On the nature of On the nature of High High FrequencyFrequency Peaker Peaker
radio sourcesradio sources
Monica Orienti
Girdwood, 22/05/2007 Monica Orienti – Extragalactic Jets
(INAF – IRA, Bologna)
Daniele Dallacasa (UniBo, Bologna)
The GoalsThe Goals
• Analysis of the variability, morphology and polarization of candidate HFPs;
• Selection of a sample of genuine young HFPs;
• What can we learn from HFPs?
Peaks > 5 GHz;
t ~ 102 - 103 years
Bright HFP sample consists of
55 objects:
• 10 galaxies;
• 34 quasars;
• 5 BL Lacs;
• 6 Empty Fields
(Dallacasa et al. 2000)
High Frequency PeakersHigh Frequency PeakersA sample of young HFPA sample of young HFP
Contamination from BL Lac objectsContamination from BL Lac objects
Young radio sources
• No flux-density variability;
• “Double/Triple” structure;
• Unpolarized
Blazars
• Strong flux density variability;
• Core-Jet structure;
• Significantly polarized
Blazars may display the characteristics of young radio sources when their emission is dominated by a flare in the jet-base.
A sample of young HFPA sample of young HFP
Multi-frequency VLA observationsMulti-frequency VLA observations
• Galaxies V<3;
• 21 sources (18 quasars and 3 BL
Lacs) V >>3;
• 12 quasars no longer show a peaked spectrum;
4 epochs of VLA observations at 9 frequencies ( 1.4 – 43 GHz)
(Si – Si)2
V= 1
mi = 1
m
i
A sample of young HFPA sample of young HFP
VLBA observationsVLBA observations
Two-frequencies VLBA observations
In the optically-thin part of the spectrum
We find that:
• 27% “Double/Triple” morphology;
• 12% “Core-Jet” morphology;
• 61% Unresolved
Orienti et al. 2006a, A&A, 450, 959
=0.2
A sample of young HFPA sample of young HFP
Polarization propertiesPolarization properties
From simultaneous VLA observations at
4.5, 8.4, 15 and 22 GHz + information
from the NVSS at 1.4 GHz, we find:
• 57% have fractional polarization >1%;
• 36% are completely unpolarized;
• All the galaxies are unpolarized;
• 70% of quasars are highly-polarized.
A sample of young HFPA sample of young HFP
ResultsResults
From the flux density variability, morphology and polarization we
find that:
Quasars are:
Variable;
“Core-Jet” morphology;
Polarized emission (>1%).
Galaxies are:
No Variability
“Double-Triple” morphology
Unpolarized or slightly (<1%) polarized
Only 25 from the HFP sample are still young radio source candidates
A sample of young HFPA sample of young HFP
HFPs and the source growthHFPs and the source growth
Strong flux-density and arm-
length asymmetries in
compact (< 15 kpc) radio
sources
Constraining the radio source evolutionConstraining the radio source evolution
The evolution modelThe evolution modelThe source growth in an ambient
medium with a King-like profile:
Asymmetries cannot be
reproduced
v t -1/2 (NLR)
Const (ISM)
L t 5/8 (NLR)
t -1/2 (ISM)
ncl
n0
n r -β
t3 t2 t1 t0 t1 t2 t3
Jet-cloud interaction:
ncl
n0
Lj,c l
9 8
2ncl
n0
vj,c v
Constraining the radio source evolutionConstraining the radio source evolution
Magnetic fieldMagnetic fieldFrom equipartition:
Heq ~ 0.16 G
Direct measurement:
H ~ 0.150.03 G
From X-ray luminosities:
H ~ 0.14 G
Consistent with a source in equipartition condition with X-ray luminosity due to Synchrotron Self-Compton
Constraining the physical conditionsConstraining the physical conditions
RXJ1459+3337
