XMM-Newton observation of the most X-ray-luminous galaxy cluster RX J1347.5-1145

Abstract

We report on an XMM-Newton observation of RX J1347.5-1145 (z=0.451), the most luminous X-ray cluster of galaxies currently known, with a luminosity L_X = 6.0 \pm 0.1 \times 10^45 erg/s in the [2-10] keV energy band. We present the first temperature map of this cluster, which shows a complex structure. It identifies the cool core and a hot region at radii 50-200 kpc to south-east of the main X-ray peak, at a position consistent with the subclump seen in the X-ray image. This structure is probably an indication of a submerger event. Excluding the data of the south-east quadrant, the cluster appears relatively relaxed and we estimate a total mass within 1.7 Mpc of 2.0 \pm 0.4 \times 10^15 M_sun. We find that the overall temperature of the cluster is kT=10.0 \pm 0.3 keV. The temperature profile shows a decline in the outer regios and a drop in the centre, indicating the presence of a cooling core which can be modelled by a cooling flow model with a minimum temperature ~2 keV and a very high mass accretion rate, \dot{M} ~ 1900 M_sun/yr. We compare our results with previous observations from ROSAT, ASCA and Chandra. Comment: 4 pages, 6 figures, accepted for publication in Astronomy & Astrophysics Letters

Full text

Page 1

arXiv:astro-ph/0409627v1 27 Sep 2004
Astronomy & Astrophysics manuscript no.
(will be inserted by hand later)
XMM-Newton observation of the most X-ray-luminous galaxy
cluster RX J1347.5−1145
Myriam Gitti and Sabine Schindler
Institut f¨ ur Astrophysik, Leopold-Franzens Universit¨ at Innsbruck, Technikerstraße 25, A-6020 Innsbruck, Austria
Received / Accepted
Abstract. We report on an XMM-Newton observation of RX J1347.5−1145 (z=0.451), the most luminous X-ray cluster of
galaxies currently known, with a luminosity LX = 6.0 ± 0.1 × 1045erg/s in the [2-10] keV energy band. We present the first
temperature map of this cluster, which shows a complex structure. It identifies the cool core and a hot region at radii 50-200
kpc to south-east of the main X-ray peak, at a position consistent with the subclump seen in the X-ray image. This structure
is probably an indication of a submerger event. Excluding the data of the south-east quadrant, the cluster appears relatively
relaxed and we estimate a total mass within 1.7 Mpc of 2.0±0.4 × 1015M⊙. We find that the overall temperature of the cluster
is kT = 10.0 ± 0.3 keV. The temperature profile shows a decline in the outer regions and a drop in the centre, indicating the
presence of a cooling core which can be modelled by a cooling flow model witha minimum temperature ∼2keV and a very high
mass accretion rate, ˙ M ∼ 1900 M⊙/yr. We compare our results with previous observations from ROSAT, ASCA and Chandra.
Key words. Galaxies:clusters:particular: RX J1347.5−1145 – X-ray:galaxies:clusters – cooling flows
1. Introduction
In this paper we present the first results from an XMM-Newton
observation of RX J1347.5−1145, the most X-ray-luminous
galaxy cluster known (Schindler et al. 1995). This cluster has
been detected in the ROSAT All-Sky Survey and further stud-
ied with ROSAT HRI and ASCA (Schindler et al. 1995, 1997).
It shows a very peaked X-ray emission profile and presents a
strong cooling flow in its central region. Submm observations
in its direction showed a very deep SZ decrement (Komatsu
et al. 1999, 2001; Pointecouteau et al. 1999, 2001). Due to the
presenceof gravitationalarcs, this cluster is also well suited for
a comparison of lensing mass and X-ray mass. Optical stud-
ies of weak lensing have been performed by Fischer & Tyson
(1997) and Sahu et al. (1998). Recent Chandra observations
(Allen et al. 2002) discovered a region of relatively hot, bright
X-ray emission, located approximately 20 arsec to the south-
east of the main X-ray peak at a position consistent with the
region of enhanced SZ effect. This could be an indication for a
subcluster merger, pointing to a complex dynamical evolution.
A comparison of the XMM-Newton and SZ results, a more de-
tailedanalysisofthecomplexdynamicalstateoftheclusterand
a comparisonof lensingmass and X-raymass will be presented
in a forthcoming paper (Gitti et al. in prep.).
RX J1347.5−1145 is at a redshift of 0.451. With H0 =
70 km s−1Mpc−1, and ΩM = 1 − ΩΛ = 0.3, the luminosity
distance is 2506 Mpc and 1 arcsec corresponds to 5.77 kpc.
Send
myriam.gitti@uibk.ac.at
offprint requeststo:Myriam Gitti,e-mail:
2. Observation and data preparation
RX J1347.5−1145was observedbyXMM-NewtoninJuly 2002
during rev. 484 with the MOS and pn detectors in Full Frame
Mode with THIN filter. We used the SASv6.0.0 processing
tasks emchain and epchain to generate calibrated event files
fromraw data. Standardprocessingwas appliedto preparedata
and reject the soft proton flares. The remaining exposure times
after cleaning are 32.2 ks for MOS1, 32.5 ks for MOS2 and
27.9 ks for pn. The background estimates were obtained us-
ing a blank-sky observation consisting of several high-latitude
pointings with sources removed (Lumb et al. 2002). The back-
ground subtraction was performed as described in full detail in
Arnaud et al. (2002). The source and background events were
corrected for vignetting using the weighted method described
in Arnaud et al. (2001).
3. Morphological analysis
The
(MOS+pn) in the [0.9-10] keV energy band is presented
in Fig. 1. The image is obtained from the mosaic of the raw
images corrected for the mosaic of the exposure maps by
running the task asmooth set to a desired signal-to-noise
ratio of 20. A number of notable features are visible. In
particular, we note a sharp central surface brightness peak at
13h47m30s.6 − 11◦45′09′′.0 (J2000), in very good agreement
with the optical centroid for the dominant cluster galaxy
(Schindler et al. 1995). We also confirm the presence of a
region of enhanced emission ∼ 20 arcsec to the south-east
adaptivelysmoothed,exposurecorrectedimage

