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The JWST has captured the sharpest IR images ever taken of the Horsehead nebula, a prototypical moderately irradiated PDR that is fully representative of most of the UV-illuminated molecular gas in the Milky Way and star-forming galaxies. We investigate the impact of FUV radiation of a molecular cloud and constrain the structure of the edge of the PDR and its illumination conditions. We used NIRCam and MIRI to obtain 17 broadband and 6 narrowband maps from 0.7 to 28 $\mu$m. We mapped the dust emission, scattered light, and several gas phase lines. We also used HST-WFC3 maps at 1.1 and 1. 6 $\mu$m, along with HST-STIS spectroscopic observations of the H$\alpha$ line. We probed the structure of the edge of the Horsehead and resolved its spatial complexity. We detected a network of faint striated features extending perpendicularly to the PDR front into the H\,II region in filters sensitive to nano-grain emission and light scattered by larger grains. This may indeed figure as the first detection of the entrainment of dust particles in the evaporative flow. The map of the 1-0 S(1) line of H$_2$ presents sharp sub-structures on scales as small as 1.5 arcsec. The ionization and dissociation fronts appear at distances 1-2 arcsec behind the edge of the PDR and seem to spatially coincide, indicating a thickness of the neutral atomic layer below 100 au. All broadband maps present strong color variations which can be explained by dust attenuation. Deviations of the emissions in the H$\alpha$, Pa$\alpha,$ and Br$\alpha$ lines also indicate dust attenuation. With a very simple model, we derive the main features of the extinction curve. A small excess of extinction at 3 $\mu$m may be attributed to icy H$_2$O mantles onto grains. In all lines of sight crossing the inner regions of the Horsehead, it appears that dust attenuation is non-negligible over the entire spectral range., Comment: 25 pages, 17 figures

The metallicity and gas density dependence of interstellar depletions, the dust-to-gas (D/G), and dust-to-metal (D/M) ratios have important implications for how accurately we can trace the chemical enrichment of the universe; either by using FIR dust emission as a tracer of the ISM; or by using spectroscopy of damped Lyman-alpha systems (DLAs) to measure chemical abundances over a wide range of redshifts. We collect and compare large samples of depletion measurements in the Milky Way (MW), LMC (Z=0.5 Zsun), and SMC (Z=0.2 Zsun). The relation between the depletions of different elements do not strongly vary between the three galaxies, implying that abundance ratios should trace depletions accurately down to 20% solar metallicity. From the depletions, we derive D/G and D/M. The D/G increases with density, consistent with the more efficient accretion of gas-phase metals onto dust grains in the denser ISM. For log N(H) > 21 cm^-2, the depletion of metallicity tracers (S, Zn) exceeds -0.5 dex, even at 20% solar metallicity. The gas fraction of metals increases from the MW to the LMC (factor 3) and SMC (factor 6), compensating the reduction in total heavy element abundances and resulting in those three galaxies having the same neutral gas-phase metallicities. The D/G derived from depletions are a factor of 2 (LMC) and 5 (SMC) higher than the D/G derived from FIR, 21 cm, and CO emission, likely due to the combined uncertainties on the dust FIR opacity and on the depletion of carbon and oxygen., Comment: 26 pages, 12 figures

We present deep far-infrared observations of the nearby edge-on galaxy NGC 891 obtained with the Herschel Space Observatory and the Spitzer Space Telescope. The maps confirm the detection of thermal emission from the inner circumgalactic medium (halo) and spatially resolve a dusty superbubble and a dust spur (filament). The dust temperature of the halo component is lower than that of the disk but increases across a region of diameter ~8.0 kpc extending at least 7.7 kpc vertically from one side of the disk, a region we call a superbubble because of its association with thermal X-ray emission and a minimum in the synchrotron scaleheight. This outflow is breaking through the thick disk and developing into a galactic wind, which is of particular interest because NGC 891 is not considered a starburst galaxy; the star formation rate surface density, 0.03 Msun/year per square kiloparsec, and gas fraction, just 10% in the inner disk, indicate the threshold for wind formation is lower than previous work has suggested. We conclude that the star formation surface density is sufficient for superbubble blowout into the halo, but the cosmic ray electrons may play a critical role in determining whether this outflow develops into a fountain or escapes from the gravitational potential. The high dust-to-gas ratio in the dust spur suggests the material was pulled out of NGC 891 through the collision of a minihalo with the disk of NGC 891. We conclude that NGC 891 offers an example of both feedback and satellite interactions transporting dust into the halo of a typical galaxy., Comment: Accepted for publication in MNRAS

New HST/STIS optical spectra were obtained for a sample of early type stars with existing IUE UV spectra. These data were used to construct optical extinction curves whose general properties are discussed elsewhere. In this paper, we identify extinction features in the curves that are wider than diffuse interstellar bands (DIBs) but narrower than the well known broad band variability. This intermediate scale structure, or ISS, contains distinct features whose peaks can contribute a few percent to 20% of the total extinction. Most of the ISS variation can be captured by three principal components. We model the ISS with three Drude profiles and show that their strengths and widths vary from one sight line to another, but their central positions are stable, near 4370, 4870 and 6300A. The Very Broad Structure, VBS, in optical curves appears to be a minimum between the 4870 and 6300A absorption peaks. We find relations among the fit parameters and provide a physical interpretation of them in terms of a simplistic grain model. Finally, we note that the strengths of the 4370 and 4870A features are correlated to the strength of the 2175A UV bump, but that the 6300A feature is not, and that none of the ISS features are related to R(V). However, we verify that the broad band curvature of the continuous optical extinction is strongly related to R(V)., Comment: 13 pages, 10 Figures, accepted by ApJ

Dust and starlight are modeled for the KINGFISH project galaxies. With data from 3.6 micron to 500 micron, models are strongly constrained. For each pixel in each galaxy we estimate (1) dust surface density; (2) q_PAH, the dust mass fraction in PAHs; (3) distribution of starlight intensities heating the dust; (4) luminosity emitted by the dust; and (5) dust luminosity from regions with high starlight intensity. The models successfully reproduce both global and resolved spectral energy distributions. We provide well-resolved maps for the dust properties. As in previous studies, we find q_PAH to be an increasing function of metallicity, above a threshold Z/Z_sol approx 0.15. Dust masses are obtained by summing the dust mass over the map pixels; these "resolved" dust masses are consistent with the masses inferred from model fits to the global photometry. The global dust-to-gas ratios obtained from this study correlate with galaxy metallicities. Systems with Z/Z_sol > 0.5 have most of their refractory elements locked up in dust, whereas when Z/Z_sol < 0.3 most of these elements tend to remain in the gas phase. Within galaxies, we find that q_PAH is suppressed in regions with unusually warm dust with nu L_nu(70 um) > 0.4L_dust. With knowledge of one long-wavelength flux density ratio (e.g., f_{160}/f_{500}), the minimum starlight intensity heating the dust (U_min) can be estimated to within ~50%. For the adopted dust model, dust masses can be estimated to within ~0.07 dex accuracy using the 500 micron luminosity nu L_nu(500) alone. There are additional systematic errors arising from the choice of dust model, but these are hard to estimate. These calibrated prescriptions may be useful for studies of high-redshift galaxies., Comment: ApJ, accepted

We have fit the far-ultraviolet (FUV) to sub-millimeter (850 micron) spectral energy distributions (SEDs) of the 61 galaxies from the "Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel" (KINGFISH). The fitting has been performed using three models: the Code for Investigating GALaxy Evolution (CIGALE), the GRAphite-SILicate approach (GRASIL), and the Multi-wavelength Analysis of Galaxy PHYSical properties (MAGPHYS). We have analyzed the results of the three codes in terms of the SED shapes, and by comparing the derived quantities with simple "recipes" for stellar mass (Mstar), star-formation rate (SFR), dust mass (Mdust), and monochromatic luminosities. Although the algorithms rely on different assumptions for star-formation history, dust attenuation and dust reprocessing, they all well approximate the observed SEDs and are in generally good agreement for the associated quantities. However, the three codes show very different behavior in the mid-infrared regime, in particular between 25 and 70 micron where there are no observational constraints for the KINGFISH sample. We find that different algorithms give discordant SFR estimates for galaxies with low specific SFR, and that the standard "recipes" for calculating FUV absorption overestimate the extinction compared to the SED-fitting results. Results also suggest that assuming a "standard" constant stellar mass-to-light ratio overestimates Mstar relative to the SED fitting, and we provide new SED-based formulations for estimating Mstar from WISE W1 (3.4 micron) luminosities and colors. From a Principal Component Analysis of Mstar, SFR, Mdust, and O/H, we reproduce previous scaling relations among Mstar, SFR, and O/H, and find that Mdust can be predicted to within roughly 0.3 dex using only Mstar and SFR., Comment: 42 pages, 23 figures, 8 tables, 2 appendices: updated to v2, A&A, accepted

