143 research outputs found
CLASH-VLT: Dissecting the Frontier Fields Galaxy Cluster MACS J0416.1-2403 with ∼800 Spectra of Member Galaxies
We present VIMOS-Very Large Telescope (VLT) spectroscopy of the Frontier Fields cluster MACS J0416.1-2403 (z = 0.397). Taken as part of the CLASH-VLT survey, the large spectroscopic campaign provided more than 4000 reliable redshifts over ~600 arcmin^2, including ~800 cluster member galaxies. The unprecedented sample of cluster members at this redshift allows us to perform a highly detailed dynamical and structural analysis of the cluster out to ~2.2 r _(200) (~4 Mpc). Our analysis of substructures reveals a complex system composed of a main massive cluster (M _(200) ~ 0.9 × 10^(15) M_⊙ and σ_(V,r200) ~ 1000 km s^(−1)) presenting two major features: (i) a bimodal velocity distribution, showing two central peaks separated by ΔV _(rf) ~ 1100 km s^(−1) with comparable galaxy content and velocity dispersion, and (ii) a projected elongation of the main substructures along the NE–SW direction, with a prominent sub-clump ~600 kpc SW of the center and an isolated BCG approximately halfway between the center and the SW clump. We also detect a low-mass structure at z ~ 0.390, ~10' south of the cluster center, projected at ~3 Mpc, with a relative line-of-sight velocity of ΔV_(rf) ~ −1700 km s^(−1). The cluster mass profile that we obtain through our dynamical analysis deviates significantly from the "universal" NFW, being best fit by a Softened Isothermal Sphere model instead. The mass profile measured from the galaxy dynamics is found to be in relatively good agreement with those obtained from strong and weak lensing, as well as with that from the X-rays, despite the clearly unrelaxed nature of the cluster. Our results reveal an overall complex dynamical state of this massive cluster and support the hypothesis that the two main subclusters are being observed in a pre-collisional phase, in agreement with recent findings from radio and deep X-ray data. In this article, we also release the entire redshift catalog of 4386 sources in the field of this cluster, which includes 60 identified Chandra X-ray sources and 105 JVLA radio sources
Probing the Cluster Mass Distribution using Subaru Weak Lensing Data
We present results from a weak lensing analysis of the galaxy cluster A1689
(z=0.183) based on deep wide-field imaging data taken with Suprime-Cam on
Subaru telescope. A maximum entropy method has been used to reconstruct
directly the projected mass distribution of A1689 from combined lensing
distortion and magnification measurements of red background galaxies.The
resulting mass distribution is clearly concentrated around the cD galaxy, and
mass and light in the cluster are similarly distributed in terms of shape and
orientation. The azimuthally-averaged mass profile from the two-dimensional
reconstruction is in good agreement with the earlier results from the Subaru
one-dimensional analysis of the weak lensing data, supporting the assumption of
quasi-circular symmetry in the projected mass distribution of the cluster.Comment: To appear in Mod. Phys. Lett. A, 8pages, 5 figures, minor typo errors
corrected, Fig.5 modifie
VLA Radio Observations of the HST Frontier Fields Cluster Abell 2744: The Discovery of New Radio Relics
Cluster mergers leave distinct signatures in the ICM in the form of shocks
and diffuse cluster radio sources that provide evidence for the acceleration of
relativistic particles. However, the physics of particle acceleration in the
ICM is still not fully understood. Here we present new 1-4 GHz Jansky Very
Large Array (VLA) and archival Chandra observations of the HST Frontier Fields
Cluster Abell 2744. In our new VLA images, we detect the previously known
Mpc radio halo and Mpc radio relic. We carry out a radio
spectral analysis from which we determine the relic's injection spectral index
to be . This corresponds to a shock Mach
number of = 2.05 under the assumption of
diffusive shock acceleration. We also find evidence for spectral steepening in
the post-shock region. We do not find evidence for a significant correlation
between the radio halo's spectral index and ICM temperature. In addition, we
observe three new polarized diffuse sources and determine two of these to be
newly discovered giant radio relics. These two relics are located in the
southeastern and northwestern outskirts of the cluster. The corresponding
integrated spectral indices measure and for
the SE and NW relics, respectively. From an X-ray surface brightness profile we
also detect a possible density jump of co-located with
the newly discovered SE relic. This density jump would correspond to a shock
front Mach number of .Comment: accepted for publication in Ap
A weak lensing analysis of the Abell 383 cluster
In this paper we use deep CFHT and SUBARU archival images of the
