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There and Back Again: Cycles of Activity in

Radio Galaxies

Stefi Baum and Chris O’DeaRochester Institute of

Technology

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The Life Cycle Paradigm

• Birth Infancy (GPS/CSO) Youth (CSS) Adulthood (FR1/2) Death Rebirth

• 0 <NLR (10-1000pc) <Gal (1-20Kpc) IGM (20-1000Kpc) …

• IR GHZ Peaked 100MHz Peaked Steep Spectrum Combo

• 0 102-104 yrs 104-106 yrs 106-108 yrs Combo

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Spectral Energy Distribution of AGN

• radio IRoptical

uv

X-ray

Sanders et al, 1988

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Radio Output continuued

NGC 1365

• Late type galaxy AGN hosts have weak radio emission, & small jets

• Early type galaxy AGN hosts have strong radio emission, & large scale jets

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•RGs constrain the total energy output of central engine (“kinetic” plus radiative)

•Lifetime & stability of ejection axis constrain accretion disk & BH physics

•RGs may be an important source of magnetic field and cosmic rays in the ICM/IGM

•The interaction of jets, outflow and energy with the ambient medium probes the gaseous environment of and affects evolution of the host galaxy ands it surrounding cluster.

•RGs at high z are obscuration-independent signposts to the early formation of massive bulges

•But we don’t understand how RGs evolve during their life times

Cygnus A. VLA 6 cm 0.5” resolution image, courtesy of Chris Carilli (NRAO)

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Schematic of Supersonic Jet Model

Concept from Scheuer 1974, Blandford & Rees 1974. Illustration from Carvalho & O’Dea 2001.

Models of classical doubles assume radio sources are supersonic flows.

The jets terminate in strong shocks and fill an over pressured cocoon which drives a bow shock into the ambient medium.

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Luminosity Function

• Luminosity function depends on host galaxy magnitude & AGN luminosity– Field galaxies 10-1 Mpc-3

– Bright spirals 10-2 Mpc-3

– Bright ellipticals 5x10-

3 – Seyferts 10-4 Mpc-3

– Radio galaxies 10-6 Mpc-3

– QSOs 10-7 Mpc-3

– Quasars 10-9 Mpc-3

The fractional luminosity function of radio-loud AGNs in integral form. Fk(>P1.4) denotes the fraction of all galaxies which host a radio–loud AGN with radio power greater than P1.4. (Mauch & Sadler 2007, MNRAS, 375, 931)

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Demographics of AGN

• Luminosity function is dependent on AGN luminosity and host galaxy magnitude

• Radio output is strongly host galaxy dependent

• Strong number density redshift evolution seen, paralleling star formation evolution

• ~1% of galaxies brighter than L* have AGN with Lbol > 1043 erg/sec

• 1% of AGN are radio loud, 99% are radio quiet

• factor of ~30 increase in number density from z=0 to z=2.

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Key AGN Questions

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Key AGN Questions • What is the realized parameter space of Macc, MBH, angular momentum of BH. How is that realized parameter space represented in our categorization of the Zoo of AGN? Do (how do) individual sources evolve in the Macc, MBH, angular momentum space?

• What is the total extracted energey and What fraction of extracted energy is emitted radiantly, in energetic particles, and in directed outflow and how does that relate to the basic parameters?

• How are BH demographics, hosts properties and galaxy and cluster evolution linked?

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The Life Cycle Paradigm

• What are the Life Cycles of Radio Galaxies and what Physics is Driving them? – Which galaxies are active and at which times and at what luminosities as a function of cosmic time?– How does the radio luminosity function evolve with z?– What is the duty cycle of activity in active galaxies?– What is the “Activity Path” of an individual galaxy as it forms and evolves? How is that activity path tied to the evolution of the galaxy itself and its nuclear black hole?• Birth -> Death -> Rebirth?

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The Game: Get Clues from Ages & Duty Cycles

•The fractional representation of an AGN population gives its life time (e.g., Schmidt 1966).

•Combination of Radio jet modelling, size & luminosity functions, spectral aging studies, stellar age studies, and proper motion/jet propagation measurements all used to constrain lifetimes and on/off cycles.

•Complications arise because of the many manifestations of activity (are they linked evolutionarily or are they distinct beasts) and the ties to uncertain physical models.

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Fueling the AGN

Harris 1988

Reviews: Phinney 1994; Rees 1984; Heckman & Balick 1982; Gunn 1979

> kpc scalekpc - pc scale

< pc scale

Miracle:

Inflow? Stellar bars? Interactions? Feedback?

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Fueling structures and origins?

