Kavli Affiliate: Jing Wang
| First 5 Authors: Kana Morokuma-Matsui, Kenji Bekki, Jing Wang, Paolo Serra, Yusei Koyama
| Summary:
We conduct a $^{12}$C$^{16}$O($J$=1-0) (hereafter CO) mapping survey of 64
galaxies in the Fornax cluster using the ALMA Morita array in cycle 5. CO
emission is detected from 23 out of the 64 galaxies. Our sample includes dwarf,
spiral and elliptical galaxies with stellar masses of $M_{rm
star}sim10^{6.3-11.6}$~M$_odot$. The achieved beam size and sensitivity are
$15”times8”$ and $sim12$~mJy~beam$^{-1}$ at the velocity resolution of
$sim10$~km~s$^{-1}$, respectively. We study the cold-gas (molecular- and
atomic-gas) properties of 38 subsamples with $M_{rm star}>10^9$~M$_odot$
combined with literature HI data. We find that: (1) the low star-formation (SF)
activity in the Fornax galaxies is caused by the decrease in the cold-gas mass
fraction with respect to stellar mass (hereafter, gas fraction) rather than the
decrease of the SF efficiency from the cold gas; (2) the atomic-gas fraction is
more heavily reduced than the molecular-gas fraction of such galaxies with low
SF activity. A comparison between the cold-gas properties of the Fornax
galaxies and their environmental properties suggests that the atomic gas is
stripped tidally and by the ram pressure, which leads to the molecular gas
depletion with an aid of the strangulation and consequently SF quenching.
Pre-processes in the group environment would also play a role in reducing
cold-gas reservoirs in some Fornax galaxies.
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