The Circumgalactic Medium
18 Aug 2017-Annual Review of Astronomy and Astrophysics (Annual Reviews)-Vol. 55, Iss: 1, pp 389-432
TL;DR: The circumgalactic medium (CGM) as mentioned in this paper is a multiphase medium characterized by rich dynamics and complex ionization states, and it is a source for a galaxy's star-forming fuel, the venue for galactic feedback and recycling, and perhaps the key regulator of the galactic gas supply.
Abstract: The gas surrounding galaxies outside their disks or interstellar medium and inside their virial radii is known as the circumgalactic medium (CGM). In recent years this component of galaxies has assumed an important role in our understanding of galaxy evolution owing to rapid advances in observational access to this diffuse, nearly invisible material. Observations and simulations of this component of galaxies suggest that it is a multiphase medium characterized by rich dynamics and complex ionization states. The CGM is a source for a galaxy's star-forming fuel, the venue for galactic feedback and recycling, and perhaps the key regulator of the galactic gas supply. We review our evolving knowledge of the CGM with emphasis on its mass, dynamical state, and coevolution with galaxies. Observations from all redshifts and from across the electromagnetic spectrum indicate that CGM gas has a key role in galaxy evolution. We summarize the state of this field and pose unanswered questions for future research.
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University of Oxford1, California Institute of Technology2, National Radio Astronomy Observatory3, Tel Aviv University4, Princeton University5, Texas Tech University6, Hebrew University of Jerusalem7, University of Sydney8, University of Wisconsin–Milwaukee9, Commonwealth Scientific and Industrial Research Organisation10, Stockholm University11, Tata Institute of Fundamental Research12, Swinburne University of Technology13, Radboud University Nijmegen14, Indian Institute of Technology Bombay15, Chalmers University of Technology16, Goddard Space Flight Center17
TL;DR: The cocoon model explains the radio light curve of GW170817, as well as the γ-ray and X-ray emission (and possibly also the ultraviolet and optical emission), and is the model that is most consistent with the observational data.
Abstract: GW170817 was the first gravitational-wave detection of a binary neutron-star merger. It was accompanied by radiation across the electromagnetic spectrum and localized to the galaxy NGC 4993 at a distance of 40 megaparsecs. It has been proposed that the observed γ-ray, X-ray and radio emission is due to an ultra-relativistic jet being launched during the merger (and successfully breaking out of the surrounding material), directed away from our line of sight (off-axis). The presence of such a jet is predicted from models that posit neutron-star mergers as the drivers of short hard-γ-ray bursts. Here we report that the radio light curve of GW170817 has no direct signature of the afterglow of an off-axis jet. Although we cannot completely rule out the existence of a jet directed away from the line of sight, the observed γ-ray emission could not have originated from such a jet. Instead, the radio data require the existence of a mildly relativistic wide-angle outflow moving towards us. This outflow could be the high-velocity tail of the neutron-rich material that was ejected dynamically during the merger, or a cocoon of material that breaks out when a jet launched during the merger transfers its energy to the dynamical ejecta. Because the cocoon model explains the radio light curve of GW170817, as well as the γ-ray and X-ray emission (and possibly also the ultraviolet and optical emission), it is the model that is most consistent with the observational data. Cocoons may be a ubiquitous phenomenon produced in neutron-star mergers, giving rise to a hitherto unidentified population of radio, ultraviolet, X-ray and γ-ray transients in the local Universe.
383 citations
TL;DR: In this paper, the authors provide an overview of the methods used to constrain the chemical enrichment in galaxies and their environment, and discuss the observed scaling relations between metallicity and galaxy properties, the observed relative chemical abundances, how the chemical elements are distributed within galaxies, and how these properties evolve across the cosmic epochs.
