Astron. J., 132, 2289-2295 (2006/December-0)
Extended star formation and molecular gas in the tidal arms near NGC 3077.
WALTER F., MARTIN C.L. and OTT J.
Abstract (from CDS):
We report the detection of ongoing star formation in the prominent tidal arms near NGC 3077 (member of the M81 triplet). In total, 36 faint compact H II regions are identified, covering an area of ∼4x6 kpc2. Most of the H II regions are found at H I column densities above 1x1021/cm2 (on scales of 200 pc), well within the range of threshold columns measured in normal galaxies. The H II luminosity function resembles those derived for other low-mass dwarf galaxies in the same group; we derive a total star formation rate of 2.3x10–3 M☉/yr in the tidal feature. We also present new high-resolution imaging of the molecular gas distribution in the tidal arm using CO observations obtained with the Owens Valley Radio Observatory interferometer. We recover about one-sixth of the CO flux (or MH2∼2x106 M☉, assuming a Galactic conversion factor) originally detected in the IRAM 30 m single-dish observations, indicating the presence of a diffuse molecular gas component in the tidal arm. The brightest CO peak in the interferometer map (comprising half of the detected CO flux) is coincident with one of the brightest H II regions in the feature. Assuming a constant star formation rate since the creation of the tidal feature (presumably ∼3x108 yr ago), a total mass of ∼7x105 M☉ has been transformed from gas into stars. Over this period the star formation in the tidal arm has resulted in an additional enrichment of ΔZ>0.002. The reservoir of atomic and molecular gas in the tidal arm is ∼3x108 M☉, allowing star formation to continue at its present rate for a Hubble time. Such widespread, low-level star formation would be difficult to image around more distant galaxies but may be detectable through intervening absorption in quasar spectra.
Galaxies: Individual: NGC Number: NGC 3077 - Galaxies: Interactions - Galaxies: ISM - ISM: H II Regions - Radio Lines: Galaxies
Table 1, Fig.2: [WMO2006b] NN (Nos 1-36). Table 2, Fig.3: [WMO2006b] A (Nos A-F).
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