Modeling the total and polarized emission in evolving galaxies: “Spotty” magnetic structures

Future radio observations with the Square Kilometre Array (SKA) and its precursors will be sensitive to trace spiral galaxies and their magnetic field configurations up to redshift z ≈ 3. We suggest an evolutionary model for the magnetic configuration in star‐forming disk galaxies and simulate the magnetic field distribution, the total and polarized synchrotron emission, and the Faraday rotation measures for disk galaxies at z ≲ 3. Since details of dynamo action in young galaxies are quite uncertain, we model the dynamo action heuristically relying only on well‐established ideas of the form and evolution of magnetic fields produced by the mean‐field dynamo in a thin disk. We assume a small‐scale seed field which is then amplified by the small‐scale turbulent dynamo up to energy equipartition with kinetic energy of turbulence. The large‐scale galactic dynamo starts from seed fields of 100 pc and an averaged regular field strength of 0.02 μG, which then evolves to a “spotty” magnetic field configuration in about 0.8 Gyr with scales of about one kpc and an averaged regular field strength of 0.6 μG. The evolution of these magnetic spots is simulated under the influence of star formation, dynamo action, stretching by differential rotation of the disk, and turbulent diffusion. The evolution of the regular magnetic field in a disk of a spiral galaxy, as well as the expected total intensity, linear polarization and Faraday rotation are simulated in the rest frame of a galaxy at 5GHz and 150 MHz and in the rest frame of the observer at 150 MHz. We present the corresponding maps for several epochs after disk formation. Dynamo theory predicts the generation of large‐scale coherent field patterns (“modes”). The timescale of this process is comparable to that of the galaxy age. Many galaxies are expected not to host fully coherent fields at the present epoch, especially those which suffered from major mergers or interactions with other galaxies. A comparison of our predictions with existing observations of spiral galaxies is given and discussed (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Interacting Galaxies — the X-ray View

We have selected a complete, flux-limited sample of bright point-like sources with absorbed X-ray spectra from the ROSAT All-Sky survey, the ROSAT Hard Survey (RHS). The sample is drawn from the high-galactic latitude sky, |b^II| > ±30°, and avoids the general direction of the Magellanic Clouds and the Virgo Cluster. It comprises a total of 182 objects of which 118 were previosly catalogued objects and 64 were new AGN candidates. Through optical follow-up studies at La Silla, Calar Alto and the 6m Zelentchuk telescope we could identify 56 of the new objects, thus achieving a spectrscopic completeness of 96% of the sample. The selection strategy turned out to be extremely useful. Out of the new identifications, 84% are indeed active galaxies or emission line galaxies. While 14 objects are new BL Lac candidates 33 of the new AGN are Seyfert galaxies with a redshift distribution in the range 0.021–0.63, peaking at around 0.06, i.e. relatively local. Surprisingly, about 40% of the X-ray selected Seyfert galaxies seem to reside in interacting systems. With smaller selection uncertainties this fraction exceeds the number of paired galaxies in optically selected samples and therefore gives strong support to the idea that AGN activity is triggered by interaction.     

Identification of “small” dust impacts in the Ulysses dust detector data

Since October 1990, 3 weeks after the launch of the Ulysses spacecraft, the dust detector onboard recorded impacts of cosmic dust particles. Besides dust impacts, the detector recorded noise from a variety of sources. So far, a very rigid scheme had been applied to eliminate noise from impact data. The data labeled “big” dust impacts previously led to the identification of interstellar dust and of dust streams from Jupiter. The analysis presented here is concerned with data of signals of small amplitudes which are strongly contaminated by noise. Impacts identified in this data set are called “small” impacts. It is shown that dust impacts can be clearly distinguished from noise for most of the events due to the multi-coincidence characteristics of the instrument. 516 “small” impacts have been identified. For an additional 119 events, strong arguments can be given that they are probably small dust impacts. Thereby, the total number of dust impacts increases from 333 to 968 in the time period from 28 October 1990 to 31 December 1992. This increase permits a better statistical analysis, especially of the Jupiter dust streams which consist mostly of small and fast particles. Additional dust streams have been identified between the already known streams before and after Jupiter flyby. The dependence of the deflection from the Jupiter direction, the stream intensity and width on Jupiter distance support the assertion that they have been emitted from the Jovian system. The masses of the 635 “small” dust particles range from 6 × 10⁻¹⁷ to 3 × 10⁻¹⁰ g with a mean value of 1 × 10⁻¹² g, which compares to a range from 1 × 10⁻¹⁶ to 4 × 10⁻⁹ g with a mean value of 2 × 10⁻¹¹ g for the previously identified 333 “big” dust particles.     

