The radio sources CTA 21 and OF+247: The hot spots of radio galaxies

The physical conditions in the radio sources CTA 21 and OF+247 are studied assuming that the low-frequency spectral turnovers are due to synchrotron self-absorption. The physical parameters of the radio sources are estimated using a technique based on a nonuniform synchrotron source model. It is shown that the magnetic-field distributions in the dominant compact components of these radio sources are strongly inhomogeneous. The magnetic fields at the center of the sources are B ～ 10^?1 G, and the fields are two to three orders of magnitude weaker at the periphery. The magnetic field averaged over the compact component is B ～ 10^?3 G, and the density of relativistic electrons is n _e ～ 10^?3 cm^?3. Assuming that there is equipartition of the energies of the magnetic field and relativistic particles, averaged over the source, 〈E _H 〉 = 〈E _e 〉 ～ 10^?7–10^?6 erg cm^?3. The energy density of the magnetic field exceeds that of the relativistic electrons at the centers of the radio sources. The derived parameters of CTA 21 and OF+247 are close to those of the hot spots in the radio galaxy Cygnus A. On this basis, it is suggested that CTA 21 and OF+247 are radio galaxies at an early stage of their evolution, when the hot spots (dominant compact radio components) have appeared, and the radio lobes (weak extended components) are still being formed.     

Study of the physical conditions in active galactic nuclei. Physical conditions in the cores of two nearby radio galaxies

We have carried out a search for compact radio sources in the cores of 16 nearby radio galaxies. We detected compact components in four radio galaxies, and found upper limits for the flux density in compact components in ten radio galaxies. VLBI observations enabled the detection of a turnover in the spectra of the two nearby radio galaxies 3C 111 and 3C 465. Using a method based on an inhomogeneous model for a synchrotron source, we estimate the magnetic-field strength and the energy densities in the magnetic field and relativistic electrons in the cores of these radio galaxies. Strong inhomogeneity in the distribution of the magnetic fields in the cores of 3C 111 and 3C 465 is implied by our analysis. The magnetic-field strengths in the central regions of these galactic nuclei, on scales of ～0.1 pc, exceed the mean strength by four to five orders of magnitude, and lie in the range 10² G < H < 10⁴ G.     

Physical conditions in the nucleus of the radio galaxy 3C 274

Interplanetary scintillation observations of the compact nucleus of 3C 274 have been carried out at 111 MHz on on the Large Phased Array radio telescope. We have derived an upper limit for the flux density of the compact radio source, and determined the parameters of the low-frequency cutoff of the spectrum of this source. We have analyzed the observational data assuming that the low-frequency spectral cutoff is due to synchrotron self-absorption. In this case, the magnetic field in the nucleus of 3C 274 must be very nonuniform. At the center, on scales of < 0.01 pc, the magnetic field varies in the range 0.4 G < H < 40 G, while its mean value over the entire radio source is 〈H〉 ～ 10^?3 ? 10^?4 G. The energy density of the relativistic electrons exceeds the energy density of the magnetic field everywhere within the nucleus, though energy equipartition is also possible near the center.     

Radio-induced activity in galaxy pairs

The close proximity of a radio-loud active galactic nucleus (AGN) can trigger star formation in nearby objects containing gas if they are hit by a radio jet emerging from the active nucleus (as is observed, for example, in the case of Minkowski’s Object). The predicted frequency of such events is modest for close pairs of galaxies—of the order of several percent of all close (with separations of the order of several tens of parsec) pairs containing a radio AGN. A statistical study of this effect is carried out using the SDSS and FIRST surveys, by searching for spatially close pairs (projected separations <150 kpc, relative radial velocities <600 km/s) containing AGNs with radio jets. The frequency of galaxies with bursts of star formation, f _SF, and active nuclei f _AGN, in pairs either containing or not containing an AGN with radio jets are evaluated as functions of the separation of the galaxies in the pair. It is concluded that (1) the predicted effect should be of the order of 5%, falling off with increasing separation between the galaxies in the pair; (2) the observed values of f _SF and f _AGN and their dependences on the galaxy separation are consistent withmodel predictions, but the large uncertainties associated with the limited size of the studied sample hinders firm conclusions about the existence of radio-induced activity in close galaxy pairs; (3) further investigations using a larger volume of observational material are required, for example, using only photometric redshifts.     

