Marc Sauvage, Jonathan Seale, Marta Sewiło, Kirill Tchernyshyov, and Ramin Skibba 1 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA 2 Sterrenkundig Observatorium, Universiteit Gent, Gent, Belgium 3 Observatoire astronomique de Strasbourg, Université de Strasbourg, CNRS, UMR 7550, 11 rue de lUniversité, F-67000 Strasbourg, France 4 Department of Astronomy, 475 North Charter Street, University of Wisconsin, Madison, WI 53706, USA 5 CESR, Université de Toulouse, UPS, 9 Avenue du Colonel Roche, F-31028 Toulouse, Cedex 4, France 6 Université de Toulouse, UPS-OMP, IRAP, 31028 Toulouse Cedex 4, France 7 Department of Astronomy, Lab for Millimeter-wave Astronomy, University of Maryland, College Park, MD 20742, USA 8 Observational Cosmology Lab, Code 665, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA 9 Oak Ridge Associated Universities (ORAU), Oak Ridge, TN 37831, USA 10 Louisiana State University, Department of Physics & Astronomy, 233-A Nicholson Hall, Tower Dr., Baton Rouge, LA 70803, USA 11 Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA 12 Raytheon Company, 1151 East Hermans Road, Tucson, AZ 85756, USA 13 Department of Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan 14 European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching-bei-Mnchen, Germany 15 CEA, Laboratoire AIM, Irfu/SAp, Orme des Merisiers, F-91191 Gif-sur-Yvette, France 16 Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany 17 Department of Astronomy, University of Virginia, and National Radio Astronomy Observatory, 520 Edgemont Road, Charlottesville, VA 22903, USA 18 Sterrewacht Leiden, Leiden University, P.O. Box 9513, NL-2300 RA Leiden, The Netherlands 19 National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo, 181-8588, Japan 20 314 Physics Building, Department of Physics and Astronomy, University of Missouri, Columbia, MO 65211, USA 21 Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK 22 Department of Astrophysics, Graduate School of Science, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan 23 CNRS, Observatoire de Paris—Lab. GEPI, Bat. 11, 5, place Jules Janssen, 92195 Meudon CEDEX, France 24 Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile 25 The Johns Hopkins University, Department of Physics and Astronomy, 366 Bloomberg Center, 3400 N. Charles Street, Baltimore, MD 21218, USA 26 Center for Astrophysics and Space Sciences, Department of Physics, University of California, 9500 Gilman Dr, La Jolla, San Diego, CA 92093, USA Received 2017 February 10; published 2017 March 7

Observations suggest that there is a significant fraction of O stars in the field of the Milky Way that appear to have formed in isolation or in low-mass clusters (< 100 M-circle dot). The existence of these high-mass stars that apparently formed in the field challenges the generally accepted paradigm, which requires star formation to occur in clustered environments. In order to understand the physical conditions for the formation of these stars, it is necessary to observe isolated high-mass stars while they are still forming. With the Hubble. Space. Telescope, we observe the seven most isolated massive (> 8 M-circle dot) young stellar objects (MYSOs) in the Large. Magellanic. Cloud. The observations show that while these MYSOs are remote from other MYSOs, OB associations, and even known giant molecular clouds, they are actually not isolated at all. Imaging reveals similar to 100 to several hundred pre-mainsequence (PMS) stars in the vicinity of each MYSO. These previously undetected PMS stars form prominent compact clusters around the MYSOs, and in most cases they are also distributed sparsely across the observed regions. Contrary to what previous high-mass field star studies show, these observations suggest that high-mass stars may not be able to form in clusters with masses less than 100 M-circle dot. If these MYSOs are indeed the best candidates for isolated high-mass star formation, then the lack of isolation is at odds with random sampling of the initial mass function. Moreover, while isolated MYSOs may not exist, we find evidence that isolated clusters containing O stars can exist, which in itself is rare.

