The Effect of Environment on the Ultraviolet Color-Magnitude Relation of Early-Type Galaxies
The Effect of Environment on the Ultraviolet Color-Magnitude Relation of Early-Type Galaxies
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DOI：
10.1086/516631
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发表时间：
2006-01
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影响因子：
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通讯作者：
K. Schawinski;S. Kaviraj;S. Khochfar;Suk-Jin Yoon;Suk-Jin Yoon;S. Yi;S. Yi;J. Deharveng;A. Boselli
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作者：
K. Schawinski;S. Kaviraj;S. Khochfar;Suk-Jin Yoon;Suk-Jin Yoon;S. Yi;S. Yi;J. Deharveng;A. Boselli
我们用近紫外(NUV)测光技术研究了SDSS(斯隆数字巡天)早期类型星系的紫外颜色-星等关系(CMR)。NUV−r颜色是一种很好的示踪剂，可以追踪最近(≲1 Gyr)恒星形成的极少量(~1%质量分数)恒星，因此NUV−r CMR使我们能够研究环境对最近恒星形成历史的影响。我们分析了839个早期类型星系的体积有限的样本，这些星系的红移范围比MR OF-21.5亮0.05<；z<；0.10，并去除了任何可能的发射线或无线电选择的活动星系核(AGN)，以避免污染。我们发现，活动星系核候选者和晚型入侵者的污染严重偏离了任何关于早型星系新近恒星形成的研究，并且，在去除这些污染后，我们对显示出新星形成迹象的大质量早型星系的下限大约是30%±3%。这表明，即使在当今早期类型的星系群体中，残余恒星的形成也很常见。我们发现，在低密度环境中，紫外线明亮的早期类型星系的比例要高出25%。而密度效应只有在密度最低的仓位才明显。然而，对于最亮的早期类型星系的亚样本，蓝色星系的比例表现出非常强烈的密度依赖性，在高密度区域蓝色星系比例较低。
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 Mr 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.