Structure of the galaxies of the NGC 80 group: Two-tiered disks

Two-color photometric data obtained on the 6-m telescope of the Special Astrophysical Observatory are used to analyze the structure of 13 large disk galaxies in the NGC 80 group. Nine of the 13 studied galaxies are classified as lenticular galaxies. The stellar populations in the galaxies are very diverse, from old stars with ages of T > 10 billion years (IC 1541) to relatively young stars with ages of T ∼ 1–3 billion years (IC 1548, NGC 85); in one case, star formation is ongoing (UCM 0018+2216). In most of the studied galaxies, more precisely in all of them brighter than M B ∼ −18, two-tiered stellar disks are detected, whose radial surface-brightness profiles can be described by two exponential segments with different characteristic scales—shorter near the center and longer at the periphery. All of the dwarf S0 galaxies with single-tiered disks are close companions to larger galaxies. Except for this fact, no dependence of the properties of S0 galaxies on distance from the center of the group is found. Morphological signs of a “minor merger” are found in the lenticular galaxy NGC 85. Based on these last two results, it is concluded that the most probable mechanism for their transformation of spiral into lenticular galaxies in groups is gravitational (minor mergers and tidal interactions).     

The active galaxy NGC 3862 in a compact group in the cluster A1367

We study a compact group of 18 galaxies in the cluster A1367 with redshifts z = 0.0208–0.025. The group’s center of activity in the radio is the galaxy NGC 3862, whose radio flux is an order of magnitude stronger than for the other members of the group. We present coordinates derived from the Palomar plate archive together with recessional velocities, and analyze other characteristics of the group’s galaxies. The results of 1400 MHz observations of NGC 3862 with the RATAN-600 radio telescope are presented. These observations indicate that the galaxy’s radio emission is variable.     

Supermassive black holes and galaxy kinematics

The statistical relation between the masses of supermassive black holes (SMBHs) in disk galaxies and the kinematic properties of their host galaxies is analyzed. Velocity estimates for several galaxies obtained earlier at the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences and the data for other galaxies taken from the literature are used. The SMBH masses correlate well with the rotational velocities at a distance of R ≈ 1 kpc, V ₁, which characterize the mean density of the central region of the galaxy. The SMBH masses correlate appreciably weaker with the asymptotic velocity at large distances from the center and the angular velocity at the optical radius R ₂₅. We have found for the first time a correlation between the SMBH mass and the total mass of the galaxy within the optical radius R ₂₅, M ₂₅, which includes both baryonic and “dark” mass. The masses of the nuclear star clusters in disk galaxies (based on the catalog of Seth et al.) are also related to the dynamical mass M ₂₅; the correlations with the luminosity and rotational velocity of the disk are appreciably weaker. For a given value of M ₂₅, the masses of the central cluster are, on average, an order of magnitude higher in S0-Sbc galaxies than in late-type galaxies, or than the SMBH masses. We suggest that the growth of the SMBH occurs in the forming “classical” bulge of the galaxy over a time < 10⁹ yr, during a monolithic collapse of gas in the central region of the protogalaxy. The central star clusters form on a different time scale, and their stellar masses continue to grow for a long time after the growth of the central black hole has ceased, if this process is not hindered by activity of the nucleus.     

Method for Estimating the Doppler Factors of Relativistic Radio Jets

An expression for the intensity of synchrotron emission from a radio source (in the optically thin regime) in terms of the energy densities in the magnetic field and particles is obtained, based on a definition of a relativistic electron related to its rest energy. A relationship is obtained between the energy densities in particles E_e and the magnetic field E_H for a physical system containing a magnetic field and relativistic electrons in a minimum-energy state. A method for estimating the Doppler factors of the relativistic electrons has been developed. This method does not requires that all radio sources have the same radiation energies (brightness temperatures): it is sufficient that the energies of the magnetic fields and relativistic particles in the source be approximately equal. The method yields Doppler-factor estimates with reasonably good accuracy, even when there are modest deviations from energy equipartition in the radio source,making it applicable to many radio sources. The method is used to estimate the Doppler factor of the radio jet in CTA 21.