Abstract: The evolution of the content of heavy elements in galaxies, the relative chemical abundances, their spatial distribution, and how these scale with various galactic properties, provide unique information on the galactic evolutionary processes across the cosmic epochs. In recent years major progress has been made in constraining the chemical evolution of galaxies and inferring key information relevant to our understanding of the main mechanisms involved in galaxy evolution. In this review we provide an overview of these various areas. After an overview of the methods used to constrain the chemical enrichment in galaxies and their environment, we discuss the observed scaling relations between metallicity and galaxy properties, the observed relative chemical abundances, how the chemical elements are distributed within galaxies, and how these properties evolve across the cosmic epochs. We discuss how the various observational findings compare with the predictions from theoretical models and numerical cosmological simulations. Finally, we briefly discuss the open problems and the prospects for major progress in this field in the nearby future.
257 citations
Abstract: We determine the Milky Way (MW) mass profile inferred from fitting physically motivated models to the
Gaia DR2 Galactic rotation curve and other data. Using various hydrodynamical simulations of MW-mass
haloes, we show that the presence of baryons induces a contraction of the dark matter (DM) distribution in
the inner regions, r . 20 kpc. We provide an analytic expression that relates the baryonic distribution to
the change in the DM halo profile. For our galaxy, the contraction increases the enclosed DM halo mass by
factors of roughly 1.3, 2 and 4 at radial distances of 20, 8 and 1 kpc, respectively compared to an uncontracted
halo. Ignoring this contraction results in systematic biases in the inferred halo mass and concentration. We
provide a best-fitting contracted NFW halo model to the MW rotation curve that matches the data very well†.
The best-fit has a DM halo mass, MDM
200 = 0.97+0.24
−0.19×1012 M, and concentration before baryon contraction
of 9.4
+1.9
−2.6
, which lie close to the median halo mass–concentration relation predicted in ΛCDM. The inferred
total mass, Mtotal
200 = 1.08+0.20
−0.14 × 1012 M, is in good agreement with recent measurements. The model
gives a MW stellar mass of 5.04+0.43
−0.52 × 1010 M and infers that the DM density at the Solar position is
ρ
DM
= 8.8
+0.5
−0.5 ×10−3 M pc−3 ≡ 0.33+0.02
−0.02 GeV cm−3
. The rotation curve data can also be fitted with an
uncontracted NFW halo model, but with very different DM and stellar parameters. The observations prefer
the physically motivated contracted NFW halo, but the measurement uncertainties are too large to rule out
the uncontracted NFW halo.
216 citations
Institute for the Physics and Mathematics of the Universe1, University of California, Santa Cruz2, Curtin University3, University of Washington4, Swinburne University of Technology5, Australia Telescope National Facility6, Macquarie University7, North Carolina State University8, Gwangju Institute of Science and Technology9, University of Sydney10, Pontifical Catholic University of Valparaíso11
TL;DR: In this article, the authors reported the detection of a fast radio burst (FRB 181112), localized with arcsecond precision, that passes through the halo of a foreground galaxy.
Abstract: Present-day galaxies are surrounded by cool and enriched halo gas extending for hundreds of kiloparsecs. This halo gas is thought to be the dominant reservoir of material available to fuel future star formation, but direct constraints on its mass and physical properties have been difficult to obtain. We report the detection of a fast radio burst (FRB 181112), localized with arcsecond precision, that passes through the halo of a foreground galaxy. Analysis of the burst shows that the halo gas has low net magnetization and turbulence. Our results imply predominantly diffuse gas in massive galactic halos, even those hosting active supermassive black holes, contrary to some previous results.
179 citations
TL;DR: In this article, the authors present simulations from the new "Figuring Out Gas & Galaxies in Enzo" (FOGGIE) project, which focuses on extreme spatial and mass resolution in the circumgalactic medium (CGM) surrounding galaxies.
