Issue |
A&A
Volume 401, Number 1, April I 2003
|
|
---|---|---|
Page(s) | 113 - 127 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20021752 | |
Published online | 17 March 2003 |
The shroud around the twin radio jets in NGC 1052
1
Netherlands Foundation for Research in Astronomy, PO Box 2, 7990 AA Dwingeloo, The Netherlands
2
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
3
National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA
4
California Institute of Technology, Pasadena, CA 91125, USA
5
Joint Institute for VLBI in Europe, PO Box 2, 7990 AA Dwingeloo, The Netherlands
Corresponding author: R. C. Vermeulen, rvermeulen@astron.nl
Received:
7
August
2002
Accepted:
25
November
2002
We discuss multiple Very Long Baseline Interferometry (VLBI)
continuum and spectral line imaging observations and Westerbork
Synthesis Radio Telescope spectroscopy of the compact variable
nuclear radio jet source in the elliptical galaxy NGC 1052.
Absorption and emission signatures reveal ionised, atomic, and
molecular components of the surrounding medium.
Ten epochs of Very Long Baseline Array (VLBA) data at 15 GHz,
spanning almost six years, show bi-symmetric jets, in which multiple
sub-parsec scale features display outward motions of typically
(
km s-1 Mpc-1) on
each side. The jets are most likely oriented near the plane of the
sky.
Multi-frequency VLBA observations at seven frequencies between 43 and
1.4 GHz show free-free absorption in the inner parsec around the
nucleus, probably together with synchrotron self-absorption. The
free-free absorption is apparently due to a structure which is
geometrically thick and oriented roughly orthogonal to the jets, but
which is patchy. The western jet is covered more deeply and
extensively, and hence is receding.
Hi spectral line VLBI observations reveal atomic gas in front
of the approaching as well as the receding jet. There appear to be
three velocity systems. Broad, shallow absorption asymmetrically
straddles the systemic velocity spanning -35 to
85 km s-1. This gas could be local to the AGN environment, or
distributed on galactic scales. Superimposed in the range 25 to
95 km s-1 are several sharper (3–15 km s-1) features,
each detectable over a few tenths of a pc at various places along the
inner 2 pc of the approaching jet. The third, deepest system is at
“high velocities", which is receding by 125 to 200 km s-1
with respect to the systemic velocity of NGC 1052. It may
have a continuous velocity gradient across the nucleus of some
10 km s-1 pc-1. This atomic gas seems restricted to a
shell 1–2 pc away from the core, within which it might be largely
ionised.
Westerbork Synthesis Radio Telescope spectroscopy has revealed the
18 cm OH main lines (1667 and 1665 MHz) in absorption along the
full velocity span of -35 to 200 km s-1, with their line
ratio varying roughly from 1:1 to 2:1. They are deepest in the high
velocity system, where the OH profiles are similar to Hi,
suggesting co-location of that atomic and molecular gas, and leaving
unclear the connection to the H2O masing gas seen elsewhere. In
the high velocity system we have also detected the 18 cm OH
satellite lines: 1612 MHz in absorption, and 1720 MHz in
emission. The conjugate behaviour of the satellite line profiles, and
the variable main line ratio resemble the situation in Cen A
and NGC 253.
Key words: galaxies: active / galaxies: jets / galaxies: nuclei / galaxies: individual: NGC 1052 / radio lines: galaxies
© ESO, 2003
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