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Low-frequency HRRLs pin dense warm ionized gas in the Galactic plane to electron densities of 6–15 cm^{-3}, but temperature and emission measure stay underconstrained without priors or higher S/N.

2026-07-10 05:40 UTC pith:WPIJPI2Z

load-bearing objection Solid multi-frequency HRRL work that cleanly recovers n_e = 6–15 cm^{-3} under stated assumptions; the continuum geometry and single-zone model are the known soft spots, already quantified by the authors. the 2 major comments →

arxiv 2607.08542 v1 pith:WPIJPI2Z submitted 2026-07-09 astro-ph.GA astro-ph.IM

Constraints on the properties of warm ionized gas from low-frequency hydrogen radio recombination lines

Pedro Salas , Kimberly L. Emig , Matteo Luisi , D. Anish Roshi , Loren Anderson This is my paper
classification astro-ph.GA astro-ph.IM
keywords radio recombination lineswarm ionized mediumelectron densityGalactic planestimulated emissionnon-LTEGreen Bank TelescopeGDIGS
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

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

This paper asks what physical properties of the dense warm ionized medium in the Galactic plane can be recovered from multi-frequency hydrogen radio recombination lines. The authors obtained new 342 MHz and 800 MHz spectra toward three positions chosen to avoid known H II regions, stacked them with matched-resolution 5.8 GHz GDIGS spectra, and used a forward model of non-LTE line formation (including stimulated emission) to fit the full line profiles. The model recovers electron density robustly in the range 6–15 cm^{-3}; temperature and emission measure remain degenerate unless an informative temperature prior or substantially higher signal-to-noise data are supplied. A sympathetic reader cares because these densities, path lengths, and ionization budgets speak directly to whether the dense ionized gas is an extension of the high-latitude WIM, envelopes of discrete H II regions, or a distinct component powered by leaked Lyman continuum, and because the same method can be scaled to large-area surveys with next-generation low-frequency arrays.

Core claim

When low-frequency (342 and 800 MHz) and 5.8 GHz HRRL profiles are modeled jointly with a non-LTE radiative-transfer forward model, the electron density of the emitting gas is constrained to 6–15 cm^{-3} at the observed positions; temperature and emission measure cannot be recovered independently without an external prior or higher signal-to-noise observations.

What carries the argument

The non-LTE brightness formula for a recombination line (including background and internal continuum, departure coefficients, and Voigt pressure broadening) evaluated across three principal quantum numbers and sampled with MCMC; this is the object that maps observed line profiles onto n_e, T_e and EM.

Load-bearing premise

The model assumes that the observed continuum can be split into a homogeneous background fraction and a non-thermal fraction that scales simply with path length and distance; if the continuum is clumpy or the filling factors differ, the stimulated-emission term changes and the recovered density shifts by tens of percent.

What would settle it

A factor-of-four increase in signal-to-noise at 800 MHz (or the addition of a high-S/N ~180 MHz HRRL) toward the same three positions, followed by a re-run of the same MCMC without a temperature prior, would either collapse the T_e–EM posterior onto unique values or leave it still unconstrained, directly testing the claim that higher S/N alone can break the degeneracy.

Watch this falsifier — get emailed when new claim-graph text bears on it.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

2 major / 5 minor

Summary. The paper presents new GBT observations of hydrogen radio recombination lines at 342 MHz and 800 MHz toward three Galactic-plane positions chosen to minimize known HII regions, combined with GDIGS 5.8 GHz HRRL cubes. Using a forward-modeling approach based on the non-LTE line brightness formula of Shaver (1975), the authors recover electron densities of 6–15 cm^{-3} for the emitting gas. Synthetic-data validation shows that n_e is constrained to ~20 % while T_e and EM remain degenerate without an informative temperature prior (taken from the Quireza et al. 2006 Galactic curve). Continuum fractions are fixed geometrically following Roshi & Anantharamaiah (2001). The abstract and §4.3 correctly state that T_e and EM require either priors or higher S/N.

Significance. The work updates classic low-frequency HRRL analyses with modern instrumentation, fully sampled higher-frequency cubes, and an explicit MCMC treatment of line profiles rather than separate intensity/width ratios. The synthetic validation (§4.2, Fig. 6) is a clear methodological strength: it quantifies the T_e–EM–v_rms degeneracy and the residual bias in n_e under free continuum fractions. The derived densities sit between earlier ORT results and FIR [NII] values, and the ionization-budget comparison (§4.8) is a useful, falsifiable check. The paper is appropriately caveated and does not over-claim temperature or path-length constraints.

