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Resolving Ionisation and Metallicity on Parsec Scales Across Mrk 71 (NGC2363) with HST-WFC3 | | Bethan L. James
; Matthew Auger
; Alessandra Aloisi
; Daniela Calzetti
; Lisa Kewley
; | | Date: |
8 Oct 2015 | | Abstract: | Blue Compact Dwarf (BCD) Galaxies in the nearby Universe provide a means for
studying feedback mechanisms and star-formation processes in low-metallicity
environments in great detail. Due to their vicinity, these local analogues to
young galaxies are well suited for high-resolution studies that would be
unfeasible for primordial galaxies in the high-redshift universe. Here we
present HST-WFC3 observations of one such BCD, Mrk 71 (NGC 2363), one of the
most powerful local starbursts known, in the light of [O II], He II, Hb, [O
III], Ha, and [S II]. At D=3.44 Mpc, this extensive suite of emission line
images enables us to explore the chemical and physical conditions of Mrk 71 on
~2 pc scales. Using these high spatial-resolution observations, we use emission
line diagnostics to distinguish ionisation mechanisms on a pixel-by-pixel basis
and show that despite the previously reported hypersonic gas and super-bubble
blow out, the gas in Mrk 71 is photoionised, with no sign of shock-excited
emission. Using strong-line metallicity diagnostics, we present the first
’metallicity image’ of a galaxy, revealing chemically inhomogeneity on scales
of <50 pc. We additionally demonstrate that while chemical structure can be
lost at large spatial scales, metallicity-diagnostics can break down on spatial
scales smaller than a HII region. HeII emission line images are used to
identify up to six Wolf-Rayet stars in Mrk 71, three of which lie on the edge
of blow-out region. This study not only demonstrates the benefits of
high-resolution spatially-resolved observations in assessing the effects of
feedback mechanisms, but also the limitations of fine spatial scales when
employing emission-line diagnostics. Both aspects are especially relevant as we
enter the era of extremely large telescopes, when observing structure on ~10 pc
scales will no longer be limited to the local universe. | | Source: | arXiv, 1510.2447 | | Services: | Forum | Review | PDF | Favorites | |
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