Submillimeter local oscillators for spaceborne heterodyne applications

Existing and prospective submillimeter local oscillator technologies are surveyed and compared with respect to criteria of suitability for application in spaceborne submillimeter heterodyne receivers as those proposed for the Large Deployable Reflector (LDR). Solid-state and plasma devices are considered in terms of fundamental limitations

The Dialectics of Salvation History

An analysis of Jewish and Christian views on salvation history

Very Extended X-ray and H-alpha Emission in M82: Implications for the Superwind Phenomenon

We discuss the properties and implications of a 3.7x0.9 kpc region of spatially-coincident X-ray and H-alpha emission about 11.6 kpc to the north of the galaxy M82 previously discussed by Devine and Bally (1999). The PSPC X-ray spectrum is fit by thermal plasma (kT=0.80+-0.17 keV) absorbed by only the Galactic foreground column density. We evaluate the relationship of the X-ray/H-alpha ridge to the M82 superwind. The main properties of the X-ray emission can all be explained as being due to shock-heating driven as the superwind encounters a massive ionized cloud in the halo of M82. This encounter drives a slow shock into the cloud, which contributes to the excitation of the observed H-alpha emission. At the same time, a fast bow-shock develops in the superwind just upstream of the cloud, and this produces the observed X-ray emission. This interpretation would imply that the superwind has an outflow speed of roughly 800 km/s, consistent with indirect estimates based on its general X-ray properties and the kinematics of the inner kpc-scale region of H-alpha filaments. The gas in the M82 ridge is roughly two orders-of-magnitude hotter than the minimum "escape temperature" at this radius, so this gas will not be retained by M82. (abridged)Comment: 24 pages (latex), 3 figures (2 gif files and one postscript), accepted for publication in Part 1 of The Astrophysical Journa

Carbon monoxide in the solar atmosphere I. Numerical method and two-dimensional models

The radiation hydrodynamic code CO5BOLD has been supplemented with the time-dependent treatment of chemical reaction networks. Advection of particle densities due to the hydrodynamic flow field is also included. The radiative transfer is treated frequency-independently, i.e. grey, so far. The upgraded code has been applied to two-dimensional simulations of carbon monoxide (CO) in the non-magnetic solar photosphere and low chromosphere. For this purpose a reaction network has been constructed, taking into account the reactions which are most important for the formation and dissociation of CO under the physical conditions of the solar atmosphere. The network has been strongly reduced to 27 reactions, involving the chemical species H, H2, C, O, CO, CH, OH, and a representative metal. The resulting CO number density is highest in the cool regions of the reversed granulation pattern at mid-photospheric heights and decreases strongly above. There, the CO abundance stays close to a value of 8.3 on the usual logarithmic abundance scale with [H]=12 but is reduced in hot shock waves which are a ubiquitous phenomenon of the model atmosphere. For comparison, the corresponding equilibrium densities have been calculated, based on the reaction network but also under assumption of instantaneous chemical equilibrium by applying the Rybicki & Hummer (RH) code by Uitenbroek (2001). Owing to the short chemical timescales, the assumption holds for a large fraction of the atmosphere, in particular the photosphere. In contrast, the CO number density deviates strongly from the corresponding equilibrium value in the vicinity of chromospheric shock waves. Simulations with altered reaction network clearly show that the formation channel via hydroxide (OH) is the most important one under the conditions of the solar atmosphere.Comment: 15 pages, 6 figures, final version will contain online materia

ISO LWS Spectroscopy of M82: A Unified Evolutionary Model

We present the first complete far-infrared spectrum (43 to 197 um) of M82, the brightest infrared galaxy in the sky, taken with the Long Wavelength Spectrometer of the Infrared Space Observatory (ISO). We detected seven fine structure emission lines, [OI] 63 and 145 um, [OIII] 52 and 88 um, [NII] 122 um, [NIII] 57 um and [CII] 158 um, and fit their ratios to a combination starburst and photo-dissociation region (PDR) model. The best fit is obtained with HII regions with n = 250 cm^{-3} and an ionization parameter of 10^{-3.5} and PDRs with n = 10^{3.3} cm^{-3} and a far-ultraviolet flux of G_o = 10^{2.8}. We applied both continuous and instantaneous starburst models, with our best fit being a 3-5 Myr old instantaneous burst model with a 100 M_o cut-off. We also detected the ground state rotational line of OH in absorption at 119.4 um. No excited level OH transitions are apparent, indicating that the OH is almost entirely in its ground state with a column density ~ 4x10^{14} cm^{-2}. The spectral energy distribution over the LWS wavelength range is well fit with a 48 K dust temperature and an optical depth, tau_{Dust} proportional to lambda^{-1}.Comment: 23 pages, 4 figures, accepted by ApJ, Feb. 1, 199

