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To understand the origin of extended disks of low-surface brightness (LSB) galaxies, we studied in detail 4 such systems with large disks seen edge-on. Two of them are edge-on giant LSB galaxies (gLSBGs) recently identified by our team. The edge-on orientation of these systems boosts their surface brightnesses that provided an opportunity to characterize stellar populations spectroscopically and yielded the first such measurements for edge-on gLSBGs. We collected deep images of one galaxy using the 1.4-m Milankovi\'c Telescope which we combined with the archival Subaru Hyper Suprime-Cam and DESI Legacy Surveys data available for the three other systems, and measured the structural parameters of the disks. We acquired deep long-slit spectra with the Russian 6-meter telescope and the 10-m Keck II telescope and estimated stellar population properties in the high- and low-surface brightness regions as well as the gas-phase metallicity distribution. The gas metallicity gradients are shallow to flat in the range between 0 and -0.03 dex per exponential disk scale length, which is consistent with the extrapolation of the gradient -- scale length relation for smaller disk galaxies. Our estimates of stellar velocity dispersion in the LSB disks as well as the relative thickness of the disks indicate the dynamical overheating. Our observations favor mergers as the essential stage in the formation scenario for massive LSB galaxies., Comment: 21 pages, 12 figures, accepted for publication in ApJ

We present re-processed flux calibrated spectra of 406 stars from the UVES-POP stellar library in the wavelength range 320-1025 nm, which can be used for stellar population synthesis. The spectra are provided in the two versions having spectral resolving power R=20,000 and R=80,000. Raw spectra from the ESO data archive were re-reduced using the latest version of the UVES data reduction pipeline with some additional algorithms that we developed. The most significant improvements in comparison with the original UVES-POP release are: (i) an updated Echelle order merging, which eliminates "ripples" present in the published spectra, (ii) a full telluric correction, (iii) merging of non-overlapping UVES spectral setups taking into account the global continuum shape, (iv) a spectrophotometric correction and absolute flux calibration, and (v) estimates of the interstellar extinction. For 364 stars from our sample, we computed atmospheric parameters $T_\mathrm{eff}$, surface gravity log $g$, metallicity [Fe/H], and $\alpha$-element enhancement [$\alpha$/Fe] by using a full spectrum fitting technique based on a grid of synthetic stellar atmospheres and a novel minimization algorithm. We also provide projected rotational velocity $v\sin i$ and radial velocity $v_{rad}$ estimates. The overall absolute flux uncertainty in the re-processed dataset is better than 2% with sub-% accuracy for about half of the stars. A comparison of the recalibrated UVES-POP spectra with other spectral libraries shows a very good agreement in flux; at the same time, $Gaia$ DR3 BP/RP spectra are often discrepant with our data, which we attribute to spectrophotometric calibration issues in $Gaia$ DR3., Comment: 26 pages, 19 figures, accepted for publication in ApJS

Rare giant low surface brightness galaxies (gLSBGs) act as a stress test for the current galaxy formation paradigm. To answer the question `How rare are they?' we estimate their volume density in the local Universe. A visual inspection of 120~sq.~deg. covered by deep Subaru Hyper Suprime-Cam data was performed independently by four team members. We detected 42 giant disky systems (30 of them isolated) at $z\leq0.1$ with either $g$-band 27.7~mag~arcsec$^{-2}$ isophotal radius or four disc scalelengths $4h \geq 50$~kpc, 37 of which (including 25 isolated) had low central surface brightness ($\mu_{0,g}\ge 22.7$ mag~arcsec$^{-2}$). This corresponds to volume densities of 4.70$\times 10^{-5}$ Mpc$^{-3}$ for all galaxies with giant extended discs and 4.04$\times 10^{-5}$ Mpc$^{-3}$ for gLSBGs, which converts to $\sim $12,700 such galaxies in the entire sky out to $z<0.1$. These estimates agree well with the result of the EAGLE cosmological hydrodynamical simulation. Giant disky galaxies represent the large-size end of the volume density distribution of normal-sized spirals, suggesting the non-exceptional nature of giant discs. We observe a high active galactic nucleus fraction among the newly found gLSBGs., Comment: 5 pages, 2 tables, 5 figures, accepted for publication in MNRAS Letters

