arXiv subjects

A. A. Ermash

Publications and source records attributed to A. A. Ermash.

8 recordsLinked to original sources

arXiv2021

Sources of confusion noise in the infrared wavelength range

In this paper we use the model of extragalactic background light to investigate the factors that have influence on the confusion noise. It was shown that (1) Large-Scale Structure of the Universe is an important factor; (2) gravitational lensing does not have a significant effect on the confusion noise; (3) lower redshift limit of objects that contribute to the confusion noise does not depend on the wavelength and is about $z_{min}\sim 0.5-0.6$, while upper redshift limit gradually changes from $\sim4$ to $\sim3$ with the increase of wavelength from 70$μm$ up to 2000$μm$; (4) at rather short wavelengths ($\simeq70μm$) galaxies with luminosities in the range $10^7L_\odot$ -- $10^9L_\odot$ give the most contribution to the confusion noise, while at larger wavelengths (650-2000$μm$) their luminosities are greater than $L\geq10^{10}L_\odot$; (5) contribution from objects with different color characteristics is considered; (6) the variability of the extragalactic background on the timescale from 1 day to 1 year is noticeable at short wavelengths (70--350$μm$) and manifests at fluxes ${}^<_\sim$ 1~mJy.

astro-ph.GA↗

arXiv2020

Estimating the confusion noise for the Millimetron space telescope

Sensitivity of future far infrared 10m class space telescopes will be limited by a confusion noise created by distant galaxies. Our primary goal is to create a model that will allow us to estimate the confusion noise parameters of the Millimetron mission. We construct a model of the Cosmic Infrared Background (CIB) aimed at exploring the methods of prediction and reduction of the confusion noise. The model is based on the publicly available eGALICS simulation. For each simulated galaxy we construct a spectral energy distribution with the help of the GRASIL code. To put our model in the context of the current CIB investigations, we compare the outputs of the model with the available observational data and with three other models. One is a well known "backwards evolution" model of Bethermin et al. 2011 and two others are based on a simple mass-luminosity (M-L) relation applied to simulated dark matter halo catalogs. We conclude that our model reproduces the observational data reasonably well. All four models show significant differences in the predictions of the distribution of sources on the flux-redshift plane, especially at high redshifts. We give estimations of the confusion noise based on number counts (source density criterion, probability of deflection criterion etc.) and based on the analysis of the simulated maps. We show that resolution effects influence the number counts curves and noise estimations.

astro-ph.GA↗

arXiv2019

Prospects of observation of gravitationally lensed sources by space submillimeter telescopes

In the current paper we consider the prospects of observation of gravitationally lensed sources in far-infrared and submillimeter wavelength ranges by the future space telescopes equipped with actively cooled main mirrors. We consider the possibility of solving some of the important cosmological and astrophysical scientific tasks by observation of gravitationally lensed sources. The number counts of lensed sources for wavelengths from 70$μm$ up to 2000$μm$ were calculated. We discuss the distribution of lensed sources at different redshifts and magnification coefficients and also mass distribution of lenses. Model sky maps that illustrate the contribution of lensed sources were created.

astro-ph.GA↗

arXiv2017

A Model of the Cosmic Infrared Background Produced by Distant Galaxies

The extragalactic background radiation produced by distant galaxies emitting in the far infrared limits the sensitivity of telescopes operating in this range due to confusion. We have constructed a model of the infrared background based on numerical simulations of the large-scale structure of the Universe and the evolution of dark matter halos. The predictions of this model agree well with the existing data on source counts. We have constructed maps of a sky field with an area of 1 deg$^2$ directly from our simulated observations and measured the confusion limit. At wavelengths $100-300$ $μ$m the confusion limit for a 10-m telescope has been shown to be at least an order of magnitude lower than that for a 3.5-m one. A spectral analysis of the simulated infrared background maps clearly reveals the large-scale structure of the Universe. The two-dimensional power spectrum of these maps has turned out to be close to that measured by space observatories in the infrared. However, the fluctuations in the number of intensity peaks observed in the simulated field show no clear correlation with superclusters of galaxies; the large-scale structure has virtually no effect on the confusion limit.

astro-ph.CO↗

arXiv2013

Narrow-line Seyfert Galaxies. Connection between abundance and the large-scale structure

