101 research outputs found
The Mystery Deepens: Spitzer Observations of Cool White Dwarfs
We present 4.5m and 8m photometric observations of 18 cool white
dwarfs obtained with the Spitzer Space Telescope. Our observations demonstrate
that four white dwarfs with T_eff< 6000 K show slightly depressed mid-infrared
fluxes relative to white dwarf models. In addition, another white dwarf with a
peculiar optical and near-infrared spectral energy distribution (LHS 1126) is
found to display significant flux deficits in Spitzer observations. These
mid-infrared flux deficits are not predicted by the current white dwarf models
including collision induced absorption due to molecular hydrogen. We postulate
that either the collision induced absorption calculations are incomplete or
there are other unrecognized physical processes occuring in cool white dwarf
atmospheres. The spectral energy distribution of LHS 1126 surprisingly fits a
Rayleigh-Jeans spectrum in the infrared, mimicking a hot white dwarf with
effective temperature well in excess of 10 K. This implies that the source
of this flux deficit is probably not molecular absorption but some other
process.Comment: 17 pages, 4 figures, ApJ in press, 10 May 200
CLASH-VLT: Strangulation of cluster galaxies in MACSJ0416.1-2403 as seen from their chemical enrichment
(abridged) We explore the Frontier Fields cluster MACS J0416.1-2403 at
z=0.3972 with VIMOS/VLT spectroscopy from the CLASH-VLT survey covering a
region which corresponds to almost three virial radii. We measure fluxes of 5
emission lines of 76 cluster members enabling us to unambiguously derive O/H
gas metallicities, and also SFRs from Halpha. For intermediate massses we find
a similar distribution of cluster and field galaxies in the MZR and mass vs.
sSFR diagrams. Bulge-dominated cluster galaxies have on average lower sSFRs and
higher O/Hs compared to their disk-dominated counterparts. We use the location
of galaxies in the projected velocity vs. position phase-space to separate our
cluster sample into a region of objects accreted longer time ago and a region
of recently accreted and infalling galaxies. We find a higher fraction of
accreted metal-rich galaxies (63%) compared to the fraction of 28% of
metal-rich galaxies in the infalling regions. Intermediate mass galaxies
falling into the cluster for the first time are found to be in agreement with
predictions of the fundamental metallicity relation. In contrast, for already
accreted star-forming galaxies of similar masses, we find on average
metallicities higher than predicted by the models. This trend is intensified
for accreted cluster galaxies of the lowest mass bin, that display
metallicities 2-3 times higher than predicted by models with primordial gas
inflow. Environmental effects therefore strongly influence gas regulations and
control gas metallicities of log(M/Msun)<10.2 (Salpeter IMF) cluster galaxies.
We also investigate chemical evolutionary paths of model galaxies with and
without inflow of gas showing that strangulation is needed to explain the
higher metallicities of accreted cluster galaxies. Our results favor a
strangulation scenario in which gas inflow stops for log(M/Msun)<10.2 galaxies
when accreted by the cluster.Comment: Version better matched to the published version, including table with
observed and derived quantities for the 76 cluster galaxie
CLASH-VLT: Environment-driven evolution of galaxies in the z=0.209 cluster Abell 209
The analysis of galaxy properties and the relations among them and the
environment, can be used to investigate the physical processes driving galaxy
evolution. We study the cluster A209 by using the CLASH-VLT spectroscopic data
combined with Subaru photometry, yielding to 1916 cluster members down to a
stellar mass of 10^{8.6} Msun. We determine: i) the stellar mass function of
star-forming and passive galaxies; ii) the intra-cluster light and its
properties; iii) the orbits of low- and high-mass passive galaxies; and iv) the