We use the Spitzer SAGE survey of the Magellanic Clouds to evaluate the relationship between the 8-mic PAH emission, 24-mic hot dust emission, and HII region radiative transfer. We confirm that in the higher-metallicity Large Magellanic Cloud, PAH destruction is sensitive to optically thin conditions in the nebular Lyman continuum: objects identified as optically thin candidates based on nebular ionization structure show 6 times lower median 8-mic surface brightness (0.18 mJy arcsec^-2) than their optically thick counterparts (1.2 mJy arcsec^-2). The 24-mic surface brightness also shows a factor of 3 offset between the two classes of objects (0.13 vs 0.44 mJy arcsec^-2, respectively), which is driven by the association between the very small dust grains and higher density gas found at higher nebular optical depths. In contrast, PAH and dust formation in the low-metallicity Small Magellanic Cloud is strongly inhibited such that we find no variation in either 8-mic or 24-mic emission between our optically thick and thin samples. This is attributable to extremely low PAH and dust production together with high, corrosive UV photon fluxes in this low-metallicity environment. The dust mass surface densities and gas-to-dust ratios determined from dust maps using Herschel HERITAGE survey data support this interpretation., Comment: Accepted to ApJ, May 15, 2017. 10 pages, 9 figures

The radiative transport of photons through arbitrary three-dimensional (3D) structures of dust is a challenging problem due to the anisotropic scattering of dust grains and strong coupling between different spatial regions. The radiative transfer problem in 3D is solved using Monte Carlo or Ray Tracing techniques as no full analytic solution exists for the true 3D structures. We provide the first 3D dust radiative transfer benchmark composed of a slab of dust with uniform density externally illuminated by a star. This simple 3D benchmark is explicitly formulated to provide tests of the different components of the radiative transfer problem including dust absorption, scattering, and emission. This benchmark includes models with a range of dust optical depths fully probing cases that are optically thin at all wavelengths to optically thick at most wavelengths. This benchmark includes solutions for the full dust emission including single photon (stochastic) heating as well as two simplifying approximations: One where all grains are considered in equilibrium with the radiation field and one where the emission is from a single effective grain with size-distribution-averaged properties. A total of six Monte Carlo codes and one Ray Tracing code provide solutions to this benchmark. Comparison of the results revealed that the global SEDs are consistent on average to a few percent for all but the scattered stellar flux at very high optical depths. The image results are consistent within 10%, again except for the stellar scattered flux at very high optical depths. The lack of agreement between different codes of the scattered flux at high optical depths is quantified for the first time. We provide the first 3D dust radiative transfer benchmark and validate the accuracy of this benchmark through comparisons between multiple independent codes and detailed convergence tests., Comment: 21 pages, 18 figures, Astronomy & Astrophysics, in press

We present an update to the ultraviolet-to-radio database of global broadband photometry for the 79 nearby galaxies that comprise the union of the KINGFISH (Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel) and SINGS (Spitzer Infrared Nearby Galaxies Survey) samples. The 34-band dataset presented here includes contributions from observational work carried out with a variety of facilities including GALEX, SDSS, PS, NOAO, 2MASS, WISE, Spitzer, Herschel, Planck, JCMT, and the VLA. Improvements of note include recalibrations of previously-published SINGS BVRcIc and KINGFISH far-infrared/submillimeter photometry. Similar to previous results in the literature, an excess of submillimeter emission above model predictions is seen primarily for low-metallicity dwarf/irregular galaxies. This 34-band photometric dataset for the combined KINGFISH$+$SINGS sample serves as an important multi-wavelength reference for the variety of galaxies observed at low redshift. A thorough analysis of the observed spectral energy distributions is carried out in a companion paper., Comment: Accepted for publication in the Astrophysical Journal; object, sky, and contaminant apertures are available from the first author

We present Spitzer/Infrared Spectrograph (IRS) 5-21 micron spectroscopic maps towards 12 regions in the Andromeda galaxy (M31). These regions include the nucleus, bulge, an active region in the star-forming ring, and 9 other regions chosen to cover a range of mid-to-far-infrared colours. In line with previous results, PAH feature ratios (6.2 micron and 7.7 micron features compared to the 11.2 micron feature) measured from our extracted M31 spectra, except the nucleus, strongly correlate. The equivalent widths of the main PAH features, as a function of metallicity and radiation hardness, are consistent with those observed for other nearby spiral and starburst galaxies. Reprocessed data from the ISOCAM instrument on the Infrared Space Observatory agree with the IRS data; early reports of suppressed 6-8 micron features and enhanced 11.3 micron feature intensity and FWHM apparently resulted from background-subtraction problems. The nucleus does not show any PAH emission but does show strong silicate emission at 9.7 micron. Furthermore, different spectral features (11.3 micron PAH emission, silicate emission and [NeIII] 15.5 micron line emission) have distinct spatial distributions in the nuclear region: the silicate emission is strongest towards the stellar nucleus, while the PAH emission peaks 15 arcsec north of the nucleus. The PAH feature ratios at this position are atypical with strong emission at 11.2 microns and 15-20 microns but weak emission at 6--8 microns. The nucleus itself is dominated by stellar light giving rise to a strong blue continuum and silicate emission., Comment: 14 pages, 13 figures; MNRAS in press

In this article, we describe the MIRI Imager module (MIRIM), which provides broad-band imaging in the 5 - 27 microns wavelength range for the James Webb Space Telescope. The imager has a 0"11 pixel scale and a total unobstructed view of 74"x113". The remainder of its nominal 113"x113" field is occupied by the coronagraphs and the low resolution spectrometer. We present the instrument optical and mechanical design. We show that the test data, as measured during the test campaigns undertaken at CEA-Saclay, at the Rutherford Appleton Laboratory, and at the NASA Goddard Space Flight Center, indicate that the instrument complies with its design requirements and goals. We also discuss the operational requirements (multiple dithers and exposures) needed for optimal scientific utilization of the MIRIM., Comment: 29 pages, 9 figures

MIRI (the Mid-Infrared Instrument for the James Webb Space Telescope (JWST)) operates from 5 to 28.5 microns and combines over this range: 1.) unprecedented sensitivity levels; 2.) sub-arcsec angular resolution; 3.) freedom from atmospheric interference; 4.) the inherent stability of observing in space; and 5.) a suite of versatile capabilities including imaging, low and medium resolution spectroscopy (with an integral field unit), and coronagraphy. We illustrate the potential uses of this unique combination of capabilities with various science examples: 1.) imaging exoplanets; 2.) transit and eclipse spectroscopy of exoplanets; 3.) probing the first stages of star and planet formation, including identifying bioactive molecules; 4.) determining star formation rates and mass growth as galaxies are assembled; and 5.) characterizing the youngest massive galaxies. This paper is the introduction to a series of ten covering all aspects of the instrument.

