# The warm Gaseous Disk and the Anisotropic Circumgalactic Medium of the Milky Way

## TL;DR

This study models the warm gaseous disk and circumgalactic medium of the Milky Way using absorption line data, revealing the disk's structure, mass, and anisotropic distribution of the CGM, with implications for galactic feedback processes.

## Contribution

The paper introduces a 2D disk-CGM model for warm gas in the Milky Way, constraining its density profile, mass, and anisotropic distribution based on Si IV and O VI absorption data.

## Key findings

- The warm gas disk has a scale height of 2.6 kpc and a scale length of 6.1 kpc.
- The total warm gas mass in the disk is approximately 4 million solar masses.
- The CGM shows higher column density perpendicular to the disk, indicating anisotropic distribution.

## Abstract

The warm ($\log~T\approx5$) gas is an important gaseous component in the galaxy baryonic cycle. We built a 2-dimension disk-CGM model to study the warm gas distribution of the Milky Way (MW) using the absorption line surveys of Si IV and O VI. In this model, the disk component of both ions has the same density profile ($n(r, z)=n_0\exp(-|z|/z_0)\exp(-r/r_0)$) with a scale height of $z_0=2.6\pm0.4\rm~kpc$ and a scale length of $r_0=6.1\pm1.2\rm~kpc$. For this disk component, we calculate the warm gas mass of $\log(M/M_\odot)=(7.6\pm0.2)-\log\frac{Z}{Z_\odot}$. The similar disk density profiles and total masses of Si IV and O VI-bearing gas set constraints on the ionization mechanisms. We suggest that the warm gas disk might be dominated by the Galactic fountain mechanism, which ejects and recycles gas to set both the scale height and the scale length of the warm gas disk. The CGM component in our model has a dependence on Galactic latitude with a higher column density along the direction perpendicular to the Galactic plane ($b=90^\circ$) than the column density along the radial direction ($b=0^\circ$). The column density difference between these two directions is $0.82\pm0.32\rm~dex$ at $6.3\sigma$ for both ions. This difference may be due to the enrichment of Galactic feedback to the entire CGM, or an additional interaction layer between the warm gas disk and the CGM; existing data cannot distinguish between these two scenarios. If this higher column density at $b=90^\circ$ is for the entire CGM, the total warm CGM mass is $\log(M/M_\odot)\approx(9.5-9.8)-\log\frac{Z}{0.5Z_\odot}$ within the MW virial radius of $250\rm~kpc$.