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The Astrophysical Journal Volume 660 Number 1 Create an alert RSS this journal

C. C. Dow-Hygelund et al. 2007 ApJ 660 47 doi:10.1086/512025

Spectroscopy of z ~ 6 i-Dropout Galaxies: Frequency of Lyα Emission and the Sizes of Lyα-emitting Galaxies* ** ***

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C. C. Dow-Hygelund1, B. P. Holden2, R. J. Bouwens2, G. D. Illingworth2, A. van der Wel3, M. Franx4, P. G. van Dokkum5, H. Ford3, P. Rosati6, D. Magee2 and A. Zirm3

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Abstract References Cited By

We report on deep spectroscopy, using LRIS on Keck I and FORS2 on the VLT, of a sample of 22 candidate z ~ 6 Lyman break galaxies (LBGs) selected by the i775 - z850 > 1.3 dropout criterion. Redshifts could be measured for eight objects. These redshifts are all in the range z = 5.5-6.1, confirming the efficiency of the i775 - z850 color selection technique. Six of the confirmed galaxies show Lyα emission. Assuming that the 14 objects without redshifts are z ~ 6 LBGs that lack detectable Lyα emission lines, we infer that the fraction of Lyα-emitting LBGs with Lyα equivalent widths greater than 20 Å among z ~ 6 LBGs is ≈30%, similar to that found at z ~ 3. Every Lyα-emitting object in our sample is compact, with half-light radii rhl ≤ 0.14''. Furthermore, all the Lyα-emitting objects in our sample are more compact than average relative to the observed size-magnitude relation of a large i-dropout sample (332 candidate z ~ 6 objects). We can reject the hypothesis that the Lyα-emitting population is a subset of the rest of the z ~ 6 LBG population at >97% confidence. We speculate that the small sizes of the Lyα-emitting LBGs are due to these objects being less massive than other LBGs at z ~ 6.


Footnote
***  Based on observations collected at the European Southern Observatory, Paranal, Chile (LP166.A-0701 and 169.A-045).
Footnote
*  Based on observations taken with the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and NASA.
Footnote
**  Based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs 7817, 9270, 9301, 9583, and 9803.
Subject headings

early universe; galaxies: evolution; galaxies: formation; galaxies: high-redshift; galaxies: starburst


Dates

Issue 1 (2007 May 1)

Received 2006 February 25, accepted for publication 2006 December 14



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