Ly$\alpha$ Emitters with Very Large Ly$\alpha$ Equivalent Widths, EW${}_0$(Ly$\alpha$) $\simeq 200-400$ Å, at $z\sim 2$

Abstract

We present physical properties of spectroscopically confirmed Ly$\alpha$ emitters (LAEs) with very large rest-frame Ly$\alpha$ equivalent widths EW${}_0$(Ly$\alpha$). Although the definition of large EW${}_0$(Ly$\alpha$) LAEs is usually difficult due to limited statistical and systematic uncertainties, we identify six LAEs selected from $\sim 3000$ LAEs at $z\sim 2$ with reliable measurements of EW${}_0$ (Ly$\alpha$) $\simeq 200-400$ Å given by careful continuum determinations with our deep photometric and spectroscopic data. These large EW${}_0$(Ly$\alpha$) LAEs do not have signatures of AGN, but notably small stellar masses of $M_{\ast }=10^{7-8}$ $M_{\odot }$ and high specific star-formation rates (star formation rate per unit galaxy stellar mass) of $\sim 100$ Gyr${}^{-1}$. These LAEs are characterized by the median values of $L(\mathrm{Ly}\alpha )=3.7\times 10^{42}$ erg s${}^{-1}$ and $M_{\mathrm{UV}}=-18.0$ as well as the blue UV continuum slope of $\beta =-2.5\pm 0.2$ and the low dust extinction $E(B-V{)}_{\ast }=0.02_{-0.02}^{+0.04}$, which indicate a high median Ly$\alpha$ escape fraction of $f_{\mathrm{esc}}^{\mathrm{Ly}\alpha }=0.68\pm 0.30$. This large $f_{\mathrm{esc}}^{\mathrm{Ly}\alpha }$ value is explained by the low {\sc Hi} column density in the ISM that is consistent with FWHM of the Ly$\alpha$ line, $\mathrm{FWHM}(\mathrm{Ly}\alpha )=212\pm 32$ km s${}^{-1}$, significantly narrower than those of small EW${}_0$(Ly$\alpha$) LAEs. Based on the stellar evolution models, our observational constraints of the large EW${}_0$ (Ly$\alpha$), the small $\beta$, and the rest-frame He{\sc ii} equivalent width imply that at least a half of our large EW${}_0$(Ly$\alpha$) LAEs would have young stellar ages of $\lesssim 20$ Myr and very low metallicities of $Z<0.02Z_{\odot }$ regardless of the star-formation history.

Accepted for publication in MNRAS; 23 pages with 16 figures

References in corpus (22)

• A Highly Consistent Framework for the Evolution of the Star-Forming "Main Sequence" from z~0-6
• 3D-HST WFC3-selected Photometric Catalogs in the Five CANDELS/3D-HST Fields: Photometry, Photometric Redshifts and Stellar Masses
• The Subaru/XMM-Newton Deep Survey (SXDS). IV. Evolution of Lya Emitters from z=3.1 to 5.7 in the 1 deg^2 Field: Luminosity Functions and AGN
• The Stellar, Gas and Dynamical Masses of Star-Forming Galaxies at z~2
• Subaru Deep Survey V. A Census of Lyman Break Galaxies at z=4 and 5 in the Subaru Deep Fields: Photometric Properties
• The Chandra COSMOS Survey, I: Overview and Point Source Catalog
• Ly-alpha Emission-Line Galaxies at z = 3.1 in the Extended Chandra Deep Field South
• Using Lyman-alpha to detect galaxies that leak Lyman continuum
• Lyman Alpha Emitting Galaxies as a Probe of Reionization
• Spectroscopic detections of CIII]1909 at z~6-7: A new probe of early star forming galaxies and cosmic reionisation
• The Ly-alpha Properties of Faint Galaxies at z2-3 with Systemic Redshifts and Velocity Dispersions from Keck-MOSFIRE
• Diffuse Lyman-alpha Halos around Galaxies at z=2.2-6.6: Implications for Galaxy Formation and Cosmic Reionization
• The VIMOS Ultra-Deep Survey (VUDS): fast increase of the fraction of strong Lyman alpha emitters from z=2 to z=6
• On the Detectability of Lyman-alpha Emission in Star-forming Galaxies: The Role of Dust
• Deficiency of large equivalent width Lyman-alpha emission in luminous Lyman break galaxies at z~5-6?
• The HETDEX Pilot Survey V: The Physical Origin of Lyman-alpha Emitters Probed by Near-infrared Spectroscopy
• Lyman alpha emission in high-redshift galaxies
• Ly-alpha excess in high redshift radio galaxies: a signature of star formation
• Directional Lya equivalent boosting I. Spherically symmetric distributions of clumps
• Ly-alpha emitting galaxies at redshift z~4.5 in the LALA Cetus field
• HST Emission Line Galaxies at z ~ 2: The Ly-alpha Escape Fraction
• First Infrared-based implications for the dust attenuation and star formation of typical Ly$\alpha$ emitters

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• Spectroscopic properties of luminous Lyman-α emitters at $z\approx 6-7$ and comparison to the Lyman-break population
• The MUSE Hubble Ultra Deep Field Survey X. Ly$\alpha$ Equivalent Widths at $2.9<z<6.6$
• The Stellar Mass, Star Formation Rate and Dark Matter Halo Properties of LAEs at $z\sim 2$
• Equivalent widths of Lyman $\alpha$ emitters in MUSE-Wide and MUSE-Deep
• The MUSE Hubble Ultra Deep Field Survey. XV. The mean rest-UV spectra of Ly-alpha emitters at z>3
• Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs). XIV. A Candidate Type-II Quasar at z=6.1292