In this work the correlations between spatial concentrations of active nuclei (NLS and BLS) and concentration of galaxies of full uniform sample were obtained. Methods, developed by the author in earlier paper were used. Galaxies of this uniform sample trace the large-scale structure. We used SDSS DR 7 data. The correlations obtained are linear and the NLS/BLS ratio is constant. That leads to conclusion that amounts NLS and BLS are some fixed fraction of all galaxies independent on the density of large-scale environment. In order to check validity of our results were also confirmed the well known result that fraction of red galaxies increases with density of environment. Also it was confirmed that this trend is more prominent for less massive galaxies.

astro-ph.GA↗

arXiv2013

The Luminosity function of Narrow-Line Seyfert galaxies based on SDSS data

We present measurements of AGN type 1 luminosity function in the forbidden line [OIII]5007Åusing data from SDSS DR7. A special attention is paid to a subclass of Seyfert galaxies - the Narrow-Line Seyfert galaxies. These galaxies have relatively narrow broad permitted emission lines with FWHM $\leq 2000$ km/s. A new approach in calculation of the luminosity function is presented. We also account for the large-scale structure variations of the Universe density. The results obtained are compared with the ones from the literature. A prediction of x-ray luminosity function based on our results shows an agreement with observations. One of our preliminary conclusions is that NLSy1 seem to occupy a more narrow range in the nuclear luminosity than BLSy1, but the average values are within errors.

astro-ph.GA↗

arXiv2013

AGN III - primordial activity in nuclei of late-type galaxies with pseudobulges

1. Based on observational data on evolution of quasars and galaxies of different types along with the results of numerical simulations we make a conclusion that on low redshifts ($z<0.5$) QSOI/II objects in massive elliptical and spiral galaxies with classical bulges cannot be in late single activity event (be "primordial"). Instead of it they have had events of activity earlier in their evolution. It means that their presence on low redshifts is connected with the recurrence phenomenon, sequential wet minor mergings, because timescale of the activity does not exceed several units of $10^7$ years. 2. We define a new class - "AGN III" as active galactic nuclei in isolated late-type spirals with low-mass rapidly rotating pseudobulges. We also state that only such objects can be in the primordial phase of activity at low redshifts. Black holes in such galaxies have masses $M_{BH}<10^7M_\odot$ and also, probably very high spin. Such properties can explain their peculiar emission spectra. A good representative of AGN III might be the galaxies with narrow (${\rm FWHM}(Hβ)\leq1200$ km/s) broad permitted emission lines - NLS. It is believed that their black hole masses are less than $M_{BH}<10^7M_\odot$ and their host galaxies have pseudobulges instead of the classical ones. Because host galaxies of NLS have pseudobulges and BLS (Broad-Line Seyfert galaxies) have classical bulges these two types of objects cannot have evolutionary connection. Presumably, the parent population of NLS are the quasars of "population A".

astro-ph.GA↗

arXiv2008

The model of dynamo with small number of modes and magnetic activity of T Tauri stars

The model that describes operation of dynamo in fully convective stars is presented. It is based on representation of stellar magnetic field as a superposition of finite number of poloidal and toroidal free damping modes. In the frame of adopted low of stellar differential rotation we estimated minimal value of dynamo number D, starting from which generation of cyclic magnetic field in stars without radiative core is possible. We also derived expression for period of the cycle. It was found that dynamo cycles of fully convective stars and stars with thin convective envelopes differ in a qualitative way: 1) distribution of spots over latitude during the cycle is different in these stars; 2) the model predicts that spot formation in fully convective stars should be strongly suppressed at some phases of the cycle. We have analyzed historical lightcurve of WTTS star V410 Tau and found that long term activity of the star is not periodic process. Rather one can speak about quasi cyclic activity with characteristic time of $\sim 4$ yr and chaotic component over imposed. We concluded also that redistribution of cool spots over longitude is the reason of long term variations of V410 Tau brightness. It means that one can not compare directly results of photometric observations with predictions of our axially symmetric (for simplicity) model which allows to investigate time evolution of spot's distribution over latitude. We then discuss what kind of observations and in which way could be used to check predictions of the dynamo theory.

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