Star Formation in the Galactic Ecosystem

Over the next decade, the Canadian community will play a leading role in answering key questions about the interaction between star formation and galaxy evolution. These opportunities flow from a productive decade since LRP 2010 that has yielded new insights into the connections between how stars form and their local galactic environment. All these past and future advances have capitalized upon a broad suite of instrumental access from the long-wavelength radio to the ultraviolet. Galaxy evolution and star formation have traditionally been distinct subfields within astronomy, but the work since LRP 2010 has shown that the two are intimately connected. The buildup of the star forming main sequence and quenching of galaxies are both driven by star formation. Reciprocally, studies have also revealed that a galaxy's mass and morphology regulate the efficiency of ongoing star formation within it. These variations in efficiency are only now being clearly linked to changes in the properties of the star forming molecular medium and the conditions in the galactic interstellar medium. Over the next ten years, we will make a physically motivated connection between star formation and the broader galactic environment. This work focuses around five key questions and the survey-driven approaches that will enable Canadian researchers to come to clear answers over the next decade: How are ISM conditions and individual star formation events influenced by the galactic environment? We are carrying out the surveys of galaxy populations needed to make a census of ISM conditions across a statistically significant number of galaxies. These focus on careful work in the Milky Way and nearby galaxies where individual star formation events can be discerned. What processes regulate the formation of the molecular ISM and its organization into massive structures? Surveying a broad range of galactic environments is also a key data set for addressing this question, but this must also be done using new tracers to access obscured physics. Specifically, we will need good access to the submillimetre so we can execute high quality polarization measurements for studying the magnetic field and fine structure lines ([CI], [OI], [CII]) to trace the material being channeled into star forming clouds. What processes disrupt the neutral ISM leading to the quenching of galaxies? We will make surveys of Galactic and extragalactic star forming regions across the wavebands to calibrate how stars inject momentum and energy into their host galaxy ISM. We will establish how this feedback depends on local star formation properties, including the including cluster mass function. How does local star formation relate to the different mode of star formation seen in z>2 Universe? Studies of lensed systems, notably with ALMA, allow for resolved studies of a different mode of star formation in galactic assembly. However, these studies rely on tracers that are difficult to observe without new access to the submillimetre and far infrared. Through local mapping of the tracers typically used in high redshift studies, we can resolve how these tracers are influenced by local conditions, providing a better calibration of the properties in distant systems. How does the galactic environment predict other aspects of the star formation process beyond the star formation rate? Multiwaveband surveys will also extend our studies beyond simply answering how the star formation rate changes, turning to questions of variations in the initial mass function, the initial cluster mass function, and binary property distributions. To address these central questions in the next decade requires that we maintain and expand our access to a broad suite of observational facilities. In particular, we must remain actively engaged with ALMA, which is still in its early stages of discovery. We must also continue strong investment in high-performance computing necessary to carry out the expensive, multi-physics simulations of star formation in a galactic context. We continue to require access to single-dish radio to submillimetre facilities such as CCAT-p, the JCMT, and the GBT, and the DRAO Synthesis Telescope to carry out wide area mapping of our own Galaxy. ALMA should not be regarded as a replacement for this class of observatory. Finally, participating in next generation radio interferometers, namely the SKA and ngVLA, are needed to carry out resolved surveys of star formation and the interstellar medium beyond the nearest galaxies.

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