mass-size relation of ETGs. The stellar mass function of the star-forming
galaxies does not depend on the environment, while the slope found for passive
galaxies becomes flatter in the densest region. The color distribution of the
intra-cluster light is consistent with the color of passive members. The
analysis of the dynamical orbits shows that low-mass passive galaxies have
tangential orbits, avoiding small pericenters around the BCG. The mass-size
relation of low-mass passive ETGs is flatter than that of high mass galaxies,
and its slope is consistent with that of field star-forming galaxies. Low-mass
galaxies are also more compact within the scale radius of 0.65 Mpc. The ratio
between stellar and number density profiles shows a mass segregation in the
center. The comparative analysis of the stellar and total density profiles
indicates that this effect is due to dynamical friction. Our results are
consistent with a scenario in which the "environmental quenching" of low-mass
galaxies is due to mechanisms such as harassment out to R200, starvation and
ram-pressure stripping at smaller radii, as supported by the analysis of the
mass function, of the dynamical orbits and of the mass-size relation of passive
early-types in different regions. Our analyses support the idea that the
intra-cluster light is formed through the tidal disruption of subgiant
galaxies.Comment: 17 pages, 20 figures, A&A in pres
Super Earth Explorer: A Coronagraphic Off-Axis Space Telescope
The Super-Earth Explorer is an Off-Axis Space Telescope (SEE-COAST) designed
for high contrast imaging. Its scientific objective is to make the
physico-chemical characterization of exoplanets possibly down to 2 Earth radii
>. For that purpose it will analyze the spectral and polarimetric properties of
the parent starlight reflected by the planets, in the wavelength range 400-1250
nmComment: Accepted in Experimental Astronom
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
On the protection of extrasolar Earth-like planets around K/M stars against galactic cosmic rays
Previous studies have shown that extrasolar Earth-like planets in close-in
habitable zones around M-stars are weakly protected against galactic cosmic
rays (GCRs), leading to a strongly increased particle flux to the top of the
planetary atmosphere. Two main effects were held responsible for the weak
shielding of such an exoplanet: (a) For a close-in planet, the planetary
magnetic moment is strongly reduced by tidal locking. Therefore, such a
close-in extrasolar planet is not protected by an extended magnetosphere. (b)
The small orbital distance of the planet exposes it to a much denser stellar
wind than that prevailing at larger orbital distances. This dense stellar wind
leads to additional compression of the magnetosphere, which can further reduce
the shielding efficiency against GCRs. In this work, we analyse and compare the
effect of (a) and (b), showing that the stellar wind variation with orbital
distance has little influence on the cosmic ray shielding. Instead, the weak
shielding of M star planets can be attributed to their small magnetic moment.
We further analyse how the planetary mass and composition influence the
planetary magnetic moment, and thus modify the cosmic ray shielding efficiency.
We show that more massive planets are not necessarily better protected against
galactic cosmic rays, but that the planetary bulk composition can play an
important role.Comment: 7 figure
CLASH: z ~ 6 young galaxy candidate quintuply lensed by the frontier field cluster RXC J2248.7-4431
We present a quintuply lensed z ~ 6 candidate discovered in the field of the
galaxy cluster RXC J2248.7-4431 (z ~ 0.348) targeted within the Cluster Lensing
and Supernova survey with Hubble (CLASH) and selected in the deep HST Frontier
Fields survey. Thanks to the CLASH 16-band HST imaging, we identify the
quintuply lensed z ~ 6 candidate as an optical dropout in the inner region of
the cluster, the brightest image having magAB=24.81+-0.02 in the f105w filter.