     

Gas dynamics of a central collision of two galaxies: Merger, disruption, passage, and the formation of a new galaxy

Results of numerical simulations of a collision of the gaseous components of two identical disk galaxies during a head-on collision of the galaxies in the polar direction are presented. When the relative velocity of the galaxy collision is small, their gaseous components merge. At high relative velocities (100–500 km/s), the massive stellar components of the galaxies (M _g = 10⁹ M _⊙) pass through each other nearly freely, leaving behind the gaseous components, which are decelerated and heated by the collision. If the overall gaseous component of the colliding galaxies is able to cool to the virial temperature during the collision, a new galaxy forms. At velocities V ≥ 500 km/s, the gaseous component does not have time to cool, and the gas is scattered into intergalactic space, supplying it with heavy elements produced in supernovae in the colliding galaxies. High-velocity (V ≥ 100 km/s) collisions of identical low-mass galaxies (M _g ≤ 10⁹ M _⊙) whose mass is dominated by the mass of gas lead to the disruption of their stellar components. The overall gaseous component forms a new galaxy when V ≤ 500 km/s, and is scattered into intergalactic space if the velocity becomes higher than this. A galaxy collision increases the star-formation rates in the disk galaxies by nearly a factor of 100. Rotation of the colliding galaxies in the same direction increases the changes of the disruption of both the stellar and gaseous components of the galaxies. The merger of galaxies during their collision can explain the presence of gaseous disks rotating opposite to the rotation of the stellar component in some ordinary elliptical galaxies. Moreover, galaxy mergers can help explain the origin of a comparatively young stellar population in some elliptical galaxies.     

The motion of an emission-line region near the center of the galaxy NGC 4151

Possible orbits for the motion of a region in the gravitational field of the central body of the galaxy NGC 4151 are presented. The region is manifest through its line emission, observed in the red wing of the Hα, Pβ, and other broad lines. We carried out a computer selection of all Keplerian orbits for which the measured radial velocities of the emission-line region could be observed. We used radial-velocity data obtained by us at the Fesenkov Astrophysical Institute, as well as data from the literature. The computation results can be used to determine the mass range for the central body of NGC 4151 that provides the best agreement with the observational data: (61–65)× 10⁶ M _⊙. Suitably designed monitoring of active galactic nuclei can be used to verify these results, and to carry out similar analyses for other Seyfert galaxies.     

Star-forming regions in the ring galaxies NGC 5585 and IC 1525

We use UBVRI CCD photometry to study star-forming regions (SFRs) in the galaxies NGC 5585 and IC 1525. The observations were acquired with the 1.5-m telescope of the Mt. Maidanak Observatory of the Astronomical Institute of the Uzbek Academy of Sciences (Uzbekistan), with seeing of 0.8″–1.8″. We identified 47 SFRs in NGC 5585 and 16 SFRs in IC 1525. We estimated the ages and internal extinctions of the SFRs using the PEGASE2 evolution models. The sizes of the SFRs were also determined. We discuss in detail the techniques applied to evaluate the SFR parameters from photometric analysis. The age range for the studied SFRs is (2–40) × 10⁶ yrs, and the internal extinctions are A(V ) ≤ 1.5m. The age distributions of the SFRs in both galaxies are typical of stellar systems with intense, extended star formation. The internal extinction in the SFRs decreases with distance from the galactic centers: A(V ) ∝ −r. For both galaxies, the scale length for the decrease of the dust surface density, estimated from the A(V )−r relation for SFRs, is close to the scale length for the disk brightness decrease in the V and R bands. Relatively larger and older SFRs are observed in the galaxies’ rings, while such SFRs are not found in the spiral arms. We detected different SFR parameters for different spiral arms of NGC 5585.     