The DUSTiNGS survey (DUST in Nearby Galaxies with Spitzer) is a 3.6 and 4.5 micron imaging survey of 50 nearby dwarf galaxies designed to identify dust-producing Asymptotic Giant Branch (AGB) stars and massive stars. Using two epochs, spaced approximately six months apart, we identify a total of 526 dusty variable AGB stars (sometimes called "extreme" or x-AGB stars; [3.6]-[4.5]>0.1 mag). Of these, 111 are in galaxies with [Fe/H] < -1.5 and 12 are in galaxies with [Fe/H] < -2.0, making them the most metal-poor dust-producing AGB stars known. We compare these identifications to those in the literature and find that most are newly discovered large-amplitude variables, with the exception of approximately 30 stars in NGC 185 and NGC 147, one star in IC 1613, and one star in Phoenix. The chemical abundances of the x-AGB variables are unknown, but the low metallicities suggest that they are more likely to be carbon-rich than oxygen-rich and comparisons with existing optical and near-IR photometry confirms that 70 of the x-AGB variables are confirmed or likely carbon stars. We see an increase in the pulsation amplitude with increased dust production, supporting previous studies suggesting that dust production and pulsation are linked. We find no strong evidence linking dust production with metallicity, indicating that dust can form in very metal-poor environments., Comment: 18 pages, 16 figures, accepted for publication in ApJ

Physical conditions of the interstellar medium in galaxies are closely linked to the ambient radiation field and the heating of dust grains. In order to characterize dust properties in galaxies over a wide range of physical conditions, we present here the radial surface brightness profiles of the entire sample of 61 galaxies from Key Insights into Nearby Galaxies: Far-Infrared Survey with Herschel (KINGFISH). The main goal of our work is the characterization of the grain emissivities, dust temperatures, and interstellar radiation fields responsible for heating the dust. After fitting the dust and stellar radial profiles with exponential functions, we fit the far-infrared spectral energy distribution (SED) in each annular region with single-temperature modified black bodies using both variable (MBBV) and fixed (MBBF) emissivity indices beta, as well as with physically motivated dust models. Results show that while most SED parameters decrease with radius, the emissivity index beta also decreases with radius in some galaxies, but in others is increasing, or rising in the inner regions and falling in the outer ones. Despite the fixed grain emissivity (average beta~ 2.1) of the physically-motivated models, they are well able to accommodate flat spectral slopes with beta<= 1. We find that flatter slopes (beta<= 1.5) are associated with cooler temperatures, contrary to what would be expected from the usual Tdust-beta degeneracy. This trend is related to variations in Umin since beta and Umin are very closely linked over the entire range in Umin sampled by the KINGFISH galaxies: low Umin is associated with flat beta<=1. Both these results strongly suggest that the low apparent \beta values (flat slopes) in MBBV fits are caused by temperature mixing along the line-of-sight, rather than by intrinsic variations in grain properties. Abstract truncated for arXiv., Comment: 28 pages, 20 figures, accepted for publication in A&A

Context. Edge-on spiral galaxies with prominent dust lanes provide us with an excellent opportunity to study the distribution and properties of the dust within them. The HEROES project was set up to observe a sample of seven large edge-on galaxies across various wavelengths for this investigation. Aims. Within this first paper, we present the Herschel observations and perform a qualitative and quantitative analysis on them, and we derive some global properties of the far infrared and submillimetre emission. Methods. We determine horizontal and vertical profiles from the Herschel observations of the galaxies in the sample and describe the morphology. Modified black-body fits to the global fluxes, measured using aperture photometry, result in dust temperatures and dust masses. The latter values are compared to those that are derived from radiative transfer models taken from the literature. Results. On the whole, our Herschel flux measurements agree well with archival values. We find that the exponential horizontal dust distribution model often used in the literature generally provides a good description of the observed horizontal profiles. Three out of the seven galaxies show signatures of extended vertical emission at 100 and 160 {\mu}m at the 5{\sigma} level, but in two of these it is probably due to deviations from an exactly edge-on orientation. Only for NGC 4013, a galaxy in which vertically extended dust has already been detected in optical images, we can detect vertically extended dust, and the derived scaleheight agrees with the value estimated through radiative transfer modelling. Our analysis hints at a correlation between the dust scaleheight and its degree of clumpiness, which we infer from the difference between the dust masses as calculated from modelling of optical data and from fitting the spectral energy distribution of Herschel datapoints., Comment: 21 pages, 12 figures. Accepted for publication in Astronomy & Astrophysics

Dust has long been identified as a barrier to measuring inherent galaxy properties. However, the link between dust and attenuation is not straightforward and depends on both the amount of dust and its distribution. Herschel imaging of nearby galaxies undertaken as part of the KINGFISH project allows us to map the dust as seen in emission with unprecedented sensitivity and ~1 kpc resolution. We present here new optical integral field unit spectroscopy for eight of these galaxies that provides complementary 100-200 pc scale maps of the dust attenuation through observation of the reddening in both the Balmer decrement and the stellar continuum. The stellar continuum reddening, which is systematically less than that observed in the Balmer decrement, shows no clear correlation with the dust, suggesting that the distribution of stellar reddening acts as a poor tracer of the overall dust content. The brightest HII regions are observed to be preferentially located in dusty regions, and we do find a correlation between the Balmer line reddening and the dust mass surface density for which we provide an empirical relation. Some of the high-inclination systems in our sample exhibit high extinction, but we also find evidence that unresolved variations in the dust distribution on scales smaller than 500 pc may contribute to the scatter in this relation. We caution against the use of integrated A_V measures to infer global dust properties., Comment: 17 pages, 10 figures, accepted for publication in ApJ

A crucial aspect of 3D Monte Carlo radiative transfer is the choice of the spatial grid used to partition the dusty medium. We critically investigate the use of octree grids in Monte Carlo dust radiative transfer, with two different octree construction algorithms (regular and barycentric subdivision) and three different octree traversal algorithms (top-down, neighbour list, and the bookkeeping method). In general, regular octree grids need higher levels of subdivision compared to the barycentric grids for a fixed maximum cell mass threshold criterion. The total number of grid cells, however, depends on the geometry of the model. Surprisingly, regular octree grid simulations turn out to be 10 to 20% more efficient in run time than the barycentric grid simulations, even for those cases where the latter contain fewer grid cells than the former. Furthermore, we find that storing neighbour lists for each cell in an octree, ordered according to decreasing overlap area, is worth the additional memory and implementation overhead: using neighbour lists can cut down the grid traversal by 20% compared to the traditional top-down method. In conclusion, the combination of a regular node subdivision and the neighbour list method results in the most efficient octree structure for Monte Carlo radiative transfer simulations., Comment: 6 pages, 1 figure, accepted for publication in Astronomy and Astrophysics

We use the near--infrared Br\gamma hydrogen recombination line as a reference star formation rate (SFR) indicator to test the validity and establish the calibration of the {\it Herschel} PACS 70 \mu m emission as a SFR tracer for sub--galactic regions in external galaxies. Br\gamma offers the double advantage of directly tracing ionizing photons and of being relatively insensitive to the effects of dust attenuation. For our first experiment, we use archival CFHT Br\gamma and Ks images of two nearby galaxies: NGC\,5055 and NGC\,6946, which are also part of the {\it Herschel} program KINGFISH (Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel). We use the extinction corrected Br\gamma emission to derive the SFR(70) calibration for H{\sc ii} regions in these two galaxies. A comparison of the SFR(70) calibrations at different spatial scales, from 200 pc to the size of the whole galaxy, reveals that about 50% of the total 70\mu m emission is due to dust heated by stellar populations that are unrelated to the current star formation. We use a simple model to qualitatively relate the increase of the SFR(70) calibration coefficient with decreasing region size to the star formation timescale. We provide a calibration for an unbiased SFR indicator that combines the observed H\alpha with the 70 \mu m emission, also for use in H{\sc ii} regions. We briefly analyze the PACS 100 and 160 \mu m maps and find that longer wavelengths are not as good SFR indicators as 70\mu m, in agreement with previous results. We find that the calibrations show about 50% difference between the two galaxies, possibly due to effects of inclination., Comment: 27 pages, 6 tables, 12 figures, accepted in ApJ

