218 research outputs found
Wide-field spectroscopy of A1689 and A1835 with VIMOS: First results
We are using VIMOS to conduct a wide-field spectroscopic survey covering
fields of 0.5 x 0.5 sqdeg around the X-ray luminous clusters of galaxies Abell
1689 (z = 0.185) and Abell 1835 (z = 0.25). Here we describe the observations
and first results on the redshift distribution of subsamples of cluster
galaxies to R~22 for which we at present have obtained secure redshifts. These
subsamples constitute ~40% of the total spectroscopic sample and contain 525
and 630 cluster members in Abell 1689 and Abell 1835, respectively, placing
them amongst the largest redshift samples available for any cluster of
galaxies.Comment: 6 pages, 4 figures, to appear in Proc. of IAU Colloq. 195: "Outskirts
of Galaxy Clusters: Intense Life in the Suburbs", ed. A. Diaferio et al.,
Turin 12-16 March 200
Probing clustering features around Cl 0024+17
I present a spatial analysis of the galaxy distribution around the cluster Cl
0024+17. The basic aim is to find the scales where galaxies present a
significant deviation from an inhomogeneous Poisson statistical process. Using
the generalization of the Ripley, Besag, and the pair correlation functions for
non-stationary point patterns, I estimate these transition scales for a set of
1,000 Monte Carlo realizations of the Cl 0024+17 field, corrected for
completeness up to the outskirts. The results point out the presence of at
least two physical scales in this field at 31.4 and 112.9 arcseconds. The
second one is statistically consistent with the dark matter ring radius (about
75 arcseconds) previously identified by Jee et al. (2007). However, morphology
and anisotropy tests point out that a clump at about 120 arcseconds NW from the
cluster center could be the responsible for the second transition scale. These
results do not indicate the existence of a galaxy counterpart of the dark
matter ring, but the methodology developed to study the galaxy field as a
spatial point pattern provides a good statistical evaluation of the physical
scales around the cluster. I briefly discuss the usefulness of this approach to
probe features in galaxy distribution and N-body dark matter simulation data.Comment: Accepted for publication in New Astronomy. 14 pages. 8 figure
X-ray observations and mass determinations in the cluster of galaxies Cl0024+17
We present a detailed analysis of the mass distribution in the rich and
distant cluster of galaxies Cl0024+17. X-ray data come from both a deep
ROSAT/HRI image of the field (Bohringer et al. 1999) and ASCA spectral data.
Using a wide field CCD image of the cluster, we optically identify all the
faint X-ray sources, whose counts are compatible with deep X-ray number counts.
In addition we marginally detect the X-ray counter-part of the gravitational
shear perturbation detected by Bonnet et al. (1994) at a 2.5 level. A
careful spectral analysis of ASCA data is also presented. In particular, we
extract a low resolution spectrum of the cluster free from the contamination by
a nearby point source located 1.2 arcmin from the center. The X-ray temperature
deduced from this analysis is keV at the 90%
confidence level. The comparison between the mass derived from a standard X-ray
analysis and from other methods such as the Virial Theorem or the gravitational
lensing effect lead to a mass discrepancy of a factor 1.5 to 3. We discuss all
the possible sources of uncertainties in each method of mass determination and
give some indications on the way to reduce them. A complementary study of
optical data is in progress and may solve the X-ray/optical discrepancy through
a better understanding of the dynamics of the cluster.Comment: Revised version, accepted in Astronomy and Astrophysics (Main
Journal). Few changes in the discussio
Quantifying dwarf satellites through gravitational imaging: the case of SDSS J120602.09+514229.5
SDSS J120602.09+514229.5 is a gravitational lens system formed by a group of
galaxies at redshift z=0.422 lensing a bright background galaxy at redshift
z=2.001. The main peculiarity of this system is the presence of a luminous
satellite near the Einstein radius, that slightly deforms the giant arc. This
makes SDSS J120602.09+514229.5 the ideal system to test our grid-based Bayesian
lens modelling method, designed to detect galactic satellites independently
from their mass-to-light ratio, and to measure the mass of this dwarf galaxy
despite its high redshift. Thanks to the pixelized source and potential
reconstruction technique of Vegetti and Koopmans 2009a we are able to detect
the luminous satellite as a local positive surface density correction to the
overall smooth potential. Assuming a truncated Pseudo-Jaffe density profile,
