Galactic Dark Matter Halos and Globular Cluster Populations. III. Extension to Extreme Environments

Abstract

The total mass M GCS in the globular cluster (GC) system of a galaxy is empirically a near-constant fraction of the total mass M h ≡ M bary + M dark of the galaxy, across a range of 10 5 in galaxy mass. This trend is radically unlike the strongly nonlinear behavior of total stellar mass M versus M h . We discuss extensions of this trend to two more extreme situations: (a) entire clusters of galaxies, and (b) the Ultra-Diffuse Galaxies (UDGs) recently discovered in Coma and elsewhere. Our calibration of the ratio η M = M GCS /M h from normal galaxies, accounting for new revisions in the adopted massto-light ratio for GCs, now gives η M = 2.9 × 10 −5 as the mean absolute mass fraction. We find that the same ratio appears valid for galaxy clusters and UDGs. Estimates of η M in the four clusters we examine tend to be slightly higher than for individual galaxies, but more data and better constraints on the mean GC mass in such systems are needed to determine if this difference is significant. We use the constancy of η M to estimate total masses for several individual cases; for example, the total mass of the Milky Way is calculated to be M h = 1.1 × 10 12 M . Physical explanations for the uniformity of η M are still descriptive, but point to a picture in which massive, dense star clusters in their formation stages were relatively immune to the feedback that more strongly influenced lower-density regions where most stars form.

Detection of the Stellar Intracluster Medium in Perseus (Abell 426)

“…A better way to estimate the total GC population in Perseus at this stage may be to use the mass ratio η M ≡ (M GCS /M h ) where M GCS is the total mass in all the GCs and M h is the total mass in the entire cluster, dark plus baryonic (roughly, its virial mass M 200 ). Empirically, η M has been found to be nearly constant over a wide range of environments including dwarf or giant galaxies, spirals or ellipticals, and entire galaxy clusters; see, e.g., Blakeslee et al (1997); Spitler & Forbes (2009);Durrell et al (2014); Hudson et al (2014); Harris et al (2015Harris et al ( , 2017. The most recent calibration gives η M = (4.3 ± 0.6) × 10 −5 for entire clusters of galaxies (Harris et al 2017).…”

“…Empirically, η M has been found to be nearly constant over a wide range of environments including dwarf or giant galaxies, spirals or ellipticals, and entire galaxy clusters; see, e.g., Blakeslee et al (1997); Spitler & Forbes (2009);Durrell et al (2014); Hudson et al (2014); Harris et al (2015Harris et al ( , 2017. The most recent calibration gives η M = (4.3 ± 0.6) × 10 −5 for entire clusters of galaxies (Harris et al 2017). For the Perseus cluster, M 200 = (6.65 ± 0.45) × 10 14 M ⊙ from Simionescu et al (2011) determined from its X-ray gas pressure profile.…”

“…For the Perseus cluster, M 200 = (6.65 ± 0.45) × 10 14 M ⊙ from Simionescu et al (2011) determined from its X-ray gas pressure profile. If we then take a mean GC mass M GC = 2.8 × 10 5 M ⊙ appropriate for L ⋆ galaxies (Harris et al 2017), the resulting estimate of the total population is N GC = 102, 000 clusters. If analogies with Virgo or Coma are useful, roughly half of these should belong to the member galaxies, with the remainder in the IGM; thus, N IGC ∼ 50, 000, which agrees to within a factor of two with our estimate working directly from the observations.…”

“…In the richer Coma cluster, Peng et al (2011) find a substantial IGC population filling the cluster core regions. Three other and more distant galaxy clusters for which IGCs have been sampled with unusually deep HST imaging include A1185 (West et al 2011), A1689 (Alamo-Martínez et al 2013, and A2744 (Lee & Jang 2016), though for various reasons of either field coverage or depth these also remain more uncertain than for Virgo or Coma (see also Harris et al 2017, for additional discussion of A1689 and A2744).…”

Specific Frequencies and Luminosity Profiles of Cluster Galaxies and Intracluster Light in Abell 1689

“…Among early-type galaxies, S N varies with the absolute magnitude of the galaxy M V following a U-shape trend: it increases with luminosity on the bright side, reaches a minimum at luminosities ∼ L * V , and then increases as luminosity decreases on the faint side, though with a large dispersion (Harris 2001;Peng et al 2008). The nonlinear behavior of S N may be understood if the number of GCs (or the mass contained in them) scales with the total halo mass of the host galaxy (Blakeslee et al 1997;Blakeslee 1999;Kravtsov & Gnedin 2005;Spitler & Forbes 2009;Hudson et al 2014;Harris et al 2017), suggesting that S N scales inversely with the stellar-to-halo mass relation (Moster et al 2010;Hudson et al 2015), or the total star formation efficiency. Peng et al (2008) also found evidence for an environmental effect within Virgo, whereby the majority of dwarf ellipticals in Virgo with high S N are located within 1 Mpc of the cD galaxy M87.…”