“Sweating meteorites”—Water‐soluble salts and temperature variation in ordinary chondrites and soil from the hot desert of Oman

The common appearance of hygroscopic brine (“sweating”) on ordinary chondrites (OCs) from Oman during storage under room conditions initiated a study on the role of water‐soluble salts on the weathering of OCs. Analyses of leachates from OCs and soils, combined with petrography of alteration features and a 11‐month record of in situ meteorite and soil temperatures, are used to evaluate the role of salts in OC weathering. Main soluble ions in soils are Ca²⁺, SO₄^2?, HCO₃^?, Na⁺, and Cl^?, while OC leachates are dominated by Mg²⁺ (from meteoritic olivine), Ca²⁺ (from soil), Cl^? (from soil), SO₄^2? (from meteoritic troilite and soil), and iron (meteoritic). “Sweating meteorites” mainly contain Mg²⁺ and Cl^?. The median Na/Cl mass ratio of leachates changes from 0.65 in soils to 0.07 in meteorites, indicating the precipitation of a Na‐rich phase or loss of an efflorescent Na‐salt. The total concentrations of water‐soluble ions in bulk OCs ranges from 600 to 9000 μg g^?1 (median 2500 μg g^?1) as compared to 187–14140 μg g^?1 in soils (median 1148 μg g^?1). Soil salts dissolved by rain water are soaked up by meteorites by capillary forces. Daily heating (up to 66.3 °C) and cooling of the meteorites cause a pumping effect, resulting in a strong concentration of soluble ions in meteorites over time. The concentrations of water‐soluble ions in meteorites, which are complex mixtures of ions from the soil and from oxidation and hydrolysis of meteoritic material, depend on the degree of weathering and are highest at W3. Input of soil contaminants generally dominates over the ions mobilized from meteorites. Silicate hydrolysis preferentially affects olivine and is enhanced by sulfide oxidation, producing local acidic conditions as evidenced by jarosite. Plagioclase weathering is negligible. After completion of troilite oxidation, the rate of chemical weathering slows down with continuing Ca‐sulfate contamination.     

Galaxy distribution in a 36□° field near the north galactic pole

The results of galaxy counts on plates taken with the Tautenburg Schmidt telescope in a 36□° region around the globular cluster M3 are presented and discussed. More than 26000 galaxies on four blue plates (covering the whole region) and nearly 18000 galaxies on two red plates (covering half the region) have been counted in 5′ × 5′ cells. The discussion in the present paper includes a first determination of the two-point correlation function and a dispersion curve analysis. The results are not very different from those obtained for the Jagiellonian field. It is suggested that counting errors may influence the conclusions drawn for the space distribution of galaxies and its possible secular change.     

Comparison of dust‐to‐gas ratios in luminous,ultraluminous, and hyperluminous infrared galaxies

The dust‐to‐gas ratios in three different samples of luminous, ultraluminous, and hyperluminous infrared galaxies are calculated by modelling their radio to soft X‐ray spectral energy distributions (SED) using composite models which account for the photoionizing radiation from H II regions, starbursts, or AGNs, and for shocks. The models are limited to a set which broadly reproduces the mid‐IR fine structure line ratios of local, IR bright, starburst galaxies. The results show that two types of clouds contribute to the IR emission. Those characterized by low shock velocities and low preshock densities explain the far‐IR dust emission, while those with higher velocities and densities contribute to the mid‐IR dust emission. Clouds with shock velocities of 500 km s^–1 prevail in hyperluminous infrared galaxies. An AGN is found in nearly all of the ultraluminous infrared galaxies and in half of the luminous infrared galaxies of the sample. High IR luminosities depend on dust‐to‐gas ratios as high as ∼0.1 by mass, however most hyperluminous IR galaxies show dustto‐gas ratios much lower than those calculated for the luminous and ultraluminous IR galaxies. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Radio continuum and far-infrared emission from the galaxies in the Eridanus group

