arXiv subjects

Alexander A. Marchuk

Publications and source records attributed to Alexander A. Marchuk.

At least 19 recordsLinked to original sources

arXiv2026

Projection-Enhanced Disk Breaks: Evidence from Deep Photometric Decomposition

Radial brightness profiles of disk galaxies often exhibit so-called breaks -- locations where their exponential-scale length abruptly changes. Some galaxies have downbending (Type II) breaks, where their brightness decays faster in outer regions, while other have upbending (Type III) breaks, resulting in more extended outer disks or envelopes. Disk radial profiles without any breaks (Type I) appear to constitute a minority. The exact fractions of different break types depend on many galactic parameters -- such as Hubble type, stellar mass, spatial environment, and bar presence -- and vary significantly across different studies. Another source of discrepancy is the orientation of galaxies: projection effects may play an important role in break detectability. In this work, we utilize DESI Legacy DR10 imaging to perform photometric decomposition of a sample of 375 edge-on galaxies and investigate their radial breaks. We find that the vast majority (~90%) of disks in our sample have Type II breaks, which is a considerably higher fraction than in many previous works (~50%). We carefully tested our results to check if observed breaks can be a result of flaring or two-disk composition. We showed that a high fraction of Type II breaks can be attributed to projection effects, which enhance the observed surface brightness of breaks in edge-on galaxies.

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arXiv2026

The Edge-on Galaxies in the DESI survey (EGIDE): sample building and photometry

We present the EGIDE (The Edge-on Galaxies in the DESI survey) project - a catalogue of 149,215 edge-on galaxy candidates created using the data of the DESI Legacy Imaging Survey DR10 images. The catalogue size is ten times bigger than its predecessor and covers more than half of the sky. It is constructed in an automatic way utilizing the full power of manual annotations from the GalaxyZoo volunteers, implemented in the Zoobot neural model, which was fine-tuned to search for edge-on galaxies specifically. To ensure the credibility of the dataset, subsequent manual supervision was done. The EGIDE catalogue provides homogeneous SExtractor photometry in $griz$ bands, total stellar mass estimation, redshift values for 98% of the sample, star formation rates and other information. All of this is publicly available at The Edge-on Galaxy Database site. The preliminary analysis focused on differences between edge-on galaxies in the so-called blue sequence and red cloud populations. These galaxies demonstrate distinct properties: the number of redder galaxies drops with increasing $a/b$ ratio faster than for the bluer galaxies; galaxy thickness varies with galaxy colour: red sequence galaxies are thicker than blue cloud galaxies; the flattening ratio $q=b/a$ increases with total stellar mass $M_{\star}$ for the high-mass end. It is an intriguing result, that the same trend of $q$ increasing is detected from both the statistical models of figures of revolution and direct observations of edge-on galaxies in EGIDE independently. The full extent of the validity of this relationship can only be determined after correctly accounting for the contributions of the bulge and the PSF.

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arXiv2026

A New Cartwheel-like Collisional Ring Galaxy

We report the discovery of a new Cartwheel-type collisional ring galaxy, PGC\,1112751, which we named ``Eridanus Wheel'' (EW). Such systems result from head-on collisions between galaxies and are of considerable interest as laboratories for studying star formation in propagating density waves and the response of the star-gas disk of galaxies to strong external perturbations. During a systematic visual inspection of fields from the DESI Legacy Imaging Surveys, we identified a galaxy at a redshift of $z=0.0856$ whose morphology closely resembles that of the famous Cartwheel Galaxy. EW exhibits a well-defined inner ring and a more diffuse outer ring, with so-called ``spokes'' visible in the region between them. The ring galaxy and its possible intruder are connected by a faint optical bridge. The projected distance between the centers of the galaxies is about 60 kpc. Using data from the DESI Legacy Surveys, we performed a photometric study of galaxies in the $griz$ filters. We conclude that the Eridanus Wheel is a giant late-type galaxy with a strong radial color gradient, whose observed morphology is most likely explained by a relatively recent head-on collision with an early-type galaxy. The further evolution of this object will most likely lead to the formation of a galaxy with a low surface brightness disk.

