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The first z=0 measurement of the HI column density distribution function reaches log N_HI = 17.8 cm^-2, showing weak evolution in faint gas and a decline in denser gas since z~3.

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2026-08-02 19:17 UTC pith:HUJCCCHM

load-bearing objection First z=0 HI CDDF to LLS columns: valuable, but the faintest bin is incomplete and the HI-rich sample bias isn't corrected; needs revision before publication. the 3 major comments →

arxiv 2603.02670 v1 pith:HUJCCCHM submitted 2026-03-03 astro-ph.GA

FEASTS and MHONGOOSE: HI Column Density Distribution at z=0 for N_HI>10^(17.8)\, cm⁻²

Jing Wang , Xuchen Lin , Ze-Zhong Liang , W.J.G. De Blok , Hong Guo , Zhijie Qu , C\'eline P\'eroux , Kentaro Nagamine
show 19 more authors
Luis C. Ho Dong Yang Simon Weng Claudia Del P. Lagos Xinkai Chen George Heald J. Healy Qifeng Huang Peter Kamphuis D. Kleiner Di Li Siqi Liu F. M. Maccagni Lister Staveley-Smith Zherong Su Freeke Van De Voort Fabian Walter Fangxiong Zhong Siwei Zou
This is my paper
classification astro-ph.GA
keywords galaxy evolutionneutral hydrogenHI column density distributionLyman limit systems21-cm imagingcircumgalactic mediumHI mass functioncosmic gas
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.

The paper presents the first measurement at z=0 of the HI column density distribution function f(N_HI) down to log N_HI = 17.8 cm^-2, the Lyman-limit regime, using 21-cm emission maps at roughly 1 kpc resolution. It claims that this distribution is lower than at z~3 by 0.1-0.4 dex for log N_HI between 19.2 and 21, but comparable at 17.8-19.2, implying only weak evolution in the faintest gas. It also claims that gas at these densities lies closer to galaxies than absorption-line surveys suggest, and that a leading cosmological simulation over-predicts distant low-column gas around Milky-Way-like galaxies. These results matter because they supply the first local anchor for models of gas accretion, outflows, and galaxy evolution.

Core claim

The central discovery is a measured f(N_HI) — the sky area per logarithmic column-density bin — at z=0, extending two orders of magnitude deeper in column density than earlier 21-cm studies. The shape is well fit by a Schechter function with log N*_HI = 21.26 and slope beta = 1.15, and it matches earlier DLA-regime measurements while extending sensitivity by about 100 times. The paper then uses this function to derive a covering fraction f_cov ~0.7 for Lyman-limit gas when averaged over 1-kpc pixels, and a covering fraction ~0.006 within the virial radius of Milky-Way-like galaxies. The key comparative claims are a 0.1-0.4 dex decline at 19.2 < log N_HI < 21 since z~3, and much smaller impac

What carries the argument

The machinery is the construction of full-HI images: sensitive single-dish 21-cm data supply the large-scale diffuse gas, while interferometric data supply the small-scale structure; the two are combined via feathering with a simulated single-dish beam, then corrected for beam variation and cleaned. The column density distribution f(N_HI) is built by counting area in 0.1-dex bins from these ~1-kpc-resolution maps, weighting each of the 70 galaxies by the HI mass function at its HI mass and by the inverse sampling density in its mass bin. A Schechter function fit (power law plus exponential cutoff) characterizes the result and is integrated to obtain incidence and covering fractions.

Load-bearing premise

The whole census rests on assuming that the galaxies in the two surveys — both biased toward HI-rich, star-forming systems — represent all galaxies of the same HI mass; if HI-poor galaxies at fixed M_HI have less extended faint gas, the faint end of f(N_HI), the evolution offsets, and the impact-parameter distributions all shift.

What would settle it

A concrete test: measure the extent of low-column HI around galaxies selected without an HI-rich bias and recompute f(N_HI) with those radial profiles at the same 17.8 cm^-2 depth and roughly 1 kpc resolution; if the faint end at 17.8-19.2 changes by more than about 0.075 dex (the HIMF systematic), the claimed z=0 distribution and weak-evolution conclusion are refuted.

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

If this is right

  • The z=0 f(N_HI) gives simulations and analytic models a direct local data point for Lyman-limit gas, replacing extrapolations from higher redshift.
  • Weak evolution at 17.8-19.2 means the faint atomic gas reservoir around galaxies has been roughly stable since z~3, while the 0.1-0.4 dex decline at higher column densities indicates the denser HI reservoir has thinned.
  • The low impact parameters at fixed N_HI imply that low-redshift absorber surveys are missing many of the actual galaxy hosts; the gas may be found much closer to galaxies than previously thought.
  • The over-prediction of distant low-column HI in cosmological simulations points to a need to revise how cool gas or HI post-processing is handled.
  • The covering-fraction result (0.006 for Milky-Way-like galaxies) quantifies how little Lyman-limit gas typical halos contain, informing searches for gas accretion.

Where Pith is reading between the lines

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

  • Beyond the paper: because the largest systematic is galaxy sampling within HI mass bins, a larger, less HI-biased sample would directly test whether the faint end of f(N_HI) and the claimed weak evolution survive.
  • Beyond the paper: the b/r_001-N_HI relation could be inverted to estimate HI masses of Lyman-limit-system host galaxies from impact parameter and column density alone, converting absorption surveys into mass measurements.
  • Beyond the paper: the discrepancy between 21-cm and absorption impact parameters predicts that future sensitive surveys will find a population of low-redshift Lyman-limit systems with no bright nearby galaxy, tracing intergalactic or group gas rather than individual halos.

