paper

High-Precision Dark Halo Virial Masses from Globular Cluster Numbers: Implications for Globular Cluster Formation and Galaxy Assembly

arXiv:1901.00900 · doi:10.3847/1538-3881/ab5b0e

Abstract

We confirm that the number of globular clusters (GCs), N $_{GC}$ , is an excellent tracer of their host galaxy's halo virial mass M $_{v i r}$ . The simple linear relation M $_{v i r} = 5 \times 1 0^{9}$ M $_{⊙} \times$ N $_{GC}$ fits the data perfectly from M $_{v i r} = 1 0^{10}$ M $_{⊙}$ to M $_{v i r} = 2 \times 1 0^{15}$ M $_{⊙}$ . This result is independent of galaxy morphology and extends statistically into the dwarf galaxy regime with M $_{v i r} = 1 0^{8} - 1 0^{10}$ M $_{⊙}$ , including the extreme ultra diffuse galaxy DF44. As this correlation does not depend on GC mass it is ideally suited for high-precision determinations of M $_{v i r}$ . The linearity is most simply explained by cosmological merging of a high-redshift halo seed population that hosted on average one GC per $5 \times 1 0^{8}$ M $_{⊙}$ of dark matter. We show that hierarchical merging is also extremely powerful in restoring a linear correlation and erasing signatures of even a strong secular evolution of GC systems. The cosmological merging scenario also implies a strong decline of the scatter in $N_{GC}$ with increasing virial mass $I^´ N_{GC} / N_{GC} \sim M_{v i r}^{- 1/2}$ in contrast with the observations that show a roughly constant scatter, independent of virial mass. This discrepancy can be explained if errors in determining virial masses from kinematical tracers and gravitational lensing are on the order of a factor of 2. GCs in dwarf satellite galaxies pose a serious problem for high-redshift GC formation scenarios; the dark halo masses of dwarf galaxies hosting GCs therefore might need to be an order of magnitude larger than currently estimated.

11 pages, 4 figures, ApJ in press