We present the analysis of supernova remnants (SNRs) in the Large Magellanic Cloud (LMC) and their influence on the environment at far-infrared (FIR) and submillimeter wavelengths. We use new observations obtained with the Herschel Space Observatory and archival data obtained with the Spitzer Space Telescope, to make the first FIR atlas of these objects. The SNRs are not clearly discernible at FIR wavelengths; however, their influence becomes apparent in maps of dust mass and dust temperature, which we constructed by fitting a modified blackbody to the observed spectral energy distribution in each sightline. Most of the dust that is seen is pre-existing interstellar dust in which SNRs leave imprints. The temperature maps clearly reveal SNRs heating surrounding dust, while the mass maps indicate the removal of 3.7(-2.5)(+7.5) M-circle dot of dust per SNR. This agrees with the calculations by others that significant amounts of dust are sputtered by SNRs. Under the assumption that dust is sputtered and not merely pushed away, we estimate a dust destruction rate in the LMC of 0.037(-0.025)(+0.075) M-circle dot yr(-1) due to SNRs, yielding an average lifetime for interstellar dust of 2(-1.3)(+4.0) x 10(7) yr. We conclude that sputtering of dust by SNRs may be an important ingredient in models of galactic evolution, that supernovae may destroy more dust than they produce, and that they therefore may not be net producers of long lived dust in galaxies.

We present our study on the infrared variability of point sources in the Small Magellanic Cloud (SMC). We use the data from the Spitzer Space Telescope Legacy Program "Surveying the Agents of Galaxy Evolution in the Tidally Stripped, Low Metallicity Small Magellanic Cloud" (SAGE-SMC) and the "Spitzer Survey of the Small Magellanic Cloud" ((SMC)-M-3) survey, over three different epochs, separated by several months to 3 years. Variability in the thermal infrared is identified using a combination of Spitzer's InfraRed Array Camera 3.6, 4.5, 5.8, and 8.0 mu m bands, and the Multiband Imaging Photometer for Spitzer 24 mu m band. An error-weighted flux difference between each pair of three epochs (" variability index") is used to assess the variability of each source. A visual source inspection is used to validate the photometry and image quality. Out of similar to 2 million sources in the SAGE-SMC catalog, 814 meet our variability criteria. We matched the list of variable star candidates to the catalogs of SMC sources classified with other methods, available in the literature. Carbon-rich Asymptotic Giant Branch (AGB) stars make up the majority (61%) of our variable sources, with about a third of all of our sources being classified as extreme AGB stars. We find a small, but significant population of oxygen-rich (O-rich) AGB (8.6%), Red Supergiant (2.8%), and Red Giant Branch (<1%) stars. Other matches to the literature include Cepheid variable stars (8.6%), early type stars (2.8%), Young-stellar objects (5.8%), and background galaxies (1.2%). We found a candidate OH maser star, SSTISAGE1C J005212.88-730852.8, which is a variable O-rich AGB star, and would be the first OH/IR star in the SMC, if confirmed. We measured the infrared variability of a rare RV Tau variable (a post-AGB star) that has recently left the AGB phase. 59 variable stars from our list remain unclassified.

We present a study of the composition of gas and dust in the Large and Small Magellanic Clouds (LMC and SMC) using UV absorption spectroscopy. We measure P II and Fe II along 84 spatially distributed sightlines toward the MCs using archival Far Ultraviolet Spectroscopic Explorer observations. For 16 of those sightlines, we also measure Si II, Cr II, and Zn II from new Hubble Space Telescope Cosmic Origins Spectrograph observations. We analyze these spectra using a new spectral line analysis technique based on a semi-parametric Voigt profile model. We have combined these measurements with H I and H2 column densities and reference stellar abundances from the literature to derive gas-phase abundances, depletions, and gas-to-dust ratios (GDRs). Of our 84 P and 16 Zn measurements, 80 and 13, respectively, are depleted by more than 0.1 dex, suggesting that P and Zn abundances are not accurate metallicity indicators at and above the metallicity of the SMC. Si, Cr, and Fe are systematically less depleted in the SMC than in the Milky Way (MW) or LMC. The minimum Si depletion in the SMC is consistent with zero. We find GDR ranges of 190-565 in the LMC and 480-2100 in the SMC, which is broadly consistent with GDRs from the literature. These ranges represent actual location to location variation and are evidence of dust destruction and/or growth in the diffuse neutral phase of the interstellar medium. Where they overlap in metallicity, the gas-phase abundances of the MW, LMC, and SMC and damped Lya systems evolve similarly with metallicity.

