Halo Masses of MgII absorbers at zsim 0.5 from SDSS DR7

We present the cross-correlation function of MgII absorbers with respect to a volume-limited sample of luminous red galaxies (LRGs) at z=0.45-0.60 using the largest MgII absorber sample and a new LRG sample from SDSS DR7. We present the clustering signal of absorbers on projected scales r_p = 0.3-35 Mpc/h in four Wr(2796) bins spanning Wr(2796)=0.4-5.6A. We found that on average MgII absorbers reside in halos < log M_h > approx 12.1, similar to the halo mass of an L_* galaxy. We report that the weakest absorbers in our sample with W_r(2796)=0.4-1.1A reside in relatively massive halos with < log M_h > approx 12.5^{+0.6}_{-1.3}, while stronger absorbers reside in halos of similar or lower masses < log M_h > approx 11.6^{+0.9}. We compared our bias data points, b, and the frequency distribution function of absorbers, f_{W_r}, with a simple model incorporating an isothermal density profile to mimic the distribution of absorbing gas in halos. We also compared the bias data points with Tinker & Chen (2008) who developed halo occupation distribution models of MgII absorbers that are constrained by b and f_{W_r}. The simple isothermal model can be ruled at a approx 2.8sigma level mostly because of its inability to reproduce f_{W_r}. However, b values are consistent with both models, including TC08. In addition, we show that the mean b of absorbers does not decrease beyond W_r(2796) approx 1.6A. The flat or potential upturn of b for Wr(2796) gtrsim 1.6A absorbers suggests the presence of additional cool gas in massive halos.

Spatially Resolved Velocity Maps of Halo Gas Around Two Intermediate-redshift Galaxies

Absorption-line spectroscopy of multiply-lensed QSOs near a known foreground galaxy provides a unique opportunity to go beyond the traditional one-dimensional application of QSO probes and establish a crude three-dimensional (3D) map of halo gas around the galaxy that records the line-of-sight velocity field at different locations in the gaseous halo. Two intermediate-redshift galaxies are targeted in the field around the quadruply-lensed QSO HE0435-1223 at redshift z=1.689, and absorption spectroscopy along each of the lensed QSOs is carried out in the vicinities of these galaxies. One galaxy is a typical, star-forming L* galaxy at z=0.4188 and projected distance of rho=50 kpc from the lensing galaxy. The other is a super-L* barred spiral at z=0.7818 and rho=33 kpc. Combining known orientations of the quadruply-lensed QSO to the two foreground galaxies with the observed MgII absorption profiles along individual QSO sightlines has for the first time led to spatially resolved kinematics of tenuous halo gas on scales of 5-10 kpc at z>0.2. A MgII absorber is detected in every sightline observed through the halos of the two galaxies, and the recorded absorber strength is typical of what is seen in previous close QSO--galaxy pair studies. While the multi-sightline study confirms the unity covering fraction of MgII absorbing gas at rho < 50 kpc from star-forming disks, the galaxies also present two contrasting examples of complex halo gas kinematics. Different models, including a rotating disk, collimated outflows, and gaseous streams from either accretion or tidal/ram-pressure stripping, are considered for comparisons with the absorption-line observations, and infalling streams/stripped gas of width >~ 10 kpc are found to best describe the observed gas kinematics across multiple sightlines.

Empirical Constraints of Super-Galactic Winds at z >= 0.5

(Abridged) Under the hypothesis that MgII absorbers found near the minor axis of a galaxy originate in the cool phase of winds, we carry out a study to constrain the properties of large-scale outflows at redshift z >= 0.5 based on the observed relative motions of individual absorbing clouds with respect to the positions and orientations of the galaxies. We identify in the literature four highly inclined disk galaxies located within 50 kpc and with the minor axis oriented within 45 degrees of a background QSO sightline. Deep HST images of the galaxies are available for accurate morphologies of the galaxies. Echelle spectra of the QSO members are also available in public archives for resolving the velocity field of individual absorption clumps. Three galaxies in our sample are located at rho=8-34 kpc and exhibit strong associated MgII absorption feature with Wr(2796) >= 0.8 {AA}. One galaxy, located at an impact parameters rho=48 kpc, does not show an associated MgII absorber to a 3-sigma limit of Wr(2796)=0.01{AA}. Combining known inclination and orientation angles of the star-forming disks, and resolved absorption profiles of the associated absorbers at rho < 35 kpc, we explore the parameter space for the opening angle theta_0 and the velocity field of large-scale galactic outflows as a function of z-height, v(z). We find that the absorption profiles of the MgII doublets and FeII series are compatible with the gas being either accelerated or decelerated, depending on theta_0, though accelerated outflows are valid only for a narrow range of theta_0. Under an acceleration scenario, we compare the derived $v(z)$ with predictions from Murray et al. (2011) and find that if the gas is being accelerateted by the radiation and ram pressure forces from super star clusters, then the efficiency of thermal energy input from a supernova explosion is epsilon <= 0.01.

The Clustering of MgII Absorption Systems at z=0.5 and Detection of Cold Gas in Massive Halos

We measure the large-scale clustering of MgII lambdalambda 2796,2803 absorbers with respect to a population of luminous red galaxies (LRGs) at z sim 0.5. From the cross-correlation measurements between MgII absorbers and LRGs, we calculate the mean bias of the dark matter halos in which the absorbers reside. We investigate systematic uncertainties in the clustering measurements due to the sample selection of LRGs and due to uncertainties in photometric redshifts. First, we compare the cross-correlation amplitudes determined using a it flux-limited LRG sample and a volume-limited one. The comparison shows that the relative halo bias of MgII absorbers using a flux-limited LRG sample can be overestimated by as much as approx 20%. Next, we assess the systematic uncertainty due to photometric redshift errors using a mock galaxy catalog with added redshift uncertainties comparable to the data. We show that the relative clustering amplitude measured without accounting for photometric redshift uncertainties is overestimated by approx 10%. After accounting for these two main uncertainties, we find a 1-sigma anti-correlation between mean halo bias and absorber strength that translates into a 1-sigma anti-correlation between mean galaxy mass and W_r(2796). The results indicate that a significant fraction of the MgII absorber population of W_r(2796)=1-1.5 AA are found in group-size dark matter halos of log M_h < 13.4, whereas absorbers of W_r(2796)>1.5 AA are seen in halos of log M_h <12.7. A larger dataset would improve the precision of the clustering measurements and the relationship between W_r and halo mass. Finally, the strong clustering of MgII absorbers down to sim 0.3 h^{-1} Mpc indicates the presence of cool gas inside the virial radii of the halos hosting the LRGs.