Volume 575, March 2015
|Number of page(s)||9|
|Published online||27 February 2015|
Heating and cooling of the neutral ISM in the NGC 4736 circumnuclear ring
Institut de Radioastronomie Millimétrique (IRAM),
300 rue de la Piscine, 38406 St. Martin
2 Spitzer Science Center, California Institute of Technology, MC 314-6, Pasadena, CA 91125, USA
3 Observatoire de Paris, 61 avenue de l’Observatoire, 75014 Paris, France
4 Steward Observatory, University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721, USA
5 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
6 Department of Astrophysical Sciences, Princeton University, Princeton, NJ 08544, USA
7 Department of Physics and Astronomy, University of Toledo, Toledo, OH 43606, USA
8 European Southern Observatory, Karl-Schwarzchild-Str. 2, 85748 Garching-bei-München, Germany
9 Department of Astronomy, University of Maryland, College Park, MD 20742, USA
10 Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210, USA
11 Department of Physics & Astronomy, University of Wyoming, Laramie, WY 82071, USA
12 Department of Astronomy, University of Massachusetts, Amherst, MA 01003, USA
13 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
Received: 25 November 2014
Accepted: 21 January 2015
The manner in which gas accretes and orbits within circumnuclear rings has direct implications for the star formation process. In particular, gas may be compressed and shocked at the inflow points, resulting in bursts of star formation at these locations. Afterwards the gas and young stars move together through the ring. In addition, star formation may occur throughout the ring, if and when the gas reaches sufficient density to collapse under gravity. These two scenarios for star formation in rings are often referred to as the “pearls-on-a-string” and “popcorn” paradigms. In this paper, we use new Herschel/PACS observations, obtained as part of the KINGFISH open time key program, along with archival Spitzer and ground-based observations from the SINGS Legacy project, to investigate the heating and cooling of the interstellar medium in the nearby star-forming ring galaxy, NGC 4736. By comparing spatially resolved estimates of the stellar far-ultraviolet flux available for heating, with the gas and dust cooling derived from the far-infrared continuum and line emission, we show that while star formation is indeed dominant at the inflow points in NGC 4736, additional star formation is needed to balance the gas heating and cooling throughout the ring. This additional component most likely arises from the general increase in gas density in the ring over its lifetime. Our data provide strong evidence, therefore, for a combination of the two paradigms for star formation in the ring in NGC 4736.
Key words: galaxies: individual: NGC 4736 / galaxies: ISM / galaxies: star formation
© ESO, 2015
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