• Tens of parsec to 100s of parsecs to MPC

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Starburst-AGN Connection

• Emerging paradigms? – A starburst (not necessarily circumnuclear) always

accompanies the onset of AGN activity (e.g., Kaufman et al).

– Early stages of activity, particularly at the high luminosity end, will be highly obscured by dust and gas. Starburst dating can give indication of onset of triggering event.

– In later stages, AGN activity, SNR, and stellar winds blow gas out of the central regions, exposing the AGN, but reducing available fuel, leading to strong frequency and luminosity evolution in individual sources. (Sanders et al. 1988 ulirgs…)

– High z and low z triggers, high power and low power triggers… may be different (accretion vs interactions)

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Baby Sources

Feeding andGrowing…

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GHz Peaked Spectrum and Compact Symmetric Objects

1943+546. Contours are global VLBI 4 cm image from epoch 1997.73. Grey scale is the difference between this image and one from 1993.17. Black is positive and white is negative (Polatidis etal. 1999). Ho=100

•Sources have spectra which peak at GHz frequencies.

•Sizes ~10-100 pc

•Measured Hot spot separation velocity - 0.42c in 1943+

•Inferred age 1000 yr in 1943+

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Turnover Freq. Vs. Linear Size

•There is continuity in the properties of the GPS and CSS sources

•There is a relationship between turnover frequency and linear size νm ~ L-0.65

•Implies the mechanism for the turnover depends strongly on source size (likely to be SSA, but FFA not ruled out in GPS)O’Dea & Baum 1997; Fanti etal 1990

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Why Evolution?•RADIO MORPHOLOGY AND LUMINOSITY of the GPS and CSS galaxies are similar to those of the large scale radio sources.

•GPS and CSS sources live in the SAME HOST GALAXIES as the large radio galaxies – similar absolute magnitudes, colors, profiles, evolution on Hubble diagram (e.g. O’Dea etal 1996; Snellen etal 1996, 1998; De Vries etal 1997, 1998a,b, 1999).

•GPS and CSS sources have the SAME AGN BOLOMETRIC LUMINOSITY as the large radio galaxies – similar mid-far IR properties (Heckman etal 1994; Fanti etal 1999).

•Confinement by the ISM seems unlikely – the HOT ISM IS NOT SUFFICIENT TO CONFINE sources (O’Dea etal 1996) and there does not seem to be sufficient cold gas to achieve confinement (e.g., Conway 1996; Vermeulen etal 2003; O’Dea etal 2003).

•Proper motions ~0.1-0.2c detected in ~dozen CSOs (e.g., Owsianik & Conway 1998). (THE SMOKING GUN)

•Size 105 pc

•Hot spot separation velocity 0.42c

•Inferred age 1000 yr1943+546. Contours are global VLBI 4 cm image from epoch 1997.73. Grey scale is the difference between this image and one from 1993.17. Black is positive and white is negative (Polatidis etal. 1999). Ho=100

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The Teen Age Years

Still living at home…

Calvin becomesA teenager…

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Compact Steep Spectrum Radio Sources

• On host galaxy scales

• Well matched to provide feedback to host galaxy

• Interact with both hot and cold components of ISM

VLA 8.4 GHz image, 0.25 arcsec resolution (Akujor & Garrington 1995, A&AS, 112, 235).

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The Alignment Effect in CSS Sources• CSS radio sources at all redshifts show

emission line gas strongly aligned with the radio source (De Vries etal. 1997, 1999;Axon etal 2000;Privon et al).

• The [OIII] clouds have densities in the range 100-1000 cm-3. Path lengths of 1 pc imply N(H) ~ 1020 – 1021 cm-2.

• There is a population of dense clouds throughout the ISM which accounts for both the emission line nebulae and the atomic hydrogen.

• Jet/cloud interactions may produce observed asymmetries in radio structure.

• The bow shock compresses and heats the clouds, to sufficiently high temperatures so they need to cool before emit [OIII].

• • R(gap) ~ vhs tcool (Top) HST/WFPC2 F702W imaging. (De

Vries et al. 1997). (Bottom) 3C303.1 z=0.270. HST/WFPC2 F702W and LRF imaging. (De Vries etal 1999).

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Significant Impact on Host Galaxy

•Cooling time arguments suggest lobe expansion speed is ~6000 km/s (De Vries et al. 1999). Sound speed in 0.8 keV ISM is cs ~ 460 km/s

• Implies M ~ 13, Strong shock Rankine-Hugoniot conditions imply T ~ 43 keV.

