Search results for "Cosmology and Nongalactic Astrophysics"
showing 10 items of 608 documents
Relic galaxies: Where are they?
2016
The finding that massive galaxies grow with cosmic time fired the starting gun for the search of objects which could have survived up to the present day without suffering substantial changes (neither in their structures, neither in their stellar populations). Nevertheless, and despite the community efforts, up to now only one firm candidate to be considered one of these relics is known: NGC 1277. Curiously, this galaxy is located at the centre of one of the most rich near galaxy clusters: Perseus. Is its location a matter of chance? Should relic hunters focus their search on galaxy clusters? In order to reply this question, we have performed a simultaneous and analogous analysis using simul…
The influence of stellar objects mass distribution on their gravitational fields
2019
We study the influence of the astronomical objects masses randomness on the distribution function of their gravitational fields. Based on purely theoretical arguments and comparison with extensive data, collected from observations and numerical simulations, we have shown that while mass randomness does not alter the non-Gaussian character of the gravitational fields distribution, it changes the dependencies of mean angular momenta of galaxies and clusters on their richness. The specific form of above dependence is determined by the interplay of mass distribution character and different assumptions about cluster morphology. We trace the influence of masses distribution on the time evolution …
Some observational aspects of the orientation of galaxies
2011
We investigated the sample of galaxies belonging to the Tully groups of galaxies. We analyzed the orientation of galaxies inside the group. We did not found significant deviation from isotropy both in orientation of position angles and angles $\delta_D$ and $\eta$ giving the spatial orientation of galaxy planes. Moreover we analyzed consequences of different approximation of "true shape" of galaxies and showed possible influence of this problem for investigation of spatial orientation of galaxies. Implications of the obtained results for theory of galaxy formation was discussed as well.
The large-scale environment from cosmological simulations II: The redshift evolution and distributions of baryons
2019
Following Cui et al. 2018 (hereafter Paper I) on the classification of large-scale environments (LSE) at z = 0, we push our analysis to higher redshifts and study the evolution of LSE and the baryon distributions in them. Our aim is to investigate how baryons affect the LSE as a function of redshift. In agreement with Paper I, the baryon models have negligible effect on the LSE over all investigated redshifts. We further validate the conclusion obtained in Paper I that the gas web is an unbiased tracer of total matter -- even better at high redshifts. By separating the gas mainly by temperature, we find that about 40 per cent of gas is in the so-called warm-hot intergalactic medium (WHIM). …
Limits on the Mass and Abundance of Primordial Black Holes from Quasar Gravitational Microlensing
2017
The idea that dark matter can be made of intermediate-mass primordial black holes in the $10M_\odot \lesssim M \lesssim 200M_\odot$ range has recently been reconsidered, particularly in the light of the detection of gravitational waves by the LIGO experiment. The existence of even a small fraction of dark matter in black holes should nevertheless result in noticeable quasar gravitational microlensing. Quasar microlensing is sensitive to any type of compact objects in the lens galaxy, to their abundance, and to their mass. We have analyzed optical and X-ray microlensing data from 24 gravitationally lensed quasars to estimate the abundance of compact objects in a very wide range of masses. We…
Radio and Gamma Properties of the 2 cm Survey and MOJAVE Samples
2009
The 2 cm VLBA Survey observed since 1994 a set of ~170 Quasars, BL Lac objects, and radio galaxies, selected to be representative of the compact AGN radio population. This effort was continued as the MOJAVE project, where a statistically complete set of radio sources being monitored was defined. A comparison of the gamma-detection rates between the members of both samples shows that the MOJAVE-I sources, hosting generally faster jets, have a much higher detection rate than the sources not belonging to this sample. BL Lac objects are more favourably detected than QSOs in gamma-rays, in the same rate for both samples.
The Broadband Spectral Energy Distribution of the MOJAVE Sample
2010
We are constructing the broadband SED catalog of the MOJAVE sample from the radio to the gamma-ray band using MOJAVE, Swift UVOT/XRT/BAT, and Fermi/LAT data, in order to understand the emission mechanism of extragalactic outflows and to investigate the site of high-energy emission in AGN. Since the launch of Fermi gamma-ray Space Telescope in August 2008, two thirds of the MOJAVE sources have been detected by Fermi/LAT. Combining the results of high-resolution VLBI, X-ray, and gamma-ray observations of the jet-dominated AGN sample, we want to pin down the origin of high-energy emission in relativistic jets. Here we present our overall project and preliminary results for 6 selected sources.
Microlensing of Quasar UV Iron Emission
2013
We measure the differential microlensing of the UV Fe II and Fe III emission line blends between 14 quasar image pairs in 13 gravitational lenses. We find that the UV iron emission is strongly microlensed in 4 cases with amplitudes comparable to that of the continuum. Statistically modeling the magnifications we infer a typical size of r ~ 4*sqrt(M/Msun) light-days for the Fe line emitting regions which is comparable to the size of the region generating the UV continuum (3 ~ 7 light-days). This may indicate that a significant part of the UV Fe II and Fe III emission originates in the quasar accretion disk.
THE MISSING LINK: MERGING NEUTRON STARS NATURALLY PRODUCE JET-LIKE STRUCTURES AND CAN POWER SHORT GAMMA-RAY BURSTS
2011
Short Gamma-Ray Bursts (SGRBs) are among the most luminous explosions in the universe, releasing in less than one second the energy emitted by our Galaxy over one year. Despite decades of observations, the nature of their "central-engine" remains unknown. Considering a binary of magnetized neutron stars and solving Einstein equations, we show that their merger results in a rapidly spinning black hole surrounded by a hot and highly magnetized torus. Lasting over 35 ms and much longer than previous simulations, our study reveals that magnetohydrodynamical instabilities amplify an initially turbulent magnetic field of ~ 10^{12} G to produce an ordered poloidal field of ~ 10^{15} G along the bl…
Characteristics of the diffuse astrophysical electron and Tau neutrino flux with six years of IceCube high energy cascade data
2020
We report on the first measurement of the astrophysical neutrino flux using particle showers (cascades) in IceCube data from 2010-2015. Assuming standard oscillations, the astrophysical neutrinos in this dedicated cascade sample are dominated (∼90%) by electron and tau flavors. The flux, observed in the sensitive energy range from 16 TeV to 2.6 PeV, is consistent with a single power-law model as expected from Fermi-type acceleration of high energy particles at astrophysical sources. We find the flux spectral index to be γ=2.53±0.07 and a flux normalization for each neutrino flavor of φastro=1.66-0.27+0.25 at E0=100 TeV, in agreement with IceCube's complementary muon neutrino results and wit…