Letter to the Editor

Lyα emitters: blue dwarfs or supermassive ULIRGs? Evidence for a transition with redshift^*

¹ ST-ECF, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany e-mail: knilsson@eso.org
² European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany

Received: 5 October 2009
Accepted: 16 November 2009

Abstract

The traditional view that Lyα emission and dust should be mutually exclusive has been questioned more and more often; most notably, the observations of Lyα emission from ULIRGs seem to counter this view. In this paper we seek to address the reverse question. How large a fraction of Lyα selected galaxies are ULIRGs? Using two samples of 24/25 Lyα emitting galaxies at z = 0.3/2.3, we perform this test, including results at , and find that, whereas the ULIRG fraction at 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 Lyα 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 Lyα escape fractions for these infrared bright galaxies are in the range % in the galaxies, but are very low in the 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 .