The SLUGGS Survey: stellar kinematics, kinemetry and trends at large radii in 25 early-type galaxies

Abstract

Due to longer dynamical timescales, the outskirts of early-type galaxies retain the footprint of their formation and assembly. Under the popular two-phase galaxy formation scenario, an initial in-situ phase of star formation is followed by minor merging and accretion of ex-situ stars leading to the expectation of observable transitions in the kinematics and stellar populations on large scales. However, observing the faint galactic outskirts is challenging, often leaving the transition unexplored. The large scale, spatially-resolved stellar kinematic data from the SAGES Legacy Unifying Galaxies and GlobularS (SLUGGS) survey are ideal for detecting kinematic transitions. We present kinematic maps out to 2.6 effective radii on average, kinemetry profiles, measurement of kinematic twists and misalignments, and the average outer intrinsic shape of 25 SLUGGS galaxies. We find good overall agreement in the kinematic maps and kinemetry radial profiles with literature. We are able to confirm significant radial modulations in rotational versus pressure support of galaxies with radius so that the central and outer rotational properties may be quite different. We also test the suggestion that galaxies may be more triaxial in their outskirts and find that while fast rotating galaxies were already shown to be axisymmetric in their inner regions, we are unable to rule out triaxiality in their outskirts. We compare our derived outer kinematic information to model predictions from a two-phase galaxy formation scenario. We find that the theoretical range of local outer angular momentum agrees well with our observations, but that radial modulations are much smaller than predicted.

The SLUGGS survey: combining stellar and globular cluster metallicities in the outer regions of early-type galaxies

“…While the former is used to study the GC stellar population properties, the latter includes light from both the galaxy's stars and the night sky. Adopting the "Stellar Kinematics with Multiple Slits" (SKiMS) technique (Norris et al 2008;Proctor et al 2009;Foster et al 2009;Pastorello et al 2014;Arnold et al 2014;Foster et al 2015), it is possible to separate the two components in the background spectra and obtain an individual spectrum of the GC and the galaxy starlight at each slit location.…”

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

“…Foster et al 2013;Arnold et al 2014;Pastorello et al 2014). In particular, Foster et al (2015) obtained SKiMS kinematic measurements out to 5 R e (2.6 R e on average) and Pastorello et al (2014) metallicity measurements out to about 3 R e . The original SKiMS method was developed to extract the background galaxy stellar light spectra from the same DEIMOS slits that were primarily targeting globular cluster (GC) candidates.…”

“…7 masks). We do not compare our kinematic maps with those presented in Foster et al (2015), since the latter are based on a largely overlapping dataset, except for the very inner regions. In fact, they do not measure the stellar kinematics for R < 10 arcsec, and their kriging values at such radii are extrapolated from outer region measurements.…”

“…In order to compare with these two literature works, we extract virtual slits with similar P As and widths from both the ATLAS 3D and our kriged 2D maps. Finally, we update several results from Foster et al (2015) and Pastorello et al (2014) with the addition of the newly obtained SuperSKiMS data.…”

Planetary nebulae as kinematic tracers of galaxy stellar halos

“…The most outstanding example is given by E6 galaxy NGC 821 (Figure 2). Its PNe system ) shows a rotation axis which is ∼ 100 • misaligned from that of the stars (Proctor et al 2009;Foster et al 2016). These exceptions and, more in general, the differences between the kinematics obtained from different tracers, are seen as an indication of recent satellite accretion in the halos Foster et al 2014;Romanowsky et al 2014;Longobardi et al 2015).…”