Abell 383 cluster (z=0.187) to estimate its mass by weak lensing. To this end,
we first use simulated images to check the accuracy provided by our KSB
pipeline. Such simulations include both the STEP 1 and 2 simulations, and more
realistic simulations of the distortion of galaxy shapes by a cluster with a
Navarro-Frenk-White (NFW) profile. From such simulations we estimate the effect
of noise on shear measurement and derive the correction terms. The R-band image
is used to derive the mass by fitting the observed tangential shear profile
with a NFW mass profile. Photometric redshifts are computed from the uBVRIz
catalogs. Different methods for the foreground/background galaxy selection are
implemented, namely selection by magnitude, color and photometric redshifts,
and results are compared. In particular, we developed a semi-automatic
algorithm to select the foreground galaxies in the color-color diagram, based
on observed colors. Using color selection or photometric redshifts improves the
correction of dilution from foreground galaxies: this leads to higher signals
in the inner parts of the cluster. We obtain a cluster mass that is ~ 20%
higher than previous estimates, and is more consistent the mass expected from
X--ray data. The R-band luminosity function of the cluster is finally computed.Comment: 11 pages, 12 figures. Accepted for publication on Astronomy &
Astrophysic
CLASH: The enhanced lensing efficiency of the highly elongated merging cluster MACS J0416.1-2403
We perform a strong-lensing analysis of the merging galaxy cluster MACS
J0416.1-2403 (M0416; z=0.42) in recent CLASH/HST observations. We identify 70
new multiple images and candidates of 23 background sources in the range
0.7<z_{phot}<6.14 including two probable high-redshift dropouts, revealing a
highly elongated lens with axis ratio ~5:1, and a major axis of ~100\arcsec
(z_{s}~2). Compared to other well-studied clusters, M0416 shows an enhanced
lensing efficiency. Although the critical area is not particularly large (~0.6
\square\arcmin; z_{s}~2), the number of multiple images, per critical area, is
anomalously high. We calculate that the observed elongation boosts the number
of multiple images, \emph{per critical area}, by a factor of ~2.5\times, due to
the increased ratio of the caustic area relative to the critical area.
Additionally, we find that the observed separation between the two main mass
components enlarges the critical area by a factor of ~2. These geometrical
effects can account for the high number (density) of multiple images observed.
We find in numerical simulations, that only ~4% of the clusters (with M_{vir}>6
x 10^{14} h^{-1}M_{\odot}) exhibit as elongated critical curves as M0416.Comment: 7 pages, 4 figures, 1 table. V2: accepted to ApJ Letters; minor
changes and updates; in Fig.3 labeling error corrected. Mass models available
online: ftp://wise-ftp.tau.ac.il/pub/adiz/M0416
CLASH-VLT: The stellar mass function and stellar mass density profile of the z=0.44 cluster of galaxies MACS J1206.2-0847
Context. The study of the galaxy stellar mass function (SMF) in relation to
the galaxy environment and the stellar mass density profile, rho(r), is a
powerful tool to constrain models of galaxy evolution. Aims. We determine the
SMF of the z=0.44 cluster of galaxies MACS J1206.2-0847 separately for passive
and star-forming (SF) galaxies, in different regions of the cluster, from the
center out to approximately 2 virial radii. We also determine rho(r) to compare
it to the number density and total mass density profiles. Methods. We use the
dataset from the CLASH-VLT survey. Stellar masses are obtained by SED fitting
on 5-band photometric data obtained at the Subaru telescope. We identify 1363
cluster members down to a stellar mass of 10^9.5 Msolar. Results. The whole
cluster SMF is well fitted by a double Schechter function. The SMFs of cluster
SF and passive galaxies are statistically different. The SMF of the SF cluster
galaxies does not depend on the environment. The SMF of the passive population
has a significantly smaller slope (in absolute value) in the innermost (<0.50
Mpc), highest density cluster region, than in more external, lower density
regions. The number ratio of giant/subgiant galaxies is maximum in this
innermost region and minimum in the adjacent region, but then gently increases
again toward the cluster outskirts. This is also reflected in a decreasing
radial trend of the average stellar mass per cluster galaxy. On the other hand,
the stellar mass fraction, i.e., the ratio of stellar to total cluster mass,
does not show any significant radial trend. Conclusions. Our results appear
consistent with a scenario in which SF galaxies evolve into passive galaxies
due to density-dependent environmental processes, and eventually get destroyed
very near the cluster center to become part of a diffuse intracluster medium.Comment: A&A accepted, 15 pages, 13 figure
