具有中红外超辐射的早型星系的恒星星族
Stellar Populations of Early-type Galaxies with Mid-Infrared Excess Emission
摘要：
本文对静止（无H $α$辐射）和明亮（$M_{r}$ $<$ $-$ 21.5）的早期型星系（ETGs）进行了恒星星族分析。ETG是从SDSS星系的光谱样本中选择的，$<$为0.04 $<$ $z$ $<$ 0.11，具有{ \it WISE}中红外（IR）和{ \it GALEX}近紫外（UV）发射。我们堆叠ETG的光学光谱与不同量的中红外和近紫外过量发射，以测量强度的4000倍的突破$D_{n}$ 4000和巴耳末吸收线H $δ_{A}$的宽度，这表明最近（$\sim$ 1 Gyr）的恒星形成活动。与NUV $-r$颜色相比，{ \it WISE} [3.4] $-$ [12]颜色与光谱特征的相关性更强。我们用光谱拟合代码STARLIGHT拟合堆叠光谱，发现在具有中红外过量发射的ETG中，年轻恒星（$\leq$ 1 Gyr）和中年恒星（$\sim$ 1 $-$ 5 Gyr）的质量分数为$\sim$ 4 $-$ 11\%，这取决于用于拟合的模板光谱。这些结果表明，中红外过量发射的ETG经历了恒星形成在过去的1 $-$ 5 Gyr和中红外辐射是一个有用的诊断工具，探测最近的恒星形成活动的ETG。
英文摘要：
We present a stellar population analysis of quiescent (without H$α$ emission) and bright ($M_{r}$ $<$ $-$21.5) early-type galaxies (ETGs) with recent star formation. The ETGs are selected from a spectroscopic sample of SDSS galaxies at 0.04 $<$ $z$ $<$ 0.11 with {\it WISE} mid-infrared (IR) and {\it GALEX} near-ultraviolet (UV) emissions. We stack the optical spectra of ETGs with different amounts of mid-IR and near-UV excess emissions to measure the strength of 4000 Å break $D_{n}$4000 and the width of Balmer absorption line H$δ_{A}$ that are indicative of recent ($\sim$1 Gyr) star formation activity. The {\it WISE} [3.4]$-$[12] colors show stronger correlations with the spectral features than NUV$-r$ colors. We fit to the stacked spectra with a spectral fitting code, STARLIGHT, and find that the mass fraction of young ($\leq$1 Gyr) and intermediate-age ($\sim$1$-$5 Gyr) stars in the ETGs with mid-IR excess emission is $\sim$4$-$11\%, depending on the template spectrum used for the fit. These results show that the ETGs with mid-IR excess emission have experienced star formation within the last 1$-$5 Gyr and that the mid-IR emission is a useful diagnostic tool for probing recent star formation activity in ETGs.
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