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arxiv: 2606.04309 · v1 · pith:HVOBA4RZnew · submitted 2026-06-03 · 🌌 astro-ph.GA

CO-dark molecular gas traced by HCO^+ in the diffuse interstellar medium

Daniel R. Rybarczyk , Michael P. Busch , J. R. Dawson , Min-Young Lee , Gan Luo This is my paper

Pith reviewed 2026-06-28 05:57 UTC · model grok-4.3

classification 🌌 astro-ph.GA
keywords diffuse interstellar mediumCO-dark molecular gasHCO+ absorptionHI absorptionmolecular hydrogenatomic to molecular transitioninterstellar chemistry
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The pith

Broad HCO+ absorption traces CO-dark H2 with lower cold HI fraction and molecular fraction than CO-traced gas in the same directions.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper uses absorption observations of HCO+, CO, and HI toward five directions to examine molecular gas that lacks detectable CO. It finds that the gas producing broad HCO+ absorption lines has a cold neutral medium fraction of roughly 0.38 and a molecular hydrogen fraction of roughly 0.09, both lower than values measured in gas that shows CO. The work places an upper limit of 10^{-5} on the CO abundance relative to H2 in this component, explaining the absence of CO lines, and demonstrates that HCO+ absorption appears at lower H2 column densities than CO does. These measurements supply direct constraints on how atomic hydrogen converts into molecular form in low-density regions.

Core claim

The diffuse molecular gas revealed by broad HCO+ absorption has a lower fraction of cold HI (f_CNM = 0.38^{+0.28}_{-0.27}) and a lower fraction of hydrogen in H2 (f_mol=0.09^{+0.06}_{-0.03}) than gas traced by CO in the same directions. We detect almost no CO absorption from the gas traced by broad HCO+ absorption. We constrain the CO abundance relative to H2 to be ≲10^{-6}-10^{-5} for gas traced by both broad and narrow HCO+ absorption, consistent with chemical model predictions for the diffuse ISM. We further show that neither CO emission nor absorption is likely to be detected where N(H2)≲few×10^{19} cm^{-2}, while HCO+ absorption is readily detected for N(H2)≳few×10^{18} cm^{-2}.

What carries the argument

The kinematically broad component of HCO+ absorption, which isolates extremely diffuse CO-dark H2.

If this is right

  • CO remains undetectable in emission or absorption below H2 columns of a few times 10^{19} cm^{-2}.
  • HCO+ absorption detects H2 columns down to a few times 10^{18} cm^{-2}.
  • Modest amounts of cold HI can support the presence of H2.
  • The HI-to-H2 transition occurs at lower molecular fractions in diffuse gas than in denser regions.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • HCO+ absorption offers a practical way to map the total molecular gas reservoir beyond CO-based estimates.
  • The low CO abundance supports existing chemical models of the diffuse ISM.
  • Similar absorption surveys could refine the mass budget of CO-dark gas across the Milky Way.

Load-bearing premise

The broad kinematic component of HCO+ absorption can be cleanly separated from narrow components and directly attributed to CO-dark H2 without significant contributions from other chemical or excitation effects.

What would settle it

Detection of substantial CO absorption or emission at the velocities of the broad HCO+ component, or measurement of a significantly higher molecular fraction in that gas.

Figures

Figures reproduced from arXiv: 2606.04309 by Daniel R. Rybarczyk, Gan Luo, J. R. Dawson, Michael P. Busch, Min-Young Lee.

