Parsec-Scale
Jet-Environment
Interactions in AGN
Matthew Lister
Purdue University
Extragalactic Jets, May 2007
Girdwood, AK
Review Outline
1. Evolutionary theories for young radio jets
- Gigahertz-peaked spectrum galaxies (CSOs)
2. Numerical jet-cloud simulations
3. VLBA studies of young jets and blazars
Self-similar expansion models
• Begelman 96, Kaiser
and Alexander 97,
Bicknell et al. 97
• Hotspots in ram
pressure equilibrium
– evolution depends on
radial profile of ISM
density
– correlation between
hotspot size and
overall jet length
(Jeyakumar & Saikia
00)
CSO 0710+439
Perucho & Marti 02
Self-similar expansion models
Contemporary view :
– forward hotspot
motion >> side-to-side
 not a “dentist’s
drill”
– advancing bow shock
interacts with clumpy
ISM, creating line
emission via shock
ionization
– hotspot advance
unimpeded
– fast advance speeds
of 0.1 - 0.4 c
CSO 0710+439
Perucho & Marti 02
Young jet evolution
• Evolution models suggest rapid
dimming once jet reaches ~ 1
kpc (e.g., Snellen et al. 00)
– CSOs overrepresented in AGN jet
population
– cutoff in kinematic age distribution
Kinematic age
distribution of CSO jets
shaded = lower limits
• ISM interaction to blame?
– change in jet polarization
properties past 2-3 kpc (Cotton et
al. 03)
– first encounter with clumpy
medium? tidal effects?
(years)
Gugliucci et al. 05
GPS Galaxies: Young and not so frustrated
• Strong observational evidence for dense environments, but
dense enough?
– huge gas masses (1010 Msun) required to halt medium power jets
– HI and X-ray column densities too low
• (e.g.,Vermeulen et al. 03, Guaianazzi et al. 06, Vink et al. 06)
• Other evidence against frustration:
– ‘burst and stall’ can’t apply  in majority of cases advance speeds
are measurable (Polatidis & Conway 92)
– kinematic expansion ages ≈ spectral ages (< 104 y; Murgia et al. 99)
– no IR excess (Fanti et al. 2000)
Intermittent Jet Activity
– 5-10% of GPS galaxies show
kpc-scale emission
– X-ray shells around radio
galaxies: (e.g. M87, NGC 1275,
3C 317)
– Ultra steep spectrum (fossil) radio
galaxies
“Double-double” radio galaxies
– only ~dozen known, all large
radio galaxies
– a few to tens of Myr between jet
episodes
– symmetric inner doubles imply
stoppage at AGN nucleus, not
from cloud collisions (Kaiser et al.
00)
180 kpc
J1835+620
Saikia et al. 06
Numerical Simulations
of Jet-Cloud Interactions
Jet simulations with clumpy medium
• 3D pure hydro sims:
False color = density
– extends work of Saxton et al. 05
– light hypersonic jet, η = 10-3
– Mach 26, Γ = 5
• External medium:
– hot (107 K) ISM plus 104 K
turbulent, clumpy disk (1010
Msun)
• Main findings:
– jet forms channels through
weak points in ISM
– spherical energy-driven bubble
– jet eventually breaks free and
recollimates, forming classical
bow shock
Sutherland & Bicknell, ApJ
submitted
Comparisons with CSO 4C 31.04
50 pc
• Western lobe emission not backflow
VLBA 5 GHz: Giroletti et al. 03
– flat-spectrum region extended perpendicular to western hotspot
– high velocity filaments in simulations: particle acceleration sites
– jet near end of breakout phase?
• Eastern lobe perhaps at earlier evolutionary phase
Comparisons with CSO 4C 31.04
65 kyr
50 pc
• Western lobe emission not backflow
VLBA 5 GHz: Giroletti et al. 03
– flat-spectrum region extended perpendicular to western hotspot
– high velocity filaments in simulations: particle acceleration sites?
– jet near end of breakout phase?
