AN EMPIRICAL CHARACTERIZATION OF EXTENDED COOL GAS AROUND GALAXIES USING Mg ii ABSORPTION FEATURES

By Hsiao-Wen Chen, Jennifer Helsby, Jean-Ren'e Gauthier, S. Shectman, I. Thompson, J. Tinker. 2010

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We report results from a survey of Mg ii absorbers in the spectra of background quasi-stellar objects (QSOs) that are within close angular distances to a foreground galaxy at z < 0.5, using the Magellan Echellette Spectrograph. We have established a spectroscopic sample of 94 galaxies at a median redshift of 〈z〉 = 0.24 in fields around 70 distant background QSOs (zQSO > 0.6), 71 of which are in an “isolated” environment with no known companions and located at ρ ≲ 120 h−1 kpc from the line of sight of a background QSO. The rest-frame absolute B-band magnitudes span a range from MB − 5log h = −16.4 to MB − 5log h = −21.4 and rest-frame BAB − RAB colors range from BAB − RAB ≈ 0 to BAB − RAB ≈ 1.5. Of these “isolated” galaxies, we find that 47 have corresponding Mg ii absorbers in the spectra of background QSOs and rest-frame absorption equivalent width Wr(2796) = 0.1–2.34 Å, and 24 do not give rise to Mg ii absorption to sensitive upper limits. Our analysis shows that (1) Wr(2796) declines with increasing distance from “isolated” galaxies but shows no clear trend in “group” environments; (2) more luminous galaxies possess more extended Mg ii absorbing halos with the gaseous radius scaled by B-band luminosity according to Rgas = 75 × (LB/LB*)(0.35 ± 0.03) h−1 kpc; (3) there is little dependence between the observed absorber strength and galaxy intrinsic colors; and (4) within Rgas, we find a mean covering fraction of 〈κ0.3〉 ≈ 70% for absorbers of Wr(2796) ⩾ 0.3 Å and 〈κ0.1〉 ≈ 80% for absorbers of Wr(2796) ⩾ 0.1 Å. The results confirm that extended Mg ii absorbing halos are a common and generic feature around ordinary galaxies and that the gaseous radius is a fixed fraction of the dark matter halo radius. The lack of correlation between Wr(2796) strength and galaxy colors suggests a lack of physical connection between the origin of extended Mg ii halos and recent star formation history of the galaxies. Finally, we discuss the total gas mass in galactic halos as traced by Mg ii absorbers. We also compare our results with previous studies.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/b9eed28b6742b37130b1cf34c5a0cbfb7e2c0e60

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Citations in the corpus

The Circumgalactic Medium (2017, background): “Using a “blind” sample of Mg ii absorbers, Chen et al. (2010) estimated Mcool ≈ 6 × 109 M for the Mg ii-bearing clouds alone.”
THE RADIAL AND AZIMUTHAL PROFILES OF Mg ii ABSORPTION AROUND 0.5 < z < 0.9 zCOSMOS GALAXIES OF DIFFERENT COLORS, MASSES, AND ENVIRONMENTS (2011, methodology): “Others have suggested in falling gas as the source (Chen et al. 2010a; Chen & Tinker 2008; Kacprzak et al. 2010a), or a combination of both inflows and outflows (Chen et al. 2010b; Chelouche & Bowen 2010).”
THE BIMODAL METALLICITY DISTRIBUTION OF THE COOL CIRCUMGALACTIC MEDIUM AT z ≲ 1 (2013, background): “While it is well-known that the number density of galaxies is related to the galaxy luminosity (through the luminosity function), the cross section for LLS absorption may also depend on the luminosity (e.g., through a Holmberg scaling, see, e.g., Chen et al. 2010; Ribaudo et al. 2011a).”
EVIDENCE FOR UBIQUITOUS COLLIMATED GALACTIC-SCALE OUTFLOWS ALONG THE STAR-FORMING SEQUENCE AT z ∼ 0.5 (2013, methodology): “Indeed, the first evidence for such a relationship was presented in Chen et al. (2010), who reported a positive correlation between ΣSFR and the EW of Na I absorption tracing outflows.”
Bimodality of low-redshift circumgalactic O VI in non-equilibrium EAGLE zoom simulations (2016, background): “Other recent studies have also characterised the CGM relative to samples of galaxies, including Chen et al. (2010); Bordoloi et al. (2011); Kacprzak et al. (2011); Borthakur et al. (2013); Churchill et al. (2013); Nielsen et al. (2013); Stocke et al. (2013); Liang & Chen (2014); Kacprzak et al.…”
THE COS-HALOS SURVEY: PHYSICAL CONDITIONS AND BARYONIC MASS IN THE LOW-REDSHIFT CIRCUMGALACTIC MEDIUM (2014, background): “Galaxy environment and interactions surely play some role in the observed properties of the CGM (Chen et al. 2010a; Yoon & Putman 2013), though a comprehensive study of the role of environment has not yet emerged.”
TRACING OUTFLOWS AND ACCRETION: A BIMODAL AZIMUTHAL DEPENDENCE OF Mg ii ABSORPTION (2012, unknown): “Following Chen et al. (2010a), we adopted the color cutB − R ≤ 1.1 to represent late-type (blue) galaxies andB − R > 1.1 to represent early-type (red) galaxies.”
Gaseous Galaxy Halos (2012, background): “Star forming galaxies are more likely to have both warm and warm-hot gas in their halos (Tumlinson et al., 2011; Chen et al., 2010b).”
THE COS-DWARFS SURVEY: THE CARBON RESERVOIR AROUND SUB-L* GALAXIES (2014, background): “For star-forming galaxies, the COS-Dwarfs data clearly show a trend between virial radius (Rvir) and CIV absorption strength, that is quite similar to that observed for Mg II absorption (e.g. Chen et al. 2010, Bordoloi et al. 2011, Werk et al. 2013).”
THE COS-HALOS SURVEY: AN EMPIRICAL DESCRIPTION OF METAL-LINE ABSORPTION IN THE LOW-REDSHIFT CIRCUMGALACTIC MEDIUM (2012, methodology): “Most previous studies traced the inner CGM (R < 100 kpc) using the Mg ii doublet (e.g., Bowen et al. 1995; Barton & Cooke 2009; Chen et al. 2010; Bowen & Chelouche 2011).”
PROBING THE INTERGALACTIC MEDIUM/GALAXY CONNECTION. V. ON THE ORIGIN OF Lyα AND O vi ABSORPTION AT z < 0.2 (2011, background): “Indeed, galaxies at low-z show modest to high covering fractions of cool gas (T ∼ 104K) traced by Mg II absorption (Barton & Cooke 2009; Chen & Tinker 2008; Chen et al. 2010).”
Cosmic ray driven outflows in global galaxy disc models (2013, background): “Thus our model may help explain why star-forming galaxies show evidence for substantial amounts of multiphase gas in their haloes (e.g. Chen et al. 2010; Rubin et al. 2010; Tumlinson et al. 2011).”