77 research outputs found
NEW INSIGHTS ON THE INNER MASS DISTRIBUTION OF MASSIVE GALAXY CLUSTERS FROM A COMBINATION OF STRONG LENSING AND GALAXY KINEMATICS
Galaxy clusters are important astrophysical laboratories to study the nature of Dark Matter (DM), whose physical properties are still unknown. In particular, a detailed investigation of the mass distribution of cluster halos, by dissecting the DM and baryonic components, can provide stringent tests of the Cold Dark Matter paradigm of structure formation. Over the last decade, strong gravitational lensing has become one of the most powerful techniques to study the total mass distribution in the Universe, particularly on galaxy and cluster scale. In recent years, dedicated large imaging surveys with HST and ground-based spectroscopic campaigns on sizeable samples of massive galaxy clusters have ushered a new generation of high-precision strong lensing models, via the identification of a large number of multiple images and cluster members. In this thesis, we extend beyond the state of the art these new cluster lens models, including the stellar kinematics of a significant fraction of cluster galaxies measured with the integral field spectrograph MUSE on the VLT. This study focuses on three massive clusters MACS~J1206.20847, MACS~J0416.12403, and Abell S1063 at with HST imaging and VLT spectroscopy data of unprecedented quality. Specifically, we measured the stellar velocity dispersion, , of 40-60 member galaxies per cluster with MUSE, covering 4-5 magnitudes down to . The robustness and accuracy of the velocity dispersion measurements were tested with extensive spectral simulations. We determined the normalization and slope of the galaxy Faber-Jackson relation in each cluster, and include this prior information in the cluster lens models. We find that using this novel technique, the inherent degeneracy between different mass components and possible systematics on model parameters are strongly reduced and the mass density profiles of the cluster galaxies are now robustly constrained. Once re-normalized to the same absolute luminosity, our kinematic lens models predict consistent masses and sizes of sub-halos as a function of galaxy velocity dispersions. Moreover, extending previous findings, we derive consistent sub-halo mass velocity dispersion functions for the three clusters. By comparing the observed sub-halo mass distribution from our cluster lens models with the predictions of high-resolution N-body and hydrodynamical cosmological simulations, we find a lack of compact sub-structures in the corresponding inner regions of simulated clusters, whereas the sub-halo mass functions are found in good agreement. We still do not understand whether the origin of these differences has to be ascribed to numerical or resolution effects in the simulations, or to some physical aspect missing in the Cold Dark Matter framework. An additional method to investigate the mass distribution of cluster galaxies is to exploit galaxy scale strong lensing systems (GSSLS), in which a single cluster galaxy produces highly magnified multiple images on kpc scale around lens galaxies. We show how strong lensing modeling of GSSLS in the cluster field, in combination with spatially resolved stellar kinematics of the lens galaxies, can further constrain the structure and sizes of cluster sub-halos. Finally, in an effort to include in our lens models the measured cluster member stellar velocity dispersions and the observed scatter of the Faber-Jackson relation, we develop and made public a python module that expands the capabilities of common lens modeling tools. The methodology of high-precision lens modeling developed in this thesis will find important applications in the near future when large numbers of cosmic lenses will be discovered with large-area surveys. In particular, by exploiting lensing clusters as powerful cosmic telescopes to investigate galaxies in the early Universe and in cosmographic applications with gravitational time delay techniques
Estimation of temporal parameters during sprint running using a trunk-mounted inertial measurement unit
This research was supported by a grant of the Universit a Italo-Francese (Call Vinci) awarded to E. Bergamini.The purpose of this study was to identify consistent features in the signals supplied by a single inertial measurement unit (IMU), or thereof derived, for the identification of foot-strike and foot-off instants of time and for the estimation of stance and stride duration during the maintenance phase of sprint running. Maximal sprint runs were performed on tartan tracks by five amateur and six elite athletes, and durations derived from the IMU data were validated using force platforms and a high-speed video camera, respectively, for the two groups. The IMU was positioned on the lower back trunk (L1 level) of each athlete. The magnitudes of the acceleration and angular velocity vectors measured by the IMU, as well as their wavelet-mediated first and second derivatives were computed, and features related to foot-strike and foot-off events sought. No consistent features were found on the acceleration signal or on its first and second derivatives. Conversely, the foot-strike and foot-off events could be identified from features exhibited by the second derivative of the angular velocity magnitude. An average absolute difference of 0.005 s was found between IMU and reference estimates, for both stance and stride duration and for both amateur and elite athletes. The 95% limits of agreement of this difference were less than 0.025 s. The results proved that a single, trunk-mounted IMU is suitable to estimate stance and stride duration during sprint running, providing the opportunity to collect information in the field, without constraining or limiting athletesâ and coachesâ activities
The side chain of glutamine 13 is the acyl-donor amino acid modified by type 2 transglutaminase in subunit T of the native rabbit skeletal muscle troponin complex.