• Eastern lobe likely at an earlier evolutionary phase
Relativistic 3-D Hydro simulations
• Choi & Wiita, ApJ ‘07
• Oblique shocks deflect
the beam
– no jet deceleration
or decollimation
– bend is transient
Density
• Highest deflections
expected for lowMach jets hitting
denser clouds
Pressure
cloud/ISM density ratio = 10
Jet Lorentz factor = 2.3
Mach number = 6.4
• Model B: thicker
cloud:
– less encompassed by
bow shock, so Mach
disk interacts sooner
Density
– perpendicular
structure similar to 4C
31.04
Pressure
• Clouds can survive
impact without
fragmentation
– may be important
star formation sites
cloud/ISM density ratio = 100
Jet Lorentz factor = 2.3
Mach number = 6.4
VLBA Studies of Jet-Environment
Interactions: I. Seyferts
Jets in Seyfert galaxies
• VLBA resolution: < 104 A.U. at typical Seyfert
distances (15-20 Mpc)
• Much lower jet power and speed
– more subject to entrainment and disruption
(Bicknell et al. 98, de Young 06)
– accretion may be sporadic, leading to random jet axis
directions (King & Pringle 07)
Seyfert NGC 4151: Mundell et al. 03
red: radio jet
green: molecular
hydrogen torus
central black
region: ionized
gas
200 pc
-
Seyfert 1.5 (nearly face on), 13.3 Mpc
-
Possible deflection at site of eastern HI absorption: flat radio spectrum
NGC 4151
• Numerous [O III]
emission clouds
near radio jet
– some are high
velocity
– NLR geometry
suggests radiative
excitation from
AGN
HST image (Winge et al. 97)+ jet overlay (Mundell et al. 03)
• Some clouds are high velocity (> 1000 km/s)
– cocoon may shock ionize NLR clouds close to the jet
NGC 3079: Middelberg et al. 07
• Seyfert 2 at 15 Mpc
• Powerful water maser disk,
indicative of thick molecular
torus
• Multi-epoch VLBA monitoring:
–
–
–
–
A and B: compact, SSA/FFA radio spectra
A is moving at 0.1 c away from B
recently slowed and increased in flux density
cpts E and F may represent earlier (branching?) outflow
5 GHz VLBA
image
1345+125: A young precessing AGN Jet
• Host galaxy: gas rich ULIRG at z = 0.12
• Tidal tails, young stellar pop., double nucleus  recent merger
Stanghellini et al. 2005
PKS
1345+125:
Young radio
jet at z = 0.1
• Jet follows a conical
helix:
– intrinsic speed 0.8 c
– cone axis inclined 82
degrees from line of
sight
– 280 pc helix
wavelength
AGN
– northern jet
truncated at site of
dense HI absorption
(>1022 cm-2; Morganti
et al. 05)
VLBA 2 cm
image (Lister
et al. 2003
• High polarization at
bend and jet terminus
– shocked regions
– Mach disk implies active
hotspot: jet not stifled in
this very gas rich galaxy
fpol = 10%
fpol > 40%
• Outer (kpc-scale)
structure likely remnant
of earlier activity cycle
Lister et al. 03
VLBA Studies of Jet-Enviroment Interactions
II. Blazars
Using blazars to probe jet-ISM interactions
• Small jet viewing angles:
– small jet bends exaggerated by projection
– less obscured view through hole in torus
– trace gas via Faraday rotation of polarization
• Superluminal blobs effectively trace jet flow
– century of jet evolution in a few years
3C279: Homan et al. 2003
Feature C4 moved
steadily on linear
path for over a
decade at 8 c
– sudden
acceleration to 13 c
and change by 26°
– intrinsic change in
direction only ~1°
Event occurred a few
kpc from nucleus:
– reconfinement
following flaring of
initially
overpressured jet?
– deflection by
oblique density
gradient?
50 pc (projected)
MOJAVE / 2 cm Survey (Lister & Homan 05)
more movies at: www.physics.purdue.edu/MOJAVE
3C 120
• Broad-line Sy 1 galaxy at 145
Mpc (z = 0.033)
• Signs of merger activity
• One-sided pc-scale jet,
speeds ~6 c, viewing angle
< 20 deg. (Jorstad et al. 05)
HST archive image: Cheung and Harris
• High velocity emission line
components suggest jet
interaction with gas clouds
(Axon et al. 89)
Rosat contours + radio greyscale (Harris)
• Multiepoch, multifrequency VLBA polarimetry of inner jet (Gomez et
al. 2000, 2001, 2006, Jorstad et al. 2005)
• Spatial resolution of ~0.1 pc allows resolution across the jet
22 GHz
• Jet features brighten and rotate in polarization as they
move along southern half of the jet
– changes occur after they have left the nucleus, and no kinematic
accelerations seen
– suggestive of medium interaction
Gomez et al. 01
Dynamics of 3C 120’s Jet
• Cloud interaction?
