Growing black holes: from the first seeds to active galactic nuclei
Mar Mezcua
Université de Montréal
How supermassive black holes form and grow is still one of the
long-standing questions in astronomy. Supermassive black holes of up to
10^9 solar masses already existed when the Universe was less than ~1 Gyr
old. To reach this mass in such a short time, they should have started as
seed intermediate-mass black holes (IMBHs) of 100-10^6 solar masses and
grow very fast via accretion and mergers. Such IMBHs are the missing link
between stellar and supermassive black holes and they should be present
in the nucleus of low-mass galaxies and in the halos of large galaxies,
e.g. in the form of ultraluminous X-ray sources (ULXs).
In this talk I will present observational evidence that a population of
IMBHs in dwarf galaxies similar to those seed black holes populating the
early Universe exists. With the use of large, deep, multiwavelength surveys
like COSMOS, these sources are detected up to z~4. I will also show that,
in the local Universe, IMBHs can be additionally detected as extreme ULXs
with powerful radio emission in galaxies having undergone a minor merger
event. The later supermassive black hole growth can be explained by the
accretion of gas coming from galactic scales. At kpc scales, this gas
can be transported to the nuclear regions through galaxy mergers, which
can trigger active galactic nuclei (AGN) activity and can be detected in
the form of binary AGN. At scales of a few 100 pc, dust lanes can be the
channels of inflow of material from the outer parts of the galaxy to the
nuclear region, as evidenced by the finding that the spiral structure of
the nuclear cold molecular gas traced by ALMA observations correlates with
that of the dust. The nuclear dust lanes are in addition able to obscure
the nucleus of low-luminosity AGN and to explain the collimation of the
ionised gas, which questions the role of the dusty torus proposed by the
Unified Model of AGN.
Date: | Mardi, le 12 janvier 2016 |
Heure: | 15:30 |
Lieu: | Université McGill |
| Ernest Rutherford Physics Building, R.E. Bell Conference Room (room 103) |
Contact: | Robert Rutledge |
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