major comments (2)
  1. §4.1 continuum partition: T_bg = T_c (D_gal – D)/D_gal and T_nth = T_c L/D_gal assumes a homogeneous slab and a smooth non-thermal background. Because the observed continuum is largely non-thermal (β ≈ –2.2, §3.3), any clumpiness or free-free/non-thermal mismatch changes the stimulated-emission term that dominates the low-frequency lines. Validation (Fig. 6) already shows free f_bg shifts the n_e peak by ~20 %. The absolute scale of the reported 6–15 cm^{-3} range is therefore geometry-dependent at the tens-of-percent level. A short additional test (or explicit statement of the residual systematic) would strengthen the central claim.
  2. §4.3 and Table 5: results for G24.07–0.59 (especially the 90 km s^{-1} component) are presented alongside the other two sight-lines even though §3.1 and §4.4 note beam dilution and that the component is brighter on 5′ scales. The paper correctly flags the issue, but the tabulated densities for this position should either be omitted from the headline range or corrected for filling factor so that the claimed 6–15 cm^{-3} interval is not diluted by a known systematic.
minor comments (5)
  1. Table 2: S/N is omitted for the double-peaked G24.07–0.59 profiles; a brief note explaining the omission would help the reader.
  2. Figure 2 caption: the scaling applied to higher-frequency spectra before differencing should be stated more explicitly (peak matching is mentioned in the text but not in the caption).
  3. §4.4 multi-volume tests: the statement that unequal-EM components prevent convergence is useful; a one-sentence quantification of how often such configurations are expected would place the single-zone assumption in context.
  4. Typographical: “Hiiregions” appears repeatedly without the space or roman numeral formatting used elsewhere; consistent “H II regions” would improve readability.
  5. §2.1: the 10 % absolute flux uncertainty is adopted but never propagated into the posterior widths; a short remark on whether it is sub-dominant to the statistical errors would be helpful.

Circularity Check

1 steps flagged

Minor self-citation of continuum-partition ansatz; n_e itself is fitted from multi-frequency non-LTE line ratios with an external T_e prior and is not forced by construction.

specific steps
  1. ansatz smuggled in via citation [§4.1 (paragraph after Eq. 2)]
    "We adopt the prescription by Roshi & Anantharamaiah (2001), setting T_bg,ν = T_c (D_gal − D)/D_gal and T_nth = T_c L/D_gal, with T_c the observed continuum brightness, D_gal the size of the Galactic disk along the line of sight, D the distance to the gas responsible for the HRRL emission and L the size of the HRRL emitting region along the line of sight. This is equivalent to assuming that the ISM is homogeneous behind the HRRL emitting region."

    The continuum partition that sets the stimulated-emission term (the dominant density diagnostic at low frequency) is imported wholesale from a prior paper whose author list overlaps the present one; the prior work itself introduced the homogeneous-slab ansatz without independent derivation. Freeing f_bg (as the paper does in validation) shifts the n_e posterior peak by ~20 %, so the absolute scale of the claimed densities inherits this untested geometric assumption via self-citation.

full rationale

The derivation chain is standard RRL radiative transfer (Shaver 1975 brightness formula + Salgado et al. 2017 departure coefficients and pressure broadening). Multi-frequency (342/800/5757 MHz) line profiles are forward-modelled via MCMC; the frequency dependence of stimulated emission primarily constrains n_e (validated on synthetics to ~20 % bias). T_e is given an informative Gaussian prior taken from the independent Galactic temperature curve of Quireza et al. (2006). Continuum fractions f_bg and f_m are fixed by a geometric homogeneous-slab prescription adopted from Roshi & Anantharamaiah (2001) (a co-author), which is an ansatz rather than a fit to the present HRRL intensities; the paper itself quantifies the resulting ~20 % shift when f_bg is left free and explores multi-zone effects. No equation reduces the reported n_e range (6–15 cm^{-3}) to a previously fitted parameter of the same authors, nor is a uniqueness theorem invoked. The result is therefore model-dependent at the tens-of-percent level (as the authors state) but not circular by construction. Score 2 reflects only the single load-bearing self-citation of the continuum ansatz.