We provide a corrected Table 4 that lists the total galaxy fluxes for the HERTIAGE bands and corresponding Figure 19 which plots these fluxes in comparison to prior measurements These corrected fluxes differ by up to 41% to what we reported in the original paper. These revised fluxes utilize a more appropriate subtraction of the Milky Way Foreground Cirrus emission which contaminates especially the PACS 100 and 160 micron bands. The subtraction process uses the HI 21 cm emission to develop a model for the MW cirrus dust emission. In addition, the better subtraction process corrected for an over subtraction of the background in the SPIRE images of the SMC that occurred during the original data processing. The need for these better foreground subtractions was realized while working on an analysis of the dust masses and gas-to-dust ratios in the LMC and SMC reported by Gordon et al. (2014) and Roman-Duval et al. (2014). After the subtraction has been done, the fluxes were derived by simply summing up all the pixels in the image. The errors we quote for the fluxes reflect the absolute flux calibration errors for extended sources which are approx.10% for PACS and approx. 8% for SPIRE. In the revised Figure 19, we confirm that these corrected global fluxes remain within the range of prior global measurements for both the LMC and SMC. Indeed, the shape of the corrected spectral energy distributions appears better aligned with prior measurements.

We present an analysis of mid-and far-infrared (IR) spectrum and spectral energy distribution (SED) of the LBV R71 in the LMC.This work aims to understand the overall contribution of high-mass LBVs to the total dust-mass budget of the interstellar medium (ISM) of the LMC and compare this with the contribution from low-mass asymptotic giant branch (AGB) stars. As a case study, we analyze the SED of R71. We compiled all the available photometric and spectroscopic observational fluxes from various telescopes for a wide wavelength range (0.36 -- 250\,$\mu$m). We determined the dust composition from the spectroscopic data, and derived the ejected dust mass, dust mass-loss rate, and other dust shell properties by modeling the SED of R71. We noted nine spectral features in the dust shell of R71 by analyzing Spitzer spectroscopic data. Among these, we identified three new crystalline silicate features. We computed our model spectrum by using 3D radiative transfer code MCMax. Our model calculation shows that dust is dominated by amorphous silicates, with some crystalline silicates, metallic iron, and a very tiny amount of polycyclic aromatic hydrocarbon (PAH) molecules. The presence of both silicates and PAHs indicates that the dust has a mixed chemistry. We derived a dust mass of 0.01 M$_\odot$, from which we arrive at a total ejected mass of $\approx$ 5 M$_\odot$. This implies a time-averaged dust mass-loss rate of 2.5$\times$10$^{-6}$ M$_\odot$\,yr$^{-1}$ with an explosion about 4000 years ago. We assume that the other five confirmed dusty LBVs in the LMC loose mass at a similar rate, and estimate the total contribution to the mass budget of the LMC to be $\approx$ 10$^{-5}$ M$_\odot$\,yr$^{-1}$, which is comparable to the contribution by all the AGB stars in the LMC. Based on our analysis on R71, we speculate that LBVs as a class may be an important dust source in the ISM of the LMC.

