25 research outputs found
The complete catalogue of light curves in equal-mass binary microlensing
The light curves observed in microlensing events due to binary lenses span an
extremely wide variety of forms, characterised by U-shaped caustic crossings
and/or additional smoother peaks. However, all peaks of the binary-lens light
curve can be traced back to features of caustics of the lens system. Moreover,
all peaks can be categorised as one of only four types (cusp-grazing,
cusp-crossing, fold-crossing or fold-grazing). This enables us to present the
first complete map of the parameter space of the equal-mass case by identifying
regions in which light curves feature the same number and nature of peaks. We
find that the total number of morphologies that can be obtained is 73 out of
232 different regions. The partition of the parameter space so-obtained
provides a new key to optimise modelling of observed events through a clever
choice of initial conditions for fitting algorithms.Comment: 22 pages, 18 figures, accepted for publication in MNRA
An insight into gravitational microlensing and the search for exoplanetary systems
2013 - 2014Nature always offers astonishing shows to the humankind. Gravitational lensing is one of the most intriguing effects which can be observed, and the astrophysical applications of such a phenomenon span from particle physics to cosmology, to the search for new worlds. Although, since its formulation in the early 1900, gravitational lensing was underestimated and poorly investigated, in the last thirty years the observation of different phenomena related to gravitational lenses have revealed the real potentiality of the study of the effects of gravity on the light. Our comprehension of the Universe has been largely improved since we have studied the cosmological implications of lensing by clusters of galaxies, lensing of quasars, or effects of microlensing by non-luminous objects. The structure of the Universe, constraints on its formation theories, the mass distribution, and even proofs of the nature of dark matter can be studied by investigating magnification patterns and the effects due to gravitational lenses. Additionally, gravitational microlensing provides a unique tool to search for planetary systems in a region of the physical parameter space not probed by other methods. By observing microlensing effects to stars towards the Galactic bulge, we are able to look for small rocky planets orbiting stars in the Galactic disk or, more in general, along the line of sight. What we
observe is the source lightcurve, i.e. the measured flux as a function of time. The presence of a foreground mass, or a system of masses, between the observer and a background source, causes an amplification of the source flux, so giving to the lightcurve specific features and shapes which can be attributed to different kinds of lens (single, binary, planetary, etc...). The study of this specific effect is likely to attain more promising results with the launch of space missions like EUCLID or WFIRST, since those telescopes will be able to detect Earth-like and smaller planets in their habitable zone, i.e. at a distance from their host star allowing the planet to have an equilibrium temperature at which liquid water can exist.
This thesis work propose an insight into the gravitational microlensing, by starting with a theoretical work on the classification of binary microlensing lightcurves, and then by presenting the results of the modelling of one event from the 2013 observing season. A brief summary of some hot-Jupiter discovered with the transit method, and observed by the author, is finally presented at the end of the work. [edited by author]XIII n.s
The Luminosity Function of Low Mass X-Ray Binaries in the Globular Cluster System of NGC 1399
We present a study of the faint-end of the X-ray Luminosity Function of Low
Mass X-ray binaries in the Globular Cluster system of the cD galaxy NGC 1399 by
performing a stacking experiment on 618 X-ray undetected GCs, in order to
verify the presence of faint LMXBs and to constrain the faint-end slope of the
GC-LMXBs XLF below the individual detection threshold of erg
s in the keV band. We obtain a significant X-ray detection for
the whole GC sample, as well as for the red and blue GC subpopulations,
corresponding to an average luminosity per GC of
, $(6.9\pm2.1)\times10^{36}\ erg\
