THE GASEOUS ENVIRONMENT OF HIGH-z GALAXIES: PRECISION MEASUREMENTS OF NEUTRAL HYDROGEN IN THE CIRCUMGALACTIC MEDIUM OF z ∼ 2–3 GALAXIES IN THE KECK BARYONIC STRUCTURE SURVEY

By G. Rudie, C. Steidel, R. Trainor, Olivera Rakic, M. Bogosavljević, M. Pettini, Naveen A. Reddy, A. Shapley, D. Erb, D. Law. 2012

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We present results from the Keck Baryonic Structure Survey (KBSS), a unique spectroscopic survey of the distant universe designed to explore the details of the connection between galaxies and intergalactic baryons within the same survey volumes, focusing particularly on scales from ∼50 kpc to a few Mpc. The KBSS is optimized for the redshift range z ∼ 2–3, combining S/N ∼100 Keck/HIRES spectra of 15 of the brightest QSOs in the sky at z ≃ 2.5–2.9 with very densely sampled galaxy redshift surveys within a few arcmin of each QSO sightline. In this paper, we present quantitative results on the distribution, column density, kinematics, and absorber line widths of neutral hydrogen (H i) surrounding a subset of 886 KBSS star-forming galaxies with 2.0 ≲ z ≲ 2.8 and with projected distances ⩽3 physical Mpc from a QSO sightline. Using Voigt profile decompositions of the full Lyα forest region of all 15 QSO spectra, we compiled a catalog of ∼6000 individual absorbers in the redshift range of interest, with 12 ⩽ log (NH i) ⩽21. These are used to measure H i absorption statistics near the redshifts of foreground galaxies as a function of projected galactocentric distance from the QSO sightline and for randomly chosen locations in the intergalactic medium (IGM) within the survey volume. We find that NH i and the multiplicity of velocity-associated H i components increase rapidly with decreasing galactocentric impact parameter and as the systemic redshift of the galaxy is approached. The strongest H i absorbers within ≃ 100 physical kpc of galaxies have NH i ∼3 orders of magnitude higher than those near random locations in the IGM. The circumgalactic zone of most significantly enhanced H i absorption is found within transverse distances of ≲ 300 kpc and within ±300 km s−1 of galaxy systemic redshifts. Taking this region as the defining bounds of the circumgalactic medium (CGM), nearly half of absorbers with log(NH i) > 15.5 are found within the CGM of galaxies meeting our photometric selection criteria, while their CGM occupy only 1.5% of the cosmic volume. The spatial covering fraction, multiplicity of absorption components, and characteristic NH i remain significantly elevated to transverse distances of ∼2 physical Mpc from galaxies in our sample. Absorbers with NH i >1014.5 cm−2 are tightly correlated with the positions of galaxies, while absorbers with lower NH i are correlated with galaxy positions only on ≳Mpc scales. Redshift anisotropies on these larger scales indicate coherent infall toward galaxy locations, while on scales of ∼100 physical kpc peculiar velocities of Δv ≃ ±260 km s−1 with respect to the galaxies are indicated. The median Doppler widths of individual absorbers within 1–3 rvir of galaxies are larger by ≃ 50% than randomly chosen absorbers of the same NH i, suggesting higher gas temperatures and/or increased turbulence likely caused by some combination of accretion shocks and galactic winds around galaxies with Mhalo ≃ 1012 M☉ at z ∼ 2–3.

Subfields: Astronomy and Astrophysics, Electrical and Electronic Engineering, Instrumentation

View Paper: https://www.semanticscholar.org/paper/b1abd4b96484d34341c807fa5c88b399c439ef50

