Large-scale molecular gas distribution in the M17 cloud complex: dense gas conditions of massive star formation?. (arXiv:2001.09559v1 [astro-ph.GA])

Large-scale molecular gas distribution in the M17 cloud complex: dense gas conditions of massive star formation?. (arXiv:2001.09559v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Nguyen_Luong_Q/0/1/0/all/0/1">Quang Nguyen-Luong</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nakamura_F/0/1/0/all/0/1">Fumitaka Nakamura</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sugitani_K/0/1/0/all/0/1">Koji Sugitani</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shimoikura_T/0/1/0/all/0/1">Tomomi Shimoikura</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dobashi_K/0/1/0/all/0/1">Kazuhito Dobashi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kinoshita_S/0/1/0/all/0/1">Shinichi W. Kinoshita</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kim_K/0/1/0/all/0/1">Kee-Tae Kim</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kang_H/0/1/0/all/0/1">Hynwoo Kang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sanhueza_P/0/1/0/all/0/1">Patricio Sanhueza</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Evans_N/0/1/0/all/0/1">Neal J. Evans II</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+White_G/0/1/0/all/0/1">Glenn J. White</a>

The non-uniform distribution of gas and protostars in molecular clouds is
caused by combinations of various physical processes that are difficult to
separate. We explore this non-uniform distribution in the M17 molecular cloud
complex that hosts massive star formation activity using the $^{12}$CO
($J=1-0$) and $^{13}$CO ($J=1-0$) emission lines obtained with the Nobeyama 45m
telescope. Differences in clump properties such as mass, size, and
gravitational boundedness reflect the different evolutionary stages of the
M17-H{scriptsize II} and M17-IRDC clouds. Clumps in the M17-H{scriptsize II}
cloud are denser, more compact, and more gravitationally bound than those in
M17-IRDC. While M17-H{scriptsize II} hosts a large fraction of very dense gas
(27%) that has column density larger than the threshold of $sim$ 1 g
cm$^{-2}$ theoretically predicted for massive star formation, this very dense
gas is deficient in M17-IRDC (0.46%). Our HCO$^+$ ($J=1-0$) and HCN ($J=1-0$)
observations with the TRAO 14m telescope, {nlqb trace all gas with column
density higher than $3times 10^{22}$ cm$^{-2}$}, confirm the deficiency of
high density ($gtrsim 10^5$ cm$^{-3}$) gas in M17-IRDC. Although M17-IRDC is
massive enough to potentially form massive stars, its deficiency of very dense
gas and gravitationally bound clumps can explain the current lack of massive
star formation.

The non-uniform distribution of gas and protostars in molecular clouds is
caused by combinations of various physical processes that are difficult to
separate. We explore this non-uniform distribution in the M17 molecular cloud
complex that hosts massive star formation activity using the $^{12}$CO
($J=1-0$) and $^{13}$CO ($J=1-0$) emission lines obtained with the Nobeyama 45m
telescope. Differences in clump properties such as mass, size, and
gravitational boundedness reflect the different evolutionary stages of the
M17-H{scriptsize II} and M17-IRDC clouds. Clumps in the M17-H{scriptsize II}
cloud are denser, more compact, and more gravitationally bound than those in
M17-IRDC. While M17-H{scriptsize II} hosts a large fraction of very dense gas
(27%) that has column density larger than the threshold of $sim$ 1 g
cm$^{-2}$ theoretically predicted for massive star formation, this very dense
gas is deficient in M17-IRDC (0.46%). Our HCO$^+$ ($J=1-0$) and HCN ($J=1-0$)
observations with the TRAO 14m telescope, {nlqb trace all gas with column
density higher than $3times 10^{22}$ cm$^{-2}$}, confirm the deficiency of
high density ($gtrsim 10^5$ cm$^{-3}$) gas in M17-IRDC. Although M17-IRDC is
massive enough to potentially form massive stars, its deficiency of very dense
gas and gravitationally bound clumps can explain the current lack of massive
star formation.

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