Subunit T of the native muscle troponin complex is a recognised substrate of transglutaminase both in vitro and in situ with formation of isopeptide bonds. Using a proteomic approach, we have now determined the precise site of in vitro labelling of the protein. A preparation of troponin purified from ether powder from mixed rabbit skeletal muscles was employed as transglutaminase substrate. The only isoform TnT2F present in our preparation was recognised as acyl-substrate by human type 2 transglutaminase which specifically modified glutamine 13 in the N-terminal region. During the reaction, the troponin protein complex was polymerized. Results are discussed in relation to the structure of the troponin T subunit, in the light of the role of troponins in skeletal and cardiac muscle diseases, and to the rules governing glutamine side chain selection by tissue transglutaminase
Systematic search for lensed X-ray sources in the CLASH fields
We search for unresolved X-ray emission from lensed sources in the FOV of 11
CLASH clusters with Chandra data. We consider the solid angle in the lens plane
corresponding to a magnification , that amounts to a total of ~100
arcmin. Our main goal is to assess the efficiency of massive clusters as
cosmic telescopes to explore the faint end of X-ray extragalactic source
population. We search for X-ray emission from strongly lensed sources
identified in the optical, and perform an untargeted detection of lensed X-ray
sources. We detect X-ray emission only in 9 out of 849 lensed/background
optical sources. The stacked emission of the sources without detection does not
reveal any signal in any band. Based on the untargeted detection, we find 66
additional X-ray sources that are consistent with being lensed sources. After
accounting for completeness and sky coverage, we measure for the first time the
soft- and hard-band number counts of lensed X-ray sources. The results are
consistent with current modelization of the AGN population distribution. The
distribution of de-lensed fluxes of the sources identified in moderately deep
CLASH fields reaches a flux limit of ~ and ~ erg/s/cm
in the soft and hard bands, respectively. We conclude that, in order to match
the depth of the CDFS exploiting massive clusters as cosmic telescopes, the
required number of cluster fields is about two orders of magnitude larger than
that offered by the 20 years Chandra archive. A significant step forward will
be made when future X-ray facilities, with ~1' angular resolution and large
effective area, will allow the serendipitous discovery of rare, strongly lensed
high- X-ray sources, enabling the study of faint AGN activity in early
Universe and the measurement of gravitational time delays in the X-ray
variability of multiply imaged AGN.Comment: Accepted for publication in A&
Exploring the low-mass regime of galaxy-scale strong lensing: Insights into the mass structure of cluster galaxies
We aim at a direct measurement of the compactness of three galaxy-scale
lenses in massive clusters, testing the accuracy of the scaling laws that
describe the members in strong lensing (SL) models of galaxy clusters. We
selected the multiply imaged sources MACS J0416.12403 ID14 (), MACS
J0416.12403 ID16 (), and MACS J1206.20847 ID14 ().
Eight images were observed for the first SL system, and six for the latter two.
