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The origin of the H αline profiles in simulated disc galaxies

Ejdetjärn, Timmy LU ; Agertz, Oscar LU ; Östlin, Göran ; Rey, Martin P. LU and Renaud, Florent LU (2024) In Monthly Notices of the Royal Astronomical Society 534(1). p.135-150
Abstract

Observations of ionized H αgas in high-redshift disc galaxies have ubiquitously found significant line broadening, σH α∼10 -100 km s-1 . To understand whether this broadening reflects gas turbulence within the interstellar medium (ISM) of galactic discs, or arises from out-of-plane emission in mass-loaded outflows, we perform radiation hydrodynamic simulations of isolated Milky Way-mass disc galaxies in a gas-poor (low-redshift) and gas rich (high-redshift) condition and create mock H αemission line profiles. We find that the majority of the total (integrated) H αemission is confined within the ISM, with extraplanar gas contributing ∼45 per cent of the extended profile wings ( v z ≥200 km s-1 ) in the gas-rich galaxy. This substantiates... (More)

Observations of ionized H αgas in high-redshift disc galaxies have ubiquitously found significant line broadening, σH α∼10 -100 km s-1 . To understand whether this broadening reflects gas turbulence within the interstellar medium (ISM) of galactic discs, or arises from out-of-plane emission in mass-loaded outflows, we perform radiation hydrodynamic simulations of isolated Milky Way-mass disc galaxies in a gas-poor (low-redshift) and gas rich (high-redshift) condition and create mock H αemission line profiles. We find that the majority of the total (integrated) H αemission is confined within the ISM, with extraplanar gas contributing ∼45 per cent of the extended profile wings ( v z ≥200 km s-1 ) in the gas-rich galaxy. This substantiates using the H αemission line as a tracer of mid-plane disc dynamics. We investigate the relative contribution of diffuse and dense H αemitting gas, corresponding to diffuse ionized gas (DIG; ρ ≲ 0 . 1 cm -3 , T ∼8 000 K) and H II regions ( ρ ≳ 10 cm -3 , T ∼10 000 K), respectively, and find that DIG contributes f DIG ≲ 10 per cent of the total L H α. Ho we ver, the DIG can reach upwards of σH α∼60 -80 km s-1 while the H II regions are much less turbulent σH α∼10 -40 km s-1 . This implies that the σH αobserved using the full H αemission line is dependent on the relative H αcontribution from DIG/H II regions and a larger f DIG would shift σH αto higher v alues. Finally, we sho w that σH αevolves, in both the DIG and H II regions, with the galaxy gas fraction. Our high-redshift equi v alent galaxy is roughly twice as turbulent, except for in the DIG which has a more shallow evolution.

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author
; ; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
galaxies: disc, galaxies: star formation, ISM: evolution, ISM: kinematics and dynamics, methods: numerical, turbulence
in
Monthly Notices of the Royal Astronomical Society
volume
534
issue
1
pages
16 pages
publisher
Oxford University Press
external identifiers
  • scopus:85204032233
ISSN
0035-8711
DOI
10.1093/mnras/stae2099
language
English
LU publication?
yes
id
5a7c4924-575e-43f7-b7e7-08f1216e0740
date added to LUP
2024-11-18 11:31:21
date last changed
2025-04-04 14:29:24
@article{5a7c4924-575e-43f7-b7e7-08f1216e0740,
  abstract     = {{<p>Observations of ionized H αgas in high-redshift disc galaxies have ubiquitously found significant line broadening, σH α∼10 -100 km s-1 . To understand whether this broadening reflects gas turbulence within the interstellar medium (ISM) of galactic discs, or arises from out-of-plane emission in mass-loaded outflows, we perform radiation hydrodynamic simulations of isolated Milky Way-mass disc galaxies in a gas-poor (low-redshift) and gas rich (high-redshift) condition and create mock H αemission line profiles. We find that the majority of the total (integrated) H αemission is confined within the ISM, with extraplanar gas contributing ∼45 per cent of the extended profile wings ( v z ≥200 km s-1 ) in the gas-rich galaxy. This substantiates using the H αemission line as a tracer of mid-plane disc dynamics. We investigate the relative contribution of diffuse and dense H αemitting gas, corresponding to diffuse ionized gas (DIG; ρ ≲ 0 . 1 cm -3 , T ∼8 000 K) and H II regions ( ρ ≳ 10 cm -3 , T ∼10 000 K), respectively, and find that DIG contributes f DIG ≲ 10 per cent of the total L H α. Ho we ver, the DIG can reach upwards of σH α∼60 -80 km s-1 while the H II regions are much less turbulent σH α∼10 -40 km s-1 . This implies that the σH αobserved using the full H αemission line is dependent on the relative H αcontribution from DIG/H II regions and a larger f DIG would shift σH αto higher v alues. Finally, we sho w that σH αevolves, in both the DIG and H II regions, with the galaxy gas fraction. Our high-redshift equi v alent galaxy is roughly twice as turbulent, except for in the DIG which has a more shallow evolution.</p>}},
  author       = {{Ejdetjärn, Timmy and Agertz, Oscar and Östlin, Göran and Rey, Martin P. and Renaud, Florent}},
  issn         = {{0035-8711}},
  keywords     = {{galaxies: disc; galaxies: star formation; ISM: evolution; ISM: kinematics and dynamics; methods: numerical; turbulence}},
  language     = {{eng}},
  number       = {{1}},
  pages        = {{135--150}},
  publisher    = {{Oxford University Press}},
  series       = {{Monthly Notices of the Royal Astronomical Society}},
  title        = {{The origin of the H αline profiles in simulated disc galaxies}},
  url          = {{http://dx.doi.org/10.1093/mnras/stae2099}},
  doi          = {{10.1093/mnras/stae2099}},
  volume       = {{534}},
  year         = {{2024}},
}