Page 2

2 Gitti & Schindler.: XMM-Newton observation of the most X-ray-luminous galaxy cluster RX J1347.5−1145
Fig.1. Total (MOS+pn) XMM-Newton EPIC mosaic image of
RX J1347.5−1145 in the [0.9-10] keV energy band. The im-
age is corrected for vignetting and exposure and is adaptively
smoothed.
(SE) of the X-ray peak and, on large scale (∼ 80 arcsec), the
extension of the X-ray emission to the south, already revealed
in previous observations with Chandra (Allen et al. 2002). In
Fig. 2 we show an overlay of the VLT image of the central
region of RX J1347.5−1145 with the X-ray contours derived
from Fig. 1.
Fig.2. VLT image of the central region of RX J1347.5−1145
(Erbenet al. inprep.).Superposedarethe([0.9-10]keV)XMM
X-raycontours(levels:0.003,0.015,0.045,0.06,0.15,0.3,0.6,
1.5, 3 cts/s/arcmin2). The image is ∼ 4.4 × 4.3 arcmin2(North
is up, East is left).
We compute a background-subtractedvignetting-corrected
radial surface brightness profile in the [0.3-2]keV energy band
for each camera separately. The profiles for the three detectors
are then added into a single profile, binned such that at least
a sigma-to-noise ratio of 3 was reached. The cluster emission
is detected up to 1.7 Mpc (∼ 5′). In Fig. 3 we show the X-ray
surface brightness profiles for the disturbed SE quadrant com-
paredto that fromdata excludingthe SE quadrant.We notethat
the data excludingthe SE quadrant(hereafterundisturbedclus-
ter) appear regular,while those for the SE quadrant (containing
the X-ray subclump) show a clear excess of emission between
radii of ∼ 100 and 300 kpc relative to other directions.
0.11
0.001
0.01
0.1
1
10
Fig.3. Background subtracted, azimuthally averaged radial
surface brightness profile for SE quadrant data in the [0.3-2]
keV range. The dotted line shows the profile in other directions
(undisturbed cluster), which appears relatively regular and re-
laxed. An excess of emission in the SE quadrant between radii
of ∼ 20-50 arcsec (100-300 kpc) is visible.
The surface brightness profile of the undisturbed cluster
is fitted in the CIAO tool Sherpa with various models, which
are convolved with the XMM-Newton PSF. A single β-model
(Cavaliere & Fusco Femiano 1976) is not a good description
of the entire profile: a fit to the outer regions (350 kpc - 1.7
Mpc)shows a strongexcessin the centrewhen comparedto the
model.The peakedemission is a strongindicationfora cooling
core in this cluster. We found that for 350 kpc-1.7Mpc the data
can be described by a β-model with a core radius rc= 367 ± 3
kpcandaslopeparameterβ = 0.93±0.01,whileforr <350kpc
the data can be approximated by a β-model with rc= 40 ± 0.2
kpc and β = 0.55± 0.02 (90% confidence levels).
4. Temperature map
The temperature image of the central cluster region shown in
Fig. 4 is build from X-ray colours. Specifically, we producethe
mosaics of MOS images in four different energy bands ([0.3-
1] keV, [1-2] keV, [2-4.5] keV and [4.5-8] keV), subtract the
background and divide the resulting images by the exposure
maps. A temperature is obtained by fitting the values in each
pixel with a thermal plasma. In particular we note that the very
central regionappearscooler thanthe surroundingmediumand
the SE quadrant, which corresponds to the subclump seen in
the X-ray image, is significantly hotter than the gas in other
directions.
5. Spectral analysis
For the spectral analysis we treat the SE quadrant containing
the X-ray subclump separately from the rest of the cluster. The
data for the undisturbed cluster are divided into the annular re-
gions detailed in Table 1. A single spectrum is extracted for
each region and then regrouped to contain a minimum of 25

