VLBI Observations of
Nearby Radio Loud AGNs
Dipartimento di Astronomia, Bologna University
Istituto di Radioastronomia - INAF
In collaboration with: E. Liuzzo – PhD Bologna Univ. + IRA - INAF
M. Giroletti – IRA - INAF Bologna
G.B. Taylor - UNM Albuquerque USA
The Bologna Complete Sample
B2 and 3CR radio sources with z < 0.1
Being selected at low frequency it is not affected by
observational biases related to orientation effects.
Nearby sources: good linear resolution; high + low power
VLBI data are available for 78/95 sources
(arcsecond core > 5 mJy)
The large scale morphology of observed sources is:
50 FR I
15 FR II
12 compact sources:Bl_Lacs, CSO, CSS, flat spectrum
Two-sided sources on the pc scale are 30 % to be compared with
11% in PR sample and 4.6 % in the Caltech-Jodrell Bank survey
In a random oriented sample the probability that a source is
at an angle between θ1 and θ2 with respect to the line of sight is
P(θ1,θ2) = cos(θ1) – cos(θ2)
the percentage of FR I + FR II is 65/78 = 80% corresponding to
θ > 35o-40o in agreement with unified models.
The percentage of two-sided sources is 30% corresponding to
angles > 70o.
Consistent with a j/cj ratio R ≤ 5 if jet velocity = 0.9 – 0.99c
-All FR II two-sided are NLR.
-Two-sided sources show low power radio cores.
- In most sources there is a good agreement between the pc-kpc
scale jet orientation in agreement with the suggestion that
large distortions seen in BL-Lac and BLAZAR sources are due
to small intrinsic bends amplified by projection effects
-In all sources pc scale jets move at high velocity.
No correlation has been found with core or total radio power
3C192 z = 0.0597 arcsecond core: 8 mJy at 5 GHz
VLBI phase reference mode
Peak: 1.7 mJy/b
noise: 0.05 mJy/b
VLA B+C at 1.4 GHz
LS 200 kpc
3C 452 a NL FR II radio galaxy
0331+39 a low power compact
3C 338 a FR I radio galaxy
Sources with a faint radio core:
more complex structures
-- restarted activity
-- different orientation angle between pc and
-- complex pc scale structure with no dominant core
A statistical problem or we are starting to study
sources with different properties?
Different ambient medium (e.g. galaxy cluster)
Is it important?
VLBI 20 cm
Phase ref. Mode
Peak 24 mJy/b
Noise 0.07 mJy/b
VLBA 6 cm – phase ref. mode
Spectral index image between 6 and 20 cm
3C 310 VLA B+C
Linear size 300 kpc
In agreement with Gizani and
Garrett (2002) 6th EVN Symp.
5 pc Peak flux 1.3 mJy/b
Noise 0.07 mJy/b
Jamrozy et al.
Van Breugel et al. 1986
VLA A+B at 20cm
100Myr 0836+29B 4C29.30
Jamrozy et al. 2007 A galaxy merger
Core – most compact
only flat spectrum component
VLA – A array at 6 cm
Strong outburst after 1990
Jamrozy et al. 2007
• The parsec scale jet morphology is the same in high (FR II) and
low (FR I) power sources
• The pc scale morphology is in agreement with expectations
from unified models
• There is a good agreement between the pc and kpc scale
• The pc scale jet velocity is highly relativistic in FR II and FR I
sources. It is not related to the total or core radio power of the
source. No correlation with the kpc scale structure.
• In some sources with a low power nuclear source we find a
peculiar morphology: restarted activity and a complex mas scale
structure not yet understood, misaligned with the kpc scale
• In a few sources a large symmetric Z shaped distortion occurs.
Since these sources are oriented near to the plane of the sky, the
distortion it is not amplified by projection effect.
It could be due to the jet interaction with a rotating disk (3C 293).
Other possible environmental effects could be at work. In the future
we plan to consider also the host galaxy environment as traced by
X-ray emission, atomic or molecular absorption/emission.