arXiv subjects

Leonid S. Pilyugin

Publications and source records attributed to Leonid S. Pilyugin.

9 recordsLinked to original sources

arXiv2026

Resolved Dust-Gas-Metallicity relations in nearby spiral galaxies

Context: Understanding the interstellar medium (ISM) requires high-resolution, multi-component mapping to capture its complex physical structure. Nearby spiral galaxies, with their abundant and diverse ISM, provide an ideal laboratory for such a comprehensive analysis at sub-galactic scales. Aims: We investigate dust-to-gas (DGR) and dust-to-metal (DMR) ratios as a functions of gas-phase metallicity (Z), on spatial scales ranging from 0.6 to 2.3 kpc, in a sample of 10 nearby spiral galaxies, spanning more than an order of magnitude in stellar mass (9.7 \le \log(M_*/M_\odot) \leq 11.0), star formation rate (SFR, \sim 0.3--3 \, M_\odot \, \rm yr^{-1}) and metallicity ranging from 8.3 \lesssim 12 + \log( O/H) \lesssim 8.8. We explore how the DGR-Z and DMR-Z relations are shaped by the assumptions behind the CO-to-H_2 conversion factor (α_{CO}). Methods: We homogeneously combine maps of dust, atomic gas, molecular gas, and metallicity. Motivated by the diversity in L_{CO(1-0)}/SFR ratios and metallicity across our sample, we introduce a hybrid α_{CO} prescription to distinguish between CO-bright and CO-dark regimes. The derived DGR-Z and DMR-Z relations are compared with other global and resolved observational results, and with the predictions of dust and chemical evolution models. Results: Both DGR-Z and DMR-Z relations are dependent on the adopted α_{CO} prescription, and no single α_{CO} can reproduce the properties of the entire sample, motivating the use of a hybrid approach. The DGR increases with metallicity, spanning \sim 1 dex across the sampled range; while the DMR remains approximately constant at \log(\mathrm{DMR}) = -0.53 \pm 0.13, implying that \sim 30 \% of metals are locked into dust grains. This flat behavior indicates an evolved dust phase where efficient ISM grain growth drives a saturation regime balancing dust formation and destruction.

astro-ph.GA↗

arXiv2025

Metal-THINGS: gas metallicity gradients in nearby galaxies

This paper explores the gas metallicity gradients in a sample of 25 nearby galaxies using new Integral Field Spectroscopy observations from the Metal-THINGS survey. We derive and study the resolved diffuse ionised gas content, Baldwin, Phillips and Terlevich diagrams and gas metallicities for our entire sample, at spatial resolutions of 40-300 pc. Gas metallicity gradients are studied as a function of the galaxy's stellar mass, H I gas fraction, diffuse ionised gas content, and using different parametric length scales for normalisation. The metallicity gradients are analysed using Bayesian statistics based on data from the Metal-THINGS survey. Bayesian MCMC models are developed to explore how metallicity gradients vary with a galaxy's mass and how they correlate with properties such as the stellar mass or the atomic gas fraction. For our sample, we find that the metallicity typically decreases with galactic radius, consistent with inside-out galaxy growth. We find a trend dependent on the stellar mass, with a break at log(M_star/M_sun)=9.5, and another between the metallicity gradients and the atomic gas fraction (f_g,HI) of a galaxy at fg,HI=0.75, indicating relatively shallower gradients for lower gas fractions. We find that normalisation using NUV-band effective radii are preferable for galaxies with a higher atomic gas content and lower stellar masses, while r-band radii are better suited for those with lower atomic gas fractions and more massive ones. Our results highlight a strong connection between gas content, stellar mass, and metallicity gradients. The breaks at log(M_star/M_sun)=9.5 and fg,HI=0.75 mark shifts in chemical enrichment behaviour, with low-mass galaxies showing greater sensitivity to gas processes. Overall, this points to gas accretion and removal as key drivers of chemical evolution in low-mass systems.

astro-ph.GA↗

arXiv2020

Metal-THINGS: On the metallicity and ionization of ULX sources in NGC 925

We present an analysis of the optical properties of three Ultra Luminous X-ray (ULX) sources identified in NGC 925. We use Integral field unit data from the George Mitchel spectrograph in the context of the Metal-THINGS survey. The optical properties for ULX-1 and ULX-3 are presented, while the spaxel associated with ULX-2 had a low S/N, which prevented its analysis. We also report the kinematics and dimensions of the optical nebula associated with each ULX using ancillary data from the PUMA Fabry-Perot spectrograph. A BPT analysis demonstrates that most spaxels in NGC 925 are dominated by star-forming regions, including those associated with ULX-1 and ULX-3. Using the resolved gas-phase metallicities, a negative metallicity gradient is found, consistent with previous results for spiral galaxies, while the ionization parameter tends to increase radially throughout the galaxy. Interestingly, ULX-1 shows a very low gas metallicity for its galactocentric distance, identified by two independent methods, while exhibiting a typical ionization. We find that such low gas metallicity is best explained in the context of the high-mass X-ray binary population, where the low-metallicity environment favours active Roche lobe overflows that can drive much higher accretion rates. An alternative scenario invoking accretion of a low-mass galaxy is not supported by the data in this region. Finally, ULX-3 shows both a high metallicity and ionization parameter, which is consistent with the progenitor being a highly-accreting neutron star within an evolved stellar population region.

