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The FR Divide in Radio Galaxies through Environmental Interactions
T. Maciel (Astrophysics Group) , P. Alexander (Astrophysics Group)

Radio-Loud Galaxies
·Galaxies which are dominated by their radio emission (10MHz -100GHz) and show extended morphology: -Jets Active Galactic Nuclei -Lobes powered by (AGN) -Hotspots -Central black hole -Accretion disc -Strong B fields -Dusty torus
Chandra X-Ray image of Perseus cluster with VLA radio inset, showing clear feedback between radio jets and cluster gas. (Fabian et. al. 2003)

Fanaroff-Riley Dichotomy
Two Morphology Types: FRI
·Peak radio flux occurs length ·Diffuse, less-powerful, ·No terminating hotspot lobes ·Lower radio luminosity

(Fanaroff and Riley 1974)

The Fanaroff-Riley dichotomy between radio-loud galaxies may reveal to what extent the lobes and jets of these galaxies interact with their local environments, and indicate the role that AGN feedback plays in galaxy evolution. But the dominant cause of this FR dichotomy remains unclear.

in first half of total jet

FRII

less-relativistic jets and possibly turbulent (1022-10
24.4

W Hz-1 sr-1)

·Peak emission at the end of the jets ·Highly relativistic (~0.87c) and radiatively efficient (therefore dim) jets ·Bright hotspots and clear lobes ·High total radio luminosity (>1024.4 W Hz-1 sr-1)

Radio-loud galaxies make up only ~10% of total extragalactic radio sources, but their extreme luminosities and ability to perform work on their local environment via the jets and lobes make them strong candidates for central feedback to offset excess cluster gas cooling. Injecting radiative and mechanical energy into a cluster/local galaxies can slow star formation rates and dictate future AGN activity. (Fabian 1994 and McNamara & Nulsen 2007)

What are the factors that determine level of AGN feedback? Need to look at morphology for signs of interaction

Above: FRI galaxy 3C31 shown in 1.4GHz radio (red) and optical (blue). Right: FRII galaxy 3C175 at 5GHz. (Kaiser & Alexander 1997; and Kaiser & Best 2007)

Classifying a sample of radio galaxies by their extended morphology also divides the sample into distinct groups of high and low luminosity, with a divide at ~1024.4 W Hz-1 sr-1 at 1.4 GHz

Jet Evolution and PD Diagram
Environment
· · · · · Cluster scale length Initial core density Initial core pressure Density decay factor Adiabatic index ao o pxo x Qo Lj/t j j ~2 kpc 1.7 x 10-22 kg m-3 10-11 ­ 10-13 N m-2 1.5-1.9 5/3

Environment density profile:

Evolution of electron Lorentz factor (synchrotron, adiabatic, and inverse-Compton losses:

Lobe and jet pressure:

Jet
· · · ·

Initial jet power Length/age Lorentz factor Adiabatic index

1.3 x 1038 W 2 4/3

Jet length as a function of source age, t:

Lobe
· · · ·
*

Lobe length = jet length Length-width radio R Adiabatic index c Pressure pc

2* 4/3

Total non-thermal luminosity from a source of radiating electrons, occupying volume V and traveling with Lorentz factors (t, ti): Want to match analytic model to observations:

Self-similar evolution, therefore constant ratio

CoNFIG Sample
·Sources pulled from overlap between NVSS (Condon et al. 1998) and FIRST (Becker et al. 1995) VLA surveys at 1.4 GHz ·Four samples: CoNFIG-1,-2,-3,-4 corresponding to flux limits 1.3, 0.8, 0.2, and 0.05 Jy respectively ·859 sources in total -466 FRII -71 FRI -285 Compact (C, C*, or S*) -37 Uncertain (U) ·Optical cores and redshifts for 74.6%

Combined NVSS-FIRST Galaxies (Gendre & Wall 2008; and Gendre et. al. 2010)

P-D Diagram with CoNFIG sources

Can match jet evolutionary tracks to CoNFIG sample on P-D plane by comparing predicted population densities to observed. By considering source ages (jet length equation), we expect sources to spend the longest time between 100-1000 kpc, as observed. Additional observations planned for next year with the eMERLIN array at 1.4 GHz to determine morphology of uncertain and extended 'compact' sources

Manually measured angular sizes for extended sources, and converted to projected linear size using redshift:

· · · · ·

·Consider optical-radio luminosity relationship as a way of quantifying feedback between radio core and host galaxy. Test whether density of sources with P1.4 increases as Lumopt1.5 (Auriemma et. al. 1977) Using ratio of lobe fluxes and possible depolarization information, constrain orientation angle and thus intrinsic linear size Estimate source ages from spectral indices, and compare with predicted ages based on intrinsic jet length Estimate lobe pressure based on lobe volume and assumption of equipartition between electron and magnetic field energy densities Constrain environmental pressure of host galaxy/cluster via x-ray observations of gas, and compare with lobe pressure. Environmental interaction likely? Conclude by determining likely level of environmental contribution to jet evolution through both analytic models and observational statistics

Future Work

References