The dust properties in the Large and Small Magellanic clouds (LMC/SMC) are studied using the HERITAGE Herschel Key Project photometric data in five bands from 100 to 500 mu m. Three simple models of dust emission were fit to the observations: a single temperature blackbody modified by a power-law emissivity (SMBB), a single temperature blackbody modified by a broken power-law emissivity (BEMBB), and two blackbodies with different temperatures, both modified by the same power-law emissivity (TTMBB). Using these models, we investigate the origin of the submillimeter excess, defined as the submillimeter emission above that expected from SMBB models fit to observations <200 mu m. We find that the BEMBB model produces the lowest fit residuals with pixel-averaged 500 mu m submillimeter excesses of 27% and 43% for the LMC and SMC, respectively. Adopting gas masses from previous works, the gas-to-dust ratios calculated from our fitting results show that the TTMBB fits require significantly more dust than are available even if all the metals present in the interstellar medium (ISM) were condensed into dust. This indicates that the submillimeter excess is more likely to be due to emissivity variations than a second population of colder dust. We derive integrated dust masses of (7.3 +/- 1.7) x 10(5) and (8.3 +/- 2.1) x 10(4) M-circle dot for the LMC and SMC, respectively. We find significant correlations between the submillimeter excess and other dust properties; further work is needed to determine the relative contributions of fitting noise and ISM physics to the correlations.

The spatial variations of the gas-to-dust ratio (GDR) provide constraints on the chemical evolution and lifecycle of dust in galaxies. We examine the relation between dust and gas at 10-50 pc resolution in the Large and Small Magellanic Clouds (LMC and SMC) based on Herschel far-infrared (FIR), Hi 21 cm, CO, and Ha observations. In the diffuse atomic interstellar medium (ISM), we derive the GDR as the slope of the dust-gas relation and find GDRs of 380(-130)(+250) +/- 3 in the LMC, and 1200(-420)(+1600) +/- 120 in the SMC, not including helium. The atomicto- molecular transition is located at dust surface densities of 0.05M(circle dot) pc(-2) in the LMC and 0.03M(circle dot) pc(-2) in the SMC, corresponding to A(V) similar to 0.4 and 0.2, respectively. We investigate the range of CO-to-H-2 conversion factor to best account for all the molecular gas in the beam of the observations, and find upper limits on X-CO to be 6 x 10(20) cm(-2) K-1 km(-1) s in the LMC (Z = 0.5Z(circle dot)) at 15 pc resolution, and 4 x 10(21) cm(-2) K-1 km(-1) s in the SMC (Z = 0.2Z(circle dot)) at 45 pc resolution. In the LMC, the slope of the dust-gas relation in the dense ISM is lower than in the diffuse ISM by a factor similar to 2, even after accounting for the effects of CO-dark H-2 in the translucent envelopes of molecular clouds. Coagulation of dust grains and the subsequent dust emissivity increase in molecular clouds, and/or accretion of gas-phase metals onto dust grains, and the subsequent dust abundance (dust-to-gas ratio) increase in molecular clouds could explain the observations. In the SMC, variations in the dust-gas slope caused by coagulation or accretion are degenerate with the effects of CO-dark H-2. Within the expected 5-20 times Galactic X-CO range, the dust-gas slope can be either constant or decrease by a factor of several across ISM phases. Further modeling and observations are required to break the degeneracy between dust grain coagulation, accretion, and CO-dark H-2. Our analysis demonstrates that obtaining robust ISM masses remains a non-trivial endeavor even in the local Universe using state-of-the-art maps of thermal dust emission.

The Herschel Space Observatory completed its last observation on 2013 April 29 after completing 35 000 astronomical observations resulting in numerous discoveries. In this review, we describe the capabilities and general scope of the Herschel mission. In particular, we review the science results from one of the open time key programs, the HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE) in the Magellanic Clouds. The HERITAGE project mapped the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) at 100, 160, 250, 350, and 500 mu m using the SPIRE/PACS parallel mode. The total global fluxes for the LMC and SMC agree with measurements by other missions, including Planck. The HERITAGE maps of the LMC and SMC are dominated by the ISM dust emission and bear most resemblance to the tracers of ISM gas rather than the stellar content of the galaxies. The overriding science goal of HERITAGE is to study the life cycle of matter as traced by dust in the LMC and SMC. The far-infrared and submillimeter emission is an effective tracer of the interstellar medium (ISM) dust, the most deeply embedded young stellar objects (YSOs) and the dust ejected by the most massive stars which are discussed briefly in this review. The HERITAGE team has delivered the maps and source catalogs created for each of the 5 bands to the Herschel Science Center archive which will hold the legacy of Herschel. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