the satellite has a mass M=(2.75+-0.04)10^10 M_sun inside its tidal radius of
r_t=0.68". We determine for the satellite a luminosity of L_B=(1.6+-0.8)10^9
L_sun, leading to a total mass-to-light ratio within the tidal radius of
(M/L)_B=(17.2+-8.5) M_sun/L_sun. The central galaxy has a sub-isothermal
density profile as in general is expected for group members. From the SDSS
spectrum we derive for the central galaxy a velocity dispersion of
sigma_kinem=380+-60 km/s within the SDSS aperture of diameter 3". The
logarithmic density slope of gamma=1.7+0.25-0.30 (68% CL), derived from this
measurement, is consistent within 1-sigma with the density slope of the
dominant lens galaxy gamma~1.6, determined from the lens model. This paper
shows how powerful pixelized lensing techniques are in detecting and
constraining the properties of dwarf satellites at high redshift.Comment: Submitted to MNRAS; Abstract abridge
A combined HST/CFH12k/XMM survey of X-ray luminous clusters of galaxies at z~0.2
We describe a project to study a sample of X-ray luminous clusters of
galaxies at redshift z~0.2 at several scales (with HST/WFPC2 and CFHT/CFH12k)
and wavebands (optical and X-ray). The main aims of the project are (i) to
determine the mass profiles of the clusters on scales ranging from ~10 kpc/h to
>1.5 Mpc/h using weak and strong lensing, thereby testing theoretical
predictions of a ``universal mass profile'', and (ii) to calibrate the M_tot -
T_X relation in view of future application in the study of the evolution of the
cluster mass function at higher redshift.Comment: 4 pages, 2 figures, Proceedings of the XXth Moriond Astrophysics
Meeting ``Cosmological Physics with Gravitational Lensing'', J.-P. Kneib, Y.
Mellier, M. Moniez and J. Tran Thanh Van eds., 200
CLASH-VLT: Is there a dependence in metallicity evolution on galaxy structures?
We investigate the environmental dependence of the mass-metallicty (MZ)
relation and it's connection to galaxy stellar structures and morphologies. In
our studies, we analyze galaxies in massive clusters at z~0.4 from the CLASH
(HST) and CLASH-VLT surveys and measure their gas metallicities, star-formation
rates, stellar structures and morphologies. We establish the MZ relation for 90
cluster and 40 field galaxies finding a shift of ~-0.3 dex in comparison to the
local trends seen in SDSS for the majority of galaxies with logM<10.5. We do
not find significant differences of the distribution of 4 distinct
morphological types that we introduce by our classification scheme (smooth,
disc-like, peculiar, compact). Some variations between cluster and field
galaxies in the MZ relation are visible at the high mass end. However, obvious
trends for cluster specific interactions (enhancements or quenching of SFRs)
are missing. In particular, galaxies with peculiar stellar structures that hold
signs for galaxy interactions, are distributed in a similar way as disc-like
galaxies - in SFRs, masses and O/H abundances. We further show that our sample
falls around an extrapolation of the star-forming main sequence (the SFR-M*
relation) at this redshift, indicating that emission-line selected samples do
not have preferentially high star-formation rates (SFRs). However, we find that
half of the high mass cluster members (M*>10^10Msun) lie below the main
sequence which corresponds to the higher mass objects that reach solar
abundances in the MZ diagram.Comment: Proceedings of IAU Symposium 309, Vienna, ed. B.L. Ziegler, F.
Combes, H. Dannerbauer, M. Verdug
The Rate of Type Ia Supernovae at High Redshift
We derive the rates of Type Ia supernovae (SNIa) over a wide range of
redshifts using a complete sample from the IfA Deep Survey. This sample of more
than 100 SNIa is the largest set ever collected from a single survey, and
therefore uniquely powerful for a detailed supernova rate (SNR) calculation.
Measurements of the SNR as a function of cosmological time offer a glimpse into
the relationship between the star formation rate (SFR) and Type Ia SNR, and may
provide evidence for the progenitor pathway. We observe a progressively
increasing Type Ia SNR between redshifts z~0.3-0.8. The Type Ia SNR
measurements are consistent with a short time delay (t~1 Gyr) with respect to
the SFR, indicating a fairly prompt evolution of SNIa progenitor systems. We
derive a best-fit value of SFR/SNR 580 h_70^(-2) M_solar/SNIa for the
conversion factor between star formation and SNIa rates, as determined for a
delay time of t~1 Gyr between the SFR and the Type Ia SNR. More complete
measurements of the Type Ia SNR at z>1 are necessary to conclusively determine
the SFR--SNR relationship and constrain SNIa evolutionary pathways.Comment: 37 pages, 9 figures, accepted for publication in Astrophysical
Journal. Figures 7-9 correcte
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