Astron. Astrophys. 336, 815-822 (1998)

Cosmologically distant OH megamasers: a test of the galaxy merging rate at Z 2 and a contaminant of blind HI surveys in the 21cm line

F.H. Briggs

Kapteyn Astronomical Institute, P.O. Box 800, 9700 AV Groningen, The Netherlands

Received 30 September 1997 / Accepted 20 May 1998

Abstract

Bright OH megamaser galaxies, radiating 1667/1665 MHz lines, could be detected at redshifts from to 3 in moderate integration times with existing radio telescopes. The superluminous FIR galaxies that host the megamasers are relatively rare at , but they may have been more common at high redshift, if the galaxy merger rate increases steeply with redshift. Therefore, blind radio spectroscopic surveys at frequencies of 400 to 1000 Mhz can form an independent test of the galaxy merger rate as a function of time over the redshift interval 4 to 0.7.

The redshift range to will be difficult to survey for OH masers, since spectroscopic survey signals will be confused with HI emission from normal galaxies at redshifts less than 0.3. In fact, the signals from OH masers are likely to dominate over 21cm line emission from normal galaxies at frequencies below 1200 MHz (i.e. large redshifts and ). Surveyors of nearby galaxies in the 21cm line may find that OH masers form a contaminant to deep, blind HI surveys for redshift velocities less than a few hundred kilometers per second. At frequencies just above 1420 MHz, sensitive sky surveys might detect OH masers, which could be mistaken for a population of "infalling, compact High Velocity Clouds" but would ultimately be traced to luminous FIR background galaxies at once optical and IR follow-up has been performed.

Key words: techniques: radar astronomy galaxies: active galaxies: evolution galaxies: interaction infrared: galaxies radio lines: galaxies

Send offprint requests to: fbriggs@astro.rug.nl

© European Southern Observatory (ESO) 1998

Online publication: July 27, 1998

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