2006/01/31 by Kevin Schawinski, K. Schawinski, S. Kaviraj +42 · 3 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics #Computer science #Galaxies: Formation, Evolution, Phenomena #Galaxy #Magnitude (astronomy) #Optoelectronics #Physics #Relation (database) #Stellar, planetary, and galactic studies #Ultraviolet #astro-ph
paper · pdf · doi:10.1086/516631
published as Astrophys.J.Suppl.173:512,2007 · Accepted for publication in ApJ, paper with high-resolution figures can be downloaded at: http://www-astro.physics.ox.ac.uk/~kevins/PAPERS/uv_environment.ps
arxiv created 2006/01/31 · openalex publication_date 2007/12/01 · arxiv updated 2014/10/13 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We use GALEX near-UV (NUV) photometry of a sample of early-type galaxies selected in the SDSS (Sloan Digital Sky Survey) to study the UV color-magnitude relation (CMR). NUV − r color is an excellent tracer of even small amounts (~1% mass fraction) of recent (≲1 Gyr) star formation, and so the NUV − r CMR allows us to study the effect of environment on the recent star formation history. We analyze a volume-limited sample of 839 visually inspected early-type galaxies in the redshift range 0.05 < z < 0.10 brighter than M r of –21.5 with any possible emission-line or radio-selected active galactic nuclei (AGNs) removed to avoid contamination. We find that contamination by AGN candidates and late-type interlopers highly bias any study of recent star formation in early-type galaxies and that, after removing those, our lower limit to the fraction of massive early-type galaxies showing signs of recent star formation is roughly 30% ± 3% . This suggests that residual star formation is common even among the present day early-type galaxy population. We find that the fraction of UV-bright early-type galaxies is 25% higher in low-density environments. However, the density effect is clear only in the lowest density bin. The blue galaxy fraction for the subsample of the brightest early-type galaxies, however, shows a very strong density dependence, in the sense that the blue galaxy fraction is lower in a higher density region.