Probing ISM Models with H-alpha observations

I review the capabilities of H$\alpha$ observations to constrain some aspects of the current models of the interstellar medium. In particular, it is shown that turbulence is a necessary ingredient of any viable model, since most of the energy produced by supernova explosions and ionizing radiation is stored in kinetic form in the ISM. Various forms of turbulent energy dissipation, including cloud collisions, are analyzed. Two additional aspects, concerning the existence of galactic fountains and their relation with High Velocity Clouds, and the extended ionized layer of spiral galaxies are discussed; some crucial experiments are suggested.Comment: 9 pages, plain LaTeX, 5 figures; Invited Talk at the "AAO/UKST Galactic Plane H-alpha Survey" International Workshop, Sydney, Australi

The Final Legal-Writing Class: Parting Wisdom for Students

The last class of a legal-writing course is a beginning rather than an end for our students. Soon, they will have the opportunity to employ, in real life, the skills they have learned in the course. And professors want their students not only to succeed, but to excel, in practice. To help realize this goal, and as a fitting finale to the course, a professor may choose to provide students with tips for the immediate and long-term future in their profession

The Final Legal-Writing Class: Parting Wisdom for Students

The last class of a legal-writing course is a beginning rather than an end for our students. Soon, they will have the opportunity to employ, in real life, the skills they have learned in the course. And professors want their students not only to succeed, but to excel, in practice. To help realize this goal, and as a fitting finale to the course, a professor may choose to provide students with tips for the immediate and long-term future in their profession

Massive Star Formation

The enormous radiative and mechanical luminosities of massive stars impact a vast range of scales and processes, from the reionization of the universe, to the evolution of galaxies, to the regulation of the interstellar medium, to the formation of star clusters, and even to the formation of planets around stars in such clusters. Two main classes of massive star formation theory are under active study, Core Accretion and Competitive Accretion. In Core Accretion, the initial conditions are self-gravitating, centrally concentrated cores that condense with a range of masses from the surrounding, fragmenting clump environment. They then undergo relatively ordered collapse via a central disk to form a single star or a small-N multiple. In this case, the pre-stellar core mass function has a similar form to the stellar initial mass function. In Competitive Accretion, the material that forms a massive star is drawn more chaotically from a wider region of the clump without passing through a phase of being in a massive, coherent core. In this case, massive star formation must proceed hand in hand with star cluster formation. If stellar densities become very high near the cluster center, then collisions between stars may also help to form the most massive stars. We review recent theoretical and observational progress towards understanding massive star formation, considering physical and chemical processes, comparisons with low and intermediate-mass stars, and connections to star cluster formation.Comment: Accepted for publication as a chapter in Protostars and Planets VI, University of Arizona Press (2014), eds. H. Beuther, R. Klessen, C. Dullemond, Th. Hennin

The Escape of Ionizing Photons from OB Associations in Disk Galaxies: Radiation Transfer Through Superbubbles

By solving the time-dependent radiation transfer problem of stellar radiation through evolving superbubbles within a smoothly varying HI distribution, we estimate the fraction of ionizing photons emitted by OB associations that escapes the HI disk of our Galaxy into the halo and intergalactic medium (IGM). We consider both coeval star-formation and a Gaussian star-formation history with a time spread sigma_t = 2 Myr. We consider both a uniform H I distribution and a two-phase (cloud/intercloud) model, with a negligible filling factor of hot gas. We find that the shells of the expanding superbubbles quickly trap or attenuate the ionizing flux, so that most of the escaping radiation escapes shortly after the formation of the superbubble. For the coeval star-formation history, the total fraction of Lyman Continuum photons that escape both sides of the disk in the solar vicinity is f_esc approx 0.15 +/- 0.05. For the Gaussian star formation history, f_esc approx 0.06 +/- 0.03, a value roughly a factor of two lower than the results of Dove & Shull (1994), where superbubbles were not considered. For a local production rate of ionizing photons Psi_LyC = 4.95 X 10^7 cm^{-2} s^{-1}, the flux escaping the disk is Phi_LyC approx (1.5-3.0) X 10^6 cm^{-2} s^{-1} for coeval and Gaussian star formation, comparable to the flux required to sustain the Reynolds layer.Comment: Revised version (expanded), accepted for publication by ApJ, 38 pages, 8 figures, aasms4.sty and aabib.sty files include

Ancient giants: on the farthest galaxy at z=8.6

The observational frontiers for the detection of high-redshift galaxies have recently been pushed to unimaginable distances with the record-holding Lyman Alpha Emitter (LAE) UDFy-38135539 discovered at redshift z=8.6. However, the physical nature and the implications of this discovery have yet to be assessed. By selecting galaxies with observed luminosities similar to UDFy-38135539 in state-of-the-art cosmological simulations tuned to reproduce the large scale properties of LAEs, we bracket the physical nature of UDFy-38135539: it has a star formation rate ~ 2.7-3.7 solar masses/yr, it contains ~ 10^{8.3-8.7} solar mass of stars 50-80 Myr old, with stellar metallicity ~ 0.03-0.12 of the solar value. For any of the simulated galaxies to be visible as a LAE in the observed range, the intergalactic neutral hydrogen fraction at z=8.6 must be <= 0.2 and extra ionizing radiation from sources clustered around UDFy-38135539 is necessary. Finally, we predict that there is a 70% (15%) probability of detecting at least 1 such source from JWST (HST/WFC3) observations in a physical radius ~ 0.4 Mpc around UDFy-38135539.Comment: Accepted to MNRAS letter

Wheelchair and seating assistive technology provision: a gateway to freedom

Aim: The meaning of wheelchair and seating assistive technology and the impact inappropriate provision has on people’s lives from a service user’s perspective within an Irish context is highlighted. There is a dearth in evidence examining the process of wheelchair and seating provision and the interconnectedness between satisfaction, performance and participation from an equality and human rights perspective. The purpose if the study is to investigate wheelchair service users’ perspectives of wheelchair and seating provision in Ireland.Method: This is a mixed-methods study with an exploratory sequential design that includes two phases. During phase one, wheelchair service users were invited to take part in qualitative in-depth semi-structured interviews, which were thematically analysed and formed part of a larger ethnographic study involving multiple stakeholders in sustainable wheelchair and seating provision strategy development. In phase two, an online Survey Monkey questionnaire was distributed to obtain a wider overview of wheelchair service provision from a wheelchair service users perspective. Data obtained from the closed questions and content analysis for open comments was analysed descriptively for this phase.Results: Eight wheelchair service users agreed to participate in the interviews and 273 responded to the online survey. Thematic analysis and questionnaire frequency and content analysis revealed the vital meaning of wheelchair and seating assistive technology provision. However, bottlenecks within the system affect daily living, with qualitative data highlighting the obstruction to experiences of independent living from initial appointment to wheelchair breakdowns during daily life.Conclusion: Appropriate wheelchair and seating assistive technology provision is a basic human right, supported by the essential and embodied nature of the wheelchair as demonstrated through the wheelchair service users’ perspective throughout this study. These findings highlight the impact of ad-hoc services on individual freedoms and how the overall pace of the system affects a person’s ability to organise their time as an equal member of the community across the lifespan. A national review of wheelchair and seating assistive technology provision services is called for, giving consideration to access to services, assessment and delivery, follow up and management, education and training