The Galactic ecosystem: Outflow and infall in the halo of the Milky Way

The evolution, dynamics and eventual fate of galaxies is largely determined by access to and distribution of their primary fuel: atomic neutral hydrogen. Neutral hydrogen is not only pervasive in the disk of galaxies such as the Milky Way, but can also be found in the hot halo surrounding galaxies. The signatures of hydrogen detected in galactic haloes are caused by three key processes: outflow, due to energetic events associated with the galactic disk; infall, due to interactions with other nearby galaxies or the intergalactic medium; and circulation within the galactic ecosystem. In this thesis, a nearby Galactic supershell GSH 006-15+7 is studied, in order to understand how supershells are able to circulate cold gas between the disk and halo. By analysing HI self-absorption in the shell wall, the spin temperature of the gas is constrained to be cold and dense. Based on the morphology of the supershell and its estimated distance, GSH 006-15+7 has a likely origin in the Sagittarius OB 1 association of young stars. There is also evidence that the shell is transitioning into a chimney structure based on fragmentation at high Galactic latitudes, with an associated ionised hydrogen feature indicating a potential position of break-out into the Milky Way halo. This result is supported by findings in optical emission lines of high energy activity. Anomalous velocity gas deviates from that expected of Galactic rotation, and as such pinpoints hydrogen that is part of the cycle of outflow, infall and circulation. The Galactic All Sky Survey (GASS) of southern-sky neutral hydrogen is used to catalogue anomalous velocity gas in the halo of the Milky Way. Both classical high-velocity clouds and anomalous velocity clouds are included in the catalogue. With their lower velocities, anomalous velocity clouds are intrinsically closer to Galactic rotation and hence can be expected to probe the bridge between the Galactic disk and the halo. The GASS catalogue features unprecedented combination of high sensitivity with high angular and spectral resolution in the southern sky, and will be useful for studies of anomalous velocity gas on various scales. Several GASS clouds are followed up, some of known origin, at high angular resolution with the Australia Telescope Compact Array in order to determine the relative influences of origin and environment in clouds showing evidence of interaction. By combining the population of GASS high-velocity clouds with a very sensitive survey of neutral hydrogen in the halo, a Milky Way halo hidden from typical surveys of neutral hydrogen due to sensitivity limits is revealed, where the brightest neutral hydrogen merges with a diffuse prevalent medium that is likely to contribute just as much gas content as the bright high-velocity clouds. These results are consistent with findings in other wavelengths indicating the presence of more hydrogen in the halo than detected in the high-velocity cloud population. If the detected diffuse gas follows predicted supernova-driven models of cooling, then these two populations of neutral hydrogen combined can potentially account for the entire Galactic star formation rate. Overall, the studies in this thesis have revealed an active and dynamic Galaxy that maintains strong connections between its disk and the surrounding halo environment, in which neutral hydrogen remains a pivotal and powerful key to unlocking its evolutionary past and star-forming future

Ultra- and Hyper-compact HII regions at 20 GHz

We present radio and infrared observations of 4 hyper-compact HII regions and 4 ultra-compact HII regions in the southern Galactic plane. These objects were selected from a blind survey for UCHII regions using data from two new radio surveys of the southern sky; the Australia Telescope 20 GHz survey (AT20G) and the 2nd epoch Molonglo Galactic Plane Survey (MGPS-2) at 843 MHz. To our knowledge, this is the first blind radio survey for hyper- and ultra-compact HII regions. We have followed up these sources with the Australia Telescope Compact Array to obtain H70-alpha recombination line measurements, higher resolution images at 20 GHz and flux density measurements at 30, 40 and 95 GHz. From this we have determined sizes and recombination line temperatures as well as modeling the spectral energy distributions to determine emission measures. We have classified the sources as hyper-compact or ultra-compact on the basis of their physical parameters, in comparison with benchmark parameters from the literature. Several of these bright, compact sources are potential calibrators for the Low Frequency Instrument (30-70 GHz) and the 100-GHz channel of the High Frequency Instrument of the Planck satellite mission. They may also be useful as calibrators for the Australia Telescope Compact Array, which lacks good non-variable primary flux calibrators at higher frequencies and in the Galactic plane region. Our spectral energy distributions allow the flux densities within the Planck bands to be determined, although our high frequency observations show that several sources have excess emission at 95 GHz (3 mm) that can not be explained by current models.Comment: 13 pages, 7 figures, accepted for publication in MNRA

