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Smooth HI Low Column Density Outskirts In Nearby Galaxies

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contributor authorIanjamasimanana, Roger
contributor authorWalter, Fabian
contributor authorBlok, W. J. G. de
contributor authorHeald, George H.
contributor authorBrinks, Elias
date accessioned2018-07-05T16:03:43Z
date available2018-07-05T16:03:43Z
date issued2018-05-14
identifier citationIanjamasimanana , R , Walter , F , Blok , W J G D , Heald , G H & Brinks , E 2018 , ' Smooth HI Low Column Density Outskirts In Nearby Galaxies ' The Astronomical Journal , vol 155 , no. 6 , 233 . DOI: 10.3847/1538-3881/aabbaaen
identifier issn0004-6256
identifier otherPURE: 13638827
identifier otherPURE UUID: 02e0c4bb-82af-4cf7-8504-e58467244651
identifier otherArXiv:
identifier uri
descriptionThis is an author-created, un-copyedited version of an article published in The Astronomical Journal. The Version of Record is available online at
description abstractThe low column density gas at the outskirts of galaxies as traced by the 21 cm hydrogen line emission (HI) represents the interface between galaxies and the intergalactic medium, i.e., where galaxies are believed to get their supply of gas to fuel future episodes of star formation. Photoionization models predict a break in the radial profiles of HI at a column density of 5x10E+19 cm^-2 due to the lack of self-shielding against extragalactic ionizing photons. To investigate the prevalence of such breaks in galactic disks and to characterize what determines the potential "edge" of the HI disks, we study the azimuthally-averaged HI column density profiles of 17 nearby galaxies from The HI Nearby Galaxy Survey (THINGS) and supplemented in two cases with published Hydrogen Accretion in LOcal GAlaxieS (HALOGAS) data. To detect potential faint HI emission that would otherwise be undetected using conventional moment map analysis, we line up individual profiles to the same reference velocity and average them azimuthally to derive stacked radial profiles. To do so, we use model velocity fields created from a simple extrapolation of the rotation curves to align the profiles in velocity at radii beyond the extent probed with the sensitivity of traditional integrated HI maps. With this method, we improve our sensitivity to outer-disk HI emission by up to an order of magnitude. Except for a few disturbed galaxies, none show evidence for a sudden change in the slope of the HI radial profiles, the alleged signature of ionization by the extragalactic background.en
format extent22en
language isoeng
relation ispartofThe Astronomical Journalen
subjectgalaxies: evolutionen
subjectgalaxies: halosen
subjectgalaxies: ISMen
subjectradio lines: ISMen
titleSmooth HI Low Column Density Outskirts In Nearby Galaxiesen
contributor institutionSchool of Physics, Astronomy and Mathematicsen
contributor institutionCentre for Astrophysics Researchen
identifier doi
description versionauthorsversionen
description statusPeer revieweden

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