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Register a new userA New Einstein Cross: A Highly Magnified, Intrinsically Faint Lyman-Alpha Emitter at z=2.7
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Authors
Adam S. Bolton
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We report the discovery of a new Einstein cross at redshift z_S = 2.701 based on Lyman-alpha emission in a cruciform configuration around an SDSS luminous red galaxy (z_L = 0.331). The system was targeted as a possible lens based on an anomalous emission line in the SDSS spectrum. Imaging and spectroscopy from the W. M. Keck Observatory confirm the lensing nature of this system. This is one of the widest-separation galaxy-scale lenses known, with an Einstein radius of ~1.84 arcsec. We present simple gravitational lens models for the system and compute the intrinsic properties of the lensed galaxy. The total mass of the lensing galaxy within the 8.8 +/- 0.1 kpc enclosed by the lensed images is (5.2 +/- 0.1) x 10^11 M_sun. The lensed galaxy is a low mass galaxy (0.2 L*) with a high equivalent-width Lyman-alpha line (EW_Lya_rest = 46 +/- 5 Angstroms). Follow-up studies of this lens system can probe the mass structure of the lensing galaxy, and can provide a unique view of an intrinsically faint, high-redshift, star-forming galaxy at high signal-to-noise ratio.
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We present a flux-limited sample of $zsim0.3$ Ly$alpha$ emitters (LAEs) from Galaxy Evolution Explorer (GALEX) grism spectroscopic data. The published GALEX $zsim0.3$ LAE sample is pre-selected from continuum-bright objects and thus is biased against high equivalent width (EW) LAEs. We remove this continuum pre-selection and compute the EW distribution and the luminosity function of the Ly$alpha$ emission line directly from our sample. We examine the evolution of these quantities from $zsim0.3$ to $2.2$ and find that the EW distribution shows little evidence for evolution over this redshift range. As shown by previous studies, the Ly$alpha$ luminosity density from star-forming galaxies declines rapidly with declining redshift. However, we find that the decline in Ly$alpha$ luminosity density from $z=2.2$ to $z=0.3$ may simply mirror the decline seen in the H$alpha$ luminosity density from $z=2.2$ to $z=0.4$, implying little change in the volumetric Ly$alpha$ escape fraction. Finally, we show that the observed Ly$alpha$ luminosity density from AGNs is comparable to the observed Ly$alpha$ luminosity density from star-forming galaxies at $z=0.3$. We suggest that this significant contribution from AGNs to the total observed Ly$alpha$ luminosity density persists out to $zsim2.2$.
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