We determine the mass profile of an ensemble cluster built from 3056 galaxies in 59 nearby clusters observed in the ESO Nearby Abell Cluster Survey. The mass profile is derived from the distribution ...and kinematics of the early- type (elliptical and S0) galaxies only, with projected distances from the centers of their clusters <1.5r sub(200). These galaxies are most likely to meet the conditions for the application of the Jeans equation, since they are the oldest cluster population and are thus quite likely to be in dynamical equilibrium with the cluster potential. In addition, the assumption that the early-type galaxies have isotropic orbits is supported by the shape of their velocity distribution. For galaxies of other types (the brightest elliptical galaxies, with M sub(R) <-22 + 5 log h, and the early and late spirals) these assumptions are much less likely to be satisfied. For the determination of the mass profile we also exclude early-type galaxies in subclusters. Application of the Jeans equation yields a nonparametric estimate of the cumulative mass profile M(<r), which has a logarithmic slope of-2.4 plus or minus 0.4 in the density profile at r sub(200) (approximately the virial radius). We compare our result with several analytical models from the literature and estimate their best-fit parameters from a comparison of observed and predicted velocity-dispersion profiles. We obtain acceptable solutions for all models (NFW, Moore et al. softened isothermal sphere SIS, and Burkert). Our data do not provide compelling evidence for the existence of a core; as a matter of fact, the best-fitting core models have core-radii well below 100 h super(-1) kpc. The upper limit that we put on the size of the core-radius provides a constraint for the scattering cross section of dark matter particles. The total-mass density appears to be traced remarkably well by the luminosity density of the early-type galaxies. On the contrary, the luminosity density of the brightest elliptical galaxies increases faster toward the center than the mass density, while the luminosity density profiles of the early and late spirals are somewhat flatter than the mass density profile.
We report the serendipitous detection by GALEX of fast (<1 day) rising (image1 mag) UV emission from two Type II plateau (II-P) supernovae (SNe) at image and 0.324 discovered by the Supernova Legacy ...Survey. Optical photometry and VLT spectroscopy 2 weeks after the GALEX detections link the onset of UV emission to the time of shock breakout. Using radiation hydrodynamics and non-LTE radiative transfer simulations, and starting from a standard red supergiant (RSG; Type II-P SN progenitor) star evolved self- consistently from the main sequence to iron core collapse, we model the shock breakout phase and the 55 hr that follow. The small scale height of our RSG atmosphere model suggests that the breakout signature is a thermal soft X-ray burst (image Aa) with a duration of image2000 s. Longer durations are possible but require either an extended and tenuous nonstandard envelope or an unusually dense RSG wind with image yr super(-1). The GALEX observations miss the peak of the luminous UV burst but unambiguously capture the rise of the emission and a subsequent 2 day long plateau. The postbreakout, UV-bright plateau is a prediction of our model in which the shift of the peak of the spectral energy distribution (SED) from image100 to image1000 Aa and the ejecta expansion both counteract the decrease in bolometric luminosity from image10 super(11) to image10 super(9) image over that period. Based on the observed detection efficiency of our study, we make predictions for the breakout detection rate of the GALEX Time Domain Survey.
Neutrino alert systems for Gamma Ray Bursts and transient astronomical sources Basa, Stéphane; Dornic, Damien; Lelaizant, Gabrielle ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2009, Letnik:
602, Številka:
1
Journal Article
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Gamma Ray Bursts (GRBs) are the most energetic events in the Universe, associated with the death of massive stars (core-collapse supernovae) or the merging of neutron stars or black holes. Discovered ...in the early 1970s, their cosmological origin was demonstrated only in 1997, when the first distance was measured. Theoretical models predict that the very energetic processes at work in GRBs accelerate charged particles to such energies that they could contribute to the observed high energy neutrinos.
These processes will be discussed and the observational consequences, in particular for current and forthcoming neutrino telescopes, presented.
The ANTARES telescope has the opportunity to detect transient neutrino sources, such as gamma-ray bursts, core-collapse supernovae, flares of active galactic nuclei. In order to enhance the ...sensitivity to these sources, we have developed a new detection method based on the follow-up by optical telescopes of “golden” neutrino events, such as neutrino doublets coincident in time and space or single neutrinos of very high energy. The ANTARES collaboration has therefore implemented a very fast on-line reconstruction with a good angular resolution. These characteristics allow us to trigger an optical telescope network. Since February 2009, ANTARES is sending alert triggers once or twice per month to the two 25
cm robotic telescope of TAROT. This optical follow-up of such special events would not only give access to the nature of the sources, but also would improve the sensitivity to transient neutrino sources.
