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Register a new userStar-formation in the central kpc of the starburst/LINER galaxy NGC1614
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A high angular resolution, multi-wavelength study of the LINER galaxy NGC1614 has been carried out. OVRO CO 1-0 observations are presented together with extensive multi-frequency radio continuum and HI absorption observations with the VLA and MERLIN. Toward the center of NGC1614, we have detected a ring of radio continuum emission with a radius of 300 pc. This ring is coincident with previous radio and Paschen-alpha observations. The dynamical mass of the ring based on HI absorption is 3.1 x 10E9 Msun. The peak of the integrated CO 1-0 emission is shifted by 1 to the north-west of the ring center and a significant fraction of the CO emission is associated with a crossing dust lane. An upper limit to the molecular gas mass in the ring region is 1.7 x 10E9 Msun. Inside the ring, there is a north to south elongated 1.4GHz radio continuum feature with a nuclear peak. This peak is also seen in the 5GHz radio continuum and in the CO. We suggest that the R=300 pc star forming ring represents the radius of a dynamical resonance - as an alternative to the scenario that the starburst is propagating outwards from the center into a molecular ring. The ring-like appearance probably part of a spiral structure. Substantial amounts of molecular gas have passed the radius of the ring and reached the nuclear region. The nuclear peak seen in 5GHz radio continuum and CO is likely related to previous star formation, where all molecular gas was not consumed. The LINER-like optical spectrum observed in NGC1614 may be due to nuclear starburst activity, and not to an Active Galactic Nucleus (AGN). Although the presence of an AGN cannot be excluded.
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We report on the star formation histories and extinction in the central kpc region of a sample of starburst galaxies that have similar far infrared (FIR), 10 micron and K-band luminosities as those of the archetype starburst M82. Our study is based on new optical spectra and previously published K-band photometric data, both sampling the same area around the nucleus. Model starburst spectra were synthesized as a combination of stellar populations of distinct ages formed over the Hubble time, and were fitted to the observed optical spectra and K-band flux. The model is able to reproduce simultaneously the equivalent widths of emission and absorption lines, the continuum fluxes between 3500-7000 Ang, the K-band and the FIR flux. We require a minimum of 3 populations -- (1) a young population of age < 8 Myr, with its corresponding nebular emission, (2) an intermediate-age population (age < 500 Myr), and (3) an old population that forms part of the underlying disk or/and bulge population. The contribution of the old population to the K-band luminosity depends on the birthrate parameter and remains above 60% in the majority of the sample galaxies. Even in the blue band, the intermediate age and old populations contribute more than 40% of the total flux in all the cases. A relatively high contribution from the old stars to the K-band nuclear flux is also apparent from the strength of the 4000 Ang break and the CaII K line. The extinction of the old population is found to be around half of that of the young population. The contribution to the continuum from the relatively old stars has the effect of diluting the emission equivalent widths below the values expected for young bursts. The mean dilution factors are found to be 5 and 3 for the Halpha and Hbeta lines respectively.
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