The SAMI Galaxy Survey: kinematics of dusty early-type galaxies

Abstract

Recently, large samples of visually classified early-type galaxies (ETGs) containing dust have been identified using space-based infrared observations with the Herschel Space Telescope. The presence of large quantities of dust in massive ETGs is peculiar as X-ray halos of these galaxies are expected to destroy dust in ∼10 7 yr (or less). This has sparked a debate regarding the origin of the dust: is it internally produced by asymptotic giant branch (AGB) stars, or is it accreted externally through mergers? We examine the 2D stellar and ionised gas kinematics of dusty ETGs using IFS observations from the SAMI galaxy survey, and integrated star-formation rates, stellar masses, and dust masses from the GAMA survey. Only 8% (4/49) of visually-classified ETGs are kinematically consistent with being dispersion-supported systems. These "dispersion-dominated galaxies" exhibit discrepancies between stellar and ionised gas kinematics, either offsets in the kinematic position angle or large differences in the rotational velocity, and are outliers in star-formation rate at a fixed dust mass compared to normal star-forming galaxies. These properties are suggestive of recent merger activity. The remaining ∼90% of dusty ETGs have low velocity dispersions and/or large circular velocities, typical of "rotation-dominated galaxies". These results, along with the general evidence of published works on X-ray emission in ETGs, suggest that they are unlikely to host hot, X-ray gas consistent with their low M * when compared to dispersion-dominated galaxies. This means dust will be long lived and thus these galaxies do not require external scenarios for the origin of their dust content.

Star-forming, rotating spheroidal galaxies in the GAMA and SAMI surveys

“…We find that a similar fraction of our low-mass Es are also rotation dominated. Significant rotation has previously been observed in the stellar kinematics of early-type galaxies and, in particular, appears to be more common for low-mass early types (see e.g., Emsellem et al 2007;Brough et al 2017;van de Sande et al 2017a;Bassett et al 2017). It is also not surprising that Sd-Irr galaxies in this sample are typically found to be rotation dominated.…”

The evolution of the gas fraction of quiescent galaxies modeled as a consequence of their creation rate

“…However, its gas content would likely be substantially different from that of pSB galaxies. In particular, we should expect dry merger remnants to be even more gas-depleted than noninteracting QGs (see, e.g., Bassett et al 2017); while in its present state, our model would assign a higher f gas to them. This is illustrated by the different behavior at > 3 × 10 11 M of tracks with fixed and varying f g,0, f (Fig.…”

Modelling dust rings in early-type galaxies through a sequence of radiative transfer simulations and 2D image fitting

“…Xu, Narayanan, & Walker 2010), although recent integral field spectroscopy results have shown that ETGs do not necessarily require to accrete their dust content from merger events (e.g. Bassett et al 2017). These studies mostly concern large-scale structures, while the cases of inner rings similar to those presented in this paper remain still mysterious.…”