The Eridanus galaxies follow the well-known radio—FIR correlation. The majority (70%) of these galaxies have their star formation rates below that of the Milky Way. The galaxies that have a significant excess of radio emission are identified as low luminosity AGNs based on their radio morphologies obtained from the GMRT observations. There are no powerful AGNs (L _20cm > 10²³ W Hz⁻¹) in the group. The two most far-infrared and radio luminous galaxies in the group have optical and HI morphologies suggestive of recent tidal interactions. The Eridanus group also has two far-infrared luminous but radio-deficient galaxies. It is believed that these galaxies are observed within a few Myr of the onset of an intense star formation episode after being quiescent for at least a 100 Myr. The upper end of the radio luminosity distribution of the Eridanus galaxies (L _20cm ∼ 10²² W Hz⁻¹) is consistent with that of the field galaxies, other groups, and late-type galaxies in nearby clusters.     

Complex exposure histories for meteorites with “short” exposure ages

Abstract— We report measurements of ²⁶Al and ¹⁰Be activities in nine ordinary chondrites and of the light noble gas concentrations and ³⁶Cl and ⁴¹Ca activities in subsets of those meteorites. All but Murray have low ²¹Ne concentrations (<1.0 × 10^?8cm³STP/g) and have previously been used to estimate ²¹Ne production rates. Ladder Creek, Murchison, Sena, and Timochin have inventories of cosmogenic radionuclides that are compatible with a single stage of irradiation and give ²¹Ne production rates that are consistent with the standard L-chondrite value of 0.33 × 10^?8cm³STP/g/Ma. In contrast, Cullison, Guenie, Shaw, and Tsarev experienced complex irradiation histories. They and several other meteorites with low nominal exposure ages also have lower ³He/²¹Ne ratios than expected based on their ²²Ne/²¹Ne ratios. A general association between low ²¹Ne contents and ³He losses suggests that meteorites with short lifetimes often occupy orbits with small perihelia. However, meteorites with low ²¹Ne contents, one-stage exposure histories, and losses of cosmogenic ³He are rare. Possible explanations for the scarcity are (1) statistical, (2) that it is harder for more deeply buried protometeoroids to lose gas in a liberating collision, and (3) that it is harder to insert more deeply buried protometeoroids directly into orbits with small perihelia.     

On the D́ust content of nearby galaxies

By inspection of photographs of the Hubble Atlas of Galaxies the frequency distribution of the sizes of dark cloud complexes in the four nearby galaxies NGC 3031, 5128, 5194 and 5457 is derived and the total amount of dust in these systems is estimated. The frequency distribution of the clouds is nearly the same in all the considered galaxies and may be approximated by n(R) ∼ e^−kR, k ≈︂ 0.050 pc⁻¹. The total amount of dust yields to roughly 10⁶M⊙.     

Decoherence time scales for “meteoroid streams”

Abstract— We explore the orbital dynamics of Earth‐crossing objects with the intent to understand the time scales under which an “orbital stream” of material could produce time‐correlated meteorite falls. These “meteoroid streams” have been suggested to be associated with three well‐known meteorite‐dropping fireballs (Innisfree, Peekskill, and P?íbram). We have performed two different analyses of the statistical significance of the “orbital similarity,” in particular calculating how often orbits of the same level of similarity would come from a random sample. Secondly, we have performed extremely detailed numerical integrations related to these three cases, and we find that if they were streams of objects in similar orbits, then they would become “decoherent” (in the sense that the day‐of‐fall of meteorites of these streams become almost random) on time scales of 10⁴–10⁵ yr. Thus, an extremely recent breakup would be required, much more recent that the cosmic ray exposure ages of the recovered falls in each case. We conclude that orbital destruction is too efficient to allow the existence of long‐lived meteoroid streams and that the statistical evidence for such streams is insufficient; random fall patterns show comparable levels of clustering.     

