Search Results (111)

The star formation rate (SFR) is a crucial astrophysical characteristic for understanding the formation and evolution of galaxies, determining the interplay between the interstellar medium and stellar activity. The mainstream approach to studying stellar properties in galaxies relies on stellar population synthesis models. However, these methods neglect nebular emission, which can bias SFR estimates. Recent studies have indicated that nebular emission is non-negligible in strongly star-forming regions. However, targeted research is currently limited, particularly regarding galaxies at slightly higher redshifts ($z<0.4$). In this work, 696 star-formation galaxies with stellar mass in ${10}^9-{10}^{11}{M}_{\odot }$ are selected from the SDSS-DR18 and their spectra are fitted via the fitting analysis using differential evolution optimization (FADO) technique. FADO self-consistently fits both stellar and nebular emissions in galaxy spectra. The results show that the median $H_{\alpha }$ flux from FADO fitting differs from that of qsofitmore by approximately 0.028 dex. Considering the stellar mass effect, we found that although the nebular emission contribution (Nebular Ratio hereafter) is minimal, it increases modestly with redshift. We advocate explicitly accounting for nebular emission in the spectral fitting of higher-redshift galaxies, as its inclusion is essential to obtaining higher precision in future analyses. Full article

Galactic cosmic rays (GCRs), composed of protons and atomic nuclei, are accelerated in sources such as supernova remnants and pulsar wind nebulae, reaching energies up to the PeV range. As they propagate through the interstellar medium, their interactions with dense regions like molecular clouds produce secondary particles, including gamma-rays and neutrinos. In this study, we use the Geant4 Monte Carlo toolkit to simulate secondary particle production from GCR interactions within the Perseus molecular cloud, a nearby star-forming region. Our model incorporates realistic cloud composition, a wide range of incidence angles, and both hadronic and electromagnetic processes across a broad energy spectrum. The results highlight molecular clouds as significant sites of multi-messenger emissions and contribute to understanding the propagation of GCRs and the origin of diffuse gamma-ray and neutrino backgrounds in the Galaxy. Full article

Using the results of numerical simulations and astrophysical observations (mainly in the WMAP and Planck frequency bands), it is shown that Galactic foreground emission becomes more sensitive to the mean magnetic field with the frequency, resulting in the appearance of two levels of its randomization due to the chaotic/turbulent dynamics of a magnetized interstellar medium dominated by magnetic helicity. The galactic foreground emission is more randomized at higher frequencies. The Galactic synchrotron and polarized dust emissions have been studied in detail. It is shown that the magnetic field imposes its level of randomization on the synchrotron and dust emission. The main method for the theoretical consideration used in this study is the Kolmogorov–Iroshnikov phenomenology in the frames of distributed chaos notion. Despite the vast differences in the values of physical parameters and spatio-temporal scales between the numerical simulations and the astrophysical observations, there is a quantitative agreement between the results of the astrophysical observations and the numerical simulations in the frames of the distributed chaos notion. Full article

The disk of the Milky Way fills the interstellar medium in the form of discrete clouds, many (∼30) light-years across. The average density of this medium is 1 hydrogen atom per cm³ (Oort limit), in the clouds—several dozen atoms, and between the clouds about 0.01 atoms per cm³. It is well documented that physical properties of individual interstellar clouds are evidently different using high-resolution spectroscopic observations of slightly reddened stars. We prove here that the 5780/5797 strength ratio is nearly constant for all slightly reddened targets. The reason for this phenomenon remains unknown. All optically thin clouds are apparently of σ-type. The question of at which value of color excess one may expect a ζ-type cloud remains unanswered. For some (unknown) reason ζ-type clouds are always relatively opaque and contain a lot of molecular species. In all slightly reddened objects we always observe σ-type intervening clouds, almost free of simple molecules. Full article

Motivated by two of the most unexpected discoveries in recent years—the detection of ArH⁺ and ${\mathrm{HeH}}^{+}$ noble gas molecules in the cold, low-pressure regions of the Universe—we investigate [He₂H]⁺ and [Ne₂H]⁺ as potentially detectable species in the interstellar medium, providing new insights into their energetic and spectral properties. These findings are crucial for advancing our understanding of noble gas chemistry in astrophysical environments. To achieve this, we employed a data-driven approach to construct a high-accuracy machine-learning potential energy surface using the reproducing kernel Hilbert space method. Training and testing datasets are generated via high-level CCSD(T)/CBS[56] quantum chemistry computations, followed by a rigorous validation protocol to ensure the reliability of the potential. The ML-PES is then used to compute vibrational states within the MCTDH framework, and assign spectral transitions for the most common isotopologues of these species in the interstellar medium. Our results are compared with previously recorded values, revealing that both cations exhibit a prominent proton-shuttle motion within the infrared spectral range, making them strong candidates for telescopic observation. This study provides a solid computational foundation, based on rigorous, fully quantum treatments, aiming to assist in the identification of these yet unobserved He/Ne hydride cations in astrophysical environments. Full article