ALMA reveals a chemically evolved submillimeter galaxy at z=4.76

The chemical properties of high-z galaxies provide important information to constrain galaxy evolutionary scenarios. However, widely-used metallicity diagnostics based on rest-frame optical emission lines are not usable for heavily dust-enshrouded galaxies (such as Sub-Millimeter Galaxies; SMGs), especially at z>3. Here we focus on the flux ratio of the far-infrared fine-structure emission lines [NII]205um and [CII]158um to assess the metallicity of high-z SMGs. Through ALMA cycle 0 observations, we have detected the [NII]205um emission in a strongly [CII]-emitting SMG, LESS J033229.4-275619 at z=4.76. The velocity-integrated [NII]/[CII] flux ratio is 0.043 +/- 0.008. This is the first measurement of the [NII]/[CII] flux ratio in high-z galaxies, and the inferred flux ratio is similar to the ratio observed in the nearby universe (~0.02-0.07). The velocity-integrated flux ratio and photoionization models suggest that the metallicity in this SMG is consistent with solar, implying the chemical evolution has progressed very rapidly in this system at z=4.76. We also obtain a tight upper limit on the CO(12-11) transition, which translates into CO(12-11)/CO(2-1) <3.8 (3 sigma). This suggests that the molecular gas clouds in LESS J033229.4-275619 are not affected significantly by the radiation field emitted by the AGN in this system.Comment: 5 pages, 3 figures, accepted for publication in Astronomy and Astrophysics Letter

First observations with CONDOR, a 1.5 THz heterodyne receiver

The THz atmospheric windows centered at roughly 1.3 and 1.5~THz, contain numerous spectral lines of astronomical importance, including three high-J CO lines, the N+ line at 205 microns, and the ground transition of para-H2D+. The CO lines are tracers of hot (several 100K), dense gas; N+ is a cooling line of diffuse, ionized gas; the H2D+ line is a non-depleting tracer of cold (~20K), dense gas. As the THz lines benefit the study of diverse phenomena (from high-mass star-forming regions to the WIM to cold prestellar cores), we have built the CO N+ Deuterium Observations Receiver (CONDOR) to further explore the THz windows by ground-based observations. CONDOR was designed to be used at the Atacama Pathfinder EXperiment (APEX) and Stratospheric Observatory For Infrared Astronomy (SOFIA). CONDOR was installed at the APEX telescope and test observations were made to characterize the instrument. The combination of CONDOR on APEX successfully detected THz radiation from astronomical sources. CONDOR operated with typical Trec=1600K and spectral Allan variance times of 30s. CONDOR's first light observations of CO 13-12 emission from the hot core Orion FIR4 (= OMC1 South) revealed a narrow line with T(MB) = 210K and delta(V)=5.4km/s. A search for N+ emission from the ionization front of the Orion Bar resulted in a non-detection. The successful deployment of CONDOR at APEX demonstrates the potential for making observations at THz frequencies from ground-based facilities.Comment: 4 pages + list of objects, 3 figures, to be published in A&A special APEX issu

A clumpy-cloud PDR model of the global far-infrared line emission of the Milky Way

The fractal structure of the interstellar medium suggests that the interaction of UV radiation with the ISM as described in the context of photon-dominated regions (PDR) dominates most of the physical and chemical conditions, and hence the far-infrared and submm emission from the ISM in the Milky Way. We investigate to what extent the Galactic FIR line emission of the important species CO, C, C+, and O, as observed by the Cosmic Background Explorer (COBE) satellite can be modeled in the framework of a clumpy, UV-penetrated cloud scenario. The far-infrared line emission of the Milky Way is modeled as the emission from an ensemble of clumps with a power law clump mass spectrum and mass-size relation with power-law indices consistent with the observed ISM structure. The individual clump line intensities are calculated using the KOSMA-tau PDR-model for spherical clumps. The model parameters for the cylindrically symmetric Galactic distribution of the mass density and volume filling factor are determined by the observed radial distributions. A constant FUV intensity, in which the clumps are embedded, is assumed. We show that this scenario can explain, without any further assumptions and within a factor of about 2, the absolute FIR-line intensities and their distribution with Galactic longitude as observed by COBE.Comment: 14 pages, 13 figures, accepted by A&A at the 7th of July, 200

Nonthermal Emission from Star-Forming Galaxies

The detections of high-energy gamma-ray emission from the nearby starburst galaxies M82 & NGC253, and other local group galaxies, broaden our knowledge of star-driven nonthermal processes and phenomena in non-AGN star-forming galaxies. We review basic aspects of the related processes and their modeling in starburst galaxies. Since these processes involve both energetic electrons and protons accelerated by SN shocks, their respective radiative yields can be used to explore the SN-particle-radiation connection. Specifically, the relation between SN activity, energetic particles, and their radiative yields, is assessed through respective measures of the particle energy density in several star-forming galaxies. The deduced energy densities range from O(0.1) eV/cm^3 in very quiet environments to O(100) eV/cm^3 in regions with very high star-formation rates.Comment: 17 pages, 5 figures, to be published in Astrophysics and Space Science Proceeding