We present new empirical calibrations to estimate resolved and integrated total infrared luminosities from Spitzer and Herschel bands used as monochromatic or combined tracers. We base our calibrations on resolved elements of nearby galaxies (3 to 30 Mpc) observed with Herschel. We perform a resolved SED modelling of these objects using the Draine and Li (2007) dust models and investigate the influence of the addition of SPIRE measurements in the estimation of LTIR. We find that using data up to 250 um leads to local LTIR values consistent with those obtained with a complete coverage (up to 500 um) within 10 per cent for most of our resolved elements. We then study the distribution of energy in the resolved SEDs of our galaxies. The bulk of energy (30-50 per cent) is contained in the (70-160 um) band. The (24-70 um) fraction decreases with increasing metallicity. The (160-1100 um) submillimeter band can account for up to 25 per cent of the LTIR in metal-rich galaxies. We investigate the correlation between TIR surface brightnesses/luminosities and monochromatic Spitzer and Herschel surface brightnesses/luminosities. The three PACS bands can be used as reliable monochromatic estimators of the LTIR, the 100 um band being the most reliable monochromatic tracer. There is also a strong correlation between the SPIRE 250um and LTIR, although with more scatter than for the PACS relations. We also study the ability of our monochromatic relations to reproduce integrated LTIR of nearby galaxies as well as LTIR of z=1-3 sources. Finally, we provide calibration coefficients that can be used to derive TIR surface brightnesses/luminosities from a combination of Spitzer and Herschel surface brightnesses/fluxes and analyse the associated uncertainties., Comment: 34 pages, 12 figures, accepted for publication in MNRAS

We derive the distribution of the synchrotron spectral index across NGC6946 and investigate the correlation between the radio continuum (synchrotron) and far-infrared (FIR) emission using the KINGFISH Herschel PACS and SPIRE data. The radio--FIR correlation is studied as a function of star formation rate, magnetic field strength, radiation field strength, and the total gas surface brightness. The synchrotron emission follows both star-forming regions and the so-called magnetic arms present in the inter-arm regions. The synchrotron spectral index is steepest along the magnetic arms ($\alpha_n \sim 1$), while it is flat in places of giant H{\sc ii} regions and in the center of the galaxy ($\alpha_n \sim 0.6-0.7$). The map of $\alpha_n$ provides an observational evidence for aging and energy loss of cosmic ray electrons propagating in the disk of the galaxy. Variations in the synchrotron--FIR correlation across the galaxy are shown to be a function of both star formation and magnetic fields. We find that the synchrotron emission correlates better with cold rather than with warm dust emission, when the interstellar radiation field is the main heating source of dust. The synchrotron--FIR correlation suggests a coupling between the magnetic field and the gas density. NGC6946 shows a power-law behavior between the total (turbulent) magnetic field strength B and the star formation rate surface density $\Sigma_{\rm SFR}$ with an index of 0.14\,(0.16)$\pm$0.01. This indicates an efficient production of the turbulent magnetic field with the increasing gas turbulence expected in actively star forming regions. The scale-by-scale analysis of the synchrotron--FIR correlation indicates that the ISM affects the propagation of old/diffused cosmic ray electrons, resulting in a diffusion coefficient of $D_0=4.6\times 10^{28}$\,cm$^2$\,s$^{-1}$ for 2.2\,GeV CREs., Comment: 23 pages, 13 figures, accepted for publication in Astronomy & Astrophysics Journal

We characterize the dust in NGC628 and NGC6946, two nearby spiral galaxies in the KINGFISH sample. With data from 3.6um to 500um, dust models are strongly constrained. Using the Draine & Li (2007) dust model, (amorphous silicate and carbonaceous grains), for each pixel in each galaxy we estimate (1) dust mass surface density, (2) dust mass fraction contributed by polycyclic aromatic hydrocarbons (PAH)s, (3) distribution of starlight intensities heating the dust, (4) total infrared (IR) luminosity emitted by the dust, and (5) IR luminosity originating in regions with high starlight intensity. We obtain maps for the dust properties, which trace the spiral structure of the galaxies. The dust models successfully reproduce the observed global and resolved spectral energy distributions (SEDs). The overall dust/H mass ratio is estimated to be 0.0082+/-0.0017 for NGC628, and 0.0063+/-0.0009 for NGC6946, consistent with what is expected for galaxies of near-solar metallicity. Our derived dust masses are larger (by up to a factor 3) than estimates based on single-temperature modified blackbody fits. We show that the SED fits are significantly improved if the starlight intensity distribution includes a (single intensity) "delta function" component. We find no evidence for significant masses of cold dust T<12K. Discrepancies between PACS and MIPS photometry in both low and high surface brightness areas result in large uncertainties when the modeling is done at PACS resolutions, in which case SPIRE, MIPS70 and MIPS160 data cannot be used. We recommend against attempting to model dust at the angular resolution of PACS., Comment: To be published in Apj, September 2012. See the full version at http://www.astro.princeton.edu/~ganiano/Papers/

We present Herschel/SPIRE images at 250, 350, and 500 {\mu}m of NGC 4244, a typical low-mass, disk-only and edge-on spiral galaxy. The dust disk is clumpy and shows signs of truncation at the break radius of the stellar disk. This disk coincides with the densest part of the Hi disk. We compare the Spectral Energy Distribution, including the new SPIRE fluxes, to 3D radiative transfer models; a smooth model disk and a clumpy model with embedded heating. Each model requires a very high value for the dust scale-length (h(dust) = 2 - 5 h(stars)), higher dust masses than previous models of NGC 4244 (Md = 0.47 - 1.39 \times 10e7 Msun) and a face-on optical depth of {\tau}(V) = 0.4 - 1.12, in agreement with previous disk opacity studies. The vertical scales of stars and dust are similar. The clumpy model much better mimics the general morphology in the submm images and the general SED. The inferred gas-to-dust mass ratio is compatible with those of similar low-mass disks. The relatively large radial scale-length of the dust disk points to radial mixing of the dusty ISM within the stellar disk. The large vertical dust scale and the clumpy dust distribution of our SED model are both consistent with a scenario in which the vertical structure of the ISM is dictated by the balance of turbulence and self-gravity., Comment: 4 pages, 3 figures, 1 table, accepted for A&A Letters

We present an analysis of the dust and gas in Andromeda, using Herschel images sampling the entire far-infrared peak. We fit a modified-blackbody model to ~4000 quasi-independent pixels with spatial resolution of ~140pc and find that a variable dust-emissivity index (beta) is required to fit the data. We find no significant long-wavelength excess above this model suggesting there is no cold dust component. We show that the gas-to-dust ratio varies radially, increasing from ~20 in the center to ~70 in the star-forming ring at 10kpc, consistent with the metallicity gradient. In the 10kpc ring the average beta is ~1.9, in good agreement with values determined for the Milky Way (MW). However, in contrast to the MW, we find significant radial variations in beta, which increases from 1.9 at 10kpc to ~2.5 at a radius of 3.1kpc and then decreases to 1.7 in the center. The dust temperature is fairly constant in the 10kpc ring (ranging from 17-20K), but increases strongly in the bulge to ~30K. Within 3.1kpc we find the dust temperature is highly correlated with the 3.6 micron flux, suggesting the general stellar population in the bulge is the dominant source of dust heating there. At larger radii, there is a weak correlation between the star formation rate and dust temperature. We find no evidence for 'dark gas' in M31 in contrast to recent results for the MW. Finally, we obtained an estimate of the CO X-factor by minimising the dispersion in the gas-to-dust ratio, obtaining a value of (1.9+/-0.4)x10^20 cm^-2 [K kms^-1]^-1., Comment: 19 pages, 18 figures. Submitted to ApJ April 2012; Accepted July 2012

NGC 1097 is a nearby Seyfert 1 galaxy with a bright circumnuclear starburst ring, a strong large-scale bar and an active nucleus. We present a detailed study of the spatial variation of the far infrared (FIR) [CII]158um and [OI]63um lines and mid-infrared H2 emission lines as tracers of gas cooling, and of the polycyclic aromatic hydrocarbon (PAH) bands as tracers of the photoelectric heating, using Herschel-PACS, and Spitzer-IRS infrared spectral maps. We focus on the nucleus and the ring, and two star forming regions (Enuc N and Enuc S). We estimated a photoelectric gas heating efficiency ([CII]158um+[OI]63um)/PAH in the ring about 50% lower than in Enuc N and S. The average 11.3/7.7um PAH ratio is also lower in the ring, which may suggest a larger fraction of ionized PAHs, but no clear correlation with [CII]158{\mu}m/PAH(5.5 - 14um) is found. PAHs in the ring are responsible for a factor of two more [CII]158um and [OI]63um emission per unit mass than PAHs in the Enuc S. SED modeling indicates that at most 25% of the FIR power in the ring and Enuc S can come from high intensity photodissociation regions (PDRs), in which case G0 ~ 10^2.3 and nH ~ 10^3.5 cm^-3 in the ring. For these values of G0 and nH PDR models cannot reproduce the observed H2 emission. Much of the the H2 emission in the starburst ring could come from warm regions in the diffuse ISM that are heated by turbulent dissipation or shocks., Comment: 17 pages, 14 figures, 5 tables; accepted for publication in ApJ