Giant low surface brightness galaxies (gLSBGs) with the disk radii of up to 130 kpc represent a challenge for currently accepted theories of galaxy formation and evolution, because it is difficult to build-up such large dynamically cold systems via mergers preserving extended disks. We summarize the in-depth study of the sample of 7 gLSBGs based on the results of the performed spectral long-slit observations at the Russian 6-m BTA telescope of SAO RAS, surface photometry and HI data available in literature. Our study revealed that most gLSBGs do not deviate from the Tully-Fisher relation. We discovered compact elliptical (cE) satellites in 2 out of these 7 galaxies. Provided the low statistical frequencies of gLSBGs and cEs, the chance alignment is improbable, so it can indicate that gLSBGs and cE are evolutionary connected and gives evidence in favor of the major merger formation scenario. Other formation paths of gLSBGs are also discussed., Comment: 5 pages, 1 figure. Astronomy at the epoch of multimessenger studies. Proceedings of the VAK-2021 conference, Aug 23-28, 2021 - Moscow, 2021

RCSEDv2 (https://rcsed2.voxastro.org/), the second Reference Catalog of Spectral Energy Distributions of galaxies includes the largest homogeneously processed photometric dataset for 4 million galaxies assembled from several wide-field surveys. Here we describe the methodology of the photometric data homogenization. We first correct all photometric measurements for the foreground Galactic extinction, then convert them into the photometric system we adopted as a standard (GALEX + SDSS + UKIDSS + WISE). We computed aperture corrections into several pre-defined apertures by using published galaxy sizes / light profiles and image quality for each of the surveys. We accounted for k-corrections using our own analytic approximations. Such a homogeneous photometric catalog allows us to build fully calibrated SEDs for the galaxies in our sample (defined by the availability of their spectra) and enables direct scientific analysis of this unique extragalactic dataset., Comment: 4 pages, 3 figure; to appear in the proceedings of the XXXI Astronomical Data Analysis Software and Systems (ADASS) conference (published by ASP)

We present a set of open-source web tools for visualization of spectral and imaging data, which we use in the second Reference Catalogue of Spectral Energy Distributions of galaxies RCSEDv2 (https://rcsed2.voxastro.org/). Using modern web frameworks Quasar and Vue.js we developed interactive viewers to visualize spectra and SEDs of galaxies and the diagrams presenting emission line ratios determined from the analysis of their spectra (BPT diagrams). The viewers are built in Javascript which puts a minimum load on the server side while providing full interactivity for the user. The use of modern web frameworks provides full customization making the viewers easily embeddable into web-sites of astronomical archives and databases. It also provides compatibility with popular third-party web-tools such as Aladin Lite., Comment: 4 pages, 4 figure; to appear in the proceedings of the XXXI Astronomical Data Analysis Software and Systems (ADASS) conference (published by ASP)

RCSEDv2 (https://rcsed2.voxastro.org/), the second Reference Catalog of Spectral Energy Distributions of galaxies, provides the largest homogeneously analyzed collection of optical galaxy spectra originating from several ground-based surveys collected between 1994 and 2019. The database contains astrophysical parameters obtained using the same data analysis approach from a sample of over 4 million optical spectra of galaxies and quasars: kinematics of stellar populations and ionized gas, chemical composition and age of stellar populations, gas phase metallicity. The dataset is available via Virtual Observatory access interfaces (IVOA TAP and SSAP) and through the web-site. Here we describe the RCSEDv2 spectroscopic dataset and the data processing and analysis., Comment: 4 pages, 2 figure; to appear in the proceedings of the XXXI Astronomical Data Analysis Software and Systems (ADASS) conference (published by ASP)

The Reference Catalog of Spectral Energy Distributions of 800,000 galaxies (RCSED) includes the results of uniform re-processing of 800,000 SDSS DR7 galaxies at redshifts $0.007

