Nectaria Gizani

Probing the pc-& kpc-scale environment of the powerful radio galaxy Hercules A: 

Probing the pc-andamp; kpc-scale environment of the powerful radio galaxy Hercules A Environment Kpc-scale pc-scale (Gizani andamp; Leahy) (Gizani, Garrett andamp; Leahy) VLA radio data, 1'.4 L-band (A+B+C confign) 1665, 1435, 1365 andamp; 1295 MHz X-band (B+C+D confign) 8465 andamp; 8415 Mhz C-band (B+C+D confgn) EVN + MERLIN radio study of the core

Slide2: 

Kpc-scale environment continued.... L+C, X+C data at 1'.4 resolution andgt; andgt; Radio + X-ray data andgt; andgt; External B-field, Inclination of radio axis with axis along the l.o.s. DP-, RM-, a-map ROSAT X-ray PSPC andamp; HRI data Temperature of the intracluster gas, NH, hydrogen column density, no, central electron density, Radius of the X-ray core, Cooling flow cluster

Slide3: 

HST image Baum et al., 1996 MR = -23.75 Very elongated cD galaxy with double nucleus and a tail

Slide4: 

Logarithmic Contours separated by factors Ö2, 1st non-negative contour @ 0.16 mJy/beam Total intensity contour map

Slide5: 

R.A. 16h 48 m 40 s Total intensity map Hercules A: Dec. +05 ° 04' 36'.0 18 cm, 1'.4 z = 0.154, FR1.5 A+B+C radio data Total radio luminosity ~ 6.2´1037 W, Ho = 65 km/s, qo = 0 linear size ~ 194' (540 kpc), width ~ 250 kpc power density P178 Mhz = 2.3 ´1027 WHz-1sr-1

Slide6: 

The PSPC image of the Hercules A cluster at 32 arcsec Abell richness 0 to 1 Contours are separated by ratios of Ö2; 1st contour at 5.03´10 -10 Wm-2sr-1. Background level at »1.5´10-10 Wm-2sr-1 Total extent of X-ray emission »220'

Slide7: 

Contour map: The HRI X-ray image at 11.5 ars effective resolution Grey-scale map: Radio, VLA, map at 18 cm, 1.4 arcsec Contours separated by factors Ö2, starting at 3.26´10-9Wm-2sr-1.Backg. level at 0.54´10-9Wm-2sr-1 X-ray luminosity » 3.16´1037 W; of point source » 2´1036 W

Slide8: 

Contour map: Summed PSPC andamp; HRI image in 0.5-2 keV band at 32 arcsec Grey-scale: 20cm radio map in log display at 1'.4 kT » 2.45 keV for NH » 6.2´1020cm-2 (BeppoSax: 3 £ kT (keV) £ 5, Trussoni et al., 2001, ASCA: kT » 4.25 keV, Siebert andamp; Brinkmann, 1999) b-model fitting: b @ 0.74, rc @ 121 kpc no » 7.8´103m-3 , quite dense environment

Slide9: 

Contour map: total intensity radio map at 6 cm, 1.4 arcsec contours separated by factors Ö2, apart from 1st . 1st contour at 0.145 mJy/beam Vector magnitude: m B-vectors ^ m-vectors. Projected B-field follows closely the edges, jets andamp; ring-like structures in the lobes

Slide10: 

Hercules A: steep spectrum, a @ -1.5; young jets, rings a @ -.7; older lobes a @ -1.5; faint material -2.5 £ a £ -1.5 Snµna , aandlt;0 acore » -1.3, steep spectrum(!), optically thin

Slide11: 

Depoln map DP3.66 at 1.4 arcsec DPl1l2= ml1/ml2 , where l1andgt;l2 m = p/I, fractional poln p: polarized intensity, I: total intensity

Slide12: 

Depoln map DP186 at 1.4 arcsec The western side of the radio emission is more depolarized than the eastern side (Laing-Garrington effect)

Slide13: 

Depoln map DP236 at 1.4 arcsec

Slide14: 

