DISCREPANT MASS ESTIMATES IN THE CLUSTER OF GALAXIES ABELL 1689
- MKI, Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)
We present a new mass estimate of a well studied gravitational lensing cluster, Abell 1689, from deep Chandra observations with a total exposure of 200 ks. Within r = 200 h-{sup 1} kpc, the X-ray mass estimate is systematically lower than that of lensing by 30%-50%. At r>200 h{sup -1} kpc, the mass density profiles from X-ray and weak lensing methods give consistent results. The most recent weak lensing work suggests a steeper profile than what is found from the X-ray analysis, while still in agreement with the mass at large radii. Fitting the total mass profile to a Navarro-Frenk-White model, we find M{sub 200} = (1.16{sup +0.45}{sub -0.27}) x 10{sup 15} h{sup -1} M {sub sun} with a concentration, c{sub 200} = 5.3{sup +1.3}{sub -1.2}, using nonparametric mass modeling. With parametric profile modeling, we find M{sub 200} = (0.94{sup +0.11}{sub -0.06}) x 10{sup 15} h{sup -1} M{sub sun} and c{sub 200} = 6.6{sup +0.4}{sub -0.4}. This is much lower compared to masses deduced from the combined strong and weak lensing analysis. Previous studies have suggested that cooler small-scale structures can bias X-ray temperature measurements or that the northern part of the cluster is disturbed. We find these scenarios unlikely to resolve the central mass discrepancy since the former requires 70%-90% of the space to be occupied by these cool structures, and excluding the northern substructure does not significantly affect the total mass profiles. A more plausible explanation is a projection effect. Assuming that the gas temperature and density profiles have a prolate symmetry, we can bring the X-ray mass estimate into a closer agreement with that of lensing. We also find that the previously reported high hard-band to broadband temperature ratio in A1689, and many other clusters observed with Chandra, may be resulting from the instrumental absorption that decreases 10%-15% of the effective area at {approx}1.75 keV. Caution must be taken when analyzing multiple spectral components under this calibration uncertainty.
- OSTI ID:
- 21319579
- Journal Information:
- Astrophysical Journal, Vol. 701, Issue 2; Other Information: DOI: 10.1088/0004-637X/701/2/1283; Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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