Molecular gas and dust in ARP 94

The formation of a recycled galaxy in an interacting system

U. Lisenfeld, C. G. Mundell, E. Schinnerer, P. N. Appleton, J. Allsopp

Research output: Contribution to journalArticle

13 Citations (Scopus)

Abstract

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 12CO(1-0) and 12CO(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 × 5.9 kpc. The molecular gas is found to be abundant over the entire H I cloud, with H2-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 μm show that young SF is restricted to the southern part of the cloud. Despite the relatively uniform H2 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 ∼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 (AB = 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.

Original languageEnglish
Pages (from-to)181-193
Number of pages13
JournalAstrophysical Journal
Volume685
Issue number1
DOIs
Publication statusPublished - 20 Sep 2008

Fingerprint

molecular gases
dust
galaxies
dwarf galaxies
gases
gas
hydrogen clouds
ionized gases
spectral energy distribution
mass ratios
metals
intersections
metallicity
photometry
extinction
kinematics
telescopes
metal
stars
spectroscopy

Keywords

  • Galaxies: active
  • Galaxies: interactions
  • Galaxies: ISM
  • Molecular data

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Molecular gas and dust in ARP 94 : The formation of a recycled galaxy in an interacting system. / Lisenfeld, U.; Mundell, C. G.; Schinnerer, E.; Appleton, P. N.; Allsopp, J.

In: Astrophysical Journal, Vol. 685, No. 1, 20.09.2008, p. 181-193.

Research output: Contribution to journalArticle

Lisenfeld, U. ; Mundell, C. G. ; Schinnerer, E. ; Appleton, P. N. ; Allsopp, J. / Molecular gas and dust in ARP 94 : The formation of a recycled galaxy in an interacting system. In: Astrophysical Journal. 2008 ; Vol. 685, No. 1. pp. 181-193.
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AB - 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 12CO(1-0) and 12CO(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 × 5.9 kpc. The molecular gas is found to be abundant over the entire H I cloud, with H2-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 μm show that young SF is restricted to the southern part of the cloud. Despite the relatively uniform H2 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 ∼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 (AB = 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.

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