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Please use this identifier to cite or link to this item: http://hdl.handle.net/10481/28395

Title: Molecular gas and dust in Arp 94: the formation of a recycled galaxy in an interacting system
Authors: Lisenfeld, Ute
Mundell, C.
Shinnerer, E.
Appleton, P. N.
Allsopp, J.
Issue Date: 2008
Abstract: We present new results for the molecular gas, dust emission and the ionized gas in J1023+1952, an HI rich intergalactic star-forming tidal dwarf galaxy candidate. It is located at the projected intersection of two faint stellar tidal streams wrapped around the interacting pair of galaxies NGC 3227/6 (Arp~94). Using the IRAM 30m telescope, emission from CO(1-0) and CO(2-1) was detected across the entire extent of the neutral hydrogen cloud associated with J1023+1952, a region of the size of 8.9$ x 5.9 kpc, as well as in the nuclear region and outer disk of NGC 3227. The molecular gas is found to be abundant over the entire HI cloud, with H2-to-HI gas mass ratios between 0.5 and 1.7. New Spitzer mid-infrared observations at 3.6, 4.5, 5.8, 8.0, 15 and 24mu show that young SF is restricted to the southern part of the cloud. Despite the relatively uniform H$_2$ and HI column density across the cloud, young SF occurs only where the velocity dispersion in the CO and HI is a factor of $\sim$two lower (FWHM of 30 - 70 \kms) than elsewhere in the cloud (FWHM of 80 - 120 \kms). Thus the kinematics of the gas, in addition to its column density, seems to be a crucial factor in triggering SF. Optical/infrared spectral energy distributions (SEDs) and Halpha photometry confirm that all the knots are young, with a tentative age sequence from the south-west (oldest knots) to the north-east (youngest). Optical spectroscopy of the brightest SF region allowed us to determine the metallicity (12+log(O/H) = 8.6 +- 0.2) and the extinction ($A_B$=2.4). This shows that J1023+1952 is made from metal-enriched gas which is inconsistent with the hypothesis that it represents a pre-existing dwarf galaxy. Instead, it must be formed from recycled, metal-enrichd gas, expelled from NGC 3227 or NGC 3226 in a previous phase of the interaction.
Sponsorship: U. L. acknowledges financial support from the research project AYA 2005-07516-C02-01 and ESP 2004-06870-C02-02 from the Spanish Ministerio de Ciencia y Educación and from the Junta de Anaducía. C. G. M. acknowledges financial support from the Royal Society and the RCUK.
Publisher: American Astronomical Society; Institute of Physics (IOP)
Keywords: Molecular data
Arp 94
NGC 3227
URI: http://hdl.handle.net/10481/28395
ISSN: 0004-637X
Rights : Creative Commons Attribution-NonCommercial-NoDerivs 3.0 License
Citation: Lisenfeld, U.; et al. Molecular gas and dust in Arp 94: the formation of a recycled galaxy in an interacting system. Astrophysical Journal, 685(1): 181-193 (2008). [http://hdl.handle.net/10481/28395]
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