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arXiv2026

Clumps in spiral galaxies at $z \lesssim 3$: Disentangling two spatial modes of star formation

At high redshifts, star formation in galaxies is more often concentrated in clumps than in spiral arms. Although clumps are actively studied, it is rarely done considering spiral arms as objects for study as well, and the connection between clumps and spirals remains understudied. We used a sample of 159 spiral galaxies at $0.1 \leq z \leq 3.3$ observed by HST and JWST. Using the residual images from photometric models with spiral arms constructed before, which was not done previously, we have done identification of clumps and measured their properties with photometric decomposition, finding 3003 clumps in overall, and performing SED fitting for a fraction of them. We examined the overall properties of clumps, focusing on the properties of spiral structure. We found that clumps luminosities, masses and sizes are smaller than commonly accepted in literature, either for the reason spiral arms were modelled separately, or because clumps in spiral galaxies are different compared to clumpy ones. We demonstrate the connection between clumps and spirals, in particular clumps are spatially concentrated towards spirals and various parameters of clumps and spirals correlate. Also, clumps in spiral arms tend to be smaller but brighter compared to clumps in inter-arm area, but their colours are similar. There are also some differences between clumps and spirals such as colour, emphasizing the importance of their separate analysis. Our results probably indicate that spiral arms stimulate the formation of clumps, although star formation properties of clumps in spiral arms is not changed compared to inter-arm region.

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arXiv2026

Analysis of Galactic cirrus filaments in HSC-SSP high-resolution deep images using artificial neural networks

The existence of Galactic optical cirrus poses a challenge for observing faint objects within our Galaxy and dim extragalactic structures. To investigate individual cirrus filaments in the Hyper Suprime-Cam Subaru Strategic Program public data release 3 (HSC-SSP DR3) we use a technique based on convolutional neural networks and ensemble learning. This approach allows us to distinguish cirrus filaments from foreground and background objects across the entire HSC-SSP, using optical images in the $g$, $r$, and $i$ wavebands. A comparison with previous work using deep Sloan Digital Sky Survey Stripe~82 (SDSS Stripe~82) data reveals that the cirrus clouds identified in this study are highly consistent in location within the overlapping survey region. However, in the deeper HSC-SSP dataset, we were able to detect $4.5$ times more cirrus clouds. Our study indicates that the sky background in HSC-SSP coadd images is over-subtracted, as evidenced by the surface brightness distribution in cirrus filaments and surrounding regions. Objects with surface brightness of $m = 29~\mbox{mag~arcsec}^{-2}$ near large filaments can be dimmed by over-subtraction of $0.5$ magnitude in the $r$ band. This suggests that cirrus clouds should be taken into account in algorithms for estimating the sky background. For practical use, we provide a catalog of filaments and a framework that allows one to train neural network models for segmenting cirri in HSC-SSP coadd images.

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arXiv2026

Galactic disc warps from $z = 2.5$ to modern epoch: ruling out observational effects

A significant fraction of galaxies show warps in their discs, usually noticeable at its periphery. The exact origin of this phenomenon is not fully established, although multiple warp formation mechanisms are proposed. In this study, we create a sample of more than 1000 distant ($z \lesssim 2.5$) edge-on galaxies imaged by HST and JWST. For these galaxies, we measurd characteristics of warps and finally analyse how their parameters and frequency change with time. We focus on our main result that galaxies with strong warps were more prevalent in the past compared to the modern epoch. We check how selection effects and varying image quality between objects in our sample could influence our results and conclude that varying fraction of warped galaxies is not caused by observational effects, but represents a genuine evolution. Such a trend may be consistent with mergers and interactions between galaxies being the primary mechanism of warp formation, as number density of galaxies decreases with time, implying higher rate of mergers and interactions in the past.

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arXiv2026

Isochrone Fitting of Galactic Globular Clusters -- VII. NGC1904 (M79), NGC4372, and revision of NGC288, NGC362, NGC5904 (M5), NGC6205 (M13), and NGC6218 (M12)

We estimate key parameters for the Galactic globular clusters NGC1904 and NGC4372 and update the parameters for NGC288, NGC362, NGC5904, NGC6205, and NGC6218, which were analysed in our previous papers. We fit various colour-magnitude diagrams (CMDs) of the clusters using isochrones from the DSED and BaSTI. The CMDs are constructed from data sets provided by the HST, Gaia, SMSS, a large compilation of Stetson, and other sources, using multiple filters for each cluster. Our cross-identification of almost all the data sets with those from Gaia or HST allows us to use their astrometry to precisely select cluster members in all the data sets. We obtain the following estimates for NGC288, NGC362, NGC1904, NGC4372, NGC5904, NGC6205 and NGC6218, respectively: metallicities [Fe/H]$=-1.28$, $-1.26$, $-1.64$, $-2.28$, $-1.33$, $-1.56$, and $-1.27$ dex; ages $12.94$, $10.33$, $13.16$, $12.81$, $11.53$, $12.75$, and $13.03$ Gyr; distances $8.83$, $9.00$, $12.66$, $5.17$, $7.24$, $7.39$, and $4.92$ kpc; reddenings $E(B-V)=0.022$, $0.029$, $0.031$, $0.545$, $0.045$, $0.024$, and $0.210$ mag; extinctions $Av=0.09$, $0.09$, $0.11$, $1.58$, $0.13$, $0.09$, and $0.67$ mag; and extinction-to-reddening ratio $Rv=3.9$, $3.0$, $3.8$, $2.9$, $2.9$, $3.6$, and $3.2$. We confirm that the differences in horizontal branch morphology among the 16 Galactic globular clusters analysed in our studies can be explained by variations in their metallicity, age, mass-loss efficiency, and the loss of low-mass members during cluster evolution. Accordingly, most clusters indicate a relatively high mass-loss efficiency, consistent with the Reimers mass-loss law with $\eta>0.3$.