The Panchromatic Hubble Andromeda Treasury (PHAT) is an on-going HST Multicycle Treasury program to image ~1/3 of M31's star forming disk in 6 filters, from the UV to the NIR. The full survey will resolve the galaxy into more than 100 million stars with projected radii from 0-20 kpc over a contiguous 0.5 square degree area in 828 orbits, producing imaging in the F275W and F336W filters with WFC3/UVIS, F475W and F814W with ACS/WFC, and F110W and F160W with WFC3/IR. The resulting wavelength coverage gives excellent constraints on stellar temperature, bolometric luminosity, and extinction for most spectral types. The photometry reaches SNR=4 at F275W=25.1, F336W=24.9, F475W=27.9, F814W=27.1, F110W=25.5, and F160W=24.6 for single pointings in the uncrowded outer disk; however, the optical and NIR data are crowding limited, and the deepest reliable magnitudes are up to 5 magnitudes brighter in the inner bulge. All pointings are dithered and produce Nyquist-sampled images in F475W, F814W, and F160W. We describe the observing strategy, photometry, astrometry, and data products, along with extensive tests of photometric stability, crowding errors, spatially-dependent photometric biases, and telescope pointing control. We report on initial fits to the structure of M31's disk, derived from the density of RGB stars, in a way that is independent of the assumed M/L and is robust to variations in dust extinction. These fits also show that the 10 kpc ring is not just a region of enhanced recent star formation, but is instead a dynamical structure containing a significant overdensity of stars with ages >1 Gyr. (Abridged), Comment: 48 pages including 22 pages of figures. Accepted to the Astrophysical Journal Supplements. Some figures slightly degraded to reduce submission size

We estimate the total dust input from the cool evolved stars in the Small Magellanic Cloud (SMC), using the 8 micron excess emission as a proxy for the dust-production rate. We find that Asymptotic Giant Branch (AGB) and red supergiant (RSG) stars produce (8.6-9.5) x 10^7 solar masses per year of dust, depending on the fraction of far-infrared sources that belong to the evolved star population (with 10%-50% uncertainty in individual dust-production rates). RSGs contribute the least (<4%), while carbon-rich AGB stars (especially the so-called "extreme" AGB stars) account for 87%-89% of the total dust input from cool evolved stars. We also estimate the dust input from hot stars and supernovae (SNe), and find that if SNe produce 10^-3 solar masses of dust each, then the total SN dust input and AGB input are roughly equivalent. We consider several scenarios of SNe dust production and destruction and find that the interstellar medium (ISM) dust can be accounted for solely by stellar sources if all SNe produce dust in the quantities seen around the dustiest examples and if most SNe explode in dense regions where much of the ISM dust is shielded from the shocks. We find that AGB stars contribute only 2.1% of the ISM dust. Without a net positive contribution from SNe to the dust budget, this suggests that dust must grow in the ISM or be formed by another unknown mechanism., Comment: 10 pages, 5 figures. Accepted for publication in ApJ

We have obtained Herschel images at five wavelengths from 100 to 500 micron of a ~5.5x2.5 degree area centred on the local galaxy M31 (Andromeda), our nearest neighbour spiral galaxy, as part of the Herschel guaranteed time project "HELGA". The main goals of HELGA are to study the characteristics of the extended dust emission, focusing on larger scales than studied in previous observations of Andromeda at an increased spatial resolution, and the obscured star formation. In this paper we present data reduction and Herschel maps, and provide a description of the far-infrared morphology, comparing it with features seen at other wavelengths. We use high--resolution maps of the atomic hydrogen, fully covering our fields, to identify dust emission features that can be associated to M31 with confidence, distinguishing them from emission coming from the foreground Galactic cirrus. Thanks to the very large extension of our maps we detect, for the first time at far-infrared wavelengths, three arc-like structures extending out to ~21, ~26 and ~31 kpc respectively, in the south-western part of M31. The presence of these features, hosting ~2.2e6 Msol of dust, is safely confirmed by their detection in HI maps. Overall, we estimate a total dust mass of ~5.8e7 Msol, about 78% of which is contained in the two main ring-like structures at 10 and 15 kpc, at an average temperature of 16.5 K. We find that the gas-to-dust ratio declines exponentially as a function of the galacto-centric distance, in agreement with the known metallicity gradient, with values ranging from 66 in the nucleus to ~275 in the outermost region. [Abridged], Comment: 15 Pages, 9 Figures. Accepted for publication in Astronomy and Astrophysics. A high resolution version of the paper can be found at http://wazn.ugent.be/jfritz/HelgaI_final.pdf

New far-infrared and sub-millimeter photometry from the Herschel Space Observatory is presented for 61 nearby galaxies from the Key Insights on Nearby Galaxies: A Far-Infrared Survey with Herschel (KINGFISH) sample. The spatially-integrated fluxes are largely consistent with expectations based on Spitzer far-infrared photometry and extrapolations to longer wavelengths using popular dust emission models. Dwarf irregular galaxies are notable exceptions, as already noted by other authors, as their 500um emission shows evidence for a sub-millimeter excess. In addition, the fraction of dust heating attributed to intense radiation fields associated with photo-dissociation regions is found to be (21+/-4)% larger when Herschel data are included in the analysis. Dust masses obtained from the dust emission models of Draine & Li are found to be on average nearly a factor of two higher than those based on single-temperature modified blackbodies, as single blackbody curves do not capture the full range of dust temperatures inherent to any galaxy. The discrepancy is largest for galaxies exhibiting the coolest far-infrared colors., Comment: Accepted for publication in ApJ

The KINGFISH project (Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel) is an imaging and spectroscopic survey of 61 nearby (d < 30 Mpc) galaxies, chosen to cover a wide range of galaxy properties and local interstellar medium (ISM) environments found in the nearby Universe. Its broad goals are to characterize the ISM of present-day galaxies, the heating and cooling of their gaseous and dust components, and to better understand the physical processes linking star formation and the ISM. KINGFISH is a direct descendant of the Spitzer Infrared Nearby Galaxies Survey (SINGS), which produced complete Spitzer imaging and spectroscopic mapping and a comprehensive set of multi-wavelength ancillary observations for the sample. The Herschel imaging consists of complete maps for the galaxies at 70, 100, 160, 250, 350, and 500 microns. The spectal line imaging of the principal atomic ISM cooling lines ([OI]63um, [OIII]88um, [NII]122,205um, and [CII]158um) covers the subregions in the centers and disks that already have been mapped in the mid-infrared with Spitzer. The KINGFISH and SINGS multi-wavelength datasets combined provide panchromatic mapping of the galaxies sufficient to resolve individual star-forming regions, and tracing the important heating and cooling channels of the ISM, across a wide range of local extragalactic ISM environments. This paper summarizes the scientific strategy for KINGFISH, the properties of the galaxy sample, the observing strategy, and data processing and products. It also presents a combined Spitzer and Herschel image atlas for the KINGFISH galaxies, covering the wavelength range 3.6 -- 500 microns. All imaging and spectroscopy data products will be released to the Herschel user generated product archives., Comment: 52 pages, 10 figures, 2 tables. Accepted for publication in PASP. A pdf copy of the image atlas can be downloaded separately at the KINGFISH public website, http://www.ast.cam.ac.uk/sites/default/files/Kingfish_reduced.pdf

