The VIMOS Ultra Deep Survey: Lyα emission and stellar populations of star-forming galaxies at 2 < z < 2.5

The aim of this paper is to investigate spectral and photometric properties of 854 faint (i(AB) less than or similar to 25 mag) star-forming galaxies (SFGs) at 2 \textless z \textless 2.5 using the VIMOS Ultra-Deep Survey (VUDS) spectroscopic data and deep multi-wavelength photometric data in three extensively studied extragalactic fields (ECDFS, VVDS, COSMOS). These SFGs were targeted for spectroscopy as a result of their photometric redshifts. The VUDS spectra are used to measure the UV spectral slopes (beta) as well as Ly alpha equivalent widths (EW). On average, the spectroscopically measured beta (-1.36 +/- 0.02), is comparable to the photometrically measured beta (-1.32 +/- 0.02), and has smaller measurement uncertainties. The positive correlation of beta with the spectral energy distribution (SED)-based measurement of dust extinction E-s(B-V) emphasizes the importance of beta as an alternative dust indicator at high redshifts. To make a proper comparison, we divide these SFGs into three subgroups based on their rest-frame Ly alpha EW: SFGs with no Ly alpha emission (SFGN; EW \textless= 0 angstrom), SFGs with Ly alpha emission (SFG(L); EW \textgreater 0 angstrom), and Ly alpha emitters (LAEs; EW \textgreater= 20 angstrom). The fraction of LAEs at these redshifts is beta 10%, which is consistent with previous observations. We compared best-fit SED-estimated stellar parameters of the SFG(N), SFG(L) and LAE samples. For the luminosities probed here (similar to L*), we find that galaxies with and without Ly alpha in emission have small but significant differences in their SED-based properties. We find that LAEs have less dust, and lower star-formation rates (SFR) compared to non-LAEs. We also find that LAEs are less massive compared to non-LAEs, though the difference is smaller and less significant compared to the SFR and E-s(B-V). When we divide the LAEs according to their Spitzer/IRAC 3.6 mu m fluxes, we find that the fraction of IRAC-detected (m(3.6) less than or similar to 25 mag) LAEs is much higher than the fraction of IRAC-detected narrow band (NB)-selected LAEs at z similar or equal to 2-3. This could imply that UV-selected LAEs host a more evolved stellar population, which represents a later stage of galaxy evolution, compared to NB-selected LAEs.