Raman Research Institute, Bangalore, India

Giant radio galaxies of Mpc size are often located in the filamentary large-scale structure of the universe. In regions of moderate over-density. Is there a relationship between the radio structure and large scale galaxy distribution? The question:

Simulations of structure Simulations of structure formation suggest that moderate formation suggest that moderate over-densities have an IGM in the form of warm-hot gas. over-densities have an IGM in the form of warm-hot gas. The physical state of the IGM is uncertain due to complex astrophysics and feedback. Need to have good observational constraints on the gas!

On galaxy scales the morphologies of double radio sources is influenced by interactions with thermal gas – On galaxy scales the morphologies of double radio sources is influenced by interactions with thermal gas – inter-stellar medium inter-stellar medium galactic X-ray halo, galactic X-ray halo, emission-line gas emission-line gas Both the forward propagation of jets as well as backflow from hotspots in the lobes are influenced by the gas they meet. Both the forward propagation of jets as well as backflow from hotspots in the lobes are influenced by the gas they meet.

Observations of interaction between lobe material and thermal plasma 3C381 3C28 McCarthy et al C28 3CRR Atlas Leahy & Perley, 1991 McCarthy et al. 1995

Elliptical X-ray halo observed in 3C403, which is an X-shaped radio galaxy Kraft et al X-ray contours

Case studies of the relationship between radio structures and ambient galaxy distribution in in MSH J and MRC B Ravi Subrahmanyan (RRI, Bangalore, India) Lakshmi Saripalli (RRI, Bangalore, India) Vicky Safouris (ATNF & ANU, Australia) Dick Hunstead (University of Sydney, Australia) Geoff Bicknell (ANU, Australia)

MRC B0319  454 Redshift z = (1” = 1.2 kpc) 26 arcmin LLS = 1.9 Mpc b J = 15 M R =  23.7 ATCA 1378 MHz Source previously studied by Jones 1989 Saripalli et al. 1994

Very asymmetric source Different lobe lengths from the core Different lobe surface brightness Different lobe structures - off axis distortions Emission gaps S (1378 MHz) = 3.86 Jy P (1378 MHz) = 4 x W/Hz

Radio polarization ( Polarized intensity & E vectors ~ % pol) RM ~ 0  7 rad/m 2 DR 1.0 DR 0.9 DR 0.75 DR 1.0 DR 0.6

Radio spectral Index Distribution Whole source  =  0.84

Large-scale galaxy distribution from 6dFGS R = 6 Mpc top-hat smoothing Radio source Is embedded In a filament 60 Mpc x 15 Mpc x 8 Mpc (depth) (assuming no `Kaiser effect’)

g  = 250 km/s at the host galaxy This is small, consistent with the embedded nature of the host

Zoom-in view of the large-scale structure: 1. AAOmega and 2dF instruments on the Anglo-Australian Telescope 664 galaxy redshifts over a 2 degree field with 73% completeness to b J <

Conc 1 + Conc 2 Galaxy distribution Is not uniform Concentrations And Voids (e.g. NE of radio src)

Identify galaxy concentrations Using friends-of-friends algorithm (Huchra & Geller 1982) D L = 1 Mpc, V L = 400 km/s 1.Host is a member of a group 2.A second concentration is located 40’ = 2.8 Mpc SW of the host group

Group associated with the host galaxy ( a loose group) 1 Mpc projected linear extent 200 km/s velocity dispersion Host galaxy is brightest member (b J = 16.1 – – 17.2) and at the centre in 3D Concentration to SW 1.5 Mpc projected size 270 km/s velocity dispersion Mean velocity 300 km/s greater than the host group  v = 0 Mpc  v = +3.8 Mpc R=1.25 Mpc Top-hat smoothing

How do we understand the NE lobe? 1.The jet terminates within the thermal halo of the loose group, of which the host is a member. 2.The backflow is confined by the thermal halo, the backflow is relatively strong because of the relatively denser environment: these cause the NE lobe to have higher surface brightness and the backflow extends back to the core.

How do we understand the SW lobe? 1.The SW jet terminates outside of the thermal halo associated with the host group 2.The relatively lower ambient gas density results in weaker backflow, lower surface brightness lobe 3.The deflection of backflow from the SW lobe is difficult to understand As a buoyant bubble, or As a buoyant backflow The backflow is probably deflected N because of gas gradient associated with the host-group thermal halo, as in X-shaped radio sources.

MSH J A giant radio source of 40 arcmin size z = Mpc projected size Source previously studied by Saripalli et al. 1986; Subrahmanya & Hunstead MHz MOST 1.8 Mpc

1520 MHz VLA CnB array

No hotspots S (1.4 GHz) = 3 Jy P (1.4 GHz) = 1.1 x W/Hz The radio lobes of MSH J are not sharply bounded Radio spectral index  = Relict lobes?

