Browsing by Author "Jarrett, Thomas H."

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    Calibrating the James Webb Space telescope filters as star formation rate indicators
    (American Astronomical Society, 2018) Senarath, Madhooshi R.; Brown, Michael J. I.; Cluver, Michelle E.; Moustakas, John; Armus, Lee; Jarrett, Thomas H.
    We have calibrated the 6.5m James Webb Space Telescope (JWST) mid-infrared (MIR) filters as star formation rate (SFR) indicators, using JWST photometry synthesized from Spitzer spectra of 49 low-redshift galaxies, which cover a wider luminosity range than most previous studies. We use Balmer-decrement-corrected Hα luminosity and synthesized MIR photometry to empirically calibrate the Spitzer, WISE, and JWST filters as SFR indicators. Our Spitzer and WISE calibrations are in good agreement with recent calibrations from the literature. While MIR luminosity may be directly proportional to SFR for high-luminosity galaxies, we find a power-law relationship between MIR luminosity and SFR for low-luminosity galaxies. We find that for galaxies with an Hα luminosity of 1040 erg s-1 (corresponding to an SFR of~0.055 M yr-1), the corresponding JWST MIR ν Lν luminosity is between 1040.50 and 1041.00 erg s-1. Power-law fits of JWST luminosity as a function of Hα luminosity have indices between 1.17 and 1.32. We find that the scatter in the JWST filter calibrations decreases with increasing wavelength from 0.39 to 0.20 dex, although F1000W is an exception where the scatter is just 0.24 dex.
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    Constraining the stellar populations of ultra-diffuse galaxies in the MATLAS survey using spectral energy distribution fitting
    (Oxford University Press, 2024) Buzzo, Maria Luisa; Jarrett, Thomas H.; Forbes, Duncan A.
    We use spectral energy distribution fitting to place constraints on the stellar populations of 59 ultra-diffuse galaxies (UDGs) in the low-to-moderate density fields of the MATLAS survey. We use the routine PROSPECTOR, coupled with archival data in the optical from the Dark Energy Camera Legacy Survey, and near- and mid-infrared imaging from the Wide-field Infrared Survey Explorer, to recover the stellar masses, ages, metallicities, and star formation time-scales of the UDGs. We find that a subsample of the UDGs lies within the scatter of the mass–metallicity relation (MZR) for local classical dwarfs. However, another subsample is more metal-poor, being consistent with the evolving MZR at high redshift. We investigate UDG positioning trends in the mass–metallicity plane as a function of surface brightness, effective radius, axis ratio, local volume density, mass-weighted age, star formation time-scale, globular cluster (GC) counts, and GC specific frequency. We find that our sample of UDGs can be separated into two main classes: Class A: comprised of UDGs with lower stellar masses, prolonged star formation histories (SFHs), more elongated, inhabiting less dense environments, hosting fewer GCs, younger, consistent with the classical dwarf MZR, and fainter. Class B: UDGs with higher stellar masses, rapid SFHs, rounder, inhabiting the densest of our probed environments, hosting on average the most numerous GC systems, older, consistent with the high-redshift MZR (i.e. consistent with early-quenching), and brighter.