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Ivan Katkov

Publications and source records attributed to Ivan Katkov.

36 records · Page 2Linked to original sources
arXiv2021

RCSEDv2: Processing and analysis of 4+ million galaxy spectra

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.

astro-ph.IM↗
arXiv2021

RCSEDv2: the largest database of galaxy properties from a homogeneously processed multi-wavelength dataset

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 $0.007<z<0.6$ complemented with ultraviolet-to-infrared photometric data from GALEX, SDSS, and UKIDSS. The key difference between RCSED and existing databases of galaxy properties (NED, HyperLeda, part of SIMBAD) is that rather than providing a compilation of literature data, we perform homogeneous data analysis of spectral and photometric data using our own tools and publish derived physical properties of galaxies along with re-calibrated spectra and photometry and their best-fitting models. Here we present the 2nd release of our catalog, RCSEDv2 where we substantially expanded the spectral dataset to 4 million objects by including spectral data analysis for 10 large spectroscopic surveys (SDSS, SDSS/eBOSS, LAMOST, Hectospec, CfA redshift surveys, 2dFGRS, 6dFGS, DEEP2/3, WiggleZ). The photometric part has also been expanded by including DESI Legacy Survey, DES, UHS, ESO Public Surveys, and WISE in addition to GALEX, SDSS, and UKIDSS used in the original RCSED. This makes RCSEDv2 the largest database of galaxy properties and homogeneously processed spectral and photometric data up-to-date and creates a foundation for the analysis of future large-scale spectral surveys DESI and 4MOST.

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arXiv2021

RCSEDv2: Open-source web tools for visualization of imaging and spectral data

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.

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arXiv2021

RCSEDv2: homogenization of multi-wavelength photometric data

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.

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arXiv2021

Hybrid minimization algorithm for computationally expensive multi-dimensional fitting

Multi-dimensional optimization is widely used in virtually all areas of modern astrophysics. However, it is often too computationally expensive to evaluate a model on-the-fly. Typically, it is solved by pre-computing a grid of models for a predetermined set of positions in the parameter space and then interpolating. Here we present a hybrid minimization approach based on the local quadratic approximation of the $χ^2$ profile from a discrete set of models in a multidimensional parameter space. The main idea of our approach is to eliminate the interpolation of models from the process of finding the best-fitting solution. We present several examples of applications of our minimization technique to the analysis of stellar and extragalactic spectra.

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arXiv2021

Multi-segment and Echelle stellar spectra processing issues and how to solve them

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

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arXiv2021

Transforming gas-rich low-mass disky galaxies into ultra-diffuse galaxies by ram pressure

Faint extended elliptically-shaped ultra-diffuse galaxies and slightly brighter and more compact dwarf elliptical and lenticular stellar systems are common in galaxy clusters. Their poorly constrained evolutionary paths can be studied by identifying young ultra-diffuse galaxy and dwarf elliptical analogs populated with bright, massive stars. Using data mining we identified 11 such low-mass ($2\times10^8<M_*<2\times10^9 M_{\odot}$) galaxies with large half-light radii ($2.0<r_e<5$ kpc) and recently quenched star formation in the Coma and Abell 2147 galaxy clusters. All galaxies happen to have ram-pressure-stripped tails with signs of current or recent star formation. Deep spectroscopic observations revealed rotating stellar discs containing 70-95% dark matter by mass. A large fraction of the disc stars (10-60%) formed in intense star bursts 180-970 Myr ago, probably triggered by ram pressure. Observed global gradients of stellar age corroborate this scenario. Passive evolution in the next 10 Gyr will transform 9 of the 11 galaxies into ultra-diffuse galaxies. If we assume a constant rate of galaxy infall, 44$\pm$16% of the most luminous present-day ultra-diffuse galaxies in Coma must have formed via ram pressure stripping of disky progenitors.

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arXiv2021

Observational insights on the origin of giant low surface brightness galaxies

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.

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arXiv2019

UGC 1378 -- a Milky Way-sized galaxy embedded in a giant low-surface brightness disc

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.

