Sharp Images of Galaxy Groups: Chandra and XMM Uncover New Intricacies J. M. Vrtilek 1 , E. J. O’Sullivan 1 , T. J. Ponman 2 , L. P. David 1 ,D. E. Harris 1 , W. Forman 1 , C. Jones 1 , N. Soker 3 , W. M. Lane 4 , N. Kassim 4 1 CfA 2 Univ. of Birmingham 3 Technion 4 Naval Research Lab.
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Sharp Images of Galaxy Groups: Chandra and XMM Uncover New Intricacies J. M. Vrtilek 1, E. J. O’Sullivan 1, T. J. Ponman 2, L. P. David 1,D. E. Harris.
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Sharp Images of Galaxy Groups: Chandra and XMM
Uncover New Intricacies
J. M. Vrtilek1, E. J. O’Sullivan1, T. J. Ponman2, L. P. David1,D. E. Harris1, W. Forman1, C. Jones1, N. Soker3, W. M. Lane4, N. Kassim4
1 CfA2 Univ. of Birmingham3 Technion4 Naval Research Lab.
Why observe Groups (in X-rays)?• Location of many (most?) galaxies?
Geller & Huchra 1983: CfA Redshift Survey; density contrast ≥ 20
Nolthenius & White 1987: comparison with numerical modelsand numerous following papers
• Prerequisite for understanding formation and evolution of structure:galaxy => group => cluster hierarchye.g., Blumenthal, Faber, Primack, Rees 1983 and large subsequent enterprise
• Cool (~1 keV) => strong lines of O, Si, S, as well as of FeKaastra, Kahn, Paerels, Peterson, et al.: XMM RGS
• “Simpler” environment than rich clusters for examining heavy element enrichment?
O’Sullivan et al. 2003, 2004: MKW 4, AWM 4Buote, Lewis, Brighenti, Mathews, et al.: NGC 5044
Opportunities from Chandra and XMM Effective areas
Angular resolutions
XMM
Chandra
ROSAT
ASCA
(XMM Users’ Handbook)
(Pareschi et al. 2003)
Opportunities from Chandra and XMM (#2)
• Extraction of physical parameters
Deprojection techniques
• Examination of disturbancesBubbles, shocks, …
• Comparison with features observed at other wavelengths
Extended radio features
• PROBLEMS:groups are faint (Lx < 1043-44 erg s-1 — about 2 orders of magnitudeless than rich clusters), therefore inaccessible at high z
groups are extended, therefore nearby ones fill the field-of-view, leading to issues with understanding of the outer regions and with background removal
• Recent X-ray data include50 ks Chandra ACIS-S12 ks XMM
4’
DSS image
HCG 62: a gallery of X-ray images
XMM MOS1+2, adaptively-smoothed
8’
Chandra ACIS-S
8’4’
Wavelet-smoothed Chandra image
HCG 62: radial dependences of physical parameters
5 kpc 50 kpc
Data from XMM: Cycle 1 GTO program
Radial profile of temperature from ROSAT(Ponman & Bertram 1993)
50 kpc
HCG 62annular and deprojected abundance profiles
(left) Radial temperature distribution. Free parameters: temperature, metalAbundance, neutral hydrogen column density, and normalization.(right) As to the left, but showing metallicity as a function of radius.
Adaptively-binned temperature map(Chandra ACIS S3)
Multiphase gas?• So far, have discussed models that describe gas with a single set of
physical parameters at each point
generally varying as a function of r only, with spherical or ellipsoidal symmetry
• However: gas could be mixed on very fine spatial scales (multiphase)(Mathews, Brighenti, & Buote 2004; Arabadjis & Bautz 2003;
Buote et al. 2002, 2003,…)• Evidence for multiphase gas:
complex appearance of intensity, temperature at high resolutiondetails of spectral fitting (e.g., NGC 5044)
• Consequences of multiphase gas:Affects determination of metal abundancesImplications for regulation of cooling: e.g., AGNs, heat conduction, small-scale inhomogeneities
HCG 62: Chandra + VLA
Color: Chandra ACIS S3 50 ksContours: VLA 1.4 GHz
X-ray image has been wavelet-smoothed.Circles indicate “cavities” of reduced X-ray surface brightness ~10 kpc to NE and SW of X-ray peak.Radio map has a clean beam size of 18x12 arcsec and an rms noise level of 80 µJy;Contours are spaced by factors of 2 with lowest at 0.3 mJy/beam.
HCG 62: cavities and radio emission• Only unresolved 5 mJy (1.4 GHz) core radio source originally known;
motivated VLA observations:3.3 hrs at 1.4 GHz in CnB configuration (12x18 arsec beam)9 hrs at 330 MHz in BnA configuration (8x15 arcsec beam)
• Detection only at 1.4 GHz in SW “tail”: 1.2±0.4 mJy• Where detected, the equipartition magnetic field pressure is a factor of
a few less than the thermal pressure, but could be increased by adjustments in filling factor, presence of relativistic protons…
Timescales and energetics of cavities
• Parameters of HCG 62 cavities are very typical, though radio luminosity, ~few x 1038 erg s-1, is at the very low end of the range (cf. Birzan et al. 2004)
• Cavity ages:by time to rise at sound speed, time to rise buoyantly,and time to refill displaced volume: ~ (1.5 - 3)x107 yr
• “Energy content” (work done on surrounding medium to produce a cavity) is ~few x 1056 erg
• Current radio source is far too weak to produce cavities in required time. But a very modest AGN (1041 - 1042 erg s-1) would suffice.
• Cavities are seen in ~20% of clusters. Is the same true for groups?
NGC 741 group
• Close pair of early-type galaxies
• z = 0.019D = 81 Mpc (1’ = 24 kpc
• Core of approx. 41-member group (Zabludoff & Mulchaey 1998), with r ~ 430 km s-1
9’
DSS image
2MASS image
4’
NGC 742
NGC 741
NGC 741 group
• Narrow-angle tail radio source; bright, complex morphology
• Angular extent of features well matched to ACIS detector
• Well-studied previously in X-ray, optical, and radio bands -- but X-ray angular resolution poor
• How does sharply-bent jet structure arise in poor group with low IGM density?6cm VLA map