Figure 1
Figure 1. Figure 1: The absorption spectra, e −τ , of H I (filled black), HCO+ (filled pink), and CO (filled blue) in the direction of the five background sources listed in [PITH_FULL_IMAGE:figures/full_fig_p007_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Same as [PITH_FULL_IMAGE:figures/full_fig_p008_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: The integrated CO optical depth versus the in￾tegrated HCO+ optical depth for different velocity inter￾vals (listed in [PITH_FULL_IMAGE:figures/full_fig_p009_3.png] view at source ↗
Figure 5
Figure 5. Figure 5: The integrated HCO+ optical depth versus ⟨Ts⟩ (Equation 3). Results for regions with narrow HCO+ absorp￾tion are shown as squares. Results for regions with broad HCO+ absorption are shown as circles. Results for regions where only atomic gas is detected in absorption are shown as triangles. New results from this work are plotted in opaque orange (for narrow absorption regions), purple (for broad ab￾sorptio… view at source ↗
Figure 4
Figure 4. Figure 4: Top: the implied CO abundance relative to H2 versus the H2 column density (derived from the HCO+ col￾umn density) for all regions listed in [PITH_FULL_IMAGE:figures/full_fig_p011_4.png] view at source ↗
Figure 6
Figure 6. Figure 6: Box plot of ⟨Ts⟩ (Equation 3) for regions with narrow HCO+ absorption (orange, rightmost), broad HCO+ absorption (purple, middle), and no HCO+ absorption (gray, leftmost). The boundaries of the box are drawn at the first and third quartiles, with the median indicated by a horizon￾tal line. The “whiskers” show the extent of the data, with outliers shown as diamond points. row HCO+ (and narrow CO absorption)… view at source ↗
Figure 7
Figure 7. Figure 7: Spectra showing the differential column density in each velocity channel contributed by H2 (pink, calculated from HCO+), H I (black, using an isothermal approximation in each channel), and the total hydrogen column (dashed dark green, using the sum of H I and 2 × H2). The molecu￾lar fraction in each velocity bin where HCO+ is detected is shown as a blue scatter point. Spectra have been smoothed to 1 km s−1… view at source ↗
Figure 8
Figure 8. Figure 8: The optical depth sensitivity (color map) re￾quired to detect CO at 3σ for a given H2 column density (x-axis) and CO abundance (y-axis). The semi-transparent white window shows the theoretical detectability limit for a CO optical depth sensitivity ∼ 0.003 (typical of what we obtain here; see [PITH_FULL_IMAGE:figures/full_fig_p015_8.png] view at source ↗
read the original abstract

A classic problem in the study of the interstellar medium (ISM) is the near-invisibility of molecular hydrogen (H$_2$) in cold environments. Observations of CO emission are typically used to indirectly trace H$_2$, but a significant fraction of H$_2$ in the diffuse ISM is not associated with any detectable CO emission (``CO-dark'' molecular gas). Meanwhile, observations of H$_2$ absorption trace nearly all of the H$_2$ in diffuse directions. In particular, a kinematically broad HCO$^+$ absorption signature traces extremely diffuse, CO-dark H$_2$. We have used sensitive observations of HCO$^+$, CO, and atomic hydrogen (HI) in absorption to constrain the properties of such diffuse molecular gas in five directions. The diffuse molecular gas revealed by broad HCO$^+$ absorption has a lower fraction of cold HI ($f_{\mathrm{CNM}} = 0.38^{+0.28}_{-0.27}$) and a lower fraction of hydrogen in H$_2$ ($f_{\mathrm{mol}}=0.09^{+0.06}_{-0.03}$) than gas traced by CO in the same directions. We detect almost no CO absorption from the gas traced by broad HCO$^+$ absorption. We constrain the CO abundance relative to H$_2$ to be $\lesssim10^{-6}$-$10^{-5}$ for gas traced by both broad and narrow HCO$^+$ absorption, consistent with chemical model predictions for the diffuse ISM. We further show that neither CO emission nor absorption is likely to be detected where $N(\mathrm{H_2})\lesssim\mathrm{few}\times10^{19}$ $\mathrm{cm^{-2}}$ - a result of both the low CO abundance and the low H$_2$ column - while HCO$^+$ absorption is readily detected for $N(\mathrm{H_2})\gtrsim\text{few}\times10^{18}$ $\mathrm{cm^{-2}}$. These results demonstrate that even modest amounts of cold HI can bear H$_2$, providing critical constraints on the HI-to-H$_2$ transition in the ISM.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The paper reports absorption-line observations of HCO+, CO, and HI toward five sightlines, claiming that the kinematically broad HCO+ component traces a distinct CO-dark molecular phase with lower cold-neutral-medium fraction (f_CNM = 0.38^{+0.28}_{-0.27}) and lower molecular fraction (f_mol = 0.09^{+0.06}_{-0.03}) than CO-traced gas in the same directions. It further reports non-detection of CO absorption from this gas and derives CO/H2 abundance upper limits of ≲10^{-6}–10^{-5}, consistent with chemical models, while showing that HCO+ absorption is detectable at lower N(H2) than CO.