East side:-200 £ RM(rad/m2 ) £ 200; Western side: RM exceeds ± 500 rad/m2 RM = kandlt;fandgt;, where f(r) = 0.81òr0neB×dl Faraday depth, l: line of sight Points are plotted if error in RM andlt; 5 rad/m2

Slide15: 

Conclusions of the kpc-scale study VLA Radio data: Hercules A exhibits a strong Laing-Garrington effect (Laing, 1988; Garrington et al., 1988). The depolarization asymmetry maybe explained in terms of the relativistic beaming model as a simple geometric effect: Hercules A is embedded in a centrally condensed medium at an angle of @ 50° to the l.o.s. The stronger jet is on the near side of the source (eastern side) and hense it is seen through less depolarized gas. A steep spectrum extended radio emission is revealed surrounding the jets of Hercules A. The more depolarized western side has a steeper spectrum than the less depolarised eastern side. Jets, rings (especially in the western lobe) have a much less steep spectrum than the lobe material: We maybe witnessing a renewed outburst from the active nucleus . ROSAT PSPC andamp; HRI X-ray data: Extended X-ray emission elongated along the radio axis, on roughly the same scales andamp; a weak nuclear component. The Hercules A cluster is quite dense with a significant

Slide16: 

concentration of gas towards the center (no @ 7.8´ 103 m-3) andamp; isothermal profile at radii, suggesting a cooling flow core. RM-, DP-maps + model fitting andamp; b-model fitting andgt;andgt; estimate of the central value of the external B-field strength 3 £ Bo(mG) £ 9. There is a radial dependence of the magnetic field and the electron density and the density of the gas.

Slide17: 

The study of the pc-scale environment A VLA B+C+D contour map of the core region at 3.6 cm, at 0.74 arcsec. Noise of the map: 11 mJy Contours just over 2s apart Core flux: 6.0 mJy at 3.6 cm (X-band) 44 mJy at 20 cm (L-band)

Slide18: 

The MERLIN detection at 18 cm, 0.51 arcsec. The diffuse emission not well mapped by MERLIN EVN+MERLIN Observations of the core of Hercules A at 18 cm with phase referencing The EVN detection at 18 cm, at 0.018 arcsec: ~30% of the flux of the core detected with the VLA is detected with EVN

Slide19: 

VLA+MERLIN map at 18 cm, at 0.51 arcsec

Slide20: 

Core flux @ 14.6 mJy, size: 18.2´7 mas, posn angle 139° Tb @ 2 ´ 107 K Hercules A asymmetric on pc-scales: NW-SE emission probably from the eastern pc-scale jet due to Doppler boosting andgt;andgt; Misalignment of 35° between pc- and kpc-scale jets EVN map at 18 cm, at 0.018 arcsec; rms » 0.45 mJy/beam; contours at -1,1,2,3,4,5,6,7,9,11,13. 1st non-neg. At 0.8 mJy/beam Direction of kpc-jets 35°

Slide21: 

Conclusions on the pc-scale study EVN data at 18 cm, 18 mas: The radio core, still unresolved. The core is very weak! Phase referencing did not work. NW-SE emission, probably from the eastern pcscale jet andgt;andgt; The detected asymmetry in the mas-scale, while there is symmetry on kpc-scales should be due to the Doppler Beaming: The mas scale jet is always on the same side as the kpc-scale jet, which is the brightest with respect to the core. MERLIN got confused by Hercules A's extended structure andgt;andgt; VLA+MERLIN map, but... Further observations at 6 cm could confirm the detected misalignment.

Slide22: 

Future multi-l Work (Hercules A, 3C310) OAL HI observations of each galaxy with emphasis on their nuclear region (Wb array; Morganti, Gizani andamp; Garrett; Summer 2001), and more... Infrared observations of the ring-like and helical-structures of the radio emission; Near IR polarimetric observations (Automn 2001; Gizani andamp; Gonzalez-Serrano). X-ray follow-ups, where possible. Chandra Observations for 3C310 HST observations of 3C310; V, R, I-band observations ...obtain Ha map of the nuclear region. UV observations, to use together with other wavelength observations, as diagnostic of the ISM; Study the UV emission from nuclear region