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Alexander S. Gusev

Publications and source records attributed to Alexander S. Gusev.

15 recordsLinked to original sources
arXiv2024

Cross-method analysis of co-rotation radii dataset for spiral galaxies

A co-rotation radius is a key characteristic of disc galaxies that is essential to determine the angular speed of the spiral structure $Ω_{p}$, and therefore understand its nature. In the literature, there are plenty of methods to estimate this value, but do these measurements have any consistency? In this work, we collected a dataset of corotation radius measurements for 547 galaxies, 300 of which had at least two values. An initial analysis reveals that most objects have rather inconsistent corotation radius positions. Moreover, a significant fraction of galactic discs is distinguished by a large error coverage and almost uniform distribution of measurements. These findings do not have any relation to spiral type, Hubble classification, or presence of a bar. Among other reasons, obtained results could be explained by the transient nature of spirals in a considerable part of galaxies. We have made our collected data sample publicly available, and have demonstrated on one example how it could be useful for future research by investigating a winding time value for a sample of galaxies with possible multiple spiral arm patterns.

astro-ph.GA↗
arXiv2023

Regular chains of star formation regions in spiral arms and rings of disk galaxies

The regularity in the distribution of young stellar groups along the spiral arms of galaxies, first discovered by Bruce and Debra Elmegreen in 1983, was considered a rather rare phenomenon. However, recent studies of the spatial regularities in the distribution of the young stellar populations along the arms of the spiral galaxies NGC 628, NGC 895, NGC 4321, NGC 5474, NGC 6946, as well as along the rings of the spiral galaxy NGC 6217 and the lenticular galaxy NGC 4324, have revealed that this spatial (quasi) regularity and/or the presence of regular chains of star-forming regions is a fairly common phenomenon. Across all galaxies, the characteristic regularity scale is 350-500 pc or a multiple thereof. It should be noted that theoretical models predict an instability scale of a stellar-gas disk on the order of a few kpc, which is several times larger than what has been observed. The paper is partly based on the report presented at the Modern Stellar Astronomy 2022 Conference held at the Caucasian Mountain Observatory of the Sternberg Astronomical Institute, Moscow State University, on November 8-10, 2022.

astro-ph.GA↗
arXiv2022

Spatial regularity of the young stellar population in spiral arms of late type galaxies NGC 895, NGC 5474, and NGC 6946

We investigate the spatial regularity in the distribution of the young stellar population along spiral arms of three late type spiral galaxies: NGC 895, NGC 5474, and NGC 6946. This study is based on an analysis of photometric properties of spiral arms using {\it GALEX} ultraviolet, optical UBVRI, Halpha, and 8mum {IRAC} infrared surface photometry data. Using the Fourier analysis approach, we found features of spatial regularity or quasi-regularity in the distribution of the young stellar population or (and) regular chains of star formation regions in all arms of NGC 895, NGC 5474, and NGC 6946 with characteristic scales of spacing from 350 to 500 pc in different arms, and (or) scales which are multiples of them. These characteristic scales are close to the those found earlier in NGC 628, NGC 6217, and M100.

astro-ph.GA↗
arXiv2021

Peculiarities of the chemical abundance distribution in galaxies NGC 3963 and NGC 7292

Spectroscopic observations of 32 HII regions in the spiral galaxy NGC 3963 and the barred irregular galaxy NGC 7292 were carried out with the 2.5-m telescope of the Caucasus Mountain Observatory of the Sternberg Astronomical Institute using the Transient Double-beam Spectrograph with a dispersion of 1A/pixel and a spectral resolution of 3A. These observations were used to estimate the oxygen and nitrogen abundances and the electron temperatures in HII regions through modern strong-line methods. In general, the galaxies have oxygen and nitrogen abundances typical of stellar systems with similar luminosities, sizes, and morphology. However, we have found some peculiarities in chemical abundance distributions in both galaxies. The distorted outer segment of the southern arm of NGC 3963 shows an excess oxygen and nitrogen abundances. Chemical elements abundances in NGC 7292 are constant and do not depend on the galactocentric distance. These peculiarities can be explained in terms of external gas accretion in the case of NGC 3963 and major merging for NGC 7292.

astro-ph.GA↗
arXiv2020

Spatial regularity of the young stellar population in the ring of NGC 6217

The relative contribution of various physical processes to the spatial and temporal distribution of molecular clouds and star-forming regions in the disks of galaxies has not been fully studied. The spatial regularity in the distribution of the young stellar population in spiral and ring structures is a good test to study this contribution. We investigate photometric properties of the ring and spiral arms in the barred spiral galaxy NGC 6217 based on analysis of GALEX ultraviolet, optical UBVRI and Halpha surface photometry data. The ring in the galaxy is located near the corotation area. A spatial regularity in the distribution of the young stellar population along the galaxy ring was found. The characteristic scale of spacing is about 700 pc. At the same time, we did not find a similar regularity in the distribution of the young stellar population along the spiral arms of NGC 6217. The spatial regularity in concentration of young stellar groupings along spiral arms is a quite rare phenomenon, and it has never been found before in galactic rings.

