The SLUGGS Survey: A New Mask Design to Reconstruct the Stellar Populations and Kinematics of Both Inner and Outer Galaxy Regions

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.

The SLUGGS survey: a comparison of total-mass profiles of early-type galaxies from observations and cosmological simulations, to ∼4 effective radii

“…A suggested cause of the σ offset is the binning in the edges of the ATLAS 3D data (Pastorello et al 2016;van de Sande et al 2017), resulting in augmented velocity dispersion values. If this is the case, then the offset would be greatest in the outer regions of the ATLAS 3D data, coincident with the radial range over which the offset is measured.…”

“…For these galaxies, the data were collected in broadly the same manner as for the main SLUGGS survey, using central slits to collect stellar light out to 2-3 effective radii (Re), and additional slits in the galaxy outskirts to collect spectra for globular clusters (a catalogue of SLUGGS globular clusters was published by Forbes et al 2017a). To maximise the central slits focussing on stellar light, we utilise the SuperSKiMS method outlined by Pastorello et al (2016). We do not use the globular cluster spectra in this paper, as an adaptation of the JAM method to discrete tracers is beyond the scope of this work.…”

The SLUGGS survey: using extended stellar kinematics to disentangle the formation histories of low-mass S0 galaxies

“…We also present the first complete data taken using the SuperSKiMS 3 technique of Pastorello et al (2016) for the galaxy NGC 2549. This technique maximises slits across the central part of the galaxy in order to increase the sampling density of galaxy stellar light out to large radii.…”

“…We draw the reader's attention to the structural difference in the distribution of data points for NGC 2549 (Figure 2), where we have more thorough spatial sampling along the major axis. This is due to the application of the new Su-perSKiMS mask design (Pastorello et al 2016). In the mean velocity map for NGC 2549 (Figure 2), we identify a thinner rotational component in the central Re (whereas typical rotating features increase in projected width with radius, this feature maintains a constant narrow width for ∼ 20 along the major axis) than in the outer regions of the galaxy.…”

“…Potential sources of this offset were discussed by Foster et al, but no firm conclusions were reached. Pastorello et al (2016) compared SLUGGS measurements of individual slits to ATLAS 3D measurements in overlapping regions for the galaxy NGC 1023, and found that the σ offset is larger in the outer regions, where σ is lower. Since the binning is larger in ATLAS 3D points in the outer regions of the galaxy, this suggests that the binning might be responsible for the offset.…”