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Galactic outflows of molecular gas are a common occurrence in galaxies andmay represent a mechanism by which galaxies self-regulate their growth,redistributing gas that could otherwise have formed stars. We previouslypresented the first survey of molecular outflows at z > 4 towards a sample ofmassive, dusty galaxies. Here we characterize the physical properties of themolecular outflows discovered in our survey. Using low-redshift outflows as atraining set, we find agreement at the factor-of-two level between severaloutflow rate estimates. We find molecular outflow rates 150-800Msun/yr andinfer mass loading factors just below unity. Among the high-redshift sources,the molecular mass loading factor shows no strong correlations with any othermeasured quantity. The outflow energetics are consistent with expectations formomentum-driven winds with star formation as the driving source, with no needfor energy-conserving phases. There is no evidence for AGN activity in oursample, and while we cannot rule out deeply-buried AGN, their presence is notrequired to explain the outflow energetics, in contrast to nearby obscuredgalaxies with fast outflows. The fraction of the outflowing gas that willescape into the circumgalactic medium (CGM), though highly uncertain, may be ashigh as 50%. This nevertheless constitutes only a small fraction of the totalcool CGM mass based on a comparison to z~2-3 quasar absorption line studies,but could represent >~10% of the CGM metal mass. Our survey offers the firststatistical characterization of molecular outflow properties in the very earlyuniverse.

Massive galaxy-scale outflows of gas are one of the most commonly-invokedmechanisms to regulate the growth and evolution of galaxies throughout theuniverse. While the gas in outflows spans a large range of temperatures anddensities, the cold molecular phase is of particular interest because molecularoutflows may be capable of suppressing star formation in galaxies by removingthe star-forming gas. We have conducted the first survey of molecular outflowsat z > 4, targeting 11 strongly-lensed dusty, star-forming galaxies (DSFGs)with high-resolution Atacama Large Millimeter Array (ALMA) observations of OH119um absorption as an outflow tracer. In this first paper, we give an overviewof the survey, focusing on the detection rate and structure of molecularoutflows. We find unambiguous evidence for outflows in 8/11 (73%) galaxies,more than tripling the number known at z > 4. This implies that molecular windsin z > 4 DSFGs must have both a near-unity occurrence rate and large openingangles to be detectable in absorption. Lensing reconstructions reveal that500pc-scale clumpy structures in the outflows are common. The individual clumpsare not directly resolved, but from optical depth arguments we expect thatfuture observations will require 50-200pc spatial resolution to do so. We donot detect high-velocity [CII] wings in any of the sources with clear OHoutflows, indicating that [CII] is not a reliable tracer of molecular outflows.Our results represent a first step toward characterizing molecular outflows atz > 4 at the population level, demonstrating that large-scale outflows areubiquitous among early massive, dusty galaxies.

Astrophysical observations currently provide the only robust, empiricalmeasurements of dark matter. In the coming decade, astrophysical observationswill guide other experimental efforts, while simultaneously probing uniqueregions of dark matter parameter space. This white paper summarizesastrophysical observations that can constrain the fundamental physics of darkmatter in the era of LSST. We describe how astrophysical observations willinform our understanding of the fundamental properties of dark matter, such asparticle mass, self-interaction strength, non-gravitational interactions withthe Standard Model, and compact object abundances. Additionally, we highlighttheoretical work and experimental/observational facilities that will complementLSST to strengthen our understanding of the fundamental characteristics of darkmatter.

Astrophysical and cosmological observations currently provide the onlyrobust, empirical measurements of dark matter. Future observations with LargeSynoptic Survey Telescope (LSST) will provide necessary guidance for theexperimental dark matter program. This white paper represents a communityeffort to summarize the science case for studying the fundamental physics ofdark matter with LSST. We discuss how LSST will inform our understanding of thefundamental properties of dark matter, such as particle mass, self-interactionstrength, non-gravitational couplings to the Standard Model, and compact objectabundances. Additionally, we discuss the ways that LSST will complement otherexperiments to strengthen our understanding of the fundamental characteristicsof dark matter. More information on the LSST dark matter effort can be found athttps://lsstdarkmatter.github.io/ .