Search results for "Observational astronomy"
showing 7 items of 97 documents
3C 279 Event Horizon Telescope imaging
2020
3C 279 is an archetypal blazar with a prominent radio jet that show broadband flux density variability across the entire electromagnetic spectrum. We use an ultra-high angular resolution technique - global Very Long Baseline Interferometry (VLBI) at 1.3mm (230GHz) - to resolve the innermost jet of 3C 279 in order to study its fine-scale morphology close to the jet base where highly variable gamma-ray emission is thought to originate, according to various models. The source was observed during four days in April 2017 with the Event Horizon Telescope (EHT) at 230 GHz, including the phased Atacama Large Millimeter/submillimeter Array (ALMA), at an angular resolution of ~20uarcsec (at a redshif…
Baryon Acoustic Oscillations in LRGs
2012
Baryon Acoustic Oscillations (BAO) have been previously detected using correlation functions and power spectra of the galaxy distribution. In this work, we present a new method for the detection of the real-space structures associated with this feature. These baryon acoustic structures are spherical shells with a relatively small density contrast, surrounding high density central regions. We design a specific wavelet adapted to the search for shells, and exploit the physics of the process by making use of two different mass tracers, introducing a specific statistic to detect the BAO features. We apply our method to the detection of BAO in a galaxy sample drawn from the Sloan Digital Sky Sur…
Galaxy clusters from SDSS DR8
2012
The study of the signatures of multimodality in groups and clusters of galaxies, an environment for most of the galaxies in the Universe, gives us information about the dynamical state of clusters and about merging processes, which affect the formation and evolution of galaxies, groups and clusters, and larger structures - superclusters of galaxies and the whole cosmic web. We search for the presence of substructure, a non-Gaussian, asymmetrical velocity distribution of galaxies, and large peculiar velocities of the main galaxies in clusters with at least 50 member galaxies, drawn from the SDSS DR8. Cone search capability for table J/A+A/540/A123/table3 (Data on clusters)
Orientation of galaxies in galaxy clusters
2012
We present an analysis of the spatial orientations of galaxies in 247 optically selected rich Abell clusters which have at least 100 members in the considered area. We investigated the relation between angles that give information about galaxy angular momenta and the number of members in each structure. The position angles of the galaxies' major axes, as well as two angles describing the spatial orientation of the galaxy plane, were tested for isotropy by applying three different statistical tests. It is found that the values of the statistics increase with the amount of the galaxies' members, which is equivalent to the existence of a relation between anisotropy and the number of galaxies i…
REFLEX galaxies redshifts
2009
We present the final data from the spectroscopic survey of the ROSAT-ESO Flux-Limited X-ray (REFLEX) catalogue of galaxy clusters. The REFLEX survey covers 4.24 steradians (34% of the entire sky) below a declination +2.50{deg} and at high galactic latitude (|b|<20{deg}). The full survey includes 447 galaxy clusters with a median redshift of 0.08 and is better than 90% complete to a limiting flux of f_X_=3x10^-12^ergs/s/cm^2^ (3fW/m^2^, 0.1 to 2.4keV), representing the largest statistically homogeneous sample of clusters to date drawn from the ROSAT All-Sky Survey (RASS). Here we describe the details of the spectroscopic observations carried out at the ESO 1.5m, 2.2m and 3.6m telescopes, the…
Post-AGB candidates in LMC and SMC SALT spectra
2020
We selected a sample of post-AGB candidates in the Magellanic Clouds on the basis of their near- and mid-infrared colour characteristics. Fifteen of the most optically bright post-AGB candidates were observed with the South African Large Telescope in order to determine their stellar parameters and thus to validate or discriminate their nature as post-AGB objects in the Magellanic Clouds. The spectral types of absorption-line objects were estimated according to the MK classification, and effective temperatures were obtained by means of stellar atmosphere modelling. Emission-line objects were classified on the basis of the fluxes of the emission lines and the presence of the continuum. Out of…
Catching the radio flare in CTA 102
2013
Very Long Baseline Interferometry (VLBI) observations can resolve the radio structure of active galactic nuclei (AGN) and provide estimates of the structural and kinematic characteristics on parsec-scales in their jets. The changes in the kinematics of the observed jet features can be used to study the physical conditions in the innermost regions of these sources. We performed multifrequency multiepoch Very Long Baseline Array (VLBA) observations of the blazar CTA102 during its 2006 radio flare, the strongest ever reported for this source. These observations provide an excellent opportunity to investigate the evolution of the physical properties of blazars, especially during these flaring e…