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 ≈ 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.

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 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

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 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)

GMRT 610 MHz on SDSSComposite XMM - optical image 4C +24.36

20 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/0804.1906

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

Beq = 5 μG

t rad ~ 1.6 x 108 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 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)

610 MHz on the 0.3-2 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 galaxiesGMRT 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 galaxiesGMRT 610 MHz

NGC 3411 - 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

tOFF /ts=0.3

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