To compare photometric properties of galaxies at different redshifts, we need to correct fluxes for the change of effective rest-frame wavelengths of filter bandpasses, called $k$-corrections. At redshifts $z>0.3$, the wavelength shift becomes so large that typical broadband photometric bands shift into the neighboring rest frame band. At $z=0.6-0.8$ the shift reaches two or even three bands. Therefore, we need perform $k$-corrections from one observed bandpass to another. Here we expand the methodology proposed by Chilingarian et al. (2010) and fit cross-band $k$-corrections by smooth low-order polynomial functions of one observed color and a redshift - this approach but without cross-band is implemented as standard functions in {\sc topcat}, which can be used for galaxies at $z<0.5$. We also computed analytic approximations for WISE bands, which were not available in the past. We now have a complete set of $k$-corrections coefficients, which allow us to process photometric measurements for galaxies out to redshift $z=1$. We calculated standard and cross-band $k$-corrections for about 4 million galaxies in second Reference Catalog of Spectral Energy Distributions (RCSEDv2) of galaxies and we showed that, in cases of widely used UV, optical and near-infrared filters, our analytic approximations work very well and can be used for extragalactic data from future wide-field surveys., Comment: 4 pages, 2 figure; to appear in the proceedings of the XXXI Astronomical Data Analysis Software and Systems (ADASS) conference (published by ASP)

Panoramic IFU spectroscopy is a core tool of modern observational astronomy and is especially important for galaxy physics. Many massive IFU surveys, such as SDSS MaNGA (10k targets), SAMI (3k targets), Califa (600 objects), Atlas3D (260 objects) have recently been released and made publicly available to the broad astronomical community. The complexity and massiveness of the derived data products from spectral cubes makes visualization of the entire dataset challenging, but nevertheless very important and crucial for scientific output. Based on our past experience with visualization of spectral and imaging data built in the frame of the VOxAstro Initiative projects, we are now developing online web service for interactive visualizing spectroscopic IFU datasets (ifu.voxastro.org). Our service will provide a convenient access and visualization tool for spectral cubes from publicly available surveys (MaNGA, SAMI, Califa, Atlas3D) and results of their modeling, as well as maps of parameters derived from cubes, implementing the connected views concept. Here we describe the core components and functionality of the service, including REST API implementation on top of the Django+Postgres backend as well as a fast and responsive user interface built using the modern Vue.js-based framework Quasar., Comment: 4 pages, 1 figure; to appear in the proceedings of the XXXI Astronomical Data Analysis Software and Systems (ADASS) conference (published by ASP)

High-quality stellar spectra are in great demand now - they are the most important ingredient in the stellar population synthesis to study galaxies and star clusters. Here we describe the procedures to increase the quality of flux calibration of stellar spectra. We use examples of NIR intermediate-resolution Echelle spectra collected with the Folded InfraRed Echellete (R~6500, Magellan Baade) and high-resolution UV-optical spectra observed with UVES (R~80000, ESO VLT). By using these procedures, we achieved the quality of the global spectrophotometric calibration as good as 1-2%, which fulfills the requirements for the quality of stellar spectra intended to be used in the stellar population synthesis, Comment: 4 pages, 3 figures. ADASS-XXXI proceedings

Giant low surface brightness galaxies (gLSBGs) with dynamically cold stellar discs reaching the radius of 130 kpc challenge currently considered galaxy formation mechanisms. We analyse new deep long-slit optical spectroscopic observations, archival optical images and published HI and optical spectroscopic data for a sample of seven gLSBGs, for which we performed mass modelling and estimated the parameters of dark matter haloes assuming the Burkert dark matter density profile. Our sample is not homogeneous by morphology, parameters of stellar populations and total mass, however, six of seven galaxies sit on the high-mass extension of the baryonic Tully-Fisher relation. In UGC 1382 we detected a global counterrotation of the stellar high surface brightness (HSB) disc with respect to the extended LSB disc. In UGC 1922 with signatures of a possible merger, the gas counterrotation is seen in the inner disc. Six galaxies host active galactic nuclei, three of which have the estimated black hole masses substantially below those expected for their (pseudo-)bulge properties suggesting poor merger histories. Overall, the morphology, internal dynamics, and low star formation efficiency in the outer discs indicate that the three formation scenarios shape gLSBGs: (i) a two-stage formation when an HSB galaxy is formed first and then grows an LSB disc by accreting gas from an external supply; (ii) an unusual shallow and extended dark matter halo; (iii) a major merger with fine-tuned orbital parameters and morphologies of the merging galaxies., Comment: 20 pages, 17 figures, 8 tables, accepted version after proofreading

