Ly emitters: blue dwarfs or supermassive ULIRGs? Evidence for a transition with redshiftK. K. Nilsson1 and P. Møller2
1 ST-ECF, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany
2 European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany
Received 5 October 2009 / Accepted 16 November 2009
The traditional view that Ly emission and dust should be mutually exclusive has been questioned more and more often; most notably, the observations of Ly emission from ULIRGs seem to counter this view. In this paper we seek to address the reverse question. How large a fraction of Ly selected galaxies are ULIRGs? Using two samples of 24/25 Ly emitting galaxies at z = 0.3/2.3, we perform this test, including results at z = 3.1, and find that, whereas the ULIRG fraction at z = 3.1 is very small, it systematically increases towards lower redshifts. There is a hint that this evolution may be quite sudden and that it happens around a redshift of z ~ 2.5. After measuring the infrared luminosities of the Ly emitters, we find that they are in the normal to ULIRG range in the lower redshift sample, while the higher redshift galaxies all have luminosities in the ULIRG category. The Ly escape fractions for these infrared bright galaxies are in the range 1-100% in the z = 0.3 galaxies, but are very low in the z = 2.3 galaxies, 0.4% on average. The unobscured star formation rates are very high, ranging from 500 to more than 5000 yr-1, and the dust attenuation derived are in the range 0.0 < AV < 3.5.
Key words: cosmology: observations -- galaxies: high- redshift
© ESO 2009