The H$α$ sky in three dimensions
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arXiv
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| Main Authors: | , , , , , , |
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| Format: | Preprint |
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2025
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| _version_ | 1866917960078065664 |
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| author | McCallum, Lewis Wood, Kenneth Benjamin, Robert Krishnarao, Dhanesh Zucker, Catherine Edenhofer, Gordian Haffner, L. Matthew |
| author_facet | McCallum, Lewis Wood, Kenneth Benjamin, Robert Krishnarao, Dhanesh Zucker, Catherine Edenhofer, Gordian Haffner, L. Matthew |
| contents | We combine parallax distances to nearby O stars with parsec-scale resolution three-dimensional dust maps of the local region of the Milky Way (within 1.25 kpc of the Sun) to simulate the transfer of Lyman continuum photons through the interstellar medium. Assuming a fixed gas-to-dust ratio, we determine the density of ionized gas, electron temperature, and H$α$ emissivity throughout the local Milky Way. There is good morphological agreement between the predicted and observed H$α$ all-sky map of the Wisconsin H$α$ Mapper. We find that our simulation underproduces the observed H$α$ emission while overestimating the sizes of HII regions, and we discuss ways in which agreement between simulations and observations may be improved. Of the total ionizing luminosity of $5.84 \times 10^{50}~{\rm photons~s^{-1}}$, 15% is absorbed by dust, 64% ionizes "classical'' HII regions, 11% ionizes the diffuse warm ionized medium, and 10% escapes the simulation volume. We find that 18% of the high altitude ($|b| > 30^{\circ}$) H$α$ arises from dust-scattered rather than direct emission. These initial results provide an impressive validation of the three-dimensional dust maps and O-star parallaxes, opening a new frontier for studying the ionized ISM's structure and energetics in three dimensions. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2503_14348 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | The H$α$ sky in three dimensions McCallum, Lewis Wood, Kenneth Benjamin, Robert Krishnarao, Dhanesh Zucker, Catherine Edenhofer, Gordian Haffner, L. Matthew Astrophysics of Galaxies We combine parallax distances to nearby O stars with parsec-scale resolution three-dimensional dust maps of the local region of the Milky Way (within 1.25 kpc of the Sun) to simulate the transfer of Lyman continuum photons through the interstellar medium. Assuming a fixed gas-to-dust ratio, we determine the density of ionized gas, electron temperature, and H$α$ emissivity throughout the local Milky Way. There is good morphological agreement between the predicted and observed H$α$ all-sky map of the Wisconsin H$α$ Mapper. We find that our simulation underproduces the observed H$α$ emission while overestimating the sizes of HII regions, and we discuss ways in which agreement between simulations and observations may be improved. Of the total ionizing luminosity of $5.84 \times 10^{50}~{\rm photons~s^{-1}}$, 15% is absorbed by dust, 64% ionizes "classical'' HII regions, 11% ionizes the diffuse warm ionized medium, and 10% escapes the simulation volume. We find that 18% of the high altitude ($|b| > 30^{\circ}$) H$α$ arises from dust-scattered rather than direct emission. These initial results provide an impressive validation of the three-dimensional dust maps and O-star parallaxes, opening a new frontier for studying the ionized ISM's structure and energetics in three dimensions. |
| title | The H$α$ sky in three dimensions |
| topic | Astrophysics of Galaxies |
| url | https://arxiv.org/abs/2503.14348 |