CYANOACETYLENE IN IC 342: AN EVOLVING DENSE GAS COMPONENT WITH STARBURST AGE

Journal Article · Fri Jul 15 04:00:00 EDT 2011 · Astronomical Journal (New York, N.Y. Online)

DOI:https://doi.org/10.1088/0004-6256/142/1/32· OSTI ID:21583050

Meier, David S ^[1]; Turner, Jean L ^[2]; Schinnerer, Eva ^[3]

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1. New Mexico Institute of Mining and Technology, 802 Leroy Place, Socorro, NM 87801 (United States)
2. Department of Physics and Astronomy, UCLA, Los Angeles, CA 90095-1562 (United States)
3. Max-Planck-Institut fuer Astronomie, Koenigstuhl 17, D-69117 Heidelberg (Germany)

We present the first images of the J = 5-4 and J = 16-15 lines of the dense gas tracer, cyanoacetylene, HC{sub 3}N, in an external galaxy. The central 200 pc of the nearby star-forming spiral galaxy, IC 342, was mapped using the Very Large Array and the Plateau de Bure Interferometer. HC{sub 3}N(5-4) line emission is found across the nuclear mini-spiral, but is very weak toward the starburst site, the location of the strongest mid-IR and radio emission. The J = 16-15 and 10-9 lines are also faint near the large H II region complex, but are brighter relative to the 5-4 line, consistent with higher excitation. The brightest HC{sub 3}N emission is located in the northern arm of the nuclear mini-spiral, 100 pc away from the radio/IR source to the southwest of the nucleus. This location appears less affected by ultraviolet radiation and may represent a more embedded, earlier stage of star formation. HC{sub 3}N excitation temperatures are consistent with those determined from C{sup 18}O; the gas is dense 10{sup 4} - 10{sup 5} cm{sup -3} and cool, T{sub k} < 40 K. So as to not violate limits on the total H{sub 2} mass determined from C{sup 18}O, at least two dense components are required to model IC 342's giant molecular clouds. These observations suggest that HC{sub 3}N(5-4) is an excellent probe of the dense, quiescent gas in galaxies. The high excitation combined with faint emission toward the dense molecular gas at the starburst indicates that it currently lacks large masses of very dense gas. We propose a scenario where the starburst is being caught in the act of dispersing or destroying its dense gas in the presence of the large H II region. This explains the high star formation efficiency seen in the dense component. The little remaining dense gas appears to be in pressure equilibrium with the starburst H II region.

• OSTI ID: 21583050
• Journal Information: Astronomical Journal (New York, N.Y. Online), Journal Name: Astronomical Journal (New York, N.Y. Online) Journal Issue: 1 Vol. 142; ISSN 1538-3881
• Country of Publication: United States
• Language: English

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