SPATIALLY RESOLVED STELLAR, DUST, AND GAS PROPERTIES OF THE POST-INTERACTING WHIRLPOOL GALAXY SYSTEM
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abstract
Using infrared imaging from the Herschel Space Observatory, observed as part
of the VNGS, we investigate the spatially resolved dust properties of the
interacting Whirlpool galaxy system (NGC 5194 and NGC 5195), on physical scales
of 1 kpc. Spectral energy distribution modelling of the new infrared images in
combination with archival optical, near- through mid-infrared images confirms
that both galaxies underwent a burst of star formation ~370-480 Myr ago and
provides spatially resolved maps of the stellar and dust mass surface
densities. The resulting average dust-to-stellar mass ratios are comparable to
other spiral and spheroidal galaxies studied with Herschel, with NGC 5194 at
log M(dust)/M(star)= -2.5+/-0.2 and NGC 5195 at log M(dust)/M(star)=
-3.5+/-0.3. The dust-to-stellar mass ratio is constant across NGC 5194
suggesting the stellar and dust components are coupled. In contrast, the mass
ratio increases with radius in NGC 5195 with decreasing stellar mass density.
Archival mass surface density maps of the neutral and molecular hydrogen gas
are also folded into our analysis. The gas-to-dust mass ratio, 94+/-17, is
relatively constant across NGC 5194. Somewhat surprisingly, we find the dust in
NGC 5195 is heated by a strong interstellar radiation field, over 20 times that
of the ISRF in the Milky Way, resulting in relatively high characteristic dust
temperatures (~30 K). This post-starburst galaxy contains a substantial amount
of low-density molecular gas and displays a gas-to-dust ratio (73+/-35) similar
to spiral galaxies. It is unclear why the dust in NGC 5195 is heated to such
high temperatures as there is no star formation in the galaxy and its active
galactic nucleus is 5-10 times less luminous than the one in NGC 5194, which
exhibits only a modest enhancement in the amplitude of its ISRF.