Comparisons of u ‐, g ‐, r ‐, i ‐, and z ‐band luminosity distributions between galaxy members of compact groups and isolated galaxies

To investigate the environmental dependence of u ‐, g ‐, r ‐, i ‐, and z ‐band luminosities, we perform comparative studies of luminosity distributions between galaxy members of compact groups (CGs) and isolated galaxies. It is found that for the r, i, and z bands isolated galaxies have a higher proportion of faint galaxies and a lower proportion of luminous galaxies than galaxy members of CGs, but for the u band an opposite trend is observed. The correlation between the g ‐band luminosity and the environment has different trends in different luminosity regions (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

<Emphasis Type="Italic">BVRI</Emphasis> CCD-photometry of comparison stars in the neighborhoods of galaxies with active nuclei. III

Observations with a matrix photometer are reported. The stellar magnitudes in the BVRcIc bands are estimated for 80 comparison stars in the neighborhoods of 10 galaxies with active nuclei: 2 Seyfert galaxies, 4 quasars, and 4 BL Lac objects. The stellar magnitudes of the observed stars range from 11 to 19^m.5. For stars with magnitudes of 14–15^m the typical photometric errors are 0^m.011, 0^m.008, 0^m.006, and 0^m.007 in the B, V, R, and I bands, respectively. The BVRI magnitudes for most of these stars were not known previously. 14′ × 14′ finding charts for these stars are included. These results can be used for differential BVRI photometry of active galactic nuclei. __________ Translated from Astrofizika, Vol. 50, No. 1, pp. 57–72 (February 2007).     

Analysis of the properties of clusters of galaxies in the region of the Ursa Major supercluster

We analyze the properties of the clusters of galaxies in the region of the Ursa Major (UMa) supercluster using observational data from SDSS and 2MASS catalogs. The region studied includes a supercluster (with a galaxy and cluster overdensity of 3 and 15, respectively) and field clusters inside the 150-Mpc diameter surrounding region. The total dynamical mass of 10 clusters of galaxies in UMa is equal to 2.25 × 10¹⁵ M _⊙, and the mass of 11 clusters of galaxies in the UMa neighborhood is equal to 1.70 × 10¹⁵ M _⊙. The fraction of early-type galaxies brighter than M _K ^* + 1 in the virialized regions of clusters is, on the average, equal to 70%, and it is virtually independent on the mass of the cluster. The fraction of these galaxies and their average photometric parameters are almost the same both for UMa clusters and for the clusters located in its surroundings. Parameters of the clusters of galaxies, such as infrared luminosities up to a fixed magnitude, the mass-to-luminosity ratio, and the number of galaxies have almost the same correlations with the cluster mass as in other samples of galaxies clusters. However, the scatter of these parameters for UMa member clusters is twice smaller than the corresponding scatter for field clusters, possibly, due to the common origin of UMa clusters and synchronized dynamical evolution of clusters in the supercluster.     

Existence and amount of intergalactic dust

The existence of intergalactic dust has been proved by the following observational facts: the decrease of the numbers of distant galaxies and clusters of galaxies behind the central regions of near clusters of galaxies; the different distributions of RR Lyrae stars and galaxies near ι Microscopii (Hoffmeister's cloud); the dependence of colour excesses of galaxies on supergalactic coordinates as well as on the surface density of bright galaxies; the colour index vs redshift correlation of quasistellar objects. The densities of intergalactic dust are estimated to be between 5×10^?30 g cm^?3 (near the centers of clusters of galaxies) and 2×10^?34 g cm^?3 (in general intergalactic space). The grains may be formed either in the early phases of the Universe (25相似文献   

Possible dark matter in spiral galaxies of the coma cluster

The relationship between the rotation curves for the galaxies and the distribution of mass and angular momentum within the galaxies is examined. The theory of angular momentum transfer is applied to the observed properties of the galaxies. The coupling between the dynamical mass of a spiral galaxy and its luminosity is studied. Most of the spiral galaxies in subclusters surrounding NGC 4889, NGC 4874, and NGC 4839 in the Coma cluster are galaxies that have lower luminosities, with M_B fainter than −21^m.5. These galaxies are characterized by a higher mass-to-luminosity ratio than that of the galaxies with higher luminosities M_B brighter than −21^m.5, which suggests the presence of a large fraction of dark matter in the spiral galaxies of the subclusters. Translated from Astrofizika, Vol. 52, No. 1, pp. 75–84 (February 2009).     

