Kavli Affiliate: Jing Wang
| First 5 Authors: Xiao Li, Xiao Li, , ,
| Summary:
While massive quiescent galaxies are known to be poor in atomic hydrogen
(HI), their true HI content remains poorly constrained due to the limited
sensitivity and morphological biases of existing surveys. We present deep HI
observations using the Five-hundred-meter Aperture Spherical radio Telescope
(FAST) for a representative sample of 78 low-redshift massive quiescent
galaxies, selected by stellar mass ($M_ast > 10^10 M_odot$) and color
(NUV$-r > 5$). Our observations reach an exceptional detection limit of
$log(M_HI/M_ast) = -3$. We find that one-third of the sample follows the
predicted HI mass fraction distribution based on previous surveys. However, the
majority ($sim$2/3) exhibit significantly lower HI content, with a $3sigma$
upper limit of $log(M_HI/M_ast) < -3.46$ derived from stacking the
non-detections. As a consequence of this enormous dynamic range and the high
fraction of non-detections, the HI mass fraction shows no clear correlation
with parameters tracing star formation, structure, or morphology. Our FAST
sample shows remarkable similarity to the $ATLAS^3D$ sample which only
includes early-type galaxies, both in its high fraction of HI-poor galaxies and
its high satellite fraction among HI-poor galaxies, as indicated by three
different environmental characteristics: projected cross-correlation functions,
background-subtracted neighbour counts, and central/satellite classification in
the SDSS galaxy group catalog. These results suggest that while early-type
morphology and environment play crucial roles in suppressing HI reservoirs,
neither factor alone fully explains the observed gas depletion, indicating that
additional physical mechanisms must be responsible for the extreme HI
deficiency prevalent in massive quiescent galaxies.
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