We perform a detailed photometric analysis to verify its high-z and lensed
nature. We get as photometric redshift z_phot ~ 5.9, and given the extended
nature and NIR colours of the lensed images, we rule out low-z early type and
galactic star contaminants. We perform a strong lensing analysis of the
cluster, using 13 families of multiple lensed images identified in the HST
images. Our final best model predicts the high-z quintuply lensed system with a
position accuracy of 0.8''. The magnifications of the five images are between
2.2 and 8.3, which leads to a delensed UV luminosity of L_1600 ~ 0.5L*_1600 at
z=6. We also estimate the UV slope from the observed NIR colours, finding a
steep beta=-2.89+-0.38. We use singular and composite stellar population SEDs
to fit the photometry of the hiz candidate, and we conclude that it is a young
(age <300 Myr) galaxy with mass of M ~ 10^8Msol, subsolar metallicity
(Z<0.2Zsol) and low dust content (AV ~ 0.2-0.4).Comment: 21 pages, 13 figures, 6 tables, submitted to MNRAS on 11 Aug 2013,
accepted on 23 Nov 201
CLASH-VLT: Substructure in the galaxy cluster MACS J1206.2-0847 from kinematics of galaxy populations
In the effort to understand the link between the structure of galaxy clusters
and their galaxy populations, we focus on MACSJ1206.2-0847 at z~0.44 and probe
its substructure in the projected phase space through the spectrophotometric
properties of a large number of galaxies from the CLASH-VLT survey. Our
analysis is mainly based on an extensive spectroscopic dataset of 445 member
galaxies, mostly acquired with VIMOS@VLT as part of our ESO Large Programme,
sampling the cluster out to a radius ~2R200 (4 Mpc). We classify 412 galaxies
as passive, with strong Hdelta absorption (red and blue galaxies, and with
emission lines from weak to very strong. A number of tests for substructure
detection are applied to analyze the galaxy distribution in the velocity space,
in 2D space, and in 3D projected phase-space. Studied in its entirety, the
cluster appears as a large-scale relaxed system with a few secondary, minor
overdensities in 2D distribution. We detect no velocity gradients or evidence
of deviations in local mean velocities. The main feature is the WNW-ESE
elongation. The analysis of galaxy populations per spectral class highlights a
more complex scenario. The passive galaxies and red strong Hdelta galaxies
trace the cluster center and the WNW-ESE elongated structure. The red strong
Hdelta galaxies also mark a secondary, dense peak ~2 Mpc at ESE. The emission
line galaxies cluster in several loose structures, mostly outside R200. The
observational scenario agrees with MACS J1206.2-0847 having WNW-ESE as the
direction of the main cluster accretion, traced by passive galaxies and red
strong Hdelta galaxies. The red strong Hdelta galaxies, interpreted as
poststarburst galaxies, date a likely important event 1-2 Gyr before the epoch
of observation. The emission line galaxies trace a secondary, ongoing infall
where groups are accreted along several directions.Comment: A&A accepted, 19 pages, 30 figures, minor language change
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
CLASH-VLT: spectroscopic confirmation of a z=6.11 quintuply lensed galaxy in the Frontier Fields Cluster RXC J2248.7-4431
We present VIsible Multi-Object Spectrograph (VIMOS) observations of a z 6
galaxy quintuply imaged by the Frontier Fields galaxy cluster RXC J2248.7-4431
(z=0.348). This sub-L^*, high-z galaxy has been recently discovered by Monna et
al. (2013) using dropout techniques with the 16-band HST photometry acquired as
part of the Cluster Lensing And Supernova survey with Hubble (CLASH). Obtained
as part of the CLASH-VLT survey, the VIMOS medium-resolution spectra of this
source show a very faint continuum between ~8700A and ~9300A and a prominent
emission line at 8643A, which can be readily identified with Lyman-alpha at
z=6.110. The emission line exhibits an asymmetric profile, with a more
pronounced red wing. The rest-frame equivalent width of the line is EW=79+-10A.
After correcting for magnification, the star-formation rate (SFR) estimated
from the Lya line is SFR(Lya)=11 M_{sol}/yr and that estimated from the UV data
is SFR(UV)=3 M_{sol}/yr. We estimate that the effective radius of the source is
R_e6
M_{sol}/yr/kpc^2 and, using the Kennicutt-Schmidt relation, a gas surface mass
density Sigma_{gas}>10^3 M_{sol}/pc^2. Our results support the idea that this
magnified, distant galaxy is a young and compact object with 0.4 L^* at z=6,
with comparable amount of mass in gas and stars. Future follow-up observations
with ALMA will provide valuable insight into the SFR and molecular gas content
of this source. In the spirit of the Frontier Fields initiative, we also
publish the redshifts of several multiply imaged sources and other background
objects which will help improving the strong lensing model of this galaxy
cluster.Comment: 4 pages, 3 figures, 1 table, Accepted for publication in A&A (minor
changes, published version
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