High velocity clouds in the Galactic All Sky Survey I. Catalogue

We present a catalogue of high-velocity clouds (HVCs) from the Galactic All Sky Survey (GASS) of southern-sky neutral hydrogen, which has 57 mK sensitivity and 1 km/s velocity resolution and was obtained with the Parkes Telescope. Our catalogue has been derived from the stray-radiation corrected second release of GASS. We describe the data and our method of identifying HVCs and analyse the overall properties of the GASS population. We catalogue a total of 1693 HVCs at declinations < 0 deg, including 1111 positive velocity HVCs and 582 negative velocity HVCs. Our catalogue also includes 295 anomalous velocity clouds (AVCs). The cloud line-widths of our HVC population have a median FWHM of ~19 km/s, which is lower than found in previous surveys. The completeness of our catalogue is above 95% based on comparison with the HIPASS catalogue of HVCs, upon which we improve with an order of magnitude in spectral resolution. We find 758 new HVCs and AVCs with no HIPASS counterpart. The GASS catalogue will shed an unprecedented light on the distribution and kinematic structure of southern-sky HVCs, as well as delve further into the cloud populations that make up the anomalous velocity gas of the Milky Way.Comment: 21 pages, 14 figures, accepted for publication in ApJ

Overcoming inconsistencies in placement assessment : the case for developmental assessment centers

Placements are integral to many university courses and to increasing student employability skills. Nevertheless, several complications, such as the assessment of placement experiences which often go against the principles of procedural justice, may limit placement effectiveness. For example, procedures are not applied uniformly across students; and evaluations of intangible qualities are susceptible to biases. As a result, effort and learning can be compromised. This paper advocates the use of developmental assessment centers to help solve these shortcomings. Developmental assessment centers are often used in organizations to evaluate capabilities of individuals and to facilitate development. Participants complete a series of work related and standardized tasks. Multiple raters then utilize a systematic approach to evaluate participants on a range of competencies, and consequently present constructive feedback to facilitate learning. Therefore, developmental assessment center principles match the key determinants of procedural justice and thus overcome many problems with traditional placement assessments

Grounded in Relationships of Support: Indigenous Teacher Mentorship in the Rural West

This article explores the power of Indigenous teacher mentorship as essential to address “the change in point of view” long called for in Indigenous education. Drawing from a longitudinal, ethnographic study of an Indigenous teacher education program in a predominantly rural, high need region, we examine the basic questions: What do Indigenous master teachers uniquely bring to teacher education? In what ways do Indigenous master teachers support the development of socially, culturally, linguistically, and place-responsive teachers? Using the theoretical frameworks of Tribal Critical Race Theory (TribalCrit) and situated learning, our findings elucidate the importance of Indigenous mentorship for re-membering and re-claiming Indigenous epistemologies, ontologies, and axiologies in relational and intergenerational learning—practices that interrupt coloniality in teacher education and school leadership. Discussion of Indigenous teacher mentorship centers the importance of relationships between people and place in teaching and learning and asks educators and school leaders to conceptualize Indigenous teacher education as a long-term project of tribal nation building and community wellbeing

Detection of radio emission from stars via proper-motion searches

We present a method for identifying radio stellar sources using their proper-motion. We demonstrate this method using the FIRST, VLASS, RACS-low and RACS-mid radio surveys, and astrometric information from Gaia Data Release 3. We find eight stellar radio sources using this method, two of which have not previously been identified in the literature as radio stars. We determine that this method probes distances of ~90pc when we use FIRST and RACS-mid, and ~250pc when we use FIRST and VLASS. We investigate the time baselines required by current and future radio sky surveys to detect the eight sources we found, with the SKA (6.7 GHz) requiring <3 years between observations to find all eight sources. We also identify nine previously known and 43 candidate variable radio stellar sources that are detected in FIRST (1.4 GHz) but are not detected in RACS-mid (1.37 GHz). This shows that many stellar radio sources are variable, and that surveys with multiple epochs can detect a more complete sample of stellar radio sources.Comment: 20 pages, 6 figures, 6 tables, accepted for publication in PAS

Observations of cold extragalactic gas clouds at z=0.45z = 0.45 towards PKS 1610-771

