Radio Galaxies part 4

Apart from the radio the thin accretion disk around the AGN produces optical, UV, X-ray radiation The optical spectrum emitted by the gas depends upon the abundances of different elements, local ionization, density and temperature.  Photons with energy > 13.6 eV are absorbed by hydrogen atoms. In the process of recombining, line photons are emitted and this is the origin e.g. of Balmer-line spectra.  Collision between thermal electrons and ions excites the low-energy level of the ions, downward transition leads to the emission of so-called “forbidden-line” spectrum (possible in low density conditions).

Example of broad line radio galaxy (3C390.3)

Optical spectrum, what can we derive: which lines flux/luminosity width (kinematics) ionization mechanism (line ratios) density/temperature of the emitting gas morphology of the ionized gas (any relation with the radio?) continuum and stellar population using spectra and narrow band images

 Ionization parameter: ratio between ionizing photon flux / gas density  Temperature of the emitting gas  Mass of the emitting gas

Examples of diagnostic diagrams photoionization models for different ionization parameters

Broad line regions (BLR):  typical size (from variability) of light-days (Seyferts) up to few light-years (few x 0.3 pc, quasars).  electron density is at least 10 8 cm -3 (from the absence of broad forbidden lines)  typical velocities km/s Narrow line regions (NLR):  typical density 10 3 to 10 6 cm -3  gas velocity 300 – 1000 km/s  large range in size: from pc to tens of kpc

Powerful radio galaxies: energetics " Radiation " Jets " Winds + Starburst-induced superwinds…. Total wind power:10 43 — erg s -1 Wind power integrated over lifetime:10 56 — erg Jet power:10 43 —10 47 erg s -1 Jet power integrated over lifetime: — erg Quasar luminosity:10 44 — erg s -1 Luminosity integrated over lifetime:10 57 —10 62 erg

Emission line nebulae: what can we learn?

Emission line haloes: <1kpc scale " Kinematics. The emission line kinematics comprise a combination of gravitational motions, AGN-induced outflows, and AGN-induced turbulence " Black hole masses. Now possible to determine direct dynamical masses for nearby PRG using near-nuclear emission line kinematics " Feedback. The outflow component provides direct evidence for the AGN-induced feedback in the near- nuclear regions the presence of the nuclear activity could influence the evolution of the galaxy (e.g. clear gas away from the nuclear regions)

Cygnus A viewed by HST Optical images NICMOS 2.0  m

2.0 micron image HST/NICMOS Evidence for a super-massive black hole in Cygnus A

Correlation between black hole mass and galaxy bulge mass/luminosity Cygnus A

 broad permitted line seen in polarized line: only the scattered component can be seen Broad- and narrow line radio galaxies become undistinguishable

Emission line nebulae: 1-5kpc scale " Kinematics. Emission line kinematics a combination of AGN-induced and gravitational motions " Ionization. Gas predominantly photoionized by the AGN Outflows. Clear evidence for emission line outflows in Cygnus A and some compact radio sources, but outflow driving mechanism uncertain

Example of complex kinematics (IC5063) 700 km/s Complex kinematics of the ionized gas in coincidence with the radio emission: this suggests interaction between radio plasma and ISM

Emission lines in (powerful) radio galaxies Relative flux [O III]λλ4959,5007 z = ± FWHM ~ 1350 km s -1 [O II] [Ne III] [O III] HH [Ne V] [O II] λλ3727 z = ± FWHM ~ 650 km s -1 Δ z ~ 600 km s - 1 (Tadhunter et al 2001) Wavelength (Å)

Diagnostic diagrams including ionization from shocks

Emission line nebulae: 5-100kpc scale " Kinematics. Activity-induced gas motions are important along the full spatial extent of the radio structures, regardless of the ionization mechanism " Jet-induced shocks. The shocks that boost the surface brightness of the structures along the radio axes also induce extreme kinematics disturbance " Gravitational motions. Require full spatial mapping of the emission line kinematics in order to disentangle gravitational from AGN-induced gas motions " Starbursts. Starburst-induced superwinds may also affect the gas kinematics out to 10’s of kpc

Gas with very high ionization at 8 kpc from the nucleus Even if the nucleus is obscured by the torus, the extended emission line regions can tell us about the UV radiation from the nucleus.

Emission line “clouds” in the halo of CenA CenA: D~3Mpc

1000 km/s

Diagnostic diagrams important to understand which mechanism is dominant Contours: radio Colors: ionized gas In some cases the radio galaxy seems to have a strong effect on the medium around.

Radio galaxies at high redshift  Morphology of the extended emission line regions depends on the size of the radio source  Alignment between the emission lines and the radio axis  Interaction between radio and medium: does this also trigger star formation?

Any difference (in the optical lines) between low and high power radio galaxies?

What makes the difference? Intrinsic differences in the nuclear regions? Accretion occurring at low rate and/or radiative efficiency? No thick tori? Well known dichotomy: low vs high power radio galaxies Differences not only in the radio WHY? low-power radio galaxy high-power radio galaxy

Optical core No optical core The central regions of low-power radio galaxies No strong obscuration: optical core very often detected

From HST and X-ray The HST observations: Correlation between fluxes of optical and radio cores High rate of optical cores detected But so far we haven’t seen broad permitted lines

More on the host galaxy

The optical continuum of Radio Galaxies 3C321 old stellar pop. young stellar pop. power law Usually the old stellar population is the dominant - as usual in elliptical galaxies - but in some cases a young stellar population component is observed (typical ages between 0.5 and 2 Gyr).  consistent with the merger hypothesis for the triggering of the radio activity.  but not a single type of merger  AGN appears late after the merger

Results from UV imaging Allen et al C305 3C2933C321

The young stellar component may come from a recent merger o We can use the age of the stars to date when this merger occurred o To be compared with the age of the radio source

Cavities created by the radio emission in the hot (X-ray) gas

Emission line nebulae: what they can tell us  AGN Physics. Tests of the unified schemes, jet physics, black hole masses  Host galaxy properties. Mass distributions, abundances, gas masses  Galaxy Evolution. Clues to the assembly of massive galaxies at both high and low redshifts  Feedback. The importance of AGN-induced feedback effects in the evolution of the host galaxies