THE STRUCTURE AND KINEMATICS OF THE CIRCUMGALACTIC MEDIUM FROM FAR-ULTRAVIOLET SPECTRA OF z ≃ 2–3 GALAXIES

By C. Steidel, D. Erb, A. Shapley, M. Pettini, Naveen A. Reddy, M. Bogosavljević, G. Rudie, Olivera Rakic. 2010

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We present new results on the kinematics and spatial distribution of metal-enriched gas within ∼125 kpc of star-forming (“Lyman break”) galaxies at redshifts 2 ≲ z ≲ 3. In particular, we focus on constraints provided by the rest-frame far-ultraviolet (far-UV) spectra of faint galaxies, and demonstrate how galaxy spectra can be used to obtain key spatial and spectral information more efficiently than possible with QSO sightlines. Using a sample of 89 galaxies with 〈z〉 = 2.3 ± 0.3 and with both rest-frame far-UV and Hα spectra, we re-calibrate the measurement of accurate galaxy systemic redshifts using only survey-quality rest-UV spectra. We use the velocity-calibrated sample to investigate the kinematics of the galaxy-scale outflows via the strong interstellar (IS) absorption lines and Lyα emission (when present), as well as their dependence on other physical properties of the galaxies. We construct a sample of 512 close (1″–15″) angular pairs of z ∼ 2–3 galaxies with redshift differences indicating a lack of physical association. Sightlines to the background galaxies provide new information on the spatial distribution of circumgalactic gas surrounding the foreground galaxies. The close pairs sample galactocentric impact parameters 3–125 kpc (physical) at 〈z〉 = 2.2, providing for the first time a robust map of cool gas as a function of galactocentric distance for a well-characterized population of galaxies. We propose a simple model of circumgalactic gas that simultaneously matches the kinematics, depth, and profile shape of IS absorption and Lyα emission lines, as well as the observed variation of absorption line strength (H i and several metallic species) versus galactocentric impact parameter. Within the model, cool gas is distributed symmetrically around every galaxy, accelerating radially outward with vout(r) increasing with r (i.e., the highest velocities are located at the largest galactocentric distances r). The inferred radial dependence of the covering fraction of cool gas (which modulates the absorption line strength) is fc(r) ∝ r−γ with 0.2 ≲ γ ≲ 0.6 depending on transition. We discuss the results of the observations in the context of “cold accretion,” in which cool gas is accreting via filamentary streams directly onto the central regions of galaxies. At present, we find little observational evidence for cool infalling material, while evidence supporting the large-scale effects of superwind outflows is strong. This “pilot” study using faint galaxy spectra demonstrates the potential of using galaxies to trace baryons within galaxies, in the circumgalactic medium, and ultimately throughout the intergalactic medium.

Subfields: Astronomy and Astrophysics, Electrical and Electronic Engineering, Global and Planetary Change

View Paper: https://www.semanticscholar.org/paper/2a27a9c4ec8a0f39c9cbd179ab10f8af04560ba8

