1,539 research outputs found
Quantification of finite-temperature effects on adsorption geometries of -conjugated molecules
The adsorption structure of the molecular switch azobenzene on Ag(111) is
investigated by a combination of normal incidence x-ray standing waves and
dispersion-corrected density functional theory. The inclusion of non-local
collective substrate response (screening) in the dispersion correction improves
the description of dense monolayers of azobenzene, which exhibit a substantial
torsion of the molecule. Nevertheless, for a quantitative agreement with
experiment explicit consideration of the effect of vibrational mode
anharmonicity on the adsorption geometry is crucial.Comment: 12 pages, 3 figure
The story of supernova 'Refsdal' told by MUSE
We present MUSE observations in the core of the HFF galaxy cluster MACS
J1149.5+2223, where the first magnified and spatially-resolved multiple images
of SN 'Refsdal' at redshift 1.489 were detected. Thanks to a DDT program with
the VLT and the extraordinary efficiency of MUSE, we measure 117 secure
redshifts with just 4.8 hours of total integration time on a single target
pointing. We spectroscopically confirm 68 galaxy cluster members, with redshift
values ranging from 0.5272 to 0.5660, and 18 multiple images belonging to 7
background, lensed sources distributed in redshifts between 1.240 and 3.703.
Starting from the combination of our catalog with those obtained from extensive
spectroscopic and photometric campaigns using the HST, we select a sample of
300 (164 spectroscopic and 136 photometric) cluster members, within
approximately 500 kpc from the BCG, and a set of 88 reliable multiple images
associated to 10 different background source galaxies and 18 distinct knots in
the spiral galaxy hosting SN 'Refsdal'. We exploit this valuable information to
build 6 detailed strong lensing models, the best of which reproduces the
observed positions of the multiple images with a rms offset of only 0.26". We
use these models to quantify the statistical and systematic errors on the
predicted values of magnification and time delay of the next emerging image of
SN 'Refsdal'. We find that its peak luminosity should should occur between
March and June 2016, and should be approximately 20% fainter than the dimmest
(S4) of the previously detected images but above the detection limit of the
planned HST/WFC3 follow-up. We present our two-dimensional reconstruction of
the cluster mass density distribution and of the SN 'Refsdal' host galaxy
surface brightness distribution. We outline the roadmap towards even better
strong lensing models with a synergetic MUSE and HST effort.Comment: 21 pages, 9 figures, 6 tables; accepted for publication in the
Astrophysical Journal - extra information on data analysis added, all model
predictions and results unchange
A highly-ionized region surrounding SN Refsdal revealed by MUSE
Supernova (SN) Refsdal is the first multiply-imaged, highly-magnified, and
spatially-resolved SN ever observed. The SN exploded in a highly-magnified
spiral galaxy at z=1.49 behind the Frontier Fields Cluster MACS1149, and
provides a unique opportunity to study the environment of SNe at high z. We
exploit the time delay between multiple images to determine the properties of
the SN and its environment, before, during, and after the SN exploded. We use
the integral-field spectrograph MUSE on the VLT to simultaneously target all
observed and model-predicted positions of SN Refsdal. We find MgII emission at
all positions of SN Refsdal, accompanied by weak FeII* emission at two
positions. The measured ratios of [OII] to MgII emission of 10-20 indicate a
high degree of ionization with low metallicity. Because the same high degree of
ionization is found in all images, and our spatial resolution is too coarse to
resolve the region of influence of SN Refsdal, we conclude that this high
degree of ionization has been produced by previous SNe or a young and hot
stellar population. We find no variability of the [OII] line over a period of
57 days. This suggests that there is no variation in the [OII] luminosity of
the SN over this period, or that the SN has a small contribution to the
integrated [OII] emission over the scale resolved by our observations.Comment: 5 pages, 4 figures, accepted for publication in A&
Shapley Supercluster Survey: Construction of the photometric catalogues and i-band data release
The Shapley Supercluster Survey is a multi-wavelength survey covering an area of ∼23 deg² (∼260 Mpc² at z = 0.048) around the supercluster core, including nine Abell and two poor clusters, having redshifts in the range 0.045–0.050. The survey aims to investigate the role of the cluster-scale mass assembly on the evolution of galaxies, mapping the effects of the environment from the cores of the clusters to their outskirts and along the filaments. The optical (ugri) imaging acquired with OmegaCAM on the VLT Survey Telescope is essential to achieve the project goals providing accurate multi-band photometry for the galaxy population down to m∗ + 6. We describe the methodology adopted to construct the optical catalogues and to separate extended and point-like sources. The catalogues reach average 5σ limiting magnitudes within a 3 arcsec diameter aperture of ugri = [24.4,24.6,24.1,23.3] and are 93 per cent complete down to ugri = [23.8,23.8,23.5,22.0] mag, corresponding to ∼m∗ r + 8.5. The data are highly uniform in terms of observing conditions and all acquired with seeing less than 1.1 arcsec full width at half-maximum. The median seeing in r band is 0.6 arcsec, corresponding to 0.56 kpc h⁻¹ 70 at z = 0.048. While the observations in the u, g and r bands are still ongoing, the i-band observations have been completed, and we present the i-band catalogue over the whole survey area. The latter is released and it will be regularly updated, through the use of the Virtual Observatory tools. This includes 734 319 sources down to i = 22.0 mag and it is the first optical homogeneous catalogue at such a depth, covering the central region of the Shapley supercluster
CLASH-VLT: Testing the Nature of Gravity with Galaxy Cluster Mass Profiles
We use high-precision kinematic and lensing measurements of the total mass
profile of the dynamically relaxed galaxy cluster MACS J1206.2-0847 at
to estimate the value of the ratio between the two scalar
potentials in the linear perturbed Friedmann-Lemaitre-Robertson-Walker
metric.[...] Complementary kinematic and lensing mass profiles were derived
from exhaustive analyses using the data from the Cluster Lensing And Supernova
survey with Hubble (CLASH) and the spectroscopic follow-up with the Very Large
Telescope (CLASH-VLT). Whereas the kinematic mass profile tracks only the
time-time part of the perturbed metric (i.e. only ), the lensing mass
profile reflects the contribution of both time-time and space-space components
(i.e. the sum ). We thus express as a function of the mass
profiles and perform our analysis over the radial range . Using a spherical Navarro-Frenk-White mass profile, which
well fits the data, we obtain \eta(r_{200})=1.01\,_{-0.28}^{+0.31} at the
68\% C.L. We discuss the effect of assuming different functional forms for mass
profiles and of the orbit anisotropy in the kinematic reconstruction.
Interpreting this result within the well-studied modified gravity model,
the constraint on translates into an upper bound to the interaction
length (inverse of the scalaron mass) smaller than 2 Mpc. This tight constraint
on the interaction range is however substantially relaxed when
systematic uncertainties in the analysis are considered. Our analysis
highlights the potential of this method to detect deviations from general
relativity, while calling for the need of further high-quality data on the
total mass distribution of clusters and improved control on systematic effects.Comment: 18 pages, 3 figures, submitted to JCA
Ionising the Intergalactic Medium by Star Clusters: The first empirical evidence
We present a VLT/X-Shooter spectroscopy of the Lyman continuum (LyC) emitting
galaxy 'Ion2' at z=3.2121 and compare it to that of the recently discovered
strongly lensed LyC-emitter at z=2.37, known as the 'Sunburst' arc. Three main
results emerge from the X-Shooter spectrum: (a) the Lya has three distinct
peaks with the central one at the systemic redshift, indicating a ionised
tunnel through which both Lya and LyC radiation escape; (b) the large O32
oxygen index ([OIII]4959-5007 / [OII]3727-3729) of 9.18(-1.32/+1.82) is
compatible to those measured in local (z~0.4) LyC leakers; (c) there are narrow
nebular high-ionisation metal lines with \sigma_v < 20 km/s, which confirms the
presence of young hot, massive stars. The HeII1640 appears broad, consistent
with a young stellar component including Wolf-Rayet stars. Similarly, the
Sunburst LyC-emitter shows a triple-peaked Lya profile and from VLT/MUSE
spectroscopy the presence of spectral features arising from young hot and
massive stars. The strong lensing magnification, (\mu > 20), suggests that this
exceptional object is a gravitationally-bound star cluster observed at a
cosmological distance, with a stellar mass M <~ 10^7 Msun and an effective
radius smaller than 20 pc. Intriguingly, sources like Sunburst but without
lensing magnification might appear as Ion2-like galaxies, in which unresolved
massive star clusters dominate the ultraviolet emission. This work supports the
idea that dense young star clusters can contribute to the ionisation of the IGM
through holes created by stellar feedback.Comment: 13 pages, 9 figures and 1 table, MNRAS accepted. Some typos fixe
Seeded x-ray free-electron laser generating radiation with laser statistical properties
The invention of optical lasers led to a revolution in the field of optics
and even to the creation of completely new fields of research such as quantum
optics. The reason was their unique statistical and coherence properties. The
newly emerging, short-wavelength free-electron lasers (FELs) are sources of
very bright coherent extreme-ultraviolet (XUV) and x-ray radiation with pulse
durations on the order of femtoseconds, and are presently considered to be
laser sources at these energies. Most existing FELs are highly spatially
coherent but in spite of their name, they behave statistically as chaotic
sources. Here, we demonstrate experimentally, by combining Hanbury Brown and
Twiss (HBT) interferometry with spectral measurements that the seeded XUV FERMI
FEL-2 source does indeed behave statistically as a laser. The first steps have
