arXiv subjects

Daria Kosenko

Publications and source records attributed to Daria Kosenko.

4 recordsLinked to original sources

arXiv2025

First detections of CO absorption in the Magellanic Clouds and direct measurement of the CO-to-H$_2$ ratio

Molecular hydrogen (H$_2$) is by far the most abundant molecule in the Universe. However, due to the low emissivity of H$_2$, carbon monoxide (CO) is widely used instead to trace molecular gas in galaxies. The relative abundances of these molecules is expected to depend on both physical (e.g., density) and chemical (e.g., metal enrichment) properties of the gas, making direct measurements in diverse environments crucial. We present a systematic search for CO in absorption toward 34 stars behind H$_2$ gas in the Magellanic Clouds using the Hubble Space Telescope. We report the first two definitive detections of CO absorption in the Large Magellanic Cloud (LMC) and one in the Small Magellanic Cloud (SMC), along with stringent upper limits for the remaining sightlines. Non-detections of CO are consistent with models of low thermal pressures and/or low metallicities while detections at the lower metallicities of the Magellanic Clouds require higher thermal pressures, $P_{\rm th}=10^5-10^6$$\,$K$\,$cm$^{-3}$ than detections the Milky Way at similar $N({\rm H_2})$. Notably, the high density derived from the rotational excitation of CO towards SK$\,$143 in the SMC suggests full molecularization of CO in the absorbing cloud, with CO/H$_2 = 8.3^{+2.0}_{-1.6}\times10^{-5}$ consistent with the standard ratio ($3.2\times10^{-4}$) measured in dense molecular gas in the Milky Way, scaled to the SMC's $0.2\,Z_{\odot}$ metallicity.

astro-ph.GA↗

arXiv2024

Neutral carbon in diffuse interstellar medium: abundance matching with H2 for DLAs at high redshifts

We present the study of CI/H$_2$ relative abundance in the diffuse cold neutral medium. Using the chemical and thermal balance model we calculated the dependence of CI/H$_2$ on the main parameters of the medium: hydrogen number density, metallicity, strength of the UV field, and cosmic ray ionization rate (CRIR). We show that observed relative CI and H$_2$ column densities in damped Lyman alpha systems (DLAs) at high redshifts can be reproduced within our model assuming the typically expected conditions in the diffuse cold neutral medium (CNM). Using the additional observed information the on metallicity, HI column density, and excitation of CI fine-structure levels, as well as temperature we estimated for a wide range metallicities in the CNM at high redshifts that CRIRs to be in the range from $\sim10^{-16}$ to $\rm few \times 10^{-15}\rm s^{-1}$, hydrogen number densities to be in range $\sim10 - 10^3$cm$^{-3}$, and UV field in range from $10^{-2}$ to $\rm few \times 10^2$ of Mathis field. We argue, that since the observed quantities used in this work are quite homogeneous and much less affected by the radiative transfer effects (in comparison with e.g. dissociation of HD and UV pumping of H$_2$ rotational levels) our estimates are quite robust against the assumption of the exact geometrical model of the cloud and local sources of the UV field.

astro-ph.GA↗

arXiv2020

OH in the diffuse interstellar medium: physical modelling and prospects with upcoming SKA precursor/pathfinder surveys

Hydroxyl ($\rm OH$) is known to form efficiently in cold gas ($T\sim 100$K) along with the molecule $\rm H_2$ and can be used as an efficient tracer of the diffuse molecular gas in the interstellar medium (ISM). Using a simple formalism describing the $\rm H\,I/H_2$ transition and a reduced network of major chemical reactions, we present a semi-analytical prescription to estimate the abundances of O-bearing molecules in the diffuse ISM. We show that predictions based on our prescription are in good agreement with the estimates obtained using the MEUDON PDR code which utilizes the full reaction network. We investigate the dependence of the relative abundances of $\rm OH/H\,I$ and $\rm OH/H_2$ on the variations of physical conditions i.e., the metallicity, number density ($n$), cosmic ray ionization rate ($ζ$) and strength of UV field ($χ$) in the medium. We find that the $\rm OH/H\,I$ abundances observed in the Galactic ISM can be reproduced by models with $n\sim 50$cm$^{-3}$, $χ\sim 1$ (Mathis field) and $ζ\sim3\times10^{-17}$s$^{-1}$, with a variation of about one dex allowed around these values. Using the constrained $\rm H_2$ column density distribution function at $z\sim3$, we estimate the $\rm OH$ column density distribution function and discuss future prospects with the upcoming large radio absorption line surveys.

astro-ph.GA↗

arXiv2010

The kinematics and chemical stratification of the Type Ia supernova remnant 0519-69.0

We present an analysis of the XMM-Newton and Chandra X-ray data of the young Type Ia supernova remnant 0519-69.0 in the Large Magellanic Cloud. We used data from both the Chandra ACIS and XMM-Newton EPIC-MOS instruments, and high resolution X-ray spectra obtained with the XMM-Newton Reflection Grating Spectrometer. The Chandra data show that there is a radial stratification of oxygen, intermediate mass elements and iron, with the emission from more massive elements more toward the center. Using a deprojection technique we measure a forward shock radius of 4.0(3) pc and a reverse shock radius of 2.7(4) pc. We took the observed stratification of the shocked ejecta into account in the modeling of the X-ray spectra with multi-component NEI models, with the components corresponding to layers dominated by one or two elements. An additional component was added in order to represent the ISM, which mostly contributed to the continuum emission. This model fits the data well, and was also employed to characterize the spectra of distinct regions extracted from the Chandra data. From our spectral analysis we find that the fractional masses of shocked ejecta for the most abundant elements are: M(O)=32%, M(Si/S)=7%/5%, M(Ar+Ca)=1%, and M(Fe) = 55%. From the continuum component we derive a circumstellar density of nH= 2.4(2)/cm^3. This density, together with the measurements of the forward and reverse shock radii suggest an age of 450+/-200 yr,somewhat lower than, but consistent with the estimate based on the optical light echo (600+/-200 yr). From the RGS spectra we measured a Doppler broadening of sigma=1873+/-50 km/s, from implying a forward shock velocity of vS = 2770+/-500 km/s. We discuss the results in the context of single degenerate explosion models, using semi-analytical and numerical modeling, and compare the characteristics of 0519-69.0 with those of other Type Ia supernova remnants.

astro-ph.HE↗