Significance. If the kinematic attribution holds, the results supply direct observational constraints on the HI-to-H2 transition and the prevalence of CO-dark gas at low columns, reinforcing the role of HCO+ absorption as a tracer where CO fails. The consistency with existing chemical models and the quantitative limits on CO abundance are strengths.

major comments (2)
  1. [Abstract and methods] Abstract and implied methods: the headline values of f_CNM and f_mol, as well as the CO/H2 limits, rest on the clean kinematic separation of broad versus narrow HCO+ absorption and the attribution of the broad component to a distinct diffuse molecular phase. The manuscript must supply explicit separation criteria, quantitative tests against velocity crowding or overlapping narrow components, and assessment of possible non-LTE excitation or chemical broadening effects; without these, the derived fractions do not follow from the observations.
  2. [Results] Results section: the reported uncertainties (e.g., f_mol = 0.09^{+0.06}_{-0.03}) and abundance limits require full column-density tables, error budgets, and exclusion criteria for the five sightlines to be verifiable; these details are not visible in the provided text and are load-bearing for the quantitative claims.
minor comments (1)
  1. [Abstract] Notation for f_mol and f_CNM should be defined at first use with explicit reference to the underlying column-density definitions.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the positive evaluation of our work's significance and for the constructive major comments. We address each point below and will revise the manuscript to improve clarity and verifiability of the kinematic separation and supporting data.

read point-by-point responses

  1. Referee: [Abstract and methods] Abstract and implied methods: the headline values of f_CNM and f_mol, as well as the CO/H2 limits, rest on the clean kinematic separation of broad versus narrow HCO+ absorption and the attribution of the broad component to a distinct diffuse molecular phase. The manuscript must supply explicit separation criteria, quantitative tests against velocity crowding or overlapping narrow components, and assessment of possible non-LTE excitation or chemical broadening effects; without these, the derived fractions do not follow from the observations.

    Authors: We agree that the kinematic separation is central to the derived fractions and that the current text would benefit from greater explicitness. In the revised manuscript we will add a dedicated Methods subsection that states the separation criteria (Gaussian decomposition with velocity dispersion thresholds), includes Monte Carlo tests of velocity crowding using the observed line profiles and spectral resolution, and provides a brief assessment showing that non-LTE and chemical-broadening contributions are sub-dominant to the kinematic widths at the low densities involved. These additions will make the attribution of the broad component transparent. revision: yes

  2. Referee: [Results] Results section: the reported uncertainties (e.g., f_mol = 0.09^{+0.06}_{-0.03}) and abundance limits require full column-density tables, error budgets, and exclusion criteria for the five sightlines to be verifiable; these details are not visible in the provided text and are load-bearing for the quantitative claims.

    Authors: The column densities, uncertainties, and sightline selection are summarized in Table 1 and described in Sections 2 and 3, but we acknowledge that the error budget and exclusion criteria could be presented more accessibly. We will expand the Results section with a consolidated table listing all measured columns, the full statistical-plus-systematic error budget, and the explicit exclusion criteria applied to arrive at the final five sightlines. Machine-readable versions of the tables will also be provided as supplementary material to allow direct verification of the reported values and limits. revision: yes

Circularity Check

0 steps flagged

No circularity: results are direct observational measurements

full rationale

The paper derives f_CNM, f_mol, and CO/H2 limits from measured absorption profiles of HCO+, CO, and HI in five sightlines. These quantities are computed from observed column densities and velocity components without any self-referential equations, fitted inputs renamed as predictions, or load-bearing self-citations. The broad/narrow kinematic separation is an empirical profile decomposition step whose validity rests on the data rather than on prior results by the same authors. No derivation chain reduces to its own inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

Based on abstract only; key assumptions include standard conversion from absorption to column density and that chemical models provide independent validation rather than fitting targets.

axioms (2)
  • domain assumption HCO+ absorption reliably traces H2 column density in diffuse gas
    Invoked when interpreting broad absorption as direct tracer of CO-dark H2.
  • domain assumption Velocity component decomposition cleanly separates broad and narrow features without blending
    Required for attributing properties specifically to broad HCO+ gas.

pith-pipeline@v0.9.1-grok · 5944 in / 1385 out tokens · 33471 ms · 2026-06-28T05:57:00.298473+00:00 · methodology

discussion (0)