– occurs at 8 pc
(deprojected) from the
nucleus
– jet remains well
collimated
– strong and variable
RM indicates dynamic
interaction
Gómez et al. in prep.
Future research avenues
• Finding the youngest AGN jets:
– only ~ 40 currently identified CSOs
– large area radio surveys above 15 GHz:
ATCA 20 GHz, 9th Cambridge, Planck
– large VLBA surveys: VIPS, VCS
• Studies of low-power CSOs:
– intermediate stage before classical FR II?
– very few currently known, especially at scales > 1 kpc:
(e.g., Giroletti et al. 06, Augusto et al. 06)
– identification a challenge for VLBA: science driver for space VLBI
• Can we identify the beamed CSOs?
– how relativistic are young radio jets? similarities with blazars?
Summary
• VLBI studies indicate clumpy, asymmetric ISM
– jet evolution likely affected, but not stifled on pc-scale
• Drop-off in jet population at ~1 kpc size:
– jet disruption, or central engine turn off?
• Variety of powerful tools available:
– x-ray and radio absorption measures
– high resolution optical emission line imaging
– VLBA polarimetry
– numerical simulations
• The VLBA offers unparalleled means of probing dynamics
of jet-cloud interactions on sub-decade timescales
Future research avenues
• Finding the youngest AGN jets:
– only ~ 40 currently identified CSOs
– large area radio surveys above 15 GHz:
ATCA 20 GHz, 9th Cambridge, Planck
– large VLBA surveys: VIPS, VCS
• Studies of low-power CSOs:
– intermediate stage before classical FR II?
– very few currently known, especially at scales > 1 kpc:
(e.g., Giroletti et al. 06, Augusto et al. 06)
– identification a challenge for VLBA: science driver for space VLBI
• Can we identify the beamed CSOs?
– how relativistic are young radio jets? similarities with blazars?
Nagging Questions For Discussion
• Is the ~kpc size cutoff related to merger
activity/fueling, or jet stifling?
• Where does deceleration of GPS lobes occur?
– classical radio galaxies have much slower hotspot
advance speeds
• Could more powerful jets be evolving in less
clumpy environments?
– role of Roche tidal radius?
X = 10
Γ = 7.1
M = 11.6
Seyfert 2: NGC 1068 (Das et al. 06)
• Seyfert 2
Jet precession and interaction
• well established phenomenon in microquasars (eg. SS 433, GRO J
1655-40)
• jets constantly encountering new material
• S-shaped morphologies more common in CSOs than blazars
• causes:
–
–
–
–
KH instability
current driven instability
pressure-driven instability
precession of jet nozzle
• merger
• binary BH
• accretion disk warp (Lai 03, Quillen 01, Pringle 96)
• Lu 1990: offset accretion disk exerts torque
– Peck and Taylor 01 find offset torus needed to explain HI absorption
distribution in CSO 1946+708
Precession and interaction
• Jet precession periods too short to be from
warped accretion disks (Bardeen-Peterson
effect; Lodato & Pringle 06)
• Binary BH have been proposed in several AGN:
– OJ 287 (Valtonen XXX)
– 3C 345 (Lobanov and Roland 05)
– 0402+379 (Rodriguez et al. 06)
Entrainment
• Entrainment of external material
excites K-H surface instabilities
that can penetrate jet and disrupt
lower Mach flows (Perucho et al.
05, de Young 06)
• Slower speed, turbulent surface
mixing layer forms (Aloy et al.
99, Laing & Bridle 02,06, Attridge
et al. 99)
de Young 2006
• Difficult to study observationally
Brown & Roshko 74
• Limb brightening in resolved jets:
– Centaurus A (Kataoka et al. 06)
– 3C 353 (Swain et al. 98)
– M87 (Ly et al. 07, Kovalev et al. in prep)
• Possible major sites of particle acceleration (Stawarz &
Ostrowski 02)
– implications for beaming models of high energy emission
Centaurus A
M87
VLBA 7 mm: Ly et al. 07
Chandra X-ray: Kataoka et al. 06
Jet-medium interactions in Seyfert galaxies
Much lower jet power
and speed
– more subject to
entrainment and
disruption
– accretion may be
sporadic, leading to
random jet axis
directions (King &
Pringle 07)
VLBA resolution: < 104
A.U. at typical Seyfert
distances (15-20 Mpc).