Spectroscopy and photometry of ShCG 191 – Abell 1097

In the course of investigation of Shakhbazian compact groups we studied the group ShCG 191 which has been identified also as the Abell cluster A1097. By its richness it may be classified as a rich compact group or a poor cluster. We determined redshifts of 14 objects in the area of the cluster and found that two of the supposed members of the group are stars. Redshifts of 12 galaxies show that the system is gravitationally bound. The V and R magnitudes of 23 member galaxies and their morphological types are determined. We present in this paper also the surface brightness contours of member galaxies in the central area of the cluster, the curves of isophotal twisting and the Fourier parameter a₄. It is shown that some galaxies in the cluster are interacting with each other. Physical parameters of the group are close to those of ShCGs. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

GRIER(b), A “MONOMICT,” BRECCIATED CHONDRITE

The Grier(b), New Mexico meteorite, a single mass of 929.4 grams, was found in 1969. This brecciated chondrite can be classified as an L-group from the bulk chemical analysis, ～ 8 wt % metal with an estimated total iron content of 25 wt %, and the constant olivine (Fa_25.5) and orthopyroxene (Fs₂₃) compositions. The main portion of the meteorite fits the criteria for an L5 (grey to intermediate hypersthene) chondrite. A conspicuous, large (several cm³) dense fragment, texturally an L6–7 chondrite, contains practically no metal or chondrules. However, there is little variation in the bulk silicate and individual phase compositions between the fragment and the matrix. In spite of this, it seems unlikely that the fragment was created in situ because metal and sulfide are not found in the fragment-matrix contact zone; thus the formation of olivines and pyroxenes in both parts, as well as the “draining” of metal from the fragment, occurred prior to accretion with little, if any, subsequent thermal metamorphism.     

Luminosity function of the field galaxies

The Schmidt method for constructing the luminosity function of galaxies is generalized to include the dependence of the density of galaxies on distance in the near universe. The logarithmic luminosity function (LLF) of the field galaxies as a function of morphological type is constructed. It is found that the LLF for all the galaxies, as well as separately for elliptical and lenticular galaxies, can be represented as a Schechter function within a narrow range of absolute magnitudes. The LLF for spiral galaxies is a Schechter function over a rather wide range of absolute magnitudes, −21.0 ≤ M ≤ −14 . The parameter M_* varies little over the spiral galaxies. The parameter α in the Schechter function decreases on going from early to later spirals. On going from elliptical to lenticular galaxies, from early spiral galaxies and onward to later spiral galaxies, a decrease in the average luminosity of the galaxies is observed in the bright end, −23 ≤ M ≤ −17.8 . The completeness and average density of the samples are estimated for galaxies of different morphological types. The average number density of all the galaxies within the range −23 ≤ M ≤ −13 is 0.126 Mpc^-3.     

GMRTHI observations of the Eridanus group of galaxies

The GMRTHI 21 cm-line observations of galaxies in the Eridanus group are presented. The Eridanus group, at a distance of ≈ 23 Mpc, is a loose group of ≈200 galaxies. The group extends to more than 10 Mpc in projection. The velocity dispersion of the galaxies in the group is ≈240 km s⁻¹. The galaxies are clustered into different sub-groups. The overall population mix of the group is 30% (E + S0) and 70% (Sp + Irr). The observations of 57 Eridanus galaxies were carried out with the GMRT for ≈ 200 h. HI emission was detected from 31 galaxies. The channel rms of ≈ 1 mJy beam⁻¹ was achieved for most of the image-cubes made with 4 h of data. The corresponding HI column density sensitivity (3σ) is ≈ 1 × 10²⁰ cm⁻² for a velocity-width of ≈ 13.4 km s⁻¹. The 3σ detection limit of HI mass is ≈ 1.2 X 10⁷ Mpd for a line-width of 50 km s⁻¹. Total HI images, HI velocity fields, global HI line profiles, HI mass surface densities, HI disk parameters and HI rotation curves are presented. The velocity fields are analysed separately for the approaching and the receding sides of the galaxies. These data will be used to study the HI and the radio continuum properties, the Tully-Fisher relations, the dark matter halos, and the kinematical and HI lopsidedness in galaxies.