Evolution of radio-loud young compact AGNs
Magdalena Kunert-Bajraszewska1
Andrzej Marecki1
Ralph E. Spencer2
Toruń Centre for Astronomy, N. Copernicus University, Toruń, Poland
2
Jodrell Bank Observatory, University of Manchester, UK
1
Abstract
The VLBA+Effelsberg 1.6 GHz observations were made in order to study the morphology
and evolution of radio-loud compact steep spectrum AGNs selected from the VLA FIRST
catalogue. It is possible that some young sources are short-lived phenomena due to a lack
of stable fuelling from the black hole.
Table 1: Basic parameters of 6 CSS sources observed with VLBA
Total flux at Total flux at
GHz
1.4 GHz
4.85 GHz 14..485GHz
mJy
mJy
Sorce
name
RA
hms
DEC
º ′ ″
ID
z
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
0809+404
0949+287
1159+395
1315+396
1502+291
1616+366
08 12 53.124
09 52 06.091
12 01 49.965
13 17 18.635
15 04 26.696
16 18 23.581
0.551
—
2.370
1.560
—
—
1068
1354
603
615
567
536
392
529
249
227
261
268
-0.81
-0.76
-0.71
-0.80
-0.63
-0.56
40 18 59.878 G
28 28 32.406 —
39 19 11.023 G
39 25 28.141 G
28 54 30.548 —
36 32 01.811 —
LAS
mas
LLS
pc h-1
(9)
(10)
14.87 76.27
308.8
—
41.08 224.06
30.00 177.72
41.60
—
55.00
—
(1) – Source name in the IAU format;
(7) – Total flux density at 4.85 GHz extracted from GB6;
(2), (3) – Source coordinates (J2000);
(8) – Spectral index (S~ vα) computed between 1.4 and 4.85 GHz;
(4) – Optical identification:G-galaxy, Q-quasar;
(9) – Largest Angular Size (LAS) from the present paper;
(5) – redshift;
(10) – Largest Linear Size (LLS), adopted cosmological parameters are
(6) – Total flux density at 1.4 GHz extracted from FIRST;
q0=0.5 and H0=72 km s-1 Mpc-1 (Freedman et al., 2001).
Introduction
Readhead et al. (1996) proposed an evolutionary scheme for radio-loud AGNs, which has
been discussed recently in detail by Snellen et al. (1999, 2000). In particular they
concluded that the radio luminosity of GPS/CSO (Gigahertz-Peaked Spectrum/Compact
Symmetric Objects) objects increases as they evolve, reaches its maximum for CSS /MSO
(Compact Steep Spectrum/Medium-sized Symmetric Objects) phase and then gradually
decreases as these objects grow further to become LSOs (Large Symmetric Objects).
What seems quite natural to us now is to claim that this evolutionary track is not
necessarily the only one. We think that the choice of a particular evolutionary track
depends on the duration of the activity period of the host galaxy.
A complete evolutionary track of a radio-loud AGN looks as follows:
ignition of activity  GPS/CSO  CSS/MSO  FRII  FRI
 decline of activity
 quiescence.
But if the energy supply cuts off earlier, the evolutionary track will shrink to:
ignition of activity  GPS/CSO  CSS/MSO
 decline of activity  quiescence
or even to:
ignition of activity  GPS/CSO  decline of activity
 quiescence.
This claim can be firmly underpinned with the theory of SMBH accretion disc instabilities
– Hatziminaoglou et al. 2001. According to them the SMBH determines the length of the
activity phase of the AGN as well as the timescale of the activity re-occurrence.
Observations
Using the VLA FIRST catalogue we selected a new sample of candidates for weak CSS
sources and surveyed them with MERLIN at C-band. Among the observed sources we
distinguished a group of sources with angular sizes < 0.2 arcsec and steep spectra in a
very strict sense i.e. they are not (Gigahertz-Peaked sources) that remained unresolved or
barely resolved with MERLIN. We observed them with VLBA supplemented with the
Effelsberg 100-m telescope at 1.6 GHz in a snapshot mode. We were looking for
symmetric, double structures with evidence of weak or non-existent hotspots within the
diffuse lobes and with weak cores thereby suggesting that the central energy source has
turned off.