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arXiv2025

Galactic warps: from cosmic noon to the current epoch

Approximately half of all disc galaxies exhibit appreciable warps in both their stellar and HI discs. The typical warp amplitude is small (a few degrees), and only becomes noticeable at the periphery of the galaxy disc. As a result, warps remain a relatively poorly studied phenomenon. In this study, we investigate a large sample of distant edge-on galaxies (approximately 1,000 objects) in order to examine the frequency and characteristics of stellar disc warps up to a redshift of $z \sim 2$. For the selected galaxies, we utilize HST data from the Cosmic Evolution Survey field and JWST observations from the Cosmic Dawn Center Archive. We measured the properties of disc warps and investigate their evolution as a function of redshift. Our results indicate a potential evolution in the observed frequency of strong S-shaped warps (with an amplitude greater than 4$^\circ$) in stellar discs as a function of redshift. At $z \approx 2$, the frequency of strong warps reaches approximately 50%, while at $z \approx 0$, this fraction decreases to around 10-15%. We attribute the observed evolution in the occurrence of strong warps to the changing frequency of galaxy interactions and mergers. If galaxy interactions represent one of the primary mechanisms responsible for the formation of warps, then the prevalence of vertical disc deformations should increase in tandem with the rising interaction and merger rate.

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arXiv2025

Examination of the functional form of the light and mass distribution in spiral arms

Spiral arms are a common feature of local galaxies, but the exact form of the distribution of mass and light in them is not well known. In this work, we aim to measure this distribution as accurately as possible, focusing on individual spiral arms and using the so-called slicing method. The sample consists of 19 well-resolved, viewed face-on spiral galaxies from the S$^4$G survey. We work primarily with infrared images at 3.6 $\mu$m from the same survey, and, secondarily, with ultraviolet data from the GALEX telescope. We derive the properties of the spiral arms step by step, starting from their overall shape, then measuring their brightness profile and width variation along the arm, and then examining the fine structure of the profile across the arm, namely its skewness and S\'{e}rsic index. We construct a 2D photometric function of the spiral arm that can be used in further decomposition studies, validate it and identify the most and least important parameters. Finally, we show how our results can be used to unravel the nature of the spiral arms, supporting the evidence that NGC 4535 has a density wave in its disc.

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arXiv2025

Less Wound and More Asymmetric: JWST Confirms the Evolution of Spiral Structure in Galaxies at $z \lesssim 3$

Spiral galaxies are ubiquitous in the local Universe. However the properties of spiral arms in them are still not well studied, and there is even less information concerning spiral structure in distant galaxies. We aim to measure the most general parameters of spiral arms in remote galaxies and trace their changes with redshift. We perform photometric decomposition, including spiral arms, for 159 galaxies from the HST COSMOS and JWST CEERS and JADES surveys, which are imaged in optical and near-infrared rest-frame wavelengths. We confirm that, in our representative sample of spiral galaxies, the pitch angles increase, and the azimuthal lengths decrease with increasing redshift, implying that the spiral structure becomes more tightly wound over time. For the spiral-to-total luminosity ratio and the spiral width-to-disc scale length ratio, we find that band-shifting effects can be as significant as, or even stronger than, evolutionary effects. Additionally, we find that spiral structure becomes more asymmetric at higher redshifts.

