The Origin of the Observed Lyman alpha EW Distribution of Dwarf Galaxies at z~2

C. Snapp-Kolas, B. Siana, T. Gburek, A. Alavi, N. Emami, J. Richard, D. P. Stark, C. Scarlata

Submitted on 31 October 2022


We present a rest-UV selected sample of 32 lensed galaxies at z2 observed with joint Keck/LRIS rest-UV and Keck/MOSFIRE rest-optical spectra behind the clusters Abell 1689, MACS J0717, and MACS J1149. The sample pushes towards the faintest UV luminosities observed (19MUV17) at this redshift. The fraction of dwarf galaxies identified as Lyα emitters (EW20 A) is XLAE=2510+15%. We use the Balmer lines and UV continuum to estimate the intrinsic EW allowing us to distinguish the effects of the ionizing spectra and Lyα escape fraction on the observed EW distribution. Fainter galaxies (MUV>19) show larger intrinsic EWs and escape fractions than brighter galaxies. Only galaxies with intrinsic EWs greater than 40 A have escape fractions larger than 0.05. We find an anti-correlation between the escape fraction and AV as well as UV spectral slope. The volumetric escape fraction of our sample is fescLyα=4.591.4+2.0% in agreement with measurements found elsewhere in the literature. About half of the total integrated Lyα luminosity density comes from galaxies with EWobs>20 A.


Comment: 11 pages, 13 figures

Subject: Astrophysics - Astrophysics of Galaxies


Three example spectra from our sample of galaxies. The red line is the fit for each spectrum. The fitting method is described in section \ref{Methods}. Top: An example of an ``emission" spectrum where we have Ly$\alpha$ in emission only. Middle: An example of an ``absorption" spectrum. Bottom: An example of a ``combination" spectrum where we see absorption and emission around Ly$\alpha$