We determine the mass profile of an ensemble cluster built from 3056 galaxies in 59 nearby clusters observed in the ESO Nearby Abell Cluster Survey. The mass profile is derived from the distribution ...and kinematics of the Early-type (elliptical and S0) galaxies only, which are most likely to meet the conditions for the application of the Jeans equation. We assume that the Early-type galaxies have isotropic orbits, as supported by the shape of their velocity distribution. The brightest ellipticals (with M_R < -22+5 log h), and the Early-type galaxies in subclusters are excluded from the sample. Application of the Jeans equation yields a non-parametric estimate of the cumulative mass profile M(
Group analysis in the SSRS2 catalog Adami, C.; Mazure, A.
Astronomy and astrophysics (Berlin),
01/2002, Letnik:
381, Številka:
2
Journal Article
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We present an automated method to detect populations of groups in galaxy redshift catalogs. This method uses both analysis of the redshift distribution along lines of sight in fixed cells to detect ...elementary structures and a friend-of-friend algorithm to merge these elementary structures into physical structures. We apply this method to the SSRS2 galaxy redshift catalog. The groups detected with our method are similar to group catalogs detected with pure friend-of-friend algorithms. They have similar mass distribution, similar abundance versus redshift, a similar 2-point correlation function (modeled by a power law: $ (r/r_0)^\gamma $ with $r_0=7~h^{-1}~{\rm Mpc}$ and $\gamma =-1.79$) and the same redshift completeness limit, close to 5000 km s-1. If instead of SSRS2, we use catalogs of the new generation (deep redshift surveys obtained with 10 m class telescopes), it would lead to a completeness limit of $z\sim0.7$. We model the luminosity function for nearby galaxy groups by a Schechter function with parameters $M_{\rm SSRS2}^{*}=(-19.99\pm 0.36)+5~{\rm log}h$ and $\alpha =-1.46\pm 0.17$ to compute the mass to light ratio. The median value of the mass to light ratio is 360 $hM_{\odot }$/$L_{\odot }$ (in the SSRS2 band, close to a B band magnitude) and we deduce a relation between mass to light ratio and velocity dispersion $\sigma $ ($ M/L=(3.79\pm 0.64)\sigma -(294\pm 570)$). The more massive the group, the higher the mass to light ratio, and therefore, the larger the amount of dark matter inside the group. Another explanation is a significant stripping of the gas of the galaxies in massive groups as opposed to low mass groups. This extends to groups of galaxies the mild tendency already detected for rich clusters of galaxies. Finally, we detect a barely significant fundamental plane for these groups ($L\propto R_{\rm Vir}^{2.26\pm 1.39}\times \sigma ^{2.93\pm 1.64}$ for groups with more than 8 galaxies) but it is much less narrow than for clusters of galaxies.
The cluster of galaxies SC2008 – 57 (A3667) Sodré, Laerte; Capelato, Hugo V.; Steiner, João E. ...
Monthly notices of the Royal Astronomical Society,
11/1992, Letnik:
259, Številka:
2
Journal Article
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We present the results of photometric and spectroscopic observations of the cluster of galaxies SC2008 – 57 (A3667). The observations have resulted in a catalogue with positions and magnitudes for ...203 galaxies, complete at $b_{25}=18.0$, and radial velocities for 128 galaxies, 91 per cent complete at $b_{25}=17.5$. The cluster can be classified as type L because its galaxy distribution is highly flattened. It shows two strong concentrations: a main concentration, centred on the cluster brightest galaxy (a D galaxy) and coincident with the peak of X-ray emission, and a substructure around the second brightest galaxy (also a D galaxy). Most of the galaxies in this substructure seem to be bound to the second-brightest galaxy, forming a dynamical subunit inside the cluster. The extreme flattening of the cluster may at least partially be due to the presence of the substructure. The cluster also shows evidence for luminosity segregation, with the brightest galaxies being preferentially found in high galaxy density regions. Most of the luminosity segregation, however, is produced by galaxies associated with the two clumps around the D galaxies, suggesting that dynamical friction is effective in subclusters with low velocity dispersions and may be associated with the formation of D galaxies. The velocity dispersion of SC2008 – 57 is high, about 1200 km s−1, but consistent with the observed X-ray luminosity. The cluster mass, derived using several estimators, is about $2.6 \times10^{15} \enspace \text M_\odot$. Both the cluster mass and velocity dispersion may be overestimates due to the presence of the substructure.
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