arXiv subjects

E. O. Vasiliev

Publications and source records attributed to E. O. Vasiliev.

At least 19 recordsLinked to original sources

arXiv2025

Interstellar Medium in Extremely High Star-Formation Regions: A Prospect of Observations on the Millimetron Space Observatory

High star-formation rate and active galactic nucleus' emission can significantly transform the interstellar medium. In ultra-luminous infrared galaxies, in which the star-formation rate reaches thousands of solar masses per year, the gas and dust are considerably affected by the ionizing radiation, cosmic rays and shock waves, that can be about a factor of 100--1000 larger than typical values in quiet star-forming galaxies. In these conditions, the emissivity of the gas and dust changes: in dense gas, high ionic and molecular transitions become excited, while dust grains are heated to high temperatures. In this paper, we analyze the possibilities for studying the interstellar medium in extreme conditions of ultra-luminous infrared galaxies at redshifts of $\sim 0-3$, utilizing the atomic and molecular lines, and dust continuum in far infrared range of $100-500μ$m. We discuss the prospect of observations using the instruments of the Millimetron Space Observatory.

astro-ph.GA↗

arXiv2025

Far-Infrared Emission from a Late Supernova Remnant in an Inhomogeneous Medium

The interstellar dust grains are swept up during the expansion of the supernova (SN) remnant, they penetrate behind the shock front, where they are heated and destroyed in the hot gas. This leads to a change in emissivity of such grains. In this work, we consider the evolution of the infrared (IR) luminosity of the SN remnant expanding into an inhomogeneous interstellar medium with lognormal distribution of the density fluctuations. The IR luminosity of the swept-up interstellar dust rapidly increases during the first several thousand years after the SN explosion, and reaches the maximum value. Afterwards, it decreases due to the destruction of the dust grains in hot gas and their declining emissivity in the cooling down gas of the shell. We show how the IR luminosity of dust in the SN remnant depends on the dispersion of the gas density in front of the SN shock front. We find that for the significant period of time (40 - 50 kyr) the maximum of the dust IR luminosity peaks at the range centered at 70$μ$m. Therefore, this band can be considered as the most optimal range for studying the late SN remnants. We illustrate that during evolution, the dust temperature changes from 70 to 20 K, and only slightly depends on the inhomogeneity of the medium. In the radiative phase, the strong emission lines of metal ions emerge above the dust continuum. Their luminosity rapidly increases and exceeds the dust continuum luminosity by $\sim 10-10^3$ times. The point in time when the high luminosity in the lines is reached strongly depends on the inhomogeneity of the medium. We discuss possibilities for detection of the IR emission both in dust continuum and in lines. We expect that their ratios will allow to estimate the inhomogeneity of the medium, where the remnant is expanding.

astro-ph.GA↗

arXiv2025

Infrared and X-ray emission of a supernova remnant in a clumpy medium

The infrared (IR) to X-ray luminosity ratio (IRX) is an indicator of the role of the dust plays in cooling of hot gas in supernova remnants (SNR). Using the 3D dynamics of gas and interstellar polydisperse dust grains we analyze the evolution of SNR in the inhomogeneous medium. We obtain spatial distributions of the surface brigthness both of the X-ray emission from hot gas inside SNR and the IR emission from the SNR swept-up shell, as well as, the average gas temperature in the SNR, $T_X$. We find that the IRX changes significantly (by a factor of $\sim 3-30$) as a function of impact distance within the SNR and its age. In a low inhomogeneous medium the IRX drops rapidly during the SNR evolution. On the other hand, if large inhomogeneities are present in the medium, the IRX is maintained at higher levels during the late SNR evolution at radiative phase due to replenishment of dust in the hot gas by incompletely destroyed fragments behind the shock front. We show that the onset of the radiative phase determines the evolution of the $T_X - {\rm IRX}$ diagram. We illustrate that decreasing gas metallicity or density leads to high values of temperature and IRX ratio. We discuss how our results can be applied to the observational data to analyse the SNR older than 10 kyr (i.e. when the mass of the swept-up dust in the shell is expected to exceed that produced in the SNR) in the Galaxy and Large Magellanic Cloud.

