Relation between parameters of dust and parameters of molecular and atomic gas in extragalactic star-forming regions

The relationships between atomic and molecular hydrogen and dust of various sizes in extragalactic star-forming regions are considered, based on observational data from the Spitzer and Herschel infrared space telescopes, the Very Large Array (atomic hydrogen emission) and IRAM (CO emission). The source sample consists of approximately 300 star-forming regions in 11 nearby galaxies. Aperture photometry has been applied to measure the fluxes in eight infrared bands (3.6, 4.5, 5.8, 8, 24, 70, 100, and 160$\mu$m), the atomic hydrogen (21cm) line and CO (2--1) lines. The parameters of the dust in the starforming regions were determined via synthetic-spectra fitting, such as the total dust mass, the fraction of polycyclic aromatic hydrocarbons (PAHs), etc. Comparison of the observed fluxes with the measured parameters shows that the relationships between atomic hydrogen, molecular hydrogen, and dust are different in low- and high-metallicity regions. Low-metallicity regions contain more atomic gas, but less molecular gas and dust, including PAHs. The mass of dust constitutes about $1\%$ of the mass of molecular gas in all regions considered. Fluxes produced by atomic and molecular gas do not correlate with the parameters of the stellar radiation, whereas the dust fluxes grow with increasing mean intensity of stellar radiation and the fraction of enhanced stellar radiation. The ratio of the fluxes at 8 and 24$\mu$m, which characterizes the PAH content, decreases with increasing intensity of the stellar radiation, possibly indicating evolutionary variations of the PAH content. The results confirm that the contribution of the 24$\mu$m emission to the total IR luminosity of extragalactic star-forming regions does not depend on the metallicity.Comment: Published in Astronomy Reports, 2017, vol. 61, issue

Planar infall of CH3OH gas around Cepheus A HW2

Aims: In order to test the nature of an (accretion) disk in the vicinity of Cepheus A HW2, we measured the three-dimensional velocity field of the CH3OH maser spots, which are projected within 1000au of the HW2 object, with an accuracy of the order of 0.1km/s. Methods: We made use of the European VLBI Network (EVN) to image the 6.7GHz CH3OH maser emission towards Cepheus A HW2 with 4.5 milli-arcsecond resolution (3au). We observed at three epochs spaced by one year between 2013 and 2015. During the last epoch, on mid-march 2015, we benefited from the new deployed Sardinia Radio Telescope. Results: We show that the CH3OH velocity vectors lie on a preferential plane for the gas motion with only small deviations of 12+/-9 degrees away from the plane. This plane is oriented at a position angle of 134 degrees east of north, and inclined by 26 degrees with the line-of-sight, closely matching the orientation of the disk-like structure previously reported by Patel et al.(2005). Knowing the orientation of the equatorial plane, we can reconstruct a face-on view of the CH3OH gas kinematics onto the plane. CH3OH maser emission is detected within a radius of 900au from HW2, and down to a radius of about 300au, the latter coincident with the extent of the dust emission at 0.9mm. The velocity field is dominated by an infall component of about 2km/s down to a radius of 300au, where a rotational component of 4km/s becomes dominant. We discuss the nature of this velocity field and the implications for the enclosed mass. Conclusions: These findings bring direct support to the interpretation that the high-density gas and dust emission, surrounding Cepheus A HW2, trace an accretion disk.Comment: 9 pages, 4 figures, 2 tables, accepted by Astronomy & Astrophysic

Sources of Radiation in the Early Universe: The Equation of Radiative Transfer and Optical Distances

We have derived the radiative-transfer equation for a point source with a specified intensity and spectrum, originating in the early Universe between the epochs of annihilation and recombination, at redshifts z_\s =10^8\div 10^4. The direct radiation of the source is separated from the diffuse radiation it produces. Optical distances from the source for Thomson scattering and bremsstrahlung absorption at the maximum of the thermal background radiation are calculated as a function of the redshift z.The distances grow sharply with decreasing z, approaching asymptotic values, the absorption distance increasing more slowly and reaching their limiting values at lower z. For the adopted z values, the optical parameters of the Universe can be described in a flat model with dusty material and radiation, and radiative transfer can be treated in a grey approximation.Comment: 14 pages, 2 figure

