Astronomy and Astrophysics – Astrophysics
Scientific paper
Aug 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...288..103g&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 288, no. 1, p. 103-121
Astronomy and Astrophysics
Astrophysics
23
Distance, Galactic Evolution, Galaxies, Imagery, Line Of Sight, Lyman Alpha Radiation, Narrowband, Optical Thickness, Quasars, Red Shift, Ultraviolet Spectra, Color-Magnitude Diagram, Image Analysis, Image Processing, Spectral Energy Distribution, Spectrum Analysis, Stellar Spectrophotometry
Scientific paper
In this paper we describe deeper observations, both imaging and spectroscopy, of the most distant radio-quiet Ly-alpha galaxy known so far, at redshift of z = 3.428 (galaxy G2) and of other faint objects in the field around the QSO 0000 - 2619. Galaxy G2, which we discovered in the field around the damped absorber of the QSO with narrow-band imaging tuned to detect Ly-alpha emission at the redshift of the absorption system, is the best primaeval galaxy candidate identified so far. Here we report measurements of its restframe UV spectral energy distribution in the interval lambda lambda 1000, 1700 A, in particular the depression of the continuum due to the blanketing of the intervening Ly-alpha forest and the Ly-alpha emission line, and give better upper limits for the high-ionization emission lines, such as NV and CIV. We conclude that this object is very likely a primaeval galaxy observed during a major episode of star formation and in which dust does not extinguish the Ly-alpha emission. We also present Ly-alpha narrow-band imaging of the galaxy which causes the damped absorber in the spectrum of the QSO. No emission is detected, down to a 3 sigma upper limit of 1.2 x 10-17 erg/s/sq cm in an aperture of 2 arcsec in diameter. A corresponding upper limit to the rest-frame equivalent width is 6 A. Similar limits apply also to other 13 flat-spectrum z greater than 3 galaxy candidates identified in the same field by Steidel & Hamilton, if their redshift is such that their Ly-alpha emission falls within our narrow-band filter. However, from their rest-frame UV continuum luminosity, we estimate that the star formation rates for these galaxies are in the range 30 to 100 solar mass/yr. This would suggest that radioquiet primaeval galaxies, though in a star-forming phase, are not characterized by the intense Ly-alpha emission and large star formation rates (SFRs) typical of radio-galaxies. If these candidates are confirmed to be at similar redshifts than those of G2 and the galaxy responsible for the damped system of the QSO, then this association of galaxies would be the most distant cluster observed so far, with a total stellar mass of the order of 1013 solar mass (throughout this paper we assume H0 = 50 km/s/Mpc and Omega = 0, unless differently stated).
Giavalisco Mauro
Macchetto Ferdinando D.
Sparks William B.
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