•Numerical simulations suggest volume of shocked gas is ~ 3 times radio luminous cocoon,

•so Vsh ~ 14 kpc3, consistent with XMM spectra

3C 303.1. (Top) Spectral fits to two temperature model (O’Dea et al., 2006, ApJ, 653, 1115). (Bottom) Cartoon of evolution of outline of jet, cocoon and bow shock (based on Carvalho and O’Dea 2002, ApJS, 141, 337)

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The Adult Years

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Radio jets and lobes, tens to 1000 KPC

Two main flavors of

radio structure:FR1 and

FR2

Fanaroff and RileyLaing and Bridle 1987Bridle et al 1994

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Fanaroff and Riley Class I Paradigm

• lower power radio galaxies• jet initially relativistic on parsec scale• source would be seen as a BL Lac object at small inclination angle

• jet decelerates on tens to hundreds of pc scale becoming mildly or sub relativistic• on large scales both jets are seen due to lack of strong Doppler boosting

• jet is transonic - no strong shock at end of jet• bendable by ISM/ICM “weather”

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Fanaroff and Riley Class II Paradigm

• more powerful radio galaxies• jet relativistic on all scales up to hot spot• quasar or OVV/blazar at small inclination angles

• Doppler boosting on kpcscales is important

• typically jets are either both not observed (Doppler de-boosting) or only one jet is seen (favoritism)

• jet is super sonic - strong shocks at end of jet• orientation extremely stable• jet back-flow from hot spot inflates over-pressured cocoon (lobes).

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Two Accretion Modes?• At a given radio power, FRIs have

fainter nuclear X-ray and UV emission, suggesting they have fainter accretion disks.

• Does the correspond to a different

accretion mode? (e.g., Fabian & Rees 1995, BZO)

• Do RGs change from FR1 to FR2 or visa versa?

(Top) X-ray luminosity of accretion component vs 178 MHz radio luminosity. Open circles are LERG, filled circles are NLRG, open stars are BLRG, and filled stars are quasars. Large circles indicate an FRI. (Hardcastle etal 2006, MNRAS, 370, 1893. (Bottom) Optical line luminosity vs. radio core luminosity. (Baum, Zirbel, & O’Dea 1995, ApJ, 451, 88; BZO)

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Do Low Power Radio Galaxies Live

Longer ? •Low power sources have spectral and model ages t ~ 10 7-8 yr

• High power sources have ages t ~ 10 6-7 yr

•This suggests low power sources may live longer than high power sources.

Estimated synchrotron ages vs radio power at 1.4 GHz for a sample of radio galaxies. Filled circles and triangles: B2 sources with type 1 and type 2 spectra, respectively; crosses: 3C galaxies with z < 0.2; open circles: 3C galaxies with z > 0.2; asterisks: 3C quasars. (Parma et al. 1999)

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Old Age and Death

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Dying Radio Sources• When the jet outflow stops the compact components: core, jets, hot spots should fade first

• The lobes will then become more diffuse and their spectra will steepen due to radiative losses.

• Observed examples of dying sources are rare: only about ten candidates are currently known (e.g., Cordey 1987; Parma et al 2007). Suggests time over which a dying source is observable & recognizable is short (~10% of source active lifetime, Parma etal 2007).

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Candidate Dying Radio Source

• Candidates selected from steep spectrum sources in the WENSS catalog.

• WNB1150.0+3749 shows no bright core, jets, or hot spots.

• The integrated spectrum is steep (implies age of 50 Myr)

• The spectrum also steepens away from the center.

• (Parma et al. 2007).

(top left) total intensity image (contours) on DSS2 image. (top right) integrated radio spectrum. (bottom left) contours of radio emission on spectral index map. (bottom right) spectral index profile along the lobes (Parma et al. 2007).

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Reincarnation

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Cluster Feedback May Suggest Repetitive Activity

• multiple episodes of radio activity • May be suggested by the X-ray morphologies?

• are required to account for the heating of the ICM

(Top) Unsharp masked image from Chandra Image. (Bottom) Radio image in blue superimposed on pressure difference map in red (Fabian et al 2006)

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Born Again Radio Galaxies?

•About 10% of GPS sources exhibit faint, diffuse extended emission.

•Some of these could be “contamination” by core-dominated sources with peaked core spectra.

•Others could be genuinely young sources which are repetitive (e.g., 0108+388, Baum et al. 1990).

•These “born again” sources show the current radio source propagating outwards amidst the relic of the previous epoch of activity.

•In double-double sources, the previous radio source is still identifiable as a classical double source (Schoenmakers et al. 2002). (and don’t forget the X shaped sources…)

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Double-Doubles• 5-10% of > 1 Mpc radio sources show double-double structure.

• Working hypothesis: the radio galaxy turned off and then turned back on --creating a new double propagating outwards amidst the relic of previous activity.

