The Gas Properties of the W3 GMC: A HARP study

We present 12CO, 13CO and C18O J=3-2 maps of the W3 GMC made at the James Clerk Maxwell Telescope. We combine these observations with Five Colleges Radio Astronomy Observatory CO J=1-0 data to produce the first map of molecular-gas temperatures across a GMC and the most accurate determination of the mass distribution in W3 yet obtained. We measure excitation temperatures in the part of the cloud dominated by triggered star formation (the High Density Layer, HDL) of 15-30 K, while in the rest of the cloud, which is relatively unaffected by triggering (Low Density Layer, LDL), the excitation temperature is generally less than 12 K. We identify a temperature gradient in the HDL which we associate with an age sequence in the embedded massive star-forming regions. We measure the mass of the cloud to be 4.4+/-0.4 x 10^5 solar masses, in agreement with previous estimates. Existing sub-mm continuum data are used to derive the fraction of gas mass in dense clumps as a function of position in the cloud. This fraction, which we interpret as a Clump Formation Efficiency (CFE), is significantly enhanced across the HDL, probably due to the triggering. Finally, we measure the 3D rms Mach Number as a function of position and find a correlation between the Mach number and the CFE within the HDL only. This correlation is interpreted as due to feedback from the newly-formed stars and a change in its slope between the three main star-forming regions is construed as another evolutionary effect. We conclude that triggering has affected the star-formation process in the W3 GMC primarily by creating additional dense structures that can collapse into stars. Any traces of changes in CFE due to additional turbulence have since been overruled by the feedback effects of the star-forming process itself.Comment: 14 pages, 11 figures, 1 table, accepted for publication in MNRA

Dust Resurgence in Protoplanetary Disks Due to Planetesimal-Planet Interactions

Observational data on the dust content of circumstellar disks show that the median dust content in disks around pre-main-sequence stars in nearby star-forming regions seems to increase from ~1 to ~2 Myr and then decline with time. This behavior challenges the models where the small dust grains steadily decline by accumulating into larger bodies and drifting inwards on a short timescale (≤1 Myr). In this Letter we explore the possibility to reconcile this discrepancy in the framework of a model where the early formation of planets dynamically stirs the nearby planetesimals and causes high-energy impacts between them, resulting in the production of second-generation dust. We show that the observed dust evolution can be naturally explained by this process within a suite of representative disk-planet architectures

Changes of dust opacity with density in the Orion A molecular cloud

We have studied the opacity of dust grains at submillimeter wavelengths by estimating the optical depth from imaging at 160, 250, 350, and 500 μm from the Herschel Gould Belt Survey and comparing this to a column density obtained from the Two Micron All Sky Survey derived color excess E(J – Ks). Our main goal was to investigate the spatial variations of the opacity due to "big" grains over a variety of environmental conditions and thereby quantify how emission properties of the dust change with column (and volume) density. The central and southern areas of the Orion A molecular cloud examined here, with NH ranging from 1.5 × 1021 cm–2 to 50 × 1021 cm–2, are well suited to this approach. We fit the multi-frequency Herschel spectral energy distributions (SEDs) of each pixel with a modified blackbody to obtain the temperature, T, and optical depth, τ1200, at a fiducial frequency of 1200 GHz (250 μm). Using a calibration of NH/E(J – Ks ) for the interstellar medium (ISM) we obtained the opacity (dust emission cross-section per H nucleon), σe(1200), for every pixel. From a value ~1 × 10–25 cm2 H–1 at the lowest column densities that is typical of the high-latitude diffuse ISM, σe(1200) increases as N 0.28H over the range studied. This is suggestive of grain evolution. Integrating the SEDs over frequency, we also calculated the specific power P (emission power per H) for the big grains. In low column density regions where dust clouds are optically thin to the interstellar radiation field (ISRF), P is typically 3.7 × 10–31 W H–1, again close to that in the high-latitude diffuse ISM. However, we find evidence for a decrease of P in high column density regions, which would be a natural outcome of attenuation of the ISRF that heats the grains, and for localized increases for dust illuminated by nearby stars or embedded protostars

A Multi-Wavelength Study of the Star Formation Process in the W3 Giant Molecular Cloud

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Filaments and Pre-stellar Sources in the Orion A L1641 Molecular Clouds

The Herschel Gould Belt Survey far-IR maps of the Orion L 1641 molecular clouds have revealed a wealth of interconnected filaments and dense sources in the region. We report here the first estimation of the total mass of the L 1641 clouds as derived from dust (3: 7 x 10(4)M(circle dot)). We further present our initial analysis of the physical properties of these dense sources as a result of their immediate environment. We have extracted a robust and statistically significant sample of 321 pre-stellar sources with a mass distribution that spans a range of 0.1-20M(circle dot). We show that there are two mass range distributions that depend on the location of the dense cores on or off the identified filaments

From Clouds to Young Stellar Objects and back again: the all-in-one view from the Herschel infrared Galactic Plane Survey

From diffuse interstellar cirrus to dense atomic and molecular clouds, from protostellar to post-AGB envelopes, from super-shells to supernovae remnants, the Herschel Hi-GAL survey offer an unprecedented snapshot of all the different phases of the Galactic ISM, its evolution and interactions. I will present early results on a variety of topics including the lifetime of massive pre-stellar phases, the fragmentation and collapse of extended structures, the timeline for massive star formation, dust properties in cirrus and molecular clouds