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# The discovery of a massive supercluster at z= 0.9 in the UKIDSS Deep eXtragalactic Survey

Centre for Astrophysics, Science & Technology Research Institute, University of Hertfordshire, Hatfield, Herts AL10 9AB; Gemini Observatory, 670 North A'ohoku Place, Hilo, HI 96720, USA; Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ
Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.52). 07/2007; 379(4):1343 - 1351. DOI:10.1111/j.1365-2966.2007.12037.x
Source: arXiv

ABSTRACT We analyse the first publicly released deep field of the UK Infrared Deep Sky Survey (UKIDSS) Deep eXtragalactic Survey to identify candidate galaxy overdensities at z∼ 1 across ∼1 deg2 in the ELAIS-N1 field. Using I−K, J−K and K− 3.6 μm colours, we identify and spectroscopically follow up five candidate structures with Gemini/Gemini Multi-Object Spectrograph and confirm that they are all true overdensities with between five and 19 members each. Surprisingly, all five structures lie in a narrow redshift range at z= 0.89 ± 0.01, although they are spread across 30 Mpc on the sky. We also find a more distant overdensity at z= 1.09 in one of the spectroscopic survey regions. These five overdense regions lying in a narrow redshift range indicate the presence of a supercluster in this field and by comparing with mock cluster catalogues from N-body simulations we discuss the likely properties of this structure. Overall, we show that the properties of this supercluster are similar to the well-studied Shapley and Hercules superclusters at lower redshift.

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##### Article: The Ratio of Luminous to Faint Red Sequence Galaxies in X-Ray and Optically Selected Low-Redshift Clusters
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ABSTRACT: We study the ratio of luminous-to-faint red sequence galaxies in both optically and X-ray selected galaxy clusters in the poorly studied redshift range 0.05< z<0.19. The X-ray selected sample consists of 112 clusters based on the ROSAT All-Sky Survey, while the optical sample consists of 266 clusters from the Sloan Digital Sky Survey. Our results are consistent with the presence of a trend in luminous-to-faint ratio with redshift, confirming that downsizing is continuous from high to low redshift. After correcting for the variations with redshift using a partial Spearman analysis, we find no significant relationship between luminous-to-faint ratio and X-ray luminosity of the host cluster sample, in contrast to recent suggestions. Finally, we investigate the stacked colour-magnitude relations of these samples finding no significant differences between the slopes for optically and X-ray selected clusters. The colour-magnitude slopes are consistent with the values obtained in similar studies, but not with predictions of theoretical models. Comment: 11 pages, 6 figures, 3 tables. Accepted for publication by MNRAS
Monthly Notices of the Royal Astronomical Society 12/2009; · 5.52 Impact Factor
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##### Article: DM haloes and their environment in the fifth-force cosmology
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ABSTRACT: We investigate how long-range scalar interactions affect the properties of dark matter haloes and their large scale distribution. For doing so we employ the ReBEL model which implements an additional interaction between dark matter particles. On the phenomenological level this is equivalent to a modification of gravity. We analyse the differences between five ReBEL models and $\Lambda$CDM using a series of high resolution cosmological simulations. In the first part of our study we investigate how halo properties change in the presence of a fifth force. We report that the density profile of ReBEL haloes is well described by the NFW profile but with mean concentrations from 5% to a few times higher than the standard $\Lambda$CDM value. We also find a slight increase of the halo spin for haloes more massive than $5\times10^{11}\Msol$, reflecting a higher rotational support of the haloes due to scalar forces. In addition, the dark matter haloes in our models are more spherical than their counterparts in $\Lambda$CDM. The ReBEL haloes are also more virialised, with a large difference from $\Lambda$CDM for strong fifth forces and a much smaller change for weak scalar interactions. In the second part we analyse how the halo environment changes in the presence of the fifth force. We find that ReBEL predicts more mass and volume in filaments at the downside of walls and voids which become noticeably more empty. Even though voids have less mass, they have many more haloes in fifth force models than in $\Lambda$CDM. This is because more of the mass in voids is inside gravitationally bound structures. We report that the halo population in voids seems to be a particularly sensitive probe of modified gravity since the mass function of these objects is very sensitive to the presence of even a weak fifth force.
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##### Article: The Chandra Deep Protocluster Survey: point‐source catalogues for a 400‐ks observation of the z= 3.09 protocluster in SSA22
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ABSTRACT: We present X-ray point-source catalogues for a deep ≈400-ks Chandra ACIS-I (Advanced CCD Imaging Spectrometer) exposure of the SSA22 field. The observations are centred on a z= 3.09 protocluster, which is populated by Lyman break galaxies (LBGs), Lyα emitters (LAEs) and extended Lyα-emitting blobs (LABs). The survey reaches ultimate (3 count) sensitivity limits of ≈5.7 × 10−17 and ≈3.0 × 10−16 erg cm−2 s−1 for the 0.5–2 and 2–8 keV bands, respectively (corresponding to L2-10 keV≈5.7 × 1042 erg s−1 and L10-30 keV≈2.0 × 1043 erg s−1 at z= 3.09, respectively, for an assumed photon index of Γ= 1.4). These limits make SSA22 the fourth deepest extragalactic Chandra survey yet conducted, and the only one focused on a known high-redshift structure. In total, we detect 297 X-ray point sources and identify one obvious bright extended X-ray source over a ≈330 arcmin2 region. In addition to our X-ray catalogues, we provide all available optical spectroscopic redshifts and near-infrared and mid-infrared photometry available for our sources. The basic X-ray and infrared properties of our Chandra sources indicate a variety of source types, although absorbed active galactic nuclei (AGN) appear to dominate. In total, we have identified 12 X-ray sources (either via optical spectroscopic redshifts or LAE selection) at z= 3.06 – 3.12 that are likely to be associated with the SSA22 protocluster. These sources have X-ray and multiwavelength properties that suggest they are powered by AGN with 0.5–8 keV luminosities in the range of ≈1043–1045 erg s−1. We have analysed the AGN fraction of sources in the protocluster as a function of local LAE source density and find suggestive evidence for a correlation between AGN fraction and local LAE source density (at the ≈96 per cent confidence level), implying that supermassive black hole growth at z≈ 3 is strongest in the highest density regions.
Monthly Notices of the Royal Astronomical Society 11/2009; 400(1):299 - 316. · 5.52 Impact Factor