Exploring the galaxy cluster-group transition regime at high redshifts

Abstract

Context. Multi-wavelength surveys for clusters of galaxies are opening a window on the elusive high-redshift (z > 1) cluster population. Well controlled statistical samples of distant clusters will enable us to answer questions about their cosmological context, early assembly phases and the thermodynamical evolution of the intracluster medium. Aims. We report on the detection of two z > 1 systems, XMMU J0302.2-0001 and XMMU J1532.2-0836, as part of the XMM-Newton Distant Cluster Project (XDCP) sample. We investigate the nature of the sources, measure their spectroscopic redshift and determine their basic physical parameters. Methods. The results of the present paper are based on the analysis of XMM-Newton archival data, optical/near-infrared imaging and deep optical follow-up spectroscopy of the clusters. Results. We confirm the X-ray source XMMU J0302.2-0001 as a gravitationally bound, bona fide cluster of galaxies at spectroscopic redshift z = 1.185. We estimate its M 500 mass to (1.6 ± 0.3) × 10 14 M from its measured X-ray luminosity. This ranks the cluster among intermediate mass system. In the case of XMMU J1532.2-0836 we find the X-ray detection to be coincident with a dynamically bound system of galaxies at z = 1.358. Optical spectroscopy reveals the presence of a central active galactic nucleus, which can be a dominant source of the detected X-ray emission from this system. We provide upper limits of X-ray parameters for the system and discuss cluster identification challenges in the high-redshift low-mass cluster regime. A third, intermediate redshift (z = 0.647) cluster, XMMU J0302.1-0000, is serendipitously detected in the same field as XMMU J0302.2-0001. We provide its analysis as well.

First simultaneous optical/near-infrared imaging of an X-ray selected, high-redshift cluster of galaxies with GROND

“…However, based on the luminosity scaling relation in Pratt et al (2009), first rough estimates on the expected temperature of T X ∼ 2.4 keV and the total mass of M 500 ∼ 7 × 10 13 M ⊙ (i.e., M 200 ∼ 10 14 M ⊙ ) can be obtained from the previous values. Hence, XMMU J0338.7+0030 appears to be a system at the boundary between X-ray selected groups and clusters, as XMMU J1532.2−0836 at z = 1.358 ( Suhada et al 2011) and XMMU J0338.8+0021 at z = 1.49 (Nastasi et al 2011).…”

“…The XMM-Newton field containing XMMU J0338.7+0030 was reprocessed with SAS v10.0.0 following Suhada et al (2011). These observations are strongly flared and an automatic flare removal is impossible; hence, the contaminated periods were excised manually and the automatic two-step flare cleaning process was run on the remaining good part of the data for the removal of high background periods.…”

“…For each library of galaxy SEDs, we considered two separate families of models, by including the contribution to the total flux from line emission or not. We opted to do this because there is independent evidence that the bright end of the galaxy luminosity function of a high-z cluster can be populated by [O II] line emitters (as for XMMU J0302.2−0001 at z = 1.186, Suhada et al 2011), sometimes with vigorous starburst activity (as for XMMU J1007.4+1237 at z = 1.555, Fassbender et al 2011b).…”

“…Interestingly, there is evidence of sustained star-formation activity at the bright end of the galaxy luminosity function in the X-ray luminous cluster XMMU J1007.4+1237 at z = 1.555 (Fassbender et al 2011b) and in dense environments at z ∼ 1 (e.g., Elbaz et al 2007;Gerke et al 2007;Cooper et al 2008). Several [O II] line emitters are found in the luminous, red galaxy population of XMMU J0302.2−0001 at z = 1.185 with a total mass of a few times 10 14 M ⊙ ( Suhada et al 2011). Spectroscopic cluster members with [O II] line emission can populate the locus of old, passively evolving galaxies or be even redder than the red sequence (see XMMU J2235.3−2557; Lidman et al 2008).…”

The XMM Cluster Survey: optical analysis methodology and the first data release

“…After applying this cut, 9 345 z lit values remain. To these, we have added by hand 11 redshifts that were not in NED at the time when the automated z lit extraction was performed [four of these 11 redshifts were taken from a recent data release by the XMM ‐Large‐Scale Structure ( XMM ‐LSS) survey by Adami et al (2011), three redshifts were taken from a parallel study, Harrison et al (2012) (hereafter H12; see ), two redshifts were taken from Šuhada et al (2011), a single redshift was taken from Lamer et al (2008), and a single redshift was taken from Boehringer et al (2005)]. In addition, we updated eight of the default NED redshifts with improved values available in the literature [six redshifts from Adami et al (2011) for XMM ‐LSS clusters, a single redshift from Hashimoto et al (2005) (for RX J105346.6+573517), and a single redshift from Stanford et al (2006) (for XMMXCS J2215.9−1738; see Table 2)].…”