries of potentially habitable planets around nearby low-mass stars. Currently, the field is rapidly progressing toward detailed spectroscopic observations to characterize the atmospheres of these planets. Various surveys from space and the ground are expected to detect numerous more exoplanets orbiting nearby stars that make the planets conducive for atmospheric characterization. The current state of this frontier of exoplanetary atmospheres may be summarized as follows. ▪ We have entered the era of comparative exoplanetology thanks to high-fidelity atmospheric observations now available for tens of exoplanets. ▪ Recent studies reveal a rich diversity of chemical compositions and atmospheric processes hitherto unseen in the Solar System. ▪ Elemental abundances of exoplanetary atmospheres place important constraints on exoplanetary formation and migration histories. ▪ Upcoming observational facilities promise to revolutionize exoplanetary spectroscopy down to rocky exoplanets. ▪ The detection of a biosignature in an exoplanetary atmosphere is conceivable over the next decade. In the present review, we discuss the modern and future landscape of this frontier area of exoplanetary atmospheres. We start with a brief review of the area, emphasising the key insights gained from different observationalmethods and theoretical studies. This is followed by an in-depth discussion of the state of the art, challenges, and future prospects in three forefront branches of the area.","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2019-04-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1146/annurev-astro-081817-051846","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48904602","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-02-27DOI: 10.1146/annurev-astro-091918-104423
P. Ferreira
Cosmological observations are beginning to reach a level of precision that allows us to test some of the most fundamental assumptions in our working model of the Universe. One such assumption is that gravity is governed by the theory of general relativity. In this review, we discuss how one might go about extending general relativity and how such extensions can be described in a unified way on large scales. This allows us to describe the phenomenology of modified gravity in the growth and morphology of the large-scale structure of the Universe. On smaller scales, we explore the physics of gravitational screening and how it might manifest itself in galaxies, clusters, and, more generally, in the cosmic web. We then analyze the current constraints from large-scale structure and conclude by discussing the future prospects of the field in light of the plethora of surveys currently being planned. Key results include the following: ▪ There are a plethora of alternative theories of gravity that are restricted by fundamental physics considerations. ▪ There is now a well-established formalism for describing cosmological perturbations in the linear regime for general theories of gravity. ▪ Gravitational screening can mask modifications to general relativity on small scales but may, itself, lead to distinctive signatures in the large-scale structure of the Universe. ▪ Current constraints on both linear and nonlinear scales may be affected by systematic uncertainties that limit our ability to rule out alternatives to general relativity. ▪ The next generation of cosmological surveys will dramatically improve constraints on general relativity, by up to two orders of magnitude.
{"title":"Cosmological Tests of Gravity","authors":"P. Ferreira","doi":"10.1146/annurev-astro-091918-104423","DOIUrl":"https://doi.org/10.1146/annurev-astro-091918-104423","url":null,"abstract":"Cosmological observations are beginning to reach a level of precision that allows us to test some of the most fundamental assumptions in our working model of the Universe. One such assumption is that gravity is governed by the theory of general relativity. In this review, we discuss how one might go about extending general relativity and how such extensions can be described in a unified way on large scales. This allows us to describe the phenomenology of modified gravity in the growth and morphology of the large-scale structure of the Universe. On smaller scales, we explore the physics of gravitational screening and how it might manifest itself in galaxies, clusters, and, more generally, in the cosmic web. We then analyze the current constraints from large-scale structure and conclude by discussing the future prospects of the field in light of the plethora of surveys currently being planned. Key results include the following: ▪ There are a plethora of alternative theories of gravity that are restricted by fundamental physics considerations. ▪ There is now a well-established formalism for describing cosmological perturbations in the linear regime for general theories of gravity. ▪ Gravitational screening can mask modifications to general relativity on small scales but may, itself, lead to distinctive signatures in the large-scale structure of the Universe. ▪ Current constraints on both linear and nonlinear scales may be affected by systematic uncertainties that limit our ability to rule out alternatives to general relativity. ▪ The next generation of cosmological surveys will dramatically improve constraints on general relativity, by up to two orders of magnitude.","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2019-02-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1146/annurev-astro-091918-104423","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42067931","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-01-16DOI: 10.1146/annurev-astro-091918-104453
J. Simon
The lowest luminosity ([Formula: see text] L[Formula: see text]) Milky Way satellite galaxies represent the extreme lower limit of the galaxy luminosity function. These ultra-faint dwarfs are the oldest, most dark matter–dominated, most metal-poor, and least chemically evolved stellar systems known. They therefore provide unique windows into the formation of the first galaxies and the behavior of dark matter on small scales. In this review, we summarize the discovery of ultra-faint dwarfs in the Sloan Digital Sky Survey in 2005 and the subsequent observational and theoretical progress in understanding their nature and origin. We describe their stellar kinematics, chemical abundance patterns, structural properties, stellar populations, orbits, and luminosity function, as well as what can be learned from each type of measurement. We conclude the following: ▪ In most cases, the stellar velocity dispersions of ultra-faint dwarfs are robust against systematic uncertainties such as binary stars and foreground contamination. ▪ The chemical abundance patterns of stars in ultra-faint dwarfs require two sources of r-process elements, one of which can likely be attributed to neutron star mergers. ▪ Even under conservative assumptions, only a small fraction of ultra-faint dwarfs may have suffered significant tidal stripping of their stellar components. ▪ Determining the properties of the faintest dwarfs out to the virial radius of the Milky Way will require very large investments of observing time with future telescopes. Finally, we offer a look forward at the observations that will be possible with future facilities as the push toward a complete census of the Local Group dwarf galaxy population continues.
