On the depletion and accretion time-scales of cold gas in local early-type galaxies. Issue 1 (20th January 2016)

• Record Type: Journal Article
• Authors: Davis, Timothy A.; Bureau, Martin
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 457:Issue 1(2016)
• Page Start: 272
• Page End: 280
• Publication Date: 2016-01-20
• Subjects: ISM: evolution -- ISM: molecules -- galaxies: elliptical and lenticular, cD -- galaxies: evolution -- galaxies: ISM -- galaxies: kinematics and dynamics; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stv2998
• Languages: English
• ISSNs: 0035-8711

Abstract

Abstract: We consider what can be learnt about the processes of gas accretion and depletion from the kinematic misalignment between the cold/warm gas and stars in local early-type galaxies. Using simple analytic arguments and a toy model of the processes involved, we show that the lack of objects with counter-rotating gas reservoirs strongly constrains the relaxation, depletion and accretion time-scales of gas in early-type galaxies. Standard values of the accretion rate, star-formation efficiency and relaxation rate are not simultaneously consistent with the observed distribution of kinematic misalignments. To reproduce that distribution, both fast gas depletion ( t dep ≲ 10 8 yr; e.g. more efficient star formation) and fast gas destruction (e.g. by active galactic nucleus feedback) can be invoked, but both also require a high rate of gas-rich mergers (>1 Gyr −1 ). Alternatively, the relaxation of misaligned material could happen over very long time-scales (≃100 dynamical times or ≈1–5 Gyr). We explore the various physical processes that could lead to fast gas depletion and/or slow gas relaxation, and discuss the prospects of using kinematic misalignments to probe gas-rich accretion processes in the era of large integral-field spectroscopic surveys.