Star-galaxy separation by far-infrared color-color diagrams for the AKARI FIS all-sky survey (bright source catalog version β-1)^*,**

¹ The Andrzej Sołtan Institute for Nuclear Studies, ul. Hoża 69, 00-681 Warsaw, Poland e-mail: apollo@fuw.edu.pl
² The Astronomical Observatory of the Jagiellonian University, ul. Orla 171, 30-244 Kraków, Poland
³ Institute for Advanced Research, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan

Received: 8 October 2009
Accepted: 1 March 2010

Abstract

Aims. To separate stars and galaxies in the far infrared AKARI all-sky survey data, we have selected a sample with the complete color information available in the low extinction regions of the sky and constructed color-color plots for these data. We looked for the method of separating stars and galaxies using the color information.

Methods. We performed an extensive search for the counterparts of these selected all-sky survey objects in the NED and SIMBAD databases. Among 5176 selected objects, we found 4272 galaxies, 382 other extragalactic objects, 349 Milky Way stars, 50 other Galactic objects, and 101 sources detected before in various wavelengths but of an unknown origin. Twenty-two sources were left unidentified. 
Then, we checked the colors of stars and galaxies in the far-infrared flux-color and color-color plots.

Results. In the resulting diagrams, stars form two clearly separated clouds. One of them is easily distinguished from galaxies and allows for a simple method of excluding a large part of stars using the far-infrared data. The other smaller branch, overplotting galaxies, consists of stars known to have an infrared excess, like Vega and some fainter stars discovered by IRAS or 2MASS. The color properties of these objects in any case make them very difficult to distinguish from galaxies.

Conclusions. We conclude that the FIR color-color diagrams allow for a high-quality star-galaxy separation. With the proposed simple method we can select more that 95% of galaxies rejecting at least 80% of stars.