In 2007, R Coronae Borealis (R CrB) went into an historically deep and long decline. In this state, the dust acts like a natural coronagraph at visible wavelengths, allowing faint nebulosity around the star to be seen. Imaging has been obtained from 0.5 to 500 micron with Gemini/GMOS, HST/WFPC2, Spitzer/MIPS, and Herschel/SPIRE. Several of the structures around R CrB are cometary globules caused by wind from the star streaming past dense blobs. The estimated dust mass of the knots is consistent with their being responsible for the R CrB declines if they form along the line of sight to the star. In addition, there is a large diffuse shell extending up to 4 pc away from the star containing cool 25 K dust that is detected all the way out to 500 micron. The SED of R CrB can be well fit by a 150 AU disk surrounded by a very large diffuse envelope which corresponds to the size of the observed nebulosity. The total masses of the disk and envelope are 10^-4 and 2 M(Sun), respectively, assuming a gas-to-dust ratio of 100. The evidence pointing toward a white-dwarf merger or a final-helium-shell flash origin for R CrB is contradictory. The shell and the cometary knots are consistent with a fossil planetary nebula. Along with the fact that R CrB shows significant Lithium in its atmosphere, this supports the final-helium-shell flash. However, the relatively high inferred mass of R CrB and its high fluorine abundance support a white-dwarf merger., Comment: 30 pages, 11 figures, ApJ in press

We report far-infrared and submillimeter observations of Supernova 1987A, the star that exploded on February 23, 1987 in the Large Magellanic Cloud, a galaxy located 160,000 lightyears away. The observations reveal the presence of a population of cold dust grains radiating with a temperature of ~17-23 K at a rate of about 220 solar luminosity. The intensity and spectral energy distribution of the emission suggests a dust mass of ~0.4-0.7 solar mass. The radiation must originate from the SN ejecta and requires the efficient precipitation of all refractory material into dust. Our observations imply that supernovae can produce the large dust masses detected in young galaxies at very high redshifts., Comment: This is the author's version of the work. It is posted here by permission of the AAAS for personal use, not for redistribution. To appear in Science; available in Science Express on 7th July, DOI:10.1126/science.1205983 at http://www.sciencemag.org/lookup/doi/10.1126/science.1205983 ; 14 pages, 2 figures, 4 tables. High resolution images are available from the authors

Multi-wavelength study of extended astronomical objects requires combining images from instruments with differing point spread functions (PSFs). We describe the construction of convolution kernels that allow one to generate (multi-wavelength) images with a common PSF, thus preserving the colors of the astronomical sources. We generate convolution kernels for the cameras of the Spitzer Space Telescope, Herschel Space Observatory, Galaxy Evolution Explorer (GALEX), Wide-field Infrared Survey Explorer (WISE), ground-based optical telescopes (Moffat functions and sum of Gaussians), and Gaussian PSFs. These kernels allow the study of the Spectral Energy Distribution (SED) of extended objects, preserving the characteristic SED in each pixel. The convolution kernels and the IDL packages used to construct and use them are made publicly available.

We present a galaxy (SAGE1CJ053634.78-722658.5) at a redshift of 0.14 of which the IR is entirely dominated by emission associated with the AGN. We present the 5-37 um Spitzer/IRS spectrum and broad wavelength SED of SAGE1CJ053634, an IR point-source detected by Spitzer/SAGE (Meixner et al 2006). The source was observed in the SAGE-Spec program (Kemper et al., 2010) and was included to determine the nature of sources with deviant IR colours. The spectrum shows a redshifted (z=0.14+-0.005) silicate emission feature with an exceptionally high feature-to-continuum ratio and weak polycyclic aromatic hydrocarbon (PAH) bands. We compare the source with models of emission from dusty tori around AGNs from Nenkova et al. (2008). We present a diagnostic diagram that will help to identify similar sources based on Spitzer/MIPS and Herschel/PACS photometry. The SED of SAGE1CJ053634 is peculiar because it lacks far-IR emission and a clear stellar counterpart. We find that the SED and the IR spectrum can be understood as emission originating from the inner ~10 pc around an accreting black hole. There is no need to invoke emission from the host galaxy, either from the stars or from the interstellar medium, although a possible early-type host galaxy cannot be excluded based on the SED analysis. The hot dust around the accretion disk gives rise to a continuum, which peaks at 4 um, whereas the strong silicate features may arise from optically thin emission of dusty clouds within ~10 pc around the black hole. The weak PAH emission does not appear to be linked to star formation, as star formation templates strongly over-predict the measured far-IR flux levels. The SED of SAGE1CJ053634 is rare in the local universe but may be more common in the more distant universe. The conspicuous absence of host-galaxy IR emission places limits on the far-IR emission arising from the dusty torus alone., Comment: Accepted for publication in A&A, 7 pages, 6 figures

The absolute flux calibration of the James Webb Space Telescope will be based on a set of stars observed by the Hubble and Spitzer Space Telescopes. In order to cross-calibrate the two facilities, several A, G, and white dwarf (WD) stars are observed with both Spitzer and Hubble and are the prototypes for a set of JWST calibration standards. The flux calibration constants for the four Spitzer IRAC bands 1-4 are derived from these stars and are 2.3, 1.9, 2.0, and 0.5% lower than the official cold-mission IRAC calibration of Reach et al. (2005), i.e. in agreement within their estimated errors of ~2%. The causes of these differences lie primarily in the IRAC data reduction and secondarily in the SEDs of our standard stars. The independent IRAC 8 micron band-4 fluxes of Rieke et al. (2008) are about 1.5 +/- 2% higher than those of Reach et al. and are also in agreement with our 8 micron result., Comment: 16 pages, 6 figures

We present a study of the dust properties of 12 classical and superbubble HII regions in the Large Magellanic Cloud. We use infrared photometry from Spitzer (8, 24, 70, and 160 \mum bands), obtained as part of the Surveying the Agents of a Galaxy's Evolution (SAGE) program, along with archival spectroscopic classifications of the ionizing stars to examine the role of stellar sources on dust heating and processing. Our infrared observations show surprisingly little correlation between the emission properties of the dust and the effective temperatures or bolometric magnitudes of stars in the HII regions, suggesting that the HII region evolutionary timescale is not on the order of the dust processing timescale. We find that the infrared emission of superbubbles and classical HII regions shows little differentiation between the two classes, despite the significant differences in age and morphology. We do detect a correlation of the 24 \mum emission from hot dust with the ratio of 70 to 160 \mum flux. This correlation can be modeled as a trend in the temperature of a minority hot dust component, while a majority of the dust remains significantly cooler., Comment: 15 pages, 5 figures. Accepted to ApJ

Gamma-ray burst (GRB) host galaxies have been studied extensively in optical photometry and spectroscopy. Here we present the first mid-infrared spectrum of a GRB host, HG031203. It is one of the nearest GRB hosts at z=0.1055, allowing both low and high-resolution spectroscopy with Spitzer-IRS. Medium resolution UV-to-K-band spectroscopy with the X-shooter spectrograph on the VLT is also presented, along with Spitzer IRAC and MIPS photometry, as well as radio and sub-mm observations. These data allow us to construct a UV-to-radio spectral energy distribution with almost complete spectroscopic coverage from 0.3-35 micron of a GRB host galaxy for the first time, potentially valuable as a template for future model comparisons. The IRS spectra show strong, high-ionisation fine structure line emission indicative of a hard radiation field in the galaxy, suggestive of strong ongoing star-formation and a very young stellar population. The selection of HG031203 via the presence of a GRB suggests that it might be a useful analogue of very young star-forming galaxies in the early universe, and hints that local BCDs may be used as more reliable analogues of star-formation in the early universe than typical local starbursts. We look at the current debate on the ages of the dominant stellar populations in z~7 and z~8 galaxies in this context. The nebular line emission is so strong in HG031203, that at z~7, it can reproduce the spectral energy distributions of z-band dropout galaxies with elevated IRAC 3.6 and 4.5 micron fluxes without the need to invoke a 4000A break., Comment: Published in ApJ. 9 pages, 6 figures, emulateapj style

Recently, we have discovered an error in our Monte-Carlo spectral fitting routine, more specifically where the errors on the fluxes were rescaled to get a reduced chi2 of 1. The rescaled errors were too big, resulting in too wide a range of good fits in our 100 step Monte-Carlo routine. This problem affects Figs. 7-9 and Tables A.1, A.2 in Gielen et al. (2008), Table 3 in Gielen et al. (2009a), and Table 4 in Gielen et al. (2009b). We corrected for this error and present the new values and errors in the tables below. The new values and errors nearly all fall within the old error range. Our best chi2 values and overall former scientific results are not affected. With these new errors some possible new trends in the dust parameters might be observed. These will be discussed in an upcoming paper where we extend the sample presented in Gielen et al. (2008) with newly obtained SPITZER-IRS data., Comment: Erratum for Gielen et al. 2008, Gielen et al. 2009ab

