Volume 527, March 2011
|Number of page(s)||6|
|Published online||08 February 2011|
Letters to the Editor
The dawn of starburst activity in cluster cores
Max-Planck-Institut für extraterrestrische Physik (MPE),
2 INAF - Osservatorio Astronomico di Trieste, via Tiepolo 11, 34131 Trieste, Italy
3 European Southern Observatory (ESO), Karl-Scharzschild-Str. 2, 85748 Garching, Germany
4 Departamento de Astronomía y Astrofísica, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22, Chile
5 Astrophysikalisches Institut Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
6 University Observatory Munich, Ludwigs-Maximillians University Munich, Scheinerstr. 1, 81679 Munich, Germany
7 CEASaclay, Service d’Astrophysique, L’Orme des Merisiers, Bât. 709, 91191 Gif-sur-Yvette Cedex, France
8 Excellence Cluster Universe, Boltzmannstr. 2, 85748 Garching, Germany
Received: 18 November 2010
Accepted: 4 January 2011
Context. Observational galaxy cluster studies at z > 1.5 probe the formation of the first massive M > 1014 M⊙ dark matter halos, the early thermal history of the hot ICM, and the emergence of the red-sequence population of quenched early-type galaxies.
Aims. We present first results for the newly discovered X-ray luminous galaxy cluster XMMU J1007.4+1237 at z = 1.555, detected and confirmed by the XMM-Newton Distant Cluster Project (XDCP) survey.
Methods. We selected the system as a serendipitous weak extended X-ray source in XMM-Newton archival data and followed it up with two-band near-infrared imaging and deep optical spectroscopy.
Results. We can establish XMMU J1007.4+1237 as a spectroscopically confirmed, massive,bona fide galaxy cluster with a bolometric X-ray luminosity of erg/s, a red galaxy population centered on the X-ray emission, and a central radio-loud brightest cluster galaxy. However, we see evidence for the first time that the massive end of the galaxy population and the cluster red-sequence are not yet fully in place. In particular, we find ongoing starburst activity for the third ranked galaxy close to the center and another slightly fainter object.
Conclusions. At a lookback time of 9.4 Gyr, the cluster galaxy population appears to be caught in an important evolutionary phase, prior to full star-formation quenching and mass assembly in the core region. X-ray selection techniques are an efficient means of identifying and probing the most distant clusters without any prior assumptions about their galaxy content.
Key words: galaxies: clusters: individual: XMMU J1007.4+1237 / X-rays: galaxies: clusters / Galaxy: evolution
Based on observations under programme ID 081.A-0312 collected at the European Organisation for Astronomical Research in the Southern Hemisphere, Chile, and observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, operated jointly by the Max-Planck Institut für Astronomie and the Instituto de Astrofísica de Andalucía (CSIC).
Figure 2 and Tables 1 and 2 are only available in electronic form at http://www.aanda.org
© ESO, 2011
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