SPATIALLY RESOLVED STELLAR, DUST, AND GAS PROPERTIES OF THE POST-INTERACTING WHIRLPOOL GALAXY SYSTEM

Abstract

Using infrared imaging from the Herschel Space Observatory, observed as part\nof the VNGS, we investigate the spatially resolved dust properties of the\ninteracting Whirlpool galaxy system (NGC 5194 and NGC 5195), on physical scales\nof 1 kpc. Spectral energy distribution modelling of the new infrared images in\ncombination with archival optical, near- through mid-infrared images confirms\nthat both galaxies underwent a burst of star formation ~370-480 Myr ago and\nprovides spatially resolved maps of the stellar and dust mass surface\ndensities. The resulting average dust-to-stellar mass ratios are comparable to\nother spiral and spheroidal galaxies studied with Herschel, with NGC 5194 at\nlog M(dust)/M(star)= -2.5+/-0.2 and NGC 5195 at log M(dust)/M(star)=\n-3.5+/-0.3. The dust-to-stellar mass ratio is constant across NGC 5194\nsuggesting the stellar and dust components are coupled. In contrast, the mass\nratio increases with radius in NGC 5195 with decreasing stellar mass density.\nArchival mass surface density maps of the neutral and molecular hydrogen gas\nare also folded into our analysis. The gas-to-dust mass ratio, 94+/-17, is\nrelatively constant across NGC 5194. Somewhat surprisingly, we find the dust in\nNGC 5195 is heated by a strong interstellar radiation field, over 20 times that\nof the ISRF in the Milky Way, resulting in relatively high characteristic dust\ntemperatures (~30 K). This post-starburst galaxy contains a substantial amount\nof low-density molecular gas and displays a gas-to-dust ratio (73+/-35) similar\nto spiral galaxies. It is unclear why the dust in NGC 5195 is heated to such\nhigh temperatures as there is no star formation in the galaxy and its active\ngalactic nucleus is 5-10 times less luminous than the one in NGC 5194, which\nexhibits only a modest enhancement in the amplitude of its ISRF.\n