Time-dependent metal ionization and persistence of collisionally excited emission lines in the diffuse ionized gas of star forming galaxies

Lewis McCallum; Kenny Wood; Robert Benjamin; Dhanesh Krishnarao; Bert Vandenbroucke

doi:10.1093/mnras/stae2549

Time-dependent metal ionization and persistence of collisionally excited emission lines in the diffuse ionized gas of star forming galaxies

Lewis McCallum^*
, Kenny Wood
, Robert Benjamin
, Dhanesh Krishnarao
, Bert Vandenbroucke

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

Abstract

We extend our time-dependent hydrogen ionization simulations of diffuse ionized gas to include metals important for collisional cooling and diagnostic emission lines. The combination of heating from supernovae and time-dependent collisional and photoionization from mid-plane OB stars produces emission line intensities (and emission line ratios) that follow the trends observed in the Milky Way and other edge-on galaxies. The long recombination times in low-density gas result in persistent large volumes of ions with high ionization potentials, such as O iii and Ne iii. In particular, the vertically extended layers of Ne iii in our time-dependent simulations result in [Ne iii] 15 μm/[Ne ii] 12 μm emission line ratios in agreement with observations of the edge-on galaxy NGC 891. Simulations adopting ionization equilibrium do not allow for the persistence of ions with high ionization states and therefore cannot reproduce the observed emission lines from low-density gas at high altitudes.

Original language	English
Pages (from-to)	2889-2902
Number of pages	14
Journal	Monthly Notices of the Royal Astronomical Society
Volume	535
Issue number	3
Early online date	23 Nov 2024
DOIs	https://doi.org/10.1093/mnras/stae2549
Publication status	Published - 1 Dec 2024

Keywords

Methods: numerical
H11 regions
ISM: kinematics and dynamics
ISM: structure
Galaxies: star formation

Access to Document

10.1093/mnras/stae2549Licence: CC BY

McCallum_2024_MNRAS_Time-dependent-metal-ionization-persistence-collisionally_CC
Copyright © 2024 The Author(s). This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.
Final published version, 3.6 MBLicence: CC BY

Handle.net

Persistent link to portal record

Time-dependent metal ionization and persistence of collisionally excited emission lines in the diffuse ionized gas of star forming galaxies (code)
McCallum, L. (Creator) & Wood, K. (Creator), GitHub, 2024
https://github.com/LewisSMcCallum/CMacIonize/tree/sne2
Dataset: Software

Numerical insights into the origin and nature of the ionized interstellar medium
McCallum, L. (Author), Wood, K. (Supervisor), 30 Jun 2025
Student thesis: Doctoral Thesis (PhD)

Cite this

@article{3a19540581224e338f5893f6e4d7d0b6,

title = "Time-dependent metal ionization and persistence of collisionally excited emission lines in the diffuse ionized gas of star forming galaxies",

abstract = "We extend our time-dependent hydrogen ionization simulations of diffuse ionized gas to include metals important for collisional cooling and diagnostic emission lines. The combination of heating from supernovae and time-dependent collisional and photoionization from mid-plane OB stars produces emission line intensities (and emission line ratios) that follow the trends observed in the Milky Way and other edge-on galaxies. The long recombination times in low-density gas result in persistent large volumes of ions with high ionization potentials, such as O iii and Ne iii. In particular, the vertically extended layers of Ne iii in our time-dependent simulations result in [Ne iii] 15 μm/[Ne ii] 12 μm emission line ratios in agreement with observations of the edge-on galaxy NGC 891. Simulations adopting ionization equilibrium do not allow for the persistence of ions with high ionization states and therefore cannot reproduce the observed emission lines from low-density gas at high altitudes.",

keywords = "Methods: numerical, H11 regions, ISM: kinematics and dynamics, ISM: structure, Galaxies: star formation",

author = "Lewis McCallum and Kenny Wood and Robert Benjamin and Dhanesh Krishnarao and Bert Vandenbroucke",

note = "Funding: LM acknowledges financial support from a UK-STFC PhD studentship. DK acknowledges support from an HST Archival Theory Program 17060, provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.",

year = "2024",

month = dec,

day = "1",

doi = "10.1093/mnras/stae2549",

language = "English",

volume = "535",

pages = "2889--2902",

journal = "Monthly Notices of the Royal Astronomical Society",

issn = "0035-8711",

publisher = "Oxford University Press",

number = "3",

}

TY - JOUR

T1 - Time-dependent metal ionization and persistence of collisionally excited emission lines in the diffuse ionized gas of star forming galaxies

AU - McCallum, Lewis

AU - Wood, Kenny

AU - Benjamin, Robert

AU - Krishnarao, Dhanesh

AU - Vandenbroucke, Bert

N1 - Funding: LM acknowledges financial support from a UK-STFC PhD studentship. DK acknowledges support from an HST Archival Theory Program 17060, provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.

PY - 2024/12/1

Y1 - 2024/12/1

N2 - We extend our time-dependent hydrogen ionization simulations of diffuse ionized gas to include metals important for collisional cooling and diagnostic emission lines. The combination of heating from supernovae and time-dependent collisional and photoionization from mid-plane OB stars produces emission line intensities (and emission line ratios) that follow the trends observed in the Milky Way and other edge-on galaxies. The long recombination times in low-density gas result in persistent large volumes of ions with high ionization potentials, such as O iii and Ne iii. In particular, the vertically extended layers of Ne iii in our time-dependent simulations result in [Ne iii] 15 μm/[Ne ii] 12 μm emission line ratios in agreement with observations of the edge-on galaxy NGC 891. Simulations adopting ionization equilibrium do not allow for the persistence of ions with high ionization states and therefore cannot reproduce the observed emission lines from low-density gas at high altitudes.

AB - We extend our time-dependent hydrogen ionization simulations of diffuse ionized gas to include metals important for collisional cooling and diagnostic emission lines. The combination of heating from supernovae and time-dependent collisional and photoionization from mid-plane OB stars produces emission line intensities (and emission line ratios) that follow the trends observed in the Milky Way and other edge-on galaxies. The long recombination times in low-density gas result in persistent large volumes of ions with high ionization potentials, such as O iii and Ne iii. In particular, the vertically extended layers of Ne iii in our time-dependent simulations result in [Ne iii] 15 μm/[Ne ii] 12 μm emission line ratios in agreement with observations of the edge-on galaxy NGC 891. Simulations adopting ionization equilibrium do not allow for the persistence of ions with high ionization states and therefore cannot reproduce the observed emission lines from low-density gas at high altitudes.

KW - Methods: numerical

KW - H11 regions

KW - ISM: kinematics and dynamics

KW - ISM: structure

KW - Galaxies: star formation

U2 - 10.1093/mnras/stae2549

DO - 10.1093/mnras/stae2549

M3 - Article

SN - 0035-8711

VL - 535

SP - 2889

EP - 2902

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

IS - 3

ER -

Time-dependent metal ionization and persistence of collisionally excited emission lines in the diffuse ionized gas of star forming galaxies

Abstract

Keywords

Access to Document

Handle.net

Fingerprint

Datasets

Time-dependent metal ionization and persistence of collisionally excited emission lines in the diffuse ionized gas of star forming galaxies (code)

Student theses

Numerical insights into the origin and nature of the ionized interstellar medium

Cite this