An Investigation of Disk Thickness in M51 from H-alpha, Pa-alpha, and Mid-Infrared Power Spectra

Bruce G. Elmegreen; Daniela Calzetti; Angela Adamo; Karin Sandstrom; Daniel Dale; Varun Bajaj; Martha L. Boyer; Ana Duarte-Cabral; Ryan Chown; Matteo Correnti; Julianne J. Dalcanton; Bruce T. Draine; Brandt Gaches; John S. Gallagher III; Kathryn Grasha; Benjamin Gregg; Leslie K. Hunt; Kelsey E. Johnson; Robert Kennicutt, Jr.; Ralf S. Klessen; Adam K. Leroy; Sean Linden; Anna F. McLeod; Matteo Messa; Goran Ostlin; Mansi Padave; Julia Roman-Duval; J. D. Smith; Fabian Walter; Tony D. Weinbeck

arXiv · 2504.05430

An Investigation of Disk Thickness in M51 from H-alpha, Pa-alpha, and Mid-Infrared Power Spectra

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Abstract

Power spectra (PS) of high-resolution images of M51 (NGC 5194) taken with the Hubble Space Telescope and the James Webb Space Telescope have been examined for evidence of disk thickness in the form of a change in slope between large scales, which map two-dimensional correlated structures, and small scales, which map three-dimensional correlated structures. Such a slope change is observed here in H-alpha, and possibly Pa-alpha, using average PS of azimuthal intensity scans that avoid bright peaks. The physical scale of the slope change occurs at ~120 pc and ~170 pc for these two transitions, respectively. A radial dependence in the shape of the H-alpha PS also suggests that the length scale drops from ~180 pc at 5 kpc, to ~90 pc at 2 kpc, to ~25 pc in the central ~kpc. We interpret these lengths as comparable to the thicknesses of the star-forming disk traced by HII regions. The corresponding emission measure is ~100 times larger than what is expected from the diffuse ionized gas. PS of JWST Mid-IR Instrument (MIRI) images in 8 passbands have more gradual changes in slope, making it difficult to determine a specific value of the thickness for this emission.

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Bruce G. Elmegreen, Daniela Calzetti, Angela Adamo, Karin Sandstrom, Daniel Dale, Varun Bajaj, Martha L. Boyer, Ana Duarte-Cabral, Ryan Chown, Matteo Correnti, Julianne J. Dalcanton, Bruce T. Draine, Brandt Gaches, John S. Gallagher III, Kathryn Grasha, Benjamin Gregg, Leslie K. Hunt, Kelsey E. Johnson, Robert Kennicutt, Jr., Ralf S. Klessen, Adam K. Leroy, Sean Linden, Anna F. McLeod, Matteo Messa, Goran Ostlin, Mansi Padave, Julia Roman-Duval, J. D. Smith, Fabian Walter, Tony D. Weinbeck. 2025-04-09. An Investigation of Disk Thickness in M51 from H-alpha, Pa-alpha, and Mid-Infrared Power Spectra. https://arxiv.org/abs/2504.05430

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