Suppression of star formation in early-type galaxies by feedback from supermassive black holes

Abstract

Detailed high resolution observations of the innermost central parts of nearby galaxies have revealed the presence of supermassive black holes 1-4 . These black holes may interact with 1 their host galaxies by means of 'feedback' in the form of energy and material jets; this feedback affects the evolution of the host and gives rise to the observed relations between the black hole and the host 5 . Here we report observations of the ultraviolet emissions of massive early-type galaxies. We derive an empirical relation for a critical black-hole mass (as a function of velocity dispersion) above which the outflows from these black holes suppress star formation in their hosts by heating and expelling all available cold gas. Supermassive black holes are negligible in mass compared to their hosts but nevertheless seem to play a critical role in the star formation history of galaxies.The near-UV (NUV) detector of the Galaxy Evolution Explorer satellite GALEX 6 covers a range in wavelength between 1771 and 2831Å and is extremely sensitive to young stellar populations. With it, we can detect small mass fractions of 1-3% of young stars formed within the last billion years 7, 8 . This high sensitivity allows us to trace ongoing residual star formation in present day early-type galaxies (ETGs). We select a volume-limited sample of visually inspected ETGs from the Sloan Digital Sky Survey 9 that have been observed by GALEX. We remove active galactic nucleus (AGN) candidates from our sample to avoid confusion between the observed UV emissions from the AGN and from young stars 1 .We use NUV − r colour as a probe of small amounts of recent star formation (RSF) and find that the fraction of ETGs that show signs of RSF is strongly correlated with the stellar velocity dispersion σ, (hereafter "RSF-σ relation"), but not with the luminosity of the galaxy (see Figure 1). The correlation with σ cannot be explained by a systematic trend of σ with internal extinction, 2 because such a trend would be exact opposite 11 to that observed.We use a semi-analytic model of galaxy evolution in the ΛCDM paradigm to interpret these results 2, 3, 14 (for model details see Supplements). Our simulation includes all the systematic processes that affect galaxy evolution and takes into account the different merger and star formation histories of galaxies 15 . When we run this simulation and investigate the predicted amount of recent star formation in low redshift ETGs, we find that all galaxies underwent enough star formation within the last billion years to be detected by the extremely sensitive GALEX NUV detector. Massive galaxies continued to gain cold gas as fuel for star formation from mergers with satellites and through the cooling of hot gas present in those galaxies.This overproduction of stars in massive galaxies is a known problem in models of galaxy evolution. In order to prevent star formation, a shutdown mechanism is required: cold gas must be heated up and expelled to prevent it from turning into stars. Feedback from supernovae (SNe) was o...

Destruction of Molecular Gas Reservoirs in Early-Type Galaxies by Active Galactic Nucleus Feedback

“…The low-and intermediate-mass galaxies studied in our undergo very minor episodes of star formation and thus allow us to study this suppression process. Apparently, the AGN in this lower mass range is not powerful enough to inhibit residual star formation completely (see also Schawinski et al 2006). As shown in Figure 4, however, without the energy input from AGNs, those episodes of star formation would be more significant and would drive the objects even further away from the red sequence.…”

“…As new molecular gas is continuously supplied by accretion, mergers, and stellar mass loss, most current models of galaxy formation suppress residual star formation by invoking a phase of accretion onto the supermassive black hole at the center of the galaxy (Silk & Rees 1998;Cattaneo et al 2005;Schawinski et al 2006;Croton et al 2006) as the energy liberated by corecollapse supernovae is insufficient (Dekel & Silk 1986;Benson et al 2003). The resulting active galactic nucleus (AGN) phase includes jets, radiation and outflows liberating sufficient energy to destroy the molecular gas reservoir by heating and expelling it, thus suppressing star formation by depriving the host galaxy of its fuel.…”

“…The red population is dominated by elliptical and lenticular (early-type) galaxies, and in order to explain the properties of these systems as we observe them, almost all residual star formation in them must be suppressed. This suppression must take place via the heating or expulsion of the molecular gas which is the fuel for star formation (Dekel & Silk 1986;Benson et al 2003) and is thought to be driven by the energy input from accreting supermassive black holes at the galaxies' centers in a process called active galactic nucleus (AGN) feedback (Silk & Rees 1998;Benson et al 2003;Di Matteo et al 2005;Cattaneo et al 2005;Kawata & Gibson 2005;Schawinski et al 2006;Kaviraj et al 2007a;Khalatyan et al 2008).…”

Truncated Star Formation in Compact Groups of Galaxies: A Stellar Population Study

“…From this new perspective, the failure of HCGs to display traces of ongoing or recent SF does not seem so disappointing. Observational evidence of SF suppression by active galactic nuclei (AGNs) feedback has been presented by Schawinski et al (2006).…”

The Nuclear Activities of Nearby S0 Galaxies

“…This percentage can be even as high as 30% by using near-ultraviolet data from GALEX (Kaviraj et al 2007). Recent studies indicate that the fraction of star-forming early-type galaxies depends on observational wavelengths and galaxy masses (Schawinski et al 2006(Schawinski et al , 2007. Constantin & Vogeley (2006) showed that low-ionization nuclear emission-line regions (LINERs) appear to be even more popular in S0 galaxies (Magliocchetti et al 1999(Magliocchetti et al , 2004Overzier et al 2003).…”