A 100 pc Elliptical and Twisted Ring of Cold and Dense Molecular Clouds Revealed by Herschel Around the Galactic Center

Thermal images of cold dust in the Central Molecular Zone of the Milky Way, obtained with the far-infrared cameras on board the Herschel satellite, reveal a ~3 × 10^7 M_☉ ring of dense and cold clouds orbiting the Galactic center. Using a simple toy model, an elliptical shape having semi-major axes of 100 and 60 pc is deduced. The major axis of this 100 pc ring is inclined by about 40° with respect to the plane of the sky and is oriented perpendicular to the major axes of the Galactic Bar. The 100 pc ring appears to trace the system of stable x_2 orbits predicted for the barred Galactic potential. Sgr A⋆ is displaced with respect to the geometrical center of symmetry of the ring. The ring is twisted and its morphology suggests a flattening ratio of 2 for the Galactic potential, which is in good agreement with the bulge flattening ratio derived from the 2MASS data

Aromatic emission from the ionised mane of the Horsehead nebula

We study the evolution of the Aromatic Infrared Bands (AIBs) emitters across the illuminated edge of the Horsehead nebula and especially their survival and properties in the HII region. We present spectral mapping observations taken with the Infrared Spectrograph (IRS) at wavelengths 5.2-38 microns. A strong AIB at 11.3 microns is detected in the HII region, relative to the other AIBs at 6.2, 7.7 and 8.6 microns. The intensity of this band appears to be correlated with the intensity of the [NeII] at 12.8 microns and of Halpha, which shows that the emitters of the 11.3 microns band are located in the ionised gas. The survival of PAHs in the HII region could be due to the moderate intensity of the radiation field (G0 about 100) and the lack of photons with energy above about 25eV. The enhancement of the intensity of the 11.3 microns band in the HII region, relative to the other AIBs can be explained by the presence of neutral PAHs. Our observations highlight a transition region between ionised and neutral PAHs observed with ideal conditions in our Galaxy. A scenario where PAHs can survive in HII regions and be significantly neutral could explain the detection of a prominent 11.3 microns band in other Spitzer observations.Comment: 9 pages, 9 figures, accepted for publication in A&

PAHs in protoplanetary disks: emission and X-ray destruction

We study the PAH emission from protoplanetary disks. First, we discuss the dependence of the PAH band ratios on the hardness of the absorbed photons and the temperature of the stars. We show that the photon energy together with a varying degree of the PAH hydrogenation accounts for most of the observed PAH band ratios without the need to change the ionization degree of the molecules. We present an accurate treatment of stochastic heated grains in a vectorized three dimensional Monte Carlo dust radiative transfer code. The program is verified against results using ray tracing techniques. Disk models are presented for T Tauri and Herbig Ae stars. Particular attention is given to the photo-dissociation of the molecules. We consider beside PAH destruction also the survival of the molecules by vertical mixing within the disk. By applying typical X-ray luminosities the model accounts for the low PAH detection probability observed in T Tauri and the high PAH detection statistics found in Herbig Ae disks. Spherical halos above the disks are considered. We show that halos reduce the observed PAH band-to-continuum ratios when observed at high inclination. Finally, mid-IR images of disks around Herbig Ae disks are presented. We show that they are easier to resolve when PAH emission dominate.Comment: Accepted for publication in A&A. 10 pages, 7 figures, 2 tabl

Study Abroad in the Age of Social Media

University of Technology Sydney. Faculty of Arts and Social Sciences.The advancement of information and communication technology has radically transformed the nature of study abroad and the way in which students apprehend this experience. As part of this larger shift, social media and digital communications have changed the way people interact, communicate and socialise and therefore also transformed the nature of study abroad as an immersive context for second language learning. This thesis aims to better understand the holistic and socially transformative dimensions of study abroad and explores the impact of what has become a quasi-constant digital connection to home on two traditional models of study abroad: the model of social network development (Bochner, McLeod, & Lin, 1977; Coleman, 2013, 2015; Furnham & Alibhai, 1985; Hendrickson, Rosen, & Aune, 2011, Rienties & Nolan, 2014; Schartner, 2015) and the theory of study abroad being a rite of passage (Grabowski, Wearing, Lyons, Tarrant, & Landon, 2017; Murphy-Lejeune, 2002; Starr-Glass, 2016) to transition to emerging adulthood (Arnett, 2000, 2010, 2012) effected through a strict separation from home. The study is based on a digital ethnography of seven Australian university students learning French in France or Switzerland on a year-long study abroad program. Data were collected by following and cataloguing participants’ posts on both Facebook and Instagram. These textual and photographic posts subsequently served as prompts for in-depth photo-elicitation interviews. Findings indicate that using social media as a research tool in the study abroad context raises new questions and provides new insights. First, participants’ narratives highlight the need to rethink students’ social networking paradigms as the traditional circles of study aboard socialisation are challenged by the use of social media in study abroad contexts and the shifting student objectives and motivations inherent in the larger study abroad sector. Second, the digital ethnography revealed the central role played by travel experiences while studying abroad. Contrary to expectations, these travel experiences fostered participants’ feelings of belonging in their host environment and their identity transition to emerging adulthood. These outcomes at once support and complicate the conceptualisation of study abroad as a rite of passage that impacts students’ identity. Third, the online ethnography revealed an unstudied but important phenomenon: the visit from participants’ relatives, specifically their parents. These visits disrupted the separation from home, disturbed participants’ experience and negatively impacted their identity transition to emerging adulthood. The thesis accordingly acknowledges the changing landscape of study abroad and the need for researchers to adapt to it. Consequently it advocates for the use of research tools aligned with rather than simply evaluative or critical of students’ established digital practices

