1999A&A...342..665V -
Astronomy and Astrophysics, volume 342, 665-670 (1999/2-3)
Discovery of distant high luminosity infrared galaxies.
VAN DER WERF P.P., CLEMENTS D.L., SHAVER P.A. and HAWKINS M.R.S.
Abstract (from CDS):
We have developed a method for selecting the most luminous galaxies detected by IRAS based on their extreme values of R, the ratio of 60µm and B-band luminosity. These objects have optical counterparts that are close to or below the limits of Schmidt surveys. We have tested our method on a 1079deg2 region of sky, where we have selected a sample of IRAS sources with 60µm flux densities greater than 0.2Jy, corresponding to a redshift limit z∼1 for objects with far-IR luminosities of 1013L☉. Optical identifications for these were obtained from the UK Schmidt Telescope plates, using the likelihood ratio method. Optical spectroscopy has been carried out to reliably identify and measure the redshifts of six objects with very faint optical counterparts, which are the only objects with R>100 in the sample. One object is a hyperluminous infrared galaxy (HyLIG) at z=0.834. Of the remaining, fainter objects, five are ultraluminous infrared galaxies (ULIGs) with a mean redshift of 0.45, higher than the highest known redshift of any non-hyperluminous ULIG prior to this study. High excitation lines reveal the presence of an active nucleus in the HyLIG, just as in the other known infrared-selected HyLIGs. In contrast, no high excitation lines are found in the non-hyperluminous ULIGs. We discuss the implications of our results for the number density of HyLIGs at z<1 and for the evolution of the infrared galaxy population out to this redshift, and show that substantial evolution is indicated. Our selection method is robust against the presence of gravitational lensing if the optical and infrared magnification factors are similar, and we suggest a way of using it to select candidate gravitationally lensed infrared galaxies.
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Journal keyword(s):
infrared: galaxies - galaxies: starburst - galaxies: evolution - galaxies: distances and redshifts
Simbad objects:
9
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