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Works this paper leans on

59 extracted references · 55 canonical work pages · 4 internal anchors

  1. [1]

    J., Hogg, D

    Allen, R. J., Hogg, D. E., & Engelke, P. D. 2015, AJ, 149, 123, doi: 10.1088/0004-6256/149/4/123

    work page doi:10.1088/0004-6256/149/4/123 2015

  2. [2]

    2020, A&A, 643, A36, doi: 10.1051/0004-6361/202038593

    Bellomi, E., Godard, B., Hennebelle, P., et al. 2020, A&A, 643, A36, doi: 10.1051/0004-6361/202038593

    work page doi:10.1051/0004-6361/202038593 2020

  3. [3]

    2008, AJ, 136, 2846, doi: 10.1088/0004-6256/136/6/2846

    Bigiel, F., Leroy, A., Walter, F., et al. 2008, AJ, 136, 2846, doi: 10.1088/0004-6256/136/6/2846

    work page doi:10.1088/0004-6256/136/6/2846 2008

  4. [4]

    D., Wolfire, M., & Leroy, A

    Bolatto, A. D., Wolfire, M., & Leroy, A. K. 2013, ARA&A, 51, 207, doi: 10.1146/annurev-astro-082812-140944

    work page internal anchor Pith review doi:10.1146/annurev-astro-082812-140944 2013

  5. [5]

    Busch, M. P. 2024, ApJ, 967, 148, doi: 10.3847/1538-4357/AD3AF6

    work page doi:10.3847/1538-4357/ad3af6 2024

  6. [6]

    P., Allen, R

    Busch, M. P., Allen, R. J., Engelke, P. D., et al. 2019, ApJ, 883, 158, doi: 10.3847/1538-4357/ab3a4b

    work page doi:10.3847/1538-4357/ab3a4b 2019

  7. [7]

    P., Engelke, P

    Busch, M. P., Engelke, P. D., Allen, R. J., & Hogg, D. E. 2021, ApJ, 914, 72, doi: 10.3847/1538-4357/abf832

    work page doi:10.3847/1538-4357/abf832 2021

  8. [8]

    Cazaux, S., & Tielens, A. G. G. M. 2002, ApJL, 575, L29, doi: 10.1086/342607

    work page doi:10.1086/342607 2002

  9. [9]

    M., Hartmann, D., & Thaddeus, P

    Dame, T. M., Hartmann, D., & Thaddeus, P. 2001, ApJ, 547, 792, doi: 10.1086/318388

    work page internal anchor Pith review doi:10.1086/318388 2001

  10. [10]

    M., & Thaddeus, P

    Dame, T. M., & Thaddeus, P. 2022, ApJS, 262, 5, doi: 10.3847/1538-4365/ac7e53 19

    work page doi:10.3847/1538-4365/ac7e53 2022

  11. [11]

    2017, MNRAS, 472, 3169, doi: 10.1093/mnras/stx2211

    Donate, E., & Magnani, L. 2017, MNRAS, 472, 3169, doi: 10.1093/mnras/stx2211

    work page doi:10.1093/mnras/stx2211 2017

  12. [12]

    , keywords =

    Edenhofer, G., Zucker, C., Frank, P., et al. 2024, A&A, 685, A82, doi: 10.1051/0004-6361/202347628

    work page doi:10.1051/0004-6361/202347628 2024

  13. [13]

    2018, Monthly Notices of the Royal Astronomical Society, 478, 2315, doi: 10.1093/mnras/sty1168

    Esteban, C., & Garc´ ıa-Rojas, J. 2018, Monthly Notices of the Royal Astronomical Society, 478, 2315, doi: 10.1093/mnras/sty1168

    work page doi:10.1093/mnras/sty1168 2018

  14. [14]

    R., Huntress, Jr., W

    Federman, S. R., Huntress, Jr., W. T., & Prasad, S. S. 1990, ApJ, 354, 504, doi: 10.1086/168711 Gildas Team. 2013, GILDAS: Grenoble Image and Line Data Analysis Software, Astrophysics Source Code Library, record ascl:1305.010. http://ascl.net/1305.010

    work page doi:10.1086/168711 1990

  15. [15]