The pros and cons of the inversion method approach to derive 3D dust emission properties in the ISM: the Hi-GAL field centred on (l, b) = (30°, 0°)

Herschel far-infrared continuum data obtained as part of the Hi-GAL survey have been used, together with the GLIMPSE 8 μm and MIPSGAL 24 μm data, to attempt the first 3D-decomposition of dust emission associated with atomic, molecular and ionized gas at 15 arcmin angular resolution. Our initial test case is a 2 × 2 square degrees region centred on (l, b) = (30°, 0°), a direction that encompasses the origin point of the Scutum–Crux Arm at the tip of the Galactic Bar. Coupling the IR maps with velocity maps specific for different gas phases (H i 21cm, ^(12)CO and ^(13)CO, and radio recombination lines), we estimate the properties of dust blended with each of the gas components and at different Galactocentric distances along the line of sight (LOS). A statistical Pearson's coefficients analysis is used to study the correlation between the column densities estimated for each gas component and the intensity of the IR emission. This analysis provides evidence that the 2 × 2 square degree field under consideration is characterized by the presence of a gas component not accounted for by the standard tracers, possibly associated with warm H_2 and cold H I. We demonstrate that the IR radiation in the range 8 < λ < 500 μm is systematically dominated by emission originating within the Scutum–Crux Arm. By applying an inversion method, we recover the dust emissivities associated with atomic, molecular and ionized gas. Using the DustEM model, we fit the spectral energy distributions for each gas phase, and find average dust temperatures of T_(d,H I) = 18.82 ± 0.47 K, T_(d,H_2) = 18.84 ± 1.06 K and T_(d,H II) = 22.56 ± 0.64 K, respectively. We also obtain an indication for polycyclic aromatic hydrocarbons depletion in the diffuse ionized gas. We demonstrate the importance of including the ionized component in 3D-decompositions of the total IR emission. However, the main goal of this work is to discuss the impact of the missing column density associated with the dark gas component on the accurate evaluation of the dust properties, and to shed light on the limitations of the inversion method approach when this is applied to a small section of the Galactic plane and when the working resolution allows sufficient de-blending of the gas components along the LOS

Hi-GAL: The Herschel Infrared Galactic Plane Survey

Hi-GAL, the Herschel infrared Galactic Plane Survey, is an Open Time Key Project of the Herschel Space Observatory. It will make an unbiased photometric survey of the inner Galactic plane by mapping a 2° wide strip in the longitude range midlmid < 60° in five wavebands between 70 μm and 500 μm. The aim of Hi-GAL is to detect the earliest phases of the formation of molecular clouds and high-mass stars and to use the optimum combination of Herschel wavelength coverage, sensitivity, mapping strategy, and speed to deliver a homogeneous census of star-forming regions and cold structures in the interstellar medium. The resulting representative samples will yield the variation of source temperature, luminosity, mass and age in a wide range of Galactic environments at all scales from massive YSOs in protoclusters to entire spiral arms, providing an evolutionary sequence for the formation of intermediate and high-mass stars. This information is essential to the formulation of a predictive global model of the role of environment and feedback in regulating the star-formation process. Such a model is vital to understanding star formation on galactic scales and in the early universe. Hi-GAL will also provide a science legacy for decades to come with incalculable potential for systematic and serendipitous science in a wide range of astronomical fields, enabling the optimum use of future major facilities such as JWST and ALMA

Herschel-SPIRE spectroscopy of G29.96-0.02: Fitting the full SED

We use the SPIRE Fourier-transform spectrometer (FTS) on-board the ESA Herschel Space Observatory to analyse the submillimetre spectrum of the Ultra-compact HII region G29.96-0.02. Spectral lines from species including (CO)-C-13, CO, [CI], and [NII] are detected. A sparse map of the [NII] emission shows at least one other HII region neighbouring the clump containing the UCHII. The FTS spectra are combined with ISO SWS and LWS spectra and fluxes from the literature to present a detailed spectrum of the source spanning three orders of magnitude in wavelength. The quality of the spectrum longwards of 100 mu m allows us to fit a single temperature greybody with temperature 80.3 +/- 0.6 K and dust emissivity index 1.73 +/- 0.02, an accuracy rarely obtained with previous instruments. We estimate a mass of 1500 M-circle dot for the clump containing the HII region. The clump's bolometeric luminosity of 4 x 10(6) L-circle dot is comparable to, or slightly greater than, the known O-star powering the UCHII region

VizieR Online Data Catalog: Hi-GAL. inner Milky Way: +68>=l>=70 (Molinari+, 2016)

This is the first public data release of high-quality products from the Herschel Hi-GAL survey. The release comes two years after the end of the Herschel observing campaign and is the result of extensive testing of the data reduction and extraction procedures created by members of the Hi-GAL consortium. The complexity and the large variation of the background conditions in all Herschel wavelength bands makes source extraction on the Galactic plane a challenging task. With Hi-GAL DR1, we provide access (http://vialactea.iaps.inaf.it) through a cutout service to high-quality images and compact source catalogues for the Galactic plane at 70, 160, 250, 350, and 500um in the region 68°>=l>=-70° and |b|<= 1°