Page 3

Gitti & Schindler.: XMM-Newton observation of the most X-ray-luminous galaxy cluster RX J1347.5−11453
Fig.4. Temperature map obtained by using 4 X-ray colours
([0.3-1], [1-2], [2-4.5], [4.5-8] keV) and estimating the ex-
pected count rate with XSPEC for a thermal MEKAL model,
with fixed Galactic absorption NH = 4.85 × 1020cm−2and
metallicity Z = 0.3Z⊙. Superposedare the X-ray contours.The
features outside the last contours are not significant, as they are
mainly due to noise fluctuations.
counts per channel, thereby allowing χ2statistics to be used.
Thedata fromthe threecameraswere modelledsimultaneously
using the XSPEC code, version 11.3.0. Spectral fitting is per-
formedinthe [0.5-8]keV band.Thespectraare modelledusing
a simple, single-temperaturemodel (MEKAL plasma emission
codein XSPEC) with the absorbingcolumndensity fixedto the
Galactic value (NH = 4.85 × 1020cm−2, Dickey & Lockman
1990). The free parameters in this model are the temperature
kT, metallicity Z (measured relative to the solar values) and
normalization (emission measure).
The best-fitting parameter values and 90% confidence lev-
els derived from the fits to the annular spectra are summarized
in Table 1. The projected temperature profile determined with
this model is shown in Fig. 5. The temperature rises from a
mean value of 8.8±0.3 keV within 115 kpc to kT = 11.1±0.4
keV overthe 0.1-0.5Mpc region,then declines down to a mean
valueof6.0+2.6
we also show for comparison the projected temperature profile
measured by Chandra (Allen et al. 2002). We note that while
the general trend observed by the two satellites is consistent,
there are some discrepancies in the measurements of the ab-
solute temperature values. The discrepancy between Chandra
and XMM temperature profile has been found in other clusters
of galaxies (e.g. A1835, Schmidt et al. 2001, Majerowicz et al.
2002), and can be partially due to the effect of the XMM PSF
(see Markevitch 2002). A fit with the same model to the data
for the SE quadrant between radii 50-200 kpc yields a best-
fitting temperature kT = 13.3 ± 1.0 keV. In other directions,
the mean value is kT = 11.0+0.5
derived with the single-temperature model is consistent with
being constant, with an overall value of Z = 0.26 ± 0.04Z⊙.
However, as shown in Table 2, the structure in the innermost
−1.6keVintheouterregions(1.0-1.7Mpc).InFig.5
−0.4keV. The metallicity profile
Table 1. The results from the spectral fitting in concentric annular
regions (undisturbed cluster). Temperatures (kT) are in keV, metallic-
ities (Z) in solar units and [2-10] keV luminosities (LX) in units of
1044erg s−1. The total χ2values and numbers of degrees of freedom
(DOF) in the fits are listed in column 5. Errors are 90% confidence
levels (∆χ2= 2.71) on a single parameter of interest.
Radius (kpc)
0-115
115-230
230-345
345-520
520-690
690-1040
1040-1730
0-1730
kT ZLX
16.7
10.1
5.44
4.52
1.92
1.64
0.91
41.8
χ2/DOF
982/880
696/664
433/384
350/341
239/210
293/264
593/421
1957/1452
8.9+0.3
−0.3
10.7+0.7
11.9+1.6
10.7+1.1
9.0+1.4
−1.1
9.4+2.1
−1.4
6.0+2.6
−1.7
9.4+0.3
−0.3
0.34+0.05
0.26+0.08
0.16+0.14
0.24+0.13
0.16+0.18
0.19+0.26
0.40+0.50
0.26+0.04
−0.05
−0.6
−0.08
−1.3
−0.15
−1.0
−0.13
−0.16
−0.19
−0.37
−0.04
Fig.5. Circles: the projected X-ray gas temperature profile
(and errors at 90% confidence levels) measured from XMM
data in the [0.5-8] keV energy band. Triangles: the projected
X-ray gas temperature profile (and 1σ errors) measured from
Chandra data in the [0.5-7] keV energy band (Allen et al.
2002). The data of the SE quadrant are excluded in both pro-
files.
bin is better modelled by multi-temperature models having
higher metallicities.
Within the radius of 1.7 Mpc (∼ 5′), a fit to the full 360◦
data gives an overall kT = 10.0 ± 0.3 keV, Z = 0.26 ± 0.03Z⊙
and LX(2-10 keV) = 6.0±0.1×1045erg s−1. These values are
in agreement with ROSAT and ASCA results (Schindler et al.
1997).
6. Mass determination
The total gravitating mass distribution shown in Fig. 6 (solid
line) was calculated under the usual assumptions of hydro-
static equilibrium and spherical symmetry using the depro-
jected density distribution calculated from the parameters of
the β-model derived in Sect. 3. Only data beyond 30′′(∼ 175
kpc) are considered: in the central bins the temperature as esti-
mated in Sect. 5 is affected by the XMM PSF and projection ef-
fects, while for the outer regions these effects can be neglected

