40,676 research outputs found
Galaxy Zoo Morphology and Photometric Redshifts in the Sloan Digital Sky Survey
It has recently been demonstrated that one can accurately derive galaxy
morphology from particular primary and secondary isophotal shape estimates in
the Sloan Digital Sky Survey imaging catalog. This was accomplished by applying
Machine Learning techniques to the Galaxy Zoo morphology catalog. Using the
broad bandpass photometry of the Sloan Digital Sky Survey in combination with
with precise knowledge of galaxy morphology should help in estimating more
accurate photometric redshifts for galaxies. Using the Galaxy Zoo separation
for spirals and ellipticals in combination with Sloan Digital Sky Survey
photometry we attempt to calculate photometric redshifts. In the best case we
find that the root mean square error for Luminous Red Galaxies classified as
ellipticals is as low as 0.0118. Given these promising results we believe
better photometric redshift estimates for all galaxies in the Sloan Digital Sky
Survey (350 million) will be feasible if researchers can also leverage
their derived morphologies via Machine Learning. These initial results look to
be promising for those interested in estimating Weak-Lensing, Baryonic Acoustic
Oscillation, and other fields dependent upon accurate photometric redshifts.Comment: Submitted to ApJL, 4 pages, 3 figure
The Sloan Digital Sky Survey
The Sloan Digital Sky Survey is an ambitious, multi-institutional project to
create a huge digital imaging and spectroscopic data bank of 25% of the
celestial sphere, approximately 10,000 deg^2 centred on the north galactic
polar cap. The photometric atlas will be in 5 specially-chosen colours,
covering the pi ster of the Survey area to a limiting magnitude of r~23.1, on
0.4" pixels, resulting in a 1 Tpixel map. This data base will be automatically
analysed to catalog the photometric and astrometric properties of 10^8 stellar
images, 10^8 galaxies, and 10^6 colour-selected QSO candidates; the galaxy data
will in addition include detailed morphological data. The photometric data are
used to autonomously and homogeneously select objects for the spectroscopic
survey, which will include spectra of 10^6 galaxies, 10^5 QSOs, and 10^5
unusual stars. Although the project was originally motivated by the desire to
study Large Scale Structure, we anticipate that these data will impact
virtually every field of astronomy, from Earth-crossing asteroids to QSOs at
z>6. In particular, the ~12 TByte multi-colour, precision calibrated imaging
archive should be a world resource for many decades of the next century.Comment: On behalf of the entire scientific and technical team of the Survey.
Paper presented at "Discussion Meeting on Large Scale Structure in the
Universe," Royal Society, London, March 1998; 11 pages including 2 figures
and no tables. To appear in Philosophical Transactions of the Royal Society
of London A, 1998. Requires LaTeX and rspublic.sty. Revised version: typos
corrected, very slight additions, references update
Oxygen abundance in the Sloan Digital Sky Survey
We present two samples of \hii galaxies from the Sloan Digital Sky Survey
(SDSS) spectroscopic observations data release 3. The electron
temperatures() of 225 galaxies are calculated with the photoionized \hii
model and of 3997 galaxies are calculated with an empirical method. The
oxygen abundances from the methods of the two samples are determined
reliably. The oxygen abundances from a strong line metallicity indicator, such
as , , , and , are also calculated. We compared oxygen
abundances of \hii galaxies obtained with the method, method,
method, method, and method. The oxygen abundances derived with
the method are systematically lower by 0.2 dex than those derived
with the method, consistent with previous studies based on \hii
region samples. No clear offset for oxygen abundance was found between
metallicity and , and metallicity. When we studied the relation
between N/O and O/H, we found that in the metallicity regime of \zoh > 7.95,
the large scatter of the relation can be explained by the contribution of small
mass stars to the production of nitrogen. In the high metallicity regime, \zoh
> 8.2, nitrogen is primarily a secondary element produced by stars of all
masses.Comment: 7 pages, 3 figures. A&A accepte
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