    2010, A&A, 520, A20, doi: 10.1051/0004-6361/201014283

    Luca, M. 2010, A&A, 520, A20, doi: 10.1051/0004-6361/201014283

    work page doi:10.1051/0004-6361/201014283 2010

  16. [16]

    Goldsmith, P. F. 2013, ApJ, 774, 134, doi: 10.1088/0004-637X/774/2/134

    work page doi:10.1088/0004-637x/774/2/134 2013

  17. [17]

    F., Li, D., & Krˇ co, M

    Goldsmith, P. F., Li, D., & Krˇ co, M. 2007, ApJ, 654, 273, doi: 10.1086/509067

    work page doi:10.1086/509067 2007

  18. [18]

    2019, ApJ, 887, 93, doi: 10.3847/1538-4357/ab5362

    Finkbeiner, D. 2019, ApJ, 887, 93, doi: 10.3847/1538-4357/ab5362 G¨ uver, T., &¨Ozel, F. 2009, MNRAS, 400, 2050, doi: 10.1111/j.1365-2966.2009.15598.x

    work page internal anchor Pith review doi:10.3847/1538-4357/ab5362 2019

  19. [19]

    R., Nguyen, H., et al

    Hafner, A., Dawson, J. R., Nguyen, H., et al. 2023, PASA, 40, e015, doi: 10.1017/pasa.2023.8

    work page doi:10.1017/pasa.2023.8 2023

  20. [20]

    2023, Monthly Notices of the Royal Astronomical Society, 525, 3318, doi: 10.1093/mnras/stad1244

    Hawkins, K. 2023, Monthly Notices of the Royal Astronomical Society, 525, 3318, doi: 10.1093/mnras/stad1244

    work page doi:10.1093/mnras/stad1244 2023

  21. [21]

    Heiles, C., & Troland, T. H. 2003, ApJS, 145, 329, doi: 10.1086/367785

    work page doi:10.1086/367785 2003

  22. [22]

    J., Wolfire, M

    Kaufman, M. J., Wolfire, M. G., & Hollenbach, D. J. 2006, ApJ, 644, 283, doi: 10.1086/503596

    work page doi:10.1086/503596 2006

  23. [23]

    C., & Kim, W.-T

    Kim, C.-G., Ostriker, E. C., & Kim, W.-T. 2014, ApJ, 786, 64, doi: 10.1088/0004-637X/786/1/64

    work page doi:10.1088/0004-637x/786/1/64 2014

  24. [24]

    2018, ApJS, 235, 1, doi: 10.3847/1538-4365/aaa762

    Li, D., Tang, N., Nguyen, H., et al. 2018, ApJS, 235, 1, doi: 10.3847/1538-4365/aaa762

    work page doi:10.3847/1538-4365/aaa762 2018

  25. [25]

    2023a, A&A, 675, A145, doi: 10.1051/0004-6361/202346259 —

    Liszt, H., & Gerin, M. 2023a, A&A, 675, A145, doi: 10.1051/0004-6361/202346259 —. 2023b, ApJ, 943, 172, doi: 10.3847/1538-4357/acae83

    work page doi:10.1051/0004-6361/202346259

  26. [26]

    2019, A&A, 627, A95, doi: 10.1051/0004-6361/201935436

    Liszt, H., Gerin, M., & Grenier, I. 2019, A&A, 627, A95, doi: 10.1051/0004-6361/201935436

    work page doi:10.1051/0004-6361/201935436 2019

  27. [27]

    2000, A&A, 355, 333

    Liszt, H., & Lucas, R. 2000, A&A, 355, 333

    2000

  28. [28]

    2005, in Astrochemistry: Recent Successes and Current Challenges, ed

    Liszt, H., Lucas, R., & Pety, J. 2005, in Astrochemistry: Recent Successes and Current Challenges, ed. D. C. Lis, G. A. Blake, & E. Herbst, Vol. 231, 187–196, doi: 10.1017/S1743921306007186

    work page doi:10.1017/s1743921306007186 2005

  29. [29]

    Liszt, H. S. 2017, ApJ, 835, 138, doi: 10.3847/1538-4357/835/2/138

    work page doi:10.3847/1538-4357/835/2/138 2017

  30. [30]

    S., & Lucas, R

    Liszt, H. S., & Lucas, R. 1998, A&A, 339, 561

    1998

  31. [31]

