Low frequency radio observations of galaxy groups

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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
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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?

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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 _at_ 610 MHz
• rms 300-500 microJy/b _at_ 235 MHz
• high resolution from 5 arcsec _at_ 610 MHz to
  12 arsec _at_ 235 MHz

2-3 hrs obs.
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Targets and status of the GMRT observations
Group Name 235 MHz 610 MHz
UGC 408 Aug 08 X
NGC 315 Aug 08 X
NGC 383 Aug 08 X
NGC 507 Aug 08 X
NGC 741 X X
HCG 15 Aug 08 X
NGC 1407 Aug 08 X
NGC 1587 Aug 08 X
MKW 2 X X
Group Name 235 MHz 610 MHz
NGC 3411 X X
NGC 4636 X X
HCG 62 X X
NGC 5044 X X
NGC 5813 Aug 08 Aug 08
NGC 5846 X
AWM 4 X X
NGC 6269 X X
NGC 7626 Aug 08 X
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

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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
  OSullivan et al. 2005, see also OSullivans
  poster)

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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 ? ? 81-87

VLA 5 GHz
ß 0.5 0.2
GMRT 610 MHz (res. 5 arcsec)
Giacintucci et al. (2008) , astro-ph/0804.1906
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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 ?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 ainj 0.5 ?b 350 MHz
t rad 1.6 x 108 yr
Beq 5 µG
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Gas heating at the core of AWM 4?

• AWM 4 occupies an unusual place among groups and
  clusters

• 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
OSullivan 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)
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New 80 ksec Chandra observation (Cycle 9)
610 MHz on the 0.3-2 keV smoothed Chandra image
Preliminary!
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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 Sullivans poster)
• Statistical analysis of the whole sample
  (completion of the GMRT observations at 235/610
  MHz in August 2008)

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Large scale radio galaxies
NGC 7626 (NCC?)
GMRT 610 MHz (resolution 5 arcsec)
NGC 383 (3C 31) CC?
NGC 741/742 (CC) (S. Raychaudhurys talk)
NGC 741 NGC 7626 see also E.OSullivans
poster
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Small scale radio galaxies
HCG 62 - res. 14 (CC) (S. Raychaudhurys
talk)
GMRT 610 MHz (res. 5)
NGC 1407 (CC)
NGC 4636 (CC) (see E. OSullivan A. Baldi
posters)
NGC 6269 (CC)
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Amorphous radio galaxies
GMRT 610 MHz
NGC 3411 - res. 6 (NCC) (E. OSullivans
poster)
HCG 15 - res. 18 (NCC?)
NGC 1587 (NCC?) - res. 5 20
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Active and dying radio galaxies
UGC 408 GMRT 610 MHz (res. 5)
NGC 507 (CC)
CI OFF pow
a0.8 power law
tOFF /ts0.3
Dying
Active
Murgia et al. submitted
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UGC 408 GMRT 610 MHz (res. 5)
0.3-2.5 keV smoothed Chandra image