The Kinematic Connection between absorbing Gas toward QSOs and Galaxies at Intermediate Redshift

Abstract

We present complementary data on five intermediate-redshift (0:44 z 0:66) Mg ii-absorbing galaxies, combining high spatial resolution imaging from the Hubble Space Telescope, high-resolution quasi-stellar object (QSO) spectroscopy from the Keck High Resolution Echelle Spectrometer, and galaxy kinematics from intermediate-resolution spectroscopy using the Keck Low-Resolution Imaging Spectrometer. These data allow a direct comparison of the kinematics of gas at large galactocentric impact parameters with the galaxy kinematics obtained from the faint galaxy spectroscopy. All five galaxies appear to be relatively normal spirals, with measured rotation curves yielding circular velocities in the range 100 v c 260 km s À1 . The QSO sight lines have projected impact parameters to the absorbing galaxies in the range 14:5 h À1 kpc d 75 h À1 kpc; the galaxies have inclination angles with respect to the line of sight ranging from 40 to 75 . We find that in four of the five cases examined, the velocities of all of the Mg ii-absorption components lie entirely to one side of the galaxy systemic redshift. The fifth case, for which the galaxy is much less luminous than the other four, has narrow absorption centered at zero velocity with respect to systemic, despite having the largest disk inclination angle in the sample. These observations are consistent with rotation being dominant for the absorbing-gas kinematics; however, the total range of velocities observed is inconsistent with simple disk rotation in every case. Simple kinematic models that simultaneously explain both the systemic offset of the absorbing material relative to the galaxy redshifts and the total velocity width spanned by the absorption require either extremely thick rotating gas layers, rotation velocities that vary with z-height above the extrapolation of the galactic plane, or both. In any case, our small sample suggests that rotating '' halo '' gas is a common feature of intermediate-redshift spiral galaxies and that the kinematic signature of rotation dominates over radial infall or outflow even for gas well away from the galactic plane. We discuss possible explanations for this behavior and compare our observations with possible local analogs.

Four phases of angular-momentum buildup in high-z galaxies: from cosmic-web streams through an extended ring to disc and bulge

“…A detection of low-metallicity CGM gas at 54 kpc from the center of a z = 2.4 galaxy is also reported by Crighton et al (2013). Observed MgII absorption lines at large radii in intermediate-redshift galaxies (z < 1) indicate velocities consistent with rotation in terms of magnitude and in terms of residing in one side of the galaxy systemic velocity, typically aligned with one arm of the rotation curve (Steidel et al 2002;Kacprzak et al 2010).…”

The Physical Conditions of Intermediate-Redshift M[CLC]g[/CLC] [CSC]ii[/CSC] Absorbing Clouds from Voigt Profile Analysis

“…0.3 Å absorption, the gas kinematics directly trace the outer extensions of the stellar disk rotation curves (Steidel et al 2002). However, the data are difficult to under- Clues to the nature of the broader component to the TPCF might be connected to the redshift evolution of W r (2796).…”

Absorption-Line Systems and Galaxies in Front of the Second-brightest Quasar, PHL 1811

“…Although the size of the intermediate-redshift Mg ii absorbers has been examined in detail, the exact origin of the absorption is still under investigation, and numerous explanations have been suggested to account for the data. For example, Steidel et al (2002) have recently contributed to the notion that extended, diffuse galactic disks might explain the Mg ii systems (Wagoner 1967;Bowen 1991;Lanzetta & Bowen 1992;Charlton & Churchill 1996, 1998Churchill & Vogt 2001). They find evidence that the thick corotating disks of identified Mg ii-absorbing galaxies whose major axes are closely pointing toward a QSO sight line can explain the kinematical substructure of the absorption complexes.…”