    S., & Pety, J

    Liszt, H. S., & Pety, J. 2012, A&A, 541, A58, doi: 10.1051/0004-6361/201218771

    work page doi:10.1051/0004-6361/201218771 2012

  32. [32]

    S., Pety, J., Gerin, M., & Lucas, R

    Liszt, H. S., Pety, J., Gerin, M., & Lucas, R. 2014, A&A, 564, A64, doi: 10.1051/0004-6361/201323320

    work page doi:10.1051/0004-6361/201323320 2014

  33. [33]

    2013, ApJL, 775, L2, doi: 10.1088/2041-8205/775/1/L2

    Liu, T., Wu, Y., & Zhang, H. 2013, ApJL, 775, L2, doi: 10.1088/2041-8205/775/1/L2

    work page doi:10.1088/2041-8205/775/1/l2 2013

  34. [34]

    1996, A&A, 307, 237

    Lucas, R., & Liszt, H. 1996, A&A, 307, 237

    1996

  35. [35]

    2020, ApJL, 889, L4, doi: 10.3847/2041-8213/ab6337

    Luo, G., Li, D., Tang, N., et al. 2020, ApJL, 889, L4, doi: 10.3847/2041-8213/ab6337

    work page doi:10.3847/2041-8213/ab6337 2020

  36. [36]

    G., et al

    Luo, G., Zhang, Z.-Y., Bisbas, T. G., et al. 2023, ApJ, 946, 91, doi: 10.3847/1538-4357/acbf34

    work page doi:10.3847/1538-4357/acbf34 2023

  37. [37]

    2024, A&A, 685, L12, doi: 10.1051/0004-6361/202450067

    Luo, G., Li, D., Zhang, Z.-Y., et al. 2024, A&A, 685, L12, doi: 10.1051/0004-6361/202450067

    work page doi:10.1051/0004-6361/202450067 2024

  38. [38]

    M., Stanimirovi´ c, S., & Rybarczyk, D

    McClure-Griffiths, N. M., Stanimirovi´ c, S., & Rybarczyk, D. R. 2023, ARA&A, 61, 19, doi: 10.1146/annurev-astro-052920-104851

    work page doi:10.1146/annurev-astro-052920-104851 2023

  39. [39]

    M., Pisano, D

    McClure-Griffiths, N. M., Pisano, D. J., Calabretta, M. R., et al. 2009, ApJS, 181, 398, doi: 10.1088/0067-0049/181/2/398

    work page doi:10.1088/0067-0049/181/2/398 2009

  40. [40]

    E., Stanimirovi´ c, S., Goss, W

    Murray, C. E., Stanimirovi´ c, S., Goss, W. M., et al. 2018, ApJS, 238, 14, doi: 10.3847/1538-4365/aad81a

    work page doi:10.3847/1538-4365/aad81a 2018

  41. [41]

    E., Stanimirovi´ c, S., Heiles, C., et al

    Murray, C. E., Stanimirovi´ c, S., Heiles, C., et al. 2021, ApJS, 256, 37, doi: 10.3847/1538-4365/ac0f0b

    work page doi:10.3847/1538-4365/ac0f0b 2021

  42. [42]

    E., Stanimirovi´ c, S., Goss, W

    Murray, C. E., Stanimirovi´ c, S., Goss, W. M., et al. 2015, ApJ, 804, 89, doi: 10.1088/0004-637X/804/2/89

    work page doi:10.1088/0004-637x/804/2/89 2015

  43. [43]

    R., Lee, M.-Y., et al

    Nguyen, H., Dawson, J. R., Lee, M.-Y., et al. 2019, ApJ, 880, 141, doi: 10.3847/1538-4357/ab2b9f

    work page doi:10.3847/1538-4357/ab2b9f 2019

  44. [44]

    R., Miville-Deschˆ enes, M.-A., et al

    Nguyen, H., Dawson, J. R., Miville-Deschˆ enes, M.-A., et al. 2018, ApJ, 862, 49, doi: 10.3847/1538-4357/aac82b

    work page doi:10.3847/1538-4357/aac82b 2018

  45. [45]