astro-ph.GA↗

arXiv2015

GMCs scaling relations: role of the cloud definition

We investigate physical properties of molecular clouds in disc galaxies with different morphology: a galaxy without prominent structure, a spiral barred galaxy and a galaxy with flocculent structure. Our $N$-body/hydrodynamical simulations take into account non-equilibrium H$_2$ and CO chemical kinetics, self-gravity, star formation and feedback processes. For the simulated galaxies the scaling relations of giant molecular clouds or so called Larson's relations are studied for two types of a cloud definition (or extraction methods): the first one is based on total column density position-position (PP) datasets and the second one is indicated by the CO~(1-0) line emission used position-position-velocity (PPV) data. We find that the cloud populations obtained by using both cloud extraction methods generally have similar physical parameters. Except that for the CO data the mass spectrum of clouds has a tail with low-massive objects $M\sim 10^3-10^4$~\Msun. Varying column density threshold the power-law indices in the scaling relations are significantly changed. In contrast, the relations are invariant to CO brightness temperature threshold. Finally, we find that the mass spectra of clouds for the PPV data are almost insensitive to the galactic morphology, whereas the spectra for the PP data demonstrate significant variations.

astro-ph.GA↗

arXiv2015

Dynamics of a Supernova Envelope in a Cloudy Interstellar Medium

The evolution of a supernova remnant in a cloudy medium as a function of the volume filling factor of the clouds is studied in a three-dimensional axially symmetrical model. The model includes the mixing of heavy elements (metals) ejected by the supernova and their contribution to radiative losses. The interaction of the supernova envelope with the cloudy phase of the interstellar medium leads to nonsimultaneous, and on average earlier, onsets of the radiative phase in different parts of the supernova envelope. Growth in the volume filling factor $f$ leads to a decrease in the time for the transition of the envelope to the radiative phase and a decrease in the envelope's mean radius, due to the increased energy losses by the envelope in the cloudy medium. When the development of hydrodynamical instabilities in the supernova envelope is efficient, the thermal energy falls as $E_t\sim t^{-2.3}$, for the propagation of the supernova remnant through either a homogeneous or a cloudy medium. When the volume filling factor is $f\simgt 0.1$, a layer with excess kinetic energy andmomentumforms far behind the global shock front from the supernova, which traps the hot gas of the cavity in the central part of the supernova remnant. Metals ejected by the supernova are also enclosed in the central region of the remnant, where the initial (high) metallicity is essentially preserved. Thus, the interaction of the supernova envelope with the cloudy interstellar medium appreciably changes the dynamics and structure of the distribution of the gas in the remnant. This affects the observational characteristics of the remnant, in particularly, leading to substantial fluctuations of the emission measure of the gas with $T>10^5$~K and the velocity dispersion of the ionized gas.

astro-ph.GA↗

arXiv2015

Numerical code for multi-component galaxies: from N-body to chemistry and magnetic fields

We present a numerical code for multi-component simulation of the galactic evolution. Our code includes the following parts: $N$-body is used to evolve dark matter, stellar dynamics and dust grains, gas dynamics is based on TVD-MUSCL scheme with the extra modules for thermal processes, star formation, magnetic fields, chemical kinetics and multi-species advection. We describe our code in brief, but we give more details for the magneto-gas dynamics. We present several tests for our code and show that our code have passed the tests with a reasonable accuracy. Our code is parallelized using the MPI library. We apply our code to study the large scale dynamics of galactic discs.

physics.comp-ph↗

arXiv2014

Extended OVI haloes of starforming galaxies

We consider evolution of metal-enriched gas exposed to a superposition of time-dependent radiation field of a nearby starburst galaxy and nearly invariant (on timescales 100 Myr) extragalactic ionization background. Within nonequilibrium (time-dependent) photoionization models we determine ionization fraction of the OVI ion commonly observed in galactic circumference. We derive then conditions for OVI to appear in absorptions in extended galactic haloes depending on the galactic mass and star formation rate. We have found that the maximum OVI fraction can reach $\sim 0.4-0.9$ under combined action of the galactic and the extragalactic ionizing radiation fields. We conclude that soft X-ray emission with $E\simgt 113$~eV from the stellar population of central starforming galaxies is the main source of such a high fraction of OVI. This circumstance can explain high column densities ${\rm N(OVI)} \sim 10^{14.5 - 15.3}$~cm$^{-2}$ observed in the haloes of starforming galaxies at low redshifts (Tumlinson etal 2011) {\it even} for a relatively low ({ $\sim 0.01-0.1\zsun$}) metallicity. As a result, the requirements to the sources of oxygen in the extended haloes relax to a reasonably conservative level. We show that at $z\simlt 0.5$ ionization kinetics of oxygen in a relatively dense plasma $n\simgt 10^{-4}$ cm$^{-3}$ of outer halo exposed to a low extragalactic ionizing flux is dominated by nonequilibrium effects.