Table 2: Flux densities of sources principal components at observed frequencies
Source name
RA
DEC
S1.6 GHz
θ1
θ2
PA
hms
º ′ ″
mJy
″
″
º
(1)
(2)
(3)
(4)
(5)
(6)
(7)
0809+404
08 12 53.123
08 12 53.124
08 12 53.126
09 52 06.102
09 52 06.79
09 52 06.082
12 01 49.964
12 01 49.965
12 01 49.965
13 17 18.635
15 04 26.697
15 04 26.696
15 04 26.698
16 18 23.581
16 18 23.580
40 18 59.880
40 18 59.871
40 18 59.851
28 28 32.400
28 28 32.415
28 28 32.421
39 19 11.041
39 19 11.003
39 19 11.028
39 25 28.142
28 54 30.554
28 54 30.545
28 54 30.582
36 32 01.813
36 32 01.802
155.45
154.29
—
154.97
353.40
55.00
257.01
154.44
—
244.81
115.45
207.66
27.58
68.08
—
0.018
0.021
—
0.013
0.040
0.016
0.009
0.008
—
0.005
0.005
0.002
0.011
0.014
—
0.011
0.012
—
0.007
0.018
0.010
0.003
0.004
—
0.001
0.003
0.001
0.004
0.003
—
142
148
—
83
98
63
172
170
—
106
29
99
49
46
—
0949+287
1159+395
1315+396
1502+291
1616+366
(1) – Source name in IAU format;
(6) – Deconvolved minor component angular size at 1.6 GHz obtained by JMFIT;
(2), (3) – Components coordinates (J2000) as measured at 1.6 GHz;
(7) – Deconvolved major axis position angle at 1.6 GHz obtained by JMFIT.
(4) – VLBA flux density at 1.6 GHz;
(5) – Deconvolved major component angular size at 1.6 GHz obtained by JMFIT;
Conclusions and future plans
We present here the results of VLBA+Effelsberg observations of the most compact
sources in our parent MERLIN sample.
· At least 2 of the observed sources (0809+404, 0949+287) seem to fit to the picture of
‘dying’ radio sources. Two sources (1315+396, 1616+366) still remain unresolved
with VLBA+Effelsberg.
· 0809+404 and 0949+287 have symmetric double structures and the two visible
components are most likely the radio lobes. It is possible that we can see hotspots in
the radio lobes of 0949+287. These two sources are our candidates for ‘dying’ CSS
objects.
· 1159+395 is another double source and we identify it as a GPS/CSO because of its
high redshift.
· 1502+291 shows a core-jet structure directed to the north-east, so it is not a dying
source.
The sources presented here have just been observed with the VLBA at higher frequencies
(5, 8.4 and 15 GHz) to exclude the existence of compact , flat spectrum components in the
structures of our candidates for dying sources and to discern the radio morphology of
those unresolved ones.
References
Freedman W.L., Madore B.F., Gibson B.K., et al. 2001, ApJ, 553, 47
Hatziminaoglou E., Siemiginowska A., Elvis M., 2001, ApJ, 547, 90
Readhead A.C.S., Taylor G.B. Xu W., et al., 1996, ApJ, 460, 612
Snellen I.A.G., 1999, NewAR, 43, 675
Snellen I.A.G., Schilizzi R.T., Miley G.K., et al., 2000, MNRAS, 319, 445
Acknowledgements.
We thank EAS for its support in MK-B participation in JENAM conference.
Fig. 1. VLBA+Effelsberg map of 0809+404 at 1.6 GHz. Contours increase by a factor 2 and the first
contour level corresponds to ≈ 3σ.
Fig. 2. VLBA+Effelsberg map of 0949+287 at 1.6 GHz. Contours increase by a factor 2 and the first
contour level corresponds to ≈ 3σ.
Fig. 3. VLBA+Effelsberg map of 1159+395 (up) and 1315+396 (bottom) at 1.6 GHz. Contours increase
by a factor 2 and the first contour level corresponds to ≈ 3σ.
Fig. 3. VLBA+Effelsberg map of 1502+291 (up) and 1616+366 (bottom) at 1.6 GHz. Contours increase
by a factor 2 and the first contour level corresponds to ≈ 3σ.