1,677 research outputs found
The Quasar Pair Q 1634+267 A, B and the Binary QSO vs. Dark Lens Hypotheses
Deep HST/NICMOS H (F160W) band observations of the z=1.96 quasar pair Q
1634+267A,B reveal no signs of a lens galaxy to a 1 sigma threshold of
approximately 22.5 mag. The minimum luminosity for a normal lens galaxy would
be a 6L_* galaxy at z > 0.5, which is 650 times greater than our detection
threshold. Our observation constrains the infrared mass-to-light ratio of any
putative, early-type, lens galaxy to (M/L)_H > 690h_65 (1200h_65) for
Omega_0=0.1 (1.0) and H_0=65h_65 km/s/Mpc. We would expect to detect a galaxy
somewhere in the field because of the very strong Mg II absorption lines at
z=1.1262 in the Q 1634+267 A spectrum, but the HST H-band, I-band (F785LP) and
V-band (F555W) images require that any associated galaxy be very under-luminous
less than 0.1 L^*_H (1.0 L^*_I) if it lies within less than 40 h^{-1} (100
h^{-1}) kpc from Q 1634+267 A,B.
While the large image separation (3.86 arcsec) and the lack of a lens galaxy
strongly favor interpreting Q 1634+267A,B as a binary quasar system, the
spectral similarity remains a puzzle. We estimate that at most 0.06% of
randomly selected quasar pairs would have spectra as similar to each other as
the spectra of Q 1634+267 A and B. Moreover, spectral similarities observed for
the 14 quasar pairs are significantly greater than would be expected for an
equivalent sample of randomly selected field quasars. Depending on how strictly
we define similarity, we estimate that only 0.01--3% of randomly drawn samples
of 14 quasar pairs would have as many similar pairs as the observational
sample.Comment: 24 pages, including 4 figures, LaTex, ApJ accepted, comments from the
editor included, minor editorial change
LBQS 1429-0053: a binary quasar rather than a lensed quasar
Very deep ESO/VLT FORS1 and ISAAC images, as well as HST NICMOS2 data are
used to infer the nature of the quasar pair LBQS 1429-0053 A and B, either a
binary quasar or a doubly-imaged lensed quasar. Direct search of a putative
lensing galaxy is unsuccessful . Moreover, no galaxy overdensity close to the
quasar pair is found. A weak shear analysis of the field also fails at
detecting any concentration of dark matter and weakens the hypothesis of a dark
lens. The only sign of a possible lens consists in a group of 5 objects at z~1,
within a radius of 5'', from the quasar pair. Considering this group as the
lensing potential does not allow to reproduce the image position and flux ratio
of the quasars. Our deep R-band image shows a blue, extended object at the
position of quasar A, which is consistent with either being the lensed quasar A
host, or being an intervening galaxy at lower redshift. Unless future very deep
optical images demonstrate that this object is actually the lensed host of LBQS
1429-0053, we conclude that there is very little evidence for this quasar being
lensed. Therefore, we are led to declare LBQS 1429-0053 A and B a genuine
binary quasar.Comment: 9 pages, 6 jpg images, accepted for publication in A&
Optical and Radio Properties of Extragalactic Sources Observed by the FIRST and SDSS Surveys
We discuss the optical and radio properties of 30,000 FIRST sources
positionally associated with an SDSS source in 1230 deg of sky. The
majority (83%) of the FIRST sources identified with an SDSS source brighter
than r=21 are optically resolved. We estimate an upper limit of 5% for the
fraction of quasars with broad-band optical colors indistinguishable from those
of stars. The distribution of quasars in the radio flux -- optical flux plane
supports the existence of the "quasar radio-dichotomy"; 8% of all quasars with
i<18.5 are radio-loud and this fraction seems independent of redshift and
optical luminosity. The radio-loud quasars have a redder median color by 0.08
mag, and a 3 times larger fraction of objects with red colors. FIRST galaxies
represent 5% of all SDSS galaxies with r<17.5, and 1% for r<20, and are
dominated by red galaxies. Magnitude and redshift limited samples show that
radio galaxies have a different optical luminosity distribution than non-radio
galaxies selected by the same criteria; when galaxies are further separated by
their colors, this result remains valid for both blue and red galaxies. The
distributions of radio-to-optical flux ratio are similar for blue and red
galaxies in redshift-limited samples; this similarity implies that the
difference in their luminosity functions, and resulting selection effects, are
the dominant cause for the preponderance of red radio galaxies in flux-limited
samples. We confirm that the AGN-to-starburst galaxy number ratio increases
with radio flux, and find that radio emission from AGNs is more concentrated
than radio emission from starburst galaxies (abridged).Comment: submitted to AJ, color gif figures, PS figures available from
[email protected]
Emission within a Damped Lyman Alpha Absorption Trough: the Complex Sight Line Towards Q2059-360
We present new spectroscopic observations of the quasar Q2059-360, confirming
the existence of an emission feature within the Damped Lyman Alpha (DLA)
absorption trough. By observing also at slit positions offset from the quasar,
we show that the emission is spatially extended by at least a few arcseconds,
and hence confirm that the feature seen must be due to emission rather than
unusual absorption characteristics. We find that the DLA trough is very close
in redshift to the broad Lyman~ emission line of the QSO, with the
result that the DLA absorption removes much of the peak region of that line.
