Using constrained simulations of the local Universe for generic cold dark matter and for 1keV warm dark matter, we investigate the difference in the abundance of dark matter halos in the local environment. We find that the mass function within 20 Mpc/h of the Local Group is ~2 times larger than the universal mass function in the 10^9-10^13 M_odot/h mass range. Imposing the field of view of the on-going HI blind survey ALFALFA in our simulations, we predict that the velocity function in the Virgo-direction region exceeds the universal velocity function by a factor of 3. Furthermore, employing a scheme to translate the halo velocity function into a galaxy velocity function, we compare the simulation results with a sample of galaxies from the early catalog release of ALFALFA. We find that our simulations are able to reproduce the velocity function in the 80-300 km/s velocity range, having a value ~10 times larger than the universal velocity function in the Virgo-direction region. In the low velocity regime, 35-80 km/s, the warm dark matter simulation reproduces the observed flattening of the velocity function. On the contrary, the simulation with cold dark matter predicts a steep rise in the velocity function towards lower velocities; for V_max=35 km/s, it forecasts ~10 times more sources than the ones observed. If confirmed by the complete ALFALFA survey, our results indicate a potential problem for the cold dark matter paradigm or for the conventional assumptions about energetic feedback in dwarf galaxies.
The coevolution of the velocity and mass functions of galaxies and dark haloes
我们采用偏差校正的丰度匹配技术，调查的LCDM暗晕质量函数（HMF），观测导出的速度色散和恒星质量函数（VDF，SMF）的z=1和0之间的星系的共同演化。我们首次使用Chae（2010）通过强透镜统计约束的VDF演化进行星系-晕丰度匹配研究。作为本地基准，我们使用了两个z ~ 0 VDF（基于SDSS DR 5的Monte-Carlo实现的VDF和基于SDSS DR 6的直接测量的VDF）。然后，我们专注于连接的VDF演化的HMF演化预测的N体模拟和SMF演化星系调查的约束。在VDF-HMF联系上，我们发现局域暗晕维里质量-中心恒星速度色散（Mvir-sigma）关系与已被研究的低红移暗晕的个别性质吻合得很好，并且VDF演化与HMF演化密切平行，意味着Mvir-sigma关系几乎没有演化.在VDF-SMF联系上，把丰度匹配结果与其他独立观测结果和流体动力学模拟结果结合起来，恒星质量-恒星速度色散（Mstar-sigma）关系也可能演化不大。我们的研究结果支持的简单的图片，作为晕层次的增长，恒星质量和中央恒星速度色散平行增长。我们讨论了这种平行的共同演化的星系形成和演化下的LCDM范式的可能影响。
The SWELLS survey. IV. Precision measurements of the stellar and dark matter distributions in a spiral lens galaxy
We construct a fully self-consistent mass model for the lens galaxy J2141 at z=0.14, and use it to improve on previous studies by modelling its gravitational lensing effect, gas rotation curve and stellar kinematics simultaneously. We adopt a very flexible axisymmetric mass model constituted by a generalized NFW dark matter halo and a stellar mass distribution obtained by deprojecting the MGE fit to the high-resolution K'-band LGSAO imaging data of the galaxy, with the (spatially constant) M/L ratio as a free parameter. We model the stellar kinematics by solving the anisotropic Jeans equations…
