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The theory of galaxy formation posits a clear correlation between the spin of galaxies and the orientation of the elements of the large-scale structure of the Universe, particularly cosmic filaments. A substantial number of observational and modelling studies have been undertaken with the aim of identifying the dependence of spin orientation on the components of the large-scale structure. However, the findings of these studies remain contradictory. In this paper, we present an analysis of the orientation of the spins of 2 861 galaxies with respect to the filaments of the large-scale structure of the Universe. All galaxies in our sample have an inclination to the line of sight greater than 85 degrees, enabling an unambiguous determination of the spin axis direction in space. We investigate the alignment of galaxy spin axes relative to cosmic web filaments as a function of various properties for galaxies. Our results reveal a statistically significant tendency for the galaxy spin axes to align along the filament axes of the large-scale structure.
We compare the properties of stellar populations for globular clusters (GCs) and field stars in two dwarf spheroidal galaxies (dSphs): ESO269-66, a close neighbour of NGC5128, and KKs3, one of the few isolated dSphs within 10 Mpc. We analyse the surface density profiles of low and high metallicity (blue and red) stars in two galaxies using the Sersic law. We argue that 1) the density profiles of red stars are steeper than those of blue stars, which evidences in favour of the metallicity and age gradients in dSphs; 2) globular clusters in KKs3 and ESO 269-66 contain 4 and 40 percent of all stars with [Fe / H] ~ 1.6 dex and the age of 12 Gyr, correspondingly. Therefore, GCs are relics of the first powerful star-forming bursts in the central regions of the galaxies. KKs 3 has lost a smaller percentage of old low-metallicity stars than ESO269-66, probably, thanks to its isolation.
We present a database of galaxies in the Local Volume (LV) (https://www.sao.ru/lv/lvgdb/) Kaisina et al. (2012) having individual distance estimates within 11Â Mpc or corrected radial velocities VLG < 600 km s-1. It collects data on the following galaxy observables: angular diameters, apparent magnitudes in far-UV, B, and Ks bands, Hα and HI fluxes, morphological types, HI -line widths, radial velocities, and distance estimates. It also contains a consolidated set of optical images of all the galaxies from the SDSS and DSS surveys and Hα images of galaxies that were derived with the 6-m BTA telescope. The latest version of the Updated Nearby Galaxy Catalog (UNGC) Karachentsev et al. (2013) contains 869 objects, now the database consist of 1175 objects. We present basic relations, describing the updated LV sample: Hubble flow, distribution galaxies according to their distance estimates and on the sky, et al.
Using high accuracy distance estimates, we study the three-dimensional distribution of galaxies in five galaxy groups at a distance less than 5 Mpc from the Milky Way. Due to proximity of these groups our sample of galaxies is nearly complete down to extremely small dwarf galaxies with absolute magnitudes MB = -12. We find that the average number-density profile of the groups shows a steep power-law decline dn/dV ∼ R-3 at distances R=(100–500) kpc consistent with predictions of the standard cosmological model. We also find that there is no indication of a truncation or a cutoff in the density at the expected virial radius: the density profile extends at least to 1.5 Mpc. Vast majority of galaxies within 1.5 Mpc radius around group centres are gas-rich star-forming galaxies. Early-type galaxies are found only in the central ∼ 300 kpc region. Lack of dwarf spheroidal and dwarf elliptical galaxies in the field and in the outskirts of large groups is a clear indication that these galaxies experienced morphological transformation when they came close to the central region of forming galaxy group.
We study the correlations of rotation velocity and absolute magnitude with surface brightness for low surface brightness dwarf irregular galaxies (dIrrs). We find that isolated objects contribute most to the scatter in the Tully–Fisher relation (TFR). Excluding these extreme cases, we develop a three-parameter (luminosity, Hi line width at 20% of peak flux level, i.e., W20, effective surface brightness) TFR for 60 dIrrs (with revised Hubble type T > 8) in the Local Volume (LV) with Cepheid and tip-of-the-red-giant-branch distance measurements. The relation is applied to galaxies of the same morphological type with radial velocities vLG ≤ 3500 km s−1 in the Local Supercluster. We obtained surface photometry and determined structural parameters using sdss images. The rotational velocities and derived photometric parameters for most galaxies in small groups agree well with those corresponding to the three-parameter TFR. However, isolated galaxies appear to have systematically lower surface brightnesses and longer scale lengths for the same luminosity than galaxies in small groups. This may indicate on average twice larger Hi-to-optical disk size ratios for our sample of isolated dIrrs, because their Hi surface densities calculated using the optical diameters look normal.
