Galaxy formation and evolution

Abstract:

High-resolution JWST images of nearby spiral galaxies reveal polycyclic aromatic hydrocarbon (PAH) structures that potentially trace molecular clouds, even CO-dark regions. For this paper, we identified ISM cloud structures in PHANGS-JWST 7.7μm PAH emission maps for 66 galaxies, smoothed to a common physical resolution of 30 pc and at native resolution. We extracted 108,466 cloud structures in the 30 pc sample and 146,040 clouds in the native resolution sample. We then calculated their molecular properties following a linear conversion from PAH to CO. Given the tendency for clouds in galaxy centers to overlap in velocity space, we opted to flag these clouds and omit them from the analysis in this work. The remaining clouds correspond to giant molecular clouds, such as those detected in CO(2-1) emission by ALMA, or lower surface density clouds that either fall below the ALMA detection limits of existing maps or genuinely have no molecular counterpart. We specifically used the homogenized sample for our analysis. Upon cross-matching the PAH clouds to the ALMA CO clouds at a homogenized resolution of 90 pc in 27 galaxies, we find that 41 $%$ of the PAH clouds are associated with a CO counterpart. We also show that the converted molecular cloud properties of the PAH clouds do not differ much when compared in different galactic environments. However, outside the central environment, the highest molecular mass surface density clouds are preferentially found in spiral arms. We further apply a lognormal fit to the mass spectra to an unprecedented extragalactic completeness limit of 2 , 10^ 3 , and find that spiral arms contain the most massive clouds compared to other galactic environments. Our findings support the idea that spiral arm gravitational potentials foster the formation of high surface density clouds, and that lower surface density clouds form in the interarm regions. The cloud values show a decline of a factor of ∼ 1.5-2 toward the outer 2-3 R_e. However, the trend largely varies in individual galaxies, with flat, decreasing, and even no trend as a function of R_̊m gal. Factors such as large-scale processes, galaxy types, and morphologies might influence the observed trends. We note that combining homogenized molecular properties of individual galaxies leads to the loss of information about the physical processes that are driving deviations in trends of those properties across different galactic environments. We published two catalogs at the CDS, one at the common resolution of 30 pc and another at the native resolution. We expect them to have broad utility for future studies of PAH clouds, molecular clouds, and star formation.

Abstract:

Understanding the cold atomic hydrogen gas (H i) within cosmic filaments has the potential to pin down the relationship between the low density gas in the cosmic web and how the galaxies that lie within it grow using this material. We report the discovery of a cosmic filament using 14 H i-selected galaxies that form a very thin elongated structure of 1.7 Mpc. These galaxies are embedded within a much larger cosmic web filament, traced by optical galaxies, that spans at least Mpc. We find that the spin axes of the H i galaxies are significantly more strongly aligned with the cosmic web filament () than cosmological simulations predict, with the optically selected galaxies showing alignment to a lesser degree (). This structure demonstrates that within the cosmic filament, the angular momentum of galaxies is closely connected to the large-scale filamentary structure. We also find strong evidence that the galaxies are orbiting around the spine of the filament, making this one of the largest rotating structures discovered thus far, and from which we can infer that there is transfer of angular momentum from the filament to the individual galaxies. The abundance of H i galaxies along the filament and the low dynamical temperature of the galaxies within the filament indicates that this filament is at an early evolutionary stage where the imprint of cosmic matter flow on galaxies has been preserved over cosmic time.

Abstract:

Dwarf galaxies provide powerful laboratories for studying galaxy formation physics. Their early assembly, shallow gravitational potentials, and bursty, clustered star formation histories make them especially sensitive to the processes that regulate baryons through multiphase outflows. Using high-resolution, cosmological zoom-in simulations of a dwarf galaxy from the Pandora suite, we explore the impact of stellar radiation, magnetic fields, and cosmic ray feedback on star formation, outflows, and metal retention. We find that our purely hydrodynamical model without non-thermal physics – in which supernova feedback is boosted to reproduce realistic stellar mass assembly – drives violent, overly enriched outflows that suppress the metal content of the host galaxy. Including radiation reduces the clustering of star formation and weakens feedback. However, the additional incorporation of cosmic rays produces fast, mass-loaded, multiphase outflows consisting of both ionized and neutral gas components, in better agreement with observations. These outflows, which entrain a denser, more temperate interstellar medium, exhibit broad metallicity distributions while preserving metals within the galaxy. Furthermore, the star formation history becomes more bursty, in agreement with recent James Webb Space Telescope findings. These results highlight the essential role of non-thermal physics in galaxy evolution and the need to incorporate it in future galaxy formation models.