Volume 551, March 2013
|Number of page(s)||11|
|Section||Cosmology (including clusters of galaxies)|
|Published online||19 February 2013|
Chandra and optical/IR observations of CXO J1415.2+3610, a massive, newly discovered galaxy cluster at z ~ 1.5
INAF-Osservatorio Astronomico di Trieste, via Tiepolo 11,
2 INFN-National Institute for Nuclear Physics, via Valerio 2, 34127 Trieste, Italy
3 European Space Astronomy Centre (ESAC)/ESA, Madrid, Spain
4 European Southern Observatory, Karl-Schwarzschild Strasse 2, 85748 Garching, Germany
5 Università di Trieste, Dipartimento di Fisica, via Valerio, 2, 34127 Trieste, Italy
6 University Observatory, Ludwig-Maximillians University Munich, Scheinerstrasse 1, 81679 Munich, Germany
7 Excellence Cluster Universe, Boltzmannstrasse 2, 85748 Garching, Germany
Accepted: 12 December 2012
Aims. We report the discovery of CXO J1415.2+3610, a distant (z ~ 1.5) galaxy cluster serendipitously detected as an extended source with a very high significance level (S/N ~ 11) in a deep, high-resolution Chandra observation targeted to study the cluster WARP J1415.1+3612 at z = 1.03. This is the highest-z cluster discovered with Chandra so far. Moreover, the total exposure time of 280 ks with ACIS-S provides the deepest X-ray observation currently achieved on a cluster at z ≥ 1.5.
Methods. We perform an X-ray spectral fit of the extended emission of the intracluster medium (ICM) with Xspec assuming a single-temperature thermal mekal model. We use optical and infrared (IR) observations from Subaru-Suprime (BVRiz), Moircs (JKs), and Spitzer-IRAC (3.6 μm) to confirm the presence of an overdensity of red galaxies matching the X-ray extended emission. We use optical and IR data to investigate the color−magnitude relation of the candidate member galaxies.
Results. From a preliminary X-ray spectral analysis, we detect at a 99.5% confidence level the rest frame 6.7−6.9 keV Iron Kα line complex, from which we obtain zX = 1.46 ± 0.025. Our X-ray redshift measurement is supported by the optical and IR data. The analysis of the z − 3.6 μm color−magnitude diagram shows a well-defined sequence of red galaxies within 1′ from the cluster X-ray emission peak with a color range [5 < z − 3.6 μm < 6]. The photometric redshift obtained by spectral energy distribution fitting is zphot = 1.52 ± 0.06. After fixing the redshift to z = 1.46, we perform the final spectral analysis and measure the average gas temperature with a 20% error, kT = 5.8-1.0+1.2 keV, and the Fe abundance ZFe = 1.3-0.5+0.8 Z⊙. We fit the background-subtracted surface brightness with a single beta-model out to 35 arcsec (the maximum radius where the X-ray emission is detected), and derive the deprojected electron density profile. The ICM mass is 1.09-0.2+0.3 × 1013 M⊙ within 300 kpc. Under the assumption of hydrostatic equilibrium, the total mass is M2500 = 8.6-1.7+2.1 × 1013 M⊙ for R2500 = (220 ± 55) kpc. Extrapolating the profile at larger radii, we find M500 = 2.1-0.5+0.7 × 1014 M⊙ for R500 = 510-50+55 kpc. This analysis establishes CXOJ1415.2+3610 as one of the best characterized distant galaxy clusters based on X-ray data alone.
Key words: galaxies: clusters: individual: CXO J1415.2+3610 / galaxies: clusters: intracluster medium / X-rays: galaxies: clusters
© ESO, 2013
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.