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    K-corrections – a necessary ingredient for converting between flux in observed bands to flux in rest-frame bands – are critical for comparing galaxies at differing redshifts. These corrections often rely on fits to empirical or theoretical spectral energy distribution (SED) templates of galaxies. However, templates can only produce reliable K-corrections in regimes where SED models are robust. For instance, the templates utilized in some popular software packages are not well-constrained in some bands (e.g. WISE W4 in Kcorrect), which results in ill-behaved K-corrections. We address this shortcoming by developing an empirically driven approach to K-corrections that limits the dependence on SED templates. We perform a polynomial fit for the K-correction as a function of a galaxy’s rest-frame colour determined in a pair of well-constrained bands (e.g. 0(g − r)) and redshift, exploiting the fact that galaxy SEDs can be approximated as a one-parameter family at low redshift. For bands well-constrained by SED templates, our empirically driven K-corrections yield results comparable to the SED fitting methods used by Kcorrect and the GSWLC-M2 catalogue (the updated medium-deep GALEX–SDSS–WISE Legacy Catalogue). However, our method dramatically outperforms Kcorrect derived K-corrections for WISE W4. Our method is also robust to incorrect template assumptions outside of the optical bands and enforces that the K-correction must be zero at z = 0. Our K-corrected photometry and code are publicly available.

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  2. null (Ed.)
    Understanding the properties of dust attenuation curves in galaxies and the physical mechanisms that shape them are among the fundamental questions of extragalactic astrophysics, with great practical significance for deriving the physical properties of galaxies. Attenuation curves result from a combination of dust grain properties, dust content, and the spatial arrangement of dust and different populations of stars. In this review, we assess the state of the field, paying particular attention to extinction curves as the building blocks of attenuation laws. We introduce a quantitative framework to characterize extinction and attenuation curves, present a theoretical foundation for interpreting empirical results, overview an array of observational methods, and review observational results at low and high redshifts. Our main conclusions include the following: ▪  Attenuation curves exhibit a wide range of UV-through-optical slopes, from curves with shallow (Milky Way–like) slopes to those exceeding the slope of the Small Magellanic Cloud extinction curve. ▪  The slopes of the curves correlate strongly with the effective optical opacities, in the sense that galaxies with lower dust column density (lower visual attenuation) tend to have steeper slopes, whereas the galaxies with higher dust column density have shallower (grayer) slopes. ▪  Galaxies exhibit a range of 2175-Å UV bump strengths, including no bump, but, on average, are suppressed compared with the average Milky Way extinction curve. ▪  Theoretical studies indicate that both the correlation between the slope and the dust column as well as variations in bump strength may result from geometric and radiative transfer effects. 
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  3. Abstract

    We investigate the relationship between dust attenuation and stellar mass (M*) in star-forming galaxies over cosmic time. For this analysis, we compare measurements from the MOSFIRE Deep Evolution Field survey atz∼ 2.3 and the Sloan Digital Sky Survey (SDSS) atz∼ 0, augmenting the latter optical data set with both UV Galaxy Evolution Explorer (GALEX) and mid-infrared Wide-field Infrared Survey Explorer (WISE) photometry from the GALEX-SDSS-WISE Catalog. We quantify dust attenuation using both spectroscopic measurements of Hαand Hβemission lines, and photometric measurements of the rest-UV stellar continuum. The Hα/Hβratio is used to determine the magnitude of attenuation at the wavelength of Hα,AHα. Rest-UV colors and spectral energy distribution fitting are used to estimateA1600, the magnitude of attenuation at a rest wavelength of 1600 Å. As in previous work, we find a lack of significant evolution in the relation between dust attenuation andM*over the redshift rangez∼ 0 toz∼ 2.3. Folding in the latest estimates of the evolution ofMdust, (Mdust/Mgas), and gas surface density at fixedM*, we find that the expectedMdustand dust mass surface density are both significantly higher atz∼ 2.3 than atz∼ 0. These differences appear at odds with the lack of evolution in dust attenuation. To explain the striking constancy in attenuation versusM*, it is essential to determine the relationship between metallicity and (Mdust/Mgas), the dust mass absorption coefficient and dust geometry, and the evolution of these relations and quantities fromz∼ 0 toz∼ 2.3.

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  4. Abstract

    We explore the relationship between mid-infrared (mid-IR) and CO rotational line emission from massive star-forming galaxies, which is one of the tightest scalings in the local universe. We assemble a large set of unresolved and moderately (∼1 kpc) spatially resolved measurements of CO (1–0) and CO (2–1) intensity,ICO, and mid-IR intensity,IMIR, at 8, 12, 22, and 24μm. TheICOversusIMIRrelationship is reasonably described by a power law with slopes 0.7–1.2 and normalizationICO∼ 1 K km s−1atIMIR∼ 1 MJy sr−1. Both the slopes and intercepts vary systematically with choice of line and band. The comparison between the relations measured for CO (1–0) and CO (2–1) allow us to infer thatR21IMIR0.2, in good agreement with other work. The 8μm and 12μm bands, with strong polycyclic aromatic hydrocarbon (PAH) features, show steeper CO versus mid-IR slopes than the 22 and 24μm, consistent with PAH emission arising not just from CO-bright gas but also from atomic or CO-dark gas. The CO-to-mid-IR ratio correlates with global galaxy stellar mass (M) and anticorrelates with star formation rate/M. At ∼1 kpc resolution, the first four PHANGS–JWST targets show CO-to-mid-IR relationships that are quantitatively similar to our larger literature sample, including showing the steep CO-to-mid-IR slopes for the JWST PAH-tracing bands, although we caution that these initial data have a small sample size and span a limited range of intensities.

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