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arXiv2024

Boxy/peanut shaping of a mature galactic bar in action-angle space

We study vertical resonant trapping and resonant heating of orbits. These two processes both lead to the growth of a boxy/peanut-shaped bulge in a typical $N$-body model. For the first time, we study this by means of the action variables and resonant angles of the actual orbits that compose the model itself. We used the resonant angle instead of the frequency ratio, which allowed us to clearly distinguish between these two processes in numerical simulations. We show that trapping and heating occur simultaneously, at least at the stage of a mature bar, that is, some orbits quickly pass through vertical resonance while at the same time, a substantial number of orbits remains trapped into this stage for a long time. Half of all bar orbits spend more than 2.5 Gyr in vertical resonance over an interval of 4 Gyr. Half of the orbits trapped into the bar over the last 3 Gyr of simulation remain captured in vertical resonance for more than 2 Gyr. We conclude that in the later stages of the bar evolution, the process of vertical trapping dominates in the ongoing process that causes the boxy/peanut shape of a bar in a typical $N$-body model. This contradicts the results of several recent works.

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arXiv2024

Resonance coupling in spiral arms: Patterns for flat rotation curve

To address questions about the physical nature and origin of spiral arms in galaxies, it is necessary to measure their dynamical properties, such as the angular speed, $Ω_p$, or the corotation radius. Observations suggest that galaxies may contain several independent spiral patterns simultaneously. It was shown that so-called non-linear resonance coupling plays an important role in such systems. We aim to identify cases of independent spiral patterns for galaxies with a flat rotation curve and to investigate what relative pattern velocities they might have for all possible cases of coupling between the main resonances. We solved equations for the main resonance positions (1:1, 2:1, 4:1) and estimated the ratio $\varpi$ of the corotation radii for two subsequent patterns. For six close galaxies with flat rotation curves, we collected the measurements of the corotation radii in the literature, using at least three different methods in each case for credibility. We found at least two independent spiral patterns for each galaxy and measured the $\varpi$ ratios. For three cases, we obtained $\varpi>3$, indicating that it would be difficult to fit two or even more spiral patterns in the disc. These ratios have been used to derive the wind-up time for spirals, estimated to be several galactic rotations. We find that three pairs of coupling cases, including those that have been vastly acknowledged in galaxies, namely, $OLR_{in}=CR_{out} \& CR_{in}=IUHR_{out}$, have very close $\varpi$ ratios; hence, they ought to be found simultaneously, as observed. We find a strongly confirmed apparent resonance coupling for six galaxies and we show that the observed $\varpi$ is in agreement with theory. In two of them, we identified a previously unreported form of simultaneous coupling, namely, $OLR_{in}=OUHR_{out} \& OUHR_{in}=CR_{out}$. This result was also predicted from the proximity of $\varpi$.

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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.

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arXiv2024

Galaxies decomposition with spiral arms -- II: A multiwavelength case study of M 51

Spiral structure can contribute significantly to a galaxy's luminosity. However, only rarely are proper photometric models of spiral arms used in decompositions. As we show in the previous work, including the spirals as a separate component in a photometric model of a galaxy would both allow to obtain their structural parameters, and reduce the systematic errors in estimating the parameters of other components. Doing so in different wavebands, one can explore how their properties vary with the wavelength. In this paper, second in this series, we perform decomposition of M 51 in 17 bands, from the far UV to far IR, using imaging from the DustPedia project. We use the same 2D photometric model of spiral structure where each arm is modelled independently. The complex and asymmetric spiral structure in M 51 is reproduced relatively well with our model. We analyze the differences between models with and without spiral arms, and investigate how the fit parameters change with wavelength. In particular, we find that the spiral arms demonstrate the largest width in the optical, whereas their contribution to the galaxy luminosity is most significant in the UV. The disk central intensity drops by a factor of 1.25--3 and its exponential scale changes by 5--10\% when spiral arms are included, depending on wavelength. Taking into account the full light distribution across the arms, we do not observe the signs of a long-lived density wave in the spiral pattern of M 51 as a whole.

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arXiv2024

Isochrone fitting of Galactic globular clusters -- V. NGC6397 and NGC6809 (M55)

