209 research outputs found
The Luminosity Function for L>L* Galaxies at z > 3
Through use of multiband (U, B, R, I) photometry we have isolated high
redshift (3.0<z<3.5) galaxy candidates in a survey of 1.27 deg^2 to R = 21.25
and a survey of 0.02 deg^2 to R = 23.5. Our pool of candidates constrains the
nature of the 3.0 < z < 3.5 luminosity function over the range L* < L < 100 L*,
if we grant a similar level of completeness to these data as for very faint
samples (to R = 25.5) selected in a similar fashion. Our constraints agree with
the high redshift sky density at R = 20.5 estimated from Yee et al.'s (1996)
serendipitous discovery of a bright, z = 2.7 galaxy, as well as the density at
R ~ 23 by Steidel et al. (1996b). We strongly rule out -- by more than two
orders of magnitude at M(R) = -25 -- the L > L* luminosity function for z = 3-5
galaxies obtained by a photometric redshift analysis of the Hubble Deep Field
(HDF) by Gwyn & Hartwick (1996). Our results at R ~ 23 are more consistent with
the photometric redshift analysis of the faint HDF galaxies by Sawicki & Yee
(1996), but our present upper limits at the brightest magnitudes (R < 21.5,
M(R) < -24) allow more generous volume densities of these super-L* galaxies.Comment: Accepted for publication in ApJ Letters; 14 pages Latex, including 3
figure
Survey incompleteness and the evolution of the QSO luminosity function
We concentrate on a type of QSO survey which depends on selecting QSO candidates based on combinations of colors. Since QSO's have emission lines and power-law continua, they are expected to yield broadband colors unlike those of stellar photospheres. Previously, the fraction of QSO's expected to be hiding (unselected) within the locus of stellar (U-J, J-F) colors was estimated at about 15 percent. We have now verified that the KK88 survey is at least 11 percent incomplete, but have determined that it may be as much as 34 percent incomplete. The 'missing' QSO's are expected to be predominantly at z less than or = 2.2. We have studied the proper motion and variability properties of all stellar objects with J less than or = 22.5 or F less than or = 21.5 in the SA 57 field which has previously been surveyed with a multicolor QSO search by KK88
Spectroscopy of Quasar Candidates from SDSS Commissioning Data
The Sloan Digital Sky Survey has obtained images in five broad-band colors
for several hundred square degrees. We present color-color diagrams for stellar
objects, and demonstrate that quasars are easily distinguished from stars by
their distinctive colors. Follow-up spectroscopy in less than ten nights of
telescope time has yielded 22 new quasars, 9 of them at , and one with
, the second highest-redshift quasar yet known. Roughly 80% of the
high-redshift quasar candidates selected by color indeed turn out to be
high-redshift quasars.Comment: 4 pages, 3 figures, to appear in the proceedings of "After the Dark
Ages: When Galaxies were Young (the Universe at 2<z<5)", 9th Annual October
Astrophysics Conference in Marylan
Photometric redshifts from reconstructed QSO templates
From SDSS commissioning photometric and spectroscopic data, we investigate
the utility of photometric redshift techniques to the task of estimating QSO
redshifts. We consider empirical methods (e.g. nearest-neighbor searches and
polynomial fitting), standard spectral template fitting and hybrid approaches
(i.e. training spectral templates from spectroscopic and photometric
observations of QSOs). We find that in all cases, due to the presence of strong
emission-lines within the QSO spectra, the nearest-neighbor and template
fitting methods are superior to the polynomial fitting approach. Applying a
novel reconstruction technique, we can, from the SDSS multicolor photometry,
reconstruct a statistical representation of the underlying SEDs of the SDSS
QSOs. Although, the reconstructed templates are based on only broadband
photometry the common emission lines present within the QSO spectra can be
recovered in the resulting spectral energy distributions. The technique should
be useful in searching for spectral differences among QSOs at a given redshift,
in searching for spectral evolution of QSOs, in comparing photometric redshifts
for objects beyond the SDSS spectroscopic sample with those in the well
calibrated photometric redshifts for objects brighter than 20th magnitude and
in searching for systematic and time variable effects in the SDSS broad band
photometric and spectral photometric calibrations.Comment: 21 pages, 9 figures, LaTeX AASTeX, submitted to A
New Halo White Dwarf Candidates in the Sloan Digital Sky Survey
