Communications of the Byurakan Astrophysical Observatory (ComBAO)
Volume 66, Issue 2, Dec 2019
Introduction 0.02 MB
Marat Arakelian: Life and Scientific Activity 0.7 MB
A. M. Mickaelian
Abstract. We review the life and scientific activity of one of the outstanding Armenian astronomers Marat Arakelian (1929-1983). Arakelian was one of the prominent Byurakan astronomers, the author of famous Arakelian galaxies, which at present are target for many-sided studies with ground-based and space telescopes. Arakelian is known as a distinguished specialist in the theoretical astrophysics and extragalactic astronomy.
BL Lacertae Objects: A Short Review 2 MB
Abstract. BL Lacertae objects (BLLs) constitute a class of active galactic nuclei (AGNs) with extreme observational features explained by non-thermal radiation from a relativistic jet nearly pointed along the observer’s line-of-sight. Their spectral energy distribution (SED), extending over 17-19 orders of the frequency, is of non-thermal origin and shows a typical two-humped structure. The lower-energy component, ranging from the radio to X-rays, is explained via synchrotron radiation emitted by ultra-relativistic electrons/positrons/protons, to be initially accelerated via the Blandford-Znajek mechanism or magneto-hydrodynamic processes in the vicinity of a central supermassive black hole. Afterwards, the particles should undergo further acceleration to ultra-relativistic energies by means of different mechanisms (first and second-order Fermi processes, relativistic magnetic reconnection, shear acceleration, jet-star interaction etc.) locally, in the jet emission zone. Our intensive X-ray spectral study of TeV-detected, high-energy-peaked BLLs (HBLs) often show the signatures of an effective second-order Fermi (stochastic) acceleration close to the shock front, while the processes related to the first-order Fermi acceleration are relatively rarely presented. The TeV-undetected HBLs and low-energy-peaked BLLs (LBLs) mostly do not show the signatures of efficient stochastic acceleration in their jets. Concerning the higher-energy component, the most frequently considered scenario incorporates an inverse Compton (IC) scattering of synchrotron photons by their ”parent” electron-positron population (synchrotron self-Compton model, SSC). However, this simple scenario sometimes is challenged by uncorrelated X-ray and TeV variability, more easily explained by multizone SSC, external Compton (EC) and hadronic scenarios.
Water Ice in AGN and Starbursts 0.2 MB
A. G. Yeghikyan and A. L. Samsonyan
Abstract. Complex chemical species are easier formed in a solid phase, for example in a mixture of ices of water, carbon oxides, methane, ammonia, methanole and other, less abundant molecules. Ultraviolet photons in the range 5 - 13.6 eV and the charged particles with MeV-GeV energies serve as an energy source of reactions. Icy particles containing mentioned substances, can exist only in internal areas of the interstellar molecular clouds protected from influence of external ultraviolet radiation. However cosmic rays are capable to penetrate in clouds and to cause an irradiation of ices by means of secondary ultra-violet photons necessary for initiation of chemical reactions of complexisation. In this work a survivability of ices under harsh conditions of active galaxies is discussed. Preliminary model calculations show that abundances of ices depend not only on ionization parameters of the clouds but also on the shape of incident radiation that is on presence and level of hard ultraviolet and X-ray radiation. The last circumstance is directly related to the radiation of the accretion disk of galaxies with active nuclei and can be used to classify active galaxies, for example to distinguish starburst galaxies from those with active nuclei.
AGN Activity in Brigtest Cluster Galaxies (BCGs) 0.2 MB
S. Fisek, S. Alis, E. K. Ülgen , F. K. Yelkenci
Abstract. The aim of our study is to classify the Brightest Cluster Galaxies (BCG), which are the brightest and most massive galaxies in the universe and to determine fraction of BCGs showing AGN activity. Within the scope of the study, we combine BCGs from galaxy cluster catalogs which presented by Hao et al. (2010) and Wen et al. (2009) constructed from the SDSS (Sloan Digital Sky Survey) data and BCGs identified from CFHTLS (Canada-France-Hawaii Telescope Legacy Survey) Deep fields (Alis, 2009). Our combined sample contains 42490 BCGs. We determine activity types of BCGs by means of BPT diagrams and WISE color-color diagrams. 140 BCGs show AGN activity out of 42490. In addition, we calculated star formation rates (SFR) by using Hα emission lines for 5569 BCGs with suitable spectral data and investigated the correlation between SFR and redshift.
The MAGNUM survey: a high-resolution study of the complex nuclear environment of local Seyfert galaxies 0.7 MB
M. Mingozzi, G. Venturi, F. Mannucci, A. Marconi, G. Cresci
Abstract. The central regions of Seyfert galaxies, comprising broad and narrow line regions and the inner parts of galaxy disk and bulge, is characterized by a complex interplay among many physical effects. Specifically, it is shaped by the influence of the central black hole, producing ionization by an hard continuum and gas outflows. The integral-field spectrograph MUSE at the ESO VLT allows to carry out a detailed study of these regions to obtain their ionization, dynamical, and metallicity properties. Here we present some highlights of the MAGNUM survey which is designed to study the central regions of a sample of nearby (D > 500 pc) Seyfert galaxies. We describe the rationale of the survey, the data analysis techniques used to extract information on ionization and dynamics, and the results for one galaxy, Centaurus A.