We fit various colour-magnitude diagrams (CMDs) of the Galactic globular clusters NGC\,6397 and NGC\,6809 (M55) by isochrones from the Dartmouth Stellar Evolution Database (DSED) and Bag of Stellar Tracks and Isochrones (BaSTI) for $α$-enhanced [$α$/Fe]$=+0.4$. For the CMDs, we use data sets from {\it HST}, {\it Gaia}, VISTA, and other sources utilizing 32 and 23 photometric filters for NGC\,6397 and NGC\,6809, respectively, from the ultraviolet to mid-infrared. We obtain the following characteristics for NGC\,6397 and NGC\,6809, respectively: metallicities [Fe/H]$=-1.84\pm0.02\pm0.1$ and $-1.78\pm0.02\pm0.1$ (statistic and systematic uncertainties); distances $2.45\pm0.02\pm0.06$ and $5.24\pm0.02\pm0.18$ kpc; ages $12.9\pm0.1\pm0.8$ and $13.0\pm0.1\pm0.8$ Gyr; reddenings $E(B-V)=0.178\pm0.006\pm0.01$ and $0.118\pm0.004\pm0.01$ mag; extinctions $A_\mathrm{V}=0.59\pm0.01\pm0.02$ and $0.37\pm0.01\pm0.04$ mag; extinction-to-reddening ratio $R_\mathrm{V}=3.32^{+0.32}_{-0.28}$ and $3.16^{+0.66}_{-0.56}$. Our estimates agree with most estimates from the literature. BaSTI gives systematically higher [Fe/H] and lower reddenings than DSED. Despite nearly the same metallicity, age, and helium enrichment, these clusters show a considerable horizontal branch (HB) morphology difference, which must therefore be described by another parameter. This parameter must predominantly explain why the least massive HB stars (0.58-0.63 solar masses) are only found within NGC 6809. Probably they have been lost by the core-collapse cluster NGC\,6397 during its dynamical evolution and mass segregation. In contrast, NGC\,6809 has a very low central concentration and, hence, did not undergo this process.

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arXiv2023

A multiwavelength study of spiral structure in galaxies. II. Spiral arms in deep optical observations

In this paper, we look to analyse the spiral features of grand-design, multiarmed, and flocculent spiral galaxies using deep optical imaging from DESI Legacy Imaging Surveys. We explore the resulting distributions of various characteristics of spiral structure beyond the optical radius, such as the distributions of azimuthal angle, the extent of spiral arms, and of the spiral arm widths for the aforementioned galaxy classes. We also compare the measured properties for isolated galaxies and galaxies in groups and clusters. We find that, on average, compared to multiarmed and flocculent spiral galaxies, the spiral arms of grand-design galaxies exhibit slightly larger azimuthal angles, greater extent, and larger widths in the periphery of the galaxy. Furthermore, on average, isolated galaxies tend to have slightly smaller widths of outer spiral arms compared to galaxies in tight environments, which is likely related to the tidally-induced mechanism for generating wider outer spiral arms. We also report that breaks of the disc surface brightness profiles are often related to the truncation of spiral arms in galaxies.

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arXiv2023

Galaxies decomposition with spiral arms -- II: 29 galaxies from S$^4$G

Spiral structure can occupy a significant part of the galaxy, but properly accounting for it in photometric decomposition is rarely done. This may lead to significant errors in the parameters determined. To estimate how exactly neglecting the presence of spiral arms affects the estimation of galaxy decomposition parameters, we perform fitting of 29 galaxies considering spiral arms as a separate component. In this study, we utilize 3.6$μ$m-band images from the S$^4$G survey and use a new 2D photometric model where each spiral arm is modeled independently. In our model, the light distribution both along and across the arm can be varied significantly, as well as its overall shape. We analyze the differences between models with and without spiral arms, and show that neglecting spiral arms in decomposition causes errors in estimating the parameters of the disk, the bulge, and the bar. We retrieve different parameters of the spiral arms themselves, including their pitch angles, widths, and spiral-to-total luminosity ratio, and examine various relations between them and other galaxy parameters. In particular, we find that the spiral-to-total ratio is higher for galaxies with more luminous discs and with higher bulge-to-total ratios. We report that the pitch angle of spiral arms decreases with increasing bulge or bar fraction. We measure the width of the spiral arms to be 53\% of the disc scale length, on average. We examine the contribution of the spiral arms to the azimuthally-averaged brightness profile and find that spiral arms produce a ``bump'' on this profile with a typical height of 0.3--0.7 mag.

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arXiv2023

A new, purely photometric method for determination of resonance locations in spiral galaxies

The knowledge of the positions of the corotation resonance in spiral arms is a key way to estimate their pattern speed, which is a fundamental parameter determining the galaxy dynamics. Various methods for its estimation have been developed, but they all demonstrate certain limitations and a lack of agreement with each other. Here, we present a new method for estimating the corotation radius. This method takes into account the shape of the profile across the arm and its width and, thus, only photometric data is needed. The significance of the method is that it can potentially be used for the farthest galaxies with measurable spiral arms. We apply it to a sample of local galaxies from Savchenko et al. and compare the obtained corotation radii with those previously measured in the literature by other methods. Our results are in good agreement with the literature. We also apply the new method to distant galaxies from the COSMOS field. For the first time, corotation locations for galaxies with photometric redshifts up to $z\sim0.9$ are measured.

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