The Magellanic Bridge is the nearest low-metallicity, tidally stripped environment, offering a unique high-resolution view of physical conditions in merging and forming galaxies. In this paper, we present an analysis of candidate massive young stellar objects (YSOs), i.e., in situ, current massive star formation (MSF) in the Bridge using Spitzer mid-IR and complementary optical and near-IR photometry. While we definitely find YSOs in the Bridge, the most massive are similar to 10M(circle dot), << 45M(circle dot) found in the LMC. The intensity of MSF in the Bridge also appears to be decreasing, as the most massive YSOs are less massive than those formed in the past. To investigate environmental effects on MSF, we have compared properties of massive YSOs in the Bridge to those in the LMC. First, YSOs in the Bridge are apparently less embedded than in the LMC: 81% of Bridge YSOs show optical counterparts, compared to only 56% of LMC sources with the same range of mass, circumstellar dust mass, and line-of-sight extinction. Circumstellar envelopes are evidently more porous or clumpy in the Bridge's low-metallicity environment. Second, we have used whole samples of YSOs in the LMC and the Bridge to estimate the probability of finding YSOs at a given Hi column density, N(H I). We found that the LMC has similar to 3x higher probability than the Bridge for N(H I) > 12x10(20) cm(-2), but the trend reverses at lower N(H I). Investigating whether this lower efficiency relative to Hi is due to less efficient molecular cloud formation or to less efficient cloud collapse, or to both, will require sensitive molecular gas observations.

We present parsec-scale interferometric maps of HCN(1–0) and HCO+(1–0) emission from dense gas in the star-forming region 30 Doradus, obtained using the Australia Telescope Compact Array. This extreme star-forming region, located in the Large Magellanic Cloud (LMC), is characterized by a very intense ultraviolet ionizing radiation field and sub-solar metallicity, both of which are expected to impact molecular cloud structure. We detect 13 bright, dense clumps within the 30 Doradus-10 giant molecular cloud. Some of the clumps are aligned along a filamentary structure with a characteristic spacing that is consistent with formation via varicose fluid instability. Our analysis shows that the filament is gravitationally unstable and collapsing to form stars. There is a good correlation between HCO+ emission in the filament and signatures of recent star formation activity including H2O masers and young stellar objects (YSOs). YSOs seem to continue along the same direction of the filament toward the massive compact star cluster R136 in the southwest. We present detailed comparisons of clump properties (masses, linewidths, and sizes) in 30Dor-10 to those in other star forming regions of the LMC (N159, N113, N105, and N44). Our analysis shows that the 30Dor-10 clumps have similar masses but wider linewidths and similar HCN/HCO+ (1–0) line ratios as clumps detected in other LMC star-forming regions. Our results suggest that the dense molecular gas clumps in the interior of 30Dor-10 are well shielded against the intense ionizing field that is present in the 30Doradus region.

We present near-ultraviolet Hubble Space Telescope Cosmic Origins Spectrograph (HST-COS) spectra towards sixteen stars in the Large and Small Magellanic Clouds.We use these spectra, as well as 109 archival Far Ultraviolet Spectroscopic Explorer (FUSE) spectra to measure the gasphase abundances of phosphorus, zinc, silicon, chromium, and iron in the interstellar medium of the Large and Small Magellanic Clouds.We find that the gas-phase to total interstellar medium abundance ratios of these elements are approximately the same as in the Milky Way for phosphorus and zinc and higher than in the Milky Way for silicon, chromium, and iron.This effect is greater in the Small Magellanic Cloud than in the Large Magellanic Cloud.We use these relative abundances to estimate the gas-to-dust mass ratios of the Large and Small Magellanic Clouds.

