The Milky Way halo as a QSO absorption-line system

Herenz, Peter; Richter, Philipp; Charlton, Jane C.; Masiero, J.

doi:10.1051/0004-6361/201220531

Cited by 23 publications

(38 citation statements)

References 82 publications

(162 reference statements)

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“…We find that the majority of the Ca II halo absorbers have radial velocities in the range |v LSR | ≤ 200 km s −1 , but there is an excess of absorbers with negative radial velocities. A similar trend is observed in the UV using Si II as tracer for neutral gas in the Milky Way halo (Herenz et al 2013). This excess possibly reflects a net-infall of neutral gas towards the Milky Way as part of the on-going gas accretion of the Galaxy (Richter 2012).…”

Section: Kinematics Of Local Circumgalactic Gassupporting

confidence: 72%

High‐resolution absorption spectroscopy of the circumgalactic medium of the Milky Way

et al. 2014

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In this article we discuss the importance of high-resolution absorption spectroscopy for our understanding of the distribution and physical nature of the gaseous circumgalactic medium (CGM) that surrounds the Milky Way. Observational and theoretical studies indicate a high complexity of the gas kinematics and an extreme multi-phase nature of the CGM in low-redshift galaxies. High-precision absorption-line measurements of the Milky Way's gas environment thus are essential to explore fundamental parameters of circumgalactic gas in the local Universe, such as mass, chemical composition, and spatial distribution. We shortly review important characteristics of the Milky Way's CGM and discuss recent results from our multi-wavelength observations of the Magellanic Stream. Finally, we discuss the potential of studying the warm-hot phase of the Milky Way's CGM by searching for extremely weak [Fe X] λ6374.5 and [Fe XIV] λ5302.9 absorption in optical QSO spectra.

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Section: Kinematics Of Local Circumgalactic Gassupporting

confidence: 72%

High‐resolution absorption spectroscopy of the circumgalactic medium of the Milky Way

et al. 2014

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“…Because the fits presented here take into account the censored data, the parameters of the best fit in the left panel are slightly different from those published by Borthakur et al (2015). 16 The conditions may not exactly be similar between the HVC/IVC and the COS-GASS absorbers because the HVC/IVC are within 50 kpc of the Milky Way disk (Lehner et al 2012) and not the outer CGM (see Richter 2012;Herenz et al 2013, for more on vantage point correction).…”

Section: Structurementioning

confidence: 97%

The Properties of the Circumgalactic Medium in Red and Blue Galaxies: Results From the Cos-Gass+cos-Halos Surveys

Borthakur

Heckman

Tumlinson

et al. 2016

ApJ

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We use the combined data from the COS-GASS and COS-Halos surveys to characterize the Circum-Galactic Medium (CGM) surrounding typical low-redshift galaxies in the mass range  *~-M M 10 9.5 11.5, and over a range of impact parameters extending to just beyond the halo virial radius (R vir ). We find the radial scale length of the distributions of the equivalent widths of the Lyαand Si III absorbers to be ∼1 and ∼0.4R vir , respectively. The radial distribution of equivalent widths is relatively uniform for the blue galaxies, but highly patchy (i.e., it has a low covering fraction) for the red galaxies. We also find that the Lyαand Si III equivalent widths show significant positive correlations with the specific star formation rate (sSFR) of the galaxy. We find a surprising lack of correlations between the halo mass (virial velocity) and either the velocity dispersions or velocity offsets of the Lyαlines. The ratio of the velocity offset to the velocity dispersion for the Lyαabsorbers has a mean value of ∼4, suggesting that a given line of sight is intersecting a dynamically coherent structure in the CGM, rather than a sea of orbiting clouds. The kinematic properties of the CGM are similar in the blue and red galaxies, although we find that a significantly larger fraction of the blue galaxies have large Lyαvelocity offsets (>200 km s −1 ). We show that-if the CGM clouds represent future fuel for star formation-our new results could imply a large drop in the sSFR across the galaxy mass-range we probe.

