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Low frequency radio observations of galaxy groups

Low frequency radio observations of galaxy groups. 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). With acknowledgements to:

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Low frequency radio observations of galaxy groups

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  1. Low frequency radio observations of galaxy groups 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) With acknowledgements to: R. Athreya, P. Mazzotta, T. Clarke, W. Forman, C. Jones, T. Ponman

  2. 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?

  3. 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 ≈ 50-100 microJy/b @ 610 MHz • rms ≈ 300-500 microJy/b @ 235 MHz • high resolution: from 5 arcsec @ 610 MHz to 12 arsec @ 235 MHz 2-3 hrs obs.

  4. Targets and status of the GMRT observations observed at 327 MHz • 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

  5. The prototype analysis: AWM 4 Composite XMM - optical image 4C +24.36 GMRT 610 MHz on SDSS 20 kpc • Poor cluster (~30 members) centered on giant elliptical NGC 6051 • No optical substructure (Koranyi & Geller 2002) • X-ray bright (~ 2 x 1043 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)

  6. Radio overview • 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° VLA 5 GHz β = 0.5 ± 0.2 GMRT 610 MHz (res. 5 arcsec) Giacintucci et al. (2008) , astro-ph/0804.1906

  7. Spectral analysis and age of the radio source 235-610 MHz spectral index image (res. 13 arcsec) • Fit using a JP model (Jaffe & Perola 1973) and assuming νb 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: αinj ~ 0.5 νb~ 350 MHz t rad~ 1.6 x 108 yr Beq = 5 μG

  8. Gas heating at the core of AWM 4? • 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 AWM 4 occupies an unusual place among groups and clusters BUT O’Sullivan et al. (2005) Gas (re)heating by the central AGN: • Required energy ~ 9 x 1058 ergs - Etot, RADIO ~ 2.9 x 1057 ergs (t ~ 160 Myr) - Mechanical energy?? → ~ 80 kpc bubbles No X-ray cavities in the XMM image (see Giacintucci et al. 2008 for details)

  9. New 80 ksec Chandra observation (Cycle 9) 610 MHz on the 0.3-2 keV smoothed Chandra image Preliminary!

  10. 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)

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

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

  13. Amorphous radio galaxies GMRT 610 MHz NGC 3411 - res. 6”(NCC) (E. O’Sullivan’s poster) HCG 15 - res. 18’’ (NCC?) NGC 1587 (NCC?) - res. 5’’ & 20’’

  14. Active and dying radio galaxies UGC 408 GMRT 610 MHz (res. 5’’) NGC 507 (CC) CI OFF + pow α=0.8 power law tOFF /ts=0.3 Dying Active Murgia et al. submitted

  15. UGC 408 – GMRT 610 MHz (res. 5’’) 0.3-2.5 keV smoothed Chandra image

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