A Faraday rotation template for the Galactic sky

Using a set of compilations of measurements for extragalactic radio sources, we construct all-sky maps of the Faraday rotation produced by the Galactic magnetic field. In order to generate the maps, we treat the radio source positions as a kind of 'mask' and construct combinations of spherical harmonic modes that are orthogonal on the masked sky. As long as relatively small multipoles are used, the resulting maps are quite stable to changes in the selection criteria for the sources, and show clearly the structure of the local Galactic magnetic field. We also suggest the use of these maps as templates for cosmic microwave background (CMB) foreground analysis, illustrating the idea with a cross-correlation analysis between the Wilkinson Microwave Anisotropy Probe ( WMAP ) data and our maps. We find a significant cross-correlation, indicating the presence of a significant residual contamination.     

Far-infrared detection limits – II. Probing confusion including source confusion

We present a comprehensive analysis for the determination of the confusion levels for the current and the next generation of far-infrared surveys assuming three different cosmological evolutionary scenarios. We include an extensive model for diffuse emission from infrared cirrus in order to derive absolute sensitivity levels taking into account the source confusion noise due to point sources, the sky confusion noise due to the diffuse emission, and instrumental noise. We use our derived sensitivities to suggest best survey strategies for the current and the future far-infrared space missions Spitzer , AKARI ( ASTRO-F ), Herschel and SPICA . We discuss whether the theoretical estimates are realistic and the competing necessities of reliability and completeness. We find the best estimator for the representation of the source confusion and produce predictions for the source confusion using far-infrared source count models. From these confusion limits considering both source and sky confusions, we obtain the optimal, confusion limited redshift distribution for each mission. Finally, we predict the cosmic far-infrared background (CFIRB), which includes information about the number and distribution of the contributing sources.     

The Sunyaev–Zel'dovich effect contribution to WMAP: a cross-correlation between WMAP and ROSAT

We cross-correlate WMAP and ROSAT diffuse X-ray background maps and look for common features in both data sets. We use the power spectrum of the product maps and the cross-power spectrum to highlight a possible correlation. The power spectrum of the product maps does not detect any correlation and the cross-power spectrum does not show any significant deviation from zero. We explore different explanations for this lack of correlation. A universe with a low value of  σ₈  could naturally explain the lack of correlation. We also discuss the systematic effects that can affect this result, in particular the subtraction of some cluster signal from the ROSAT diffuse maps, which could significantly suppress the correlation signal. These systematic effects considerably reduce the significance of our constraints on the cosmological model. When we include the systematic effects, we find a weaker constraint on  σ₈  , allowing models with values as large as  σ₈= 1  (for  Ω_m= 0.3  ) to be consistent with the lack of correlation. To illustrate the capabilities of the method with future high-quality data, we show how from the correlation signal it should be possible to predict the level of contamination of the Sunyaev–Zel'dovich effect on the power spectrum of the cosmic microwave background. Within the systematic errors, we find evidence that this contribution is negligible for WMAP and is expected to be small in experiments like ACBAR or CBI, but can be important for future high-resolution experiments.     

The radio–mid-infrared correlation and the contribution of 15-μm galaxies to the 1.4-GHz source counts

The radio counterparts to the 15-μm sources in the European Large Area ISO Survey southern fields are identified in 1.4-GHz maps down to ∼80 μJy. The radio–mid-infrared correlation is investigated and derived for the first time at these flux densities for a sample of this size. Our results show that radio and mid-infrared (MIR) luminosities correlate almost as well as radio and far-infrared (FIR), at least up to   z ≃ 0.6  . Using the derived relation and its spread together with the observed 15-μm counts, we have estimated the expected contribution of the 15-μm extragalactic populations to the radio source counts and the role of MIR starburst galaxies in the well-known 1.4-GHz source excess observed at sub-mJy levels. Our analysis demonstrates that IR emitting starburst galaxies do not contribute significantly to the 1.4-GHz counts for strong sources, but start to become a significant fraction of the radio source population at flux densities ≲0.5–0.8 mJy. They are expected to be responsible for more than 60 per cent of the observed radio counts at ≲0.05 mJy. These results are in agreement with the existing results on optical identifications of faint radio sources.     

