Molecular Gas and Star Formation in NGC 3077

Abstract

We present high-resolution CO(1È0) and CO(2È1) images of the central 1 kpc of NGC 3077 (D2A .5) made with the Owens Valley Millimeter Array. CO emission is distributed in three major complexes, which resolve into at least seven giant molecular clouds (GMCs). Two complexes are associated with the central starburst. A third, more distant complex is not associated with strong star formation. The GMCs are D70 pc in size and contain D106 of molecular gas. The Galactic conversion factor appears M _ applicable to NGC 3077, consistent with its solar metallicity. Galactic rotation in NGC 3077 is detected for the Ðrst time in the molecular gas. The molecular gas counterrotates with respect to the large-scale H I tidal bridge. The molecular clouds closest to the starburst have supervirial line widths, possibly related to the turbulence generated by the starburst. The 2.6 mm radio continuum Ñux indicates that thermal bremsstrahlung dominates the emission from the starburst region below 5 cm and that the N Lyc^3.7 ] 1052 s~1, or D3000 O7 stars, corresponds to a star formation rate of 0.4 yr~1. At this rate, the M _ amount of molecular gas can sustain star formation for only D10 Myr ; thus, NGC 3077 is a true starburst galaxy. The derived age of the starburst is consistent with the inferred ages of the superbubbles, which suggests that the burst is much younger than the age of the M81ÈM82ÈNGC 3077 interaction. We suggest that it is caused by gas that was pulled out of NGC 3077 during the interaction with M81, raining back down onto the galaxy.

Subarcsecond radio observations of the dwarf starburst galaxy NGC 3077

“…This value is lower than the SFR given by extinction‐free tracers of the SFR such as the millimetre continuum or the far‐infrared (FIR). In fact, the SFR given by observations at 2.6 mm by Meier et al (2001) gives a SFR of 0.3 in agreement with FIR measurements from Thronson, Wilton & Ksir (1991).…”

“…The SNR has a noticeable asymmetry that could be due to interaction with the surrounding media. In fact, a giant molecular cloud (GMC) with a mass of ∼10 7 M ⊙ has been detected in CO (Meier et al 2001). This GMC has a projected size of 79 × 62 parsec 2 (5.3 × 4.1 arcsec 2 ) and the centroid of the emission is localized just 1.1 arcsec from the SNR in the north‐east direction 1 .…”

“…The International Ultraviolet Explorer ( IUE ) ultraviolet (UV) spectra revealed the presence of massive stars no older than 7 × 10 7 yr (Benacchio & Galletta 1981). The peak of the Pα nebula – a tracer of young star formation regions – (Böker et al 1999; Meier, Turner & Beck 2001; see Fig. 1) is located between two CO complexes detected by the Owens Valley Radio Observatory (Walter et al 2002).…”

Extended Star Formation and Molecular Gas in the Tidal Arms near NGC 3077

“…As these numbers (virial mass compared to mass derived using a Galactic conversion factor) are in agreement within the errors, this implies that the CO-to-H 2 conversion factor in the tidal arm appears to be similar to the Galactic value. We note that a Galactic conversion factor was also found to hold for the centre of NGC 3077 (Meier et al 2001. We thus derive a total molecular gas mass recovered by the OVRO observations of 2.4×10 6 M ⊙ (using a Galactic conversion factor for all regions, Tab.…”

Stars, Star Clusters, and Dust in NGC 3077

“…The latter result is perhaps not surprising as previous studies have found that the SFR in NGC 3077 is high, although there is significant scatter among the estimates. Thronson et al (1991) Meier et al (2001) estimate that the SFR is 0.4 M yr À1 from the 2.6 mm continuum flux, while Ott et al (2003) estimate that the SFR is 0.6 M yr À1 based on the energy needed to create super gas shells. As noted by Ott et al (2003), the high SFR inferred in their study may suggest that the SFR has dropped recently.…”