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This white paper submitted for the 2020 Canadian Long-Range Planning process (LRP2020) presents the prospects for Canada and the Square Kilometre Array (SKA) from 2020-2030, focussing on the first phase of the project (SKA1) scheduled to begin construction early in the next decade. SKA1 will make transformational advances in our understanding of the Universe across a wide range of fields, and Canadians are poised to play leadership roles in several. Canadian key SKA technologies will ensure a good return on capital investment in addition to strong scientific returns, positioning Canadian astronomy for future opportunities well beyond 2030. We therefore advocate for Canada's continued scientific and technological engagement in the SKA from 2020-2030 through participation in the construction and operations phases of SKA1., Comment: 14 pages, 4 figures, 2020 Canadian Long-Range Plan (LRP2020) white paper

The source responsible for the reionization of the Universe is believed to be the population of star-forming galaxies at $z\sim6$ to 12. The biggest uncertainty concerns the fraction of Lyman-continuum photons that actually escape from the galaxies. In recent years, several relatively small samples of "leaky" galaxies have been uncovered, and clues have begun to emerge as to both the indirect signposts of leakiness and of the conditions/processes that enable the escape of ionizing radiation. In this paper we present the results of a pilot program aimed to test a new technique for finding leaky galaxies---using the weakness of the [SII] nebular emission-lines relative to typical star-forming galaxies as evidence that the interstellar medium is optically-thin to the Lyman continuum. We use the Cosmic Origins Spectrograph on the Hubble Space Telescope to detect significant emerging flux below the Lyman edge in two out of three [SII]-weak star-forming galaxies at $z\sim0.3$. We show that these galaxies differ markedly in their properties from the class of leaky "Green-Pea" galaxies at similar redshifts: our sample galaxies are more massive, more metal-rich, and less extreme in terms of their stellar population and the ionization state of the interstellar medium. Like the Green Peas, they have exceptionally high star-formation rates per unit area. They also share some properties with the known leaky galaxies at $z\sim3$, but are significantly dustier. Our results validate a new way to identify local laboratories for exploring the processes that made it possible for galaxies to reionize the Universe., Comment: Accepted for publication in ApJ. 17 pages, 8 figures, 8 tables

This white paper submitted for the 2020 Canadian Long-Range Planning process (LRP2020) presents the prospects for Canada and the Square Kilometre Array (SKA) from 2020-2030, focussing on the first phase of the project (SKA1) scheduled to begin construction early in the next decade. SKA1 will make transformational advances in our understanding of the Universe across a wide range of fields, and Canadians are poised to play leadership roles in several. Canadian key SKA technologies will ensure a good return on capital investment in addition to strong scientific returns, positioning Canadian astronomy for future opportunities well beyond 2030. We therefore advocate for Canada's continued scientific and technological engagement in the SKA from 2020-2030 through participation in the construction and operations phases of SKA1., Comment: 14 pages, 4 figures, 2020 Canadian Long-Range Plan (LRP2020) white paper

The source responsible for the reionization of the Universe is believed to be the population of star-forming galaxies at $z\sim6$ to 12. The biggest uncertainty concerns the fraction of Lyman-continuum photons that actually escape from the galaxies. In recent years, several relatively small samples of "leaky" galaxies have been uncovered, and clues have begun to emerge as to both the indirect signposts of leakiness and of the conditions/processes that enable the escape of ionizing radiation. In this paper we present the results of a pilot program aimed to test a new technique for finding leaky galaxies---using the weakness of the [SII] nebular emission-lines relative to typical star-forming galaxies as evidence that the interstellar medium is optically-thin to the Lyman continuum. We use the Cosmic Origins Spectrograph on the Hubble Space Telescope to detect significant emerging flux below the Lyman edge in two out of three [SII]-weak star-forming galaxies at $z\sim0.3$. We show that these galaxies differ markedly in their properties from the class of leaky "Green-Pea" galaxies at similar redshifts: our sample galaxies are more massive, more metal-rich, and less extreme in terms of their stellar population and the ionization state of the interstellar medium. Like the Green Peas, they have exceptionally high star-formation rates per unit area. They also share some properties with the known leaky galaxies at $z\sim3$, but are significantly dustier. Our results validate a new way to identify local laboratories for exploring the processes that made it possible for galaxies to reionize the Universe., Comment: Accepted for publication in ApJ. 17 pages, 8 figures, 8 tables

Using ultra-violet absorption-lines, we analyze the systematic properties of the warm ionized phase of starburst-driven winds in a sample of 39 low-redshift objects that spans broad ranges in starburst and galaxy properties. Total column densities for the outflows are $\sim$10$^{21}$ cm$^{-2}$. The outflow velocity (v$_{out}$) correlates only weakly with the galaxy stellar mass (M$_*$), or circular velocity (v$_{cir}$), but strongly with both SFR and SFR/area. The normalized outflow velocity (v$_{out}/v_{cir}$) correlates well with both SFR/area and SFR/M$_*$. The estimated outflow rates of warm ionized gas ($\dot{M}$) are $\sim$ 1 to 4 times the SFR, and the ratio $\dot{M}/SFR$ does not correlate with v$_{out}$. We show that a model of a population of clouds accelerated by the combined forces of gravity and the momentum flux from the starburst matches the data. We find a threshold value for the ratio of the momentum flux supplied by the starburst to the critical momentum flux needed for the wind to overcome gravity acting on the clouds ($R_{crit}$). For $R_{crit} >$ 10 (strong-outflows) the outflow momentum flux is similar to the total momentum flux from the starburst and the outflow velocity exceeds the galaxy escape velocity. Neither is the case for the weak-outflows ($R_{crit} <$ 10). For the weak-outflows, the data severely disagree with many prescriptions in numerical simulations or semi-analytic models of galaxy evolution. The agreement is better for the strong-outflows, and we advocate the use of $R_{crit}$ to guide future prescriptions., Comment: Accepted for publication in ApJ. Contains 16 pages, 11 figure, and 2 tables

Using ultra-violet absorption-lines, we analyze the systematic properties of the warm ionized phase of starburst-driven winds in a sample of 39 low-redshift objects that spans broad ranges in starburst and galaxy properties. Total column densities for the outflows are $\sim$10$^{21}$ cm$^{-2}$. The outflow velocity (v$_{out}$) correlates only weakly with the galaxy stellar mass (M$_*$), or circular velocity (v$_{cir}$), but strongly with both SFR and SFR/area. The normalized outflow velocity (v$_{out}/v_{cir}$) correlates well with both SFR/area and SFR/M$_*$. The estimated outflow rates of warm ionized gas ($\dot{M}$) are $\sim$ 1 to 4 times the SFR, and the ratio $\dot{M}/SFR$ does not correlate with v$_{out}$. We show that a model of a population of clouds accelerated by the combined forces of gravity and the momentum flux from the starburst matches the data. We find a threshold value for the ratio of the momentum flux supplied by the starburst to the critical momentum flux needed for the wind to overcome gravity acting on the clouds ($R_{crit}$). For $R_{crit} >$ 10 (strong-outflows) the outflow momentum flux is similar to the total momentum flux from the starburst and the outflow velocity exceeds the galaxy escape velocity. Neither is the case for the weak-outflows ($R_{crit} <$ 10). For the weak-outflows, the data severely disagree with many prescriptions in numerical simulations or semi-analytic models of galaxy evolution. The agreement is better for the strong-outflows, and we advocate the use of $R_{crit}$ to guide future prescriptions., Comment: Accepted for publication in ApJ. Contains 16 pages, 11 figure, and 2 tables