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arXiv2016

RCSED - A Value-Added Reference Catalog of Spectral Energy Distributions of 800,299 Galaxies in 11 Ultraviolet, Optical, and Near-Infrared Bands: Morphologies, Colors, Ionized Gas and Stellar Populations Properties

We present RCSED, the value-added Reference Catalog of Spectral Energy Distributions of galaxies, which contains homogenized spectrophotometric data for 800,299 low and intermediate redshift galaxies (0.007<z<0.6) selected from the Sloan Digital Sky Survey spectroscopic sample. Accessible from the Virtual Observatory (VO) and complemented with detailed information on galaxy properties obtained with the state-of-the-art data analysis, RCSED enables direct studies of galaxy formation and evolution during the last 5Gyr. We provide tabulated color transformations for galaxies of different morphologies and luminosities and analytic expressions for the red sequence shape in different colors. RCSED comprises integrated k-corrected photometry in up-to 11 ultraviolet, optical, and near-infrared bands published by the GALEX, SDSS, and UKIDSS wide-field imaging surveys; results of the stellar population fitting of SDSS spectra including best-fitting templates, velocity dispersions, parameterized star formation histories, and stellar metallicities computed for instantaneous starburst and exponentially declining star formation models; parametric and non-parametric emission line fluxes and profiles; and gas phase metallicities. We link RCSED to the Galaxy Zoo morphological classification and galaxy bulge+disk decomposition results by Simard et al. We construct the color-magnitude, Faber-Jackson, mass-metallicity relations, compare them with the literature and discuss systematic errors of galaxy properties presented in our catalog. RCSED is accessible from the project web-site and via VO simple spectrum access and table access services using VO compliant applications. We describe several SQL query examples against the database. Finally, we briefly discuss existing and future scientific applications of RCSED and prospectives for the catalog extension to higher redshifts and different wavelengths.

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arXiv2016

The insight into the dark side. I. The pitfalls of the dark halo parameters estimation

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 $χ^2$ 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.

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arXiv2015

Stellar atmosphere interpolator for empirical and synthetic spectra

We present a new stellar atmosphere interpolator which we will use to compute stellar population models based on empirical and/or synthetic spectra. We combined observed and synthetic stellar spectra in order to achieve more or less uniform coverage of the (T_eff , log g, [Fe/H]) parameter space. We validated our semi-empirical stellar population models by fitting spectra of early-type galaxies from the SDSS survey

astro-ph.IM↗
arXiv2014

Properties of Stellar Populations in Isolated Lenticular Galaxies

In this paper we present the results of long-slit spectral observations for a sample of isolated lenticular galaxies, made with the SCORPIO and SCORPIO-2 spectrographs of the 6-meter BTA telescope of the SAO RAS. By applying full spectral fitting technique using the stellar population evolutionary synthesis models, we have measured the radial profiles of the stellar line-of-sight velocity as well as the velocity dispersion, SSP-equivalent age and SSP-equivalent metallicity of stars along the radius in 12 targets. The resulting averaged ages of the stellar population in bulges and discs cover an entire range of possible values from 1.5 to 15 Gyr which indicates the absence of a certain formation epoch for the structural components in the isolated lenticular galaxies, unlike in the members of clusters and rich groups: they could have been formed at a redshift of $z>2$ as well as only a few billion years ago. Unlike S0 galaxies in more dense environments, the isolated galaxies typically have the same age of stars in the bulges and discs. The disc-embedded lenses and rings of increased stellar brightness, identified from the photometry in 7 of 11 galaxies, do not differ strongly from the stellar discs as concerning the properties of stellar populations and stellar velocity dispersion. We conclude that the final shaping of the morphological type of a lenticular galaxy in complete isolation is critically dependent on the possible regimes of cold-gas accretion from outside.

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arXiv2013

Decoupled gas kinematics in isolated early-type disc galaxies

We have studied a sample of completely isolated galaxies by means of long-slit spectroscopy at the 6-m telescope. We have found that 7 of 12 (58 +/- 14 %) galaxies have revealed a presence of large-scale ionized-gas component which angular momentum is mostly differ from stellar one: 5 of 7 (71 +/- 17 %) show a visible counterrottation. The diagnostic diagram demonstrates a wide range of gas excitation mechanism. We have estimated the gas oxygen abundance in the cases where excitation mechanism by young stars dominates and have found that ionized gas has a subsolar metallicity. We concluded that cold-gas accretion from primordial cosmological filaments is unlikely for these objects, while external accretion from dwarf gas-rich satellites is more suitable.

