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Smooth HI Low Column Density Outskirts In Nearby Galaxies

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Smooth HI Low Column Density Outskirts In Nearby Galaxies. / Ianjamasimanana, Roger; Walter, Fabian; Blok, W. J. G. de; Heald, George H.; Brinks, Elias.

In: The Astronomical Journal , Vol. 155, No. 6, 233, 14.05.2018.

Research output: Contribution to journalArticlepeer-review

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APA

Ianjamasimanana, 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 , 155(6), [233]. https://doi.org/10.3847/1538-3881/aabbaa

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Author

Ianjamasimanana, Roger ; Walter, Fabian ; Blok, W. J. G. de ; Heald, George H. ; Brinks, Elias. / Smooth HI Low Column Density Outskirts In Nearby Galaxies. In: The Astronomical Journal . 2018 ; Vol. 155, No. 6.

Bibtex

@article{02e0c4bb82af4cf78504e58467244651,
title = "Smooth HI Low Column Density Outskirts In Nearby Galaxies",
abstract = "The low column density gas at the outskirts of galaxies as traced by the 21 cm hydrogen line emission (H i) 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 H i at a column density of ∼5 × 10 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 H i disks, we study the azimuthally averaged H i column density profiles of 17 nearby galaxies from the H i Nearby Galaxy Survey and supplemented in two cases with published Hydrogen Accretion in LOcal GAlaxieS data. To detect potential faint H i 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 H i maps. With this method, we improve our sensitivity to outer-disk H i emission by up to an order of magnitude. Except for a few disturbed galaxies, none show evidence of a sudden change in the slope of the H i radial profiles: the alleged signature of ionization by the extragalactic background. ",
keywords = "galaxies: evolution, galaxies: halos, galaxies: ISM, radio lines: ISM",
author = "Roger Ianjamasimanana and Fabian Walter and Blok, {W. J. G. de} and Heald, {George H.} and Elias Brinks",
note = "This is an author-created, un-copyedited version of an article published in The Astronomical Journal. The Version of Record is available online at https://doi.org/10.3847/1538-3881/aabbaa.",
year = "2018",
month = may,
day = "14",
doi = "10.3847/1538-3881/aabbaa",
language = "English",
volume = "155",
journal = "The Astronomical Journal ",
issn = "0004-6256",
publisher = "IOP Publishing Ltd.",
number = "6",

}

RIS

TY - JOUR

T1 - Smooth HI Low Column Density Outskirts In Nearby Galaxies

AU - Ianjamasimanana, Roger

AU - Walter, Fabian

AU - Blok, W. J. G. de

AU - Heald, George H.

AU - Brinks, Elias

N1 - This is an author-created, un-copyedited version of an article published in The Astronomical Journal. The Version of Record is available online at https://doi.org/10.3847/1538-3881/aabbaa.

PY - 2018/5/14

Y1 - 2018/5/14

N2 - The low column density gas at the outskirts of galaxies as traced by the 21 cm hydrogen line emission (H i) 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 H i at a column density of ∼5 × 10 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 H i disks, we study the azimuthally averaged H i column density profiles of 17 nearby galaxies from the H i Nearby Galaxy Survey and supplemented in two cases with published Hydrogen Accretion in LOcal GAlaxieS data. To detect potential faint H i 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 H i maps. With this method, we improve our sensitivity to outer-disk H i emission by up to an order of magnitude. Except for a few disturbed galaxies, none show evidence of a sudden change in the slope of the H i radial profiles: the alleged signature of ionization by the extragalactic background.

AB - The low column density gas at the outskirts of galaxies as traced by the 21 cm hydrogen line emission (H i) 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 H i at a column density of ∼5 × 10 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 H i disks, we study the azimuthally averaged H i column density profiles of 17 nearby galaxies from the H i Nearby Galaxy Survey and supplemented in two cases with published Hydrogen Accretion in LOcal GAlaxieS data. To detect potential faint H i 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 H i maps. With this method, we improve our sensitivity to outer-disk H i emission by up to an order of magnitude. Except for a few disturbed galaxies, none show evidence of a sudden change in the slope of the H i radial profiles: the alleged signature of ionization by the extragalactic background.

KW - galaxies: evolution

KW - galaxies: halos

KW - galaxies: ISM

KW - radio lines: ISM

UR - http://www.scopus.com/inward/record.url?scp=85048408235&partnerID=8YFLogxK

U2 - 10.3847/1538-3881/aabbaa

DO - 10.3847/1538-3881/aabbaa

M3 - Article

VL - 155

JO - The Astronomical Journal

JF - The Astronomical Journal

SN - 0004-6256

IS - 6

M1 - 233

ER -