A Herschel study of AGB stars in the Milky Way

The Asymptotic Giant Branch (AGB) stars are low to intermediate-mass post-MS stars that undergo thermal pulses characterized by a strong wind-driven mass loss from its surface into the interstellar medium. They are responsible for the majority of the dust contained within the Galactic plane and thus, their study is crucial to understand the life cycle of dust in our Galaxy. The Hi-GAL Survey constitutes the perfect survey to detect and study AGB stars since it uses the PACS and SPIRE Herschel instruments in parallel mode to map the |l|< 60°; |b| <1° region of the Galactic plane in the 70 µm, 160 µm, 250 µm, 350 µm and 500 µm bands, which trace the emission of the dust in which AGB stars are embedded. In this thesis I use the Hi-GAL 1 maps processed with the ROMAGAL Pipeline to create a total of four catalogues: The SMA Hi-GAL 1 Point Source Catalogue - this is, to date, the most reliable Hi-GAL 1 PSC published. It contains the position and fluxes of all the Hi-GAL 1 compact sources detected by CUTEX in the 70 µm Herschel band and the corresponding counterparts found in the other Herschel bands. The SMA Hi-GAL 1 PSC AGB star candidate catalogue - this is the first catalogue including a list of possible Hi-GAL 1 AGB star candidates. The source classification was done by means of colour cuts that efficiently separate 95 reference Hi-GAL 1 AGB stars from 205 reference YSOs, 178 HII regions and 59 PNe. This is, to date, the largest sample of reference Hi-GAL 1 sources used on colour-colour separation methods. These colour cuts involve the Herschel 70 µm band and prove that this band plays a decisive role in identifying AGB stars and that it is highly effective in distinguishing AGB stars from other stellar types. The SMA Hi-GAL 1 PSC C-rich and O-rich AGB star candidate catalogues - these are the first two catalogues including a list of possible Hi-GAL 1 PSC C-rich and O-rich AGB star candidates and constitute the largest compilation of AGB stars detected within the Hi-GAL 1 Galactic region. The source classification was done by means of colour cuts that successfully separate 101 reference OH/IR-stars from 56 reference C-stars. These colour cuts involve the MSX 8.28 µm band, the AKARI 9 µm and 18 µm bands and the WISE 12 µm and 22 µm bands, which cover the silicate and carbonaceous features of O-rich and C-rich AGB stars, and prove that these bands are highly efficient in distinguishing C-rich from O-rich AGB stars. The analysis of the stellar properties derived for the Hi-GAL 1 PSC C-rich and O-rich AGB star candidates allowed us to define a series of equations that establish the relation between the stars' mass-loss rates and their colour temperatures, NIR [J]-[K] colour, luminosities and outflow velocities. These equations are of great importance since they enable us to derive the mass-loss rates of unknown AGB stars using only their colour temperatures

The Hi-GAL compact source catalogue – I. The physical properties of the clumps in the inner Galaxy (−71. ◦ 0 < ℓ < 67.◦ 0)

Hi-GAL (Herschel InfraRed Galactic Plane Survey) is a large-scale survey of the Galactic plane, performed with Herschel in five infrared continuum bands between 70 and 500 µm. We present a band-merged catalogue of spatially matched sources and their properties derived from fits to the spectral energy distributions (SEDs) and heliocentric distances, based on the photometric catalogues presented in Molinari et al., covering the portion of Galactic plane −71.◦ 0 < ℓ < 67.◦ 0. The band-merged catalogue contains 100 922 sources with a regular SED, 24 584 of which show a 70-µm counterpart and are thus considered protostellar, while the remainder are considered starless. Thanks to this huge number of sources, we are able to carry out a preliminary analysis of early stages of star formation, identifying the conditions that characterize different evolutionary phases on a statistically significant basis. We calculate surface densities to investigate the gravitational stability of clumps and their potential to form massive stars. We also explore evolutionary status metrics such as the dust temperature, luminosity and bolometric temperature, finding that these are higher in protostellar sources compared to pre-stellar ones. The surface density of sources follows an increasing trend as they evolve from pre-stellar to protostellar, but then it is found to decrease again in the majority of the most evolved clumps. Finally, we study the physical parameters of sources with respect to Galactic longitude and the association with spiral arms, finding only minor or no differences between the average evolutionary status of sources in the fourth and first Galactic quadrants, or between 'on-arm' and 'interarm' positions

Hi-GAL, theHerschelinfrared Galactic Plane Survey: photometric maps and compact source catalogues

Aims. We present the first public release of high-quality data products (DR1) from Hi-GAL, the Herschel infrared Galactic Plane Survey. Hi-GAL is the keystone of a suite of continuum Galactic plane surveys from the near-IR to the radio and covers five wavebands at 70, 160, 250, 350 and 500 µm, encompassing the peak of the spectral energy distribution of cold dust for 8 < T < 50 K. This first Hi-GAL data release covers the inner Milky Way in the longitude range 68◦ > t > −70◦ in a |b| ≤ 1◦ latitude strip. ∼ ∼ ∼ ∼ Methods. Photometric maps have been produced with the ROMAGAL pipeline, which optimally capitalizes on the excellent sensitivity and stability of the bolometer arrays of the Herschel PACS and SPIRE photometric cameras. It delivers images of exquisite quality and dynamical range, absolutely calibrated with Planck and IRAS, and recovers extended emission at all wavelengths and all spatial scales, from the point-spread function to the size of an entire 2◦ × 2◦ “tile” that is the unit observing block of the survey. The compact source catalogues were generated with the CuTEx algorithm, which was specifically developed to optimise source detection and extraction in the extreme conditions of intense and spatially varying background that are found in the Galactic plane in the thermal infrared. Results. Hi-GAL DR1 images are cirrus noise limited and reach the 1σ-rms predicted by the Herschel Time Estimators for parallel-mode obser- vations at 6011 s−1 scanning speed in relatively low cirrus emission regions. Hi-GAL DR1 images will be accessible through a dedicated web-based image cutout service. The DR1 Compact Source Catalogues are delivered as single-band photometric lists containing, in addition to source posi- tion, peak, and integrated flux and source sizes, a variety of parameters useful to assess the quality and reliability of the extracted sources. Caveats and hints to help in this assessment are provided. Flux completeness limits in all bands are determined from extensive synthetic source experiments and greatly depend on the specific line of sight along the Galactic plane because the background strongly varies as a function of Galactic longitude. Hi-GAL DR1 catalogues contain 123210, 308509, 280685, 160972, and 85460 compact sources in the five bands

