139 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
KECK HIRES Spectroscopy of APM 08279+5255
With an optical R-band magnitude of 15.2, the recently discovered z=3.911 BAL
quasar APM 08279+5255 is an exceptionally bright high redshift source. Its
brightness has allowed us to acquire a high signal-to-noise ratio (~100), high
resolution (~6 km/s) spectrum using the HIRES echelle spectrograph on the 10-m
Keck I telescope. Given the quality of the data, these observations provide an
unprecedented view of associated and intervening absorption systems. Here we
announce the availability of this spectrum to the general astronomical
community and present a brief analysis of some of its main features.Comment: 21 pages including 5 figures. Accepted for publication by PAS
The Metallicity of the Redshift 4.16 Quasar BR2248-1242
We estimate the metallicity in the broad emission-line region of the redshift
z=4.16 quasar, BR2248-1242, by comparing line ratios involving nitrogen to
theoretical predictions. BR2248-1242 has unusually narrow emission lines with
large equivalent widths, thus providing a rare opportunity to measure several
line-ratio abundance diagnostics. The combined diagnostics indicate a
metallicity of ~2 times solar. This result suggests that an episode of vigorous
star formation occurred near BR2248-1242 prior to the observed z=4.16 epoch.
The time available for this enrichment episode is only ~1.5 Gyr at z=4.16 (for
H_{0}=65 km s^-1 Mpc^-1, Omega_{m}=0.3 and Omega_Lambda ~< 1). This evidence
for high metallicities and rapid star formation is consistent with the expected
early-epoch evolution of dense galactic nuclei.Comment: 8 pages, 3 figures. Prepared in AAStex. Submitted to the
Astrophysical Journal Revised version: added 1 referenc
SBS 0335-052W - an Extremely Low Metallicity Dwarf Galaxy
We present Multiple Mirror Telescope (MMT) and Keck II telescope
spectrophotometry and 3.5m Calar Alto telescope R, I photometry of the western
component of the extremely low-metallicity blue compact galaxy SBS 0335-052.
The components, separated by 22 kpc, appear to be members of a unique,
physically connected system. It is shown that SBS 0335-052W consists of at
least three stellar clusters and has the same redshift as SBS 0335-052. The
oxygen abundance in its two brightest knots is extremely low, 12+log(O/H)=
7.22+/-0.03 and 7.13+/-0.08, respectively. These values are lower than in SBS
0335-052 and are nearly the same as those in I Zw 18. The (R-I) color profiles
are very blue in both galaxies due to the combined effects of ionized gas and a
young stellar population emission. We argue that SBS 0335-052W is likely to be
a nearby, young dwarf galaxy.Comment: 18 pages, 4 EPS figures, to appear in ApJ, 1 July 199
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
The FIRST Bright Quasar Survey. II. 60 Nights and 1200 Spectra Later
We have used the VLA FIRST survey and the APM catalog of the POSS-I plates as
the basis for constructing a new radio-selected sample of optically bright
quasars. This is the first radio-selected sample that is competitive in size
with current optically selected quasar surveys. Using only two basic criteria,
radio-optical positional coincidence and optical morphology, quasars and BL
Lacs can be identified with 60% selection efficiency; the efficiency increases
to 70% for objects fainter than magnitude 17. We show that a more sophisticated
selection scheme can predict with better than 85% reliability which candidates
will turn out to be quasars.
This paper presents the second installment of the FIRST Bright Quasar Survey
with a catalog of 636 quasars distributed over 2682 square degrees. The quasar
sample is characterized and all spectra are displayed. The FBQS detects both
radio-loud and radio-quiet quasars out to a redshift z>3. We find a large
population of objects of intermediate radio-loudness; there is no evidence in
our sample for a bimodal distribution of radio characteristics. The sample
includes ~29 broad absorption line quasars, both high and low ionization, and a
number of new objects with remarkable optical spectra.Comment: 41 pages plus 39 gifs which contain all quasar spectra. Accepted for
publication in the Astrophysical Journal Supplement Serie
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