Studies of Active Galaxies in Byurakan: Recent Results 0.4 MB
A. M. Mickaelian , H. V. Abrahamyan, G. M. Paronyan, G. A. Mikayelyan, M. V. Gyulzadyan
Abstract. We present the recent results of studies on active galaxies (both AGN and Starbursts) by the Extragalactic group of Byurakan Astrophysical Observatory (BAO) Research Department “Astronomical Surveys”. The research has been carried out in 2017-2019 and the results are published in 2018-2019. These studies are characterized by multiwavelength approach to statistical analysis of large amount of data obtained in different wavelengths; from X-ray to radio. Results on HRC/BHRC sample objects (optical identifications of ROSAT X-ray sources), studies of Markarian galaxies in UV and multiwavelength SEDs, abundance and star formation determinations in Mrk galaxies from SDSS spectra, revised optical classification of “LINERs”, study and classification of SDSS spectra for Byurakan-IRAS Galaxies, summary of observations and study of Byurakan-IRAS Galaxies (BIG objects), discovery of new bright ULIRGs from the IRAS PSC/FSC Combined Catalogue and their spectral classification, radio variable sources at 1400 MHz and their optical variability, classification of BZCAT objects having uncertain types (BZU objects), and optical variability of blazars are presented.
Investigations of the extended extragalactic radio sources: The quasars 1502+10 and 0923+39 and their environment 0.1 MB
M. A. Hovhannisyan , R. R. Andreasyan , G. M. Paronyan , H. V. Abrahamyan
Abstract. It was studied the environment of quasars 1502+10 and 0923+39. The investigation of the region with radius of 360 arcmin around these extended extragalactic radio sources shows that distribution of extragalactic objects around them is mainly homogeneous. This study is carried out in the framework of a large project, to find large regions with deficit of extragalactic sources around extragalactic radio sources with very large linear sizes, as it is in the case of DA240, NGC315 radiogalaxies.
Space Activities in Armenia: past, present and future 0.4 MB
A. M. Mickaelian and G. A. Mikayelyan
Abstract. A review about Space related activities in Armenia is given, particularly in the Byurakan Astrophysical Observatory (BAO, Armenia), including the first Space Astronomy projects by Grigor Gurzadian in 1960s-1970s (Orion and Orion-2 UV observatories), research projects with USA (NASA) and European (ESA) Space observatories (IRAS, ROSAT, Hubble, Spitzer, WISE, etc.) by BAO scientists, Armenian participation in International Virtual Observatory Alliance (IVOA), International Planetary Data Alliance (IPDA), and UN Committee on the Peaceful Users of the Outer Space (COPUOS), “Roscosmos” station in Byurakan established in 2014 for monitoring of Space debris, Armenian participation in NASA Space Apps Hackathons, Armenian participation in the European H2020 project, including the Space field, organization of Space related meetings and schools in Byurakan, etc. Armenia with its astronomical and other related background has great potential in establishing collaborations and promoting Space Sciences and Space Technologies.
On the role of large-scale magnetic fields of AGN in the morphology and evolution of extragalactic radio sources
Abstract. We discuss a role of large-scale dipolar magnetic field in the formation and evolution of extragalactic radio sources. From the study of dynamics of clouds of relativistic particles which are ejected from the central part the galaxy in his dipolar magnetic field it is possible to explain main morphological features and physical properties of formed extragalactic radio sources. Here we bring some results of statistical analyses and correlations between physical parameters for different type extragalactic radio sources.
Physical Consequences of the Accelerated Space Expansion Effect at Small Scales
H. A. Harutyunian
Abstract. We present here a self-consistent analysis of the physical effects recognizable if the accelerated expansion of the Universe is not the prerogative of the large structure of the Universe, but affects all the scales measurable. Some expansion phenomena observed in our vicinity are examined in detail from this point of view. The very fact that galaxies accelerate under the influence of dark energy is considered as the crucial evidence of the interaction between baryonic matter and the carrier of dark energy. Therefore, the second law of thermodynamics is applicable to this interaction process. Then one should take into account that all the baryonic objects starting with atomic nuclei and up to galaxies and their systems exist exceptionally due to their negative potential energy or mass defect in the case of atomic nuclei, while dark energy is purely positive. Bearing this in mind one arrive at a conclusion that due to this interaction: (1) the nuclear binding energy decreases gradually due to injection of positive energy into the atomic nuclei; (2) it makes the nuclei more and more unstable; (3) the decreased part of binding energy transforms into the mass, which increases the mass of nuclei. We argue that this effect shows up in all cosmic objects at all the hierarchical levels and governs their evolutional path. Particularly, this conclusion allows one to state that all the cosmic objects and the Universe as a whole increase their mass during their evolution. We suggested a method and calculated the solar mass annual growth using the relevant observational data. The results presented in the talk are published in the recent papers of the author.