Astronomy and Astrophysics, volume 551A, 45-45 (2013/3-1)
Chandra and optical/IR observations of CXO J1415.2+3610, a massive, newly discovered galaxy cluster at z ∼ 1.5.
TOZZI P., SANTOS J.S., NONINO M., ROSATI P., BORGANI S., SARTORIS B., ALTIERI B. and SANCHEZ-PORTAL M.
Abstract (from CDS):
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 280ks with ACIS-S provides the deepest X-ray observation currently achieved on a cluster at z≥1.5. 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 (3.6µm) 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. From a preliminary X-ray spectral analysis, we detect at a 99.5% confidence level the rest frame 6.7-6.9keV 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-3.6µm 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-3.6µm<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+1.2–1.0keV, and the Fe abundance ZFe=1.3–0.5+0.8Z☉. 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+0.3x1013M☉ within 300kpc. Under the assumption of hydrostatic equilibrium, the total mass is M2500=8.6–1.7+2.1x1013M☉ for R2500=(220±55)kpc. Extrapolating the profile at larger radii, we find M500=2.1–0.5+0.7x1014M☉ for R500=510–50+55kpc. This analysis establishes CXOJ1415.2+3610 as one of the best characterized distant galaxy clusters based on X-ray data alone.
galaxies: clusters: individual: CXO J1415.2+3610 - galaxies: clusters: intracluster medium - X-rays: galaxies: clusters
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