The SAMI Galaxy Survey: stellar and gas misalignments and the origin of gas in nearby galaxies

Abstract

Misalignment of gas and stellar rotation in galaxies can give clues to the origin and processing of accreted gas. Integral field spectroscopic observations of 1213 galaxies from the SAMI Galaxy Survey show that 11% of galaxies with fitted gas and stellar rotation are misaligned by more than 30 • in both field/group and cluster environments. Using SAMI morphological classifications and Sérsic indices, the misalignment fraction is 45 ± 6% in early-type galaxies, but only 5 ± 1% in late-type galaxies. The distribution of position angle offsets is used to test the physical drivers of this difference. Slower dynamical settling time of the gas in elliptical stellar mass distributions accounts for a small increase in misalignment in early-type galaxies. However, gravitational dynamical settling time is insufficient to fully explain the observed differences between early-and late-type galaxies in the distributions of the gas/stellar position angle offsets. LTGs have primarily accreted gas close to aligned rather than settled from misaligned based on analysis of the skewed distribution of PA offsets compared to a dynamical settling model. Local environment density is less important in setting the misalignment fractions than morphology, suggesting that mergers are not the main source of accreted gas in these disks. Cluster environments are found to have gas misalignment driven primarily by cluster processes not by gas accretion.

Decoupling the rotation of stars and gas – I. The relationship with morphology and halo spin

“…These results are reasonably consistent with previous findings of 36±5% (of 260 galaxies) of ETGs that are misaligned in ATLAS 3D and in SAMI (45±6% of 36 pure ellipticals, 5±1% in 221 pure late spirals) (Davis et al 2011;Bryant et al 2019). We note that our ETG misalignment fraction (∼28%) is lower than these previous findings and holds a slight tension with Bryant et al (2019). Possible reasons for the differences may be due to morphology definition, stellar mass distribution or simply sample size.…”

“…is chosen for comparison with previous literature (e.g. Davis et al 2011;Bryant et al 2019). Regardless 30 • represents a conservative choice for selecting galaxies with significant decoupling; the reasons for which are twofold.…”

Gas accretion as fuel for residual star formation in Galaxy Zoo elliptical galaxies

“…Various studies have set limits on the relative importance of these mechanisms (e.g. E-mail: DavisT@cardiff.ac.uk Sarzi et al 2006; Thomas et al 2010;Davis et al 2011Davis et al , 2015Davis et al , 2019Lagos et al 2014Lagos et al , 2015Davis & Bureau 2016;Belfiore et al 2017;Bryant et al 2019;Griffith et al 2019), but no definitive conclusions have been reached.…”

“…A significant population of low gas-phase metallicity ellipticals are found well below the mass -metallicity relation. tion of the gas (Sarzi et al 2006, Davis et al 2011, Belfiore et al 2017, Bryant et al 2019, and modelling this in concert with constraints on the large scale environment which can act to suppress external gas accretion (Davis & Bureau 2016;Davis et al 2019; see also Thomas et al 2010). Less attention has been paid to the metallicity distribution of the gas in ETGs.…”

The metallicity and elemental abundance maps of kinematically atypical galaxies for constraining minor merger and accretion histories

“…In most galaxies with large-scale, ordered motion, the stars and gas are co-planar and orbit in the same direction. A significant minority, however, are found to have misaligned gas and stellar kinematics due to the accretion of extra-galactic gas (e.g., Davis et al 2011;Bryant et al 2019). A still smaller fraction host a kinematically distinct core (KDC); a change with radius of the position angle of the kinematic axis in stellar velocity maps (e.g., Bender & Surma 1992;Krajnović et al 2008Krajnović et al , 2011.…”