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“…3.1. This strategy is similar to our previous surveys (Richter et al 2009(Richter et al , 2016Lehner et al 2012;Herenz et al 2013), but is more restrictive than other studies where also single-line detections are considered (e.g., Collins et al 2009;Shull et Article number, page 4 of 37 Richter et al: The Milky Way CGM in absorption Fig. 2.…”

Section: Cgm Identification and Absorption-line Analysismentioning

confidence: 99%

“…A commonly used approach to study the ionization conditions in individual high-velocity clouds in the Milky Way halo is the use of column density ratios of low, intermediate, and high ions together with Cloudy (Ferland et al 2013) ionization models (e.g., Richter et al 2009Richter et al , 2013Fox et al , 2015Herenz et al 2013). Such ionizations models provide useful constraints on the gas densities, ionization parameters, and metal abundances in the gas, but they require accurate information on the column densities of different ions, the velocity-component structure, and the distance of the absorbing gas from the Milky Way disk.…”

Section: Total Gas Columns and Ionization Fractionsmentioning

confidence: 99%

An HST/COS legacy survey of high-velocity ultraviolet absorption in the Milky Way’s circumgalactic medium and the Local Group

Richter

Nuza

Fox

et al. 2017

A&A

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Context. The Milky Way is surrounded by large amounts of diffuse gaseous matter that connects the stellar body of our Galaxy with its large-scale Local Group (LG) environment. Aims. To characterize the absorption properties of this circumgalactic medium (CGM) and its relation to the LG we present the so-far largest survey of metal absorption in Galactic high-velocity clouds (HVCs) using archival ultraviolet (UV) spectra of extragalactic background sources. The UV data are obtained with the Cosmic Origins Spectrograph (COS) onboard the Hubble Space Telescope (HST) and are supplemented by 21 cm radio observations of neutral hydrogen. Methods. Along 270 sightlines we measure metal absorption in the lines of Si ii, Si iii, C ii, and C iv and associated H i 21 cm emission in HVCs in the velocity range |vLSR| = 100 − 500 km s −1 . With this unprecedented large HVC sample we were able to improve the statistics on HVC covering fractions, ionization conditions, small-scale structure, CGM mass, and inflow rate. For the first time, we determine robustly the angular two point correlation function of the high-velocity absorbers, systematically analyze antipodal sightlines on the celestial sphere, and compare the HVC absorption characteristics with that of Damped Lyman α absorbers (DLAs) and constrained cosmological simulations of the LG (CLUES project). Results. The overall sky-covering fraction of high-velocity absorption is 77 ± 6 percent for the most sensitive ion in our survey, Si iii, and for column densities log N (Si iii) ≥ 12.1. This value is ∼ 4 − 5 times higher than the covering fraction of 21 cm neutral hydrogen emission at log N (H i) ≥ 18.7 along the same lines of sight, demonstrating that the Milky Way's CGM is multi-phase and predominantly ionized. The measured equivalent-width ratios of Si ii, Si iii, C ii, and C iv are inhomogeneously distributed on large and small angular scales, suggesting a complex spatial distribution of multi-phase gas that surrounds the neutral 21 cm HVCs. We estimate that the total mass and accretion rate of the neutral and ionized CGM traced by HVCs is MHVC ≥ 3.0×10 9 M⊙ and dMHVC/dt ≥ 6.1M⊙ yr −1 , where the Magellanic Stream (MS) contributes with more than 90 percent to this mass/mass-flow. If seen from an external vantage point, the Milky Way disk plus CGM would appear as a DLA that would exhibit for most viewing angles an extraordinary large velocity spread of ∆v ≈ 400 − 800 km s −1 , a result of the complex kinematics of the Milky Way CGM that is dominated by the presence of the MS. We detect a velocity dipole of high-velocity absorption at low/high galactic latitudes that we associate with LG gas that streams to the LG barycenter. This scenario is supported by the gas kinematics predicted from the LG simulations. Conclusions. Our study confirms previous results, indicating that the Milky Way CGM contains sufficient gaseous material to feed the Milky Way disk over the next Gyr at a rate of a few solar masses per year, if the CGM gas can actually reach the MW disk. We dem...

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The Milky Way halo as a QSO absorption-line system

Cited by 23 publications

References 82 publications

High‐resolution absorption spectroscopy of the circumgalactic medium of the Milky Way

High‐resolution absorption spectroscopy of the circumgalactic medium of the Milky Way

The Properties of the Circumgalactic Medium in Red and Blue Galaxies: Results From the Cos-Gass+cos-Halos Surveys

An HST/COS legacy survey of high-velocity ultraviolet absorption in the Milky Way’s circumgalactic medium and the Local Group

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