Discovery of low-redshift X-ray selected quasars: New clues to the QSO phenomenon

Journal Article · Tue Jul 15 04:00:00 EDT 1980 · Astrophys. J., Lett. Ed.; (United States)

DOI:https://doi.org/10.1086/183288· OSTI ID:7054747

Grindlay, J E; Steiner, J E; Forman, W R; Canizares, C R; McClintock, J E

Using the CTIO 4 m and 1.5 m telescopes to identify serendipitous X-ray sources discovered by the Einstein Observatory, we have identified as quasars all six sources in four high-latitude IPC fields (approx.4 deg/sup 2/). These X-ray selected QSOs have low redshifts (zapprox.0.08--0.23 for five objects and z=0.73 for the sixth) and relatively faint optical magnitudes (approx. =18) and are radio quiet. Our sample selected with intermediate (approx.10/sup 4/ s) X-ray exposures appears similar in space density, colors, and magnitude versus redshift relation to a complete optically selected sample at the same mean magnitude. Spectrophotometry of the six objects and comparisons with other X-ray QSOs and Seyfert 1 galaxies reveals a strong correlation between X-ray luminosity and both continuum and broad-line (e.g., H..beta..) emission luminosities for these radio quiet quasars and Seyfert 1 galaxies. The ratio of H..beta../(O III) emission line fluxes is found to correlate well with L/sub x/ and may be used as a luminosity indicator. No such emission line versus L/sub x/ correlations are found for radio-bright QSOs, however. The five low z objects have very similar values of L/sub x//L/sub opt/approx.0.4, although L/sub x/ varies by a factor of approx.10. We conclude that photoionization by a continuum extending to X-ray energies is the dominant excitation in radio-quiet QSOs and that X-ray selected QSO samples will enable new studies of QSO evolution and the diffuse X-ray background.

• Research Organization: Harvard-Smithsonian Center for Astrophysics
• OSTI ID: 7054747
• Journal Information: Astrophys. J., Lett. Ed.; (United States), Journal Name: Astrophys. J., Lett. Ed.; (United States) Vol. 239:2; ISSN AJLEA
• 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
COSMIC RADIO SOURCES
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
EMISSION SPECTRA
GALAXIES
IONIZATION
LUMINOSITY
OPTICAL PROPERTIES
PHOTOIONIZATION
PHYSICAL PROPERTIES
QUASARS
RED SHIFT
SEYFERT GALAXIES
SPECTRA
SPECTROPHOTOMETRY
X-RAY SPECTRA