On a new method of separating the diffuse cosmic X-ray component in balloon-borne measurements

The diffuse X-ray background from 20 to 200 keV has been measured many times by rocket-, satellite-, and balloon-borne detectors. As has been noted by a number of authors, the balloon measurements do not agree with those outside the atmosphere. This suggests some systematic difference in the derivation of the diffuse flux. In the present article we propose a method for the analysis of balloon data in which the source function (atmospherically produced and scattered primary) is derived from the experimental data and is then used to calculate the residual counting rate due only to the transmitted primary photons.     

On the origin of the 511-keV emission in the Galactic Centre

Diffuse 511-keV line emission, from the annihilation of cold positrons, has been observed in the direction of the Galactic Centre for more than 30 yr. The latest high-resolution maps of this emission produced by the SPI instrument on INTEGRAL suggest at least one component of the emission is spatially coincident with the distribution of ∼70 luminous, low-mass X-ray binaries detected in the soft gamma-ray band. The X-ray band, however, is generally a more sensitive probe of X-ray binary populations. Recent X-ray surveys of the Galactic Centre have discovered a much larger population (>4000) of faint, hard X-ray point sources. We investigate the possibility that the positrons observed in the direction of the Galactic Centre originate in pair-dominated jets generated by this population of fainter accretion-powered X-ray binaries. We also consider briefly whether such sources could account for unexplained diffuse emission associated with the Galactic Centre in the microwave (the Wilkinson Microwave Anisotropy Probe 'haze') and at other wavelengths. Finally, we point out several unresolved problems in associating Galactic Centre 511-keV emission with the brightest X-ray binaries.     

VLA observations of ‘Compact’ sources in CTB 80

High resolution (3 arcsec-4 arcsec) maps of three compact sources in CTB 80, observed with the Very Large Array at 6 and 20 cm wavelengths are presented. The central core consists of a limb-brightened shell (of diameter 30 arcsec) superimposed on a diffuse emission of size 75 arcsec x 45 arcsec. The compact sources 1949 + 324 and 1952 + 332 located near the tips of the southwest and northeast ridges are rather remarkable and possibilities for these to be fragments ejected by the SN are examined. 1949 + 324 is fully resolved by the 4 arcsec beam and shows structure with multiple components oriented perpendicular to the ridge. 1950 + 326 is a background radio source.     

Introducing PT-REX,the point-to-point TRend EXtractor

Investigating the spatial correlation between different emissions in an extended astrophysical source can provide crucial insights into their physical connection, hence it can be the key to understand the nature of the system. The point-to-point analysis of surface brightness is a reliable method to do such an analysis. In this work we present PT-REX, a software to carry out these studies between radio and X-ray emission in extended sources. We discuss how to reliably carry out this analysis and its limitation and we introduce the Monte Carlo point-to-point analysis, which allows to extend this approach to poorly-resolved sources. Finally we present and discuss the application of our tool to study the diffuse radio emission in a galaxy cluster.     

Geologic mapping of the Amirani-Gish Bar region of Io: Implications for the global geologic mapping of Io

