J/ApJ/682/821 Spectral fits of galaxy clusters in X-ray (Cavagnolo+, 2008)
Bandpass dependence of X-ray temperatures in galaxy clusters.
Cavagnolo K.W., Donahue M., Voit G.M., Sun M.
<Astrophys. J., 682, 821-834 (2008)>
=2008ApJ...682..821C 2008ApJ...682..821C
ADC_Keywords: Clusters, galaxy ; X-ray sources ; Spectroscopy
Keywords: catalogs - cosmology: observations - galaxies: clusters: general -
methods: data analysis - X-rays: galaxies: clusters
Abstract:
We explore the band dependence of the inferred X-ray temperature of
the intracluster medium (ICM) for 192 well-observed galaxy clusters
selected from the Chandra Data Archive. If the hot ICM is nearly
isothermal in the projected region of interest, the X-ray temperature
inferred from a broadband (0.7-7.0keV) spectrum should be identical to
the X-ray temperature inferred from a hard-band (2.0-7.0keV) spectrum.
However, if unresolved cool lumps of gas are contributing soft X-ray
emission, the temperature of a best-fit single-component thermal model
will be cooler for the broadband spectrum than for the hard-band
spectrum. Using this difference as a diagnostic, the ratio of
best-fitting hard-band and broadband temperatures may indicate the
presence of cooler gas even when the X-ray spectrum itself may not
have sufficient signal-to-noise ratio (S/N) to resolve multiple
temperature components. To test this possible diagnostic, we extract
X-ray spectra from core-excised annular regions for each cluster in
our archival sample. We compare the X-ray temperatures inferred from
single-temperature fits when the energy range of the fit is 0.7-7.0keV
(broad) and when the energy range is 2.0/(1+z)-7.0keV (hard). We find
that the hard-band temperature is significantly higher, on average,
than the broadband temperature. On further exploration, we find this
temperature ratio is enhanced preferentially for clusters which are
known merging systems. In addition, cool-core clusters tend to have
best-fit hard-band temperatures that are in closer agreement with
their best-fit broadband temperatures. We show, using simulated
spectra, that this diagnostic is sensitive to secondary cool
components (TX=0.5-3.0keV) with emission measures ≥10-30% of the
primary hot component.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 80 244 Summary of sample
table2.dat 120 166 Summary of excised R2500 spectral fits
table3.dat 120 192 Summary of excised R5000 spectral fits
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See also:
B/chandra : The Chandra Archive Log (CXC, 1999-)
J/ApJ/412/479 : Intracluster gas temperatures catalog (David+, 1993)
J/ApJ/504/27 : The LX-T Relation for Nearby Clusters (Markevitch, 1998)
J/PASJ/56/965 : X-ray properties of ASCA objects (Fukazawa+, 2004)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 21 A21 --- Name Cluster name (1)
23 A1 --- f_Name [di] Note on cluster (2)
25- 29 I5 --- ObsID Chandra observation identification number
31- 32 I2 h RAh Cluster center hour of Right Ascension (J2000)
34- 35 I2 min RAm Cluster center minute of Right Ascension (J2000)
37- 42 F6.3 s RAs Cluster center second of Right Ascension (J2000)
44 A1 --- DE- Cluster center sign of the Declination (J2000)
45- 46 I2 deg DEd Cluster center degree of Declination (J2000)
48- 49 I2 arcmin DEm Cluster center arcminute of Declination (J2000)
51- 55 F5.2 arcsec DEs Cluster center arcsecond of Declination (J2000)
57- 61 F5.1 ks ExpT Exposure time
63- 64 A2 --- Mode Observing mode
66- 67 A2 --- ACIS ACIS CCD location of centroid
69- 73 F5.3 --- z Redshift taken from Horner, 2001PhDT........88H 2001PhDT........88H
(all redshifts confirmed with NED)
75- 80 F6.2 10+37W Lbol Bolometric luminosity in units of 10+44erg/s
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Note (1): For clusters with multiple observations, the X-ray centers differ
by <0.5kpc.
Note (2): Flags as follows:
d = cluster analyzed within R5000 only.
i = cluster which was excluded from our analysis (discussed in Section 5.1).
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Byte-by-byte Description of file: table[23].dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- Name Cluster name (1)
19 A1 --- n_Name [*] Indicates multiple observations
21- 22 I2 kpc Rc Excluded core region size
24- 26 I3 kpc Rad Cluster radius (2)
28- 32 F5.2 10+20/cm2 NHI Galactic neutral hydrogen column density
34- 37 F4.2 10+20/cm2 E_NHI ? Upper limit uncertainty in NHI
39- 42 F4.2 10+20/cm2 e_NHI ? Lower limit uncertainty in NHI
44- 48 F5.2 keV T77 Best fit 0.7-7keV MeKaL temperature
50- 54 F5.2 keV E_T77 Upper limit uncertainty in T77
56- 59 F4.2 keV e_T77 Lower limit uncertainty in T77
61- 65 F5.2 keV T27 Best fit 2-7keV MeKaL temperature
67- 71 F5.2 keV E_T27 Upper limit uncertainty in T27
73- 76 F4.2 keV e_T27 Lower limit uncertainty in T27
78- 81 F4.2 --- THBR The T77/T22 ratio
83- 86 F4.2 --- E_THBR Upper limit uncertainty in THBR
88- 91 F4.2 --- e_THBR Lower limit uncertainty in THBR
93- 96 F4.2 Sun Z77 Best-fit 0.7-7keV MeKaL abundance
98-102 F5.2 Sun E_Z77 Upper limit uncertainty in Z77
104-107 F4.2 Sun e_Z77 Lower limit uncertainty in Z77
109-112 F4.2 --- chi77 Reduced χ2 for best-fit 0.7-7keV model
114-117 F4.2 --- chi27 Reduced χ2 for best-fit 2-7keV model
119-120 I2 % Src Percentage of emission attributable to source
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Note (1): Each observation has an independent spectrum extracted along with
an associated WARF, WRMF, normalized background spectrum, and soft
residual. Each independent spectrum is then fit simultaneously with
the same spectral model to produce the final fit.
Note (2): R2500 for table2: cluster radius where average cluster density
is 2500x the Universe critical density or R5000 for table3.
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History:
From electronic version of the journal
(End) Greg Schwarz [AAS], Emmanuelle Perret [CDS] 08-Nov-2010