Extinction Maps and Dust-to-gas Ratios in Nearby Galaxies with LEGUS
Kahre, L; Walterbos, RA; Kim, H; Thilker, D; Calzetti, D; Lee, JC; Sabbi, E; Ubeda, L; Aloisi, A; Cignoni, M; Cook, DO; Dale, DA; Elmegreen, BG; Elmegreen, DM; Fumagalli, M; Gallagher, JS; Gouliermis, DA; Grasha, K; Grebel, EK; Hunter, DA; Sacchi, E; Smith, LJ; Tosi, M; Adamo, A; Andrews, JE; Ashworth, G; Bright, SN; Brown, TM; Chandar, R; Christian, C; De Mink, SE; Dobbs, C; Evans, AS; Herrero, A; Johnson, KE; Kennicutt, RC; Krumholz, MR; Messa, M; Nair, P; Nota, A; Pellerin, A; Ryon, JE; Schaerer, D; Shabani, F; Van Dyk, SD; Whitmore, BC; Wofford, A
Description:
This is the final version. Available from American Astronomical Society via the DOI in this record
We present a study of the dust-to-gas ratios in five nearby galaxies: NGC 628 (M74), NGC 6503, NGC 7793, UGC 5139 (Holmberg I), and UGC 4305 (Holmberg II). Using Hubble Space Telescope broadband WFC3/UVIS UV and optical images from the Treasury program Legacy ExtraGalactic UV Survey (LEGUS) combined with archival HST/Advanced Camera for Surveys data, we correct thousands of individual stars for extinction across these five galaxies using an isochrone-matching (reddening-free Q) method. We generate extinction maps for each galaxy from the individual stellar extinctions using both adaptive and fixed resolution techniques and correlate these maps with neutral H i and CO gas maps from the literature, including the H i Nearby Galaxy Survey and the HERA CO-Line Extragalactic Survey. We calculate dust-to-gas ratios and investigate variations in the dust-to-gas ratio with galaxy metallicity. We find a power-law relationship between dust-to-gas ratio and metallicity, consistent with other studies of dust-to-gas ratio compared to metallicity. We find a change in the relation when H2is not included. This implies that underestimation of in low-metallicity dwarfs from a too-low CO-to-H2conversion factor XCOcould have produced too low a slope in the derived relationship between dust-to-gas ratio and metallicity. We also compare our extinctions to those derived from fitting the spectral energy distribution (SED) using the Bayesian Extinction and Stellar Tool for NGC 7793 and find systematically lower extinctions from SED fitting as compared to isochrone matching.
This work is based on observations made with the NASA/
ESA Hubble Space Telescope, obtained at the Space Telescope
Science Institute, which is operated by the Association of
Universities for Research in Astronomy under NASA contract
NAS 5-26555. These observations are associated with program
13364 (LEGUS). Support for program 13364 was provided by
NASA through a grant from the Space Telescope Science
Institute. LK and RAW acknowledge support from the Space
Telescope Science institute (grant Numbers HST-GO13773.003-A).
LK would additionally like to acknowledge
support from the Gemini Observatory in La Serena, Chile. MF
acknowledges support from the Science and Technology
Facilities Council (grant Number ST/P000541/1). DAG
kindly acknowledges financial support by the German
Research Foundation (DFG) through program GO 1659/3-2.
GA acknowledges support from the Science and Technology
Facilities Council (ST/P000541/1 and ST/M503472/1).
Show full item record