Extragalactic Jets: Theory and Observation from Radio to Gamma Ray

1
Jet Properties and Evolution in Small and
Intermediate Scale Objects

• Marcello Giroletti
• INAF Istituto di Radioastronomia Bologna

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 very different 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, TintiDe
  Zotti 06

5
the smallest radio sources

• Compact Symmetric Objects
• lt1 kpc
• doubles/triples
• low polarization
• high HI absorption
• convex radio spectrum
• useful for selection

6
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

CSS
7
age estimates kinematics (1)

• Measure Ds over Dt for the hot spot separation
• Get mean advance velocity vsepDs/Dt
• Derive 0-order estimate of source age
• tkinLS/vsep
• if vsep 0.3c, z0.05,
• Ds0.1 mas per 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
• PolatidisConway 03
• Giroletti 04
• Gugliucci 05
• ...
• HS advance velocity 0.1-0.3 c
• bias in selection?

2352398, 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 lt n
• n -(a0.5) if n gt n
• n109 x t-2 x H-3 (GHz, yr, mG)
• multifrequency observations constrain n, and
  allow us to derive tspec

10
age estimates spectral (2)

• tspec103-104yr
• Murgia99, Orienti07
• consistent with kinetics
• but care about assumptions...
• equipartition
• no reacceleration
• synchrotron losses only
• ...and observations
• integrated spectrum
• matched u,v coverage

1323321
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

2352495
13
jets in CSO

• jet-head interacts with dense ISM
• bending
• 4C31.04 Giroletti03
• 0528514 (CSS quasar) Mantovani02
• HS advance velocity not highly relativistic
• dentist drill

14
jets in CSO

• some components in the jet have higher velocity
  and polarization (Gugliucci07)
• J18261831 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?
• J19156548 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
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
lpc jets ngc4278

• P5 GHz 1022 W Hz-1, typical for LLAGNs
• VLBA two-sided pc scale jet
• 2-epochs study (Giroletti04)
• max vjet 0.1 c
• 1.2 lt G lt 1.7
• 2 lt d lt 3

103 RS
18
lpc timescales 064827

• 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
  (Emonts06, Giroletti05)
• radio spectral age lt1 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 lt1 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 ltlt 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-Bajraszewska06)
• difficult to find, nbr goes down very rapidly
  after injection stops - survives better in dense
  media (Murgia05)
• a candidate 185537 (Giroletti05)

21
185537 a jet turning off?

• 185537
• significant extended emission at low frequency
• source not detected at ngt8.4 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

23
Radio spectra

• One more piece of information
• little contamination from core
• Beq 102 mG
• Tsyn 105-106 yr
• vadv, syn ltlt c
• consistent with slow/ceased advance in the
  external medium