Ly-alpha emitters: blue dwarfs or supermassive ULIRGs? Evidence for a transition with redshift

TL;DR

This study investigates the evolution of Ly-alpha emitting galaxies, revealing a transition from blue dwarf-like to ULIRG-like properties around redshift 2.5, challenging traditional views on Ly-alpha emission and dust obscuration.

Contribution

It provides evidence for a redshift-dependent increase in ULIRG fraction among Ly-alpha emitters, highlighting a possible rapid evolutionary transition.

Findings

ULIRG fraction among Ly-alpha emitters increases at lower redshifts.

High infrared luminosities in low-redshift Ly-alpha galaxies suggest a shift in galaxy properties.

Ly-alpha escape fractions vary significantly with redshift and infrared brightness.

Abstract

The traditional view that Ly-alpha emission and dust should be mutually exclusive has been questioned more and more often; most notably, the observations of Ly-alpha emission from ULIRGs seem to counter this view. In this paper we seek to address the reverse question. How large a fraction of Ly-alpha selected galaxies are ULIRGs? Using two samples of 24/25 Ly-alpha 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-alpha 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-alpha 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 M_sun/yr, and the dust attenuation derived are in the range 0.0 < A_V < 3.5.