The Environmental Dependence of Gas Properties in Dense Cores of a Protocluster at z ∼ 2.5 Revealed with ALMA

In a protocluster USS1558-003 at z = 2.53, galaxies in the dense cores show systematically elevated star-forming activity compared to those in less dense regions. To understand its origin, we look into the gas properties of the galaxies in the dense cores by conducting deep 1.1 mm observations with the Atacama Large Millimeter/submillimeter Array. We detect interstellar dust continuum emission from 12 member galaxies and estimate their molecular gas masses. Comparing these gas masses with our previous measurements from the CO(3–2) line, we infer that the latter might be overestimated. We find that the gas to stellar mass ratios of the galaxies in the dense cores tend to be higher (at M * ∼ 1010 M ⊙ where we see the enhanced star-forming activity), suggesting that such large gas masses can sustain their high star-forming activity. However, if we compare the gas properties of these protocluster galaxies with the gas scaling relations constructed for field galaxies at a similar cosmic epoch, we find no significant environmental difference at the same stellar mass and star formation rate. Although both gas mass ratios and star-forming activity are enhanced in the majority of member galaxies, they appear to follow the same scaling relation as field galaxies. Our results are consistent with the scenario in which the cold gas is efficiently supplied to protocluster cores and to galaxies therein along surrounding filamentary structures, which leads to the high gas mass fractions and thus the elevated star formation activity, but without changing the star formation law.

Optical Properties of C−rich (12C, SiC and FeC) Dust Layered Structure of Massive Stars

The composition and structure of interstellar dust are important and complex for the study of the evolution of stars and the interstellar medium (ISM). However, there is a lack of corresponding experimental data and model theories. By theoretical calculations based on ab-initio method, we have predicted and geometry optimized the structures of Carbon-rich (C-rich) dusts, carbon (12C), iron carbide (FeC), silicon carbide (SiC), even silicon (28Si), iron (56Fe), and investigated the optical absorption coefficients and emission coefficients of these materials in 0D (zero−dimensional), 1D, and 2D nanostructures. Comparing the nebular spectra of the supernovae (SN) with the coefficient of dust, we find that the optical absorption coefficient of the 2D 12C, 28Si, 56Fe, SiC and FeC structure corresponds to the absorption peak displayed in the infrared band (5−8) µm of the spectrum at 7554 days after the SN1987A explosion. And it also corresponds to the spectrum of 535 days after the explosion of SN2018bsz, when the wavelength in the range of (0.2−0.8) and (3−10) µm. Nevertheless, 2D SiC and FeC corresponds to the spectrum of 844 days after the explosion of SN2010jl, when the wavelength is within (0.08−10) µm. Therefore, FeC and SiC may be the second type of dust in SN1987A corresponding to infrared band (5−8) µm of dust and may be in the ejecta of SN2010jl and SN2018bsz. The nano−scale C−rich dust size is ∼ 0.1 nm in SN2018bsz, which is 3 orders of magnitude lower than the value of 0.1 µm. In addition, due to the ionization reaction in the supernova remnant (SNR), we also calculated the Infrared Radiation (IR) spectrum of dust cations. We find that the cation of the 2D layered (SiC)2+ has a higher IR spectrum than those of the cation (SiC)1+ and neutral (SiC)0+.

Diastereoselective Formation of Trans-HC(O)SH through Hydrogenation of OCS on Interstellar Dust Grains

With the presence of evermore complex S-bearing molecules being detected lately, studies of their chemical formation routes need to keep up the pace to rationalize observations, suggest new candidates for detection, and provide input for chemical evolution models. In this paper, we theoretically characterize the hydrogenation channels of OCS on top of amorphous solid water (ASW) as an interstellar dust grain analog in molecular clouds. Our results show that the significant reaction outcome is trans-HC(O)SH, a recently detected prebiotic molecule toward G+0.693. The reaction is diastereoselective, explaining the apparent absence of the cis isomer in astronomical observations. We found that the reaction proceeds through a highly localized radical intermediate (cis-OCSH), which could be essential in the formation of other sulfur-bearing complex organic molecules due to its slow isomerization dynamics on top of ASW.

The Role of Terahertz and Far-IR Spectroscopy in Understanding the Formation and Evolution of Interstellar Prebiotic Molecules