s^{-1}(1.7\pm0.9)\times10^{36}\ erg\ s^{-1}\simeq 32.5\pm1.04.1\pm2.5L_{X}=(4.3\pm1.3)\times10^{37}\ erg\ s^{-1}L_{X}=(3.4\pm1.7)\times10^{37}\ erg\ s^{-1}L_{X}\leq 8\times10^{37}^{-1}>3\sigma\beta_{L}=-1.39/-1.38/-1.36L_X\gtrsim 3\times 10^{39}^{-1}$, as observed in old
ellipticals.Comment: In press on A&
The VST Early-type GAlaxy Survey: Exploring the Outskirts and Intra-cluster Regions of Galaxies in the Low-surface-brightness Regime
The VST Early-type GAlaxy Survey (VEGAS) is a deep, multi-band (u, g, r, i)
imaging survey, carried out with the 2.6-metre VLT Survey Telescope (VST) at
ESO's Paranal Observatory in Chile. VEGAS combines the wide (1-square-degree)
OmegaCAM imager and long integration times, together with a specially designed
observing strategy. It has proven to be a gold mine for studies of features at
very low surface brightness, down to levels of mu_g~27-30 magnitudes
arcsec^(-2), over 5-8 magnitudes fainter than the dark sky at Paranal. In this
article we highlight the main science results obtained with VEGAS observations
of galaxies across different environments, from dense clusters of galaxies to
unexplored poor groups and in the field.Comment: Published in The Messenger, vol. 183, p. 25-2
Intrinsic Morphology of Ultra-diffuse Galaxies
With the published data of apparent axis ratios for 1109 ultra-diffuse
galaxies (UDGs) located in 17 low-redshift (z~ 0.020 - 0.063) galaxy clusters
and 84 UDGs in 2 intermediate-redshift (z~ 0.308 - 0.348) clusters, we take
advantage of a Markov Chain Monte Carlo approach and assume a ubiquitous
triaxial model to investigate the intrinsic morphologies of UDGs. In contrast
to the conclusion of Burkert (2017), i.e., the underlying shapes of UDGs are
purely prolate (), we find that the data favor the oblate-triaxial
models () over the nearly prolate ones. We also find that the
intrinsic morphologies of UDGs are relevant to their stellar
masses/luminosities, environments, and redshifts. First, for the low-redshift
UDGs in the same environment, the more-luminous ones are always thicker than
the less-luminous counterparts, possibly due to the more voilent internal
supernovae feedback or external tidal interactions for the progenitors of the
more-luminous UDGs. The UDG thickness dependence on luminosity is distinct from
that of the typical quiescent dwarf ellipticals (dEs) and dwarf spheroidals
(dSphs) in the local clusters and groups, but resembles that of massive
galaxies; in this sense, UDGs may not be simply treated as an extension of the
dE/dSph class with similar evolutionary histories. Second, for the low-redshift
UDGs within the same luminosity range, the ones with smaller cluster-centric
distances are more puffed-up, probably attributed to tidal interactions.
Finally, the intermediate-redshift cluster UDGs are more flattened, which
plausibly suggests a `disky' origin for high-redshift, initial UDGs.Comment: Accepted for publication in ApJ; new versio
The first sample of spectroscopically confirmed ultra-compact massive galaxies in the Kilo Degree Survey
We present results from an ongoing investigation using the Kilo Degree Survey (KiDS) on the VLT Survey Telescope (VST) to provide a census of ultra-compact massive galaxies (UCMGs), defined as galaxies with stellar masses M* > 8 × 1010M⊙ and effective radii Re < 1.5 kpc. UCMGs, which are expected to have undergone very few merger events, provide a unique view on the accretion history of the most massive galaxies in the Universe. Over an effective sky area of nearly 330 deg2, we select UCMG candidates from KiDS multicolour images, which provide high quality structural parameters, photometric redshifts, and stellar masses. Our sample of ~1000 photometrically selected UCMGs at z < 0.5 represents the largest sample of UCMG candidates assembled to date over the largest sky area. In this paper, we present the first effort to obtain their redshifts using different facilities, starting with first results for 28 candidates with redshifts z < 0.5, obtained at NTT and TNG telescopes.We confirmed, as bona fide UCMGs, 19 out of the 28 candidates with new redshifts. A further 46 UCMG candidates are confirmed with literature spectroscopic redshifts (35 at z < 0.5), bringing the final cumulative sample of spectroscopically confirmed lower-z UCMGs to 54 galaxies, which is the largest sample at redshifts below 0.5. We use these spectroscopic redshifts to quantify systematic errors in our photometric selection, and use these to correct our UCMG number counts. We finally compare the results to independent data sets and simulations