The Pico dos Dias Survey Starburst Galaxies

Abstract

We discuss the nature of the galaxies found in the Pico dos Dias Survey (PDS) for young stellar objects. The PDS galaxies were selected from the IRAS Point Source catalog. They have flux density of moderate or high quality at 12, 25, and 60 μm and spectral indices in the ranges -3.00 < -1.9. As opposed to Seyfert galaxies, very few PDS starbursts are detected in X-rays. In the infrared, the starburst galaxies form a continuous sequence with normal galaxies. But they generally can be distinguished from normal galaxies by their spectral index alpha(60, 25) > -2.5. This color cutoff also marks a change in the dominant morphologies of the galaxies: the normal IRAS galaxies are preferentially late-type spirals (Sb and later), while the starbursts are more numerous among early-type spirals (earlier than Sbc). This preference of starbursts for early-type spirals is not new, but a trait of the massive starburst nucleus galaxies (Coziol et al.). As in other starburst nucleus galaxy samples, the PDS starbursts show no preference for barred galaxies. No difference is found between the starbursts detected in the FIR and those detected on the basis of UV excess. The PDS starburst galaxies represent the FIR luminous branch of the UV-bright starburst nucleus galaxies, with mean FIR luminosity log (L_IR/L_sun) = 10.3 +/- 0.5 and redshifts smaller than 0.1. They form a complete sample limited in flux in the FIR at 2 x 10^-10 ergs cm^-2 s^-1.