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arXiv2013

Decoupled gas kinematics in isolated S0 galaxies

A sample of completely isolated S0 galaxies has been studied by means of long-slit spectroscopy at the Russian 6-m telescope. 7 of 12 galaxies have revealed a presence of extended ionized-gas discs which rotation is mostly decoupled from the stellar kinematics: 5 of 7 (71+/-17%) galaxies show a visible counterrotation of the ionized-gas component with respect to the stellar component. The emission-line diagnostics demonstrates a wide range of the gas excitation mechanisms, although a pure excitation by young stars is rare. We conclude that in all cases the extended gaseous discs in our sample S0s are of external origin, despite the visible isolation of the galaxies. Possible sources of external accretion, such as systems of dwarf gas-rich satellites or cosmological cold-gas filaments, are discussed.

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arXiv2013

A new technique for the determination of the initial mass function in unresolved stellar populations

We present a new technique for the determination of the low-mass slope ($α_1$; $M_* < 0.5 M_{\odot}$) of the present day stellar mass function (PDMF) using the pixel space fitting of integrated light spectra. It can be used to constrain the initial mass function (IMF) of stellar systems with relaxation timescales exceeding the Hubble time and testing the IMF universality hypothesis. We provide two versions of the technique: (1) a fully unconstrained determination of the age, metallicity, and $α_1$ and (2) a constrained fitting by imposing the externally determined mass-to-light ratio of the stellar population. We have tested our approach by Monte-Carlo simulations using mock spectra and conclude that: (a) age, metallicity and $α_1$ can be precisely determined by applying the unconstrained version of the code to high signal-to-noise datasets (S/N=100, R=7000 yield $Δα_1 \approx 0.1$); (b) the $M/L$ constraint significantly improves the precision and reduces the degeneracies, however its systematic errors will cause biased $α_1$ estimates; (c) standard Lick indices cannot constrain the PDMF because they miss most of the mass function sensitive spectral features; (d) the $α_1$ determination remains unaffected by the high-mass IMF shape ($α_3$; $M_* \ge 1 M_{\odot}$) variation for stellar systems older than 8 Gyr, while the intermediate-mass IMF slope ($α_2$; $0.5 \le M_* < 1 M_{\odot}$) may introduce biases into the best-fitting $α_1$ values if it is different from the canonical value $α_2 = 2.3$. We analysed observed intermediate resolution spectra of ultracompact dwarf galaxies with our technique and demonstrated its applicability to real data.

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arXiv2011

Hoag's Object: Evidence for Cold Accretion onto an Elliptical Galaxy

(Abridged) We present new photometric and spectroscopic observations of the famous Hoag's Object, a peculiar ring galaxy with a central roundish core. The nature of Hoag's Object is still under controversial discussion. Previous studies demonstrated that a major accretion event that took place at least 2-3 Gyr ago can account for the observational evidence. However, the role of internal nonlinear mechanisms in forming the outer ring was not yet completely ruled out. These new data, together with HI and optical information from the literature, are used to demonstrate that Hoag's Object is a relatively isolated system surrounded by a luminous quasi-spiral pattern and a massive, low-density HI disc. The main stellar body is an old, mildly triaxial elliptical galaxy with very high angular momentum. We review previous formation scenarios of Hoag's Object in light of the new data and conclude that the peculiar morphology could not represent a late phase in barred early-type galaxies evolution. In addition, no observational evidence supports late merging events in the evolution of the galaxy, although further tests are required before safely dismissing this idea. We propose a new scenario where the elliptical core formed in the early Universe with the HI disc forming shortly after the core by prolonged "cold" accretion of primordial gas from the intergalactic medium. The low gas density does not allow intense star formation to occur everywhere in the disc, but only along a tightly wound spiral pattern of enhanced density induced by the triaxial gravitational potential.

astro-ph.CO↗