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Jet Properties and Evolution in Small and Intermediate Scale Objects

Jet Properties and Evolution in Small and Intermediate Scale Objects. Marcello Giroletti INAF Istituto di Radioastronomia Bologna. my outline. objects spanning the size range from ~10's of parsecs to a few kiloparsecs. CSO (Compact Symmetric Objects) population

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Jet Properties and Evolution in Small and Intermediate Scale Objects

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  1. Jet Properties and Evolution in Small and Intermediate Scale Objects Marcello Giroletti INAF Istituto di Radioastronomia Bologna Extragalactic Jets: Theory and Observation from Radio to Gamma Ray 21-24 May 2007, Girdwood, AK

  2. my outline • objects spanning the size range from ~10's of parsecs to a few kiloparsecs. • CSO (Compact Symmetric Objects) population • LPC (Low Power Compact) sources. • nature of small radio sources: • spectrum • kinematics • age distribution • nature of their jets • orientation • motion, polarization • final evolution of the CSO and LPC population

  3. basic facts • Different arrays reveal similar basic structures on verydifferent angular and linear scales 4C31.04, Giroletti, VLBA 5 GHz Cygnus A, Carilli, VLA 5 GHz

  4. large vs. small sources • there's a continuum of sizes in radio sources: • ok, sources are born small and then grow up! • actually, there's far more small sources than expected by counts of large ones • not all small looking sources are physically small • unified models, blazars • not all small sources go all the way to Mpc scale • frustration, short-lived activity • Kunert-Bajraszewska, Marecki 06 • luminosity decreases while size increases • Begelman 96, Alexander 00, Snellen 00, Tinti&De Zotti 06

  5. opt. thin radiation losses Log Flux density self-abs. Log Frequency the smallest radio sources • Compact Symmetric Objects • <1 kpc • doubles/triples • low polarization • high HI absorption • convex radio spectrum • useful for selection

  6. Smallest sources have highest turnover frequency: Compact Steep Spectrum sources GHz Peaked Spectrum High Frequency Peakers blazar contamination (see Orienti's talk) O'Dea 1998, Dallacasa+ 2004 npeak 10 GHz GPS HFP 100 MHz 10 pc 10 kpc LS LS vs. turnover CSS

  7. age estimates: kinematics (1) • Measure Ds over Dt for the hot spot separation • Get mean advance velocity vsep=Ds/Dt • Derive 0-order estimate of source age: • tkin=LS/vsep • if vsep ~ 0.3c, z=0.05, • Ds=0.1 masper year • need VLBI, long intervals, high frequency

  8. age estimates: kinematics (2) • Looking in small sources for the youngest radio galaxies • HS advance first detected by Owsianik et al. 1998 • more successful results in several sources: • Polatidis&Conway 03 • Giroletti+ 04 • Gugliucci+ 05 • ... • HS advance velocity ~0.1-0.3 c • bias in selection? 2352+398, Owsianik+ 4C31.04, Giroletti+

  9. age estimates: spectral (1) • N(E)=N0E-d • dE/dt = -bH2E2 • Q(t)=NE-d • S(n)= • n -a if n < n* • n -(a+0.5) if n > n* • n*=109 x t-2 x H-3(GHz, yr, mG) • multifrequency observations constrain n*, and allow us to derive tspec

  10. age estimates: spectral (2) • tspec~103-104yr • Murgia+99, Orienti+07 • consistent with kinetics: • but care about assumptions... • equipartition • no reacceleration • synchrotron losses only • ...and observations • integrated spectrum • matched u,v coverage 1323+321

  11. jets in CSO • for their nature and our selection criteria, CSOs tend to lie in the plane of the sky • we select on the basis of symmetry • little difference between approaching and receding sides • sources on the plane of the sky • if jets are relativistic, then they are debeamed

  12. jets in CSO • jets are not easy to study in CSOs • orientation (debeaming) • resolution • but some are detected • interesting properties... • ...related to interaction with medium 2352+495

  13. jets in CSO • jet-head interacts with dense ISM • bending • 4C31.04: Giroletti+03 • 0528+514 (CSS quasar): Mantovani+02 • HS advance velocity not highly relativistic • dentist drill

  14. jets in CSO • some components in the jet have higher velocity and polarization (Gugliucci+07) • J1826+1831: strongest polarization (9%) in a confirmed CSO • RM unexpectedly low (as low as -180 rad m-2) • B field below equipartition? • jet closer to on-axis than other CSOs? • J1915+6548 has jet components both polarized and (weakly) superluminal

  15. from CSOs to LPCs • on a few kpc scales, we find sources that could be evolved CSOs • we name them Low Power Compact sources • their radio power is below 1024-1025 W Hz-1 • their linear size is a few kpcs (compact in low frequency surveys - 3C, B2) • they do have active jets • they are more frequently edge dimmed (few hot spots)

  16. VLA 8.4 GHz VLA 22 GHz VLA 8.4 GHz VLBA 1.6 GHz lpc: from “blobs” to jets at low resolution, sources are compact, core dominated VLBA and high freq. VLA observations reveal rich substructures, including jets, resembling FRI and FRII on 10-1000 times smaller scales.

  17. 1 pc lpc jets: ngc4278 • P5 GHz~ 1022 W Hz-1, typical for LLAGNs • VLBA two-sided pc scale jet • 2-epochs study (Giroletti+04): • max vjet = 0.1 c • 1.2 < G < 1.7 • 2 < d < 3 103 RS

  18. lpc timescales: 0648+27 • VLA 8 GHz: symmetric double • VLA 22 GHz: resolved with compact core, no HS! • VLBA, phase-ref 1.6 GHz: detection, exact position, 3s pc scale jet • importance of multi-res and broadband obs (Emonts+06, Giroletti+05) • radio: spectral age <1 Myr • neutral hydrogen (H I): major merger 1.5 Gyr ago • optical spectroscopy: starburst activity 0.3 Gyr

  19. jets in LPCs • LPCs reveal rich, complex structures at high resolution • lobes, hot spots, fed by jets • jets typically <1 kpc long • structure is often two-sided • radio power typical of FR Is, motion studies (eg NGC 4278) suggest mildly relativistic regimes • b ~ 0.9 • seem unable to form large kpc scale lobes • LS/tspec << c

  20. cso, lpc, and then? • large scale FRI/II • intermittent activity • large scale emission around pc scale CSO (see poster #35) • premature end of activity • faders (Kunert-Bajraszewska+06) • difficult to find, nbr goes down very rapidly after injection stops - survives better in dense media (Murgia+05) • a candidate: 1855+37 (Giroletti+05)

  21. 1855+37: a jet turning off? • 1855+37 • significant extended emission at low frequency • source not detected at n>8.4 GHz • no more fresh electrons in the lobes • core much weaker than expected (even with strong debeaming) at 5 GHz • nuclear activity might be going off • the sources is in cluster

  22. final remarks • CSOs are the targets to look for jets first steps • however, they are difficult to study (debeaming) and strongly affected by interaction with dense medium • LPCs have more evolved jets, probably unable to form kpc scale lobes • some of them could even be switched off

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