We present a study of two dE/dSph members of the nearby M 81 group of galaxies, KDG 61 and KDG 64. Direct HST/ACS images and integrated-light spectra of 6 m telescope of Special Astrophysical Observatory (Russia) have been used for quantitative star formation history analysis. The spectroscopic and colour-magnitude diagrams analysis gives consistent results. These galaxies appear to be dominated by an old population (12–14 Gyr) of low metallicity ([Fe/H] ∼−1.5). Stars of ages about 1 to 4 Gyr have been detected in both galaxies. The later population shows marginal metal enrichment. Our radial velocity measurement suggests that the HII knot on the line-of-sight of KDG 61 is not gravitationally attached to the galaxy.
We present a project on study of groups composed of dwarf galaxies only. We selected such structures using HyperLEDA and NED databases with visual inspection on SDSS images and on digital copy of POSS. The groups are characterized by size of few tens of kpc and line-of-sight velocity dispersion about 18 km s−1. Our groups similar to associations of nearby dwarfs from Tully et al. (2006). This specific population of multiple dwarf galaxies such as I Zw 18 may contain significant amount of dark matter. It is very likely that we see them at the stage just before merging of its components.
We ask if Earth-like planets (terrestrial mass and habitable-zone orbit) can be detected in multi-planet systems, using astrometric and radial velocity observations. We report here the preliminary results of double-blind calculations designed to answer this question.
Demonstration of matching a laser ion source to the GSI RFQ-Maxilac linear accelerator and the acceleration of a 1.8-mA current beam of Ta10+ ions up to 45 keV/u energy is presented. A 10J/μs CO2 laser has been used to produce a hot plasma plume, emitting highly charged tantulum ions. The correct geometry and potential distribution of the matching section has been designed in accordance with the results of computer simulations by using the AXCEL code. Measurements of the charge state distribution of the accelerated beam indicate that it contains about 70% Ta10+ and 30% Ta11+ ions.
We consider the star formation properties of dwarf galaxies in the Cen A group observed within our HST/ACS projects number 9771 and 10235. We model color-magnitude diagrams of the galaxies under consideration and measure star formation rate and metallicity dependence on time. We study the environmental dependence of the galaxy evolution and probable origin of the dwarf galaxies in the group.
Searching for lopsided/interacting objects among 1500 isolated galaxies yields only eight strongly disturbed galaxies which may be explained as a result of their interaction with massive dark objects. We present results of spectral and photometric observations of these galaxies performed with the 6-m telescope that lead to significant restriction on cosmic abundance of dark galaxies.
1. The data. We study detailed star formation histories (SFH) of 14 dwarf galaxies in the central parts (≤ 300 Kpc) of the two nearby galaxy groups: M 81 (D=3.6 Mpc) and Cen A (D = 3.8 Mpc). The images of 7 galaxies were selected from the sample of about 50 nearby dwarf galaxies observed with the Advanced Camera for Surveys (ACS) at the Hubble Space Telescope within our prog. 9771 & 10235, (PI I.Karachentsev). The rest of the images (ACS and WFPC2) were taken from the Hubble Archive (prog. 9884, 5898 and 6964).
Over the last five years, enormous progress in accurate distance measurements for nearby galaxies has been attained. The Hubble Space Telescope allows us to estimate distances of about 7–10% accuracy using red giant branch (RGB) up to 8 Mpc. Now we have very accurate distances for more than 200 galaxies within ~6 Mpc.
We derive quantitative star formation histories (SFH) of the two dwarf spheroidal (KK 197 and ESO 269-066) and one dwarf irregular (ESO 381-018) galaxies in the nearby Centaurus A group. The data are part of our sample of about 50 nearby dwarf galaxies observed with the Advanced Camera for Surveys (ACS) at the Hubble Space Telescope (prog. 9771 & 10235, PI I.Karachentsev). Deep color-magnitude diagram (CMD) of KK 197 is shown in Fig.1.
The Kislovodsk series of the green (FeXIV 530.3 nm; KI$_{5303}$) and red (FeX 637.4 nm; KI$_{6374}$) corona has been used to calculate the mean monthly intensities at high latitude (45$^\circ$–90$^\circ$) zones for 1957–2002. The ratio KI$_{6374}$/KI$_{5303}$ was observed during the minimum sunspot activity. It was shown that this ratio increased by more than a factor 2 during the last 45 years at the high latitudes (45$^\circ$–90$^\circ$). This may be interpreted that the fraction of cool regions in the polar corona has more than doubled over these years. We suggest that this increase in the amount of cool regions is related to the increase in the area of the polar zones occupied by magnetic field of a single polarity at the solar minimum and possibly to a corresponding increase in the area occupied by polar coronal holes, while the magnetic field strength itself has not or barely increased.
