Dong Yang, Jing Wang, Zhijie Qu, Zezhong Liang, Xuchen Lin

| Summary:

[[{“value”:”We present a statistical study of the neutral atomic hydrogen (HI) gas
extending into the circumgalactic medium perpendicular to the disk for 7
edge-on galaxies with inclinations above $85^{circ}$ from the FEASTS program
with a $3sigma$ ($20,text{km},text{s}^{-1}$) column density
($N_{text{HI}}$) depth of $5times10^{17} text{cm}^{-2}$. We develop two
photometric methods to separate the extraplanar HI from the disk component,
based on existing interferometric data and parametric modeling of the disk flux
distribution respectively. With both methods, the FEASTS data exhibit clear
extended wings beyond the disk along the minor axis. The extraplanar HI
accounts for 5% to 20% of the total HI mass and extends to $20text{-}50$ kpc
at $N_{text{HI}}=10^{18} text{cm}^{-2}$. We find a tight positive correlation
between vertical extensions of the extraplanar HI and total HI mass
$M_text{HI}$. The iso-density shape of HI at $N_{text{HI}}=10^{18}
text{cm}^{-2}$ has an average axis ratio of $0.56pm0.11$. The off-disk
$N_{text{HI}}$ profiles of these edge-on galaxies well represent the lower
envelop of previous Lyman-$alpha$ absorption measurements at low-redshift. Our
results suggest that at $N_{text{HI}}=5times10^{17} text{cm}^{-2}$, the HI
extends considerably further than the known thin and thick disks in the
vertical direction, but still remains much flattener than a spherical
distribution, consistent with theoretical expectations that outflow,
circulation, and accretion should have different impacts in these two
directions. We show the tension of our results with Illustris and TNG
predictions, highlighting the constraining power of our results for future
simulations.”}]] 

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