ALBERT

Description: Author(s): MacKenzie L. Warren, Matthew Meixner, Grant Mathews, Jun Hidaka, and Toshitaka Kajino We have made core-collapse supernova simulations that allow oscillations between electron neutrinos (or their antiparticles) with right-handed sterile neutrinos. We have considered a range of mixing angles and sterile neutrino masses including those consistent with sterile neutrinos as a dark matter... [Phys. Rev. D 90, 103007] Published Tue Nov 18, 2014

Description: The goals of this research were to determine the physical conditions of the Photon-Dominated Regions (PDRS) surrounding the cooler stars (B0-A0) of several reflection nebulae and to test theoretical "low-density" PDR models. In contrast to the substantial investigation on "high-density" PDRS, " low-density" PDRs have been adequately modelled, but have not been adequately tested. At the start of this project, we had reduced Kuiper Airborne Observatory spectra of several far-infrared (FIR) fine structure lines on eight reflection nebulae that cover a range in cooler stellar spectral types (A0-B0). We analyzed these data in the context of "los-density" PDR models asking the question: Do the physical conditions in these reflection nebulae change with stellar spectral type as predicted?

Description: We present an overview or 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 micron 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 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 critetia used to establish a catalog for each waveband for the HERITAGE program. The 250 micron band is the most sensitive and the source catalogs for this band have approx. 25,000 objects for the LMC and approx. 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, supemova 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 conummity support aspects of the project. These HERITAGE images and catalogs provide an excellent basis for future research and follow up with other facilities.

Description: Supernova (SN) explosions are crucial engines driving the evolution of galaxies by shock heating gas, increasing the metallicity, creating dust, and accelerating energetic particles. In 2012 we used the Atacama Large Millimeter/ Submillimeter Array to observe SN1987A, one of the best-observed supernovae since the invention of the telescope. We present spatially resolved images at 450 m, 870 m, 1.4 mm, and 2.8 mm, an important transition wavelength range. Longer wavelength emission is dominated by synchrotron radiation from shock-accelerated particles, shorter wavelengths by emission from the largest mass of dust measured in a supernova remnant (〉0.2 Solar Mass). For the first time we show unambiguously that this dust has formed in the inner ejecta (the cold remnants of the exploded star's core). The dust emission is concentrated at the center of the remnant, so the dust has not yet been affected by the shocks. If a significant fraction survives, and if SN 1987A is typical, supernovae are important cosmological dust producers.

Description: 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 light years away. The observations reveal the presence of a population of cold dust grains radiating with a temperature of approx.17-23 K at a rate of about 220 stellar luminosity. The intensity and spectral energy distribution of the emission suggests a dust mass of approx.0.4-0.7 stellar 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 red shifts.

Description: We report the first extragalactic detection of the complex organic molecules (COMs) dimethyl ether (CH3OCH3) and methyl formate (CH3OCHO) with the Atacama Large Millimeter/submillimeter Array (ALMA). These COMs, together with their parent species methanol (CH3OH), were detected toward two 1.3 mm continuum sources in the N 113 star-forming region in the low-metallicity Large Magellanic Cloud (LMC). Rotational temperatures (Trot approx. 130 K) and total column densities (Nrot 10 approx. 16 cm2) have been calculated for each source based on multiple transitions of CH3OH. We present the ALMA molecular emission maps for COMs and measured abundances for all detected species. The physical and chemical properties of two sources with COMs detection, and the association with H2O and OH maser emission, indicate that they are hot cores. The fractional abundances of COMs scaled by a factor of 2.5 to account for the lower metallicity in the LMC are comparable to those found at the lower end of the range in Galactic hot cores. Our results have important implications for studies of organic chemistry at higher redshift.