Page 4

4Gitti & Schindler.: XMM-Newton observation of the most X-ray-luminous galaxy cluster RX J1347.5−1145
(e.g. Kaastra et al. 2004). Within 1 Mpc we find a total mass
of 1.0 ± 0.2 × 1015M⊙, in agreement with Chandra (Allen et
al. 2002) and weak lensing analysis (Fischer & Tyson 1997)
results and slightly higher than that derived by ROSAT/ASCA
(Schindler et al. 1997). In Fig. 6 we also show for comparison
(dashed line) the mass profile derived by assuming a constant
temperature of 9.5 keV.
Fig.6. Solid line: Profile of the integrated total mass. Dashed
line: Profile of the integrated total mass calculated assuming a
constant temperatureof 9.5 keV. Dotted line: Error on the mass
calculation coming from the temperature measurement.
7. Cooling core analysis
We accumulate the spectrum in the central 30
excluding the data for the SE quadrant. We use three different
spectralmodels.ModelAis theMEKALmodelalreadyusedin
Sect. 5. Model B includes a single temperaturecomponentplus
an isobaric multi-phase component (MEKAL + MKCFLOW
in XSPEC), where the minimum temperature, kTlow, and the
normalization of the multi-phase component, Normlow = ˙ M,
are additional free parameters. Finally, in model C the con-
stant pressure cooling flow is replaced by a second isother-
mal emission component(MEKAL + MEKAL in XSPEC). As
for model B, this model has 2 additional free parameters with
respect to model A: the temperature, kTlow, and the normal-
ization, Normlow, of the second component. The results, sum-
marized in Table 2, show that the statistical improvements ob-
tained by introducingan additional emission component(mod-
els B or C) compared to the single-temperature model (model
A) are significant at more than the 99% level according to the
F-test, although the temperature of the hot gas is unrealisti-
cally high. With our data, however, we cannot distinguish be-
tween the two multi-phase models. This means that the extra
emission component can be equally well modelled either as a
cooling flow or a second isothermal emission component. We
note that the fit with the cooling flow model sets tight con-
straints on the existence of a minimum temperature (∼ 2 keV).
The nominal mass deposition rate in this empirical model is
′′(∼175 kpc) by
Table 2.
dence limits from the spectral analysis in the central 0-30
region. Temperatures (kT) are in keV, metallicities (Z) as
a fraction of the solar value and normalizations in units
of 10−14nenpV/4πDA(1 + z)2as done in XSPEC (for the
MKCFLOW modelthenormalizationisparameterizedinterms
of the mass deposition rate ˙ M, in M⊙yr−1).
The best-fit parameter values and 90% confi-
′′
Par.
kT
Z
Norm
kTlow
Normlow
χ2/DOF
Mod. A
9.2+0.3
−0.3
0.32+0.05
0.00528+0.00009
—
—
1048/1003
Mod. B
23.8+6.1
0.39+0.06
0.00053+0.00223
2.0+0.5
−0.4
˙ M = 1880+260
1011/1001
Mod. C
17.7+5.7
0.42+0.06
0.00355+0.00051
3.9+0.7
−0.6
0.00194+0.00057
1010/1001
−4.7
−3.6
−0.05
−0.06
−0.06
−0.00008
−0.00053
−0.00048
−210
−0.00058
∼ 1900 M⊙yr−1. This extremely high ˙ M, in agreement with
Chandra results (Allen et al. 2002), is exceptional for distant