We focused on the main deflector of each galaxy-scale SL system (identified as
members 8971, 8785, and 3910, respectively), and modelled its total mass
distribution with a truncated isothermal sphere. We accounted for the lensing
effects of the remaining cluster components, and included the uncertainty on
the cluster-scale mass distribution through a bootstrapping procedure. We
measured a truncation radius value of ,
, and
for members 8971, 8785, and 3910, respectively. Alternative non-truncated
models with a higher number of free parameters do not lead to an improved
description of the SL system. We measured the stellar-to-total mass fraction
within the effective radius for the three members, finding ,
, and , respectively. We find that a parameterisation
of the properties of cluster galaxies in SL models based on power-law scaling
relations with respect to the total luminosity cannot accurately describe their
compactness over their full total mass range. Our results agree with modelling
of the cluster members based on the Fundamental Plane relation. Finally, we
report good agreement between our values of the stellar-to-total mass fraction
within and those of early-type galaxies from the SLACS Survey. Our work
significantly extends the regime of the current samples of lens galaxies.Comment: Astronomy & Astrophysics, 679, A124 (2023), 15 pages, 12 figures, 8
table
Constraints on the [C II] luminosity of a proto-globular cluster at z ⌠6 obtained with ALMA
We report on ALMA observations of D1, a system at z 3c 6.15 with stellar mass M 17 3c 107M containing globular
cluster (GC) precursors, strongly magnified by the galaxy cluster MACS J0416.1-2403. Since the discovery of GC
progenitors at high redshift, ours is the first attempt to probe directly the physical properties of their neutral gas
through infrared observations. A careful analysis of our dataset, performed with a suitable procedure designed to
identify faint narrow lines and which can test various possible values for the unknown linewidth value, allowed us
to identify a 4\u3c3 tentative detection of [CII] emission with intrinsic luminosity L[CII] = (2.9 \ub1 1.4) 106L, one of the
lowest values ever detected at high redshift. This study offers a first insight on previously uncharted regions of the
L[CII] 12 SF R relation. Despite large uncertainties affecting our measure of the star formation rate, if taken at face
value our estimate lies more than 3c 1 dex below the values observed in local and high redshift systems. Our weak
detection indicates a deficiency of [CII] emission, possibly ascribed to various explanations, such as a low-density gas
and/or a strong radiation field caused by intense stellar feedback, and a low metal content. From the non-detection
in the continuum we derive constraints on the dust mass, with 3 12 \u3c3 upper limit values as low as 3c a few 104 M,
consistent with the values measured in local metal-poor galaxies
A persistent excess of galaxy-galaxy strong lensing observed in galaxy clusters
Previous studies have revealed that the estimated probability of
galaxy-galaxy strong lensing in observed galaxy clusters exceeds the
expectations from the Cold Dark Matter cosmological model by one
order of magnitude. We aim to understand the origin of this excess by analyzing
a larger set of simulated galaxy clusters and investigating how the theoretical
expectations vary under different adopted prescriptions and numerical
implementations of star formation and feedback in simulations. We perform a
ray-tracing analysis of 324 galaxy clusters from the Three Hundred project,
comparing the Gadget-X and Gizmo-Simba runs. These simulations, which start
from the same initial conditions, are performed with different implementations
of hydrodynamics and galaxy formation models tailored to match different
observational properties of the Intra-Cluster-Medium and cluster galaxies. We
find that galaxies in the Gizmo-Simba simulations develop denser stellar cores
than their Gadget-X counterparts. Consequently, their probability for
galaxy-galaxy strong lensing is higher by a factor of . This increment
is still insufficient to fill the gap with observations, as a discrepancy by a
factor still persists. In addition, we find that several simulated
galaxies have Einstein radii that are too large compared to observations. We
conclude that a persistent excess of galaxy-galaxy strong lensing exists in
observed galaxy clusters. The origin of this discrepancy with theoretical
predictions is still unexplained in the framework of the cosmological
hydrodynamical simulations. This might signal a hitherto unknown issue with
either the simulation methods or our assumptions regarding the standard
cosmological model.Comment: 6 pages, 2 figures, accepted for publication on A&A Letters. See
companion paper Srivastava et al. (2023
Early Results from GLASS-JWST. XXI: Rapid assembly of a galaxy at z=6.23 revealed by its C/O abundance
The abundance of carbon relative to oxygen (C/O) is a promising probe of star
formation history in the early universe, as the ratio changes with time due to
production of these elements by different nucleosynthesis pathways. We present
a measurement of (stat) (sys)
in a galaxy observed as part of the GLASS-JWST Early Release Science
Program. Notably, we achieve good precision thanks to the detection of the
rest-frame ultraviolet O III], C III], and C IV emission lines delivered by
JWST/NIRSpec. The C/O abundance is 0.8 dex lower than the solar value and
is consistent with the expected yield from core-collapse supernovae, indicating
that longer-lived intermediate mass stars have not fully contributed to carbon
enrichment. This in turn implies rapid buildup of a young stellar population
with age Myr in a galaxy seen 900 million years after the
Big Bang. Our chemical abundance analysis is consistent with spectral energy
distribution modeling of JWST/NIRCam photometric data, which indicates a
current stellar mass and specific star formation rate sSFR
Gyr. These results showcase the value of chemical abundances and C/O in
particular to study the earliest stages of galaxy assembly.Comment: 16 pages, 4 figures, 2 tables. Accepted for publication in ApJ
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