astro-ph.GA↗

arXiv2013

Signatures of particle decay in 21 cm absorptions from first minihalos

The imprint of decaying dark matter (DM) particles in characteristics of the "21 cm fores" -- absorptions in 21 cm from minihalos in spectra of distant radio-loud sources -- is considered within a 1D self-consistent hydrodynamic description of minihalos from their turnaround point to virialization. The most pronounced influence of decaying DM on evolution of minihalos is found in the mass range $M=10^5-10^6\msun$, for which unstable DM with the current upper limit of the ionization rate $ξ_{L} = 0.59\times 10^{-25}$ s$^{-1}$ depresses 21 cm optical depth by an order of magnitude compared to the standard recombination scenario. Even rather a modest ionization $ξ\sim 0.3ξ_L$ practically "erases" absorption features and results in a considerable decrease (by factor of more than 2.5) of the number of strong ($W_ν^{obs} \simgt 0.3$ kHz at $z\simeq 10$) absorptions. At such circumstances broad-band observations are to be more suitable for inferring physical conditions of the absorbing gas. X-ray photons from stellar activity of initial episodes of star formation can compete the contribution from decaying DM only at $z<10$. Therefore, when observed the 21 cm signal will allow to follow evolution of decaying DM particles in the redshift range $z=10-15$. Contrary, in case of non-detection of the 21 cm signal in the frequency range $ν<140$ MHz a lower limit on the ionization rate from decaying dark matter can be established.

astro-ph.CO↗

arXiv2012

Evolution of the First Supernovae in Protogalaxies: Dynamics of Mixing of Heavy Elements

The paper considers the evolution of the supernova envelopes produced by Population III stars with masses of $M_*\sim 25-200 M_\odot$ located in non-rotating protogalaxies with masses of $M\sim 10^7 M_\odot$ at redshifts $z=12$, with dark-matter density profiles in the form of modified isothermal spheres. The supernova explosion occurs in the ionization zone formed by a single parent star. The properties of the distribution of heavy elements (metals) produced by the parent star are investigated, as well as the efficiency with which they are mixed with the primordial gas in the supernova envelope. In supernovae with high energies ($E\simgt 5\times 10^{52}$ erg), an appreciable fraction of the gas can be ejected from the protogalaxy, but nearly all the heavy elements remain in the protogalaxy. In explosions with lower energies ($E\simlt 3\times 10^{52}$ erg), essentially no gas and heavy elements are lost from the protogalaxy: during the first one to threemillion years, the gas and heavy elements are actively carried from the central region of the protogalaxy ($r\sim 0.1 r_{vir}$, where $r_{vir}$ is the virial radius of the protogalaxy), but an appreciable fraction of the mass of metals subsequently returns when the hot cavity cools and the envelope collapses. Supernovae with high energies ($E\simgt 5\times 10^{52}$ erg) are characterized by a very low efficiency of mixing of metals; their heavy elements are located in the small volume occupied by the disrupted envelope (in a volume comparable with that of the entire envelope), with most of the metals remaining inside the hot, rarified cavity of the envelope. (abridged)

astro-ph.CO↗

arXiv2012

Instabilities in the Ionization Zones Around the First Stars

We consider the evolution of the ionization zone around Population III stars with $M_*\sim 25-200 M_\odot$ in protogalaxies with $M\sim 10^7 M_\odot$ at redshifts $z = 12$, assuming that the dark matter profile is a modified isothermal sphere. We study the conditions for the growth of instabilities in the ionization zones. The Rayleigh-Taylor and thermal instabilities develop efficiently in the ionization zones around 25-40 $M_\odot$ stars, while this efficiency is lower for stars with $\sim 120 M_\odot$. For more massive stars ($\sim 200 M_\odot$), the flux of ionizing photons is strong enough to considerably reduce the gas density in the ionization zone, and the typical lifetimes of stars ($\sim 2$ Myr) are insufficient for the growth of instabilities. The gas in a protogalaxy with $M\sim 10^7 M_\odot$ with a 200 $M_\odot$ central star is completely ionized by the end of the star's lifetime; in the case of a 120 $M_\odot$ central star, only one-third of the total mass of gas is ionized. Thus, ionizing photons from stars with $M_*\simlt 120 M_\odot$ cannot leave protogalaxies with $M\simgt 10^7 M_\odot$. If the masses of the central stars are 25 and 40 $M_\odot$, the gas in protogalaxies of this mass remains essentially neutral. We discuss the consequences of the evolution of the ionization zones for the propagation of the envelope after the supernova explosions of the stars and the efficiency of enrichment of the intergalactic medium in heavy elements.

