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Astrophysics

Title: The Density of Lyman-alpha Emitters at Very High Redshift

Authors: Esther M. Hu (1), Lennox L. Cowie (1), Richard G. McMahon (2) ((1) IfA, Univ. of Hawaii, (2) IOA, Cambridge)
Abstract: We describe narrowband and spectroscopic searches for emission-line star forming galaxies in the redshift range 3 to 6 with the 10 m Keck II Telescope. These searches yield a substantial population of objects with only a single strong (equivalent width >> 100 Angstrom) emission line, lying in the 4000 - 10,000 Angstrom range. Spectra of the objects found in narrowband-selected samples at lambda ~5390 Angstroms and ~6741 Angstroms show that these very high equivalent width emission lines are generally redshifted Lyman alpha 1216 Angstrom at z~3.4 and 4.5. The density of these emitters above the 5 sigma detection limit of 1.5 e-17 ergs/cm^2/s is roughly 15,000 per square degree per unit redshift interval at both z~3.4 and 4.5. A complementary deeper (1 sigma \~1.0 e-18 ergs/cm^2/s) slit spectroscopic search covering a wide redshift range but a more limited spatial area (200 square arcminutes) shows such objects can be found over the redshift range 3 to 6, with the currently highest redshift detected being at z=5.64. The Lyman alpha flux distribution can be used to estimate a minimum star formation rate in the absence of reddening of roughly 0.01 solar masses/Mpc^3/year (H_0 = 65 km/s/Mpc and q_0 = 0.5). Corrections for reddening are likely to be no larger than a factor of two, since observed equivalent widths are close to the maximum values obtainable from ionization by a massive star population. Within the still significant uncertainties, the star formation rate from the Lyman alpha-selected sample is comparable to that of the color-break-selected samples at z~3, but may represent an increasing fraction of the total rates at higher redshifts. This higher-z population can be readily studied with large ground-based telescopes.
Comments: 7 pages, 5 encapsulated figures; aastex, emulateapj, psfig and lscape style files. Separate gif files for 2 gray-scale images also available at this http URL . Added discussion of foreground contaminants. Updated discussion of comparison with external surveys (Sec. 5 and Fig. 5). Note: continuum break strength limits (Fig. 3 caption) are correct here -- published ApJL text has a sign error
Subjects: Astrophysics (astro-ph)
Journal reference: Astrophys.J. 502 (1998) L99-L103
DOI: 10.1086/311506
Report number: IfA-98-37
Cite as: arXiv:astro-ph/9803011
  (or arXiv:astro-ph/9803011v2 for this version)

Submission history

From: Esther M. Hu [view email]
[v1] Tue, 3 Mar 1998 05:15:54 GMT (440kb)
[v2] Mon, 13 Jul 1998 05:34:33 GMT (446kb)