cooling core clusters, and its implications on the evolution of
cooling core clusters will be investigated in a forthcoming pa-
per (Gitti et al. in prep.).
8. Discussion and Conclusions
The XMM-Newton observation of RX J1347.5−1145 confirms
that it is, with a luminosity LX= 6.0± 0.1× 1045erg s−1(2-10
keV energy band), the most X-ray-luminouscluster discovered
to date. RX J1347.5−1145is a hot cluster (overalltemperature:
kT = 10.0 ± 0.3 keV), not isothermal: the temperature profile
shows the presence of a cool core and a decline of the tem-
perature in the outer regions. The temperature map reveals a
complex structure and identifies a relatively hot region at radii
50-200 kpc to the SE of the main X-ray peak. This hot region
is found at the same position as the subclump seen in the X-
ray image. The highertemperatureand enhancedX-ray surface
brightness in the SE quadrant indicate that there is probably an
ongoing subcluster merger event. On the other hand, excluding
the data of the SE quadrant the cluster appears relatively re-
laxed and the presence of a cooling core, with an exceptional
high value of the mass accretion rate (˙ M ∼ 1900 M⊙yr−1) in-
dicates that the cluster could have evolved without any distur-
bances for a relatively long interval. Therefore, the dynamical
state of RX J1347.5−1145 appears very complex and will be
presented in detail in a forthcomingpaper (Gitti et al. in prep.).
Acknowledgements. We thank S.Ettori for his advices in the spec-
tral analysis and for providing the software required to produce the
X-ray colour map in Fig.4, and T. Erben for supplying the opti-
cal image. We also thank the referee J. Kaastra for helpful com-
ments. M.G. would like to thank E. Belsole, A. Castillo-Morales, S.
Majerowicz, D. Neumann and E. Pointecouteau for suggestions con-
cerning XMM-Newton data analysis. This work was supported by the
AustrianScienceFoundationFWFunder grantP15868,¨OADAmad´ ee
Projekt 18/2003 and¨OAD Acciones Integradas Projekt 22/2003.
References
Allen S.W., Schmidt R.W., & Fabian A.C. 2002, MNRAS, 335, 256
Arnaud M., Neumann D.M., Aghanim N. et al. 2001, A&A, 365, L80

Page 5

Gitti & Schindler.: XMM-Newton observation of the most X-ray-luminous galaxy cluster RX J1347.5−11455
Arnaud M., Majerowicz S., Lumb D. et al. 2002, A&A, 390, 27
Cavaliere A., & Fusco-Femiano R. 1976, A&A, 49, 137
Dickey J.M., & Lockman F.J. 1990, ARA&A, 28, 215
Fischer P., & Tyson J.A. 1997, AJ, 114, 14
Kaastra J.S., Tamura T., Peterson J.R. et al. 2004, A&A, 413, 415
Komatsu E., Kitayama T., Suto Y. et al. 1999, ApJ, 516, L1
Komatsu E., Matsuo H., Kitayama T. et al. 2001, PASJ, 53, 57
Majerowicz S., Neumann D.M., & Reiprich T.H. 2002, A&A, 394, 77
Markevitch M. 2002, astro-ph/0205333
Pointecouteau E., Giard M., Benoit A. et al. 1999, ApJ, 519, L115
Pointecouteau E., Giard M., Benoit A. et al. 2001, ApJ, 552, 42
Sahu, K.C., Shaw R.A., Kaiser M.E. et al. 1998, ApJ, 492, L125
Schindler S., Guzzo L., Ebeling H. et al. 1995, A&A, 299, L9
Schindler S., Hattori M., Neumann D.M. et al. 1997, A&A 317, 646
Schmidt R.W., Allen S.W., & Fabian A.C. 2001, MNRAS, 327, 1057