Description: We report spectroscopic and imaging observations of rotational transitions of cold CO and SiO in the ejecta of SN1987A, the first such emission detected in a supernova remnant. In addition to line luminosities for the CO J = 1-0, 2-1, 6-5, and 7-6 transitions, we present upper limits for all other transitions up to J = 13-12, collectively measured from the Atacama Large Millimeter Array, the Atacama Pathfinder EXperiment, and the Herschel Spectral and Photometric Imaging REceiver. Simple models show the lines are emitted from at least 0.01 M of CO at a temperature 〉14 K, confined within at most 35% of a spherical volume expanding at ~2000 km s-1. Moreover, we locate the emission within 1'' of the central debris. These observations, along with a partial observation of SiO, confirm the presence of cold molecular gas within supernova remnants and provide insight into the physical conditions and chemical processes in the ejecta. Furthermore, we demonstrate the powerful new window into supernova ejecta offered by submillimeter observations.

Description: The dust properties in the Large and Small Magellanic Clouds are studied using the HERITAGE Herschel Key Project photometric data in five bands from 100 to 500 micromillimeters. Three simple models of dust emission were fit to the observations: a single temperature blackbody modified by a powerlaw 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 (submm) emission above that expected from SMBB models fit to observations 〈 200 micromillimeters. We find that the BEMBB model produces the lowest fit residuals with pixel-averaged 500 micromillimeters submillimeter excesses of 27% and 43% for the Large and Small Magellanic Clouds, 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 plus or minus 1.7) x 10 (sup 5) and (8.3 plus or minus 2.1) x 10 (sup 4) solar masses for the Large and Small Magellanic Clouds, 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.

Description: We have observed the extreme OH/IR star, OH 26.5+0.6, in the infrared dust continuum and in the sub- millimeter rotational lines of CO. Mid-infrared images reveal the compact nature of the circumstellar shell (less than 0.5 sec). A deep 9.7 microns absorption feature and an absorption at 18 microns show that the dust mass-loss rate is very high. However, the low antenna temperatures of CO J = 1-0 and 2-1 lines suggest that the outer part of the circumstellar shell is much more tenuous. In order to resolve this discrepancy, we have observed the J = 3-2 and 4-3 CO rotational transitions. We have developed a model for the circumstellar shell for OH 26.5 + 0.6 which is consistent with the infrared and submillimeter observations. The dust and gas data are well fitted by a two-shell model, consisting of a dense shell surrounded by a more tenuous shell. The former we identify with the superwind (M = 5.5 x 10(exp -4) solar mass/ yr), and the latter we identify with mass loss on the asymptotic giant branch (AGB) (M = 10(exp -6) solar mass/ yr). The transition between the two mass-loss phases is shown to be rather abrupt ((Delta)t less than 150 yr). Depending on the mass of the progenitor, this superwind phase may be the last thermal pulse (for M(sub *) less than 1.5 solar mass), or the first of a series of the superwind phases (for up to 8 solar mass), punctuated by a period of low mass-loss rates, before the star evolves off the AGB.

Description: The nature, composition, abundance, and size distribution of dust in galaxies is determined by the rate at which it is created in the different stellar sources and destroyed by interstellar shocks. Because of their extensive wavelength coverage, proximity, and nearly face-on geometry, the Magellanic Clouds (MCs) provide a unique opportunity to study these processes in great detail. In this paper we use the complete sample of supernova remnants (SNRs) in the MCs to calculate the lifetime and destruction efficiencies of silicate and carbon dust in these galaxies. We find dust lifetimes of 22+/-13 Myr (30+/-17 Myr) for silicate (carbon) grains in the LMC, and 54 +/- 32 Myr (72 +/- 43 Myr) for silicate (carbon) grains in the SMC. The significantly shorter lifetimes in the MCs, as compared to the Milky Way, are explained as the combined effect of their lower total dust mass, and the fact that the dust-destroying isolated SNe in the MCs seem to be preferentially occurring in regions with higher than average dust-to-gas (D2G) mass ratios. We also calculate the supernova rate and the current star formation rate in the MCs, and use them to derive maximum dust injection rates by asymptotic giant branch (AGB) stars and core collapse supernovae (CCSNe). We find that the injection rates are an order of magnitude lower than the dust destruction rates by the SNRs. This supports the conclusion that, unless the dust destruction rates have been considerably overestimated, most of the dust must be reconstituted from surviving grains in dense molecular clouds. More generally, we also discuss the dependence of the dust destruction rate on the local D2G mass ratio and the ambient gas density and metallicity, as well as the application of our results to other galaxies and dust evolution models.