On the nature of High Frequency Peaker radio sources

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