A Census of the Extended Neutral Hydrogen Around 18 MHONGOOSE Galaxies
Amy Sardone, D.J. Pisano, N. M. Pingel, Amidou Sorgho, Claude, Carignan, W.J.G. de Blok

TL;DR
This study investigates the low-density neutral hydrogen environment around 18 galaxies, revealing the prevalence of diffuse gas, its correlation with galaxy mass, and potential gas accretion signatures using deep GBT observations.
Contribution
It provides the first detailed analysis of diffuse HI around a sample of galaxies, quantifying the amount of gas outside disks and identifying potential accretion features.
Findings
Most galaxies contain significant diffuse HI outside their disks.
A strong correlation exists between diffuse gas fraction and baryonic mass.
Galaxies with halo mass below 10^{11.1} M_sun are more likely to have high diffuse HI fractions.
Abstract
We present the analysis of the diffuse, low column density HI environment of 18 MHONGOOSE galaxies. We obtained deep observations with the Robert C. Byrd Green Bank Telescope, and reached down to a 3sigma column density detection limit of NHI=6.3x10^{17} cm^{-2} over a 20 km/s linewidth. We analyze the environment around these galaxies, with a focus on HI gas that reaches column densities below NHI=10^{19} cm^{-2}. We calculate the total amount of HI gas in and around the galaxies revealing that nearly all of these galaxies contained excess HI outside of their disks. We quantify the amount of diffuse gas in the maps of each galaxy, defined by HI gas with column densities below 10^{19} cm^{-2}, and find a large spread in percentages of diffuse gas. However, by binning the percentage of diffuse HI into quarters, we find that the bin with the largest number of galaxies is the lowest…
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