2 research outputs found
The role of quasars in galaxy formation
We discuss evidence that quasars, and more generally radio jets, may have
played an active role in the formation stage of galaxies by inducing star
formation, i.e. through positive feedback. This mechanism first proposed in the
70's has been considered as anecdotic until now, contrary to the opposite
effect that is generally put forward, the quenching of star formation in
massive galaxies to explain the galaxy bimodality, downsizing and the universal
black hole mass over bulge stellar mass ratio. This suggestion is based on the
recent discovery of an ultra-luminous infrared galaxies, i.e. an extreme
starburst, which appears to be triggered by a radio jet from the QSO
HE0450-2958 at z=0.2863, together with the finding in several systems of an
offset between molecular gas and quasars, which may be explained by the
positive feedback effect of radio jets on their local environment.Comment: Invited talk, to appear in the Proceedings of the IAU Symposium 267,
"Co-Evolution of Central Black Holes and Galaxies", B.M. Peterson, R.S.
Somerville, T. Storchi-Bergmann, eds., in press (8 pages, 3 figures
Quasar induced galaxy formation: a new paradigm ?
We discuss observational evidence that quasars play a key role in the
formation of galaxies starting from the detailed study of the quasar
HE0450-2958 and extending the discussion to a series of converging evidence
that radio jets may trigger galaxy formation. The direct detection with VISIR
at the ESO-VLT of the 7 kpc distant companion galaxy of HE0450-2958 allows us
to spatially separate the sites of quasar and star formation activity in this
composite system made of two ultra-luminous infrared galaxies (ULIRGs). No host
galaxy has yet been detected for this quasar, but the companion galaxy stellar
mass would bring HE0450-2958 in the local M(BH)-M(stellar bulge) relation if it
were to merge with the QSO. This is bound to happen because of their close
distance (7 kpc) and small relative velocity (~60-200 km/s). We conclude that
we may be witnessing the building of the M(BH)-M(stellar bulge) relation, or at
least of a major event in that process. The star formation rate (~340 Msun/yr),
age (40-200 Myr) and stellar mass ([5-6]x10^10 Msun) are consistent with
jet-induced formation of the companion galaxy. We suggest that HE0450-2958 may
be fueled in fresh material by cold gas accretion from intergalactic filaments.
We map the projected galaxy density surrounding the QSO as a potential tracer
of intergalactic filaments and discuss a putative detection. Comparison to
other systems suggests that inside-out formation of quasar host galaxies and
jet-induced galaxy formation may be a common process. Two tests are proposed
for this new paradigm: (1) the detection of offset molecular gas or dust
emission with respect to the position of distant QSOs, (2) the delayed
formation of host galaxies as a result of QSO activity, hence the two step
building of the M(BH)/M(stellar bulge) ratio.Comment: 15 pages, 8 figures, accepted for publication in Astronomy and
Astrophysics (with minor corrections