X-ray Constraints on the Lyman-Alpha Escape Fraction

Abstract

We have coadded X-ray flux of all known Lyman Alpha Emitters (LAEs) in the 4 Msec Chandra Deep Field South (CDF-S) region, to place sensitive upper limits on the average unobscured star-formation rate (SFR_X) in these galaxies. A very small fraction of Lyman-Alpha galaxies in the field are individually detected in the X-rays, implying a low fraction of AGN activity. After excluding the few X-ray detected LAEs, we stack the undetected LAEs located in the 4 Ms CDF-S data and 250 ks Extended CDF-S (ECDFS) data, and compute a 1-σupper limit on SFR_X < 14, 28, 28, 140, 440, 880 M$_{\sun}$ yr${}^{-1}$ for LAEs located at z = 2.1, 3.1, 3.2, 4.5, 5.7 and 6.5, respectively. The upper limit of SFR_X in LAEs can be then be compared to SFR${}_{Ly\alpha }$ derived from Lyman-Alpha line and thus can constrain on the Lyman-Alpha escape fraction ($f_{Ly\alpha }^{Esc}$). We derive a lower limit on f(Lyman-Alpha Escape) > 14% (84 % confidence level, 1-σlower limit) for LAEs at redshift z ~ 2.1 and z ~ 3.1-3.2. At z > 4, the current LAE samples are not of sufficient size to constrain SFR_X well. By averaging all the LAEs at z> 2, the X-ray non-detection constrains f(Lyman-Alpha Escape) > 17% (84 % confidence level, 1-σlower limit), and rejects f(Lyman-Alpha Escape) < 5.7% at the 99.87% confidence level from 2.1 < z < 6.5.

11 pages, 3 tables, 3 figures, ApJ accepted

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Cited by in corpus (15)

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• Green Pea Galaxies Reveal Secrets of Ly$\alpha$ Escape
• Evidence for Elevated X-ray Emission in Local Lyman Break Galaxy Analogs
• Lya escape from z~0.03 star-forming galaxies: the dominant role of outflows
• Formation of Metal-Poor Globular Clusters in Lyman alpha Emitting Galaxies in the Early Universe
• Evidence for Widespread AGN Activity among Massive Quiescent Galaxies at z ~ 2
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• Constraining the Lyman Alpha Escape Fraction with Far-Infrared Observations of Lyman Alpha Emitters
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• Hubble Space Telescope Observations of Accretion-Induced Star Formation in the Tadpole Galaxy Kiso 5639
• Ultraviolet and Optical Emission-line Outflows in the Heavily Obscured Quasar SDSS J000610.67+121501.2: At the Scale of the Dusty Torus and Beyond
• Extinction Correction Significantly Influences the Estimate of Ly$\alpha$ Escape Fraction
• A z ~ 5.7 Lyα Emission Line with an Ultra Broad Red Wing