194 research outputs found
An X-ray Selected AGN at z=4.6 Discovered by the CYDER Survey
We present the discovery of a high redshift, X-ray selected AGN by the
Calan-Yale Deep Extragalactic Research (CYDER) survey: CXOCY J033716.7-050153,
located at , the second high redshift AGN discovered by this survey.
Here, we present its optical, near-IR and X-ray properties and compare it with
other optical and X-ray selected high redshift AGN. The optical luminosity of
this object is significantly lower than most optically selected high redshift
quasars. It also has a lower rest frame UV to X-ray emission ratio than most
known quasars at this redshift. This mild deviation can be explained either by
dust obscuring the UV radiation of a normal radio quiet AGN emitting at 10% of
its Eddington luminosity or because this is intrinsically a low luminosity
radio loud AGN, with a super-massive Black Hole of \sim 10^8M_\sun emitting
at 1% of its Eddington luminosity. Deep radio observations can discriminate
between these two hypotheses.Comment: ApJ accepted, 16 pages, 5 figure
Discovery of a Fifth Image of the Large Separation Gravitationally Lensed Quasar SDSS J1004+4112
We report the discovery of a fifth image in the large separation lensed
quasar system SDSS J1004+4112. A faint point source located 0.2'' from the
center of the brightest galaxy in the lensing cluster is detected in images
taken with the Advanced Camera for Surveys (ACS) and the Near Infrared Camera
and Multi-Object Spectrometer (NICMOS) on the Hubble Space Telescope. The flux
ratio between the point source and the brightest lensed component in the ACS
image is similar to that in the NICMOS image. The location and brightness of
the point source are consistent with lens model predictions for a lensed image.
We therefore conclude that the point source is likely to be a fifth image of
the source quasar. In addition, the NICMOS image reveals the lensed host galaxy
of the source quasar, which can strongly constrain the structure of the lensing
critical curves and thereby the mass distribution of the lensing cluster.Comment: 5 pages, 5 figures, accepted for publication in PAS
Discovery of Two Gravitationally Lensed Quasars with Image Separations of 3 Arcseconds from the Sloan Digital Sky Survey
We report the discovery of two doubly-imaged quasars, SDSS
J100128.61+502756.9 and SDSS J120629.65+433217.6, at redshifts of 1.838 and
1.789 and with image separations of 2.86'' and 2.90'', respectively. The
objects were selected as lens candidates from the Sloan Digital Sky Survey
(SDSS). Based on the identical nature of the spectra of the two quasars in each
pair and the identification of the lens galaxies, we conclude that the objects
are gravitational lenses. The lenses are complicated; in both systems there are
several galaxies in the fields very close to the quasars, in addition to the
lens galaxies themselves. The lens modeling implies that these nearby galaxies
contribute significantly to the lens potentials. On larger scales, we have
detected an enhancement in the galaxy density near SDSS J100128.61+502756.9.
The number of lenses with image separation of ~3'' in the SDSS already exceeds
the prediction of simple theoretical models based on the standard
Lambda-dominated cosmology and observed velocity function of galaxies.Comment: 24 pages, 9 figures, accepted for publication in Ap
The Multiwavelength Survey by Yale-Chile (MUSYC): Deep Near-Infrared Imaging and the Selection of Distant Galaxies
We present deep near-infrared JHK imaging of four 10'x10' fields. The
observations were carried out as part of the Multiwavelength Survey by
Yale-Chile (MUSYC) with ISPI on the CTIO 4m telescope. The typical point source
limiting depths are J~22.5, H~21.5, and K~21 (5sigma; Vega). The effective
seeing in the final images is ~1.0". We combine these data with MUSYC UBVRIz
imaging to create K-selected catalogs that are unique for their uniform size,
depth, filter coverage, and image quality. We investigate the rest-frame
optical colors and photometric redshifts of galaxies that are selected using
common color selection techniques, including distant red galaxies (DRGs),
star-forming and passive BzKs, and the rest-frame UV-selected BM, BX, and Lyman
break galaxies (LBGs). These techniques are effective at isolating large
samples of high redshift galaxies, but none provide complete or uniform samples
across the targeted redshift ranges. The DRG and BM/BX/LBG criteria identify
populations of red and blue galaxies, respectively, as they were designed to
do. The star-forming BzKs have a very wide redshift distribution, a wide range
of colors, and may include galaxies with very low specific star formation
rates. In comparison, the passive BzKs are fewer in number, have a different
distribution of K magnitudes, and have a somewhat different redshift
distribution. By combining these color selection criteria, it appears possible
to define a reasonably complete sample of galaxies to our flux limit over
specific redshift ranges. However, the redshift dependence of both the
completeness and sampled range of rest-frame colors poses an ultimate limit to
the usefulness of these techniques.Comment: 17 pages in emulateapj style, 13 figures. Submitted to the
Astronomical Journal. Data will be made available upon publicatio
SDSS J092455.87+021924.9: an Interesting Gravitationally Lensed Quasar from the Sloan Digital Sky Survey
We report the discovery of a new gravitationally lensed quasar from the Sloan
Digital Sky Survey, SDSS J092455.87+021924.9 (SDSS J0924+0219). This object was
selected from among known SDSS quasars by an algorithm that was designed to
select another known SDSS lensed quasar (SDSS 1226-0006A,B). Five separate
components, three of which are unresolved, are identified in photometric
follow-up observations obtained with the Magellan Consortium's 6.5m Walter
Baade telescope at Las Campanas Observatory. Two of the unresolved components
(designated A and B) are confirmed to be quasars with z=1.524; the velocity
difference is less than 100 km sec^{-1} according to spectra taken with the W.