Source is asymmetric Source is asymmetric 1:1.6 length ratio 1:1.6 length ratio N lobe shorter in length N lobe shorter in length N lobe off axis to W N lobe off axis to W N lobe extends back N lobe extends back beyond core/host galaxy

6dF galaxy redshift survey (Jones et al. 2004) Slices 216 Mpc a side and 21 Mpc deep Radio source at the centre. (a)  z =  to  (b)  z =  to  (c)  z =  to  (d)  z =  to  (e)  z =  to  (f)  z =  to  Radio source is at the bottom far boundary of a sheet of galaxies.

Raman Research Institute, Bangalore, India Gravity vectors in the plane containing the host galaxy g  = 650 km/s g  = 630 km/s on sky plane towards P.A. 60°

AAT 2dF spectroscopy to get a zoomed in view of the local galaxy distribution AAT 2dF spectroscopy to get a zoomed in view of the local galaxy distribution 592 object spectra in 2 fiber allocations 592 object spectra in 2 fiber allocations 359 galaxies within 2° diameter circle 359 galaxies within 2° diameter circle MSH J at z = 0.038

Galaxies within z = 0.03 – 0.05 Large stars  z = +/ Mpc = 2°

MSH J is at the SW edge of large-scale structure Nearest galaxy concentration at 1.8 Mpc distance at P.A. of 40° towards NE Fractional over-density with R=1 Mpc smoothing Host galaxy belongs to a low X-ray luminosity group, 300 kpc diameter Velocity dispersion 83 km/s

How do we understand the radio structure in the light of the large-scale galaxy distribution? Galaxy density gradient towards NE is consistent with Galaxy density gradient towards NE is consistent with the NE lobe being shorter the NE lobe being shorter And backflow from NE lobe being stronger And backflow from NE lobe being stronger It is plausible that the NE lobe might have moved SW as a buoyant bubble in the 1 Gyr age of the relict source It is plausible that the NE lobe might have moved SW as a buoyant bubble in the 1 Gyr age of the relict source

Estimate for minimum pressure in the relict lobe synchrotron plasma: Estimate for minimum pressure in the relict lobe synchrotron plasma: B > nT u > 1.2 × 10  14 J/m 3 p > 4.1 × 10  15 N/m 2 p > 4.1 × 10  15 N/m 2 Assuming galaxies trace the gas, and 50% baryons in WHIM, estimate for pressure in the WHIM gas: Assuming galaxies trace the gas, and 50% baryons in WHIM, estimate for pressure in the WHIM gas: p IGM ~ 4.2 x (  n/n) × (kT/1keV) N/m 2 p IGM ~ 4.2 x (  n/n) × (kT/1keV) N/m 2 If If MSH J is a relict; then is the internal pressure a measure of the external IGM pressure?

Assume pressure equilibrium between radio lobes and ambient IGM (  n/n) × (kT/1keV) > 100 The ambient pressure as inferred from the radio observations is an order of magnitude larger than what is expected from hydrodynamic shocks in the observed over-density

Additional source of heating is required for the IGM environment of giant radio sources (1) Astrophysical feedback: Do galactic super winds (GSWs) or AGN activity from galaxies and galaxy concentrations heat the IGM up to a few Mpc from galaxy concentrations? (1) Is there an over-pressured shell of swept up IGM immediately surrounding the relaxed relict radio lobes.

Summary This work is a first step towards using the relationship between giant radio galaxies and LSS as a means of probing the IGM outside clusters and group environments This work is a first step towards using the relationship between giant radio galaxies and LSS as a means of probing the IGM outside clusters and group environments The giant radio galaxies – with Mpc linear size – probe the WHIM component in the moderate density filaments. The giant radio galaxies – with Mpc linear size – probe the WHIM component in the moderate density filaments. We do observe a correspondence between the morphologies in giant radio sources and the large-scale galaxy distribution: evolution of giant radio sources is governed by the gas associated with galaxies in the large- scale structure. We do observe a correspondence between the morphologies in giant radio sources and the large-scale galaxy distribution: evolution of giant radio sources is governed by the gas associated with galaxies in the large- scale structure.

Subrahmanyan, R; Saripalli, L; Safouris, V; Hunstead, R W, “On the Relationship between a Giant Radio Galaxy MSH and the Ambient Large-Scale Galaxy Structure”, 2008 ApJ 677, p63 Subrahmanyan, R; Saripalli, L; Safouris, V; Hunstead, R W, “On the Relationship between a Giant Radio Galaxy MSH and the Ambient Large-Scale Galaxy Structure”, 2008 ApJ 677, p63 Safouris, V; Subrahmanyan, R.; Bicknell, G V; Saripalli, L, “MRC B : probing the large-scale structure with a giant radio galaxy”, submitted to MNRAS. Safouris, V; Subrahmanyan, R.; Bicknell, G V; Saripalli, L, “MRC B : probing the large-scale structure with a giant radio galaxy”, submitted to MNRAS.