Volume 591, July 2016
|Number of page(s)||18|
|Published online||08 June 2016|
Robust automatic photometry of local galaxies from SDSS
Dissecting the color magnitude relation with color profiles⋆
1 Dipartimento di Fisica G. Occhialini, Università di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
2 Institute for Computational Cosmology and Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham DH1 3LE, UK
3 Universitäts-Sternwarte München, Scheinerstrasse 1, 81679 München, Germany
4 Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
Received: 22 October 2015
Accepted: 23 March 2016
We present an automatic procedure to perform reliable photometry of galaxies on SDSS images. We selected a sample of 5853 galaxies in the Coma and Virgo superclusters. For each galaxy, we derive Petrosian g and i magnitudes, surface brightness and color profiles. Unlike the SDSS pipeline, our procedure is not affected by the well known shredding problem and efficiently extracts Petrosian magnitudes for all galaxies. Hence we derived magnitudes even from the population of galaxies missed by the SDSS which represents ~25% of all local supercluster galaxies and ~95% of galaxies with g < 11 mag. After correcting the g and i magnitudes for Galactic and internal extinction, the blue and red sequences in the color magnitude diagram are well separated, with similar slopes. In addition, we study (i) the color-magnitude diagrams in different galaxy regions, the inner (r ≤ 1 kpc), intermediate (0.2RPet ≤ r ≤ 0.3RPet) and outer, disk-dominated (r ≥ 0.35RPet)) zone; and (ii), we compute template color profiles, discussing the dependences of the templates on the galaxy masses and on their morphological type. The two analyses consistently lead to a picture where elliptical galaxies show no color gradients, irrespective of their masses. Spirals, instead, display a steeper gradient in their color profiles with increasing mass, which is consistent with the growing relevance of a bulge and/or a bar component above 1010 M⊙.
Key words: galaxies: evolution / galaxies: fundamental parameters / galaxies: star formation / galaxies: photometry
Full Table A.1 is only available at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (184.108.40.206) or via http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/A+A/591/A38
© ESO, 2016
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