On the nature of High Frequency Peaker radio sources
description
Transcript of On the nature of High Frequency Peaker radio sources
![Page 1: On the nature of High Frequency Peaker radio sources](https://reader036.fdocuments.in/reader036/viewer/2022082411/568147c3550346895db505a5/html5/thumbnails/1.jpg)
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)
![Page 2: On the nature of High Frequency Peaker radio sources](https://reader036.fdocuments.in/reader036/viewer/2022082411/568147c3550346895db505a5/html5/thumbnails/2.jpg)
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?
![Page 3: On the nature of High Frequency Peaker radio sources](https://reader036.fdocuments.in/reader036/viewer/2022082411/568147c3550346895db505a5/html5/thumbnails/3.jpg)
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
![Page 4: On the nature of High Frequency Peaker radio sources](https://reader036.fdocuments.in/reader036/viewer/2022082411/568147c3550346895db505a5/html5/thumbnails/4.jpg)
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
![Page 5: On the nature of High Frequency Peaker radio sources](https://reader036.fdocuments.in/reader036/viewer/2022082411/568147c3550346895db505a5/html5/thumbnails/5.jpg)
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
![Page 6: On the nature of High Frequency Peaker radio sources](https://reader036.fdocuments.in/reader036/viewer/2022082411/568147c3550346895db505a5/html5/thumbnails/6.jpg)
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
![Page 7: On the nature of High Frequency Peaker radio sources](https://reader036.fdocuments.in/reader036/viewer/2022082411/568147c3550346895db505a5/html5/thumbnails/7.jpg)
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
![Page 8: On the nature of High Frequency Peaker radio sources](https://reader036.fdocuments.in/reader036/viewer/2022082411/568147c3550346895db505a5/html5/thumbnails/8.jpg)
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
![Page 9: On the nature of High Frequency Peaker radio sources](https://reader036.fdocuments.in/reader036/viewer/2022082411/568147c3550346895db505a5/html5/thumbnails/9.jpg)
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
![Page 10: On the nature of High Frequency Peaker radio sources](https://reader036.fdocuments.in/reader036/viewer/2022082411/568147c3550346895db505a5/html5/thumbnails/10.jpg)
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
![Page 11: On the nature of High Frequency Peaker radio sources](https://reader036.fdocuments.in/reader036/viewer/2022082411/568147c3550346895db505a5/html5/thumbnails/11.jpg)
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