Dr Adriano Poci

Abstract:

We study trends in the slope of the total mass profiles and dark matter fractions within the central half-light radius of 258 early-type galaxies, using data from the volume-limited ATLAS3D survey. We use three distinct sets of dynamical models, which vary in their assumptions and also allow for spatial variations in the stellar mass-to-light ratio, to test the robustness of our results. We confirm that the slopes of the total mass profiles are approximately isothermal, and investigate how the total mass slope depends on various galactic properties. The most statistically significant correlations we find are a function of either surface density, Σe, or velocity dispersion, σe. However there is evidence for a break in the latter relation, with a nearly universal logarithmic slope above log10[σe/(km s−1)] ∼ 2.1 and a steeper trend below this value. For the 142 galaxies above that critical σe value, the total mass–density logarithmic slopes have a mean value 〈γ΄〉 = −2.193 ± 0.016 (1σ error) with an observed rms scatter of only σγ′=0.168±0.015. Considering the observational errors, we estimate an intrinsic scatter of σγ′intr≈0.15. These values are broadly consistent with those found by strong lensing studies at similar radii and agree, within the tight errors, with values recently found at much larger radii via stellar dynamics or H I rotation curves (using significantly smaller samples than this work).

Abstract:

Integral field unit spectrographs allow the 2D exploration of the kinematics and stellar populations of galaxies, although they are generally restricted to small fields-of-view. Using the large field-of-view of the DEIMOS multislit spectrograph on Keck and our Stellar Kinematics using Multiple Slits (SKiMS) technique, we are able to extract sky-subtracted stellar light spectra to large galactocentric radii. Here we present a new DEIMOS mask design named SuperSKiMS that explores large spatial scales without sacrificing high spatial sampling. We simulate a set of observations with such a mask design on the nearby galaxy NGC 1023, showing that the kinematic and metallicity measurements can reach radii where the galaxy surface brightness is several orders of magnitude fainter than the sky. Such a technique is also able to reproduce the kinematic and metallicity 2D distributions obtained from literature integral field spectroscopy in the innermost galaxy regions. In particular, we use the simulated NGC 1023 kinematics to model its total mass distribution to large radii, obtaining comparable results with those from published integral field unit observation. Finally, from new spectra of NGC 1023 we obtain stellar 2D kinematics and metallicity distributions that show good agreement with integral field spectroscopy results in the overlapping regions. In particular, we do not find a significant offset between our SKiMS and the ATLAS 3D stellar velocity dispersion at the same spatial locations.