Observations from the HERschel Inventory of the Agents of Galaxy Evolution (HERITAGE) have been used to identify dusty populations of sources in the Large and Small Magellanic Clouds (LMC and SMC). We conducted the study using the HERITAGE catalogs of point sources available from the Herschel Science Center from both the Photodetector Array Camera and Spectrometer (PACS; 100 and 160 mu m) and Spectral and Photometric Imaging Receiver (SPIRE; 250, 350, and 500 mu m) cameras. These catalogs are matched to each other to create a Herschel band-merged catalog and then further matched to archival Spitzer IRAC and MIPS catalogs from the Spitzer Surveying the Agents of Galaxy Evolution (SAGE) and SAGE-SMC surveys to create single mid- to far-infrared (far-IR) point source catalogs that span the wavelength range from 3.6 to 500 mu m. There are 35,322 unique sources in the LMC and 7503 in the SMC. To be bright in the FIR, a source must be very dusty, and so the sources in the HERITAGE catalogs represent the dustiest populations of sources. The brightest HERITAGE sources are dominated by young stellar objects (YSOs), and the dimmest by background galaxies. We identify the sources most likely to be background galaxies by first considering their morphology (distant galaxies are point-like at the resolution of Herschel) and then comparing the flux distribution to that of the Herschel Astrophysical Terahertz Large Area Survey (ATLAS) survey of galaxies. We find a total of 9745 background galaxy candidates in the LMC HERITAGE images and 5111 in the SMC images, in agreement with the number predicted by extrapolating from the ATLAS flux distribution. The majority of the Magellanic Cloud-residing sources are either very young, embedded forming stars or dusty clumps of the interstellar medium. Using the presence of 24 mu m emission as a tracer of star formation, we identify 3518 YSO candidates in the LMC and 663 in the SMC. There are far fewer far-IR bright YSOs in the SMC than the LMC due to both the SMC's smaller size and its lower dust content. The YSO candidate lists may be contaminated at low flux levels by background galaxies, and so we differentiate between sources with a high ("probable") and moderate ("possible") likelihood of being a YSO. There are 2493/425 probable YSO candidates in the LMC/SMC. Approximately 73% of the Herschel YSO candidates are newly identified in the LMC, and 35% in the SMC. We further identify a small population of dusty objects in the late stages of stellar evolution including extreme and post-asymptotic giant branch, planetary nebulae, and supernova remnants. These populations are identified by matching the HERITAGE catalogs to lists of previously identified objects in the literature. Approximately half of the LMC sources and one quarter of the SMC sources are too faint to obtain accurate ample FIR photometry and are unclassified.

We present an overview of the HERschel Inventory of The Agents of Galaxy Evolution (HERITAGE) in the Magellanic Clouds project, which is a Herschel Space Observatory open time key program. We mapped the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) at 100, 160, 250, 350, and 500 mu m with the Spectral and Photometric Imaging Receiver (SPIRE) and Photodetector Array Camera and Spectrometer (PACS) instruments on board Herschel using the SPIRE/PACS parallel mode. The overriding science goal of HERITAGE is to study the life cycle of matter as traced by dust in the LMC and SMC. The far-infrared and submillimeter emission is an effective tracer of the interstellar medium (ISM) dust, the most deeply embedded young stellar objects (YSOs), and the dust ejected by the most massive stars. We describe in detail the data processing, particularly for the PACS data, which required some custom steps because of the large angular extent of a single observational unit and overall the large amount of data to be processed as an ensemble. We report total global fluxes for the LMC and SMC and demonstrate their agreement with measurements by prior missions. The HERITAGE maps of the LMC and SMC are dominated by the ISM dust emission and bear most resemblance to the tracers of ISM gas rather than the stellar content of the galaxies. We describe the point source extraction processing and the criteria used to establish a catalog for each waveband for the HERITAGE program. The 250 mu m band is the most sensitive and the source catalogs for this band have similar to 25,000 objects for the LMC and similar to 5500 objects for the SMC. These data enable studies of ISM dust properties, submillimeter excess dust emission, dust-to-gas ratio, Class 0 YSO candidates, dusty massive evolved stars, supernova remnants (including SN1987A), H II regions, and dust evolution in the LMC and SMC. All images and catalogs are delivered to the Herschel Science Center as part of the community support aspects of the project. These HERITAGE images and catalogs provide an excellent basis for future research and follow up with other facilities.