MUSEQuBES: Probing Anisotropies in Gas and Metal Distributions in the Circumgalactic Medium

Abstract

We investigate the azimuthal dependence of H I and O VI-bearing gas in the circumgalactic medium (CGM) of 113 isolated galaxies in the redshift range 0.12 < z < 0.75, including 91 new measurements from the MUSE Quasar-fields Blind Emitters Survey (MUSEQuBES). The H I covering fraction (k_HI) within the virial radius (Rvir) of low-mass (7 < log10(M*/Msun)< 9) galaxies, for a threshold column density of log10(N(HI)/cm^-2) = 14.5, exhibits an enhancement along both the disk plane (azimuthal angle phi < 20 degree) and in the polar direction (phi > 70 degree). In contrast, such a bimodal distribution is not observed for higher mass galaxies (9 < log10(M*/Msun) < 11.3). Similarly, the O VI covering fraction (k_OVI), for a threshold of log10(N(OVI)/cm^-2) = 14.0, shows a tentative enhancement along both the projected major and minor axes for low-mass galaxies. In contrast, O VI-bearing gas around higher- mass galaxies appears more uniformly distributed, with no significant azimuthal dependence. Finally, using the halo circular-velocity-normalized pixel-velocity two-point correlation function (TPCF), we find that O VI absorbers are kinematically narrower along the disk plane compared to the polar directions of the host galaxies with similar stellar mass distributions. The observed isotropic distribution of O VI in high-mass halos suggests that its spatial distribution is governed by global halo properties; however, the O VI kinematics retain memory of the site of origin.

Figures (15)

• Figure 1: The stellar masses of the galaxies used in this work are plotted against redshift with solid circles. The COS-halos galaxies are indicated with open red squares. The open circles indicate the MUSEQuBES galaxies discarded from our analysis, which are either undetected or unresolved in $HST$ images (see text). The circles are color-coded by the $D/R_{\rm vir}$ of the galaxies, where the color is saturated at $D/R_{\rm vir}=3$. The filled grey histograms on the top and right side panels show the $z$ and ${\rm log}_{10}(M_{\star}/\rm M_{\odot})$ distributions, respectively. The red hollow histograms show the same for the discarded galaxies.
• Figure 2: Cutouts of 113 galaxies, sorted by increasing stellar mass, constituting the 118 quasar-galaxy pairs used in this work. Note that 5 galaxies appear more than once since they are probed by multiple quasars. Each cutout spans 20 times the effective area of the galaxies. Green borders indicate galaxies from the MUSEQuBES sample, while red borders denote the 22 galaxies from the COS-Halos sample. The white solid and dashed arrows in each panel indicate the direction of the quasar location and projected major axis, respectively. The numbers in the lower left and right in each panel represent the most probable $\phi$ and $i$, respectively.
• Figure 2: -continued.
• Figure 3: The most probable azimuthal angle ($\phi$) plotted against the most probable inclination ($i$) for the galaxies used in this work. The y error bars indicate the 68% credible intervals obtained from the posterior $PA$ distributions. The median 68% confidence interval on $i$ is shown with the red horizontal bar on the top left. The side panels on the top and right show the most probable $i$ and $\phi$ distributions. The solid red line represents a scaled ${\rm sin} ~i$ function expected for randomly oriented disk galaxies.
• Figure 4: Left: H i column density (color) shown as a function of normalized impact parameter, $D/R_{\rm vir}$, along the radial direction and the azimuthal angle, $\phi$ along the polar direction. The filled and open symbols represent detections and $3\sigma$ upper limits, respectively. The circles and squares represent measurements for edge-on (most probable $i\geq 35^{\circ}$) and face-on (most probable $i< 35^{\circ}$) galaxies, respectively. Face-on galaxies are not considered in subsequent analyses. The area of the points scales with stellar mass, as shown (only for edge-on galaxies) in the legend. Right: Same as left but for O vi. In both panels, one measurement at $D/R_{\rm vir}>4$ is not shown.