We discuss the spectral distinctions between B[e] stars and compact planetary nebulae. The differentiation between proto-planetary nebulae, transition objects between the asymptotic giant branch and planetary nebulae, and reflection nebulae in binary systems is also discussed. Infrared and millimeter-wave observations have identified many inorganic and organic molecules, as well as solid-state minerals, in the circumstellar environment. There is evidence that complex organics in the form of mixed aromatic/aliphatic nanoparticles (MAONs) are synthesized during the proto-planetary nebulae phase of evolution. Their ejection into the interstellar medium may have enriched the primordial Solar System, and the complex organics found in comets, asteroids, and planetary satellites could be stellar in origin. Full article

We propose a novel mechanism for photon–dark photon mass-state oscillations mediated by gravitational separation during propagation through the interstellar medium. This phenomenon establishes a new avenue for the detection of dark matter. By analyzing gravitational lensing data from quasars, we investigate the sensitivity of this approach to dark photons. Our analysis demonstrates constraints of $\epsilon <{10}^{-2}$ in the dark photon mass range of $1.7\times {10}^{-14}$ eV to $5.4\times {10}^{-14}$ eV. Furthermore, we propose potential applications of this mechanism to astrophysical systems with strong gravitational fields, such as neutron stars and black hole accretion disks. Full article

Star-forming galaxies are hosts of dominant populations of recently formed, hot, massive stars, which give rise to conspicuous stellar spectral features and provide the ionizing fluxes. Strong outflows of these stars shape their properties. These winds affect the evolution and the output of ionizing radiation, as well as the energy and momentum input in the interstellar medium and the chemical enrichment. Many properties of massive stars become even more extreme at a low metallicity. Owing to the pioneering observations of young, metal-poor stellar populations, both locally with HST and large ground-based facilities and at high redshift with JWST, we are at a key moment to assess our understanding of hot massive stars in these galaxies. Stellar population synthesis is a key tool. I will demonstrate how population models of hot, massive stars help to address some issues at the forefront of current research. The recent advent of new evolutionary and atmosphere models of massive stars probing new parameter space allows us to characterize the properties of nearby and distant populations. Full article

The reaction between methanol radical cations and methane, producing methyl radicals and protonated methanol, is pivotal to both astrochemical and atmospheric processes. Methanol and methane are the most abundant organic molecules in space and Earth’s atmosphere and central to molecular synthesis under different environmental conditions. Here, we present a combined experimental and theoretical investigation of the ion–molecule reaction between CH₃OH^•+ and CH₄. The study explores the reaction mechanism and energetics under ionized conditions utilizing quantum chemical methods and experimental data. The findings reveal that the reaction’s non-thermal behavior becomes pronounced when CH₃OH^•+ is vibrationally excited by photon absorption above the ionization threshold, as can happen in the presence of ionizing agents like cosmic rays. Conversely, in thermal equilibrium conditions, the reaction accelerates as temperatures decrease, as suggested by canonical rate coefficient calculations. The products can initiate further chemical reactions, shaping molecular networks in the interstellar medium and affecting atmospheric trace gas balances. Full article

We employed data from the Spitzer Space Telescope to investigate the presence of the aromatic amino acids tyrosine and phenylalanine in the interstellar gas of the young star cluster IC 348. Our analysis revealed emission lines in the observed spectrum that closely matched the strongest mid-infrared laboratory bands associated with tyrosine and phenylalanine in terms of wavelength and intensity. Through flux measurements, we estimated column densities along the line of sight toward the core of IC 348, ranging from 0.8–1.0 × 10¹¹ cm⁻². Additionally, these emission lines were evident in the combined spectra of more than 30 interstellar locations spanning various unrelated star-forming regions observed by Spitzer, indicating a widespread distribution of the molecules responsible for the emission throughout interstellar space. Prospective endeavors employing high spectral resolution mid-infrared searches for proteinogenic amino acids in protostars, protoplanetary disks, and the interstellar medium will play a pivotal role in elucidating the external origins of meteoritic amino acids and understanding the prebiotic conditions that laid the groundwork for life on early Earth. Full article

Over the past two decades, our understanding of star formation has undergone a major shift, driven by a wealth of data from infrared, submillimeter and radio surveys. The emerging view depicts star formation as a hierarchical process, which predominantly occurs along filamentary structures in the interstellar medium. These structures span a wide range of spatial scales, ultimately leading to the birth of young stars, which distribute in small groups, clusters and OB associations. Given the inherently complex and dynamic nature of star formation, a comprehensive understanding of these processes can only be achieved by examining their end products—namely, the distribution and properties of young stellar populations. In the Gaia era, the nearby OB associations are now characterised with unprecedented detail, allowing for a robust understanding of their formation histories. Nevertheless, to fully grasp the mechanisms of star formation and its typical scale, it is essential to study the much larger associations, which constitute the backbones of spiral arms. The large catalogues of young open clusters that have emerged from Gaia DR3 offer a valuable resource for investigating star formation on larger spatial scales. While the cluster parameters listed in these catalogues are still subject to many uncertainties and systematic errors, ongoing improvements in data analysis and upcoming Gaia releases promise to enhance the accuracy and reliability of these measurements. This review aims to provide a comprehensive summary of recent advancements and a critical assessment of the datasets available. Full article