astro-ph.CO↗

arXiv2012

The simulation of molecular clouds formation in the Milky Way

Using 3D hydrodynamic calculations we simulate formation of molecular clouds in the Galaxy. The simulations take into account molecular hydrogen chemical kinetics, cooling and heating processes. Comprehensive gravitational potential accounts for contributions from the stellar bulge, two and four armed spiral structure, stellar disk, dark halo and takes into account self-gravitation of the gaseous component. Gas clouds in our model form in the spiral arms due to shear and wiggle instabilities and turn into molecular clouds after $t\simgt 100$ Myr. At the times $t\sim 100 - 300$ Myr the clouds form hierarchical structures and agglomerations with the sizes of 100 pc and greater. We analyze physical properties of the simulated clouds and find that synthetic statistical distributions like mass spectrum, "mass-size" relation and velocity dispersion are close to those observed in the Galaxy. The synthetic $l-v$ (galactic longitude - radial velocity) diagram of the simulated molecular gas distribution resembles observed one and displays a structure with appearance similar to Molecular Ring of the Galaxy. Existence of this structure in our modelling can be explained by superposition of emission from the galactic bar and the spiral arms at $\sim$3-4 kpc.

astro-ph.GA↗

arXiv2012

Observational Manifestations of the First Protogalaxies in the 21 cm Line

The absorption properties of the first low-mass protogalaxies (mini-halos) forming at high redshifts in the 21-cm line of atomic hydrogen are considered. The absorption properties of these protogalaxies are shown to depend strongly on both their mass and evolutionary status. The optical depths in the line reach $\sim$0.1-0.2 for small impact parameters of the line of sight. When a protogalaxy being compressed, the influence of gas accretion can be seen manifested in a non-monotonic frequency dependence of the optical depth. The absorption characteristics in the 21-cm line are determined by the thermal and dynamical evolution of the gas in protogalaxies. Since the theoretical line width in the observer's reference frame is 1-6 kHz and the expected separation between lines 8.4 kHz, the lines from low mass protogalaxies can be resolved using ongoing and future low frequency interferometers.

astro-ph.CO↗

arXiv2012

Particle decay and 21 cm absorption from first minihaloes

We consider the influence of decaying dark matter (DM) particles on the characteristics of 21 cm absorption in spectra of distant radio-loud sources - "21 cm forest" - from minihaloes with masses $M=10^5-10^7\msun$ virialized at $z_{vir} = 10$. We use 1D self-consistent hydrodynamic description to study evolution of minihaloes, and follow up their absorption characteristics from turnaround to virialization. We find that in the presence of decaying dark matter both thermal and dynamical evolution of minihaloes demonstrate significant deviation from those in the model without dark matter decay (standard recombination). We show that optical depth in 21 cm line is strongly suppressed in the presence of decaying particles: for $M=10^5-10^6\msun$ decaying dark matter with the energy rate deposited in baryonic gas $ξ_{L} = 0.59\times 10^{-25}$ s$^{-1}$ - the current upper limit of the energy deposit - decreases the optical depth and the equivalent width by an order of magnitude compared to the standard recombination. Thus additional ionization and heating from decaying DM particles almost "erases" absorption features from minihaloes with $M=10^5-10^6\msun$ for $ξ\simgt 0.3ξ_L$, which consequently considerably decreases the number of strong absorptions: for example, the number of absorptions with the equivalent width $W_ν^{obs} \simgt 0.3$ kHz at $z\simeq10$ decreases more than 2.5 times for $ξ/ξ_{L} = 0.3$ and $\simgt$4.5 times for $ξ/ξ_{L} = 1$. We argue that "21 cm forest" absorptions might be a powerful probe of the presence of decaying dark matter in the early Universe.

astro-ph.CO↗

arXiv2008

Low-temperature primordial gas in merging halos

Thermal regime of the baryons behind shock waves arising in the process of virialization of dark matter halos is governed at cetrain conditions by radiation of HD lines. A small fraction of the shocked gas can cool down to the temperature of the cosmic microwave background (CMB). We estimate an upper limit for this fraction: at $z=10$ it increases sharply from about $q_{_T}\sim 10^{-3}$ for dark halos of $M=5\times 10^7\msun$ to $\sim 0.1$ for halos with $M=10^8\msun$. Further increase of the halo mass does not lead however to a significant growth of $q_T$ -- the asymptotic value for $M\gg 10^8\msun$ is of 0.3. We estimate star formation rate associated with such shock waves, and show that they can provide a small but not negligible fraction of the star formation. We argue that extremely metal-poor low-mass stars in the Milky Way may have been formed from primordial gas behind such shocks.

