A Wide-field High Resolution HI Mosaic of Messier 31: I. Opaque Atomic Gas and Star Formation Rate Density

摘要: We have undertaken a deep, wide-field HI imaging survey of M31, reaching maximum resolution about 50 pc and 2 km/s across 95x48 kpc region. The mass brightness sensitivity at 100 for 25 wide spectral feature is 1500 M_Sun 0.28 K. Our study reveals ubiquitous self-opacity features, discernible in the first instance as filamentary local minima images peak temperature. Local are organized into complexes more than length particularly associated with leading edge spiral arm features. Just Galaxy, there only patchy correspondence self-opaque features CO(1-0) emission. Localized opacity corrections to column density exceed an order magnitude many cases add globally 30% increase atomic gas over that inferred from integrated under usual assumption negligible self-opacity. Opaque increases 20 60 K spin temperature radius 12 but then declines again beyond kpc. extended resolved star formation law down physical scales smaller area has been possible previously. relation between total-gas-mass- star-formation-rate-density significantly tighter molecular-mass fully consistent both slope normalization power index 1.56 found molecule-dominated disk M51 500 resolution. Below gas-mass-density 5 M_Sun/pc^2, down-turn which may represent real threshold massive cloud 5x10^4 M_Sun.