Axiom & Free-Parameter Ledger

5 free parameters · 5 axioms · 0 invented entities

The central density claim rests on standard non-LTE RRL radiative transfer, published departure coefficients, a geometric continuum split taken from earlier literature, and an external temperature prior. No new physical entities are invented; free parameters are the usual gas properties fitted by MCMC.

free parameters (5)
  • n_e (electron density)
    Primary free parameter recovered by MCMC from multi-frequency line profiles; reported range 6–15 cm^{-3}.
  • EM (emission measure)
    Fitted jointly with T_e; strongly degenerate without temperature prior.
  • T_e (electron temperature)
    Given a Gaussian prior from Quireza et al. (2006) Galactic curve; otherwise unconstrained.
  • v_rms (non-thermal velocity dispersion)
    Fitted to match observed line widths after pressure-broadening correction.
  • f_bg, f_m (continuum fractions)
    Set by geometric prescription f_bg = (D_gal – D)/D_gal, f_m = L/D_gal rather than left completely free.
axioms (5)
  • domain assumption Non-LTE departure coefficients b_n computed following Salgado et al. (2017a) for n_e = 0.1–1500 cm^{-3}, T_e = 1000–21000 K.
    Used to evaluate line optical depth and brightness (Eq. 1); choice of tables changes n_e by ~30 % (§4.4).
  • domain assumption Continuum brightness is partitioned as T_bg = T_c (D_gal – D)/D_gal and T_nth = T_c L/D_gal (homogeneous slab).
    Adopted from Roshi & Anantharamaiah (2001); §4.1. Controls the stimulated-emission term.
  • domain assumption Gas is a single homogeneous volume that fills the beam (or beam-filling factor = 1).
    Explicitly stated in §4.1 and tested for multi-component cases in §4.4; multi-density volumes bias the recovered n_e toward the EM-weighted mean.
  • domain assumption Kinematic distances from Reid et al. (2014) rotation curve, with near/far ambiguity resolved by proximity to known HII regions or left open.
    §3.2; far-distance solutions lower n_e by up to 33 %.
  • standard math Voigt line profile with collisional + radiation pressure broadening from Salgado et al. (2017b).
    Standard RRL theory used to generate model spectra.

pith-pipeline@v1.1.0-grok45 · 29302 in / 2931 out tokens · 83323 ms · 2026-07-10T05:40:43.850760+00:00 · methodology

0 comments
read the original abstract

The ionized gas in the Milky Way is a major component of the interstellar medium. Observations of extinction free tracers, such as hydrogen radio recombination lines (HRRLs), have revealed the presence of a dense (electron density 1 to 100 cm$^{-3}$) warm ionized medium. Motivated by advances in radio instrumentation, the existence of fully sampled HRRL maps, and a better knowledge about the population of discrete HII regions in our Galaxy, we have acquired new low-frequency ($\nu\lesssim1$ GHz) observations of HRRLs to characterize the properties of this gas. We target three positions in the Galactic plane, with few or no known HII regions, using the 342 MHz and 800 MHz feeds of the Green Bank Telescope. We detect HRRL emission from all three positions. We combine these with the fully sampled HRRL 5.8 GHz cubes from the GBT Diffuse Ionized Gas Survey (GDIGS) to determine the gas properties using a forward modeling approach. From our analysis we find electron densities between 6 and 15 cm$^{-3}$, and that to determine the gas temperature and emission measure we require informative priors or higher signal-to-noise observations.

Figures

Figures reproduced from arXiv: 2607.08542 by D. Anish Roshi, Kimberly L. Emig, Loren Anderson, Matteo Luisi, Pedro Salas.

Figure 1
Figure 1. Figure 1: Regions observed with the GBT. The background images are moment 0 maps from GDIGS. The white circles show the beam size of the GBT at the lowest frequency used for the 800 MHz (solid) and 340 MHz (dashed) observations. The white circles are centered on the regions observed. The red, cyan, green and yellow circles show known, candidate, group and radio quiet H ii regions, respectively, from V2.3 of the WISE… view at source ↗
Figure 2
Figure 2. Figure 2: RRL spectra towards G15.85+0.10 (left), G24.07−0.59 (center) and G31.00−0.91 (right). From top to bottom each rows shows: the PF 342 MHz RRL spectra at 36′ resolution, the GDIGS spectra at 36′ resolution, the difference between the PF 342 MHz and GDIGS spectra at 36′ resolution, the PF 800 MHz RRL spectra at 16′ resolution, the GDIGS spectra at 16′ resolution, the difference between the PF 800 MHz and GDIG… view at source ↗
Figure 3
Figure 3. Figure 3: GDIGS RRL spectra towards G15.85+0.10 (left), G24.07−0.59 (center) and G31.00−0.91 (right) using three different beam sizes, 36′ , 16′ and 2. ′ 65. From top to bottom each row shows: the GDIGS spectra at 36′ resolution, the GDIGS spectra at 16′ resolution, the difference between the GDIGS spectra at 36′ and 16′ resolutions, the GDIGS spectra at 2. ′ 65 resolution, and the difference between the GDIGS spect… view at source ↗
Figure 4
Figure 4. Figure 4: Comparison between the HRRL emission at 800 MHz, 21 cm-HI and 12CO(1–0). The HI and CO spectra were extracted from a 16′ aperture, to match the resolution of the HRRL observations at 800 MHz [PITH_FULL_IMAGE:figures/full_fig_p010_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Radio continuum spectral energy distributions for the three regions observed with the GBT in RRLs. The radio continuum data has been convolved to a resolution of 56′ . The solid lines show a power-law spectra with a spectral index of β = −2.2 normalized to the brightness of the 5 GHz data point. The data for G24.07−0.59 lies behind that for G15.85+0.10 [PITH_FULL_IMAGE:figures/full_fig_p011_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: Posterior probability distributions for the model parameters from the validation exercise. The vertical and horizontal lines show the input values used to generate the synthetic spectra; ne = 10 cm−3 , Te = 8000 K, EM = 1000 pc cm−6 , fbg = 0.44, and fm = 5.5×10−4 . fm represents the fraction of the observed continuum that is non-thermal and comes from the same volume as the HRRLs. The blue dotted line sho… view at source ↗
Figure 7
Figure 7. Figure 7: Posterior distributions for the gas properties at the near and far KD. Each row shows the posterior distributions for both KD solutions for one velocity component. From top to bottom; G15.85+0.10, G24.07−0.59 component 1, G24.07−0.59 component 2, and G31.00−0.91. example, we use the region centered on ℓ = 16.1 ◦ – the closest to G15.85+0.10. For this region Roshi & Anan￾tharamaiah (2001) report ne = 6.1 cm… view at source ↗
Figure 8
Figure 8. Figure 8: Effects of increasing the S/N of one or all mea￾surements in the posterior distribution for Te. The dotted line shows the base case, with a S/N comparable to that of the observations presented in this work. The black dashed and solid lines show the effect of increasing the S/N of all measurements by factors of two and four, respectively. The red dashed and solid lines show the effect fo increasing the S/N … view at source ↗

