Mathematics – Logic
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21914804b&link_type=abstract
American Astronomical Society, AAS Meeting #219, #148.04
Mathematics
Logic
Scientific paper
We use a subsample of galaxies observed as part of THINGS (The H I Nearby Galaxy Survey) to investigate the H I extent of spiral galaxy disks. We revisit previous work on the extent of H I disks, showing the limitations set by insufficient linear resolution. We then exploit the high spatial and velocity resolution combined with good sensitivity of THINGS to investigate where the atomic gas disks in galaxies end and what might shape their outskirts. We find that the atomic gas surface density across most of the disk is constant at 5-10 x1020 cm-2 and declines at large radius. The general shape of the H I distribution can be described by a Sérsic-type function with a slope index, n = 0.18 - 0.36 and characteristic radius ri. We introduce a column density threshold of 5 x 1019 cm-2 to define the extent of the gas disk. This limit is well within reach of modern instruments and is at the level where disk gas has reached on average 85% of its maximum extent. The H I column density at which the radial profiles turn over is found to be at too high a level for it to be caused by ionization by a meta-galactic UV field and we postulate that the H I extent is set by how galaxy disks form. This is corroborated by recent simulations of the evolution of the gas content and distribution in cosmological simulations that take into account the effect of supernovae and atomic radiative cooling. The resulting simulated radial profiles are remarkably similar to those observed, i.e., confirming that their overall shape is determined by galaxy evolution, ionization by the meta-galactic radiation only playing a role at column densities below a few x 1019 cm-2.
Brinks Elias
de Blok J. G. W.
Kennicutt Robert C.
Portas António
Sommer-Larsen Jesper
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