40,676 research outputs found

    Galaxy Zoo Morphology and Photometric Redshifts in the Sloan Digital Sky Survey

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    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 (\sim350 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

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    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

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    We present two samples of \hii galaxies from the Sloan Digital Sky Survey (SDSS) spectroscopic observations data release 3. The electron temperatures(TeT_e) of 225 galaxies are calculated with the photoionized \hii model and TeT_e of 3997 galaxies are calculated with an empirical method. The oxygen abundances from the TeT_e methods of the two samples are determined reliably. The oxygen abundances from a strong line metallicity indicator, such as R23R_{23}, PP, N2N2, and O3N2O3N2, are also calculated. We compared oxygen abundances of \hii galaxies obtained with the TeT_e method, R23R_{23} method, PP method, N2N2 method, and O3N2O3N2method. The oxygen abundances derived with the TeT_e method are systematically lower by \sim0.2 dex than those derived with the R23R_{23} method, consistent with previous studies based on \hii region samples. No clear offset for oxygen abundance was found between TeT_e metallicity and PP, N2N2 and O3N2O3N2 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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