First Measurement of Extreme Ultraviolet Dust Extinction Curve in Quasars

Abstract

Dust is a ubiquitous feature of the cosmos, impinging directly or indirectly on most fields of modern astronomy. Dust grains composed of small (submicron-sized) solid particles pervade interstellar space in the Milky Way and other galaxies: they occur in a wide variety of astrophysical environments, ranging from comets to giant molecular clouds, from circum-stellar shells to galactic nuclei. The study of this phenomenon is a highly active and topical area of current research. Dust absorbs optical and Ultraviolet (UV) photons and re-emit them in the infrared. The heating and cooling of dust interact with their environment closely. Dust is closely related to the star formation process, and study on dust could put constraints on the star formation history. While extensively studied in the optical, the extinction property of dust in the UV is still an open question. UV photos are absorbed by earth atmosphere and cannot be accessed from ground-based observations. NASA space mission Galaxy Evolution Explorer (GALEX), on the other hand, provides critical data to this question by surveying the whole sky in two UV bands. By comparing the optical and UV properties of blue and red (dust-absorbed) quasars selected from Sloan Digital Sky Survey (SDSS), we shape the extreme UV dust extinction curve for the first time. The measured UV dust extinction curve will help us characterize the size distribution of dust grains and their compositions which could not be easily accessed by other methods.