Massive evolved stars can produce large amounts of dust, and far-infrared (IR) data are essential for determining the contribution of cold dust to the total dust mass. Using Herschel, we search for cold dust in three very dusty massive evolved stars in the Large Magellanic Cloud: R71 is a Luminous Blue Variable, HD36402 is a Wolf-Rayet triple system, and IRAS05280-6910 is a red supergiant. We model the spectral energy distributions using radiative transfer codes and find that these three stars have mass-loss rates up to 10^-3 solar masses/year, suggesting that high-mass stars are important contributors to the life-cycle of dust. We found far-IR excesses in two objects, but these excesses appear to be associated with ISM and star-forming regions. Cold dust (T < 100 K) may thus not be an important contributor to the dust masses of evolved stars., Comment: accepted to A&A as part of the Herschel first results special issue

We review the main advances brought by the Spitzer Space Telescope in the field of nearby galaxies studies, concentrating on a few subject areas, including: (1) the physics of the Polycyclic Aromatic Hydrocarbons that generate the mid-infrared features between ~3.5 micron and ~20 micron; (2) the use of the mid- and far-infrared emission from galaxies as star formation rate indicators; and (3) the improvement of mid-infrared diagnostics to discriminate between thermal (star-formation) and non-thermal (AGN) emission in galaxies and galaxy centers., Comment: 9 pages, contribution for the Spitzer 2009 Conference Proceedings `Reionization to Exoplanets', ed. P. Ogle, ASP Conference Series, in prep

We present clumps of dust emission from Herschel observations of the Large Magellanic Cloud (LMC) and their physical and statistical properties. We catalog cloud features seen in the dust emission from Herschel observations of the LMC, the Magellanic type irregular galaxy closest to the Milky Way, and compare these features with HI catalogs from the ATCA+Parkes HI survey. Using an automated cloud-finding algorithm, we identify clouds and clumps of dust emission and examine the cumulative mass distribution of the detected dust clouds. The mass of cold dust is determined from physical parameters that we derive by performing spectral energy distribution fits to 250, 350, and 500 micronm emission from SPIRE observations using DUSTY and GRASIL radiative transfer calculation with dust grain size distributions for graphite/silicate in low-metallicity extragalactic environments. The dust cloud mass spectrum follows a power law distribution with an exponent of gamma=-1.8 for clumps larger than 400 solar mass and is similar to the HI mass distribution. This is expected from the theory of ISM structure in the vicinity of star formation., Comment: 4 pages, 4 figures, to appear in A&A special issue

The properties of the dust grains (e.g., temperature and mass) can be derived from fitting far-IR SEDs (>100 micron). Only with SPIRE on Herschel has it been possible to get high spatial resolution at 200 to 500 micron that is beyond the peak (~160 micron) of dust emission in most galaxies. We investigate the differences in the fitted dust temperatures and masses determined using only <200 micron data and then also including >200 micron data (new SPIRE observations) to determine how important having >200 micron data is for deriving these dust properties. We fit the 100 to 350 micron observations of the Large Magellanic Cloud (LMC) point-by-point with a model that consists of a single temperature and fixed emissivity law. The data used are existing observations at 100 and 160 micron (from IRAS and Spitzer) and new SPIRE observations of 1/4 of the LMC observed for the HERITAGE Key Project as part of the Herschel Science Demonstration phase. The dust temperatures and masses computed using only 100 and 160 micron data can differ by up to 10% and 36%, respectively, from those that also include the SPIRE 250 & 350 micron data. We find that an emissivity law proportional to lambda^-1.5 minimizes the 100-350 micron fractional residuals. We find that the emission at 500 micron is ~10% higher than expected from extrapolating the fits made at shorter wavelengths. We find the fractional 500 micron excess is weakly anti-correlated with MIPS 24 micron flux and the total gas surface density. This argues against a flux calibration error as the origin of the 500 micron excess. Our results do not allow us to distinguish between a systematic variation in the wavelength dependent emissivity law or a population of very cold dust only detectable at lambda > 500 micron for the origin of the 500 micron excess., Comment: 5 pages, 3 figurers, A&A, in press

Stellar density and bar strength should affect the temperatures of the cool (T ~ 20-30 K) dust component in the inner regions of galaxies, which implies that the ratio of temperatures in the circumnuclear regions to the disk should depend on Hubble type. We investigate the differences between cool dust temperatures in the central 3 kpc and disk of 13 nearby galaxies by fitting models to measurements between 70 and 500 microns. We attempt to quantify temperature trends in nearby disk galaxies, with archival data from Spitzer/MIPS and new observations with Herschel/SPIRE, which were acquired during the first phases of the Herschel observations for the KINGFISH (key insights in nearby galaxies: a far-infrared survey with Herschel) sample. We fit single-temperature modified blackbodies to far-infrared and submillimeter measurements of the central and disk regions of galaxies to determine the temperature of the component(s) emitting at those wavelengths. We present the ratio of central-region-to-disk-temperatures of the cool dust component of 13 nearby galaxies as a function of morphological type. We find a significant temperature gradient in the cool dust component in all galaxies, with a mean center-to-disk temperature ratio of 1.15 +/- 0.03. The cool dust temperatures in the central ~3 kpc of nearby galaxies are 23(+/-3)% hotter for morphological types earlier than Sc, and only 9(+/-3)% hotter for later types. The temperature ratio is also correlated with bar strength, with only strongly barred galaxies having a ratio over 1.2. The strong radiation field in the high stellar density of a galactic bulge tends to heat the cool dust component to higher temperatures, at least in early-type spirals with relatively large bulges, especially when paired with a strong bar., Comment: Accepted for publication on the A&A Herschel Special Issue

NGC 1097 is a nearby SBb galaxy with a Seyfert nucleus and a bright starburst ring. We study the physical properties of the interstellar medium (ISM) in the ring using spatially resolved far-infrared spectral maps of the circumnuclear starburst ring of NGC 1097, obtained with the PACS spectrometer on board the Herschel Space Telescope. In particular, we map the important ISM cooling and diagnostic emission lines of [OI] 63 $\mu$m, [OIII] 88 $\mu$m, [NII] 122 $\mu$m, [CII] 158 $\mu$m and [NII] 205 $\mu$m. We observe that in the [OI] 63 $\mu$m, [OIII] 88 $\mu$m, and [NII] 122 $\mu$m line maps, the emission is enhanced in clumps along the NE part of the ring. We observe evidence of rapid rotation in the circumnuclear ring, with a rotation velocity of ~220$ km s$^{-1}$ (inclination uncorrected) measured in all lines. The [OI] 63 $\mu$m/[CII] 158 $\mu$m ratio varies smoothly throughout the central region, and is enhanced on the northeastern part of the ring, which may indicate a stronger radiation field. This enhancement coincides with peaks in the [OI] 63 $\mu$m and [OIII] 88 $\mu$m maps. Variations of the [NII] 122 $\mu$m/[NII] 205 $\mu$m ratio correspond to a range in the ionized gas density between 150 and 400 cm$^{-3}$., Comment: Accepted for publication on the A&A Herschel Special Issue

