NGC1052-DF2

观测

S´ersic index n = 0.6, axis ratio b/a = 0.85, the central surface brightness is µ(V606,0) = 24.4magarcsec−2, D=20Mpc.
effective radius along the major axis is Re = 2.2kpc, M606 = −15.4 mag, Mstars ≈ 2×10^8 Msun.
an extraordinary population of globular clusters, larger and more luminous than average GCs in the Milky Way, total mass is roughly 4 percent of the mass in stars, making DF2 one of the galaxies with the largest speciﬁc frequencies known.
the line-of-sight velocity dispersion of the GCs(10km/s) suggests a total dynamical mass for DF2 that leaves little room for any dark matter
气体含量非常低 arXiv:1810.04938 arXiv:1901.07586

测量误差很大，如果有些球状星团是背景，不能说得那么肯定 [2]
如果没有暗物质，星系和球状星团质量的比靠近，动力学摩擦效应显著（时标1-2Gyr）,大部分星团团已经被并合了[3]
考虑NGC1052的tidal效应，改变了DF2中球状星团在相空间的分布函数（真实空间外围的GC少了，GC在速度空间的弥散小了） [4]
没有暗物质的dynamical friction没那么简单, core-stalling and GC-GC interactions效应, 让星团掉不进去。反过来，如果有cuspy的NFW暗晕，里面的dynamical friction更强，会形成核心GC [5]