Panchromatic radiation from galaxies as a probe of galaxy formation and evolution

I review work on modelling the infrared and submillimetre SEDs of galaxies. The underlying physical assumptions are discussed and spherically symmetric, axisymmetric, and 3-dimensional radiative transfer codes are reviewed. Models for galaxies with Spitzer IRS data and for galaxies in the Herschel-Hermes survey are discussed. Searches for high redshift infrared and submillimetre galaxies, the star formation history, the evolution of dust extinction, and constraints from source-counts, are briefly discussed.Comment: to be published in IAU Symposium 284 'The Spectral Energy Distribution of Galaxies', Preston 2012, eds. R.J.Tiffs and C.C.Popesc

Introduction. Leave no stone unturned: Perspectives on ground stone artefact research

Ground stone tools served in many physical and social contexts through millennia, reflecting a wide variety of functions. Although ground stone tool studies were neglected for much of early archaeology, the last few decades witnessed a notable international uptick in the way archaeologists confront this multifaceted topic. Today, with the advance of archaeology as a discipline, research into ground stone artefacts is moving into a new phase that integrates high resolution documentation with new methodological, analytical techniques, and technological approaches. These open new vistas for an array of studies and wide-ranging interpretive endeavours related to understanding ground stone tool production and use. Inspired by these diverse analytical approaches and interpretive challenges, we founded the international Association for Ground Stone Tools Research (AGSTR) in order to promote dialogue and create an optimal, inclusive arena for scholars studying various aspects of ground stone artefacts. Scholars from around the globe met for a five day conference at the University of Haifa, for the first meeting of the newly founded AGSTR. This included the presentation of 47 papers and 17 posters. The current paper serves as an introduction to this special issue of JLS, devoted to the proceedings of the founding conference of the Association for Ground Stone Tool Research, held at the University of Haifa during July 2015

Introduction. Leave no stone unturned: Perspectives on ground stone artefact research

Ground stone tools served in many physical and social contexts through millennia, reflecting a wide variety of functions. Although ground stone tool studies were neglected for much of early archaeology, the last few decades witnessed a notable international uptick in the way archaeologists confront this multifaceted topic. Today, with the advance of archaeology as a discipline, research into ground stone artefacts is moving into a new phase that integrates high resolution documentation with new methodological, analytical techniques, and technological approaches. These open new vistas for an array of studies and wide-ranging interpretive endeavours related to understanding ground stone tool production and use. Inspired by these diverse analytical approaches and interpretive challenges, we founded the international Association for Ground Stone Tools Research (AGSTR) in order to promote dialogue and create an optimal, inclusive arena for scholars studying various aspects of ground stone artefacts. Scholars from around the globe met for a five day conference at the University of Haifa, for the first meeting of the newly founded AGSTR. This included the presentation of 47 papers and 17 posters. The current paper serves as an introduction to this special issue of JLS, devoted to the proceedings of the founding conference of the Association for Ground Stone Tool Research, held at the University of Haifa during July 2015

Local-scale environmental gradients in ‘snail-shell’ stable isotopes from Holocene Jordanian archaeological sites

Reconstructing environments around archaeological sites is complicated by past land management practices and regional-scale climate proxies that can be contradictory and are often located at a distance from the sites themselves. Here we explore environmental information from fossil snail shells which, even when few in number on an archaeological site, may prove invaluable in constructing site-specific data. The palaeoecology of fossil snails and the stable isotopic composition of their shell carbonate can provide context-specific information on vegetation, water availability, and relative humidity during the occupation of a site. We studied terrestrial and aquatic snails from two later Neolithic archaeological sites in the Jordanian badia, Wadi al-Qattafi and Wisad Pools. At specific archaeological site-scale our study highlights the importance of aquatic snails in the reconstruction of semi-arid environments. At Wisad pools rare aquatic snails in contexts dating between ~8.0 and ~7.6 ka demonstrate episodes of wetness; moreover, their shell isotopic compositions indicate that local watercourses were well established, corroborating previous findings that during this period the immediate environs of Wisad Pools were host to C3 plant species more typical of the Mediterranean zone. Moreover, the δ18O signal in these snail shells allow tentative reconstruction of rainwater isotopic compositions and identify the effects of evaporation. Such fine-grained environmental information is much less evident from the terrestrial snail shell data alone, showing that an ensemble of snail shell data can be highly sensitive to environmental differentials across an archaeological site. Finally, at a regional palaeoclimate-scale our Wisad Pools snail shell stable isotope data are consistent with a sustained, Rapid Climate Change (RCC)-driven wetness between 8.6 and 7.6 ka concurrent with cold and wet conditions in the wider Levant

Fast and accurate frequency-dependent radiation transport for hydrodynamics simulations in massive star formation

Context: Radiative feedback plays a crucial role in the formation of massive stars. The implementation of a fast and accurate description of the proceeding thermodynamics in pre-stellar cores and evolving accretion disks is therefore a main effort in current hydrodynamics simulations. Aims: We introduce our newly implemented three-dimensional frequency dependent radiation transport algorithm for hydrodynamics simulations of spatial configurations with a dominant central source. Methods: The module combines the advantage of the speed of an approximate Flux Limited Diffusion (FLD) solver with the high accuracy of a frequency dependent first order ray-tracing routine. Results: We prove the viability of the scheme in a standard radiation benchmark test compared to a full frequency dependent Monte-Carlo based radiative transfer code. The setup includes a central star, a circumstellar flared disk, as well as an envelope. The test is performed for different optical depths. Considering the frequency dependence of the stellar irradiation, the temperature distributions can be described precisely in the optically thin, thick, and irradiated transition regions. Resulting radiative forces onto dust grains are reproduced with high accuracy. The achievable parallel speedup of the method imposes no restriction on further radiative (magneto-) hydrodynamics simulations. Conclusions: The proposed approximate radiation transport method enables frequency dependent radiation hydrodynamics studies of the evolution of pre-stellar cores and circumstellar accretion disks around an evolving massive star in a highly efficient and accurate manner.Comment: 16 pages, 11 figure