astro-ph.GA↗
arXiv2019

Propagation of star formation at sub-kiloparsec scales

We study the propagation of star formation based on the investigation of the separation of young star clusters from HII regions nearest to them. The relation between the separation and U-B colour index (or age) of a star cluster was found. The average age of star clusters increases with the separation as the 1.0-1.2 power in the separation range from 40 to 200 pc and as the 0.4-0.9 power in the range of 100-500 pc in the galaxies with symmetric morphology. The galaxies with distorted asymmetric disc structure show more complex and steeper (power >1.2 at separations from 40 to 500 pc) dependence between the age and the separation. Our results confirm the findings of previous studies on the dominant role of turbulence in propagation of the star formation process on spatial scales up to 500 pc and on time scales up to 300 Myr. On a smaller scale (=<100 pc), other physical processes, such as stellar winds and supernova explosions, play an important role along with turbulence. On the scale of stellar associations (100-200 pc and smaller), the velocity of star formation propagation is almost constant and it has a typical value of a few km/s.

astro-ph.GA↗
arXiv2015

Studies of the stellar populations of galaxies using two-color diagrams

Variations in the photometric parameters of stellar systems as a function of their evolution and the stellar populations comprising them are investigated. A set of seven evolutionary models with an exponential decrease in the star-formation rate and 672 models with a secondary burst of star formation are considered. The occurrence of a secondary burst of star formation can shift the position of a stellar system on two-color diagrams to the right or left of the normal color sequence for galaxies and the extinction line. This makes it possible to estimate the composition of the stellar population of a galaxy with a nonmonotonic star formation history from its position on two-color diagrams. Surface photometry in both the optical (UBVRI) and near-IR (JHK) is used to study the stellar populations and star-formation histories in the structural components (nucleus, bulge, disk, spiral arms, bar, ring) of 26 galaxies of various morphological types (from S0 to Sd). Components (nucleus, bulge, bar) with color characteristics corresponding to stellar systems with secondary bursts of star formation are indicated in 10 of the 26 galaxies. The parameters of these secondary bursts are estimated. Five of the 10 galaxies with complex star-formation histories display clear structural perturbations. Appreciable differences in the photometric characteristics of relatively red early-type galaxies (S0-Sb) and relatively blue later-type galaxies (Sb-Sd) have been found. Galaxies of both early and late types are encountered among the Sb-galaxies. Lenticular galaxies do not display different photometric characteristics from early-type spiral galaxies.

astro-ph.GA↗
arXiv2015

Star formation rates and the kinematics of gas in the spiral arms of NGC 628

Relations between star formation rates along the spiral arms and the velocities of gas inflow into the arms in grand-design galaxy NGC 628 were studied. We found that the radial distribution of average star formation rate in individual star formation regions in regular spiral arms correlates with the velocity of gas inflow into the spiral arms. Both distributions have maxima at a galactocentric distance of 4.5-5 kpc. There are no correlations between the radial distributions of average star formation rate in star formation regions in spiral arms and outside spiral arms in the main disc. We also did not find a correlation between the radial distribution of average star formation rate in star formation regions in spiral arms and HI column density.

astro-ph.GA↗
arXiv2014

Hierarchy and size distribution function of star formation regions in the spiral galaxy NGC 628

Hierarchical structures and size distribution of star formation regions in the nearby spiral galaxy NGC 628 are studied over a range of scale from 50 to 1000 pc using optical images obtained with 1.5 m telescope of the Maidanak Observatory. We found hierarchically structured concentrations of star formation regions in the galaxy, smaller regions with a higher surface brightness are located inside larger complexes having a lower surface brightness. We illustrate this hierarchy by dendrogram, or structure tree of the detected star formation regions, which demonstrates that most of these regions are combined into larger structures over several levels. We found three characteristic sizes of young star groups: 65 pc (OB associations), 240 pc (stellar aggregates) and 600 pc (star complexes). The cumulative size distribution function of star formation regions is found to be a power law with a slope of approximately -1.5 on scales appropriate to diameters of associations, aggregates and complexes. This slope is close to the slope which was found earlier by B. Elmegreen et al. for star formation regions in the galaxy on scales from 2 to 100 pc.

astro-ph.GA↗
arXiv2013

Parameters of the brightest star formation regions in the two principal spiral arms of NGC 628

We study photometric properties, chemical abundances and sizes of star formation regions in the two principal arms of the galaxy NGC 628 (M74). The GALEX ultraviolet, optical UBVRI, and H-alpha? surface photometry data are used, including those obtained with the 1.5-m telescope of the Maidanak Observatory. The thirty brightest star formation regions in ultraviolet light located in the spiral arms of NGC 628 are identified and studied. We find that the star formation regions in one (longer) arm are systematically brighter and larger than the regions in the other (shorter) arm. However, both luminosity and size distribution functions have approximately the same slopes for the samples of star formation regions in both arms. The star formation regions in the longer arm have a higher star formation rate density than the regions in the shorter arm. The regions in the shorter arm show higher N/O ratio at a higher oxygen abundance, but they have lower ultraviolet and H-alpha? luminosities. These findings can be explained if we assume that star formation regions in the shorter arm had higher star formation rate in the past, but now it is lower than for those in the opposite arm. Results of stellar evolutionary synthesis show that the brightest regions in the longer arm are slightly younger than the ones in the shorter arm (3.5+-2.2 Myr versus 6.0+-1.1 Myr). Our results demonstrate that there is a difference in the inner structures and parameters of the interstellar medium between the spiral arms of NGC 628, one of which is long and hosts a regular chain of bright star formation complexes and the other, shorter one does not.