We present optical spectroscopy and near-infrared photometry of 57 faint (g = 19–22) high proper motion white dwarfs identified through repeat imaging of ≈3100 deg2 of the Sloan Digital Sky Survey footprint by Munn et al. We use ugriz and JHphotometry to perform a model atmosphere analysis, and identify 10 ultracool white dwarfs with Teff \u3c 4000 K, including the coolest pure H atmosphere white dwarf currently known, J1657+2638, with Teff = 3550 ± 100 K. The majority of the objects with cooling ages larger than 9 Gyr display thick disc kinematics and constrain the age of the thick disc to ≥11 Gyr. There are four white dwarfs in our sample with large tangential velocities (vtan \u3e 120 km s−1) and UVW velocities that are more consistent with the halo than the Galactic disc. For typical 0.6M ⊙ white dwarfs, the cooling ages for these halo candidates range from 2.3 to 8.5 Gyr. However, the total mainsequence+ white dwarf cooling ages of these stars would be consistent with the Galactic halo if they are slightly undermassive. Given the magnitude limits of the current large-scale surveys, many of the coolest and oldest white dwarfs remain undiscovered in the solar neighbourhood, but upcoming surveys such as Gaia and the Large Synoptic Survey Telescope should find many of these elusive thick disc and halo white dwarfs
New Halo White Dwarf Candidates in the Sloan Digital Sky Survey
We present optical spectroscopy and near-infrared photometry of 57 faint (g = 19–22) high proper motion white dwarfs identified through repeat imaging of ≈3100 deg2 of the Sloan Digital Sky Survey footprint by Munn et al. We use ugriz and JHphotometry to perform a model atmosphere analysis, and identify 10 ultracool white dwarfs with Teff \u3c 4000 K, including the coolest pure H atmosphere white dwarf currently known, J1657+2638, with Teff = 3550 ± 100 K. The majority of the objects with cooling ages larger than 9 Gyr display thick disc kinematics and constrain the age of the thick disc to ≥11 Gyr. There are four white dwarfs in our sample with large tangential velocities (vtan \u3e 120 km s−1) and UVW velocities that are more consistent with the halo than the Galactic disc. For typical 0.6M ⊙ white dwarfs, the cooling ages for these halo candidates range from 2.3 to 8.5 Gyr. However, the total mainsequence+ white dwarf cooling ages of these stars would be consistent with the Galactic halo if they are slightly undermassive. Given the magnitude limits of the current large-scale surveys, many of the coolest and oldest white dwarfs remain undiscovered in the solar neighbourhood, but upcoming surveys such as Gaia and the Large Synoptic Survey Telescope should find many of these elusive thick disc and halo white dwarfs
NYU-VAGC: a galaxy catalog based on new public surveys
Here we present the New York University Value-Added Galaxy Catalog
(NYU-VAGC), a catalog of local galaxies (mostly below a redshift of about 0.3)
based on a set of publicly-released surveys (including the 2dFGRS, 2MASS, PSCz,
FIRST, and RC3) matched to the Sloan Digital Sky Survey (SDSS) Data Release 2.
Excluding areas masked by bright stars, the photometric sample covers 3514
square degrees and the spectroscopic sample covers 2627 square degrees (with
about 85% completeness). Earlier, proprietary versions of this catalog have
formed the basis of many SDSS investigations of the power spectrum, correlation
function, and luminosity function of galaxies. We calculate and compile derived
quantities (for example, K-corrections and structural parameters for galaxies).
The SDSS catalog presented here is photometrically recalibrated, reducing
systematic calibration errors across the sky from about 2% to about 1%. We
include an explicit description of the geometry of the catalog, including all
imaging and targeting information as a function of sky position. Finally, we
have performed eyeball quality checks on a large number of objects in the
catalog in order to flag deblending and other errors. This catalog is
complementary to the SDSS Archive Servers, in that NYU-VAGC's calibration,
geometrical description, and conveniently small size are specifically designed
for studying galaxy properties and large-scale structure statistics using the
SDSS spectroscopic catalog.Comment: accepted by AJ; full resolution version available at
http://sdss.physics.nyu.edu/vagc/va_paper.ps; data files available at
http://sdss.physics.nyu.edu/vagc
Exploring the Local Milky Way: M Dwarfs as Tracers of Galactic Populations
We have assembled a spectroscopic sample of low-mass dwarfs observed as part
of the Sloan Digital Sky Survey along one Galactic sightline, designed to
investigate the observable properties of the thin and thick disks. This sample
of ~7400 K and M stars also has measured ugriz photometry, proper motions, and
radial velocities. We have computed UVW space motion distributions, and
investigate their structure with respect to vertical distance from the Galactic
Plane. We place constraints on the velocity dispersions of the thin and thick
disks, using two-component Gaussian fits. We also compare these kinematic
distributions to a leading Galactic model. Finally, we investigate other
possible observable differences between the thin and thick disks, such as
color, active fraction and metallicity.Comment: 11 pages, 12 figures, Accepted by A
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