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Jet Properties and Evolution in Small and Intermediate Scale Objects

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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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