71 research outputs found
The Frequency and Radio Properties of Broad Absorption Line Quasars
A sample of 67 Broad Absorption Line quasars (BALQSOs) from the Large Bright
Quasar Survey (LBQS) is used to estimate the observed and intrinsic fraction of
BAL quasars in optically--selected samples at intermediate (B_J \simeq 18.5)
magnitudes. The observed BALQSO fraction in the redshift range 1.5 < z < 3.0 is
15\pm3%. A well--determined, empirical, k--correction, to allow for the
differences in the spectral energy distributions of non--BALQSOs and BALQSOs
shortward of \simeq 2100A in the restframe, is applied to the sample. The
result is an estimate of the intrinsic fraction of BALQSOs, in the redshift
range 1.5 < z < 3.0, of 22+/-4%. This value is twice that commonly cited for
the occurrence of BALQSOs in optically--selected samples and the figure is in
reasonable agreement with that from a preliminary analysis of the SDSS Early
Data Release. The fraction of BALQSOs predicted to be present in an optical
survey with flux limits equivalent to that of the FIRST Bright Quasar Survey
(FBQS) is shown to be \simeq 20%. The BALQSO fractions derived from the FBQS
and the LBQS suggest that optically--bright BALQSOs are half as likely as
non-BALQSOs to be detectable as S_1.4GHz > 1mJy radio sources.Comment: Accepted for publication in AJ, April 2003 Issu
An Extraordinary Scattered Broad Emission Line in a Type 2 QSO
An infrared-selected, narrow-line QSO has been found to exhibit an
extraordinarily broad Halpha emission line in polarized light. Both the extreme
width (35,000 km/sec full-width at zero intensity) and 3,000 km/sec redshift of
the line centroid with respect to the systemic velocity suggest emission in a
deep gravitational potential. An extremely red polarized continuum and partial
scattering of the narrow lines at a position angle common to the broad-line
emission imply extensive obscuration, with few unimpeded lines of sight to the
nucleus.Comment: 4 pages, 1 figure, to appear in the Astrophysical Journal Letter
Emission-Line Properties of z > 4 Quasars
We present results of a program of high signal-to-noise spectroscopy for 44
QSOs at redshifts > 4 using the MMT and Keck observatories. The quasar spectra
cover 1100 -- 1700 A in the rest frame for sources spanning a luminosity range
of approximately 2 orders of magnitude. Comparisons between these data and
spectra of lower redshift quasars reveal a high degree of similarity, although
differences are present in the profiles and the strengths of some emission
features. An examination of the luminosity dependence of the emission lines
reveals evidence for a weak or absent Baldwin effect among z > 4 QSOs. We
compare measurements for objects in our sample with results from other high
redshift surveys characterized by different selection techniques. Distributions
of equivalent widths for these different ensembles are consistent with a common
parent population, suggesting that our sample is not strongly biased, or in any
case, subject to selection effects that are not significantly different from
other surveys, including the Sloan Digital Sky Survey. Based on this
comparison, we tentatively conclude that the trends identified here are
representative of high z QSOs. In particular, the data bolster indications of
supersolar metallicities in these luminous, high-z sources, which support
scenarios that assume substantial star formation at epochs preceding or
concurrent with the QSO phenomena.Comment: 26 pages (incl. 9 figures), AASTeX v5.0, to appear in The
Astrophysical Journa
Optical Spectropolarimetry of Quasi-Stellar Objects Discovered by the Two-Micron All Sky Survey
Highly polarized QSOs discovered in the Two-Micron All Sky Survey (2MASS)
have been observed to determine the source(s) of optical polarization in this
near-infrared color-selected sample. Broad emission lines are observed in the
polarized flux spectra of most objects, and the polarization of the lines is at
about the same level and position angle as the continuum. Generally, the
continuum is bluer and the broad-line Balmer decrement is smaller in polarized
light than for the spectrum of total flux. Narrow emission lines are much less
polarized than the broad lines and continuum for all polarized objects. These
properties favor scattering by material close to a partially obscured and
reddened active nucleus, but exterior to the regions producing the broad-line
emission, as the source of polarized flux in 2MASS QSOs. The largely
unpolarized narrow-line features require that the electrons or dust polarizing
the light be located at distances from the nucleus not much greater than the
extent of the narrow emission-line region. In addition to known
high-polarization objects, four 2MASS QSOs with AGN spectral types of 1.9 and 2
were observed to search for hidden broad emission-line regions. Broad lines
were detected in polarized light for two of these objects, and the polarizing
mechanism appears to be the same for these objects as for the highly polarized
QSOs in the sample that readily show broad emission lines in their spectra. The
observations also show that starlight from the host galaxy contributes a
significant amount of optical flux, especially for the narrow-line objects, and
support the suggestion that many 2MASS QSOs are measured to have low
polarization simply because of dilution of the polarized AGN light by the host
galaxy.Comment: 27 pages; 3 tables; 8 figures; Accepted for publication in The
Astrophysical Journal (Part 1
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