The Next Generation Virgo Cluster Survey Xvi: The Angular Momentum of Dwarf Early-Type Galaxies From Globular Cluster Satellites

Abstract

We analyze the kinematics of six Virgo cluster dwarf early-type galaxies (dEs) from their globular cluster (GC) systems. We present new Keck/DEIMOS spectroscopy for three of them and re-analyze the data found in the literature for the remaining three. We use two independent methods to estimate the rotation amplitude (V rot ) and velocity dispersion (σ GC ) of the GC systems and evaluate their statistical significance by simulating non-rotating GC systems with the same number of GC satellites and velocity uncertainties. Our measured kinematics agree with the published values for the three galaxies from the literature and, in all cases, some rotation is measured. However, our simulations show that the null hypothesis of being non-rotating GC systems cannot be ruled out. In the case of VCC1861, the measured V rot and the simulations indicate that it is not rotating. In the case of VCC1528, the null hypothesis can be marginally ruled out, and thus it might be rotating although further confirmation is needed. In our analysis, we find that, in general, the measured V rot tends to be overestimated and the measured σ GC tends to be underestimated by amounts that depend on the intrinsic V rot /σ GC , the number of observed GCs (N GC ), and the velocity uncertainties. The bias is negligible when N GC  20. In those cases where a large N GC is not available, it is imperative to obtain data with small velocity uncertainties. For instance, errors of 2 km s −1 lead to V rot < 10 km s −1 for a system that is intrinsically not rotating.

Dark Matter in Ultra-diffuse Galaxies in the Virgo Cluster from Their Globular Cluster Populations

“…Criteria Line-of-sight radial velocities are measured following the same steps as described in Toloba et al (2016a). In short, we feed the penalized pixel-fitting software (pPXF; Cappellari & Emsellem 2004) with 17 high signal-to-noise (100 < S/N < 800Å −1 ) stellar templates observed with the same instrumental setup as the science data.…”

“…The lower panels of Figure 3 show the measured velocity gradient for VLSB−D. We use our simulations presented in Toloba et al (2016a) to address the reliability of this velocity gradient given the low number statistics. These simulations show that for samples smaller than 10 GCs and velocity uncertainties δv 10 km s −1 (or 15 − 30% relative velocity uncertainties for low-mass galaxies with V rot /σ = 0 − −2), the velocity gradient measured for a galaxy that is not rotating and for a galaxy rotating with V rot /σ ∼ 1 is undistinguishable.…”

HALO7D I. The Line-of-sight Velocities of Distant Main-sequence Stars in the Milky Way Halo

“…Our templates consist of bright velocity standards that were observed with a very similar configuration to our science spectra. The templates used in this analysis are described in detail by Toloba et al (2016); they have high signal-to-noise ratios (100-800Å −1 ), and span a range of spectral types (from B1 to M8) and luminosity classes (from dwarfs to supergiants).…”

Gemini/GMOS Spectroscopy of Globular Clusters in the Merger Remnant Galaxy M85

“…We caution, however, that the kinematics of these GC subpopulations can be biased toward showing rotational support due to small number statistics. Toloba et al (2016) investigated the kinematics of the GC system in six Virgo early-type dwarf galaxies. They performed simulations to explore the effects of sample size on the kinematic analysis and found that the rotation amplitudes could be overestimated if the number of sample GCs is smaller than 20.…”