A panoramic view of the circumgalactic medium in the photoionized precipitation model

ABSTRACT We consider a model of the circumgalactic medium (CGM) in which feedback maintains a constant ratio of cooling time to free-fall time throughout the halo, so that the entire CGM is marginally unstable to multiphase condensation. This ‘precipitation model’ is motivated by observations of multiphase gas in the cores of galaxy clusters and the haloes of massive ellipticals. From the model, we derive the density and temperature profiles for the CGM around galaxies with masses similar to the Milky Way. After taking into consideration the geometrical position of our Solar system in the Milky Way, we show that the CGM model is consistent with observed O vi, O vii, O viii column densities and the ratio of O vii and O viii column densities only if temperature fluctuations with a lognormal dispersion σln T ∼ 0.6–1.0 are included. We show that O vi column densities observed around star-forming galaxies require systematically greater values of σln T than around passive galaxies, implying a connection between star formation in the disc and the state of the CGM. Photoionization by an extragalactic ultraviolet background radiation does not significantly change these CGM features for galaxies like the Milky Way but has much greater and significant effects on the CGM of lower mass galaxies.

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The Distribution of Young Stars in Nearby Galaxies

Symposium - International Astronomical Union ◽

10.1017/s0074180900148636 ◽

1986 ◽

Vol 116 ◽

pp. 61-80 ◽

Cited By ~ 3

Author(s):

W. L. Freedman

Keyword(s):

Spatial Distribution ◽

Milky Way ◽

Young Stars ◽

Panoramic View ◽

Star Forming ◽

Individual Stars ◽

Star Forming Regions ◽

The Galaxy ◽

External Galaxies ◽

Nearby Galaxies

Although luminous stars are relatively rare, they can potentially be studied out to large distances. In our own Milky Way, this advantage is offset by obscuration due to dust in the plane of the Galaxy. In addition, distances to these individual stars are extremely difficult to determine. The study of external galaxies allows a panoramic view of the system and its individually brightest stars which are all at a common distance. The spatial distribution of star forming regions is immediately apparent, and the effects of obscuration are minimized. Nearby resolved galaxies therefore provide a rich resource for examining the properties of the intrinsically brightest stars and their relation to other components of the galaxy.

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Turbulence, feedback, and slow star formation

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307001767 ◽

2006 ◽

Vol 2 (S237) ◽

pp. 378-383

Author(s):

Mark R. Krumholz

Keyword(s):

Star Formation ◽

Milky Way ◽

Star Formation Rate ◽

Formation Rate ◽

Free Fall ◽

Giant Molecular Clouds ◽

Star Forming ◽

Striking Result ◽

Wide Range ◽

Individual Cluster

AbstractOne of the outstanding puzzles about star formation is why it proceeds so slowly. Giant molecular clouds convert only a few percent of their gas into stars per free-fall time, and recent observations show that this low star formation rate is essentially constant over a range of scales from individual cluster-forming molecular clumps in the Milky Way to entire starburst galaxies. This striking result is perhaps the most basic fact that any theory of star formation must explain. I argue that a model in which star formation occurs in virialized structures at a rate regulated by supersonic turbulence can explain this observation. The turbulence in turn is driven by star formation feedback, which injects energy to offset radiation from isothermal shocks and keeps star-forming structures from wandering too far from virial balance. This model is able to reproduce observational results covering a wide range of scales, from the formation times of young clusters to the extragalactic IR-HCN correlation, and makes additional quantitative predictions that will be testable in the next few years.

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Characterizing the abundance, properties, and kinematics of the cool circumgalactic medium of galaxies in absorption with SDSS DR16

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab871 ◽

2021 ◽

Vol 504 (1) ◽

pp. 65-88

Author(s):

Abhijeet Anand ◽

Dylan Nelson ◽

Guinevere Kauffmann

Keyword(s):

