A Deep Ly$\alpha$ Survey in ECDF-S and COSMOS: I. General Properties of Lyman-alpha Emitters at $z\sim 2$

Abstract

Ly$\alpha$ Emitters (LAEs) may represent an important galaxy population in the low mass regime. We present our deep narrowband imaging surveys in the COSMOS and ECDF-S fields and study the properties of LAEs at $z=2.23\pm 0.03$. The narrowband surveys conducted at Magellan II telescope allow us to obtain a sample of 452 LAEs reaching a $5\sigma$ limiting magnitude of $\sim 26$ mag. Our Ly$\alpha$ luminosity functions extend to $10^{41.8}$ erg s${}^{-1}$ with steep faint-end slope. Using multi-wavelength ancillary data, especially the deep Spitzer/IRAC 3.6$\mu$m and 4.5$\mu$m photometric data, we obtained reliable stellar mass estimates for 130 IRAC-detected LAEs, spanning a range of $8<\log (M_{\star }/M_{\odot })<11.5$. For the remaining IRAC-undetected LAEs, the median-stacked spectral energy distribution yields a stellar mass of $\log (M_{\star }/M_{\odot })=7.97_{-0.07}^{+0.05}$ and the rest-frame ultraviolet emission indicates a median star formation rate of $\log (SFR/M_{\odot }$ yr${}^{-1})=-0.14\pm 0.35$. There are six LAEs detected by the Spitzer/MIPS 24$\mu$m or even Herschel far-infrared observations. Taking into account the six MIR/FIR detected LAEs, our LAEs cover a wide range in the star formation rate ($1<\mathrm{SFR}<2000$ M${}_{\odot }$ yr${}^{-1}$). Although LAEs as a population are diverse in their stellar properties, they are mostly low-mass star-forming galaxies and follow the star formation main sequence relations or their extrapolations to the low-mass end, implying a normal star-forming nature of LAEs. The clustering analysis indicates that our LAEs reside in dark matter halos with $<\log ({\mathrm{M}}_{\mathrm{h}}/{\mathrm{M}}_{\odot })>=10.8_{-1.1}^{+0.56}$, suggesting that they are progenitors of local Large Magellanic Cloud-like galaxies.

37 pages, 15 figures, accepted for publication in ApJ