Download Sharp Images of Galaxy Groups: Chandra and XMM Uncover New

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
CfA
2 Univ. of Birmingham
3 Technion
4 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 models
and numerous following papers
• Prerequisite for understanding formation and evolution of structure:
galaxy => group => cluster hierarchy
e.g., Blumenthal, Faber, Primack, Rees 1983 and large subsequent enterprise
• Cool (~1 keV) => strong lines of O, Si, S, as well as of Fe
Kaastra, 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 4
Buote, Lewis, Brighenti, Mathews, et al.: NGC 5044
Opportunities from Chandra and XMM
XMM
Effective areas
(XMM Users’ Handbook)
Chandra
ASCA
ROSAT
Angular resolutions
(Pareschi et al. 2003)
Opportunities from Chandra and XMM (#2)
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Extraction of physical parameters
Deprojection techniques
Examination of disturbances
Bubbles, 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 magnitude
less 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
Sketch of groups observed with Chandra and XMM
52 groups;
8 Chandra alone, 15 XMM alone; 29 both.
HCG 62:
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4’
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DSS image
X-ray brightest and one of the most
intrinsically luminous of the 100
Hickson compact groups;
Lx ≈ 1043 erg s-1
Central galaxies: 2 ellipticals/S0’s
very similar (∆m ≈ 0.5);
within larger loose group (Rood &
Struble 1994; Tovmassian 2001)
Nearby: 59 Mpc for h = 0.7,
giving 1’=17 kpc
Mgas ≈ 1012 Msun within “ROSAT
radius” (~20’: Ponman & Bertram
1993)
Recent X-ray data include
50 ks Chandra ACIS-S
12 ks XMM
HCG 62: a gallery of X-ray images
8’
XMM MOS1+2, adaptively-smoothed
Chandra ACIS-S
4’
8’
Wavelet-smoothed Chandra image
HCG 62: radial dependences of physical parameters
Radial profile of temperature from ROSAT
(Ponman & Bertram 1993)
50 kpc
5 kpc
50 kpc
Data from XMM: Cycle 1 GTO program
HCG 62
annular and deprojected abundance profiles
(left) Radial temperature distribution. Free parameters: temperature, metal
Abundance, neutral hydrogen column density, and normalization.
(right) As to the left, but showing metallicity as a function of radius.
HCG 62: temperature variations
0.6 keV
1.2 keV
Adaptively-smoothed hardness ratio
Image (Chandra ACIS S3):
[1.2 - 2 keV]/[0.4 - 0.8 keV].
4’
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 resolution
details of spectral fitting (e.g., NGC 5044)
• Consequences of multiphase gas:
Affects determination of metal abundances
Implications for regulation of cooling: e.g., AGNs, heat
conduction, small-scale inhomogeneities
HCG 62: Chandra + VLA
Color: Chandra ACIS S3 50 ks
Contours: 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
DSS image
NGC 741
NGC 742
• Close pair of early-type galaxies
• z = 0.019
D = 81 Mpc (1’ = 24 kpc
• Core of approx. 41-member group
(Zabludoff & Mulchaey 1998),
with r ~ 430 km s-1
9’
4’
2MASS image
NGC 741 group
8’
6cm VLA map
• Narrow-angle tail radio source;
bright, complex morphology
• Angular extent of features well
matched to ACIS detector
• Well-studied previously in Xray, optical, and radio bands -but X-ray angular resolution
poor
• How does sharply-bent jet
structure arise in poor group
with low IGM density?
NGC 741
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2’
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Chandra images (31 ks):
rawcounts above,
“true color” below
NGC 741 dominates X-ray
structure (and radio?)
X-ray structure immediately
surrounding NGC 741 is
strongly asymmetric
Weak X-ray deficient
“bubble” found to SW in
region of radio tail
What is the nature of the two
“bridges” joining NGC 741
and NGC 742, and extending
to the north?
“Taffy galaxies” in X-rays?
• Proposed by Condon et al. (1993) for UGC 12914/12915: radio bridge
explained in terms of gas and magnetic fields from postcollision
galaxies
• Could NGC 741/742 constitute such a pair?
Relative narrowness of bridge due to greater concentration of gas
in ellipticals into dense cores (in comparison with spirals)?
Age: ~few x 107 yrs since (nearly) head-on collision.
Jet pointed approximately from NGC 741 to NCG 742 confined
by enhanced magnetic field?
• Related phenomena of wakes (Sakelliou 2000; Acreman et al. 2003)
and tidal tails may also be interesting here...
Summary
• Chandra and XMM support numerous observational advances in the
study of hot gas in groups:
Associations of X-ray with radio structures
Detection of cavities and other faint/small features
Association of X-ray features with optical galaxies
Tracing of temperatures and abundances
Unmatched angular resolution of Chandra….
• Areas old and new accessible to detailed analysis:
“Isolated” galaxies <> Groups <> Clusters: evolution and
scaling
Hydrodynamic equilibrium vs. nonthermal pressure support
Temperature structure in central regions; multiphase?
Nature/regulation of cooling cores