We present results from MUSE observations of a 21-cm HI absorption system detected with the Australian Square Kilometre Array Pathfinder radio telescope at redshift $z = 0.4503$ towards the $z = 1.71$ quasar PKS 1610-771. We identify four galaxies (A, B, X and Y) at the same redshift as the 21-cm H I Damped Lyman-{\alpha} (DLA) absorption system, with impact parameters ranging from less than 10 kpc to almost 200 kpc from the quasar sightline. Ca II and Na I absorption is seen in the MUSE spectrum of the background QSO, with velocities coinciding with the initial HI 21-cm detection, but tracing less dense and warmer gas. This metal-line component aligns with the rotating ionised disc of galaxy B (impact parameter 18 kpc from the QSO) and appears to be co-rotating with the galaxy disc. In contrast, the 21-cm HI absorber is blueshifted relative to the galaxies nearest the absorber and has the opposite sign to the velocity field of galaxy B. Since galaxies A and B are separated by only 17 kpc on the sky and $70$ km s$^{-1}$ in velocity, it appears likely that the 21-cm detection traces extragalactic clouds of gas formed from their interaction. This system reveals that the cold 100 K neutral gas critical for star formation can be associated with complex structures beyond the galaxy disc, and is a first case study made in preparation for future large 21-cm absorption surveys like the ASKAP First Large Absorption Survey in HI.Comment: Accepted. 13 pages, 7 figure

Análise da amplitude de distribuição dos eritrócitos (RDW-CV e RDW-SD) em diferentes intervalos de volume corpuscular médio (VCM) / Analysis of red cell distribution width (RDW-CV and RDW-SD) at different intervals of mean corpuscular volume (MCV)

Introdução: A amplitude de distribuição eritrocitária (RDW) demonstra aplicações únicas de diagnóstico que contribuem para uma melhor compreensão sobre a condição do paciente. O RDW expresso como coeficiente de variação (RDW-CV) e como desvio-padrão (RDW-SD) são dados matemáticos e estatísticos que apresentam diferentes formas de obtenção pelo analisador hematológico. Objetivo: Avaliar as variações do RDW-CV e RDW-SD de acordo com diferentes intervalos do volume corpuscular médio (VCM): microcítico, normocítico e macrocítico. Material e Métodos: Os parâmetros avaliados no estudo foram selecionados do analisador hematológico XN-1000® (Sysmex, Kobe, Japan). Os pacientes foram divididos em três grupos de acordo com diferentes intervalos do VCM: microcítico, normocítico e macrocítico. O grau de variação de anisocitose detectado pelas diferentes expressões de RDW foi calculado em porcentagem de aumento em relação aos valores de referência. Resultados: Nos hemogramas com microcitose, 30 (58%) não exibiram alteração para o RDW-SD, no restante houve discrepância entre o grau de variação de anisocitose detectado pelo RDW-CV e RDW-SD e não houve correlação entre os parâmetros. Na normocitose observou-se maior congruência e forte correlação entre RDW-CV e RDW-SD. Na macrocitose o RDW-SD demonstrou grau de variação de anisocitose superior ao RDW-CV na maioria das amostras, com fraca correlação negativa entre RDW-CV e RDW-SD. Conclusão: O analista clínico deve estar atento aos resultados de RDW-CV e RDW-SD na interpretação de anisocitose, principalmente nos hemogramas microcíticos e macrocíticos.  

A successful search for intervening 21 cm HI absorption in galaxies at 0.4 < z <1.0 with the Australian Square Kilometre Array Pathfinder (ASKAP)

We have used the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope to search for intervening 21 cm neutral hydrogen (HI) absorption along the line of sight to 53 bright radio continuum sources. Our observations are sensitive to HI column densities typical of Damped Lyman Alpha absorbers (DLAs) in cool gas with an HI spin temperature below about 300-500 K. The six-dish Boolardy Engineering Test Array (BETA) and twelve-antenna Early Science array (ASKAP-12) covered a frequency range corresponding to redshift $0.4<z<1.0$ and $0.37<z<0.77$ respectively for the HI line. Fifty of the 53 radio sources observed have reliable optical redshifts, giving a total redshift path $\Delta z$ = 21.37. This was a spectroscopically-untargeted survey, with no prior assumptions about the location of the lines in redshift space. Four intervening HI lines were detected, two of them new. In each case, the estimated HI column density lies above the DLA limit for HI spin temperatures above 50-80 K, and we estimate a DLA number density at redshift $z\sim0.6$ of $n(z)=0.19\substack{+0.15 \\ -0.09}$. This value lies somewhat above the general trend of $n(z)$ with redshift seen in optical DLA studies. Although the current sample is small, it represents an important proof of concept for the much larger 21cm First Large Absorption Survey in HI (FLASH) project to be carried out with the full 36-antenna ASKAP telescope, probing a total redshift path $\Delta z\sim\,50,000$.Comment: 21 pages, 11 figures. Accepted for publication in MNRA