FIRST VIEWS OF A NEARBY LIRG: STAR FORMATION AND MOLECULAR GAS IN IRAS 04296+2923

We present a first look at the local luminous infrared galaxy (LIRG) IRAS 04296+2923. This barred spiral galaxy, overlooked because of its location behind the Taurus molecular cloud, is among the half dozen closest (D = 29 Mpc) LIRGs. More IR-luminous than either M82 or the Antennae, it may be the best local example of a nuclear starburst caused by bar-mediated secular evolution. We present Palomar J and Pa beta images, Very Large Array continuum maps from lambda = 20-1.3 cm, a subarcsecond Keck Long Wavelength Spectrometer image at 11.7 mu m and Owens Valley Millimeter Array CO(1-0), (13)CO(1-0), and 2.7 mm continuum images. The J-band image reveals a symmetric barred spiral galaxy. Two bright, compact mid-infrared and radio sources in the nucleus mark a starburst that is energetically equivalent to similar to 10(5) O7 stars, separated by <= 50 pc. This is probably a pair of young super star clusters, with estimated stellar masses of similar to 10(7)M(circle dot) each. The nuclear starburst is forming stars at the rate of similar to 12 +/- 6M(circle dot)yr(-1), or about half of the total star formation rate for the galaxy of similar to 25 +/- 10M(circle dot)yr(-1). IRAS 04296+2923 is very bright in CO, and among the most gas-rich galaxies in the local universe. The (12)CO luminosity of the inner half kpc is equivalent to that of the entire Milky Way. While the most intense CO emission is extended over a 15 '' (2 kpc) diameter region, the nuclear starburst is confined to within 1 ''-2 '' (150-250 pc) of the dynamical center. Based on masses obtained with (13)CO, we find that the CO conversion factor in the nucleus is lower than the Galactic value, X(CO)(Gal) by a factor of three to four, typical of gas-rich spiral nuclei. The nuclear star formation efficiency (SFE) is (nuc)M(gas)/SFR(nuc) = 2.7 x 10(-8)yr(-1), corresponding to a gas consumption timescale, tau(nuc)(SF) similar to 4 x 10(7) yr. The SFE is 10 times lower in the disk, with tau(disk)(SF) similar to 3.3 x 10(8) yr. The low absolute SFE in the disk implies that the molecular gas is not completely consumed before it drifts into the nucleus, and is capable of fueling a sustained nuclear starburst. IRAS 04296+2923 appears to be beginning a 100 Myr period as an LIRG, during which it will turn much of its 6 x 10(9) M(circle dot) of molecular gas into a nuclear cluster of stars.