Halo Gas and Galaxy Disk Kinematics Derived from Observations and LCDM Simulations of MgII Absorption Selected Galaxies at Intermediate Redshift

TL;DR

This study combines observations and simulations to analyze MgII absorption in intermediate-redshift galaxies, revealing complex kinematics involving halo gas, galaxy rotation, and infalling streams, challenging simple rotating disk models.

Contribution

It provides a detailed comparison of observed galaxy kinematics with LCDM simulations, highlighting the role of filaments and streams in MgII absorption and limitations of rotating disk models.

Findings

MgII absorption velocities often align with galaxy rotation but show complex distributions.

Simulations indicate MgII traces infalling filaments and streams, not just rotating disks.

Absorption velocity spread may depend on galaxy inclination.

Abstract

We obtained ESI/Keck rotation curves of 10 MgII absorption selected galaxies (0.3 < z < 1.0) for which we have WFPC-2/HST images and high resolution HIRES/Keck and UVES/VLT quasar spectra of the MgII absorption profiles. We perform a kinematic comparison of these galaxies and their associated halo MgII absorption. For all 10 galaxies, the majority of the absorption velocities lie in the range of the observed galaxy rotation velocities. In 7/10 cases, the absorption velocities reside fully to one side of the galaxy systemic velocity and usually align with one arm of the rotation curve. In all cases, a constant rotating thick-disk model poorly reproduces the full spread of observed MgII absorption velocities when reasonably realistic parameters are employed. In 2/10 cases, the galaxy kinematics, star formation surface densities, and absorption kinematics have a resemblance to those of high redshift galaxies showing strong outflows. We find that MgII absorption velocity spread and optical depth distribution may be dependent on galaxy inclination. To further aid in the spatial-kinematic relationships of the data, we apply quasar absorption line techniques to a galaxy (v_c=180 km/s) embedded in LCDM simulations. In the simulations, MgII absorption selects metal enriched "halo" gas out to roughly 100 kpc from the galaxy, tidal streams, filaments, and small satellite galaxies. Within the limitations inherent in the simulations, the majority of the simulated MgII absorption arises in the filaments and tidal streams and is infalling towards the galaxy with velocities between -200 < v_r < -180 km/s. The MgII absorption velocity offset distribution (relative to the simulated galaxy) spans ~200 km/s with the lowest frequency of detecting MgII at the galaxy systematic velocity.