Near‐Infrared and Star‐forming Properties of Local Luminous Infrared Galaxies

We use HST NICMOS continuum and Pa-alpha observations to study thenear-infrared and star-formation properties of a representative sample of 30local (d ~ 35-75Mpc) luminous infrared galaxies (LIRGs, infrared 8-1000umluminosities of L_IR=11-11.9[Lsun]). The data provide spatial resolutions of25-50pc and cover the central ~3.3-7.1kpc regions of these galaxies. About halfof the LIRGs show compact (~1-2kpc) Pa-alpha emission with a high surfacebrightness in the form of nuclear emission, rings, and mini-spirals. The restof the sample show Pa-alpha emission along the disk and the spiral armsextending over scales of 3-7kpc and larger. About half of the sample containsHII regions with H-alpha luminosities significantly higher than those observedin normal galaxies. There is a linear empirical relationship between the mid-IR24um and hydrogen recombination (extinction-corrected Pa-alpha) luminosity forthese LIRGs, and the HII regions in the central part of M51. This relationholds over more than four decades in luminosity suggesting that the mid-IRemission is a good tracer of the star formation rate (SFR). Analogous to thewidely used relation between the SFR and total IR luminosity of Kennicutt(1998), we derive an empirical calibration of the SFR in terms of themonochromatic 24um luminosity that can be used for luminous, dusty galaxies.Comment: Accepted for publication in ApJ. Contact first author for high qualitity version of figure