Astronomy and Astrophysics – Astrophysics – Cosmology and Extragalactic Astrophysics
Scientific paper
2011-07-27
Astronomy and Astrophysics
Astrophysics
Cosmology and Extragalactic Astrophysics
41 pages, 7 tables, 16 eps figures, 2 jpeg figures
Scientific paper
We combine data from the ATNF and SEST to investigate the neutral ISM in AM0644-741, a large robustly star forming ring galaxy. The galaxy's ISM is concentrated in the 42-kpc diameter ring and appears dominated by HI, with a global molecular fraction of only 6.2%. Outside the starburst peak, the gas ring appears gravitationally stable (Q_gas = 3-11). Including the stellar component lowers Q overall, but not enough to make Q<1 everywhere. High SFEs follow from the ring's low H2 content. AM0644-741's star formation law is highly peculiar: HI obeys a Schmidt law, but H2 is uncorrelated with SFR density. Photo-dissociation models yield low volume densities in the ring, particularly in the starburst quadrant (n=2 cm-3), implying a Warm Neutral Medium dominated ISM. The ring's pressure and ambient FUV radiation field lead to the expectation of a predominantly molecular ISM. We argue that the ring's high SFE, low molecular fraction and n, and peculiar star formation law follow from the ISM's >100 Myr confinement time in the starburst ring, which amplifies the effects of embedded massive stars and SNe. The ring's molecular ISM becomes dominated by small clouds, causing H2 to be significantly underestimated by 12CO line fluxes: in effect X_CO >> X_Gal despite the ring's >solar metallicity. The observed HI is primarily a low density photo-dissociation product, i.e., a tracer rather than a precursor of star formation. Such an "over-cooked" ISM may be a general characteristic of evolved ring galaxies.
Higdon James L.
Higdon Sarah J. U.
Rand Richard J.
No associations
LandOfFree
Wheels of Fire IV. Star Formation and the Neutral Interstellar Medium in the Ring Galaxy AM0644-741 does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Wheels of Fire IV. Star Formation and the Neutral Interstellar Medium in the Ring Galaxy AM0644-741, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Wheels of Fire IV. Star Formation and the Neutral Interstellar Medium in the Ring Galaxy AM0644-741 will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-114041