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Marseille, France

Durret F.,CNRS Paris Institute of Astrophysics | Wakamatsu K.,Gifu University | Nagayama T.,Nagoya University | Adami C.,LAM | And 2 more authors.
Astronomy and Astrophysics | Year: 2015

The Ophiuchus cluster, at a redshift z = 0.0296, is known from X-rays to be one of the most massive nearby clusters, but its optical properties have not been investigated in detail because of its very low Galactic latitude. Aims. We discuss the optical properties of the galaxies in the Ophiuchus cluster, in particular, with the aim of understanding its dynamical properties better. Methods. We have obtained deep optical imaging in several bands with various telescopes, and applied a sophisticated method to model and subtract the contributions of stars to measure galaxy magnitudes as accurately as possible. The colour.magnitude relations obtained show that there are hardly any blue galaxies in Ophiuchus (at least brighter than r'≤ 19.5), and this is confirmed by the fact that we only detect two galaxies in Hα. We also obtained a number of spectra with ESO-FORS2, which we combined with previously available redshifts. Altogether, we have 152 galaxies with spectroscopic redshifts in the 0.02 ≤ z ≤ 0.04 range, and 89 galaxies with both a redshift within the cluster redshift range and a measured r' band magnitude (limited to the Megacam 1 1 deg2 field). Results. A complete dynamical analysis based on the galaxy redshifts available shows that the overall cluster is relaxed and has a mass of 1.1 1015 M⊙. The Sernal-Gerbal method detects a main structure and a much smaller substructure, which are not separated in projection. Conclusions. From its dynamical properties derived from optical data, the Ophiuchus cluster seems overall to be a relaxed structure, or at most a minor merger, though in X-rays the central region (radius ∼ 150 kpc) may show evidence for merging effects. © 2015 ESO. Source

Durret F.,CNRS Paris Institute of Astrophysics | Lagana T.F.,University of Sao Paulo | Adami C.,LAM | Bertin E.,CNRS Paris Institute of Astrophysics
Astronomy and Astrophysics | Year: 2010

Context. The Abell 222 and 223 clusters are located at an average redshift z ∼ 0.21 and are separated by 0.26 deg. Signatures of mergers have been previously found in these clusters, both in X-rays and at optical wavelengths, thus motivating our study. In X-rays, they are relatively bright, and Abell 223 shows a double structure. A filament has also been detected between the clusters both at optical and X-ray wavelengths. Aims. We analyse the optical properties of these two clusters based on deep imaging in two bands, derive their galaxy luminosity functions (GLFs) and correlate these properties with X-ray characteristics derived from XMM-Newton data. Methods. The optical part of our study is based on archive images obtained with the CFHT Megaprime/Megacam camera, covering a total region of about 1 deg2, or 12.3 × 12.3 Mpc2 at a redshift of 0.21. The X-ray analysis is based on archive XMM-Newton images. Results. The GLFs of Abell 222 in the g' and r' bands are well fit by a Schechter function; the GLF is steeper in r' than in g'. For Abell 223, the GLFs in both bands require a second component at bright magnitudes, added to a Schechter function; they are similar in both bands. The Serna & Gerbal method allows to separate well the two clusters. No obvious filamentary structures are detected at very large scales around the clusters, but a third cluster at the same redshift, Abell 209, is located at a projected distance of 19.2 Mpc. X-ray temperature and metallicity maps reveal that the temperature and metallicity of the X-ray gas are quite homogeneous in Abell 222, while they are very perturbed in Abell 223. Conclusions. The Abell 222/Abell 223 system is complex. The two clusters that form this structure present very different dynamical states. Abell 222 is a smaller, less massive and almost isothermal cluster. On the other hand, Abell 223 is more massive and has most probably been crossed by a subcluster on its way to the northeast. As a consequence, the temperature distribution is very inhomogeneous. Signs of recent interactions are also detected in the optical data where this cluster shows a "perturbed" GLF. In summary, the multiwavelength analyses of Abell 222 and Abell 223 are used to investigate the connection between the ICM and the cluster galaxy properties in an interacting system. © 2010 ESO. Source

Jonsson J.,University of Oxford | Sullivan M.,University of Oxford | Hook I.,University of Oxford | Hook I.,National institute for astrophysics | And 8 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2010

This paper exploits the gravitational magnification of Type Ia supernovae (SNe Ia) to measure properties of dark matter haloes. Gravitationally magnified and de-magnified SNe Ia should be brighter and fainter than average, respectively. The magnification of individual SNe Ia can be computed using observed properties of foreground galaxies and dark matter halo models. We model the dark matter haloes of the galaxies as truncated singular isothermal spheres with velocity dispersion and truncation radius obeying luminosity-dependent scaling laws.A homogeneously selected sample of 175 SNe Ia from the first 3 yr of the Supernova Legacy Survey (SNLS) in the redshift range 0.2 ≲ z ≲ 1 is used to constrain models of the dark matter haloes associated with foreground galaxies. The best-fitting velocity dispersion scaling law agrees well with galaxy-galaxy lensing measurements. We further find that the normalization of the velocity dispersion of passive and star-forming galaxies are consistent with empirical Faber-Jackson and Tully-Fisher relations, respectively. If we make no assumption on the normalization of these relations, we find that the data prefer gravitational lensing at the 92 per cent confidence level. Using recent models of dust extinction, we deduce that the impact of this effect on our results is very small.We also investigate the brightness scatter of SNe Ia due to gravitational lensing, which has implications for SN Ia cosmology. The gravitational lensing scatter is approximately proportional to the SN Ia redshift. We find the constant of proportionality to be B ≃ 0.055+0.039 -0.041 mag (B ≲ 0.12 mag at the 95 per cent confidence level). If this model is correct, the contribution from lensing to the intrinsic brightness scatter of SNe Ia is small for the SNLS sample. According to the best-fitting dark matter model, gravitational lensing should, however, contribute significantly to the brightness scatter at z ≳ 1.6. © 2010 The Authors. Journal compilation © 2010 RAS. Source

Kim and Lam | Date: 2008-01-18


Lam and Nguyen | Date: 2015-09-27

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