Using infrared photometry from the Spitzer Space Telescope, we perform the first inventory of aromatic feature emission (AFE, but also commonly referred to as PAH emission) for a statistically complete sample of star-forming galaxies in the local volume. The photometric methodology involved is calibrated and demonstrated to recover the aromatic fraction of the IRAC 8 micron flux with a standard deviation of 6% for a training set of 40 SINGS galaxies (ranging from stellar to dust dominated) with both suitable mid-infrared Spitzer IRS spectra and equivalent photometry. A potential factor of two improvement could be realized with suitable 5.5 and 10 micron photometry, such as what may be provided in the future by JWST. The resulting technique is then applied to mid-infrared photometry for the 258 galaxies from the Local Volume Legacy (LVL) survey, a large sample dominated in number by low-luminosity dwarf galaxies for which obtaining comparable mid-infrared spectroscopy is not feasible. We find the total LVL luminosity due to five strong aromatic features in the 8 micron complex to be 2.47E10 solar luminosities with a mean volume density of 8.8E6 solar luminosities per cubic Megaparsec. Twenty-four of the LVL galaxies, corresponding to a luminosity cut at M = -18.22 in the B band, account for 90% of the aromatic luminosity. Using oxygen abundances compiled from the literature for 129 of the 258 LVL galaxies, we find a correlation between metallicity and the aromatic to total infrared emission ratio but not the aromatic to total 8 micron dust emission ratio. A possible explanation is that metallicity plays a role in the abundance of aromatic molecules relative to the total dust content, but other factors such as star formation and/or the local radiation field affect the excitation of those molecules., Comment: ApJ in press; 29 pages, 14 figures, 3 tables; emulateapj format

We present a catalog of 5324 massive stars in the Small Magellanic Cloud (SMC), with accurate spectral types compiled from the literature, and a photometric catalog for a subset of 3654 of these stars, with the goal of exploring their infrared properties. The photometric catalog consists of stars with infrared counterparts in the Spitzer, SAGE-SMC survey database, for which we present uniform photometry from 0.3-24 um in the UBVIJHKs+IRAC+MIPS24 bands. We compare the color magnitude diagrams and color-color diagrams to those of the Large Magellanic Cloud (LMC), finding that the brightest infrared sources in the SMC are also the red supergiants, supergiant B[e] (sgB[e]) stars, luminous blue variables, and Wolf-Rayet stars, with the latter exhibiting less infrared excess, the red supergiants being less dusty and the sgB[e] stars being on average less luminous. Among the objects detected at 24 um are a few very luminous hypergiants, 4 B-type stars with peculiar, flat spectral energy distributions, and all 3 known luminous blue variables. We detect a distinct Be star sequence, displaced to the red, and suggest a novel method of confirming Be star candidates photometrically. We find a higher fraction of Oe and Be stars among O and early-B stars in the SMC, respectively, when compared to the LMC, and that the SMC Be stars occur at higher luminosities. We estimate mass-loss rates for the red supergiants, confirming the correlation with luminosity even at the metallicity of the SMC. Finally, we confirm the new class of stars displaying composite A & F type spectra, the sgB[e] nature of 2dFS1804 and find the F0 supergiant 2dFS3528 to be a candidate luminous blue variable with cold dust., Comment: 23 pages, 17 figures, 5 tables, accepted for publication in the Astronomical Journal

(Abridged) Spitzer data at 24, 70, and 160 micron and ground-based H-alpha images are analyzed for a sample of 189 nearby star-forming and starburst galaxies to investigate whether reliable star formation rate (SFR) indicators can be defined using the monochromatic infrared dust emission centered at 70 and 160 micron. We compare recently published recipes for SFR measures using combinations of the 24 micron and observed H-alpha luminosities with those using 24 micron luminosity alone. From these comparisons, we derive a reference SFR indicator for use in our analysis. Linear correlations between SFR and the 70 and 160 micron luminosity are found for L(70)>=1.4x10^{42} erg/s and L(160)>=2x10^{42} erg/s, corresponding to SFR>=0.1-0.3 M_sun/yr. Below those two luminosity limits, the relation between SFR and 70 micron (160 micron) luminosity is non-linear and SFR calibrations become problematic. The dispersion of the data around the mean trend increases for increasing wavelength, becoming about 25% (factor ~2) larger at 70 (160) micron than at 24 micron. The increasing dispersion is likely an effect of the increasing contribution to the infrared emission of dust heated by stellar populations not associated with the current star formation. The non-linear relation between SFR and the 70 and 160 micron emission at faint galaxy luminosities suggests that the increasing transparency of the interstellar medium, decreasing effective dust temperature, and decreasing filling factor of star forming regions across the galaxy become important factors for decreasing luminosity. The SFR calibrations are provided for galaxies with oxygen abundance 12+Log(O/H)>8.1. At lower metallicity the infrared luminosity no longer reliably traces the SFR because galaxies are less dusty and more transparent., Comment: 69 pages, 19 figures, 2 tables; accepted for publication on ApJ

Using Spitzer IRAC observations from the SAGE-SMC Legacy program and archived Spitzer IRAC data, we investigate dust production in 47 Tuc, a nearby massive Galactic globular cluster. A previous study detected infrared excess, indicative of circumstellar dust, in a large population of stars in 47 Tuc, spanning the entire Red Giant Branch (RGB). We show that those results suffered from effects caused by stellar blending and imaging artifacts and that it is likely that no stars below about 1 mag from the tip of the RGB are producing dust. The only stars that appear to harbor dust are variable stars, which are also the coolest and most luminous stars in the cluster., Comment: Accepted for publication in ApJL

We present spectroscopic observations of a sample of 15 embedded young stellar objects (YSOs) in the Large Magellanic Cloud (LMC). These observations were obtained with the Spitzer Infrared Spectrograph (IRS) as part of the SAGE-Spec Legacy program. We analyze the two prominent ice bands in the IRS spectral range: the bending mode of CO_2 ice at 15.2 micron and the ice band between 5 and 7 micron that includes contributions from the bending mode of water ice at 6 micron amongst other ice species. The 5-7 micron band is difficult to identify in our LMC sample due to the conspicuous presence of PAH emission superimposed onto the ice spectra. We identify water ice in the spectra of two sources; the spectrum of one of those sources also exhibits the 6.8 micron ice feature attributed to ammonium and methanol. We model the CO_2 band in detail, using the combination of laboratory ice profiles available in the literature. We find that a significant fraction (> 50%) of CO_2 ice is locked in a water-rich component, consistent with what is observed for Galactic sources. The majority of the sources in the LMC also require a pure-CO_2 contribution to the ice profile, evidence of thermal processing. There is a suggestion that CO_2 production might be enhanced in the LMC, but the size of the available sample precludes firmer conclusions. We place our results in the context of the star formation environment in the LMC., Comment: Minor corrections to Table 2. Accepted for publication in ApJ, 66 pages, 9 figures (some in color), 4 tables

Aims: By studying the photospheric abundances of 4 RV Tauri stars in the LMC, we test whether the depletion pattern of refractory elements, seen in similar Galactic sources, is also common for extragalactic sources. Since this depletion process probably only occurs through interaction with a stable disc, we investigate the circumstellar environment of these sources. Methods: A detailed photospheric abundance study was performed using high-resolution UVES optical spectra. To study the circumstellar environment we use photometric data to construct the spectral energy distributions of the stars, and determine the geometry of the circumstellar environment, whereas low-resolution Spitzer-IRS infrared spectra are used to trace its mineralogy. Results: Our results show that, also in the LMC, the photospheres of RV Tauri stars are commonly affected by the depletion process, although it can differ significantly in strength from source to source. From our detailed disc modelling and mineralogy study, we find that this process, as in the Galaxy, appears closely related to the presence of a stable Keplerian disc. The newly studied extragalactic objects have similar observational characteristics as Galactic post-AGB binaries surrounded by a dusty disc, and are therefore also believed to be part of a binary system. One source shows a very small infrared excess, atypical for a disc source, but still has evidence for depletion. We speculate this could point to the presence of a very evolved disc, similar to debris discs seen around young stellar objects., Comment: Accepted for publication in A&A, 14 pages

The Spectrograph for Photometric Imaging with Numeric Reconstruction (SPINR) sounding rocket experiment was launched on 2000 August 4 to record far-ultraviolet (912-1450 A) spectral and spatial information for the giant reflection nebula in the Upper Scorpius region. The data were divided into three arbitrary bandpasses (912-1029 A, 1030-1200 A, and 1235-1450 A) for which stellar and nebular flux levels were derived. These flux measurements were used to constrain a radiative transfer model and to determine the dust albedo for the Upper Scorpius region. The resulting albedos were 0.28+/-0.07 for the 912-1029 A bandpass, 0.33+/-0.07 for the 1030-1200 A bandpass, and 0.77+/-0.13 for the 1235-1450 A bandpass.