We report studies of the temperature dependence of Raman lines in high quality GaN and AlN. The temperature dependence of the phonon energies and linewidths are used to produce consistent phonon decay properties of zone center optic phonons. In GaN we observe the E22 phonon to decay into three phonons, while the A1(LO) phonon is well described according to the so-called Ridley process – one TO and one LA phonon. For AlN the E22 phonon decays by two phonon emission and the A1(LO) line also exhibits a dependence consistent with the Ridley process. Along with the phonon decay processes, it is important in each case to take into account the contribution of the thermal expansion, including the temperature dependence, to describe observed temperature shifts in the phonon properties.
We study properties of globular cluster candidates (GCCs) and the diffuse stellar populations in nearby low surface brightness dwarf galaxies, using HST WFPC2 photometry in the V and I bands. Our sample consists of 18 dwarf spheroidal (dSph), 36 dwarf irregular (dIrr), and 3 transition-type galaxies, with projected linear diameters less than 3.5 kpc and mean blue surface brightness $>23$ mag/arcsec$^2$ situated at the distance 2–6 Mpc in the field and in nearby groups. Our sample dwarf spheroidal galaxies were not detected in HI and are located at the distances of up to $\sim$1 Mpc away from a nearby bright galaxy. Transition-type galaxies, which are distributed like dSph galaxies, form a very rare class of galaxies. dIrr galaxies show a weaker concentration to the nearest massive neighbors than dSph and transition-type galaxies. At a given surface brightness and luminosity, they exhibit lower mean metallicities than dSphs. In contrast to dIrr galaxies, the majority of dSph galaxies at a similar mean surface brightness contains GCCs. The percentage of GCCs located near the centers of dSph galaxies is much higher than that for dIrr galaxies. The composite population of GCCs in dSphs is spatially more concentrated than in dIrr galaxies. The color distributions of GCCs in dSph and dIrr galaxies show major differences. While the latter shows obvious bimodality with the peaks near $(V-I)_0 \sim 0.5$ and $\sim$1.0 mag, the GCC color distribution in dSph galaxies shows only one peak with a mean color $(V-I)_0 \sim 1.0$ mag. There is a tendency of increasing half-light radii with increasing projected galactocentric distances for a large number of GCCs in dSph galaxies, which is also observed in the Galactic globular cluster system. We embarked on a spectroscopic survey of GCCs in low-mass galaxies to obtain their chemical compositions and relative ages.
Until very recently, our knowledge of the local peculiar velocity field has been severely hampered by the lack of reliable distance measurements. HST has dramatically changed this situation, allowing astronomers to obtain accurate distances to more than 150 nearby galaxies. This number could easily reach 400 if enough observing time would be dedicated to snapshot observation of the objects in the catalog of Karachentsev et al (2004). Such a dense grid of objects correctly placed in their 3D position would provide key information on the amplitude of peculiar motions, the radial domain of bound groups, the clustering and morphological segregation properties of galaxies, and the incidence of extreme dwarfs galaxies. The key instrument to measure distances with HST is the Tip of the Red Giant Branch technique. The full exploitation of this powerful distance estimator requires a deeper understanding of the possible sources of errors and biases, such as the absolute calibration of the I-band magnitude of the tip and its dependency on age and metallicity of the underlying population, the possible contamination by AGB stars, the breakdown of the methodology in sparsely populated colour-magnitude diagrams and when the tip is close to the photometric limit.
Si/Ge multilayer structures formed by the deposition of relatively small amounts of Ge layers (less then the critical thickness for 3D islands formation) are obtained by molecular beam epitaxy. Their structural and optical properties are investigated in detail. Appropriate growth parameter of the stacked island structures lead to significant increasing of the luminescence efficiency even at room temperature.
Recently, an advanced technique for growing free-spreading SiC bulk crystals by sublimation has been demonstrated. This method was used to grow 6H- and 4H-SiC boules free of polycrystalline deposits on the crystal periphery, up to 35 mm in diameter with the micropipe density less than 20 cm-2 and the dislocation density about 102-103 cm-2. In this paper, we report on the numerical modeling of free-spreading crystal growth. We consider the global heat transfer in an inductively heated growth system, species transport in the growth cell and in the powder charge, and thermoelastic stress, focusing on the crystallization front dynamics, poly-SiC deposition, and powder source evolution. Special attention was given to the validation of the simulations. The computed thermal field and evolution of the powder and crystal shape were found to agree qualitatively with observations.