Abstract: We present simulations from the new "Figuring Out Gas & Galaxies in Enzo" (FOGGIE) project. In contrast to most extant simulations of galaxy formation, which concentrate computational resources on galactic disks and spheroids with fluid and particle elements of fixed mass, the FOGGIE simulations focus on extreme spatial and mass resolution in the circumgalactic medium (CGM) surrounding galaxies. Using the Enzo code and a new refinement scheme, FOGGIE reaches spatial resolutions of 381 comoving $h^{-1}$ pc and resolves extremely low masses ($\lesssim 1$--$100$ Msun out to 100 comoving $h^{-1}$ kpc from the central halo. At these resolutions, cloud and filament-like structures giving rise to simulated absorption are smaller, and better resolved, than the same structures simulated with standard density-dependent refinement. Most of the simulated absorption arises in identifiable and well-resolved structures with masses $\lesssim 10^4$ Msun, well below the mass resolution of typical zoom simulations. However, integrated quantities such as mass surface density and ionic covering fractions change at only the $\lesssim 30$% level as resolution is varied. This relatively small changes in projected quantities---even when the sizes and distribution of absorbing clouds change dramatically---indicate that commonly used observables provide only weak constraints on the physical structure of the underlying gas. Comparing the simulated absorption features to the KODIAQ (Keck Observatory Database of Ionized Absorption toward Quasars) survey of $z \sim2$--$3.5$ Lyman limit systems, we show that high-resolution FOGGIE runs better resolve the internal kinematic structure of detected absorption, and better match the observed distribution of absorber properties. These results indicate that CGM resolution is key in properly testing simulations of galaxy evolution with circumgalactic observations.
161 citations
Cites background from "The Circumgalactic Medium"
...…galaxy evolution have met with mixed success in reproducing the observed column densities of low- or highionization circumgalactic gas, despite creating realistic-looking galaxies (Hummels et al. 2013; Ford et al. 2016; Oppenheimer et al. 2016; Suresh et al. 2017; see also Tumlinson et al. 2017)....
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...…properties of the circumgalactic medium at the two resolutions are broadly the same, the ionic absorption-line tracers used to diagnose the CGM’s physical structure are highly sensitive to the distribution of gas temperature, density, and metallicity (see, e.g., Figure 6 of Tumlinson et al. 2017)....
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References
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TL;DR: Matplotlib is a 2D graphics package used for Python for application development, interactive scripting, and publication-quality image generation across user interfaces and operating systems.
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Max Planck Society1, Yale University2, Space Telescope Science Institute3, Harvard University4, University of Colorado Boulder5, Columbia University6, University of Toronto7, Argonne National Laboratory8, Ohio State University9, European Southern Observatory10, Aix-Marseille University11, ETH Zurich12, California Institute of Technology13, New York University14, Louisiana State University15, Australian National University16, Cornell University17, University College London18, Goddard Space Flight Center19, Leibniz Institute for Astrophysics Potsdam20
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TL;DR: In this paper, the relation between stellar mass and gas-phase metallicity was studied using the Sloan Digital Sky Survey imaging and spectroscopy of ~53,000 star-forming galaxies at z = 0.1.
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"The Circumgalactic Medium" refers background in this paper
...Metals have clearly been lost to outflows (Tremonti et al. 2004), but how these outflows scale with galaxy mass is unclear....
[...]
TL;DR: In this article, the relation between stellar mass and gas-phase metallicity was studied using the Sloan Digital Sky Survey imaging and spectroscopy of ~53,000 star-forming galaxies at z~0.1.
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"The Circumgalactic Medium" refers background in this paper
...The other three panels show simulated baryon budgets from Ford et al. (2014) in the upper-right, Illustris (Suresh et al. 2017) in the bottom left, and in the bottom right, the EAGLE halo shown in Figures 2 and 6 (Schaye et al. 2015; Oppenheimer et al. 2016b)....
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...6 Tumlinson, Peeples, & Werk These simulated views (from EAGLE, Schaye et al. 2015; Oppenheimer et al. 2016b) of the CGM are more sophisticated but possibly just as uncertain as Figure 1....
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...Spanning these two regimes are the so-called “zoom” simulations, which resolve enough of the large scale structure to accurately trace a single galaxy or a subset of galaxies selected out of larger boxes (Figure 2, Schaye et al. 2015)....
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