Dynamics of the NGC 4636 globular cluster system

Abstract

We present new radial velocities for 289 globular clusters around NGC 4636, the southernmost giant elliptical galaxy of the Virgo cluster. The data were obtained with FORS2/MXU at the Very Large Telescope. Together with data analysed in an earlier study, we now have a sample of 460 globular cluster velocities out to a radius of 12 arcmin (60 kpc) available -one of the largest of its kind. This new data set also provides a much more complete angular coverage. Moreover, we present new kinematical data of the inner stellar population of NGC 4636. We perform an updated Jeans analysis, using both stellar and GC data, to better constrain the dark halo properties. We find a stellar M/L-ratio of 5.8 in the R-band, higher than expected from single stellar population synthesis. We model the dark halo by cored and cuspy analytical halo profiles and consider different anisotropies for the tracer populations. Properties of NFW halos lie well within the expected range of cosmological simulations. Cored halos give central dark matter densities, which are typical for elliptical galaxies of NGC 4636's luminosity. The surface densities of the dark matter halos are higher than those of spiral galaxies. We compare the predictions of modified Newtonian dynamics with the derived halo properties and find satisfactory agreement. NGC 4636 therefore falls onto the baryonic Tully-Fisher relation for spiral galaxies. The comparison with the X-ray mass profile of Johnson et al. (2009, ApJ, 706, 980) reveals satisfactory agreement only if the abundance gradient of hot plasma has been taken into account. This might indicate a general bias towards higher masses for X-ray based mass profiles in all systems, including galaxy clusters, with strong abundance gradients.

Isolated ellipticals and their globular cluster systems

“…GCSs of elliptical galaxies can have radial extensions of up to hundreds of kpc (e.g., Richtler et al 2011;Schuberth et al 2012). Given the relatively small FOV provided by GMOS at the galaxies' distance (see Col. 10 in Table 1), a control field cannot be taken within the same telescope pointing as in wide-field studies (e.g., Rhode & Zepf 2001;Dirsch et al 2003;Paper I), but has to be selected elsewhere.…”

The SLUGGS survey: multipopulation dynamical modelling of the elliptical galaxy NGC 1407 from stars and globular clusters

“…Moreover, unlike spiral galaxies whose haloes are traced by HI gas (e.g., Oh et al 2011), the outer regions of elliptical galaxies are notoriously hard to observe because they are optically faint. Nevertheless, they can be probed with discrete tracers, such as planetary nebulae (e.g., de Lorenzi et al 2008;Napolitano et al 2009), globular clusters (GCs) (e.g., Schuberth et al 2012), or diffuse tracers, such as hot X-ray gas (e.g., Humphrey et al 2006). Lastly, some mass modelling techniques suffer from the mass-anisotropy degeneracy, driven by the fact that the orbital anisotropy of stellar systems is very hard to infer from the data (Mamon & Łokas 2005).…”

The stability and structure of primordial reservoirs in the lower mantle: insights from models of thermochemical convection in three-dimensional spherical geometry

“…Several lines of evidence from various data sets, including the anticorrelation between bulk-sound and shear wave velocity anomalies (Ishii & Tromp 1999;Masters et al 2000;Trampert et al 2004;Mosca et al 2012), support a thermochemical origin. It was recently suggested that this anticorrelation may result from wave propagation effects (Schuberth et al 2012b), or might be related to the phase change from perovskite to post-perovskite in the lowermost mantle . Because the anticorrelation between V S and V anomalies is also observed by normal mode data (Ishii & Tromp 1999;Trampert et al 2004;Mosca et al 2012), which are not affected by wave propagation effects and further show a correlation between density and seismic velocity anomalies, and because the post-perovskite hypothesis fails to predict large-scale structures, the thermochemical hypothesis appears more likely.…”