Radially extended kinematics and stellar populations of the massive ellipticals NGC1600, NGC4125 and NGC7619. Constraints on the outer dark halo density profile
S. B. Pu, R. P. Saglia, M. H. Fabricius, J. Thomas, R. Bender, Z. Han
备注：
Accepted for publication in Astronomy and Astrophysics
We present high quality long slit spectra along the major and minor axes out to 1.5-2 Re (14-22 kpc) of three bright elliptical galaxies (NGC1600, NGC4125, NGC7619) obtained at the Hobby-Eberly Telescope (HET). We derive stellar kinematic profiles and Lick/IDS indices (Hbeta, Mgb, Fe5015, Fe5270, Fe5335, Fe5406). Moreover, for NGC4125 we derive gas kinematics and emission line strengths. We model the absorption line strengths using Simple Stellar Populations models that take into account the variation of [α/Fe] and derive ages, total metallicity and element abundances. Overall, we find that the three galaxies have old and [α/Fe] overabundant stellar populations with no significant gradients. The metallicity is supersolar at the center with a strong negative radial gradient. For NGC4125, several pieces of evidence point to a recent dissipational merger event. We calculate the broad band color profiles with the help of SSP models. All of the colors show sharp peaks at the center of the galaxies, mainly caused by the metallicity gradients, and agree well with the measured colors. Using the Schwarzschild's axisymmetric orbit superposition technique, we model the stellar kinematics to constrain the dark halos of the galaxies. We use the tight correlation between the Mgb strength and local escape velocity to set limits on the extent of the halos by testing different halo sizes. Logarithmic halos - cut at 60 kpc -minimize the overall scatter of the Mgb-Vesc relation. Larger cutoff radii are found if the dark matter density profile is decreasing more steeply at large radii.
Use of spatial cross correlation function to study formation mechanism of massive elliptical galaxies
星系的空间成团性质以前曾被用自相关函数研究过。相同类型的互相关函数已被用来研究星系的参数聚类性质，例如相对于星系的质量和大小。在质量-尺寸参数平面上，通过互相关，我们设想了邻近大质量早型星系的几个组成部分的形成和演化，高红移早型星系（以下简称ETG）结果表明，在最高红移范围内，附近ETG的最内层成分与ETG有显著的相关性，称为红块，而在红移范围内，中间成分与ETG有显著的相关性z值大于0.5且小于0.75。最外侧的部分在任何范围内都没有相关性，表明通过原位增生的情景。上述形成情景与之前对NGC 5128（Chattopadhyay et al.（2009），Chattopadhyay et al.（2013））获得的结果一致，并在某种程度上与附近的椭圆星系（Huang et al.（2013））在考虑了恒星质量大于或等于108.73 M-Sun的高红移ETG样本后获得的结果一致。因此，目前的工作表明，一个三相形成的大质量附近的椭圆星系，而不是两个在以前的工作中讨论。
