Integral-field kinematics and stellar populations of early-type galaxies out to three half-light radii

Abstract

We observed twelve nearby H i-detected early-type galaxies (ETGs) of stellar mass ∼ 10 10 M M * ∼ 10 11 M with the Mitchell Integral-Field Spectrograph, reaching approximately three half-light radii in most cases. We extracted line-of-sight velocity distributions for the stellar and gaseous components. We find little evidence of transitions in the stellar kinematics of the galaxies in our sample beyond the central effective radius, with centrally fast-rotating galaxies remaining fast-rotating and centrally slow-rotating galaxies likewise remaining slow-rotating. This is consistent with these galaxies having not experienced late dry major mergers; however, several of our objects have ionised gas that is misaligned with respect to their stars, suggesting some kind of past interaction. We extract Lick index measurements of the commonly-used Hβ, Fe5015, Mg b, Fe5270 and Fe5335 absorption features, and we find most galaxies to have flat Hβ gradients and negative Mg b gradients. We measure gradients of age, metallicity and abundance ratio for our galaxies using spectral fitting, and for the majority of our galaxies find negative age and metallicity gradients. We also find the stellar mass-to-light ratios to decrease with radius for most of the galaxies in our sample. Our results are consistent with a view in which intermediate-mass ETGs experience mostly quiet evolutionary histories, but in which many have experienced some kind of gaseous interaction in recent times.

The SAMI galaxy survey: stellar population radial gradients in early-type galaxies

“…However, this trend disappears at larger radii (∼1-1.5 Re), suggesting a complex contribution of stellar populations in the outer regions, as they are formed ex-situ from a range of merging satellites. Boardman et al (2017) found that the kinematics in a sample of 12 ETGs, detected in HI, did not show any variations out to three effective radii, supporting the idea that these galaxies have not undergone dry major merging at late times. However, the IFU data revealed substantial population gradients consistent with some level of interaction in recent times.…”

The SAMI Galaxy Survey: embedded discs and radial trends in outer dynamical support across the Hubble sequence

“…Using the SAURON spectrograph, Weijmans et al (2009) confirmed the decreasing rotational support of the lenticular galaxy (S0) NGC 821 at large radii. However, Raskutti et al (2014) and Boardman et al (2017) did not find significant kinematic transitions in a sample of galaxies observed with the Mitchell Spectrograph. This discrepancy was attributed to differences in the sample selection of the respective studies.…”

“…Emsellem et al 2007;Cappellari et al 2011) and been unable to probe this transition. Notable progress has been achieved using the wide-field Mitchell Spectrograph (Raskutti et al 2014;Boardman et al 2017) and the use of wide-field multiple slit spectrographs as "proxy" IFUs (e.g. Proctor et al 2009;Arnold et al 2011).…”

Optical spectroscopy of local type-1 AGN LINERs

“…The 2D gas kinematics is disc dominated by disc rotation, classified as a near-oblate, face-on fast rotator by Boardman et al (2016). Some anisotropies and signs of warps are found at large galactocentric distance likely related to a past interaction (Boardman et al 2017). The disc kinematics is not fully captured by our ground-based spectroscopy likely due to the slit orientation with respect to the major axis (Fig.…”