Relativistic 3-D Hydro simulations
• Choi & Wiita 07
• Off-axis collision
Density
• X = cloud/ISM
density ratio
• Γ = jet Lorentz
factor
• M = Mach number
Pressure
X = 10
Γ = 2.3
M = 6.4
Γ
v shock  vbowshock
ncloud
nISM
• Model B: thick cloud:
– less encompassed by
bow shock
– Mach disk interacts
sooner
– stronger oblique
shocks deflect the
beam
– perpendicular
structure similar to 4C
31.04
Density
Pressure
X = 100
Γ = 2.3
M = 6.4
Γ
•
Model C: faster jet
– Mach disk further offset from bow shock
– thinner backflow cocoon
•
Beam deflected in all
models
– oblique shocks form, but
do not decelerate or
decollimate the jet, unlike
non-relativistic sims (Wang
et al. 00, Higgins et al. 99)
– bends appear to be
transient
•
Density
Deflection angle more
dependent on cloud density
than jet Mach number
– highest deflection
expected for low-Mach jets
hitting denser clouds
•
Clouds can survive impact
without fragmentation
– large cloud/jet density
contrast suppresses K-H
instabilities
– may be important star
formation sites
Pressure
X = 100
Γ = 7.1
M = 11.6
Γ
Compact Steep-Spectrum Sources (CSS)
• Sizes up to a few kpc
• Spectral turnovers < 100 MHz
• Strong evidence for jet/ISM
interaction:
– asymmetric jets (Saikia et al. 02, 03)
– high rotation measures and
depolarization
– high-velocity emission line systems
and jet alignments (Gelderman &
Whittle 94, Labiano et al. 05, de
Vries et al. 99)
Radio galaxy B1450+333
Schoenmakers et al. 00
Important issues addressed via pc-scale jetmedium interaction studies
• How is AGN jet activity triggered?
• What is the nature of the ISM in AGN hosts, and
how does it affect jet evolution?
• Which young jets evolve into classical radio
galaxies? (And how?)
• Model B: thicker
cloud:
– less encompassed by
bow shock, so Mach
disk interacts sooner
v shock  vbowshock
ncloud
nISM
Density
– perpendicular
structure similar to 4C
31.04
Pressure
• Clouds can survive
impact without
fragmentation
– may be important
star formation sites
cloud/ISM density ratio = 100
Jet Lorentz factor = 2.3
Mach number = 6.4
Double-double radio
galaxies
• No hotspots in inner double expected if jets propagating through
previous cocoon material
– would be difficult to observe (Marecki et al. 06, Clarke et al. 92)
– restarted jet may encounter warm, dense clouds from previous cocoon
backflow (Kaiser et al. 00)
Is CSO growth affected by dense gas?
• Gupta et al. 06 find no
dependence of jet morphology
on HI properties
– HI in obscuring torus, not
interacting with jet?
• NGC 1052: nearly identical
jet&counterjet, yet significant
absorption (Vermeulen et al. 03)
• 1345+125: well collimated jet in
very dense environment (Lister
et al. 03)
Gupta et al. 06
The youngest AGN Jets
• Gigahertz-Peaked
Spectrum (GPS) galaxies:
– 5% of AGN selected at 5 GHz
– large intrinsic radio
luminosities (not beamed)
– many host galaxies have
distorted morphologies / close
companions (O’Dea et al. 96)
• Compact Symmetric
Objects (CSOs):
– misnomer? jet asymmetries
are common
– miniature versions of twosided radio galaxies (1000x
smaller)
– jets oriented near sky plane
Gugliucci et al. 2005
Size – HI absorption anti-correlation
• Pihlström et al. fit trend with power
law ISM, index ≈ -2
– similar slope to predictions of
expansion models
– total HI gas masses ~ 108 Msun
– no trend of HI with jet asymmetry
though (Gupta et al. 06)  HI in
torus?
• Vink et al. 06: NLR may be still
forming in young CSOs
– lower [OIII] luminosities than
larger jets
– collimated jet and hotspots must
form very soon after AGN turn-on
– supported by NLR size and lobe
expansion speed of J1503+4528
(Inskip et al. 06)
Pihlström et al. 2003
Basic forms of jet-medium interaction
A. Entrainment
-
jet instabilities, sheaths, deceleration
B. Hotspot & bow shock advance
-
effects of intermittent jet activity
encounters with varying external medium
C. Jet/cloud collisions
-
bending and disruption