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Works this paper leans on

100 extracted references · 100 canonical work pages · 40 internal anchors

  1. [1]

    IEEE Transactions on Automatic Control , keywords =

    A New Look at the Statistical Model Identification. IEEE Transactions on Automatic Control , keywords =

    work page

  2. [2]

    The HIPASS survey of the Galactic plane in Radio Recombination Lines

    The HIPASS survey of the Galactic plane in radio recombination lines. , keywords =. doi:10.1093/mnras/stv751 , archivePrefix =. 1411.4497 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stv751

  3. [3]

    , keywords =

    Survey of the galactic plane at 4.875 GHz. , keywords =

    work page

  4. [4]

    Journal of Astrophysics and Astronomy , keywords =

    A survey of radio recombination line emission from the galactic plane at 325 MHz. Journal of Astrophysics and Astronomy , keywords =. doi:10.1007/BF02715005 , url =

    work page doi:10.1007/bf02715005

  5. [5]

    Journal of Astrophysics and Astronomy , keywords =

    Low density ionized gas in the inner galaxy - Interpretation of recombination line observations at 325 MHz. Journal of Astrophysics and Astronomy , keywords =. doi:10.1007/BF02715006 , adsurl =

    work page doi:10.1007/bf02715006

  6. [6]

    Journal of Astrophysics and Astronomy , keywords =

    Ionized gas towards Galactic centre - Constraints from low-frequency recombination lines. Journal of Astrophysics and Astronomy , keywords =. doi:10.1007/BF02714207 , url =

    work page doi:10.1007/bf02714207

  7. [7]

    Resolution of the Distance Ambiguity for Galactic HII Regions

    Resolution of the Distance Ambiguity for Galactic H II Regions. , keywords =. doi:10.1088/0004-637X/690/1/706 , archivePrefix =. 0810.5570 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1088/0004-637x/690/1/706

  8. [8]

    The WISE Catalog of Galactic HII Regions

    The WISE Catalog of Galactic H II Regions. , keywords =. doi:10.1088/0067-0049/212/1/1 , archivePrefix =. 1312.6202 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1088/0067-0049/212/1/1

  9. [9]

    A Green Bank Telescope Survey of Large Galactic HII Regions

    A Green Bank Telescope Survey of Large Galactic H II Regions. , keywords =. doi:10.3847/1538-4365/aa956a , archivePrefix =. 1710.07397 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.3847/1538-4365/aa956a

  10. [10]

    arXiv e-prints , keywords =

    The GBT Diffuse Ionized Gas Survey (GDIGS): Survey Overview and First Data Release. arXiv e-prints , keywords =

    work page

  11. [11]

    A VLA Census of the Galactic H II Region Population

    A VLA Census of the Galactic H II Region Population. , keywords =. doi:10.3847/1538-4365/abd5c0 , archivePrefix =. 2103.02049 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.3847/1538-4365/abd5c0

  12. [12]

