Issue |
A&A
Volume 453, Number 1, July I 2006
|
|
---|---|---|
Page(s) | 27 - 37 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20054490 | |
Published online | 09 June 2006 |
The host galaxy/AGN connection in nearby early-type galaxies
A new view of the origin of the radio-quiet/radio-loud dichotomy?
1
INAF – Osservatorio Astronomico di Torino, Strada Osservatorio 20, 10025 Pino Torinese, Italy e-mail: capetti@to.astro.it
2
Universitá di Torino, via Giuria 1, 10125, Torino, Italy e-mail: balmaverde@ph.unito.it
Received:
7
November
2005
Accepted:
2
February
2006
This is the third in a series of three papers exploring the
connection between the multiwavelength
properties of AGN in nearby early-type galaxies
and the characteristics of their hosts.
Starting from an initial sample of 332 galaxies,
we selected 116 AGN candidates requiring the detection
of a radio source with a flux limit of ~1 mJy,
as measured from 5 GHz VLA observations.
In Paper I
we classified the objects with available archival HST images into
“core” and “power-law” galaxies,
discriminating on the basis of the nuclear slope of their brightness
profiles. We used HST and Chandra data to isolate the nuclear
emission of these galaxies in the optical and X-ray bands,
thus enabling us (once combined with the radio data) to study the
multiwavelength behaviour of their nuclei.
The properties of the nuclei hosted by the
29 core galaxies were presented in Paper II
Core galaxies invariably host a radio-loud nucleus,
with a median radio-loudness of Log and
an X-ray based radio-loudness parameter of Log
.
Here we discuss the properties of the nuclei of the 22 “power-law” galaxies.
They show a substantial excess of optical and X-ray emission
with respect to core galaxies at the same level of radio luminosity.
Conversely, their radio-loudness parameters, Log
and
Log
, are similar to those measured
in Seyfert galaxies. Thus the radio-loudness
of AGN hosted by early-type galaxies appears to be univocally
related to the host's brightness profile: radio-loud AGN are
only hosted by core galaxies, while radio-quiet AGN are found only
in power-law galaxies.
The brightness profile is determined by the galaxy's evolution,
through its merger history; our results suggest that the same
process sets the AGN flavour. In this scenario,
the black holes hosted by the merging galaxies
rapidly sink toward the centre of the newly formed object,
setting its nuclear configuration, described by e.g.
the total mass, spin, mass ratio, or separation of the SMBHs.
These parameters
are most likely at the origin of the different levels of
the AGN radio-loudness.
This connection might open
a new path toward understanding the origin of the
radio-loud/radio-quiet AGN dichotomy and
provide us with a further tool
for exploring the co-evolution of galaxies and supermassive black
holes.
Key words: galaxies: active / galaxies: bulges / galaxies: nuclei / galaxies: elliptical and lenticular, cD / galaxies: structure
© ESO, 2006
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