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arXiv · astro-ph/0601036

The effect of environment on the UV colour-magnitude relation of early-type galaxies

K. Schawinski·S. Kaviraj·S. Khochfar·S. -J. Yoon·S. K. Yi·J. -M. Deharveng·A. Boselli·T. Barlow·T. Conrow·K. Forster·P. Friedman·D. C. Martin·P. Morrissey·S. Neff·D. Schiminovich·M. Seibert·T. Small·T. Wyder·L. Bianchi·J. Donas·T. Heckman·Y. -W. Lee·B. Madore·B. Milliard·R. M. Rich·A. Szalay
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Abstract

We use \textit{GALEX} (Galaxy Evolution Explorer) near-UV (NUV) photometry of a sample of early-type galaxies selected in \textit{SDSS} (Sloan Digital Sky Survey) to study the UV color-magnitude relation (CMR). $NUV-r$ color is an excellent tracer of even small amounts ($\sim 1$% mass fraction) of recent ($\la 1$ 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 AGN 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 $30 \pm 3%$ This suggests that residual star formation is common even amongst 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.

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K. Schawinski, S. Kaviraj, S. Khochfar, S. -J. Yoon, S. K. Yi, J. -M. Deharveng, A. Boselli, T. Barlow, T. Conrow, K. Forster, P. Friedman, D. C. Martin, P. Morrissey, S. Neff, D. Schiminovich, M. Seibert, T. Small, T. Wyder, L. Bianchi, J. Donas, T. Heckman, Y. -W. Lee, B. Madore, B. Milliard, R. M. Rich, A. Szalay. 2006-01-31. The effect of environment on the UV colour-magnitude relation of early-type galaxies. https://doi.org/10.1086/516631

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