    , archivePrefix = "arXiv", eprint =

    Astropy: A community Python package for astronomy. , archivePrefix = "arXiv", eprint =. doi:10.1051/0004-6361/201322068 , url =

    work page doi:10.1051/0004-6361/201322068

  13. [13]

    The Astropy Project: Building an inclusive, open-science project and status of the v2.0 core package

    The Astropy Project: Building an Open-science Project and Status of the v2.0 Core Package. , keywords =. doi:10.3847/1538-3881/aabc4f , archivePrefix =. 1801.02634 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.3847/1538-3881/aabc4f

  14. [14]

    , keywords =

    RRL Observations Using ORT at 328 MHz and WSRT at 1.4 GHz from ELDWIM. , keywords =. doi:10.1088/0004-6256/143/2/45 , url =

    work page doi:10.1088/0004-6256/143/2/45

  15. [15]

    The Analyst , year = 2015, month = jan, volume =

    Baseline correction using asymmetrically reweighted penalized least squares smoothing. The Analyst , year = 2015, month = jan, volume =. doi:10.1039/C4AN01061B , adsurl =

    work page doi:10.1039/c4an01061b 2015

  16. [16]

    Azimuthal Metallicity Structure in the Milky Way Disk

    Azimuthal Metallicity Structure in the Milky Way Disk. , keywords =. doi:10.1088/0004-637X/806/2/199 , archivePrefix =. 1505.04090 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1088/0004-637x/806/2/199

  17. [17]

    arXiv e-prints , keywords =

    Discovery of a New Population of Galactic HII Regions with Ionized Gas Velocity Gradients. arXiv e-prints , keywords =

    work page

  18. [18]

    The Green Bank Telescope Galactic H II Region Discovery Survey

    The Green Bank Telescope Galactic H II Region Discovery Survey. , keywords =. doi:10.1088/2041-8205/718/2/L106 , archivePrefix =. 1006.5929 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1088/2041-8205/718/2/l106 2041

  19. [19]

    Observing and data analysis systems, discovery and timing of 100 pulsars

    The HI Parkes All Sky Survey: southern observations, calibration and robust imaging. , keywords =. doi:10.1046/j.1365-8711.2001.04102.x , url =

    work page doi:10.1046/j.1365-8711.2001.04102.x 2001

  20. [20]

    Morphology of the Interstellar Cooling Lines Detected by COBE

    Morphology of the Interstellar Cooling Lines Detected by COBE. , keywords =. doi:10.1086/174761 , archivePrefix =. astro-ph/9311032 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1086/174761

  21. [21]

    Filling factors and scale heights of the DIG in the Milky Way

    Filling factors and scale heights of the diffuse ionized gas in the Milky Way. Astronomische Nachrichten , keywords =. doi:10.1002/asna.200510488 , archivePrefix =. astro-ph/0511172 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1002/asna.200510488

  22. [22]

    I.Catalogue of nebulous objects

    The velocity field of the outer Galaxy in the southern hemisphere. I.Catalogue of nebulous objects. , keywords =

    work page

  23. [23]

    A New 1.4GHz Radio Continuum Map of the Sky South of Declination +25 deg

    A New 1.4 GHz Radio Continuum Map of the Sky South of Declination +25. , keywords =. doi:10.1017/pasa.2013.36 , archivePrefix =. 1310.2414 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1017/pasa.2013.36 2013

  24. [24]

    S-band Polarization All Sky Survey (S-PASS): survey description and maps

    S-band Polarization All-Sky Survey (S-PASS): survey description and maps. , keywords =. doi:10.1093/mnras/stz806 , archivePrefix =. 1903.09420 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stz806 1903

  25. [25]

    The Radio Sky at Meter Wavelengths: m-Mode Analysis Imaging with the Owens Valley Long Wavelength Array

    The Radio Sky at Meter Wavelengths: m-mode Analysis Imaging with the OVRO-LWA. , keywords =. doi:10.3847/1538-3881/aac721 , archivePrefix =. 1711.00466 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.3847/1538-3881/aac721

  26. [26]

    Searching for the largest bound atoms in space

    Searching for the largest bound atoms in space. , keywords =. doi:10.1051/0004-6361/201936562 , archivePrefix =. 1910.06374 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1051/0004-6361/201936562 1910

  27. [27]

    Super Star Clusters in the Central Starburst of NGC 4945

    Super Star Clusters in the Central Starburst of NGC 4945. , keywords =. doi:10.3847/1538-4357/abb67d , archivePrefix =. 2009.05154 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.3847/1538-4357/abb67d 2009

  28. [28]

    The Vertical Structure of Warm Ionised Gas in the Milky Way

    The Vertical Structure of Warm Ionised Gas in the Milky Way. , keywords =. doi:10.1071/AS08004 , archivePrefix =. 0808.2550 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1071/as08004