Giant low surface brightness galaxies (gLSB) with radii of discs as large as 130 kpc challenge galaxy formation scenarios and it is still not well understood how they form and evolve through the cosmic time. Here we present analysis of deep long-slit spectroscopic observations of six gLSBs that we obtained with the Russian 6-m telescope: UGC 1922, Malin 2, UGC 6614, UGC1382, NGC 7589 and UGC 1378. We derived spatially resolved properties of stellar and ionized gas kinematics and characteristics of stellar populations and interstellar medium. The stars in the central regions are old and metal rich for most of the galaxies. We revealed the presence of a kinematically decoupled central component in the inner regions of UGC1922, UGC1382 and UGC6614, where we detected counter-rotating kinematical components. We combine the results of our observations with the results available in literature. There seems to be a need for diversity of gLSBs formation scenarios: (i) some of them could have formed by in-plane mergers of massive galaxies; (ii) for some others the major merger scenario is excluded by our data. We revealed that most of gLSBs are situated in low-density environment which possibly helped to preserve the giant discs. At the same time at some point of the formation history of these systems there should exist a reservoir of gas from which the massive discs were formed. Future observations and detailed comparison with numerical simulations of galaxy formation in the cosmological contest will help to clarify which gLSB formation channel is more important., Comment: Conference proceeding for the IAU Symposium 355 "The Realm of the Low Surface Brightness Universe" held in Tenerife, Spain, July 8-12, 2019

Galactic discs are known to have a complex multilayer structure. An in-depth study of the stellar population properties of the thin and thick components can elucidate the formation and evolution of disc galaxies. Even though thick discs are ubiquitous, their origin is still debated. Here we probe the thick disc formation scenarios by investigating NGC7572, an enormous edge-on galaxy having $R_{25}\approx 25$ kpc and $V_{\rm rot} \approx 370$ km s$^{-1}$, which substantially exceeds the Milky Way size and mass. We analysed DECaLS archival imaging and found that the disc of NGC7572 contains two flaring stellar discs (a thin and a thick disc) with similar radial scales. We collected deep long-slit spectroscopic data using the 6m Russian BTA telescope and analysed them with a novel technique. We first reconstructed a non-parametric stellar line-of-sight velocity distribution along the radius of the galaxy and then fitted it with two kinematic components accounting for the orbital distribution of stars in thin and thick discs. The old thick disc turned out to be 2.7 times as massive as the intermediate-age thin component, $1.6\times 10^{11}$ $\textrm{M}_{\odot}$ vs. $5.9\times10^{10}$ $\textrm{M}_{\odot}$, which is very unusual. The different duration of the formation epochs evidenced by the [Mg/Fe] values of +0.3 and +0.15 dex for the thick and thin discs respectively, their kinematics and the mass ratio suggest that in NGC7572 we observe a rapidly formed very massive thick disc and an underdeveloped thin disc, whose growth ended prematurely due to the exhaustion of the cold gas likely because of environmental effects., Comment: 16 pages, 10 figures, submitted to MNRAS

The dominant physical processes responsible for the formation and longevity of giant gaseous and stellar discs in galaxies remain controversial. Although they are rare (less than 10 confirmed as of now), giant low-surface brightness (gLSB) discy galaxies provide interesting insights given their extreme nature. We describe observations of UGC 1378 including deep spectroscopy with the Russian 6m telescope and multi-band imaging with Binospec at the MMT. Galaxy UGC 1378 has both high surface brightness and an extended low surface brightness discs. Our stellar velocity dispersion data for the high-surface brightness, Milky Way-sized, disc appears inconsistent with a recent major merger, a widely discussed formation scenario for the very extended low surface brightness disc. We estimate the star formation rates (SFR) from archival Wide-Field Infrared Survey Explorer data. The SFR surface density in the LSB disc is low relative to its gas density, consistent with recent gas accretion. We argue that the unusually large size of UGC 1378's disc may be the product of a rich gas reservoir (e.g. a cosmic filament) and an isolated environment that has preserved the giant disc., Comment: Accepted for publication in MNRAS, 10 pages, 7 figures, 3 tables