Formation Rate ◽

Sloan Digital Sky Survey ◽

Gas Absorption ◽

Dark Matter Halo ◽

Star Forming ◽

Sky Survey ◽

Optical Continuum ◽

Circumgalactic Medium ◽

Emission Line Galaxies ◽

Red Galaxies

ABSTRACT In order to study the circumgalactic medium (CGM) of galaxies we develop an automated pipeline to estimate the optical continuum of quasars and detect intervening metal absorption line systems with a matched kernel convolution technique and adaptive S/N criteria. We process ∼ one million quasars in the latest Data Release 16 (DR16) of the Sloan Digital Sky Survey (SDSS) and compile a large sample of ∼ 160 000 Mg ii absorbers, together with ∼ 70 000 Fe ii systems, in the redshift range 0.35 < zabs < 2.3. Combining these with the SDSS DR16 spectroscopy of ∼1.1 million luminous red galaxies (LRGs) and ∼200 000 emission line galaxies (ELGs), we investigate the nature of cold gas absorption at 0.5 < z < 1. These large samples allow us to characterize the scale dependence of Mg ii with greater accuracy than in previous work. We find that there is a strong enhancement of Mg ii absorption within ∼50 kpc of ELGs, and the covering fraction within 0.5rvir of ELGs is 2–5 times higher than for LRGs. Beyond 50 kpc, there is a sharp decline in Mg ii for both kinds of galaxies, indicating a transition to the regime where the CGM is tightly linked with the dark matter halo. The Mg ii-covering fraction correlates strongly with stellar mass for LRGs, but weakly for ELGs, where covering fractions increase with star formation rate. Our analysis implies that cool circumgalactic gas has a different physical origin for star-forming versus quiescent galaxies.

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On Population III Star Formation

Symposium - International Astronomical Union ◽

10.1017/s0074180900038778 ◽

1983 ◽

Vol 104 ◽

pp. 119-120

Author(s):

A. Kashlinsky ◽

M. J. Rees

Keyword(s):

Background Radiation ◽

Free Fall ◽

Compact Objects ◽

Centrifugal Forces ◽

Tidal Interactions ◽

Geometrical Cross Section ◽

Spin Parameter ◽

Small Density ◽

Major Factors ◽

Population Iii

If primordial fluctuations were isothermal their amplitude at recombination would be non-linear on scales Mo ≃ 106÷9 M⊙. Since the Jeans mass after recombination is MJo ≃ 8 × 105 Ω−1/2 M⊙ the clouds of mass Mo would be able to form the first generation of compact objects, the so-called Population III. These clouds would acquire angular momentum via tidal interactions with their neighbours. The importance of rotation can be conveniently characterised by the spin parameter λ = Vrotation/Vfree-fall and tidal interactions lead to a spin λo = 0.07 ± 0.03. As the cloud collapses λ increases as r−1/2. Any fragment forming in a rotating cloud would have the same spin λ as the whole cloud. It could therefore collapse only by ≃ λo2 in radius before centrifugal forces intervened, thus leaving a large geometrical cross-section for coalescence to be important. At radii r ≲ λo8/5 (Mo/MJo)2/15 ro the coalescence time is shorter than the free-fall time and no fragmentation is possible below this radius. In the primordial clouds two major factors prevent fragmentation at larger radii. First, the background radiation is still ‘hot’ and the trapping of it would prevent fragmentation until the whole cloud has collapsed to a radius 10−2 x−2/3 ro. Here x = 10−2(M/107 M⊙)1/3 is the ionization fraction given by the balance between gravitational contraction and recombination cooling. Furthermore, any small density fluctuation would lead to fragmentation only after the paternal cloud had collapsed by a factor (δ/5)2/3 in radius. For these reasons fragmentation is unlikely until centrifugal forces halt the collapse and a disk forms. The disk will be initially at T ≃ 104K but after a small fraction of H2 forms it will cool to T3 ≃ T/103K ≃ 1 and the final fragments mass could be as low as ≃ 0.2(λo/0.07)4 T32(MJo/Mo)1/3 M⊙.

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Properties of the circumgalactic medium in simulations compared to observations

Astronomy and Astrophysics ◽

10.1051/0004-6361/201628886 ◽

2018 ◽

Vol 609 ◽

pp. A66 ◽

Cited By ~ 3

Author(s):

R. E. G. Machado ◽

P. B. Tissera ◽

G. B. Lima Neto ◽

L. Sodré

Keyword(s):