The magnetic fields and angular sizes of radio sources displaying synchrotron self-absorption

A method for estimating the magnetic-field strengths and angular sizes of radio sources displaying synchrotron self-absorption based on their observed radio spectra is considered. The method is used to derive the angular sizes of compact radio sources (components) and the magnetic fields in these regions, as well as the energy and number of relativistic electrons and the radiative power of a number of quasars and radio galaxies.     

Radio Sources in the Central Section of the RZF Catalog. Search for Objects with Ultra-Steep Spectra

Results of reducing and selecting data from the Ratan Zenith Field (RZF) are presented. A deep survey in the region 0^h ≤ R.A. ≤ 24^h, 40.5° ≤ DEC ≤ 42.5° carried out on the RATAN-600 radio telescope was used. Within +2′ of the center of the survey region, 448 objects were detected, 69 of them with ultra-steep spectra (USS). The SDSS digital optical survey (DR12), NVSS radio maps, and the FIRST catalogs have been used to cross-identify 208 radio sources from the RZF catalog, obtained as part of the “Genetic Code of the Universe” project. The characteristics of these objects are studied, and the distribution of the SDSS galaxies in a two-color diagram is obtained. Photometric redshifts and radio luminosities at 3940 and 1400 MHz are determined for 27 objects with spectral indices α < −1.1 (S ∝ ν^α) for which magnitudes in various filters are presented in the SDSS. In the sample of USS objects, 12 galaxies have redshifts z < 0.5, are detected at wavelength λ = 7.6 cm, and have relatively high radio luminosities (type FR II or intermediate type FR I–FR II). Only one radio galaxy proved to be a rare nearby galaxy with relatively low radio luminosity L_{1400 MHz} = 1.51 × 10²⁴ W/Hz (type FR I). Two objects are candidate GHz-Peaked Spectrum objects.

     

Stellar subsystems of the galaxy NGC 2366

Hubble Space Telescope archive data are used to perform photometry of stars in seven fields at the center and periphery of the galaxy NGC 2366. The variation of the number density of stars of various ages with galactocentric radius and along the minor axis of the galaxy are determined. The boundaries of the thin and thick disks of the galaxy are found. The inferred sizes of the subsystems of NGC 2366 (Z _thin = 4 kpc and Z _thick = 8 kpc for the thin and thick disks, respectively) are more typical for spiral galaxies. Evidence for a stellar halo is found at the periphery of NGC 2366 beyond the thick disk of the galaxy.     

The dynamical evolution of galaxy clusters taking into account the deceleration of disk galaxies by the gaseous component of the cluster

Numerical simulations of the dynamical evolution of a galaxy cluster in the framework of the N-body problem taking into account dark matter are presented. These simulations are aimed at studying the role of intergalactic gas in the cluster (the ICM) in the formation of a central, supermassive cD galaxy. The numerical models indicate that deceleration of the galaxies by intergalactic gas supports the observed high temperature of this gas, and accelerates the formation of a supermassive cD galaxy in the cluster core. The accretion of interstellar gas by the cluster core can support a high accretion rate by the central, supermassive black hole associated with the nucleus of the cD galaxy. As a result, this nucleus harbors a bright quasar. The mass of the black hole can grow with time to values 10¹⁰ M _⊙, as are observed for the brightest quasars.     

The cosmic vacuum and the rotation of galaxies

The rotational effect of the cosmic vacuum is investigated. The induced rotation of elliptical galaxies due to the anti-gravity of the vacuum is found to be 10⁻²¹ s⁻¹ for real elliptical galaxies. The effect of the vacuum rotation of the entire Universe is discussed, and can be described by the invariant ω _ν = ω ₀ ∼ $ \sqrt {G\rho v} $ \sqrt {G\rho v} . The corresponding numerical angular velocity of the Universe is 10⁻¹⁹ s⁻¹, in good agreement with modern data on the temperature fluctuations of the cosmic background radiation.     

