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The structure and characteristic scales of the H I gas in galactic disks

Dib, Sami and Braine, Jonathan and Gopinathan, Maheswar and Lara-López, Maritza A. and Kravtsov, Valery V. and Soam, Archana and Sharma, Ekta and Zhukovska, Svitlana and Aouad, Charles and Belinchón, José Antonio and Helou, George and Li, Di (2021) The structure and characteristic scales of the H I gas in galactic disks. Astronomy and Astrophysics, 655 . Art. No. A101. ISSN 0004-6361. doi:10.1051/0004-6361/202141803.

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The spatial distribution of the H I gas in galactic disks holds important clues about the physical processes that shape the structure and dynamics of the interstellar medium (ISM). The structure of the ISM could be affected by a variety of perturbations internal and external to the galaxy, and the unique signature of each of these perturbations could be visible in the structure of interstellar gas. In this work, we quantify the structure of the H I gas in a sample of 33 nearby galaxies taken from the HI Nearby Galaxy Survey (THINGS) using the delta-variance (Δ-variance) spectrum. The THINGS galaxies display a large diversity in their spectra, but there are a number of recurrent features. In many galaxies, we observe a bump in the spectrum on scales of a few to several hundred parsec. We find the characteristic scales associated with the bump to be correlated with the galactic star formation rate (SFR) for values of the SFR ≳0.5 M_⊙ yr⁻¹ and also with the median size of the H I shells detected in these galaxies. We interpret this characteristic scale as being associated with the effects of feedback from supernova explosions. On larger scales, we observe in most galaxies two self-similar, scale-free regimes. The first regime, on intermediate scales (≲0.5R₂₅), is shallow, and the power law that describes this regime has an exponent in the range [0.1–1] with a mean value of 0.55 that is compatible with the density field that is generated by supersonic turbulence in the cold phase of the H I gas. The second power law is steeper, with a range of exponents between 0.5 and 2.3 and a mean value of ≈1.5. These values are associated with subsonic to transonic turbulence, which is characteristic of the warm phase of the H I gas. The spatial scale at which the transition between the two self-similar regimes occurs is found to be ≈0.5R25, which is very similar to the size of the molecular disk in the THINGS galaxies. Overall, our results suggest that on scales ≲0.5R₂₅, the structure of the ISM is affected by the effects of supernova explosions. On larger scales (≳0.5R₂₅), stellar feedback has no significant impact, and the structure of the ISM is determined by large-scale processes that govern the dynamics of the gas in the warm neutral medium, such as the flaring of the H I disk at large galactocentric radii and the effects of ram pressure stripping.

Item Type:Article
Related URLs:
URLURL TypeDescription
Dib, Sami0000-0002-8697-9808
Braine, Jonathan0000-0003-1740-1284
Gopinathan, Maheswar0000-0002-1369-0608
Lara-López, Maritza A.0000-0001-7327-3489
Kravtsov, Valery V.0000-0002-9799-5889
Soam, Archana0000-0002-6386-2906
Zhukovska, Svitlana0000-0003-2569-3627
Aouad, Charles0000-0001-6063-0344
Helou, George0000-0003-3367-3415
Additional Information:© S. Dib et al. 2021. Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Open Access funding provided by Max Planck Society. Received: 15 July 2021 Accepted: 30 September 2021. This work is dedicated to the city of Beirut and to its inhabitants for their resilience in the face of adversity. We thank the referee for a careful reading of the paper and for constructive comments. S.D. would like to thank Volker Ossenkopf-Okada for useful discussions on the calculation of the Δ-variance spectrum and Andreas Schruba and Robert Kennicutt for useful discussions on the star formation rates in nearby galaxies. We also thank Bruce Elmegreen for commenting on an earlier version of this paper and Elias Brinks and Fabian Walter for clarifications on the THINGS data. We thank Oscar Agertz and Florent Renaud for making data from their simulation available. J.A.B. was supported by Comision Nacional de Ciencias Y Tecnologia through Fondecyt Grant No. 11170083.
Group:Infrared Processing and Analysis Center (IPAC)
Funding AgencyGrant Number
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)11170083
Subject Keywords:ISM: structure / ISM: general / galaxies: structure / galaxies: ISM / radio lines: ISM / turbulence
Record Number:CaltechAUTHORS:20211208-951186000
Persistent URL:
Official Citation:The structure and characteristic scales of the H I gas in galactic disks Sami Dib, Jonathan Braine, Maheswar Gopinathan, Maritza A. Lara-López, Valery V. Kravtsov, Archana Soam, Ekta Sharma, Svitlana Zhukovska, Charles Aouad, José Antonio Belinchón, George Helou and Di Li A&A, 655 (2021) A101 DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:112310
Deposited By: George Porter
Deposited On:10 Dec 2021 19:24
Last Modified:10 Dec 2021 19:24

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