CLASH: Extending galaxy strong lensing to small physical scales with distant sources highly-magnified by galaxy cluster members
We present a strong lensing system in which a double source is imaged 5 times
by 2 early-type galaxies. We take advantage in this target of the multi-band
photometry obtained as part of the CLASH program, complemented by the
spectroscopic data of the VLT/VIMOS and FORS2 follow-up campaign. We use a
photometric redshift of 3.7 for the source and confirm spectroscopically the
membership of the 2 lenses to the galaxy cluster MACS J1206.2-0847 at redshift
0.44. We exploit the excellent angular resolution of the HST/ACS images to
model the 2 lenses in terms of singular isothermal sphere profiles and derive
robust effective velocity dispersions of (97 +/- 3) and (240 +/- 6) km/s. The
total mass distribution of the cluster is also well characterized by using only
the local information contained in this lensing system, that is located at a
projected distance of more than 300 kpc from the cluster luminosity center.
According to our best-fitting lensing and composite stellar population models,
the source is magnified by a total factor of 50 and has a luminous mass of
about (1.0 +/- 0.5) x 10^{9} M_{Sun}. By combining the total and luminous mass
estimates of the 2 lenses, we measure luminous over total mass fractions
projected within the effective radii of 0.51 +/- 0.21 and 0.80 +/- 0.32. With
these lenses we can extend the analysis of the mass properties of lens
early-type galaxies by factors that are about 2 and 3 times smaller than
previously done with regard to, respectively, velocity dispersion and luminous
mass. The comparison of the total and luminous quantities of our lenses with
those of astrophysical objects with different physical scales reveals the
potential of studies of this kind for investigating the internal structure of
galaxies. These studies, made possible thanks to the CLASH survey, will allow
us to go beyond the current limits posed by the available lens samples in the
field.Comment: 20 pages, 10 figures, accepted for publication in the Astrophysical
Journa
CLASH-VLT: Dissecting the Frontier Fields Galaxy Cluster MACS J0416.1-2403 with Spectra of Member Galaxies
We present VIMOS-VLT spectroscopy of the Frontier Fields cluster
MACS~J0416.1-2403 (z=0.397). Taken as part of the CLASH-VLT survey, the large
spectroscopic campaign provided more than 4000 reliable redshifts, including
~800 cluster member galaxies. The unprecedented sample of cluster members at
this redshift allows us to perform a highly detailed dynamical and structural
analysis of the cluster out to ~2.2 (~4Mpc). Our analysis of
substructures reveals a complex system composed of a main massive cluster
(~0.9) presenting two major features: i) a
bimodal velocity distribution, showing two central peaks separated by ~1100 km s with comparable galaxy content and velocity
dispersion, ii) a projected elongation of the main substructures along the
NE-SW direction, with a prominent subclump ~600 kpc SW of the center and an
isolated BCG approximately halfway between the center and the SW clump. We also
detect a low mass structure at z~0.390, ~10' S of the cluster center, projected
at ~3Mpc, with a relative line-of-sight velocity of ~-1700 km
s. The cluster mass profile that we obtain through our dynamical
analysis deviates significantly from the "universal" NFW, being best fit by a
Softened Isothermal Sphere model instead. The mass profile measured from the
galaxy dynamics is found to be in relatively good agreement with those obtained
from strong and weak lensing, as well as with that from the X-rays, despite the
clearly unrelaxed nature of the cluster. Our results reveal overall a complex
dynamical state of this massive cluster and support the hypothesis that the two
main subclusters are being observed in a pre-collisional phase, in line with
recent findings from radio and deep X-ray data. With this article we also
release the entire redshift catalog of 4386 sources in the field of this
cluster.Comment: Accepted for publication on ApJS. Revised to match the accepted
version; 21 pages, 18 figures, 9 tables. The CLASH-VLT spectroscopic catalogs
are publicly available at: http://sites.google.com/site/vltclashpublic
CLASH-VLT: The mass, velocity-anisotropy, and pseudo-phase-space density profiles of the z=0.44 galaxy cluster MACS 1206.2-0847
We use an unprecedented data-set of about 600 redshifts for cluster members,
obtained as part of a VLT/VIMOS large programme, to constrain the mass profile
of the z=0.44 cluster MACS J1206.2-0847 over the radial range 0-5 Mpc (0-2.5
virial radii) using the MAMPOSSt and Caustic methods. We then add external
constraints from our previous gravitational lensing analysis. We invert the
Jeans equation to obtain the velocity-anisotropy profiles of cluster members.