The influence of the decay of OB associations on the evolution of dwarf galaxies

The ejection of stars from spheroidal and disk dwarf galaxies resulting from the decay of OB associations is studied. This has substantial observational consequences for disk galaxies with escape velocities up to 20 km/s, or dynamical masses up to 10⁸ M _⊙. The ejection of stars can (i) reduce the abundances of the products of Type Ia supernovae and, to a lesser degree, Type II supernovae, in disk stars, (ii) chemically enrich the galactic halo and intergalactic medium, (iii) lead to the loss of 50% of the stellar mass in galaxies with masses ∼10⁷ M _⊙ and the loss of all stars in systems with masses ≲10⁵ M _⊙, (iv) increase the mass-to-luminosity ratio of the galaxy.     

Search for and study of hot circumstellar dust envelopes

Long-term (1984–2008) JHKLM photometry for 254 objects is presented. The observations were carried out in the standard JHKLM photometric system using an original method and a modern IR photometer designed and built at the Sternberg Astronomical Institute. Our program of studies included searches for and studies of relatively hot circumstellar dust envelopes. The most important results obtained using these observations include the following. We have detected relatively hot dust envelopes in a number of objects for the first time, including the RCB star UV Cas, RX Cas, several classical symbiotic stars, etc. A model has been calculated for the dust envelope of FG Sge, which formed around the star as a result of several successive cycles of dust condensation beginning in Autumn 1992. Several dust-condensation episodes have been traced in the envelopes of symbiotic systems (CH Cyg, V1016 Cyg, HM Sge, etc.), as well as the role of the hot component in the formation of the dust envelopes. We have established from variations of the IR emission that the cool components in the symbiotic novae V1016 Cyg and HM Sge, and possibly CH Cyg, are Miras. The binarity of V1016 Cyg and HM Sge has also been firmly established. The variability of a whole series of object has been studied, including the stellar components of close binary systems and several dozen Mira and semi-regular variables. The ellipsoidality of the components in the RX Cas system (a prototype W Ser star) and the cool component in the symbiotic systems CI Cyg and BF Cyg has been firmly established. We have obtained the first IR light curve for the eclipsing system V444 Cyg (WN5+O6), and determined the wavelength dependence of the obtained parameters of the WN5 star. Analysis of the IR light curves of several novae indicate the condensation of dust envelopes in the transition periods of Cygnus 1992, Aquila 1993, and Aquila 1995. The IR light curve of R CrB has been obtained over a long period and analyzed. IR observations of the nova-like variable V4334 Sgr have been carried out over four years, over which the star passed through four stages during its motion along its post-AGB evolutionary track; the star’s bolometric flux and optical depth of its dust envelope have been estimated, and the structure and mass of the dust layer determined. We have analyzed the IR variability of the symbiotic star V407 Cyg over 14 years, and found its cool component to be a Mira with a period of 745 days. The observed pulsations and trend are associated with the luminosity and temperature variations of the Mira, as well as the optical depth of the dust envelope. The size of the dust grains and mass-loss rate of the Mira have been determined. We have obtained JHKL light curves for the Seyfert galaxy NGC 4151 over 23 years. The IR brightness of the galaxy grew from 1985 through 1996 (by ∼0.9 ^m at 1.25 μm, ∼1 ^m at 1.65 μm, ∼1.1 ^m at 2.2 μm, and ∼1.3 ^m at 3.5 μm), while the galaxy simultaneously reddened. The “cool” variable source in NGC 4151 was still in the active state in 1998, although its luminosity had decreased by approximately 15%–20%. If the “cool” component of the variable source in this galaxy is a dust envelope heated by the central “hot” source, it should be optically thin to the radiation of this source: its mean optical depth is in the range 0.05–0.15. Emission from dust particles heated to temperatures of 600–800 K was observed in the near IR at a distance of several parsecs from the nucleus during the period of activity in 1995–1998; the inferred mass of emitting dust was 5–20 M _⊙. In 1994–2003, we observed a tendency for NGC 4151 to become bluer at 1.25–1.65 μm while simultaneously reddening at 2.2–3.5 μm. Beginning in Autumn 2000, the galaxy began to emerge from a minimum, which lasted from March 2000 through April 2001 in the IR; a flare of the galactic nucleus was observed and followed in detail in the IR in this same period. We confirm the IR variability of the nucleus of the Seyfert galaxy NGC 1068, which can be located in various stages of activity. The variability of NGC 1068 is associated with a complex source. A periodic component has been detected in the J brightness variations of the oxygen Mira V2108 Oph; we have shown that this star is immersed in a fairly dense dust envelope, and have calculated amodel for this envelope. We have calculated an (axially symmetrical) dust-envelope model for the carbon semi-regular variable RWLMi with a density distribution characteristic for the “superwind” stage. This envelope model is able to reproduce the observed fluxes over the entire observable spectrum, and displays a good agreement with the observational data. The three hot supergiants V482 Cas, QZ Sge, and HD 338926 may be variable in the IR. Long-term photometry of eight planetary nebulae in the near IR (1.25–5 μm) has enabled us to firmly establish the IR brightness and color variability of these nebulae on time scales from several tens of days to six-to-eight years. We have analyzed long-term JK photometry of the X-ray binary Cyg X-1 (V1357 Cyg). Periodicity with a characteristic time scale of ∼11.5 years is visible in the JK brightness variations of Cyg X-1 in 1984–2007, possibly due to periodic variations of the temperature, radius and luminosity of the optical component of the binary with P ∼11.5 yr. Fourteen-year IR light curves of five RV Tau stars (R Sge, RV Tau, AC Her, V Vul, and R Sct) and the yellow supergiant and protoplanetary-nebula candidate V1027 Cyg have been analyzed. A spherically symmetrical dust-envelope model has been calculated for V1027 Cyg.     

