Dust Extinction Law in Nearby Star-resolved Galaxies. II. M33 Traced by Supergiants

Abstract The dust extinction curves toward individual sight lines in M33 are derived for the first time with a sample of reddened O-type and B-type supergiants obtained from Local Group Galaxies Survey (LGGS). observed photometric data LGGS, PS1 Survey, UKIRT, PHATTER Galaxy Evolution Explorer, Swift/UVOT, XMM-SUSS. We combine intrinsic spectral energy distributions (SEDs) ATLAS9 Tlusty stellar model atmosphere extinguished by silicate-graphite to construct SEDs. traces distributed along arms M33, cover wide range shapes ( R V ≈ 2–6), indicating complexity interstellar environment inhomogeneous distribution M33. average curve 3.39 size dn / mathvariant="italic">da ∼ a − 3.45 exp stretchy="false">( 0.25 stretchy="false">) is similar that Milky Way but weaker 2175 Å bump slightly steeper rise far-UV band. band up 2 mag, median value A 0.43 mag. multiband values UV IR bands also predicted which will provide corrections future works. method adopted this work applied other star-resolved galaxies (NGC 6822 WLM), only few can be because limited observations.