The formation scenario for giant low surface brightness (gLSB) galaxies with discs as large as 100 kpc still remains unclear. These stellar systems are rare and very hard to observe, therefore a detailed insight on every additional object helps to understand their nature. Here we present a detailed observational study of the gLSB UGC 1922 performed using deep optical imaging and spectroscopic observations combined with archival ultraviolet data. We derived spatially resolved properties of stellar and ionized gas kinematics and characteristics of stellar populations and interstellar medium. We reveal the presence of a kinematically decoupled central component, which counter rotates with respect to the main disc of UGC 1922. The radial metallicity gradient of the ionised gas is in agreement with that found for moderate-size LSB galaxies. At the same time, a slowly rotating and dynamically hot central region of the galaxy hosts a large number of old metal-rich stars, which creates an appearance of a giant elliptical galaxy, that grew an enormous star forming disc. We reproduce most of the observed features of UGC 1922 in N-body/hydrodynamical simulations of an in-plane merger of giant Sa and Sd galaxies. We also discuss alternative formation scenarios of this unusual system., Comment: 15 pages, 10 figures, accepted for publication in MNRAS

Galactic stellar discs, such as that of the Milky Way, have usually a complex structure consisting of a thin and a thick component. The study of galactic disc substructures and their differences can shed light on the galaxy assembling processes and their evolution. However, due to observational difficulties there is a lack of information about the stellar populations of the thick disc components in external galaxies. Here we investigate three edge-on early-type disc galaxies in the Fornax cluster IC335, NGC1380A, NGC1381 by using publicly available photometrical data and our new deep long-slit spectroscopy along galactic mid-planes obtained with the 10-m SALT telescope. We report that significant changes of the stellar population properties beyond the radius where photometrical profiles demonstrate a knee are caused by an increasing thick disc contribution. Stellar population properties in the outermost thick-disc dominated regions demonstrate remarkably old ages and a low metallicity. We interpret these findings as a consequence of star formation quenching in the outermost regions of the discs due to ram pressure gas stripping from the disc periphery at the beginning of the cluster assembly while subsequent star formation occurring in the inner discs being gradually extinguished by starvation., Comment: 12 pages, 7 figures; Accepted for publication in MNRAS

We examined the reliability of estimates of pseudoisothermal, Burkert and NFW dark halo parameters for the methods based on the mass-modelling of the rotation curves.To do it we constructed the $\chi^2$ maps for the grid of the dark matter halo parameters for a sample of 14 disc galaxies with high quality rotation curves from THINGS. We considered two variants of models in which: a) the mass-to-light ratios of disc and bulge were taken as free parameters, b) the mass-to-light ratios were fixed in a narrow range according to the models of stellar populations. To reproduce the possible observational features of the real galaxies we made tests showing that the parameters of the three halo types change critically in the cases of a lack of kinematic data in the central or peripheral areas and for different spatial resolutions. We showed that due to the degeneracy between the central densities and the radial scales of the dark haloes there are considerable uncertainties of their concentrations estimates. Due to this reason it is also impossible to draw any firm conclusion about universality of the dark halo column density based on mass-modelling of even a high quality rotation curve. The problem is not solved by fixing the density of baryonic matter. In contrast, the estimates of dark halo mass within optical radius are much more reliable. We demonstrated that one can evaluate successfully the halo mass using the pure best-fitting method without any restrictions on the mass-to-light ratios., Comment: 20 pages, 8 figures, accepted for publication in MNRAS

Although thick stellar discs are detected in nearly all edge-on disc galaxies, their formation scenarios still remain a matter of debate. Due to observational difficulties, there is a lack of information about their stellar populations. Using the Russian 6-m telescope BTA we collected deep spectra of thick discs in three edge-on S0-a disc galaxies located in different environments: NGC4111 in a dense group, NGC4710 in the Virgo cluster, and NGC5422 in a sparse group. We see intermediate age (4-5 Gyr) metal rich ([Fe/H] $\sim$ -0.2 - 0.0 dex) stellar populations in NGC4111 and NGC4710. On the other hand, NGC5422 does not harbour young stars, its disc is thick and old (10 Gyr), without evidence for a second component, and its $\alpha$-element abundance suggests a 1.5-2 Gyr long formation epoch implying its formation at high redshift. Our results suggest the diversity of thick disc formation scenarios., Comment: Accepted for publication in MNRAS Letters, 6 pages, 3 figures, 1 table