  29. [29]

    Herschel Galactic plane survey of [NII] fine structure emission

    Herschel Galactic Plane Survey of [NII] Fine Structure Emission. , keywords =. doi:10.1088/0004-637X/814/2/133 , archivePrefix =. 1510.05706 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1088/0004-637x/814/2/133

  30. [30]

    , year = 1972, month = sep, volume =

    A Longitude Survey of Radio Recombination Lines from the Diffuse Interstellar Medium. , year = 1972, month = sep, volume =. doi:10.1086/151660 , url =

    work page doi:10.1086/151660 1972

  31. [31]

    Astrophysics and Space Science Library , year = 2009, series =

    Radio Recombination Lines. Astrophysics and Space Science Library , year = 2009, series =

    work page 2009

  32. [32]

    , year = 1970, month = nov, volume =

    Radio Recombination Lines from Diffuse Interstellar Gas. , year = 1970, month = nov, volume =. doi:10.1086/180631 , url =

    work page doi:10.1086/180631 1970

  33. [33]

    The warm ionized medium in spiral galaxies

    The warm ionized medium in spiral galaxies. Reviews of Modern Physics , keywords =. doi:10.1103/RevModPhys.81.969 , archivePrefix =. 0901.0941 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1103/revmodphys.81.969

  34. [34]

    I - Observations at southern declinations and for the North Polar region

    A 408 MHz all-sky continuum survey. I - Observations at southern declinations and for the North Polar region. , keywords =

    work page

  35. [35]

    A 408 MHz all-sky continuum survey. II. The atlas of contour maps. , keywords =

    work page

  36. [36]

    Australian Journal of Physics Astrophysical Supplement , keywords =

    A southern hemisphere survey of the galactic plane at 5 GHz. Australian Journal of Physics Astrophysical Supplement , keywords =

    work page

  37. [37]

    Radio Recombination Lines from Inner Galaxy Diffuse Gas. I. High-Sensitivity Observations: He +/H + and Carbon. , keywords =. doi:10.1086/177154 , url =

    work page doi:10.1086/177154

  38. [38]

    Radio Recombination Lines from Inner Galaxy Diffuse Gas. II. The Extended Low-Density Warm Ionized Medium and the ``Worm-ionized Medium''. , keywords =. doi:10.1086/177503 , url =

    work page doi:10.1086/177503

  39. [39]

    The Turbulent Warm Ionized Medium: Emission Measure Distribution and MHD Simulations

    The Turbulent Warm Ionized Medium: Emission Measure Distribution and MHD Simulations. , keywords =. doi:10.1086/590543 , archivePrefix =. 0805.0155 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1086/590543

  40. [40]

    The Journal of Open Source Software , year = 2016, month = aug, volume = 1, eid =

    ChainConsumer. The Journal of Open Source Software , year = 2016, month = aug, volume = 1, eid =. doi:10.21105/joss.00045 , adsurl =

    work page doi:10.21105/joss.00045 2016

  41. [41]

    Peering into the Milky Way by FAST: I. Exquisite HI structures in the inner Galactic disk from the piggyback line observations of the FAST GPPS survey

    Peering into the Milky Way by FAST: I. Exquisite HI structures in the inner Galactic disk from the piggyback line observations of the FAST GPPS survey. Science China Physics, Mechanics, and Astronomy , keywords =. doi:10.1007/s11433-022-2040-8 , archivePrefix =. 2211.11299 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1007/s11433-022-2040-8 2040

  42. [42]

    Australian Journal of Physics , year = 1963, month = mar, volume =

    On the Existence of an Ionized Layer about the Galactic Plane. Australian Journal of Physics , year = 1963, month = mar, volume =. doi:10.1071/PH630001 , url =

    work page doi:10.1071/ph630001 1963

  43. [43]

    , year = 1971, month = aug, volume =

    Detection of Radio Recombination-Line Emission Associated with Distributed Ionized Hydrogen. , year = 1971, month = aug, volume =. doi:10.1086/151057 , url =

    work page doi:10.1086/151057 1971

  44. [44]

    Timing of long-period pulsars

    The Rhodes/HartRAO 2326-MHz radio continuum survey. , keywords =. doi:10.1046/j.1365-8711.1998.01367.x , url =

    work page doi:10.1046/j.1365-8711.1998.01367.x 1998

  45. [45]

    The Dense Warm Ionized Medium in the Inner Galaxy

    The dense warm ionized medium in the inner Galaxy. , keywords =. doi:10.1051/0004-6361/202040223 , archivePrefix =. 2105.07023 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1051/0004-6361/202040223

