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