The Development of Hydrophobic and Superhydrophobic Cementitious Composites

Freezing and thawing of water in saturated concrete induces stresses, cracks, spalling, and eventually allows chlorides, sulphates and other ions to penetrate through the porous space of concrete causing the corrosion and ultimately structural failure. These detrimental factors are limited if concrete has the ability to repel water. Water repellant concrete was achieved through internal and external surface applications. Hydrophobicity, over- and super-hydrophobicity are demonstrated by the ability of a surface to repel water and are characterized by contact angles. In cementitious composites internal hydrophobization can be achieved through the addition of superhydrophobic admixtures to fresh concrete resulting in an air void system with small, well-dispersed air bubbles to provide superior resistance to freezing and thawing. Hydrophobic, over- and super-hydrophobic surface coatings were achieved by the design of hierarchical surfaces tailoring the fiber content, mixture proportion, and superhydrophobic emulsions. Contact angle tests were used to characterize the developed coatings. The use of internal hydrophobization improves freezing and thawing resistance of fiber-reinforced composites as demonstrated by a durability factor of 100 through as many as 700 accelerated (-50°C to 20°C) cycles in 5% NaCl solution

Methanol in W3(H2O) and Surrounding Regions

We present the results of an interferometric study of 38 millimeter-wave lines of CH3OH in the region around the water maser source W3(H2O) and a region extending about 30" to the south and west of the hydroxyl maser source W3(OH). The methanol emitting region around W3(H2O) has an extent of 2.0" x 1.2" (4400 x 2600 AU). The density is of order 1.e7 cm-3, sufficient to thermalize most of the methanol lines. The kinetic temperature is approximately 140 K and the methanol fractional abundance greater than 1.e-6, indicative of a high degree of grain mantle evaporation. The W3(H2O) source contains sub-structure, with peaks corresponding to the TW source and Wyrowski's B/C, separated by 2500 AU in projection. The kinematics are consistent with these being distinct protostellar cores in a wide binary orbit and a dynamical mass for the region of a few tens of Mo. The extended methanol emission to the southwest of W3(OH) is seen strongly only from the lowest excitation lines and from lines known elsewhere to be class I methanol masers, namely the 84.5 GHz 5(-1)-4(0)E and 95.2 GHz 8(0)-7(1)A+ lines. Within this region there are two compact clumps, which we denote as swA and swB, each about 15" (0.16 pc projected distance) away from W3(OH). Excitation analysis of these clumps indicates the presence of lines with inverted populations but only weak amplification. The sources swA and swB appear to have kinetic temperatures of order 50-100 K and densities of order 1.e5 - 1.e6 cm-3. The methanol fractional abundance for the warmer clump is of order 1.e-7, suggestive of partial grain mantle evaporation. The clumping occurs on mass scales of order 1 Mo.Comment: 28 pages including 6 figures and 4 tables, accepted by Ap

Non-equilibrium excitation of methanol in Galactic molecular clouds: multi-transitional observations at 2 mm

We observed 14 methanol transitions near lambda=2 mm in Galactic star-forming regions. Broad, quasi-thermal J(0)-J(-1)E methanol lines near 157 GHz were detected toward 73 sources. Together with the 6(-1)-5(0)E and 5(-2)-6(-1)E lines at 133 GHz and the 7(1)-7(0)E line at 165 GHz, they were used to study the methanol excitation. In the majority of the observed objects, the Class I 6(-1)-5(0)E transition is inverted, and the Class II 5(-2)-6(-1)E and 6(0)-6(-1)E transitions are overcooled. This is exactly as predicted by models of low gain Class I masers. The absence of the inversion of Class II transitions 5(-2)-6(-1)E and 6(0)-6(-1)E means that quasi-thermal methanol emission in all objects arises in areas without a strong radiation field, which is required for the inversion.Comment: 23 pages paper (uses aasms4.sty), 12 pages tables (uses apjpt4.sty), 10 Jpeg figures, submitted to the ApJ