{"title":"The Faintest Dwarf Galaxies","authors":"J. Simon","doi":"10.1146/annurev-astro-091918-104453","DOIUrl":"https://doi.org/10.1146/annurev-astro-091918-104453","url":null,"abstract":"The lowest luminosity ([Formula: see text] L[Formula: see text]) Milky Way satellite galaxies represent the extreme lower limit of the galaxy luminosity function. These ultra-faint dwarfs are the oldest, most dark matter–dominated, most metal-poor, and least chemically evolved stellar systems known. They therefore provide unique windows into the formation of the first galaxies and the behavior of dark matter on small scales. In this review, we summarize the discovery of ultra-faint dwarfs in the Sloan Digital Sky Survey in 2005 and the subsequent observational and theoretical progress in understanding their nature and origin. We describe their stellar kinematics, chemical abundance patterns, structural properties, stellar populations, orbits, and luminosity function, as well as what can be learned from each type of measurement. We conclude the following: ▪ In most cases, the stellar velocity dispersions of ultra-faint dwarfs are robust against systematic uncertainties such as binary stars and foreground contamination. ▪ The chemical abundance patterns of stars in ultra-faint dwarfs require two sources of r-process elements, one of which can likely be attributed to neutron star mergers. ▪ Even under conservative assumptions, only a small fraction of ultra-faint dwarfs may have suffered significant tidal stripping of their stellar components. ▪ Determining the properties of the faintest dwarfs out to the virial radius of the Milky Way will require very large investments of observing time with future telescopes. Finally, we offer a look forward at the observations that will be possible with future facilities as the push toward a complete census of the Local Group dwarf galaxy population continues.","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2019-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1146/annurev-astro-091918-104453","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43196578","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2018-12-14DOI: 10.1146/annurev-astro-081817-051948
R. Blandford, D. Meier, A. Readhead
The nuclei of most normal galaxies contain supermassive black holes, which can accrete gas through a disk and become active. These active galactic nuclei (AGNs) can form jets that are observed on scales from astronomical units to megaparsecs and from meter wavelengths to TeV energies. High-resolution radio imaging and multiwavelength/messenger campaigns are elucidating the conditions under which this happens. Evidence is presented that: ▪ Relativistic AGN jets are formed when the black hole spins and the the accretion disk is strongly magnetized, perhaps on account of gas accreting at high latitude beyond the black hole sphere of influence. ▪ AGN jets are collimated close to the black hole by magnetic stress associated with a disk wind. ▪ Higher-power jets can emerge from their galactic nuclei in a relativistic, supersonic, and proton-dominated state, and they terminate in strong, hot spot shocks; lower-power jets are degraded to buoyant plumes and bubbles. ▪ Jets may accelerate protons to EeV energies, which contribute to the cosmic ray spectrum and may initiate pair cascades that can efficiently radiate synchrotron γ-rays. ▪ Jets were far more common when the Universe was a few billion years old and black holes and massive galaxies were growing rapidly. ▪ Jets can have a major influence on their environments, stimulating and limiting the growth of galaxies. The observational prospects for securing our understanding of AGN jets are bright.
{"title":"Relativistic Jets from Active Galactic Nuclei","authors":"R. Blandford, D. Meier, A. Readhead","doi":"10.1146/annurev-astro-081817-051948","DOIUrl":"https://doi.org/10.1146/annurev-astro-081817-051948","url":null,"abstract":"The nuclei of most normal galaxies contain supermassive black holes, which can accrete gas through a disk and become active. These active galactic nuclei (AGNs) can form jets that are observed on scales from astronomical units to megaparsecs and from meter wavelengths to TeV energies. High-resolution radio imaging and multiwavelength/messenger campaigns are elucidating the conditions under which this happens. Evidence is presented that: ▪ Relativistic AGN jets are formed when the black hole spins and the the accretion disk is strongly magnetized, perhaps on account of gas accreting at high latitude beyond the black hole sphere of influence. ▪ AGN jets are collimated close to the black hole by magnetic stress associated with a disk wind. ▪ Higher-power jets can emerge from their galactic nuclei in a relativistic, supersonic, and proton-dominated state, and they terminate in strong, hot spot shocks; lower-power jets are degraded to buoyant plumes and bubbles. ▪ Jets may accelerate protons to EeV energies, which contribute to the cosmic ray spectrum and may initiate pair cascades that can efficiently radiate synchrotron γ-rays. ▪ Jets were far more common when the Universe was a few billion years old and black holes and massive galaxies were growing rapidly. ▪ Jets can have a major influence on their environments, stimulating and limiting the growth of galaxies. The observational prospects for securing our understanding of AGN jets are bright.","PeriodicalId":8138,"journal":{"name":"Annual Review of Astronomy and Astrophysics","volume":null,"pages":null},"PeriodicalIF":33.3,"publicationDate":"2018-12-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1146/annurev-astro-081817-051948","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48041447","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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