Radio emission of the cosmic gamma-ray burst GRB 080319B: Observations of the afterglow using telescopes of the Institute of Applied Astronomy of the Russian Academy of Sciences

Results of radio observations of the cosmic gamma-ray burst GRB 080319B at 8.45 GHz during the afterglow are reported. The observations were carried out on telescopes of the Zelenchukskaya and Svetloe Observatories of the Institute of Applied Astronomy, Russian Academy of Sciences. Two outbursts in the radio brightness were detected in the afterglow of GRB 080319B. A total of 148 radio observations were performed at 3.5, 6.2, and 13 cm. The observations were conducted in a mode with smooth scanning in elevation, which was also used to update the flux densities of the primary reference sources. The first powerful radio outburst was recorded on March 28, 2008, 6.86^d after the gamma-ray burst, when the maximum flux density was F _{8.45 GHz} = 44 ± 12 mJy. Almost two months later, a second increase in the radio brightness was observed. The flux density monotonically increased from 19 mJy (59.55^d) to 34mJy (59.79^d) over 6.5 h; 1.17 d later, the flux density fell to 12mJy.At this last epoch, the radio flux demonstrated variability within 3σ on timescales of 9^d−10^d. The detected radio brightness increases are interpreted in terms of MHD interactions of a fast plasma outflow with a cloud of inhomogeneous surrounding medium. This interaction is accompanied by restructuring of the relativistic plasma outflow; the analysis of this process has been carried out.     

<Emphasis Type="Italic">UBV RI</Emphasis> CCD photometry of the nearby low-surface-brightness galaxy NGC 5585

The structure and composition of the stellar population in the low-surface-brightness galaxy NGC 5585 is studied using UBV RI CCD photometry. The observations were obtained on the 1.5-m telescope of the Maidanak Observatory of the Astronomical Institute of the Academy of Sciences of Uzbekistan under conditions with seeing 1.2″–1.8″. A two-dimensional decomposition of the galaxy emission into bulge and disk components is carried out. Both components have low surface brightnessess. The Sersic parameter for the bulge is n = 1.2–1.6. The effective radius of the bulge in R and I is equal to the scale length for the brightness decrease in the disk, and comprises 30″–40″ (0.8–1.1 kpc). The spiral arms seem to form a bar, but the centers of the bar and ring do not coincide with the center of NGC 5585. A powerful star-forming region is observed 3.2″ (100 pc) from the galactic center, whose radiation swamps the nucleus in the U and B filters. Based on the positions of the various components of the galaxy in two-color diagrams, it is concluded that NGC 5585 has a complex star-forming history that may be different at different distances from the center.