astro-ph↗

arXiv2008

First supernovae in dwarf protogalaxies

(Abridged) We explore numerically the chemical, thermal, and dynamical evolution of a shell formed by a high-energy supernova explosion ($10^{53}$ erg) in dwarf protogalaxies with total mass $10^7 M_\odot$ at a redshift $z=12$. We consider two initial configurations for the baryonic matter, one without rotation and the other having the ratio of rotational to gravitational energy $β=0.17$. The (non-rotating) dark matter halo is described by a quasi-isothermal sphere. We find that the dynamics of the shell is different in protogalaxies with and without rotation. For instance, the Rayleigh-Taylor instability in the shell develops faster in protogalaxies without rotation. The fraction of a blown-away baryonic mass is approximately twice as large in models with rotation ($\sim 20%$) than in models without rotation. On the other hand, the chemical evolution of gas in protogalaxies with and without rotation is found to be similar. The relative number densities of molecular hydrogen and HD molecules in the cold gas ($T \le 10^3$ K) saturate at typical values of $10^{-3}$ and $10^{-7}$, respectively. The clumps formed in the fragmented shell move with velocities that are at least twice as large as the escape velocity. The mass of the clumps is $\sim 0.1-10 \msun$, which is lower than the Jeans mass. We conclude that the clumps are pressure supported. A supernova explosion with energy $10^{53}$ ergs destructs our model protogalaxy. The clumps formed in the fragmented shell are pressure supported. We conclude that protogalaxies with total mass $\sim 10^{7} M_\odot$ are unlikely to form stars due to high-energy supernova explosions of the first stars.

astro-ph↗

arXiv2007

Particle decay in the early universe: predictions for 21 cm

The influence of ultra-high energy cosmic rays (UHECRs) and decaying dark matter particles on the emission and absorption characteristics of neutral hydrogen in 21 cm at redshifts $z = 10-50$ is considered. In presence of UHECRs 21 cm can be seen in absorption with the brightness temperature $T_b=-(5-10)$ mK in the range $z=10-30$. Decayng particles can stimulate a 21 cm signal in emission with $T_b\sim 50-60$ mK at $z =50$, and $T_b \simeq 10$ mK at $z \sim 20$. Characteristics of the fluctuations of the brightness temperature, in particular, its power spectrum are also calculated. The maps of the power spectrum of the brightness temperature on the plane {\it wavenumber-redshift} are shown to be sensitive to the parameters of UHECRs and decaying dark matter. Observational possibilities to detect manifestations of UHECRs and/or decaying particles in 21 cm with the future radio telescopes (LOFAR, 21CMA and SKA), and to distinguish contributions from them are briefly discussed.

astro-ph↗

arXiv2006

The influence of ultra-high-energy cosmic rays on star formation in the early universe

The presence of ultra-high-energy cosmic rays (UHECR) results in an increase in the degree of ionization in the post-recombination Universe, which stimulates the efficiency of the production of H$_2$ molecules and the formation of the first stellar objects. As a result, the onset of the formation of the first stars is shifted to higher redshifts, and the masses of the first stellar systems decrease. As a consequence, a sufficient increase in the ionizing radiation providing the reionization of the Universe can take place. We discuss possible observational manifestations of these effects and their dependence on the parameters of UHECR.

astro-ph↗

arXiv2006

Primordial gas cooling behind shock waves in merging halos

We investigate thermal regime of the baryons behind shock waves arising in the process of virialization of dark matter halos. We find a fraction of the shocked gas cooled by radiation of HD molecules down to the temperature of the cosmic microwave background (CMB): this fraction increases sharply from about $f_{\rm c}\sim 10^{-3}$ for dark halos of $M=5\times 10^7\msun$ to $\sim 0.1$ for halos with $M=10^8\msun$ at $z=10$. We show, however, that further increase of the mass does not lead to a significant growth of $f_{\rm c}$ -- the assymptotic value for $M\gg 10^8\msun$ is of 0.2. We estimate star formation rate associated with such shock waves, and show that it can be a small but not negligible fraction of the star formation connected with cooling by HI and H$_2$. We argue that extremely metal-poor low-mass stars in the Milky Way may have been formed from primordial gas behind such shocks.

astro-ph↗