Gas and stellar kinematic misalignment in MaNGA galaxies: what is the origin of counter-rotating gas?

Kinematic misalignment between gas and stellar components observed in a certain fraction of galaxies. It believed to be caused by acquisition of gas from the external reservoir by major or minor mergers, accretion from cosmological filaments or circumgalactic medium, etc. We aim to constrain possible sources of the gas that forms counter-rotating component. We derived the gas-phase oxygen abundance in 69 galaxies with kinematic misalignment between gas and stellar components from MaNGA DR17 survey and compared it with the metallicity expected according to the mass-metallicity relation. We found that the oxygen abundance of the counter-rotating gas in our sample is higher than 8.2 dex that excludes significant role of inflow of pristine gas. Meanwhile, there is a significant difference in the oxygen abundance of the counter-rotating gas between red and blue galaxies. In general, the oxygen abundance is lower than expected for their stellar mass in red galaxies, but is compatible with or even higher than typical values for their stellar mass in blue galaxies. We showed that the exchange of enriched gas between galaxies is the most plausible mechanism for explaining the metallicity of counter-rotating gas components in galaxies of all masses and colors. Meanwhile, minor mergers may play a significant role in the formation of counter-rotating gas components in red and quenched galaxies.Comment: 5 pages, 3 figures, accepted for publication in A&A Letter

Millimeter and submillimeter wave astronomy today and tomorrow

В данном обзоре обсуждаются недавние достижения и актуальные задачи миллиметровой и субмиллиметровой астрономии. Приводятся сведения о действующих, строящихся и проектируемых инструментах этого диапазона, как наземных, так и космических.In this review, recent achievements and actual problems of millimeter and submillimeter astronomy are discussed. The article provides information on existing, under construction and projected instruments of this band, both ground-based and space ones.Работа выполнена при поддержке Российского фонда научных исследований (проект 17-12-01256, раздел «Основные задачи миллиметровой и субмиллиметровой астрономии») и Российского фонда фундаментальных исследований (грант 15-02-06098, раздел «Существующие и перспективные инструменты»)

A Search for Small-Scale Clumpiness in Dense Cores of Molecular Clouds

We have analyzed HCN(1-0) and CS(2-1) line profiles obtained with high signal-to-noise ratios toward distinct positions in three selected objects in order to search for small-scale structure in molecular cloud cores associated with regions of high-mass star formation. In some cases, ripples were detected in the line profiles, which could be due to the presence of a large number of unresolved small clumps in the telescope beam. The number of clumps for regions with linear scales of ~0.2-0.5 pc is determined using an analytical model and detailed calculations for a clumpy cloud model; this number varies in the range: ~2 10^4-3 10^5, depending on the source. The clump densities range from ~3 10^5-10^6 cm^{-3}, and the sizes and volume filling factors of the clumps are ~(1-3) 10^{-3} pc and ~0.03-0.12. The clumps are surrounded by inter-clump gas with densities not lower than ~(2-7) 10^4 cm^{-3}. The internal thermal energy of the gas in the model clumps is much higher than their gravitational energy. Their mean lifetimes can depend on the inter-clump collisional rates, and vary in the range ~10^4-10^5 yr. These structures are probably connected with density fluctuations due to turbulence in high-mass star-forming regions.Comment: 23 pages including 4 figures and 4 table

Chemical differentiation in regions of high mass star formation II. Molecular multiline and dust continuum studies of selected objects

The aim of this study is to investigate systematic chemical differentiation of molecules in regions of high mass star formation. We observed five prominent sites of high mass star formation in HCN, HNC, HCO+, their isotopes, C18O, C34S and some other molecular lines, for some sources both at 3 and 1.3 mm and in continuum at 1.3 mm. Taking into account earlier obtained data for N2H+ we derive molecular abundances and physical parameters of the sources (mass, density, ionization fraction, etc.). The kinetic temperature is estimated from CH3C2H observations. Then we analyze correlations between molecular abundances and physical parameters and discuss chemical models applicable to these species. The typical physical parameters for the sources in our sample are the following: kinetic temperature in the range ~ 30-50 K (it is systematically higher than that obtained from ammonia observations and is rather close to dust temperature), masses from tens to hundreds solar masses, gas densities ~ 10^5 cm^{-3}, ionization fraction ~ 10^{-7}. In most cases the ionization fraction slightly (a few times) increases towards the embedded YSOs. The observed clumps are close to gravitational equilibrium. There are systematic differences in distributions of various molecules. The abundances of CO, CS and HCN are more or less constant. There is no sign of CO and/or CS depletion as in cold cores. At the same time the abundances of HCO+, HNC and especially N2H+ strongly vary in these objects. They anti-correlate with the ionization fraction and as a result decrease towards the embedded YSOs. For N2H+ this can be explained by dissociative recombination to be the dominant destroying process. N2H+, HCO+, and HNC are valuable indicators of massive protostars.Comment: 15 pages, 8 figure