Low frequency radio observations of galaxy groups With acknowledgements to: R. Athreya, P. Mazzotta, T. Clarke, W. Forman, C. Jones, T. Ponman S.Giacintucci (CfA), J. Vrtilek (CfA), E. O'Sullivan (CfA), S. Raychaudhury (CfA, U. Birmingham), L.David (CfA), T.Venturi (INAF-IRA Italy), M. Murgia (INAF-Oss. Cagliari)

The project For a sample of nearby groups of galaxies: GMRT observations at low frequency (235, 327 & 610 MHz) X-ray data from Chandra and/or XMM-Newton Questions How do X-ray and radio structures correlate? What are the properties of central radio sources over a broad frequency range and what do they imply for ages, outburst cycles…? What are the effects of AGN at various phases of activity? What are the mechanisms of energy injection?

Why groups? Examining outbursts in systems smaller than the well-studied rich clusters is valuable for a number of reasons: shallow group potential  large impact on intragroup medium low pressure environment  more apparent radio/thermal gas interaction significant influence on galaxy evolution Why GMRT? very high sensitivity at low radio frequency: rms ≈ MHz rms ≈ MHz high resolution: from MHz to MHz 2-3 hrs obs.

Targets and status of the GMRT observations 18 galaxy groups All have Chandra and/or XMM data Temperatures 1-3 keV All have at least NVSS 1.4 GHz data initially Presence of X-ray or radio structure indicative of AGN interaction with hot gas Group Name235 MHz610 MHz UGC 408 Aug 08 X NGC 315 Aug 08 X NGC 383 Aug 08 X NGC 507 Aug 08 X NGC 741 XX HCG 15 Aug 08 X NGC 1407 Aug 08 X NGC 1587 Aug 08 X MKW 2 XX Group Name235 MHz610 MHz NGC 3411 XX NGC 4636 XX HCG 62 XX NGC 5044 XX NGC 5813 Aug 08 NGC 5846 X AWM 4 XX NGC 6269 XX NGC 7626 Aug 08 X observed at 327 MHz

The prototype analysis: AWM 4 Poor cluster (~30 members) centered on giant elliptical NGC 6051 No optical substructure (Koranyi & Geller 2002) X-ray bright (~ 2 x erg s -1 ), T~ 3 keV Apparently relaxed (but disturbance in the temperature and abundance distribution; O’Sullivan et al. 2005, see also O’Sullivan’s poster) GMRT 610 MHz on SDSS Composite XMM - optical image 4C kpc

Radio overview GMRT 610 MHz (res. 5 arcsec) VLA 5 GHz Similar WAT morphology at 235 and 327 MHz Lobes and jets are symmetric in flux, size and spectral index properties Jet-to-counterjet brightness ratio → θ ~ 81°-87° β = 0.5 ± 0.2 Giacintucci et al. (2008), astro-ph/

Spectral analysis and age of the radio source MHz spectral index image (res. 13 arcsec) Fit using a JP model (Jaffe & Perola 1973) and assuming ν b prop. to d -2 - expected under the assumption that the growth velocity is constant - reflects the fact that the electron age increases as electrons move away from the nucleus RESULTS: α inj ~ 0.5 ν b ~ 350 MHz B eq = 5 μG t rad ~ 1.6 x 10 8 yr

Gas heating at the core of AWM 4? AWM 4 occupies an unusual place among groups and clusters O’Sullivan et al. (2005) Regular X-ray emission Monotonic increase of brightness toward the centre Cooling time ~ 2 Gyr Metallicity decline from the centre to large radii Relaxed cluster with a well-established cool core BUT Gas (re)heating by the central AGN: - Required energy ~ 9 x ergs - E tot, RADIO ~ 2.9 x ergs (t ~ 160 Myr) - Mechanical energy?? → ~ 80 kpc bubbles No X-ray cavities in the XMM image (see Giacintucci et al for details)

610 MHz on the keV smoothed Chandra image New 80 ksec Chandra observation (Cycle 9) Preliminary!

Conclusions and future perspectives Our analysis of AWM 4 shows that the combination of X-ray and high sensitivity multi-(low) frequency radio observations offers useful insight into AGN/hot gas interaction, geometry, timescales, energetics... in the central region of groups and clusters A similar study will be carried out for other individual interesting groups in the sample (see preliminary results in E. O’ Sullivan’s poster) Statistical analysis of the whole sample (completion of the GMRT observations at 235/610 MHz in August 2008)

Large scale radio galaxies GMRT 610 MHz (resolution: 5 arcsec) NGC 383 (3C 31) CC? NGC 7626 (NCC?) NGC 741 & NGC 7626: see also E.O’Sullivan’s poster NGC 741/742 (CC) (S. Raychaudhury’s talk)

Small scale radio galaxies GMRT 610 MHz (res. 5’’) NGC 6269 (CC) HCG 62 - res. 14’’ (CC) (S. Raychaudhury’s talk) NGC 1407 (CC) NGC 4636 (CC) (see E. O’Sullivan & A. Baldi posters)

Amorphous radio galaxies GMRT 610 MHz NGC res. 6” (NCC) (E. O’Sullivan’s poster) HCG 15 - res. 18’’ (NCC?) NGC 1587 (NCC?) - res. 5’’ & 20’’

Active and dying radio galaxies UGC 408 GMRT 610 MHz (res. 5’’) NGC 507 (CC) Active Dying Murgia et al. submitted α=0.8 power law CI OFF + pow t OFF /t s =0.3

UGC 408 – GMRT 610 MHz (res. 5’’) keV smoothed Chandra image