We produced the first geologic map of the Amirani-Gish Bar region of Io, the last of four regional maps generated from Galileo mission data. The Amirani-Gish Bar region has five primary types of geologic materials: plains, mountains, patera floors, flows, and diffuse deposits. The flows and patera floors are thought to be compositionally similar, but are subdivided based on interpretations regarding their emplacement environments and mechanisms. Our mapping shows that volcanic activity in the Amirani-Gish Bar region is dominated by the Amirani Eruptive Center (AEC), now recognized to be part of an extensive, combined Amirani-Maui flow field. A mappable flow connects Amirani and Maui, suggesting that Maui is fed from Amirani, such that the post-Voyager designation “Maui Eruptive Center” should be revised. Amirani contains at least four hot spots detected by Galileo, and is the source of widespread bright (sulfur?) flows and active dark (silicate?) flows being emplaced in the Promethean style (slowly emplaced, compound flow fields). The floor of Gish Bar Patera has been partially resurfaced by dark lava flows, although other parts of its floor are bright and appeared unchanged during the Galileo mission. This suggests that the floor did not undergo complete resurfacing as a lava lake as proposed for other ionian paterae. There are several other hot spots in the region that are the sources of both active dark flows (confined within paterae), and SO₂- and S₂-rich diffuse deposits. Mapped diffuse deposits around fractures on mountains and in the plains appear to serve as the source for gas venting without the release of magma, an association previously unrecognized in this region. The six mountains mapped in this region exhibit various states of degradation. In addition to gaining insight into this region of Io, all four maps are studied to assess the best methodology to use to produce a new global geologic map of Io based on the newly released, combined Galileo-Voyager global mosaics. To convey the complexity of ionian surface geology, we find that a new global geologic map of Io should include a map sheet displaying the global abundances and types of surface features as well as a complementary GIS database as a means to catalog the record of surface changes observed since the Voyager flybys and during the Galileo mission.     

The opacity of spiral galaxy disks: IX. Dust and gas surface densities

Our aim is to explore the relation between gas, atomic and molecular, and dust in spiral galaxies. Gas surface densities are from atomic hydrogen and CO line emission maps. To estimate the dust content, we use the disk opacity as inferred from the number of distant galaxies identified in twelve HST/WFPC2 fields of ten nearby spiral galaxies. The observed number of distant galaxies is calibrated for source confusion and crowding with artificial galaxy counts and here we verify our results with sub‐mm surface brightnesses from archival Herschel ‐SPIRE data. We find that the opacity of the spiral disk does not correlate well with the surface density of atomic (H I) or molecular hydrogen (H₂) alone implying that dust is not only associated with the molecular clouds but also the diffuse atomic disk in these galaxies. Our result is a typical dust‐to‐gas ratio of 0.04, with some evidence that this ratio declines with galactocentric radius, consistent with recent Herschel results. We discuss the possible causes of this high dust‐to‐gas ratio; an over‐estimate of the dust surface‐density, an under‐estimate of the molecular hydrogen density from CO maps or a combination of both. We note that while our value of the mean dust‐to‐gas ratio is high, it is consistent with the metallicity at the measured radii if one assumes the Pilyugin & Thuan (2005) calibration of gas metallicity. (© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A deep Giant Metre-wave Radio Telescope 610-MHz survey of the 1HXMM–Newton/Chandra survey field

We present the results of a deep 610-MHz survey of the 1 ^H XMM–Newton / Chandra survey area with the Giant Metre-wave Radio Telescope. The resulting maps have a resolution of ∼7 arcsec and an rms noise limit of 60 μJy. To a 5σ detection limit of 300 μJy, we detect 223 sources within a survey area of 64 arcmin in diameter. We compute the 610-MHz source counts and compare them to those measured at other radio wavelengths. The well-known flattening of the Euclidean-normalized 1.4-GHz source counts below ∼2 mJy, usually explained by a population of starburst galaxies undergoing luminosity evolution, is seen at 610 MHz. The 610-MHz source counts can be modelled by the same populations that explain the 1.4-GHz source counts, assuming a spectral index of −0.7 for the starburst galaxies and the steep spectrum active galactic nucleus (AGN) population. We find a similar dependence of luminosity evolution on redshift for the starburst galaxies at 610 MHz as is found at 1.4 GHz (i.e.  ' Q '= 2.45^+0.3_−0.4  ).     

