Optical selection effects that bias quasar evolution studies

Journal Article · Fri Nov 15 04:00:00 EST 1985 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/163630· OSTI ID:6182584

Wampler, E J; Ponz, D

This paper gives a study of systematic biases that are redshift-dependent and could influence not only the optical discovery of quasars but also the evolution laws derived from counts of quasars in ''complete'' surveys. A numerical model of the optical biases suggests that the excess of quasars found at z roughly-equal 2.5 when compared to the local density is largely a result of photometric errors and the unrecognized contribution of strong UV emission lines to the blue magnitude of high-redshift quasars. An observational reexamination of the quasars brighter than M/sub B/ = -24 in the Palomar Bright Quasar Survey (BQS) shows that for the brightest quasars in the survey, the data are consistent with no evolution. A comparison of BQS quasars with the brightest quasars from the CTIO Schmidt Telescope Survey (Osmer and Smith 1980) shows that the brightest CTIO survey quasars have much stronger C IV lambda1548 lines than the brightest BQS quasars. If q/sub 0/ is taken to be near zero, the density of bright quasars in comoving Friedmann cosmology coordinates is about 15 times higher for the CTIO survey quasars (mean z roughly-equal 2.8) than for the BQS quasars (mean z roughly-equal 1.8). In this case, spectral evolution is required, since the high-redshift CTIO quasars have greater C IV lambda1548 equivalent widths than the lower redshift BQS quasars of similar luminosity. Alternatively, if q3) is taken to be near unity, the brightest CTIO survey quasars would all be fainter than the brightest BQS objects. The strong emission lines seen in the CTIO survey quasars could be understood as a consequence of the general correlation between absolute quasar luminosity and C IV lambda1548 equivalent width.

• Research Organization: Board of Studies in Astronomy and Astrophysics, University of California, Santa Cruz
• OSTI ID: 6182584
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 298:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640103* -- Astrophysics & Cosmology-- Quasi-Stellar
Radio
& X-Ray Sources-- (-1987)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
CARBON IONS
CHARGED PARTICLES
COSMIC RADIO SOURCES
COSMOLOGY
DATA ANALYSIS
DISTRIBUTION
GALACTIC EVOLUTION
IONS
LUMINOSITY
OPTICAL PROPERTIES
PHOTOMETRY
PHYSICAL PROPERTIES
QUASARS
RED SHIFT
SPATIAL DISTRIBUTION