Spitzer View of Young Massive Stars in the LMC HII Complex N44

The HII complex N44 in the Large Magellanic Cloud (LMC) provides an excellent site to perform a detailed study of star formation in a mild starburst, as it hosts three regions of star formation at different evolutionary stages and it is not as complicated and confusing as the 30 Doradus giant HII region. We have obtained Spitzer Space Telescope observations and complementary ground-based 4m uBVIJK observations of N44 to identify candidate massive young stellar objects (YSOs). We further classify the YSOs into Types I, II, and III, according to their spectral energy distributions (SEDs). In our sample of 60 YSO candidates, ~65% of them are resolved into multiple components or extended sources in high-resolution ground-based images. We have modeled the SEDs of 36 YSOs that appear single or dominant within a group. We find good fits for Types I and I/II YSOs,but Types II and II/III YSOs show deviations between their observed SEDs and models that do not include PAH emission. We have also found that some Type III YSOs have central holes in their disk components. YSO counterparts are found in four ultracompact HII regions and their stellar masses determined from SED model fits agree well with those estimated from the ionization requirements of the HII regions. The distribution of YSOs is compared with those of the underlying stellar population and interstellar gas conditions to illustrate a correlation between the current formation of O-type stars and previous formation of massive stars. Evidence of triggered star formation is also presented.Comment: 63 pages, 15 figures, accepted for publication for ApJ; some figures in jpeg format to meet the size limit; preprint with high resolution images can be found at http://www.astro.virginia.edu/~cc5ye/n44yso.pd

Radiative equilibrium in Monte Carlo radiative transfer using frequency distribution adjustment

The Monte Carlo method is a powerful tool for performing radiative equilibrium calculations, even in complex geometries. The main drawback of the standard Monte Carlo radiative equilibrium methods is that they require iteration, which makes them numerically very demanding. Bjorkman & Wood recently proposed a frequency distribution adjustment scheme, which allows radiative equilibrium Monte Carlo calculations to be performed without iteration, by choosing the frequency of each re-emitted photon such that it corrects for the incorrect spectrum of the previously re-emitted photons. Although the method appears to yield correct results, we argue that its theoretical basis is not completely transparent, and that it is not completely clear whether this technique is an exact rigorous method, or whether it is just a good and convenient approximation. We critically study the general problem of how an already sampled distribution can be adjusted to a new distribution by adding data points sampled from an adjustment distribution. We show that this adjustment is not always possible, and that it depends on the shape of the original and desired distributions, as well as on the relative number of data points that can be added. Applying this theorem to radiative equilibrium Monte Carlo calculations, we provide a firm theoretical basis for the frequency distribution adjustment method of Bjorkman & Wood, and we demonstrate that this method provides the correct frequency distribution through the additional requirement of radiative equilibrium. We discuss the advantages and limitations of this approach, and show that it can easily be combined with the presence of additional heating sources and the concept of photon weighting. However, the method may fail if small dust grains are included... (abridged)Comment: 17 pages, 2 figures, accepted for publication in New Astronom

The 2D Continuum Radiative Transfer Problem: Benchmark Results for Disk Configurations

We present benchmark problems and solutions for the continuum radiative transfer (RT) in a 2D disk configuration. The reliability of three Monte-Carlo and two grid-based codes is tested by comparing their results for a set of well-defined cases which differ for optical depth and viewing angle. For all the configurations, the overall shape of the resulting temperature and spectral energy distribution is well reproduced. The solutions we provide can be used for the verification of other RT codes.We also point out the advantages and disadvantages of the various numerical techniques applied to solve the RT problem.Comment: 13 pages, 10 figures, To appear in Astronomy and Astrophysic

Kinematics of elliptical galaxies with a diffuse dust component - III. A Monte Carlo approach to include the effects of scattering

This paper is the third one in a series, intended to investigate how the observed kinematics of elliptical galaxies are affected by dust attenuation. In Paper I and Paper II, we investigated the effects of dust absorption; here we extend our modelling in order to include the effects of scattering. We describe how kinematical information can be combined with the radiative transfer equation, and present a Monte Carlo code that can handle kinematical information in an elegant way. Compared to the case where only absorption is taken into account, we find that dust attenuation considerably affects the observed kinematics when scattering is included. For the central lines of sight, dust can either decrease or increase the central observed velocity dispersion. The most important effect of dust attenuation, however, is found at large projected radii. The kinematics at these lines of sight are strongly affected by photons scattered into these lines of sight, which were emitted by high-velocity stars in the central regions of the galaxy. These photons bias the LOSVDs towards high line-of-sight velocities, and significantly increase the observed velocity dispersion and LOSVD shape parameters. These effects are similar to the expected kinematical signature of a dark matter halo, such that dust attenuation may form an alternative explanation for the usual stellar kinematical evidence for dark matter halos around elliptical galaxies. We apply our results to discuss several other topics in galactic dynamics, where we feel dust attenuation should be taken into account. In particular, we argue that the kinematics observed at various wavelengths can help to constrain the spatial distribution of dust in elliptical galaxies.Comment: 21 pages, 10 figures, accepted for publication in MNRA