Despite the similarity of the redshifts of the DLA and the QSO, the lack of
high-ionization lines of the DLA system and the unresolved widths of the
corresponding metal lines indicate that the DLA cloud is not an associated
system. The emission feature has a large velocity offset of +490 km/s with
respect to the DLA system, and is resolved in velocity, comprising two
components with a separation of ~ 300 km/s. We consider three possibilities:
(1) Both emission and absorption occur within an object similar to the high
redshift Lyman-break galaxies; (2) The emission feature arises from an object
distinct from both the DLA absorber and the QSO, perhaps a young star-forming
galaxy or a proto-galactic clump. It could be associated with the DLA absorber
and perhaps the QSO in a compact group or cluster; (3) The redshifts are such
that the emission feature could be due to Narrow Line Region filaments of the
QSO, if the DLA absorption covers a sufficiently small angular size to allow
the filaments to be seen beyond the edge of the DLA cloud.Comment: 10 pages, 6 figures. Accepted for publication in MNRA
The Sightline to Q2343-BX415: Clues to Galaxy Formation in a Quasar Environment
(Abridged) We have discovered a strong DLA coincident in redshift with the
faint QSO Q2343-BX415 (R = 20.2, z_em = 2.57393). Follow-up observations at
intermediate spectral resolution reveal that the metal lines associated with
this 'proximate' DLA consist of two sets of absorption components. One set is
moving towards the quasar with velocities of ~ 150-600 km/s; this gas is highly
ionized and does not fully cover the continuum source, suggesting that it is
physically close to the active nucleus. The other, which accounts for most of
the neutral gas, is blueshifted relative to the QSO, with the strongest
component at ~ -160 km/s. We consider the possibility that the PDLA arises in
the outflowing interstellar medium of the host galaxy of Q2343-BX415, an
interpretation supported by strong C IV and N V absorption at nearby
velocities, and by the intense radiation field longward of the Lyman limit
implied by the high C II*/H I ratio. If Q2343-BX415 is the main source of these
UV photons, then the PDLA is located at either ~ 8 or ~ 37 kpc from the active
nucleus. Alternatively, the absorber may be a foreground star-forming galaxy
unrelated to the quasar and coincidentally at the same redshift, but our deep
imaging and follow-up spectroscopy of the field of Q2343-BX415 has not yet
produced a likely candidate. We measure the abundances of 14 elements in the
PDLA, finding an overall metallicity of ~ 1/5 solar and a normal pattern of
relative element abundances for this metallicity. Thus, in this PDLA there is
no evidence for the super-solar metallicities that have been claimed for some
proximate, high ionization, systems.Comment: Accepted for publication in the Astrophysical Journal. 27 pages, 8
tables, 21 postscript figure
Similarity of ionized gas nebulae around unobscured and obscured quasars
Quasar feedback is suspected to play a key role in the evolution of massive
galaxies, by removing or reheating gas in quasar host galaxies and thus
limiting the amount of star formation. In this paper we continue our
investigation of quasar-driven winds on galaxy-wide scales. We conduct Gemini
Integral Field Unit spectroscopy of a sample of luminous unobscured (type 1)
quasars, to determine the morphology and kinematics of ionized gas around these
objects, predominantly via observations of the [O III]5007 emission line. We
find that ionized gas nebulae extend out to ~13 kpc from the quasar, that they
are smooth and round, and that their kinematics are inconsistent with gas in
dynamical equilibrium with the host galaxy. The observed morphological and
kinematic properties are strikingly similar to those of ionized gas around
obscured (type 2) quasars with matched [O III] luminosity, with marginal
evidence that nebulae around unobscured quasars are slightly more compact.
Therefore in samples of obscured and unobscured quasars carefully matched in [O
III] luminosity we find support for the standard geometry-based unification
model of active galactic nuclei, in that the intrinsic properties of quasars,
of their hosts and of their ionized gas appear to be very similar. Given the
apparent ubiquity of extended ionized regions, we are forced to conclude that
either the quasar is at least partially illuminating pre-existing gas or that
both samples of quasars are seen during advanced stages of quasar feedback. In
the latter case, we may be biased by our [O III]-based selection against
quasars in the early "blow-out" phase, for example due to dust obscuration.Comment: 17 pages, 10 figures, 2 tables. Published in MNRAS, 201
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