A simple model for AGN feedback in nearby early-type galaxies
Kaviraj, S and Schawinski, K and Silk, J and Shabala, SS, A simple model for AGN feedback in nearby early-type galaxies, Royal Astronomical Society. Monthly Notices, 415, (4) pp. 3798-3806. ISSN 0035-8711 (2011) [Refereed Article]
This article has been accepted for publication in Royal Astronomical Society. Monthly Notices. Copyright 2011 The Authors, RAS Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Recent work (Schawinski et al.) indicates that star-forming early-type galaxies residing in
the blue cloud migrate rapidly to the red sequence within around a Gyr, passing through
several phases of increasingly strong active galactic nucleus (AGN) activity in the process.
We show that natural depletion of the cold gas reservoir through star formation (i.e. in the
absence of any feedback from the AGN) induces a blue-to-red reddening rate that is several
factors lower than that observed by Schawinski et al. This is because the gas depletion rate
due to star formation alone is too slow, implying that another process needs to be invoked
to remove cold gas from the system and accelerate the reddening rate. We develop a simple
phenomenological model, in which a fraction of the AGN’s luminosity couples to the gas
reservoir over a certain ‘feedback time-scale’ and removes part of the cold gas mass from the
galaxy, while the remaining gas continues to contribute to star formation. We use the model
to investigate scenarios which yield migration times consistent with the results of Schawinski
et al. We find that acceptable models have feedback time-scales 0.2 Gyr. The mass fraction
in young stars in the remnants is 5 per cent and the residual cold gas fractions are less than
0.6 per cent, in good agreement with the recent literature. At least half of the initial cold gas
reservoir is removed as the galaxies evolve from the blue cloud to the red sequence. If we
restrict ourselves to feedback time-scales similar to the typical duty cycles of local AGN (a
few hundred Myr) then a few tenths of a per cent of the luminosity of an early-type Seyfert
(∼1011 L) must couple to the cold gas reservoir in order to produce migration times that are
consistent with the observations.
galaxies: active – galaxies: elliptical and lenticular, cD – galaxies: evolution –