Stellar systems are often formed through the collapse of dense molecular clouds which, in turn, return copious amounts of atomic and molecular material to the interstellar medium. An in-depth understanding of chemical evolution during this cyclic interaction between the stars and the interstellar medium is at the heart of astrochemistry. Systematic chemical composition changes as interstellar clouds evolve from the diffuse stage to dense, quiescent molecular clouds to star-forming regions and proto-planetary disks further enrich the molecular diversity leading to the evolution of ever more complex molecules. In particular, the icy mantles formed on interstellar dust grains and their irradiation are thought to be the origin of many of the observed molecules, including those that are deemed to be “prebiotic”; that is those molecules necessary for the origin of life. This review will discuss both observational (e.g., ALMA, SOFIA, Herschel) and laboratory investigations using terahertz and far-IR (THz/F-IR) spectroscopy, as well as centimeter and millimeter spectroscopies, and the role that they play in contributing to our understanding of the formation of prebiotic molecules. Mid-IR spectroscopy has typically been the primary tool used in laboratory studies, particularly those concerned with interstellar ice analogues. However, THz/F-IR spectroscopy offers an additional and complementary approach in that it provides the ability to investigate intermolecular interactions compared to the intramolecular modes available in the mid-IR. THz/F-IR spectroscopy is still somewhat under-utilized, but with the additional capability it brings, its popularity is likely to significantly increase in the near future. This review will discuss the strengths and limitations of such methods, and will also provide some suggestions on future research areas that should be pursued in the coming decade exploiting both space-borne and laboratory facilities.

New Horizons Detection of the Local Galactic Lyman-α Background

Since 2007 the Alice spectrograph on the New Horizons (NH) spacecraft has been used to periodically observe the Lyman-α (Lyα) emissions of the interplanetary medium (IPM), which mostly result from resonant scattering of solar Lyα emissions by interstellar hydrogen atoms passing through the solar system. Three observations of IPM Lyα along a single great circle were made during the NH cruise to Pluto, and these have been supplemented by observations along six great circles (spread over the sky at 30° intervals), acquired one month before and one day after the NH flyby of Pluto, and on a further five occasions since then, out to just over 47 au from the Sun. These data indicate a distant Lyα background of 43 ± 3 Rayleigh brightness (equivalent to 56 ± 4 nW m−2 sr−1), which is present in all directions (i.e., not only in the upstream direction, as previously reported). This result is found independently by: (1) the falloff with distance from the Sun of the IPM Lyα brightness observed by NH–Alice in several directions on the sky, and (2) the residual between the observed brightness and a model brightness accounting for the resonantly scattered solar Lyα component alone. The repeated observations show that this distant Lyα background is constant and uniform over the sky, and represents the local Galactic Lyα background. The observations show no strong correlation with the cloud structure of the local IPM. The observed brightness constrains the absorption coefficient of interstellar dust at Lyα to 0.2 ± 0.01 kpc−1.

How many interstellar visitors are there in the Solar System?

По результатам краткого обзора наблюдений вошедших в Солнечную систему межзвездных пылинок, метеороидов и более крупных тел и на основе моделей, описывающих спектры масс таких тел, отмечен огромный разброс (много порядков величины) в оценках отношения η потока межзвездных частиц к общему потоку частиц в окрестности Земли и в целом в Солнечной системе. Этот разброс означает, что современные возможности не позволяют определенно ответить на вопрос в заголовке статьи. При анализе результатов наблюдений необходимо учитывать характер зависимости отношения η от размера частиц r, т. е. η(r). Эта зависимость определяется процессами генерации и динамической эволюции населения малых тел в Солнечной системе и за ее пределами. According to the results of a brief review of observations included in the Solar system, interstellar dust, meteoroids and larger bodies, and on the basis of models describing the spectra of the masses of these bodies, we mark a huge spread (many orders of magnitude) in estimates of the relationship η of the flow of interstellar particles to the total particle flux near the Earth and in the whole Solar system. These differences mean that modern capabilities do not allow us to definitely answer the question in the title of the article. When analyzing the results of observations, it is necessary to take into account the nature of the dependence of the ratio η on the particle size r, i.e. η(r). This dependence is determined by the processes of generation and dynamic evolution of the population of small bodies in the Solar system and beyond.

The origin of Galactic cosmic rays as revealed by their composition

ABSTRACT Galactic cosmic rays (GCRs) are thought to be accelerated in strong shocks induced by massive star winds and supernova explosions sweeping across the interstellar medium. But the phase of the interstellar medium from which the CRs are extracted has remained elusive until now. Here, we study in detail the GCR source composition deduced from recent measurements by the AMS-02, Voyager 1, and SuperTIGER experiments to obtain information on the composition, ionization state, and dust content of the GCR source reservoirs. We show that the volatile elements of the CR material are mainly accelerated from a plasma of temperature ≳ 2 MK, which is typical of the hot medium found in Galactic superbubbles energized by the activity of massive star winds and supernova explosions. Another GCR component, which is responsible for the overabundance of 22Ne, most likely arises from acceleration of massive star winds in their termination shocks. From the CR-related gamma-ray luminosity of the Milky Way, we estimate that the ion acceleration efficiency in both supernova shocks and wind termination shocks is of the order of 10−5. The GCR source composition also shows evidence for a preferential acceleration of refractory elements contained in interstellar dust. We suggest that the GCR refractories are also produced in superbubbles, from shock acceleration and subsequent sputtering of dust grains continuously incorporated into the hot plasma through thermal evaporation of embedded molecular clouds. Our model explains well the measured abundances of all primary and mostly primary CRs from H to Zr, including the overabundance of 22Ne.