Optical Multi-Band Analyses of Blue Compact Dwarf Galaxies

We are currently analysing image data for a large sample of blue compact dwarf galaxies (BCDs), obtained in multiple optical broad- and narrow-band filters. We present preliminary results of a multi-band analysis of two typical BCDs, Mrk 5 and I Zw 123, for which surface-brightness profiles, colour profiles, colour maps and H_α equivalent-width maps have been derived. We demonstrate how a combination of these different processing methods allows a separate analysis of the young and old stellar populations with respect to their colours and spatial distributions. By comparing the derived colours with the predictions of evolutionary synthesis models, we estimate ages of the distinct stellar populations. The surface-brightness profiles of Mrk 5 show an exponential decay at large photometric radii, with slopes typically found for BCDs. In the case of the very compact object I Zw 123, the surface-brightness profile of the underlying stellar component can be described either by an exponential or an R ^1/4 law. We discuss briefly how noise effects can influence the intrinsic slope of surface brightness profiles at low surface-brightness levels. For compact objects with extended starbursts, the study of the underlying stellar population can thereby be rendered difficult. This revised version was published online in July 2006 with corrections to the Cover Date.     

ROSAT PSPC observations of nearby spiral galaxies – II. Statistical properties

We present a statistical analysis of the largest X-ray survey of nearby spiral galaxies in which diffuse emission has been separated from discrete source contributions. Regression and rank-order correlation analyses are used to compare X-ray properties, such as total, source and diffuse luminosities and diffuse emission temperature, with a variety of physical and multiwavelength properties, such as galaxy mass, type and activity, and optical and infrared luminosity.
The results are discussed in terms of the way in which hot gas and discrete X-ray sources scale with the mass and activity of galaxies, and with the star formation rate. We find that the X-ray properties of starburst galaxies are dependent primarily on their star-forming activity, whilst for more quiescent galaxies, galaxy mass is the more important parameter. One of the most intriguing results is the tight linear scaling between far-infrared and diffuse X-ray luminosity across the sample, even though the hot gas changes from a hydrostatic corona to a free wind across the activity range sampled here.     

Anisotropic radiation transfer in a sphere with internal source

In this work we connect the problem of anisotropic radiation transfer in a sphere with diffuse reflectivity and containing an energy source with the problem of source free amisotropic radiation transfer with isotropic boundary condition. Exact equation for radiation heat flux for the first problem is obtained in terms of the source, the flux and the albedo of the second problem. Modeled kernel is used to represent the anisotropy of the phase function. Numerical results are given.     

Precision of diffuse 21-cm lensing

We study the limits of accuracy for weak lensing maps of dark matter using diffuse 21-cm radiation from the pre-reionization epoch using simulations. We improve on previous 'optimal' quadratic lensing estimators by using shear and convergence instead of deflection angles. This is a generalization of the deflection estimator, and is more optimal for non-Gaussian sources. The cross-power spectrum of shear and convergence is an unbiased estimator of lensing power spectrum which does not require knowledge of the source four-point function. We find that non-Gaussianity provides a limit to the accuracy of weak lensing reconstruction, even if instrumental noise is reduced to zero. The best reconstruction result is equivalent to Gaussian sources with effective independent cell of side length  2.0  h ⁻¹ Mpc  . Using a source full map from z = 10 to 20, this limiting sensitivity allows mapping of dark matter at a signal-to-noise ratio greater than 1 out to l ≲ 6000, which is better than any other proposed technique for large-area weak lensing mapping.     

Astrophysical interpretation of small-scale neutrino angular correlation searches with IceCube

The IceCube Neutrino Observatory has discovered a diffuse all-flavor flux of high-energy astrophysical neutrinos. However, the corresponding astrophysical sources have not yet been identified. Neither significant point sources nor significant angular correlations of event directions have been observed by IceCube or other instruments to date. We present a new method to interpret the non-observation of angular correlations in terms of exclusions on the strength and number of point-like neutrino sources in generic astrophysical scenarios. Additionally, we constrain the presence of these sources taking into account the measurement of the diffuse high-energy neutrino flux by IceCube. We apply the method to two types of astrophysically motivated source count distributions: The first type is obtained by considering the cosmological evolution of the co-moving density of active galaxies, while the second type is directly derived from the gamma ray source count distribution observed by Fermi-LAT. As a result, we constrain the possible parameter space for both types of source count distributions.     

