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For refcode 1995ApJ...438L..79H:
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1995ApJ...438L..79H THE DETECTION OF MOLECULAR GAS IN THE RING GALAXY ARP 143 JAMES L. HIGDON National Radio Astronomy Observatory, Array Operations Center, 1003 Lopezville Road, Socorro, NM 87801 BEVERLY J. SMITH Department of Astronomy, University of Texas at Austin, Austin, TX 78712 STEVEN D. LORD IPAC/Caltech, Pasadena, CA 91125 AND RICHARD J. RAND Department of Astronomy, University of Maryland, College Park, MD 20742 Received 1994 July 18; accepted 1994 October 18 ABSTRACT We have used the NRAO 12 m telescope to map the inner 10 kpc of NGC 2445, the ring galaxy in Arp 143, in ^12^CO(J = 1-0). Emission is peaked near the ring galaxy nucleus, but we find evidence for an additional asymmetric and extended CO component. This extended CO distribution is consistent with an ~8 kpc diameter crescent-shaped ring of molecular gas, similar to the one seen in H I, accounting for approximately half of the total CO flux. Assuming this distribution, we derive a total H_2_ mass for NGC 2445 of 0.4-2.4 x 10^10^ M_sun_, depending on whether a Galactic or low-metallicity LMC conversion factor is used, and an H_2_/H I mass ratio between 0.9 and 5. The ring is experiencing low rates of massive star formation despite very high gas column densities. We find that the gas surface density exceeds the critical threshold for star formation throughout the ring, even without a possible contribution from a significant molecular component. The absence of vigorous star formation is most simply understood in terms of its youth (30 Myr): massive stars have not had time to form in large numbers. Our results support the interpretation that NGC 2445 is a nascent ring galaxy, seen prior to its ring starburst phase. Subject headings: galaxies: individual (Arp 143) - galaxies: interactions - galaxies: ISM - galaxies: starburst
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