    2023, ApJ, 955, 145, doi: 10.3847/1538-4357/ace164

    Park, G., Lee, M.-Y., Bialy, S., et al. 2023, ApJ, 955, 145, doi: 10.3847/1538-4357/ace164

    work page doi:10.3847/1538-4357/ace164 2023

  46. [46]

    Peek, J. E. G., Heiles, C., Douglas, K. A., et al. 2011, ApJS, 194, 20, doi: 10.1088/0067-0049/194/2/20

    work page doi:10.1088/0067-0049/194/2/20 2011

  47. [47]

    Peek, J. E. G., Babler, B. L., Zheng, Y., et al. 2018, ApJS, 234, 2, doi: 10.3847/1538-4365/aa91d3

    work page doi:10.3847/1538-4365/aa91d3 2018

  48. [48]

    2005, in SF2A-2005: Semaine de l’Astrophysique Francaise, ed

    Pety, J. 2005, in SF2A-2005: Semaine de l’Astrophysique Francaise, ed. F. Casoli, T. Contini, J. M. Hameury, & L. Pagani, 721

    2005

  49. [49]

    R., Stanimirovi´ c, S., & Gusdorf, A

    Rybarczyk, D. R., Stanimirovi´ c, S., & Gusdorf, A. 2023, ApJ, 950, 52, doi: 10.3847/1538-4357/accba1

    work page doi:10.3847/1538-4357/accba1 2023

  50. [50]

    R., Stanimirovi´ c, S., Gong, M., et al

    Rybarczyk, D. R., Stanimirovi´ c, S., Gong, M., et al. 2022, ApJ, 928, 79, doi: 10.3847/1538-4357/ac5035

    work page doi:10.3847/1538-4357/ac5035 2022

  51. [51]

    Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD

    Schlafly, E. F., & Finkbeiner, D. P. 2011, ApJ, 737, 103, doi: 10.1088/0004-637X/737/2/103

    work page internal anchor Pith review doi:10.1088/0004-637x/737/2/103 2011

  52. [52]

    R., et al

    Sheffer, Y., Rogers, M., Federman, S. R., et al. 2008, ApJ, 687, 1075, doi: 10.1086/591484 Stanimirovi´ c, S., Murray, C. E., Lee, M.-Y., Heiles, C., &

    work page doi:10.1086/591484 2008

  53. [53]

    2014, ApJ, 793, 132, doi: 10.1088/0004-637X/793/2/132 20

    Miller, J. 2014, ApJ, 793, 132, doi: 10.1088/0004-637X/793/2/132 20

    work page doi:10.1088/0004-637x/793/2/132 2014

  54. [54]

    2021, ApJ, 910, 131, doi: 10.3847/1538-4357/abe5ab

    Su, Y., Yang, J., Yan, Q.-Z., et al. 2021, ApJ, 910, 131, doi: 10.3847/1538-4357/abe5ab

    work page doi:10.3847/1538-4357/abe5ab 2021

  55. [55]

    2024, The Journal of Open Source Software, 9, 7201, doi: 10.21105/joss.07201

    Wenger, T. 2024, The Journal of Open Source Software, 9, 7201, doi: 10.21105/joss.07201

    work page doi:10.21105/joss.07201 2024

  56. [56]

    V., Balser, D

    Wenger, T. V., Balser, D. S., Anderson, L. D., & Bania, T. M. 2018, ApJ, 856, 52, doi: 10.3847/1538-4357/aaaec8

    work page doi:10.3847/1538-4357/aaaec8 2018

  57. [57]

    G., Hollenbach, D., & McKee, C

    Wolfire, M. G., Hollenbach, D., & McKee, C. F. 2010, ApJ, 716, 1191, doi: 10.1088/0004-637X/716/2/1191

    work page doi:10.1088/0004-637x/716/2/1191 2010

  58. [58]

    Xu, D., Li, D., Yue, N., & Goldsmith, P. F. 2016, ApJ, 819, 22, doi: 10.3847/0004-637X/819/1/22

    work page doi:10.3847/0004-637x/819/1/22 2016

  59. [59]

    2017, MNRAS, 471, 3494, doi: 10.1093/mnras/stx1580

    Zhu, H., Tian, W., Li, A., & Zhang, M. 2017, MNRAS, 471, 3494, doi: 10.1093/mnras/stx1580

    work page doi:10.1093/mnras/stx1580 2017