On the CGM Fundamental Plane: The Halo Mass Dependency of Circumgalactic HI [GA]

We analyze the equivalent widths of HI Ly-$\alpha$ ($W_{Ly\alpha}$) from the inner (R < 160 kpc) circumgalactic medium (CGM) of 85 galaxies at $z \sim 0$ with stellar masses $M$ ranging $8 \leq log M / M_{\odot} \leq 11.6$. Across three orders of magnitude in stellar mass, the CGM of present-day galaxies exhibits a very high covering fraction of cool hydrogen gas ($f_C = 86.6 \pm 3.6$%) indicating that the CGM is ubiquitous in modern, isolated galaxies. These same galaxies show a decline in $W_{Ly\alpha}$ with increasing radius, independent of mass, but the scatter in this trend correlates closely with $M$. Using the radial and stellar mass correlations, we construct a fundamental plane describing the cool CGM of modern galaxies: $\log W^{s}_{HI 1215} \; = \; (0.34 \pm 0.02) -( 0.0026 \pm 0.0005)(R) + (0.286 \pm 0.002)* \log (M_{}/M_{\odot})$. The RMS scatter around this bivariate relation is $\sim$0.2 dex. We interpret the explicit correlation between $W_{Ly\alpha}$ and $M$ to arise from the underlying dark matter halo, i.e., $W_{Ly\alpha}$ traces the gravitational potential whereas $M*$ tracks $M_{halo}$.

R. Bordoloi, J. Prochaska, J. Tumlinson, et. al.
Fri, 8 Dec 17
4/70

Comments: 6 pages, 4 figures, submitted to ApJL