With the mass-density and velocity-anisotropy profiles we then obtain the first
determination of a cluster pseudo-phase-space density profile. The kinematics
and lensing determinations of the cluster mass profile are in excellent
agreement. This is very well fitted by a NFW model with mass M200=(1.4 +- 0.2)
10^15 Msun and concentration c200=6 +- 1, only slightly higher than theoretical
expectations. Other mass profile models also provide acceptable fits to our
data, of (slightly) lower (Burkert, Hernquist, and Softened Isothermal Sphere)
or comparable (Einasto) quality than NFW. The velocity anisotropy profiles of
the passive and star-forming cluster members are similar, close to isotropic
near the center and increasingly radial outside. Passive cluster members follow
extremely well the theoretical expectations for the pseudo-phase-space density
profile and the relation between the slope of the mass-density profile and the
velocity anisotropy. Star-forming cluster members show marginal deviations from
theoretical expectations. This is the most accurate determination of a cluster
mass profile out to a radius of 5 Mpc, and the only determination of the
velocity-anisotropy and pseudo-phase-space density profiles of both passive and
star-forming galaxies for an individual cluster [abridged]Comment: A&A in press; 22 pages, 19 figure
Evidence for Ubiquitous, High-EW Nebular Emission in z~7 Galaxies: Towards a Clean Measurement of the Specific Star Formation Rate using a Sample of Bright, Magnified Galaxies
Growing observational evidence now indicates that nebular line emission has a
significant impact on the rest-frame optical fluxes of z~5-7 galaxies observed
with Spitzer. This line emission makes z~5-7 galaxies appear more massive, with
lower specific star formation rates. However, corrections for this line
emission have been very difficult to perform reliably due to huge uncertainties
on the overall strength of such emission at z>~5.5. Here, we present the most
direct observational evidence yet for ubiquitous high-EW [OIII]+Hbeta line
emission in Lyman-break galaxies at z~7, while also presenting a strategy for
an improved measurement of the sSFR at z~7. We accomplish this through the
selection of bright galaxies in the narrow redshift window z~6.6-7.0 where the
IRAC 4.5 micron flux provides a clean measurement of the stellar continuum
light. Observed 4.5 micron fluxes in this window contrast with the 3.6 micron
fluxes which are contaminated by the prominent [OIII]+Hbeta lines. To ensure a
high S/N for our IRAC flux measurements, we consider only the brightest
(H_{160}<26 mag) magnified galaxies we have identified in CLASH and other
programs targeting galaxy clusters. Remarkably, the mean rest-frame optical
color for our bright seven-source sample is very blue, [3.6]-[4.5]=-0.9+/-0.3.
Such blue colors cannot be explained by the stellar continuum light and require
that the rest-frame EW of [OIII]+Hbeta be greater than 637 Angstroms for the
average source. The bluest four sources from our seven-source sample require an
even more extreme EW of 1582 Angstroms. Our derived lower limit for the mean
[OIII]+Hbeta EW could underestimate the true EW by ~2x based on a simple
modeling of the redshift distribution of our sources. We can also set a robust
lower limit of >~4 Gyr^-1 on the specific star formation rates based on the
mean SED for our seven-source sample. (abridged)Comment: 9 pages, 6 figures, 1 table, submitted to the Astrophysical Journa
- …