On the nature of High Frequency Peaker radio sources Monica Orienti Girdwood, 22/05/2007 Monica Orienti – Extragalactic Jets (INAF – IRA, Bologna) Daniele Dallacasa (UniBo, Bologna)

The 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 ~ years Bright HFP sample consists of 55 objects: 10 galaxies; 34 quasars; 5 BL Lacs; 6 Empty Fields (Dallacasa et al. 2000) High Frequency Peakers A sample of young HFP

Contamination 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 HFP

Multi-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) (S i – S i ) 2 V= 1 m  i = 1 m ii A sample of young HFP

VLBA 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 HFP

Polarization 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 HFP

Results 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 HFP

HFPs and the source growth HFPs and the source growth Strong flux-density and arm- length asymmetries in compact (< 15 kpc) radio sources Constraining the radio source evolution

The evolution model The 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) n cl n0n0 n  r -β t 3 t 2 t 1 t 0 t 1 t 2 t 3 Jet-cloud interaction: n cl n0n0 L j,c  l n cl n0n0 v j,c  v Constraining the radio source evolution

Magnetic field From equipartition: H eq ~ 0.16 G Direct measurement: H ~ 0.15  0.03 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 conditions RXJ

Very asymmetric sources t ~ 3x x10 3 yr v L ~ 0.08c – 0.31c v H ~ 0.01c – 0.05c n eL ~0.02 cm -3 ; n eH ~5.7 cm mas 97 mas t ~ 3x x10 4 yr v L ~ 0.04c – 0.09c v H ~ 0.002c – 0.014c n eL ~0.08 cm -3 ; n eH ~50.0 cm -3 Orienti et al. 2007, A&A, 461, 923

Jet stability To preserve the jet stability the maximum size of the cloud must be: R max 2.5kpc ~ PjPj erg/s 1212 n cl 0.1cm -1 2 (Alexander 2000)

Luminosity asymmetries Normalized instantaneous Luminosity versus time. In more realistic model the luminosity increases more smoothly

Model versus observations Hot-spot separation speed versus Linear size (Polatidis & Conway 2003) Not well fitted by a NLR with constant density

The Bright HFP sample Cross-correlation of the 87GB at 4.9 GHz and the NVSS at 1.4 GHz S 4.9 > 300 mJy;    –0.5 (S  ν -α ); Simultaneous VLA observations ( GHz) to remove variable sources. 55 objects (Dallacasa et al. 2000): 11 galaxies; 36 quasars; 8 empty fields; O’Dea 1998