Browsing UA Faculty Research by Subjects
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JINGLE – IV. Dust, H i gas, and metal scaling laws in the local UniverseScaling laws of dust, HI gas, and metal mass with stellar mass, specific star formation rate, and metallicity are crucial to our understanding of the build-up of galaxies through their enrichment with metals and dust. In this work, we analyse how the dust and metal content varies with specific gas mass (M-HI/M-star) across a diverse sample of 423 nearby galaxies. The observed trends are interpreted with a set of Dust and Element evolUtion modelS (DEUS) - including stellar dust production, grain growth, and dust destruction - within a Bayesian framework to enable a rigorous search of the multidimensional parameter space. We find that these scaling laws for galaxies with -1.0 less than or similar to log M-HI/M-star less than or similar to 0 can be reproduced using closed-box models with high fractions (37-89 per cent) of supernova dust surviving a reverse shock, relatively low grain growth efficiencies (subset of = 30-40), and long dust lifetimes (1-2 Gyr). The models have present-day dust masses with similar contributions from stellar sources (50-80 per cent) and grain growth (20-50 per cent). Over the entire lifetime of these galaxies, the contribution from stardust (>90 per cent) outweighs the fraction of dust grown in the interstellar medium (<10 per cent). Our results provide an alternative for the chemical evolution models that require extremely low supernova dust production efficiencies and short grain growth time-scales to reproduce local scaling laws, and could help solving the conundrum on whether or not grains can grow efficiently in the interstellar medium.
Less than the sum of its parts: the dust-corrected H α luminosity of star-forming galaxies explored at different spatial resolutions with MaNGA and MUSEThe H alpha and H beta emission-line luminosities measured in a single integrated spectrum are affected in non-trivial ways by pointto-point variations in dust attenuation in a galaxy. This work investigates the impact of this variation when estimating global H alpha luminosities corrected for the presence of dust by a global Balmer decrement. Analytical arguments show that the dust-corrected H alpha luminosity is always underestimated when using the global H alpha/H beta flux ratio to correct for dust attenuation. We measure this effect on 156 face-on star-forming galaxies from the Mapping Nearby Galaxies at APO (MaNGA) survey. At 1-2 kpc spatial resolution, the effect is small but systematic, with the integrated dust-corrected H alpha luminosity underestimated by 2-4 per cent (and typically not more than by 10 per cent), and depends on the specific star formation rate of the galaxy. Given the spatial resolution of MaNGA, these are lower limits for the effect. From Multi Unit Spectroscopic Explorer (MUSE) observations of NGC628 with a resolution of 36 pc, we find the discrepancy between the globally and the point-by-point dust-corrected H alpha luminosity to be 14 +/- 1 per cent, which may still underestimate the true effect. We use toy models and simulations to show that the true difference depends strongly on the spatial variance of the H alpha/H beta flux ratio, and on the slope of the relation between H alpha luminosity and dust attenuation within a galaxy. Larger samples of higher spatial resolution observations are required to quantify the dependence of this effect as a function of galaxy properties.
Mapping the Interstellar Reddening and Extinction toward Baade's Window Using Minimum Light Colors of ab-type RR Lyrae Stars: Revelations from the De-reddened Color-Magnitude DiagramsWe have obtained repeated images of six fields toward the Galactic bulge in five passbands (u, g, r, i, z) with the DECam imager on the Blanco 4 m telescope at CTIO. From more than 1.6 billion individual photometric measurements in the field centered on Baade's window, we have detected 4877 putative variable stars. A total of 474 of these have been confirmed as fundamental mode RR Lyrae stars, whose colors at minimum light yield line-of-sight reddening determinations, as well as a reddenning law toward the Galactic Bulge, which differs significantly from the standard R-V = 3.1 formulation. Assuming that the stellar mix is invariant over the 3 square-degree field, we are able to derive a line-of-sight reddening map with sub-arcminute resolution, enabling us to obtain de-reddened and extinction corrected color-magnitude diagrams (CMDs) of this bulge field using up to 2.5 million well-measured stars. The corrected CMDs show unprecedented detail and expose sparsely populated sequences: for example, delineation of the very wide red giant branch, structure within the red giant clump, the full extent of the horizontal branch, and a surprising bright feature that is likely due to stars with ages younger than 1 Gyr. We use the RR. Lyrae stars to trace the spatial structure of the ancient stars and find an exponential decline in density with Galactocentric distance. We discuss ways in which our data products can be used to explore the age and metallicity properties of the bulge, and how our larger list of all variables is useful for learning to interpret future LSST alerts.