astro-ph.GA↗

arXiv2019

Oxygen yields as a constraint on feedback processes in galaxies

We study the interplay between several properties determined from Optical and a combination of Optical/Radio measurements, such as the effective Oxygen yield (y_eff), the star formation efficiency, gas metallicity, depletion time, gas fraction, and baryonic mass(M_bar), among others. We use spectroscopic data from the SDSS survey, and HI information from the ALFALFA survey to build a statistically significant sample of more than 5,000 galaxies. Furthermore, we complement our analysis with data from the GASS and COLD GASS surveys, and with a sample of star-forming galaxies from the Virgo cluster. Additionally, we have compared our results with predictions from the EAGLE simulations, finding a very good agreement when using the high-resolution run. We explore in detail the M_bar-y_eff relation, finding a bimodal trend that can be separated when the stellar age of galaxies is considered. On one hand, y_eff increases with M_bar for young galaxies(log(t_r) < 9.2 yr), while y_eff shows an anti-correlation with M_bar for older galaxies (log(t_r) > 9.4 yr). While a correlation between M_bar and y_eff has been observed and studied before, mainly for samples of dwarfs and irregular galaxies, their anti-correlated counterpart for massive galaxies has not been previously reported. The EAGLE simulations indicate that AGN feedback must have played an important role in their history by quenching their star formation rate, whereas low mass galaxies would have been affected by a combination of outflows and infall of gas.

astro-ph.GA↗

arXiv2015

On the Influence of Minor Mergers on the Radial Abundance Gradient in Disks of Milky Way-like Galaxies

We investigate the influence of stellar migration caused by minor mergers (mass ratio from 1:70 to 1:8) on the radial distribution of chemical abundances in the disks of Milky Way-like galaxies during the last four Gyr. A GPU-based pure N-body tree-code model without hydrodynamics and star formation was used. We computed a large set of mergers with different initial satellite masses, positions, and orbital velocities. We find that there is no significant metallicity change at any radius of the primary galaxy in the case of accretion of a low-mass satellite of 10$^9$ M$_{\odot}$ (mass ratio 1:70) except for the special case of prograde satellite motion in the disk plane of the host galaxy. The accretion of a satellite of a mass $\gtrsim3\times10^9$ M$_{\odot}$ (mass ratio 1:23) results in an appreciable increase of the chemical abundances at galactocentric distances larger than $\sim10$ kpc. The radial abundance gradient flattens in the range of galactocentric distances from 5 to 15 kpc in the case of a merger with a satellite with a mass $\gtrsim3\times10^9$ M$_{\odot}$. There is no significant change in the abundance gradient slope in the outer disk (from $\sim15$ kpc up to 25 kpc) in any merger while the scatter in metallicities at a given radius significantly increases for most of the satellite's initial masses/positions compared to the case of an isolated galaxy. This argues against attributing the break (flattening) of the abundance gradient near the optical radius observed in the extended disks of Milky Way-like galaxies only to merger-induced stellar migration.

astro-ph.GA↗

arXiv2012

"Counterpart" method for abundance determinations in HII regions

We suggest a new way of the determining abundances and electron temperatures in HII regions from strong emission lines. Our approach is based on the standard assumption that HII regions with similar intensities of strong emission lines have similar physical properties and abundances. A "counterpart" for a studied HII region may be chosen among HII regions with well-measured abundances (reference HII regions) by comparison of carefully chosen combinations of strong line intensities. Then the abundances in the investigated HII region can be assumed to be the same as that in its counterpart. In other words, we suggest to determine the abundances in HII regions "by precedent". To get more reliable abundances for the considered HII region, a number of reference HII regions is selected and then the abundances in the target HII region is estimated through extra-/interpolation. We will refer to this method of abundance determination as the counterpart method or, for brevity, the C method. We define a sample of reference HII regions and verify the validity of the C method. We find that this method produces reliable abundances. Finally, the C method is used to obtain the radial abundance distributions in the extended discs of the spiral galaxies M83, NGC4625 and NGC 628.

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↗

arXiv2011

ESO 546-G34: The most metal poor LSB galaxy?

We present a re-analysis of spectroscopic data for 23 HII-regions in 12 blue, metal-poor low surface brightness galaxies (LSBGs) taking advantage of recent developments in calibrating strong-line methods. In doing so we have identified a galaxy (ESO 546-G34) which may be the most metal-poor LSB galaxy found in the local Universe. Furthermore, we see evidence that blue metal-poor LSBGs, together with blue compact galaxies (BCGs) and many other HII galaxies, fall outside the regular luminosity-metallicity relation. This suggests there might be an evolutionary connection between LSBGs and BCGs. In such case, several very metal-poor LSBGs should exist in the local Universe.

astro-ph.CO↗

arXiv2010

Galaxy downsizing and the redshift evolution of oxygen and nitrogen abundances: origin of the scatter in the N/H-O/H diagram

The oxygen and nitrogen abundance evolutions with redshift of emission-line galaxies in the Sloan Digital Sky Survey are considered for four intervals of galaxy stellar masses, ranging from 10^11.3 M_sun to 10^10.2 M_sun. We have measured their line fluxes and derived the O and N abundances using recent calibrations. The evolution of O and N abundances with redshift clearly shows the galaxy downsizing effect, where enrichment (and hence star formation) ceases in high-mass galaxies at earlier times and shifts to lower-mass galaxies at later epochs. The origin of the scatter in the N/H - O/H diagram has been examined. The most massive galaxies, where O and N enrichment and star formation has already stopped, occupy a narrow band in the N/H -- O/H diagram, defining an upper envelope. The less massive galaxies which are still undergoing star formation at the current epoch are shifted downwards, towards lower N/H values in the N/H - O/H diagram. This downward shift is caused by the time delay between N and O enrichment. This time delay together with the different star formation histories in galaxies is responsible for the large scatter in the N/H -- O/H diagram.

astro-ph.CO↗