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Molecular gas and dust in Arp 94: The formation of a recycled galaxy in an interacting system

Lisenfeld, U. and Mundell, C. G. and Schinnerer, E. and Appleton, P. N. and Allsopp, J. (2008) Molecular gas and dust in Arp 94: The formation of a recycled galaxy in an interacting system. Astrophysical Journal, 685 (1). pp. 181-193. ISSN 0004-637X. doi:10.1086/590420.

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We present new results for the molecular gas, dust emission, and the ionized gas in J1023+1952, an H I-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 30 m telescope, emission from (CO)-C-12(1-0) and (CO)-C-12(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. The molecular gas is found to be abundant over the entire H I cloud, with H-2-to-H I 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 24 mu m show that young SF is restricted to the southern part of the cloud. Despite the relatively uniform H-2 and H I column density across the cloud, young SF occurs only in those regions where the velocity dispersion in the CO and H I is a factor of similar to 2 lower (FWHM of 30-70 km s^(-1)) than elsewhere in the cloud (FWHM of 80-120 km s(-1)). 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 Hα photometry confirm that all the knots are young. 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 preexisting dwarf galaxy. Instead, it must be formed from recycled, metal-enriched gas, expelled from NGC 3227 or NGC 3226 in a previous phase of the interaction.

Item Type:Article
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URLURL TypeDescription
Lisenfeld, U.0000-0002-9471-5423
Schinnerer, E.0000-0002-3933-7677
Appleton, P. N.0000-0002-7607-8766
Additional Information:© 2008 American Astronomical Society. Received 2008 January 21; accepted 2008 May 27. Print publication: Issue 1 (2008 September 20). We would like to thank the referee for useful and detailed comments on the draft, as well as Almudena Zurita, Monica Relaño, Beatriz Ruiz, Vicent Martínez, and Cesar Husillos for carrying out the observations at Calar Alto. We would furthermore like to acknowledge the program Calar Alto Academy that allowed these observations to be taken. We are grateful to H. Teplitz (Caltech) for help with IRS peak-up imaging used in this paper and to T. Jarrett (IPAC) for useful discussions. U.L. thanks IPAC for its hospitality during a summer visit where part of this work was done and 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. Facilities: CLFST, CAO:2.2m, Spitzer, IRAM:30m
Funding AgencyGrant Number
Ministerio de Educación y Ciencia (MEC)AYA 2005-07516-C02-01
Ministerio de Educación y Ciencia (MEC)ESP 2004-06870-C02-02
Junta de AnaducíaUNSPECIFIED
Research Councils UK (RCUK)UNSPECIFIED
Subject Keywords:galaxies: active; galaxies: individual (Arp 94, J1023+1952, NGC 3227); galaxies: interactions; galaxies: ISM; molecular data
Issue or Number:1
Record Number:CaltechAUTHORS:LISapj08b
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:12601
Deposited By: Tony Diaz
Deposited On:02 Feb 2009 18:59
Last Modified:08 Nov 2021 22:30

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