Protonated hydrogen cyanide, HCNH⁺, is one of the most important molecules of interest in the astrophysical and astrochemical fields. This molecule not only plays the role of a reaction intermediary in various types of interstellar reactions but was also identified in Titan’s upper atmosphere. The cross sections for the dissociative recombination (DR) and vibrational (de-)excitation (VE and VDE) of HCNH⁺ and its ${\mathrm{CNH}}_2^{+}$ isomer are computed using a theoretical approach based on a combination of the normal mode approximation for the vibrational states of the target ions and the UK R-matrix code to evaluate electron-ion scattering matrices for fixed geometries of ions. The theoretical convoluted DR cross section for HCNH⁺ agrees well with the experimental data and a previous study. It was also found that the DR of the ${\mathrm{CNH}}_2^{+}$ isomer is important, which suggests that this ion might be present in DR experiments of HCNH⁺. Moreover, the ab initio calculations performed on the H₂CN⁺ isomer predict that this ion is a transition state. This result was confirmed by the study of the reaction path of the HCNH⁺ isomerization that was carried out by evaluating the intrinsic reaction coordinate (IRC). Finally, thermally averaged rate coefficients derived from the cross sections are provided for temperatures in the 10–10,000 K range. A comprehensive set of calculations is performed to assess the uncertainty of the obtained data. These results should help in modeling non-LTE spectra of HCNH⁺, taking into account the role of its most stable isomer, in various astrophysical environments. Full article

This work is dedicated to the study of interstellar medium (ISM) along the line of sight (LOS) of the transient low-mass X-ray binary, MXB 1659-298, capitalizing the high resolving power of XMM-Newton in the soft energy range. We emphasized the analysis of reflection grating spectrometer (RGS) data in the energy range 0.5–2.15 keV, suitable for the study of ISM. The paper includes an explanation of why, in the soft X-ray energy range, only two observations (out of seven) were deemed eligible for analysis. Three absorption lines associated with highly ionized Fe XX (1s²2p²-2p² (³p) 4d), Si XIV (1s²-1s2p), and Mg XI (1s²-1s6p) were identified in the observations, with IDs of 8620701(2001) and 748391601(2015). These new absorption lines and the absorption edge due to the neutral oxygen K edge seen in the spectra validate the multiphase structure of ISM. The predominance of interstellar medium over the ionized absorber is established along the direction of the source. The equivalent hydrogen column density measured is nearly equal to the galactic HI value derived previously. The small value of the ionic column density of Fe, Si, and Mg in the site of the high-temperature region resembles previous findings. Full article

High-resolution spectroscopy employing spatial heterodyne spectrographs (SHS) holds significant promise for forthcoming space missions, building upon its established track record in science applications. Notably, it offers exceptional performance and cost- effectiveness in the ultraviolet-visual (UV-Vis) region compared to contemporary instruments. SHS instruments provide high-resolution capabilities and substantially larger etendues than similar resolving power instruments. This study introduces a comprehensive Python-based SHS model integrated with a user-friendly web scraping interface for target star selection, parameter generation, and 2D interferogram creation. Our SHS model demonstrates double the resolving power of a grating spectrometer and a throughput comparable to a Fourier transform spectrometer (FTS) but without moving parts, enhancing robustness for deployment in space. The interferogram processing algorithm includes flat-fielding, bias removal, apodization, and an inverse Fourier transform (IFT) for accurate spectrum retrieval. Despite bandwidth limitations due to resolving power constraints, SHS models excel in applications requiring high spectral resolution over narrow wavelength ranges, such as studying isotopic emission lines. The model provides optimization results and trade-offs for system parameters, ensuring precise spectral recovery with realistic signal-to-noise ratio (SNR) values. SHS is versatile and effective for various scientific applications, including investigating atomic and molecular emissions from comets, planetary atmospheres, the Earth’s atmosphere, the Sun, and the interstellar medium (ISM). This research significantly contributes to expediting the development and deployment of SHS instruments, demonstrating their potential across numerous scientific domains. Full article

The chemical complexity in low-metallicity hot cores has been confirmed by observations. We investigate the effect of varying physical parameters, such as temperature, density and the cosmic ray ionisation rate (CRIR), on the molecular abundance evolution in low-metallicity hot cores using the UMIST gas phase chemical model. CRIR had the strongest effect on molecular abundance. The resultant molecular abundances were divided into three categories with different trends in time evolution. We compared our results with the observations of hot cores in the Large Magellanic Cloud (LMC). Our model fits best with the observations at a time of around ${10}^5$ years after the evaporation of ice and at the CRIR of $1.36\times {10}^{-16}$ ${\mathrm{s}}^{-1}$. The resultant abundances of the oxygen-bearing complex organic molecules (COMs), such as CH₃OH, HCOOCH₃ and CH₃OCH₃, do not fit with observations in the same physical condition and may be located in a different physical environment. Our results suggest that investigating the CRIR value is crucial to predict the molecular evolution in LMC hot cores. Full article