SINFONI邻近椭圆透镜巡天：两个新的低红移强透镜的发现及其对巨早型星系初始质量函数的意义
The SINFONI Nearby Elliptical Lens Locator Survey: Discovery of two new low-redshift strong lenses and implications for the initial mass function in giant early-type galaxies
摘要：
我们提出了一个盲目的调查结果，以确定强引力透镜人口中的低红移早型星系。SINFONI近距离椭圆透镜巡天（SNELLS）使用积分场红外光谱法在$z$ <0.055的大质量透镜候选物后面搜索透镜发射线源。从观测到的27个星系中，我们发现了一个已知的透镜（ESO 325-G 004），其$z$值为$z$ =0.034，并发现了两个新的系统，其$z$值分别为$z$ =0.031和$z$ =0.052。这三个透镜星系都具有高速色散（σ>300 km/s）和α元素丰度（[Mg/Fe]>0.3）。从透镜配置，我们得出总J-波段的质量-光比为1.8 $\pm$ 0.1，2.1 $\pm$ 0.1和1.9 $\pm$ 0.2内的$\sim$ 2千秒差距爱因斯坦半径。校正估计的暗物质贡献，并与银河系（Kroupa）初始质量函数（IMF）的恒星星族模型进行比较，我们确定了“质量过剩因子”，α。假设透镜星系有“老”的恒星星族（10 $\pm$ 1 Gyr），平均IMF质量因子为$\langleα\rangle$ =1.10 $\pm$ 0.08 $\pm$ 0.10，其中第一个误差是随机的，第二个是系统的。如果我们从6dF光学巡天光谱拟合出恒星星族，所有三个星系都与年龄一致，但由于有限的信噪比，年龄误差为3-4 Gyr。因此，IMF约束在这种情况下更宽松，$\langleα\rangle$ = $1.23^{+0.16}_{-0.13}\pm{0.10}$。因此，我们的结果与平均Kroupa IMF（α=1.00）一致，并强烈拒绝α>2的非常重的IMF。如果星系是古老的，那么Salpeter IMF（α=1.55）在3.5 $σ$水平上是不一致的，但是不能用从目前可用的光谱中得出的年龄限制来排除。
英文摘要：
We present results from a blind survey to identify strong gravitational lenses among the population of low-redshift early-type galaxies. The SINFONI Nearby Elliptical Lens Locator Survey (SNELLS) uses integral-field infrared spectroscopy to search for lensed emission line sources behind massive lens candidates at $z$<0.055. From 27 galaxies observed, we have recovered one previously-known lens (ESO325-G004) at $z$=0.034, and discovered two new systems, at $z$=0.031 and $z$=0.052. All three lens galaxies have high velocity dispersions (σ>300 km/s) and α-element abundances ([Mg/Fe]>0.3). From the lensing configurations we derive total J-band mass-to-light ratios of 1.8$\pm$0.1, 2.1$\pm$0.1 and 1.9$\pm$0.2 within the $\sim$2 kpc Einstein radius. Correcting for estimated dark-matter contributions, and comparing to stellar population models with a Milky Way (Kroupa) initial mass function (IMF), we determine the "mass excess factor", α. Assuming the lens galaxies have "old" stellar populations (10$\pm$1 Gyr), the average IMF mass factor is $\langleα\rangle$=1.10$\pm$0.08$\pm$0.10, where the first error is random and the second is systematic. If we instead fit the stellar populations from 6dF optical survey spectra, all three galaxies are consistent with being old, but the age errors are 3-4 Gyr, due to limited signal-to-noise. The IMF constraints are therefore looser in this case, with $\langleα\rangle$ = $1.23^{+0.16}_{-0.13}\pm{0.10}$. Our results are thus consistent with a Kroupa IMF (α=1.00) on average, and strongly reject very heavy IMFs with α>2. A Salpeter IMF (α=1.55) is inconsistent at the 3.5$σ$ level if the galaxies are old, but cannot be excluded using age constraints derived from the currently-available optical spectra.
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