Extragalactic Jets: Theory and Observation from Radio to Gamma Ray 21-24 May 2007, Girdwood, AK Jet...
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Transcript of Extragalactic Jets: Theory and Observation from Radio to Gamma Ray 21-24 May 2007, Girdwood, AK Jet...
Extragalactic Jets: Theory and Observation from Radio to Gamma Ray21-24 May 2007, Girdwood, AK
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 − 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
basic facts
• Different arrays reveal similar basic structures on very different angular and linear scales
Cygnus A, Carilli, VLA 5 GHz
4C31.04, Giroletti, VLBA 5 GHz
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
the smallest radio sources
• Compact Symmetric Objects− <1 kpc
− doubles/triples
− low polarization
− high HI absorption
− convex radio spectrum• useful for selection
5/15/2max
5/45/1max )1()( zSHe
Log Frequency
Log
Flu
x de
nsity
self-abs.
opt. thin
radiation losses
LS vs. turnover
• 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 LS10 kpc10 pc
10 GHz
100 MHz
peak
GPS
CSS
HFP
age estimates: kinematics (1)
• Measure s over t for the hot spot separation
• Get mean advance velocity vsep=s/t
• Derive 0-order estimate of source age:
− tkin=LS/vsep
• if vsep ~ 0.3c, z=0.05, − s=0.1 mas per year
− need VLBI, long intervals, high frequency
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+
age estimates: spectral (1)
• N(E)=N0E-
• dE/dt = -bH2E2
• Q(t)=NE-
• S()=• - if < *• -(+0.5) if > *
• *=109 x t-2 x H-3(GHz, yr, mG)• multifrequency observations constrain *, and
allow us to derive tspec
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
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
BB
2
)cos1(
1
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
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
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
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)
lpc: from “blobs” to jetsat 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.
VLBA 1.6 GHz VLA 22 GHz VLA 8.4 GHz VLA 8.4 GHz
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 < < 1.7
− 2 < < 3
1 pc 103 RS
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, 3 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
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− ~ 0.9
• seem unable to form large kpc scale lobes− LS/tspec << c
cso, lpc, and then?
1. large scale FRI/II
2. intermittent activity• large scale emission around pc scale CSO
(see poster #35)
3. premature end of activity• faders (Kunert-Bajraszewska+06)
• difficult to find, br goes down very rapidly after injection stops - survives better in dense media (Murgia+05)
• a candidate: 1855+37 (Giroletti+05)
1855+37: a jet turning off?
• 1855+37− significant extended emission at low
frequency
− source not detected at >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
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