Schoenmakers etal (2000)

Schoenmakers et al. (2002)

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Multiple Episodes of Fueling?

•Numerical simulations suggest that during the course of a merger there will be multiple episodes of accretion onto the nucleus producing a high luminosity phase lasting about 108 yr. Projected gas density color coded

by temperature (box 140 kpc across). Bolometric luminosity of central black hole(s), with diamonds marking the times shown above. (Hopkins et al. 2005, ApJ, 625, L71

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3C236 - 4 Mpc Radio Source

The largest radio galaxy known.

WSRT 92 cm image (55”x96”) Mack etal. 1997) overlayed on DSS image.

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The Inner 2 Kpc Double

Global VLBI 1.66 GHz image (Schilizzi etal 2001) superposed on HST WFPC2 V band image

At z=0.1, and Ho=75,

1 arcsec = 1.7 kpc

Inner 2 kpc double is well aligned with outer 4 Mpc double

Whatever provoked second epoch did not affect orientation of jet

O’Dea, Koekemoer, Baum, Sparks, Martel, Allen, Macchetto, & Miley (2001)

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Time Scales Dynamical Ages:Large radio source: t~7.8x108 (v/0.01c) yr (comparable to the age of the oldest blue knots)

Small radio source: t~3.2x105 (v/0.01c) yr (much younger than the youngest blue knots)

Dynamical time scale of the disk on the few 100 pc scale t~107 yr

O’Dea et al 2001

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The 3C236 Scenario

The small and large radio sources are due to two different events of mass infall.

Spectral aging estimates in the hot spots of the large source imply the radio source may have turned off for ~ 107 yr in between the two events.

The difference in the ages of the young and old star formation regions also implies two different triggers.

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Constraints from Radio Source Models

• Radio Power vs. Size• Number vs Size• Hot spot diameter vs. Radio Source Size

• Velocity vs Size (soon…)

(Left) Power vs Size (Blundell et al 1999); (Middle) Number vs Size (O’Dea & Baum 1997); (Right) Hot spot size vs. radio source size (Barai & Wiita 2007)

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Power – Size Diagram•The combined sample of GPS, CSS and 3CR covers 5 orders of magnitude in linear size.

•Radio galaxies will follow evolutionary tracks on this diagram (Baldwin 1982).

•The number in bins of linear size constrains the evolution.O’Dea & Baum 1997

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Number vs. Size

•Over the entire range N ~ L 0.25

•There is a possible flattening at small size

• Models which fit the data include

•Intermittent sources (Reynolds & Begelman 1997)

•A subpopulation which is disrupted on small scales (Alexander 2000)

(Top) data from the GPS, CSS, and LRL samples (O’Dea and Baum (1997, see also Fanti 2008) (Middle) Fit to the data which includes intermittent radio sources (Reynolds & Begelman 1997). (Bottom) Fit to the data which includes sources which disrupt on small scales (Alexander 2000).

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Most Models Give Similar Results on the Power-Size Plot for Large Sources

• Models assume same jet physics and ambient medium profile

• Some differences are – Spectrum of electrons

accelerated in the hot spot

– Transport of relativistic electrons from hot spot to lobe

– Prescription for evolution of hot spot size

Comparison of Models from Barai & Wiita (2007). BRW=Blundell et al 1999, MBRW=modified BRW; KDA =Kaiser etal (1997); K00 = modified KDA; MK=Manolakou & Kirk (2002); MMK=modified MK

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Compact Sources May Initially Brighten. Slow

then speed up.

• Models by Alexander (2000) and Snellen et al (2000) suggest that compact sources will brighten for the first kpc.

• Hotspot advance speed

(Top) Models from Alexander (2000). (Bottom) Kawakatu et al 2008 (doesn’t fit medium sized source measurements to date).

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Timescales, on off cycles

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Shabala et al, 2008

Suggest: More massive galaxies have longer lived radio sources that are triggered more frequently.

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Summary…

•GPS/CSO 100-1000 yr (proper motions, spectral aging)

•CSS 104-106 yr (spectral aging)

•FRII 106-107 yr (spectral aging, statistics, dynamical models)

•FRI 107-108 yr (spectral aging, statistics, maybe models)

If there is rebirth, are sources reborn with the same or differing Macc, MBH, angular momentum of BH etc.? Once an FR2 always an FR2?

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Questions

From the day we arrive on the planetAnd blinking, step into the sunThere's more to see than can ever be seenMore to do than can ever be doneThere's far too much to take in hereMore to find than can ever be foundBut the sun rolling highThrough the sapphire skyKeeps great and small on the endless roundIt's the Circle of Life (…and, perhaps, of Radio Galaxies :-)

(Tim Rice)

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The End