M. Keck Observatory's Keck II telescope on Mauna Kea. A third stellar
component, designated C, has the colors of a quasar with redshift similar to
components A and B. The maximum separation of the point sources is 1.78". The
other two sources, designated G and D, are resolved. Component G appears to be
the best candidate for the lensing galaxy. Although component D is near the
expected position of the fourth lensed component in a four image lens system,
its properties are not consistent with being the image of a quasar at z~1.5.
Nevertheless, the identical redshifts of components A and B and the presence of
component C strongly suggest that this object is a gravitational lens. Our
observations support the idea that a foreground object reddens the fourth
lensed component and that another unmodeled effect (such as micro- or
milli-lensing) demagnificates it, but we cannot rule out the possibility that
SDSS0924+0219 is an example of the relatively rare class of ``three component''
lens systems.Comment: 24 pages, 6 figures, accepted by A
The SWELLS Survey. I. A large spectroscopically selected sample of edge-on late-type lens galaxies
The relative contribution of baryons and dark matter to the inner regions of
spiral galaxies provides critical clues to their formation and evolution, but
it is generally difficult to determine. For spiral galaxies that are strong
gravitational lenses, however, the combination of lensing and kinematic
observations can be used to break the disk-halo degeneracy. In turn, such data
constrain fundamental parameters such as i) the mass density profile slope and
axis ratio of the dark matter halo, and by comparison with dark matter-only
numerical simulations the modifications imposed by baryons; ii) the mass in
stars and therefore the overall star formation efficiency, and the amount of
feedback; iii) by comparison with stellar population synthesis models, the
normalization of the stellar initial mass function. In this first paper of a
series, we present a sample of 16 secure, 1 probable, and 6 possible strong
lensing spiral galaxies, for which multi-band high-resolution images and
rotation curves were obtained using the Hubble Space Telescope and Keck-II
Telescope as part of the Sloan WFC Edge-on Late-type Lens Survey (SWELLS). The
sample includes 8 newly discovered secure systems. [abridged] We find that the
SWELLS sample of secure lenses spans a broad range of morphologies (from
lenticular to late-type spiral), spectral types (quantified by Halpha
emission), and bulge to total stellar mass ratio (0.22-0.85), while being
limited to M_*>10^{10.5} M_sun. The SWELLS sample is thus well-suited for
exploring the relationship between dark and luminous matter in a broad range of
galaxies. We find that the deflector galaxies obey the same size-mass relation
as that of a comparison sample of elongated non-lens galaxies selected from the
SDSS survey. We conclude that the SWELLS sample is consistent with being
representative of the overall population of high-mass high-inclination disky
galaxies.Comment: 21 pages, 6 figures, MNRAS, in pres
Type II-P Supernovae from the SDSS-II Supernova Survey and the Standardized Candle Method
We apply the Standardized Candle Method (SCM) for Type II Plateau supernovae
(SNe II-P), which relates the velocity of the ejecta of a SN to its luminosity
during the plateau, to 15 SNe II-P discovered over the three season run of the
Sloan Digital Sky Survey - II Supernova Survey. The redshifts of these SNe -
0.027 < z < 0.144 - cover a range hitherto sparsely sampled in the literature;
in particular, our SNe II-P sample contains nearly as many SNe in the Hubble
flow (z > 0.01) as all of the current literature on the SCM combined. We find
that the SDSS SNe have a very small intrinsic I-band dispersion (0.22 mag),
which can be attributed to selection effects. When the SCM is applied to the
combined SDSS-plus-literature set of SNe II-P, the dispersion increases to 0.29
mag, larger than the scatter for either set of SNe separately. We show that the
standardization cannot be further improved by eliminating SNe with positive
plateau decline rates, as proposed in Poznanski et al. (2009). We thoroughly
examine all potential systematic effects and conclude that for the SCM to be
useful for cosmology, the methods currently used to determine the Fe II
velocity at day 50 must be improved, and spectral templates able to encompass
the intrinsic variations of Type II-P SNe will be needed.Comment: Accepted for publication by ApJ; data used in this paper can be
downloaded from http://sdssdp47.fnal.gov/sdsssn/photometry/SNIIp.tgz;
citation errors correcte
The Sloan Digital Sky Survey Quasar Catalog IV. Fifth Data Release
We present the fourth edition of the Sloan Digital Sky Survey (SDSS) Quasar
Catalog. The catalog contains 77,429 objects; this is an increase of over
30,000 entries since the previous edition. The catalog consists of the objects
in the SDSS Fifth Data Release that have luminosities larger than M_i = -22.0
(in a cosmology with H_0 = 70 km/s/Mpc, Omega_M = 0.3, and Omega_Lambda = 0.7)
have at least one emission line with FWHM larger than 1000 km/s, or have
interesting/complex absorption features, are fainter than i=15.0, and have
highly reliable redshifts. The area covered by the catalog is 5740 sq. deg. The
quasar redshifts range from 0.08 to 5.41, with a median value of 1.48; the
catalog includes 891 quasars at redshifts greater than four, of which 36 are at
redshifts greater than five. Approximately half of the catalog quasars have i <
19; nearly all have i < 21. For each object the catalog presents positions
accurate to better than 0.2 arcsec. rms per coordinate, five-band (ugriz)
CCD-based photometry with typical accuracy of 0.03 mag, and information on the
morphology and selection method. The catalog also contains basic radio,
near-infrared, and X-ray emission properties of the quasars, when available,
from other large-area surveys. The calibrated digital spectra cover the
wavelength region 3800--9200A at a spectral resolution of ~2000. The spectra
can be retrieved from the public database using the information provided in the
catalog. The average SDSS colors of quasars as a function of redshift, derived
from the catalog entries, are presented in tabular form. Approximately 96% of
the objects in the catalog were discovered by the SDSS.Comment: 37 pages, Accepted for publication in A
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