Predictions and strategies for deep X-ray surveys V. K. Kulkarni: Frequency dependence of radio-source counts and spectral index distributions
Abstract
Summary. The extragalactic X-ray sources already identified are mainly active (Seyfert-type) galaxies or rich clusters. Using existing data, we discuss the possible outcome of the deeper surveys soon to be carried out with the next generation of X-ray telescopes. In particular, we use the quoted sensitivity of HEAO-B (for both point-like and resolved sources) to estimate how many sources of various kinds should be detectable in a given observing time. If the source population did not evolve with redshift, the X-ray source counts would be dominated by low-luminosity (1 0 -1 0 erg/s) clusters and Seyfert galaxies; a HEAO-B field, observed for l05s, would have only a 20 per cent chance of revealing a high-luminosity cluster with Z 2. There is a greater likelihood of discovering remote clusters if they have evolved through a high- luminosity phase; and many ( 10 per field) large-redshift point sources might be detected if the X-ray properties of quasars evolve at least as steeply as their optical properties. The existing evidence on small-scale isotropy excludes the possibility that rich clusters (however they have evolved) could contribute the whole X-ray background, and sets constraints on the contribution from quasars: if the background arises from discrete sources, they are mostly too faint to be detected individually by HEAO-B. General astrophysical arguments suggest that new categories of extragalactic X-ray sources - associated with (for instance) young galaxies or extended radio sources - may be discovered. We suggest how such objects might be recognized, emphasizing the importance of complementary programmes - e.g. deep radio surveys, objective prism plates, etc. - in an optimal observing strategy.
- Publication:
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Monthly Notices of the Royal Astronomical Society
- Pub Date:
- October 1978
- DOI:
- 10.1093/mnras/185.1.109
- Bibcode:
- 1978MNRAS.185..109F