arXiv subjects

Daniil Smirnov

Publications and source records attributed to Daniil Smirnov.

5 recordsLinked to original sources

arXiv2026

Two domains of extended Lyman-alpha emission around galaxies: from local radiation to environmental regulation

We examine the relation between extended Ly$α$ halos around high-redshift galaxies and the main factors responsible for driving the emission in such halos, in particular at distances around and beyond one virial radius $r_\mathrm{vir}$. To reach the required surface brightness sensitivity we take advantage of the MUSE eXtremely Deep Field (MXDF) survey, allowing us to probe levels as faint as $\sim 10^{-20}$ erg cm$^{-2}$ s$^{-1}$ arcsec$^{-2}$ in individual Ly$α$ halos. Our sample consists of the 21 apparently core- and halo-brightest (yet intrinsically low luminosity $\log_{10}$L$_{\mathrm{Ly}α} < 42.3$ erg s$^{-1}$) Ly$α$ emitters (LAEs) in the MXDF at $3<z<4$, with typical virial radii around 20 kpc. We measure their radial surface brightness profiles out to 50 kpc (more than $2r_{\mathrm{vir}}$) and investigate the correlations between surface brightness and internal (star formation rates of the host galaxies, SFR) or external influences (environmental density, $δ+1$). We find a clear break in these correlations at radii around or just below $1r_{\mathrm{vir}}$. Below this break the emission correlates tightly with SFR (as expected) and not at all with $δ+1$. Beyond $\sim 1r_\mathrm{vir}$(20 kpc) we observe the opposite trend with no dependence on SFR, but an emerging correlation with $δ+1$. We compare our measurements with the expected integrated surface brightness from ultrafaint, individually undetected LAEs and find that the latter is insufficient to drive the observed correlation. We conclude that Ly$α$ emission from the outer halos is regulated by the surrounding environment, but originates mostly from diffuse gas rather than discrete sources.

astro-ph.GA↗

arXiv2026

Lyman-alpha haloes in the aftermath of reionisation

We present a comparative study of Ly$α$ haloes (LAHs) around low-luminosity (L$_{\mathrm{Ly}α}\lesssim 10^{42}$ erg s$^{-1}$) Ly$α$-emitting galaxies (LAEs) at very high redshifts $z\geq6$ and a reference sample at $z\sim 3$ covering a similar Ly$α$ luminosity and host galaxy stellar mass range. Using data from the Multi-Unit Spectroscopic Explorer (MUSE) at the ESO VLT, we extracted the samples such that at the different redshifts we obtain the same intrinsic surface brightness sensitivity, accounting for cosmological dimming. We detect extended Ly$α$ emission around 6 out of 18 high-$z$ LAEs in the MUSE eXtremely Deep Field (MXDF), more than doubling the number of known such objects at $z\geq6$. We obtain an only slightly higher individual LAH detection fraction of 40% among the lower redshift comparison sample. Yet the typical exponential scale lengths at $z\geq6$ are three times smaller than those at $z\sim3$. Stacking the LAEs with undetected haloes gives again drastically different results for the two samples, with a highly significant halo detection at $z\sim 3$ but no trace of extended Ly$α$ emission at $z\geq6$. We also find the Ly$α$ spectral line widths of the high-$z$ sample to be $\sim$2.5 smaller in comparison to the lower redshift objects. We discuss the potential mechanisms driving such strong changes. In a reionisation-driven scenario the higher neutral fraction in the intergalactic and circumgalactic media might lead to substantial scattering losses of escaping Ly$α$ radiation, leaving detectable only emission from the vicinity of the star-forming regions. In an alternative scenario the LAH properties might be linked more closely to the evolution of their host galaxies than previously thought.

astro-ph.GA↗

arXiv2025

GigaChat Family: Efficient Russian Language Modeling Through Mixture of Experts Architecture

Generative large language models (LLMs) have become crucial for modern NLP research and applications across various languages. However, the development of foundational models specifically tailored to the Russian language has been limited, primarily due to the significant computational resources required. This paper introduces the GigaChat family of Russian LLMs, available in various sizes, including base models and instruction-tuned versions. We provide a detailed report on the model architecture, pre-training process, and experiments to guide design choices. In addition, we evaluate their performance on Russian and English benchmarks and compare GigaChat with multilingual analogs. The paper presents a system demonstration of the top-performing models accessible via an API, a Telegram bot, and a Web interface. Furthermore, we have released three open GigaChat models in open-source (https://huggingface.co/ai-sage), aiming to expand NLP research opportunities and support the development of industrial solutions for the Russian language.

cs.CL↗

arXiv2024

The Intrinsic Distribution of Lyman-$α$ Halos

The emission and escape of Lyman-$α$ photons from star-forming galaxies is determined through complex interactions between the emitted photons and a galaxy's interstellar and circumgalactic gas, causing Lyman-$α$ emitters (LAEs) to commonly appear not as point sources but in spatially extended halos with complex spectral profiles. We develop a 3D spatial-spectral model of Lyman-$α$ halos (LAHs) to replicate LAH observations in integral field spectroscopic studies, such as those made with VLT/MUSE. The profile of this model is a function of 6 key halo properties: the halo- and compact-source exponential scale lengths ($r_{sH}$ and $r_{sC}$), the halo flux fraction ($f_H$), the compact component ellipticity ($q$), the spectral line width ($σ$), and the spectral line skewness parameter ($γ$). Placing a series of model LAHs into datacubes reflecting observing conditions in the MUSE UDF-Mosaic survey, we test their detection recoverability and determine that $σ$, $r_{sH}$, and $f_H$ are expected to have the most significant effect on the detectability of the overall LAH at a given central wavelength and intrinsic line luminosity. We develop a general selection function model spanning a grid of these halo parameters, and with a sample of 145 UDF-Mosaic LAHs with measured halo properties, we derive completeness-corrected, intrinsic distributions of the values of $σ$, $r_{sH}$, and $f_H$ for $3<z<5$ LAHs. We present best-fit functional forms of the distributions, and a $σ$ distribution corrected for instrumental line-spread function (LSF) broadening, and thereby show the physical line spread distribution of the intrinsic population. Finally, we discuss implications of these distributions for Ly$α$ emission through the circumgalactic medium, finding that observations undercount LAHs with extended halo scale lengths compared to the intrinsic population.

astro-ph.GA↗

arXiv2017

Around power law for PageRank components in Buckley-Osthus model of web graph

In the paper we investigate power law for PageRank components for the Buckley-Osthus model for web graph. We compare different numerical methods for PageRank calculation. With the best method we do a lot of numerical experiments. These experiments confirm the hypothesis about power law. At the end we discuss real model of web-ranking based on the classical PageRank approach.

math.OC↗