Gas Phase ◽

Chemical Elements ◽

Star Forming ◽

Physical Conditions ◽

Cosmological Context ◽

Circumgalactic Medium ◽

Hydrodynamical Simulations ◽

Stellar Masses ◽

Lower Limits ◽

Supernova Feedback

Context. Galaxies are surrounded by extended gaseous halos that store significant fractions of chemical elements. These are syntethized by the stellar populations and later ejected into the circumgalactic medium (CGM) by different mechanism, of which supernova feedback is considered one of the most relevant. Aims. We aim to explore the properties of this metal reservoir surrounding star-forming galaxies in a cosmological context aiming to investigate the chemical loop between galaxies and their CGM, and the ability of the subgrid models to reproduce observational results. Methods. Using cosmological hydrodynamical simulations, we have analysed the gas-phase chemical contents of galaxies with stellar masses in the range 109−1011 M⊙. We estimated the fractions of metals stored in the different CGM phases, and the predicted O vi and Si iii column densities within the virial radius. Results. We find roughly 107 M⊙ of oxygen in the CGM of simulated galaxies having M⋆ ~ 1010 M⊙, in fair agreement with the lower limits imposed by observations. The Moxy is found to correlate with M⋆, at odds with current observational trends but in agreement with other numerical results. The estimated profiles of O vi column density reveal a substantial shortage of that ion, whereas Si iii, which probes the cool phase, is overpredicted. Nevertheless, the radial dependences of both ions follow the respective observed profiles. The analysis of the relative contributions of both ions from the hot, warm and cool phases suggests that the warm gas (105 K < T < 106 K) should be more abundant in order to bridge the mismatch with the observations, or alternatively, that more metals should be stored in this gas-phase. These discrepancies provide important information to improve the subgrid physics models. Our findings show clearly the importance of tracking more than one chemical element and the difficulty of simultaneously satisfying the observables that trace the circumgalactic gas at different physical conditions. Additionally, we find that the X-ray coronae around the simulated galaxies have luminosities and temperatures in decent agreement with the available observational estimates.

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How Identifying Circumgalactic Gas by Line-of-sight Velocity instead of the Location in 3D Space Affects O vi Measurements

The Astrophysical Journal ◽

10.3847/1538-4357/ac2c73 ◽

2021 ◽

Vol 923 (2) ◽

pp. 137

Author(s):

Stephanie H. Ho ◽

Crystal L. Martin ◽

Joop Schaye

Keyword(s):

High Resolution ◽

Density Profile ◽

Column Density ◽

Line Of Sight ◽

Lower Mass ◽

Star Forming ◽

3D Space ◽

High Incidence ◽

High Incidence Rate ◽

Stellar Masses

Abstract The high incidence rate of the O vi λλ1032, 1038 absorption around low-redshift, ∼L * star-forming galaxies has generated interest in studies of the circumgalactic medium. We use the high-resolution EAGLE cosmological simulation to analyze the circumgalactic O vi gas around z ≈ 0.3 star-forming galaxies. Motivated by the limitation that observations do not reveal where the gas lies along the line of sight, we compare the O vi measurements produced by gas within fixed distances around galaxies and by gas selected using line-of-sight velocity cuts commonly adopted by observers. We show that gas selected by a velocity cut of ±300 km s−1 or ±500 km s−1 produces a higher O vi column density, a flatter column density profile, and a higher covering fraction compared to gas within 1, 2, or 3 times the virial radius (r vir) of galaxies. The discrepancy increases with impact parameter and worsens for lower-mass galaxies. For example, compared to the gas within 2 r vir, identifying the gas using velocity cuts of 200–500 km s−1 increases the O vi column density by 0.2 dex (0.1 dex) at 1 r vir to over 0.75 dex (0.7 dex) at ≈ 2 r vir for galaxies with stellar masses of 109–109.5 M ⊙ (1010–1010.5 M ⊙). We furthermore estimate that excluding O vi outside r vir decreases the circumgalactic oxygen mass measured by Tumlinson et al. (2011) by over 50%. Our results demonstrate that gas at large line-of-sight separations but selected by conventional velocity windows has significant effects on the O vi measurements and may not be observationally distinguishable from gas near the galaxies.

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Evaluation of hadronic emission in starburst galaxies and star-forming galaxies

Research in Astronomy and Astrophysics ◽

10.1088/1674-4527/21/10/263 ◽

2021 ◽

Vol 21 (10) ◽

pp. 263

Author(s):

Yun-Chuan Xiang ◽

Ze-Jun Jiang ◽

Yun-Yong Tang

Keyword(s):

Supernova Remnants ◽

Milky Way ◽

Starburst Galaxies ◽

Model Parameters ◽

Zone Model ◽

Observation Data ◽

Large Area ◽

Star Forming ◽

Ngc 1068 ◽

The One

Abstract In this work, we reanalyzed 11 years of spectral data from the Fermi Large Area Telescope (Fermi-LAT) of currently observed starburst galaxies (SBGs) and star-forming galaxies (SFGs). We used a one-zone model provided by NAIMA and the hadronic origin to explain the GeV observation data of the SBGs and SFGs. We found that a protonic distribution of a power-law form with an exponential cutoff can explain the spectra of most SBGs and SFGs. However, it cannot explain the spectral hardening components of NGC 1068 and NGC 4945 in the GeV energy band. Therefore, we considered the two-zone model to well explain these phenomena. We summarized the features of two model parameters, including the spectral index, cutoff energy, and proton energy budget. Similar to the evolution of supernova remnants (SNRs) in the Milky Way, we estimated the protonic acceleration limitation inside the SBGs to be the order of 102 TeV using the one-zone model; this is close to those of SNRs in the Milky Way.

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