Dusty Lyman-alpha emitters as seen by Spitzer

Abstract

We present an analysis of Spitzer data for a large sample of low-redshift Lyα-emitting galaxies discovered by GALEX. Using the Donley et al. (2012) AGN selection region in color-color space IRAC photometry, we determined from our sample that the LAEs at z~0.3 have an AGN fraction of ~24%. The total bolometric L_IR for the sample was found using χ<super>2</super> fitting along with template SEDs, and we found that the galaxies ranged from 10<super>8.05</super>L_Sun to 10<super>11.57</super>L_Sun, with a median L_IR value of 10<super>10.39</super>L_Sun. L_IR and L_Lyα for our sample do not appear to be correlated, unlike the high-LI_IRLyα-emitting objects examined by Colbert et al. (2006) and Nilsson & Mller (2009), which may mean that their samples of LAEs, with L_IR/L_Sun > 10<super>12</super>, are qualitatively different from our own. The SFR values for the sample have a median value of 5.63 M_Sun yr<super>-1</super>, in agreement with the value of 6M_Sun yr<super>-1</super> found in Cowie et al. (2011). Also, we find that most of the sample has a contribution of SFR_IR to SFR_Total that is greater than 60%, indicating that these LAEs have a significant amount of dust extinction, and SFR_UV alone is also not a good indicator for SFR_Total. From comparing dust extinction to UV continuum slope , it was found that LAEs do not follow the same curves predicted for SF or SB galaxies, indicating that LAEs at low redshift may experience more variation in their native UV spectra, making it impossible to recover their dust attenuation from their UV slope. This would suggest that LAEs may consist of stellar populations of varying ages, leading to more intrinsic variation in their UV slope.