X-ray observations of PSR B0355+54 and its pulsar wind nebula

We present X-ray data of the middle-aged radio pulsar PSR B0355+54. The XMM-Newton and Chandra observations show not only emission from the pulsar itself, but also compact diffuse emission extending ∼50″ in the opposite direction to the pulsar’s proper motion. Our analysis also indicates the presence of fainter diffuse emission extending ∼5′ from the point source. The morphology of the diffuse component is similar to the ram-pressure confined pulsar wind nebulae detected for other sources. We find that the compact diffuse component is well-fitted with a power-law, with an index that is consistent with the values found for other pulsar wind nebulae. The core emission from the pulsar can be characterized with a thermal plus power-law fit, with the thermal emission most likely originating in a hot polar cap.     

The radio spectra of galactic centre features

The radio source Sgr A and neighbouring features have been mapped at a frequency of 843 MHz with a beamwidth of 43 × 87 arcsec. Comparisons have been made with published maps of comparable resolution at different frequencies in order to differentiate thermal and nonthermal regions. The arc feature to the north of Sgr A appears to consist of low-temperature ionized hydrogen and to extend partly over Sgr A itself causing patchy absorption at low frequencies; there is some evidence that the hydrogen in the arc has been expelled from the galactic nucleus. Previous suggestions that Sgr A East is a supernova remnant have been examined and the interpretation is found to be quite likely, but not compelling. The diffuse component of Sgr A West appears to be due entirely to ionized hydrogen surrounding the nucleus.     

Does the contribution of infrared and submillimeter sources reveal itself at low harmonics of the CMB?

We have computed and studied the mosaic correlation maps of the ILC WMAP microwave background data with the positions of infrared and submillimeter sources. Using the histograms of the signal values in pixels and angular power spectra, we studied the statistical properties of these maps. We discovered similar behavior of a number of harmonics in the maps of correlations with the FSC IRAS, 2MASX and Planck catalog objects. The most prominent multipoles among them, which may reflect the actual distribution of radiation sources are the ℓ = 6 for the FSC and Planck data, and ℓ = 3 for the Planck source data.     

Geologic mapping of the Zal region of Io

We produced a regional geologic map of the Zal region of Io's antijovian hemisphere using Galileo mission data. We discuss the geologic features, summarize the map units and structures that are present, discuss the nature of volcanic activity, and present an analysis of the volcanic, tectonic, and gradational processes that affect the region. The Zal region consists of five primary types of geologic materials: plains, mountains, paterae floors, flows, and diffuse deposits. The flows and patera floors are similar, but are subdivided based on uncertainties regarding emplacement environments and mechanisms. The Zal region includes two hotspots detected by Galileo: one along the western scarp of the Zal Patera volcano and one at the Rustam Patera volcano (name submitted to IAU). A third hotspot at the nearby At'am Patera volcano (name submitted to IAU) is the source of diffuse and pyroclastic materials that blanket north Zal Mons. The western bounding scarp of Zal Patera is the location of a fissure vent that is the source of multiple silicate lava flows. The floor of Zal Patera has been partially resurfaced by dark lava flows, although portions of the patera floor appear bright and unchanged during the Galileo mission. This suggests that the floor did not undergo complete resurfacing as a flooding lava lake but does contain a compound flow field. Mountain materials exhibit stages of degradation; lineated material degrades into mottled material. We have explored the possibility that north and south Zal Mons were originally one structure. We propose that strike-slip faulting and subsequent rifting separated the mountain units, opened a fissure which serves as a vent for lava flow, and created a depression which, by further extension during the rifting event, became Zal Patera. With comparison to other regional maps of Io, this work provides insight into the general geologic evolution of Io.