  46. [46]

    , keywords =

    Errors Associated with Fitting Gaussian Profiles to Noisy Emission-Line Spectra. , keywords =. doi:10.1086/133096 , adsurl =

    work page doi:10.1086/133096

  47. [47]

    , keywords =

    A survey of ionized hydrogen in the plane of the Galaxy. , keywords =. doi:10.1086/154737 , url =

    work page doi:10.1086/154737

  48. [48]

    , keywords =

    A Survey of Radio H II Regions in the Northern Sky. , keywords =. doi:10.1086/191383 , url =

    work page doi:10.1086/191383

  49. [49]

    Matteo Luisi and L. D. Anderson and Dana S. Balser and Trey V. Wenger and T. M. Bania , title =. doi:10.3847/1538-4357/aa8fd2 , url =

    work page doi:10.3847/1538-4357/aa8fd2

  50. [50]

    Ionization Profiles of Galactic HII Regions

    Ionization Profiles of Galactic H II Regions. , keywords =. doi:10.3847/1538-4365/aaf6a5 , archivePrefix =. 1812.01539 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.3847/1538-4365/aaf6a5

  51. [51]

    The GBT Diffuse Ionized Gas Survey: Tracing the Diffuse Ionized Gas around the Giant HII Region W43

    The GBT Diffuse Ionized Gas Survey: Tracing the Diffuse Ionized Gas around the Giant Hii Region W43. , keywords =. doi:10.3847/1538-4357/ab643e , archivePrefix =. 1912.08657 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.3847/1538-4357/ab643e 1912

  52. [52]

    Theoretical Ratio of Beam Efficiency to Aperture Efficiency

    work page

  53. [53]

    Modeling the Elevation and Frequency Dependence of Aperture Efficiency for the GBTs Pipeline

    work page

  54. [54]

    A Multiwavelength Optical Emission Line Survey of Warm Ionized Gas in the Galaxy

    A Multiwavelength Optical Emission Line Survey of Warm Ionized Gas in the Galaxy. , keywords =. doi:10.1086/508441 , archivePrefix =. astro-ph/0609558 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1086/508441

  55. [55]

    A new calibration of stellar parameters of Galactic O stars

    A new calibration of stellar parameters of Galactic O stars. , keywords =. doi:10.1051/0004-6361:20042386 , archivePrefix =. astro-ph/0503346 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1051/0004-6361:20042386

  56. [56]

    , year = 1973, month = jan, volume =

    Radio recombination line emissionfrom the galactic plane. , year = 1973, month = jan, volume =. doi:10.1093/mnras/165.2.149 , url =

    work page doi:10.1093/mnras/165.2.149 1973

  57. [57]

    The Southern Galactic Plane Survey: HI Observations and Analysis

    The Southern Galactic Plane Survey: H I Observations and Analysis. , keywords =. doi:10.1086/430114 , archivePrefix =. astro-ph/0503134 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1086/430114

  58. [58]

    Gradients of chemical abundances in the Milky Way from HII regions: distances derived from Gaia EDR3 parallaxes and temperature inhomogeneities

    Gradients of chemical abundances in the Milky Way from H II regions: distances derived from Gaia EDR3 parallaxes and temperature inhomogeneities. , keywords =. doi:10.1093/mnras/stab3782 , archivePrefix =. 2112.12600 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stab3782

  59. [59]

    , year = 1968, month = may, volume =

    Oscillator Strengths for High-level Transitions in Hydrogen. , year = 1968, month = may, volume =. doi:10.1038/218756a0 , adsurl =

    work page doi:10.1038/218756a0 1968

  60. [60]

    , year = 1978, month = nov, volume =

    The Galactic Extended Low-density HII Region and Its Relation to Star Formation and Diffuse IR Emission. , year = 1978, month = nov, volume =

    work page 1978

  61. [61]

    , keywords =

    The Luminosity Function of OB Associations in the Galaxy. , keywords =. doi:10.1086/303587 , url =

    work page doi:10.1086/303587

  62. [62]

    Star Formation in Massive Clusters via the Wilkinson Microwave Anisotropy Probe and the Spitzer Glimpse Survey

    Star Formation in Massive Clusters Via the Wilkinson Microwave Anisotropy Probe and the Spitzer Glimpse Survey. , keywords =. doi:10.1088/0004-637X/709/1/424 , archivePrefix =. 0906.1026 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1088/0004-637x/709/1/424

  63. [63]

    System configuration and initial discoveries

    Post-correlation radio frequency interference classification methods. , keywords =. doi:10.1111/j.1365-2966.2010.16471.x , archivePrefix =. 1002.1957 , primaryClass =

    work page doi:10.1111/j.1365-2966.2010.16471.x 2010

  64. [64]