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°

The Hi-GAL compact source catalogue - I. The physical properties of the clumps in the inner Galaxy (-71.degrees 0 < l < 67.degrees 0)

Hi-GAL (Herschel InfraRed Galactic Plane Survey) is a large-scale survey of the Galactic plane, performed with Herschel in five infrared continuum bands between 70 and 500 mu m. We present a band-merged catalogue of spatially matched sources and their properties derived from fits to the spectral energy distributions (SEDs) and heliocentric distances, based on the photometric catalogues presented in Molinari et al., covering the portion of Galactic plane -71.degrees 0 < l < 67.degrees 0. The band-merged catalogue contains 100 922 sources with a regular SED, 24 584 of which show a 70-mu m counterpart and are thus considered protostellar, while the remainder are considered starless. Thanks to this huge number of sources, we are able to carry out a preliminary analysis of early stages of star formation, identifying the conditions that characterize different evolutionary phases on a statistically significant basis. We calculate surface densities to investigate the gravitational stability of clumps and their potential to form massive stars. We also explore evolutionary status metrics such as the dust temperature, luminosity and bolometric temperature, finding that these are higher in protostellar sources compared to pre-stellar ones. The surface density of sources follows an increasing trend as they evolve from pre-stellar to protostellar, but then it is found to decrease again in themajority of the most evolved clumps. Finally, we study the physical parameters of sources with respect to Galactic longitude and the association with spiral arms, finding only minor or no differences between the average evolutionary status of sources in the fourth and first Galactic quadrants, or between 'on-arm' and 'interarm' positions

The Hi-GAL compact source catalogue - I. The physical properties of the clumps in the inner Galaxy (-71.degrees 0 < l < 67.degrees 0)

Hi-GAL (Herschel InfraRed Galactic Plane Survey) is a large-scale survey of the Galactic plane, performed with Herschel in five infrared continuum bands between 70 and 500 mu m. We present a band-merged catalogue of spatially matched sources and their properties derived from fits to the spectral energy distributions (SEDs) and heliocentric distances, based on the photometric catalogues presented in Molinari et al., covering the portion of Galactic plane -71.degrees 0 < l < 67.degrees 0. The band-merged catalogue contains 100 922 sources with a regular SED, 24 584 of which show a 70-mu m counterpart and are thus considered protostellar, while the remainder are considered starless. Thanks to this huge number of sources, we are able to carry out a preliminary analysis of early stages of star formation, identifying the conditions that characterize different evolutionary phases on a statistically significant basis. We calculate surface densities to investigate the gravitational stability of clumps and their potential to form massive stars. We also explore evolutionary status metrics such as the dust temperature, luminosity and bolometric temperature, finding that these are higher in protostellar sources compared to pre-stellar ones. The surface density of sources follows an increasing trend as they evolve from pre-stellar to protostellar, but then it is found to decrease again in themajority of the most evolved clumps. Finally, we study the physical parameters of sources with respect to Galactic longitude and the association with spiral arms, finding only minor or no differences between the average evolutionary status of sources in the fourth and first Galactic quadrants, or between 'on-arm' and 'interarm' positions

The Hi-GAL compact source catalogue - I. The physical properties of the clumps in the inner Galaxy (-71.0° < ℓ < 67.0°)

Hi-GAL (Herschel InfraRed Galactic Plane Survey) is a large-scale survey of the Galactic plane, performed with Herschel in five infrared continuum bands between 70 and 500 μm. We present a band-merged catalogue of spatially matched sources and their properties derived from fits to the spectral energy distributions (SEDs) and heliocentric distances, based on the photometric catalogues presented in Molinari et al., covering the portion of Galactic plane -71.0° < ℓ < 67.0°. The band-merged catalogue contains 100 922 sources with a regular SED, 24 584 of which show a 70-μm counterpart and are thus considered protostellar, while the remainder are considered starless. Thanks to this huge number of sources, we are able to carry out a preliminary analysis of early stages of star formation, identifying the conditions that characterize different evolutionary phases on a statistically significant basis. We calculate surface densities to investigate the gravitational stability of clumps and their potential to form massive stars. We also explore evolutionary status metrics such as the dust temperature, luminosity and bolometric temperature, finding that these are higher in protostellar sources compared to pre-stellar ones. The surface density of sources follows an increasing trend as they evolve from pre-stellar to protostellar, but then it is found to decrease again in the majority of the most evolved clumps. Finally, we study the physical parameters of sources with respect to Galactic longitude and the association with spiral arms, finding only minor or no differences between the average evolutionary status of sources in the fourth and first Galactic quadrants, or between 'on-arm' and 'interarm' positions