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Citations in the corpus

OVERVIEW OF THE SDSS-IV MaNGA SURVEY: MAPPING NEARBY GALAXIES AT APACHE POINT OBSERVATORY (2014, background): “…diversity of kinematic structure, including large rotating disks, compact dispersiondominated objects, and major mergers (e.g., Shapiro et al. 2008; Förster Schreiber et al. 2009; Law et al. 2009), not to mention evidence for winds and outflows (e.g., Steidel et al. 2010; Genzel et al. 2011).”
Galaxy evolution in cosmological simulations with outflows ― I. Stellar masses and star formation rates (2011, background): “Fortunately, observations of outflows across cosmic time are gaining substantial traction (Martin 2005; Weiner et al. 2009; Steidel et al. 2010), providing empirical constraints for models while the theory of outflow propagation develops.”
EVIDENCE FOR UBIQUITOUS COLLIMATED GALACTIC-SCALE OUTFLOWS ALONG THE STAR-FORMING SEQUENCE AT z ∼ 0.5 (2013, background): “…of evidence showing that the halos of 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…”
Lyα EMISSION FROM GREEN PEAS: THE ROLE OF CIRCUMGALACTIC GAS DENSITY, COVERING, AND KINEMATICS (2015, methodology): “Although higher ionization states are sometimes detected, we do not include these lines because they can have different kinematics than the low-ionization lines (when observed in other galaxies, e.g., Grimes et al. 2009; Steidel et al. 2010).”
THE COS-DWARFS SURVEY: THE CARBON RESERVOIR AROUND SUB-L* GALAXIES (2014, methodology): “At higher redshifts, Steidel et al. (2010) used stacked background galaxy spectra to characterize the CIV absorption around 512 foreground z≈ 2.2 galaxies out to 125 kpc.”
DIFFUSE Lyα EMITTING HALOS: A GENERIC PROPERTY OF HIGH-REDSHIFT STAR-FORMING GALAXIES (2011, background): “2010, MNRAS, 403, 870 Barnes, L. A., Haehnelt, M. G., Tescari, E., & Viel, M. 2011, ArXiv e-prints Bertin, E. & Arnouts, S. 1996, A&AS, 117, 393 Bolton, J. S., Haehnelt, M. G., Viel, M., & Springel, V. 2005, MNRAS, 357, 1178 Brocklehurst, M. 1971, MNRAS, 153, 471 Bunker, A. J., Marleau, F. R., & Gra”
THE BIMODAL METALLICITY DISTRIBUTION OF THE COOL CIRCUMGALACTIC MEDIUM AT z ≲ 1 (2013, methodology): “…spectra of galaxies are searched for blueshifted and redshifted absorption troughs relative to the galaxy systemic velocity as signatures of outflow and inflow, respectively (e.g., Heckman et al. 2000; Martin 2005; Tremonti et al. 2007; Weiner et al. 2009; Steidel et al. 2010; Rubin et al. 2011).”
Gusty, gaseous flows of FIRE: Galactic winds in cosmological simulations with explicit stellar feedback (2015, background): “…of kinematically distinct material from the rest frame of the host galaxy via Doppler shifted emission (e.g. Martin 1998) and absorption lines (e.g. Heckman et al. 2000; Grimes et al. 2009; Weiner et al. 2009; Steidel et al. 2010; Bouché et al. 2012; Martin et al. 2012; Rubin et al. 2014).”
FIRE-2 simulations: physics versus numerics in galaxy formation (2017, background): “…galaxy SFR (Aguirre et al. 2001; Pettini et al. 2003; Songaila 2005; Martin et al. 2010; Oppenheimer & Davé 2006), and indeed such winds are ubiquitously observed (Martin 1999, 2006; Heckman et al. 2000; Newman et al. 2012; Sato et al. 2009; Chen et al. 2010; Steidel et al. 2010; Coil et al. 2011).”
Neutral hydrogen in galaxy haloes at the peak of the cosmic star formation history (2014, methodology): “Building on previous work by Adelberger et al. (2003) and Steidel et al. (2010) on quasar-galaxy pairs, Rudie et al. (2012) reported systematic measurements of neutral hydrogen in the CGM of z ∼ 2 − 3 LBGs in the Keck Baryonic Structure Survey (KBSS), including covering fractions for different…”
First results from the TNG50 simulation: galactic outflows driven by supernovae and black hole feedback (2019, background): “…analyses of SDSS (Chen et al. 2010) through z ∼ 0.5 − 1 (Rubin et al. 2010, 2011) to the peak epoch of cosmic star formation at z ∼ 2− 3 in both absorption (Steidel et al. 2010) and emission, focusing on SF-driven outflows (Newman et al. 2012; Genzel et al. 2014) and AGN sources (Harrison et al.…”
Lyα COOLING EMISSION FROM GALAXY FORMATION (2010, background): “In the actual Universe, galactic winds are observed to be ubiquitous at high redshift (e.g., Shapley et al. 2003; Steidel et al. 2010) and simulations suggest that they are in fact needed to reproduce the observed baryonic mass function of galaxies (e.g., Kereš et al. 2009a; Oppenheimer et al.…”
RECONCILING THE STELLAR AND NEBULAR SPECTRA OF HIGH-REDSHIFT GALAXIES (2016, methodology): “Both configurations achieve a spectral resolving power of R ∼ 1300 − 1500 over the full wavelength range when combined with 1′′.2 entrance slits and typical seeing of 0′′.7 (see, e.g., Steidel et al. 2010).”
Observations of feedback from radio-quiet quasars – II. Kinematics of ionized gas nebulae (2013, background): “Existing observations and theory suggest that inflows have a small covering factor (Dekel et al. 2009; Steidel et al. 2010), so we do not expect inflows to result in the ubiquitous blue wings seen in our data.”
Metallicity gradients in local field star-forming galaxies: insights on inflows, outflows, and the coevolution of gas, stars and metals (2015, background): “…(z > 1) have provided evidences that galaxies in the early Universe undergo many, perhaps intermittent, accretion events, immense star formation and outflows (e.g.,Tacconi et al. 2010, 2013; Weiner et al. 2009; Steidel et al. 2010; Genzel et al. 2011; Newman et al. 2012; Genzel et al. 2014).”
SIMULATIONS OF DISK GALAXIES WITH COSMIC RAY DRIVEN GALACTIC WINDS (2013, background): “Additionally, outflows are required to drive metal-enriched gas out of galaxies, as suggested by both observational (e.g. Steidel et al. 2010) and theoretical (e.g. Booth et al. 2012) work.”
Gaseous Galaxy Halos (2012, background): “This quiet accretion could explain observations at higher redshifts that show substantial SFRs and outflows with little, if any, evidence for accretion (e.g., Erb, 2008; Shapley, 2011; Steidel et al., 2010).”
Spectroscopic detections of C iii] λ1909 Å at z ≃ 6–7: a new probe of early star-forming galaxies and cosmic reionization (2014, background): “If the Lyα velocity offset is similar to that found in bright UV-selected galaxies at z ' 2 (∆vLyα= 445 km s−1; Steidel et al. 2010), the IGM would likely have to be mostly neutral at z ' 7 to be consistent with the Lyα observations at the 1σ level (Mesinger et al. 2014).”
Ionized gas outflows and global kinematics of low-z luminous star-forming galaxies (2014, background): “…in high-z SFGs, as indicated by velocity centroid blueshifts with respect to the systemic in UV metal absorption lines (e.g., Pettini et al. 2000; Steidel et al. 2010), by broad atomic lines (Maiolino et al. 2012), and broad and shifted Hα lines (Shapiro et al. 2009; Genzel et al. 2011; Newman…”