been taken towards exploiting the first-order coherence of FELs, and the
present work opens the way to quantum optics experiments that strongly rely on
high-order statistical properties of the radiation.Comment: 24 pages, 10 figures, 37 reference
Time- and momentum-resolved photoemission studies using time-of-flight momentum microscopy at a free-electron laser
Time-resolved photoemission with ultrafast pump and probe pulses is an emerging technique with wide application potential. Real-time recording of nonequilibrium electronic processes, transient states in chemical reactions, or the interplay of electronic and structural dynamics offers fascinating opportunities for future research. Combining valence-band and core-level spectroscopy with photoelectron diffraction for electronic, chemical, and structural analyses requires few 10 fs soft X-ray pulses with some 10 meV spectral resolution, which are currently available at high repetition rate free-electron lasers. We have constructed and optimized a versatile setup commissioned at FLASH/PG2 that combines free-electron laser capabilities together with a multidimensional recording scheme for photoemission studies. We use a full-field imaging momentum microscope with time-of-flight energy recording as the detector for mapping of 3D band structures in (kx, ky, E) parameter space with unprecedented efficiency. Our instrument can image full surface Brillouin zones with up to 7 Å−1 diameter in a binding-energy range of several eV, resolving about 2.5 × 105 data voxels simultaneously. Using the ultrafast excited state dynamics in the van der Waals semiconductor WSe2 measured at photon energies of 36.5 eV and 109.5 eV, we demonstrate an experimental energy resolution of 130 meV, a momentum resolution of 0.06 Å−1, and a system response function of 150 fs
Paving the way for the JWST: witnessing globular cluster formation at z>3
We report on five compact, extremely young (<10Myr) and blue (\beta_UV<-2.5,
F_\lambda =\lambda^\beta) objects observed with VLT/MUSE at redshift 3.1169,
3.235, in addition to three objects at z=6.145. These sources are magnified by
the Hubble Frontier Field galaxy clusters MACS~J0416 and AS1063. Their
de-lensed half light radii (Re) are between 16 to 140pc, the stellar masses are
~1-20 X 10^6 Msun, the magnitudes are m_uv=28.8 - 31.4 (-17<Muv<-15) and
specific star formation rates can be as large as ~800Gyr^-1. Multiple images of
these systems are widely separated in the sky (up to 50'') and individually
magnified by factors 3-40. Remarkably, the inferred physical properties of two
objects are similar to those expected in some globular cluster formation
scenarios, representing the best candidate proto-globular clusters (proto-GC)
discovered so far. Rest-frame optical high dispersion spectroscopy of one of
them at z=3.1169 yields a velocity dispersion \sigma_v~20km/s, implying a
dynamical mass dominated by the stellar mass. Another object at z=6.145, with
de-lensed Muv ~ -15.3 (m_uv ~ 31.4), shows a stellar mass and a star-formation
rate surface density consistent with the values expected from popular GC
formation scenarios. An additional star-forming region at z=6.145, with
de-lensed m_uv ~ 32, a stellar mass of 0.5 X 10^6 Msun and a star formation
rate of 0.06 Msun/yr is also identified. These objects currently represent the
faintest spectroscopically confirmed star-forming systems at z>3, elusive even
in the deepest blank fields. We discuss how proto-GCs might contribute to the
ionization budget of the universe and augment Lya visibility during
reionization. This work underlines the crucial role of JWST in characterizing
the rest-frame optical and near-infrared properties of such low-luminosity
high-z objects.Comment: 19 pages, 9 figures, 2 tables. MNRAS, version accepted by the refere
Direct Lyman continuum and Lyman-alpha escape observed at redshift 4
We report on the serendipitous discovery of a z=4.0, M1500=-22.20
star-forming galaxy (Ion3) showing copious Lyman continuum (LyC) leakage (~60%
escaping), a remarkable multiple peaked Lya emission, and significant Lya
radiation directly emerging at the resonance frequency. This is the highest
redshift confirmed LyC emitter in which the ionising and Lya radiation possibly
share a common ionised cavity (with N_HI<10^17.2 cm^-2). Ion3 is spatially
resolved, it shows clear stellar winds signatures like the P-Cygni NV1240
profile, and has blue ultraviolet continuum (\beta = -2.5 +/- 0.25, F_\lambda~
\lambda^\beta) with weak low-ionisation interstellar metal lines. Deep
VLT/HAWKI Ks and Spitzer/IRAC 3.6um and 4.5um imaging show a clear photometric
signature of the Halpha line with equivalent width of 1000A rest-frame emerging
over a flat continuum (Ks-4.5um ~ 0). From the SED fitting we derive a stellar
mass of 1.5x10^9 Msun, SFR of 140 Msun/yr and age of ~10 Myr, with a low dust
extinction, E(B-V)< 0.1, placing the source in the starburst region of the
SFR-M^* plane. Ion3 shows similar properties of another LyC emitter previously
discovered (z=3.21, Ion2, Vanzella et al. 2016). Ion3 (and Ion2) represents
ideal high-redshift reference cases to guide the search for reionising sources
at z>6.5 with JWST.Comment: Accepted for publication in MNRAS. 5 pages, 4 figures, 1 tabl
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