    Carbon and hydrogen radio recombination lines from the cold clouds towards Cassiopeia A

    Carbon and hydrogen radio recombination lines from the cold clouds towards Cassiopeia A. , keywords =. doi:10.1093/mnras/stw2818 , archivePrefix =. 1609.06857 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stw2818

  65. [65]

    Spectroscopy with the Engineering Development Array: cold H$^{+}$ at 63 MHz towards the Galactic Centre

    Spectroscopy with the Engineering Development Array: cold H ^ + at 63 MHz towards the Galactic Centre. , keywords =. doi:10.1093/mnras/stz950 , archivePrefix =. 1907.03127 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stz950 1907

  66. [66]

    , keywords =

    An updated list of radio flux density calibrators. , keywords =

    work page

  67. [67]

    Expanding bubbles in Orion A: [CII] observations of M42, M43, and NGC 1977

    Expanding bubbles in Orion A: [C II] observations of M 42, M 43, and NGC 1977. , keywords =. doi:10.1051/0004-6361/202037560 , archivePrefix =. 2005.03917 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1051/0004-6361/202037560 1977

  68. [68]

    , keywords =

    Studies of low-frequency recombination lines from the direction of the Galactic Centre and other galactic sources. , keywords =. doi:10.1093/mnras/182.3.473 , url =

    work page doi:10.1093/mnras/182.3.473

  69. [69]

    , archivePrefix = "arXiv", eprint =

    An Accurate Flux Density Scale from 50 MHz to 50 GHz. , archivePrefix = "arXiv", eprint =. doi:10.3847/1538-4365/aa6df9 , url =

    work page doi:10.3847/1538-4365/aa6df9

  70. [70]

    , keywords =

    Electron Densities and Nitrogen Abundances in Ionized Gas Derived Using [N II] Fine-structure and Hydrogen Recombination Lines. , keywords =. doi:10.3847/1538-4357/ab46c2 , archivePrefix =. 1905.06935 , primaryClass =

    work page doi:10.3847/1538-4357/ab46c2 1905

  71. [71]

    Interstellar Dust and Related Topics , year = 1973, editor =

    Rocket Measurements of the Galactic Background at 100&mu. Interstellar Dust and Related Topics , year = 1973, editor =

    work page 1973

  72. [72]

    Planck 2018 results. II. Low Frequency Instrument data processing. , keywords =. doi:10.1051/0004-6361/201833293 , archivePrefix =. 1807.06206 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1051/0004-6361/201833293 2018

  73. [73]

    Pound, Marc and Teuben, Peter and Catlett, Victoria and Salas, Pedro and Smith, Evan and Chamberlin, Thomas , journal =. dysh: A. 2025 , month =

    work page 2025

  74. [74]

    2015 URSI-USNC Radio Science Meeting , year = 2015, month = jul, eid =

    The versatile GBT astronomical spectrometer (VEGAS): Current status and future plans. 2015 URSI-USNC Radio Science Meeting , year = 2015, month = jul, eid =. doi:10.1109/USNC-URSI.2015.7303578 , url =

    work page doi:10.1109/usnc-ursi.2015.7303578 2015

  75. [75]

    The Electron Temperature Gradient in the Galactic Disk

    The Electron Temperature Gradient in the Galactic Disk. , keywords =. doi:10.1086/508803 , archivePrefix =. astro-ph/0609006 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1086/508803

  76. [76]

    , keywords =

    A radio continuum survey of the northen sky at 1420 MHz - Part I. , keywords =

    work page

  77. [77]

    A radio continuum survey of the northern sky at 1420 MHz. II. , keywords =

    work page

  78. [78]

    The atlas of contour maps

    A radio continuum survey of the southern sky at 1420 MHz. The atlas of contour maps. , keywords =. doi:10.1051/0004-6361:20011000 , url =

    work page doi:10.1051/0004-6361:20011000

  79. [79]

    Trigonometric Parallaxes of High Mass Star Forming Regions: the Structure and Kinematics of the Milky Way

    Trigonometric Parallaxes of High Mass Star Forming Regions: The Structure and Kinematics of the Milky Way. , keywords =. doi:10.1088/0004-637X/783/2/130 , archivePrefix =. 1401.5377 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1088/0004-637x/783/2/130

  80. [80]

    An improved source-subtracted and destriped 408 MHz all-sky map

    An improved source-subtracted and destriped 408-MHz all-sky map. , keywords =. doi:10.1093/mnras/stv1274 , archivePrefix =. 1411.3628 , primaryClass =

    work page internal anchor Pith review Pith/arXiv arXiv doi:10.1093/mnras/stv1274

Showing first 80 references.