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Magnetized gas clouds can survive acceleration by a hot wind (2014, background): “…quasars along sightlines through foreground haloes of star-forming galaxies demonstrates that the cool gas extends to large galactocentric distances, comparable in some cases to the virial radius (e.g. Ribaudo et al. 2011; Rudie et al. 2012; Crighton, Hennawi & Prochaska 2013; Werk et al. 2014).”
Gusty, gaseous flows of FIRE: Galactic winds in cosmological simulations with explicit stellar feedback (2015, background): “The high-redshift CGM has also been extensively observed (Steidel et al. 2010; Rudie et al. 2012) and provides important constraints for theoretical models which seek to determine the origin of gas in present-day galaxies (Kereš et al. 2005; FaucherGiguère et al. 2010, 2015; Faucher-Giguère,…”
THE COS-HALOS SURVEY: RATIONALE, DESIGN, AND A CENSUS OF CIRCUMGALACTIC NEUTRAL HYDROGEN (2013, methodology): “In their characterization of the H I surrounding 886 galaxies with z ∼ 2.3 (25 of which are probed at ≤ 200 physical kpc), Rudie et al. (2012) show that the strongest absorbers, log NH I ∼ 15 − 17 concentrate within 200 kpc (physical) and ±300 km s−1 of their targeted galaxies.”
THE CIRCUMGALACTIC MEDIUM OF MASSIVE GALAXIES AT z ∼ 3: A TEST FOR STELLAR FEEDBACK, GALACTIC OUTFLOWS, AND COLD STREAMS (2012, background): “Within 2Rvir, our covering factor is 12%, below the 28± 9% observed by Rudie et al. (2012).”
Nebular Emission Line Ratios in z ≃ 2–3 Star-forming Galaxies with KBSS-MOSFIRE: Exploring the Impact of Ionization, Excitation, and Nitrogen-to-Oxygen Ratio (2016, background): “The Keck Baryonic Structure Survey (KBSS, Rudie et al. 2012; Steidel et al. 2014) is a large, targeted spectroscopic survey designed to jointly probe galaxies and their gaseous environments at the peak of galaxy assembly, z ≃ 2 − 3.”
Physical Models of Galaxy Formation in a Cosmological Framework (2014, background): “…UV is now able to probe the diffuse gas and metals in the circumgalactic medium of galaxies for galaxy-targetted sightlines spanning a diverse range of galaxy types, from nearby galaxies to z ∼ 2–3 (e.g. Peeples et al. 2014, Prochaska et al. 2013, Rudie et al. 2012, Tumlinson et al. 2013).”
A characteristic scale for cold gas (2016, background): “%) compared to that around Lyman break galaxies (Rudie et al., 2012) ( fcov ∼ 30”
The impact of star formation feedback on the circumgalactic medium (2016, background): “…UV absorption lines in the spectra of background quasars in dark matter haloes at these masses can be used to measure the amount of mass in different temperature regimes ∼ 104 − 105.5 K (e.g., Steidel et al. 2010; Tumlinson et al. 2011; Rudie et al. 2012; Werk et al. 2014; Borthakur et al. 2015).”
The Circumgalactic Medium (2017, methodology): “Ground-based redshift surveys around previously observed quasar sightlines are now a time-honored method for constructing samples of quasar/galaxy pairs (e.g., Chen et al. 1998; Stocke et al. 2006; Rudie et al. 2012).”
Bimodality of low-redshift circumgalactic O VI in non-equilibrium EAGLE zoom simulations (2016, background): “…these haloes increases by nearly a factor of five from 101 to 486 kpc, meaning that the adoption of a constant radius for the CGM, often assumed to be 300 kpc (e.g. Rudie et al. 2012; Ford et al. 2013), samples only the inner region of a group halo, but includes the diffuse IGM for a sub-L∗ halo.”
STRONG NEBULAR LINE RATIOS IN THE SPECTRA of z ∼ 2–3 STAR FORMING GALAXIES: FIRST RESULTS FROM KBSS-MOSFIRE (2014, background): “In large part for this reason, the Keck Baryonic Structure Survey (KBSS; see Rudie et al. 2012; Trainor & Steidel 2012; Rakic et al. 2012) has focused on galaxies in this redshift range over the past several years (e.g., Adelberger et al. 2004; Steidel et al. 2004; Erb et al. 2006a,c,b; Shapley et…”
THE COS-HALOS SURVEY: PHYSICAL CONDITIONS AND BARYONIC MASS IN THE LOW-REDSHIFT CIRCUMGALACTIC MEDIUM (2014, background): “…L∗ galaxies, our survey explicitly does not trace the full extent of the CGM. Data from studies that blindly probe IGM and CGM absorption and its connection to host galaxies find a gaseous extent of 300 kpc, independent of galaxy redshift and luminosity (Prochaska et al. 2011; Rudie et al. 2012).”
Neutral hydrogen in galaxy haloes at the peak of the cosmic star formation history (2014, methodology): “The CGM measurements of Rudie et al. (2012) showed that the simulations of Faucher-Giguère & Kereš (2011) and Fumagalli et al. (2011) under-predicted the covering fraction of LLSs within Rvir of z ∼ 2 LBGs by a factor ∼ 2 (though with marginal statistical significance, given the observational…”
An origin for multiphase gas in galactic winds and haloes (2015, background): “Covering fractions of low-ionization material are high out to∼ 100− 200 kpc around both star-forming and passive galaxies, while higher ionization OVI absorption is found more frequently around star-forming galaxies (Tumlinson et al. 2011).”
EVIDENCE FOR UBIQUITOUS COLLIMATED GALACTIC-SCALE OUTFLOWS ALONG THE STAR-FORMING SEQUENCE AT z ∼ 0.5 (2013, background): “…these galaxies are likely already enriched with a significant amount of material (e.g., Chen et al. 2010a; Steidel et al. 2010; Cooksey et al. 2012; Rudie et al. 2012), our neglect of drag forces is not well justified, and their inclusion may substantially modify the distances to which the…”
THE COS-HALOS SURVEY: AN EMPIRICAL DESCRIPTION OF METAL-LINE ABSORPTION IN THE LOW-REDSHIFT CIRCUMGALACTIC MEDIUM (2012, background): “Previous studies of Lyα absorption in galaxy halos have indicated that the CGM of L ≈ L∗ galaxies extends to at least 300 kpc (Rudie et al. 2012; Prochaska et al. 2011b).”