astro-ph.GA↗
arXiv2013

Regular chains of star formation complexes in spiral arms of NGC 628

We investigate photometric properties of spiral arms and stellar complexes/associations inside these arms in the grand design NGC 628 (M74) galaxy.We analyze GALEX ultraviolet, optical UBVRI, and H-alpha? surface photometry data, including those obtained with 1.5 m telescope at the Maidanak Observatory. In the longer arm, the large and bright stellar complexes are located at regular intervals along the arm, but only farther from the galaxy center. They are joined with the narrow lane of dust, visible only in the infrared bands. The usual dust lane along the stellar arm inner side is seen there only at distances closer to the galaxy center. It is well expressed in CO (H_2) image. We have found, that the second, short arm hosts two dust lanes, the strong and wide at the inner side, and narrow and irregular along its outer edge. This outer dust lane is well seen in IR images only. The shorter arm contains no star complexes at all. Gradients of age and luminosity of stars across both arms are missing (again excepting the parts of arms located closer to the center), which is confirmed by our photometric cuts across both arms. The drastic difference in the morphology of the two symmetric arms (grand design type) of a galaxy has now been confirmed by objective measurements in the case of M74. It is unclear why about two third of galaxies with beaded arms host these "beads" (star complexes) in one arm only.

astro-ph.CO↗
arXiv2013

Parameters of galactic disks at optical and NIR wavelengths

We have analyzed the radial scales, central surface brightnesses, and colors of 404 disks of various types of galaxies. The central surface brightness mu0 and linear disk scale length h vary smoothly along the Hubble sequence of galaxies within a rather narrow interval. The disks of relatively early type galaxies display higher central surface brightnesses in K, higher central surface densities, smaller sizes (relative to the diameter of the galaxy), redder integrated and central colors. The color gradient normalized to the radius of the galaxy and the blue central surface brightness mu0_{0,i}(B) of the disk, are both independent of the galaxy type. The radial disk scales in different photometric bands differ less in early-type than in late-type galaxies. The ratio of linear disk scales measured in different photometric bands increases with the isophote ellipticity e of the disk (the inclination of the galaxy); however, the range of the ratio values for each e value exceeds the range of variations of scale lengths ratio over e. The disks in S0 galaxies have more homogeneous parameters than those in spiral galaxies. However, no sharp boundary in the properties of disks in lenticular, spiral, and irregular galaxies has been found; all parameters vary smoothly along the Hubble sequence. A correlation between the central disk surface brightness and the total luminosity of the galaxy is observed. We also consider the influence of dust on the photometric parameters of the disks. We show that the dust concentrated in dust lines towards the spiral arms and bars does not influence to the scale lengths ratio.

astro-ph.CO↗
arXiv2013

Spectroscopy of H II Regions in the Late-Type Spiral Galaxy NGC 6946

We present the results of spectroscopy of 39 H II regions in the spiral galaxy NGC 6946. The spectral observations were carried out at the 6-m BTA telescope of the SAO RAS with the SCORPIO focal reducer in the multi-slit mode with the dispersion of 2.1A/px and spectral resolution of 10A. The absorption estimates for 39 H II regions were obtained. Using the "strong line" method (NS-calibration) we determined the electron temperature, and the abundances of oxygen and nitrogen for 30 H II regions. The radial gradients of O/H and N/H were constructed.

astro-ph.CO↗
arXiv2012

Oxygen and nitrogen abundances of HII regions in six spiral galaxies

Spectroscopic observations of 63 HII regions in six spiral galaxies (NGC 628, NGC 783, NGC 2336, NGC 6217, NGC 7331, and NGC 7678) were carried out with the 6-meter telescope (BTA) of Russian Special Astrophysical Observatory with the Spectral Camera attached to the focal reducer SCORPIO in the multislit mode with a dispersion of 2.1A/pixel and a spectral resolution of 10A. These observations were used to estimate the oxygen and nitrogen abundances and the electron temperatures in HII regions through the recent variant of the strong line method (NS calibration). The parameters of the radial distribution (the extrapolated central intercept value and the gradient) of the oxygen and nitrogen abundances in the disks of spiral galaxies NGC 628, NGC 783, NGC 2336, NGC 7331, and NGC 7678 have been determined. The abundances in the NGC 783, NGC 2336, NGC 6217, and NGC 7678 are measured for the first time. Galaxies from our sample follow well the general trend in the luminosity - central metallicity diagram for spiral and irregular galaxies.

astro-ph.CO↗