ALMA observations of molecular gas in the host galaxy of AT2018cow. (arXiv:1906.05446v1 [astro-ph.GA])

ALMA observations of molecular gas in the host galaxy of AT2018cow. (arXiv:1906.05446v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Morokuma_Matsui_K/0/1/0/all/0/1">Kana Morokuma-Matsui</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Morokuma_T/0/1/0/all/0/1">Tomoki Morokuma</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tominaga_N/0/1/0/all/0/1">Nozomu Tominaga</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hatsukade_B/0/1/0/all/0/1">Bunyo Hatsukade</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hayashi_M/0/1/0/all/0/1">Masao Hayashi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tamura_Y/0/1/0/all/0/1">Yoichi Tamura</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Matsuda_Y/0/1/0/all/0/1">Yuichi Matsuda</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Motogi_K/0/1/0/all/0/1">Kazuhito Motogi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Niinuma_K/0/1/0/all/0/1">Kotaro Niinuma</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Konishi_M/0/1/0/all/0/1">Masahiro Konishi</a>

We investigate the molecular gas in, and star-formation properties of, the
host galaxy (CGCG 137-068) of a mysterious transient, AT2018cow, at kpc and
larger scales, using archival band-3 data from the Atacama Large
Millimeter/submillimeter Array (ALMA). AT2018cow is the nearest Fast-Evolving
Luminous Transient (FELT), and this is the very first study unveiling
molecular-gas properties of FELTs. The achieved rms and beam size are 0.21 mJy
beam$^{-1}$ at a velocity resolution of $40$ km s$^{-1}$ and $3″.66times2″.71$
($1.1~{rm kpc} times 0.8~{rm kpc}$), respectively. CO($J$=1-0) emission is
successfully detected. The total molecular gas mass inferred from the CO data
is $(1.85pm0.04)times10^8$ M$_odot$ with the Milky Way CO-to-H$_2$
conversion factor. The H$_2$ column density at the AT2018cow site is estimated
to be $8.6times10^{20}$ cm$^{-2}$. The ALMA data reveal that (1) CGCG 137-068
is a normal star-forming (SF) dwarf galaxy in terms of its molecular gas and
star-formation properties and (2) AT2018cow is located between a CO peak and a
blue star cluster. These properties suggest on-going star formation and favor
the explosion of a massive star as the progenitor of AT2018cow. We also find
that CGCG 137-068 has a solar or super-solar metallicity. If the metallicity of
the other FELT hosts is not higher than average, then some property of SF dwarf
galaxies other than metallicity may be related to FELTs.

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