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

3 major / 3 minor

Summary. The paper combines FEASTS (FAST + interferometry) and MHONGOOSE 21-cm images to construct the z=0 HI column density distribution function f(N_HI) down to log N_HI = 17.8 cm^-2 at ~1 kpc resolution. Galaxy areas are counted in column-density bins and weighted using the HIMF and the inverse occupation of M_HI bins, following Zwaan et al. (2005). The authors report a Schechter-function fit over log N_HI = 17.8–22, compare with z~3 absorber-based measurements and with OWLS/TNG50 simulations, derive length incidence and impact-parameter distributions, and estimate covering fractions including f_cov≈0.7 for LLS-like gas and f_cov≈0.006 within the virial radius of Milky-Way-like galaxies. The main claims are that this is the first z=0 measurement at Lyman-limit columns, that f(N_HI) has declined modestly since z~3 at 19.2<log N_HI<21 while showing weaker evolution at 17.8–19.2, and that TNG50 overpredicts extended low-column HI around Milky-Way-like galaxies.

Significance. If the central measurement survives the completeness and representativeness concerns below, this would be a genuinely new and valuable anchor: the first z=0 f(N_HI) extending to Lyman-limit columns, with roughly 100 times better sensitivity than the earlier Z05 measurement at high column densities. The paper is unusually careful in several respects: it quantifies distance uncertainties, galaxy stochastic sampling, inclination bootstrapping, HIMF systematics, resolution dependence, self-absorption, and it validates the new full-HI combination procedure with mock tests. The impact-parameter constraints and the TNG50 comparison are novel and provide testable predictions for simulations and for absorber–galaxy association studies. However, the absolute normalization and the headline low-column-density claims currently rest on an uncorrected completeness effect at the quoted 17.8 limit and on an unquantified selection bias toward HI-rich systems, so the significance is real but not yet established at the claimed precision.

major comments (3)
  1. [§4.1–§4.2, Table 3] Equation (1) sums A_i(log N_HI) over galaxies with no completeness term, yet §4.1 states that the median and 90th-percentile N_HI,lim are 10^17.8 and 10^18.0 cm^-2. At log N_HI = 17.75–17.95, roughly half (and at 17.95 still a substantial fraction) of the sample contributes zero area by construction because N_HI,lim exceeds the bin. The Table 3 entries at 17.75–17.95, the direct length incidence ℓ(10^17.8)=0.267±0.033, and the weak-evolution statement at 17.8<log N_HI<19.2 are therefore lower limits, not complete measurements. If non-detected galaxies have similar low-column areas to detected ones, log f(N_HI) would be understated by up to ~0.3 dex, far above the quoted 0.04–0.06 dex errors. The statement in §5 that the points below the dashed line are 'less reliable' is not a substitute for a completeness correction. The authors should either add an explicit completeness weighting as a
  2. [§2.4, §4.4.1, §6.3.3] The HIMF-weighted construction assumes that the measured A_i(M_HI) are representative of all galaxies at fixed HI mass. Both surveys are explicitly biased toward HI-rich, star-forming galaxies: FEASTS selects f_HI>50 Jy km/s and MHONGOOSE targets star-forming systems. The error budget in §4.3 quantifies stochastic sampling among the observed galaxies but not selection against HI-poor galaxies at fixed M_HI. If HI-rich galaxies have more extended low-column HI, the absolute f(N_HI), the inferred evolution relative to z~3, and the impact-parameter distributions are all biased in a direction not captured by the quoted errors, and the shift could exceed the 0.075 dex HIMF systematic. The paper acknowledges the bias in §2.4 and gives an upper-limit interpretation in §4.4.1, but the central claim of a cosmic z=0 f(N_HI) requires either a quantitative correction or a clear statement that the re
  3. [§6.2.1, §6.2] The quoted covering fraction of ~0.7 and the inference f_cloud = 0.675±0.096 rest on integrating the best-fit Schechter function below the reliable limit to log N_HI = 17.5. The paper's own Table 3 shows a flattening below log N_HI = 17.8, and while §6.2.1 considers a forced-flattening test, the quoted uncertainty on f_cloud does not propagate the extrapolation uncertainty. Because the abstract lifts out 'a covering fraction of ~0.7', the extrapolation-dependent nature of this number should be quantified in the error budget or the claim should be reframed as an extrapolation-based estimate rather than a direct measurement.
minor comments (3)
  1. [§2.4 vs §7] The main sample is defined in §2.4 as 40 FEASTS + 30 MHONGOOSE = 70 galaxies, but the Summary in §7 says 'a sample of 65 galaxies'. Please reconcile.
  2. [Appendix A, Table 2] The text in §2.2.5 says the final FEASTS sample has 40 galaxies, while the Appendix text introducing Table 2 says 'the finally analyzed FEASTS sample of 35 galaxies'. The table caption also states 40 galaxies. This inconsistency should be fixed.
  3. [Table 3] The table's first bin is centered at log N_HI = 17.75 rather than at 17.8, and the abstract states the limit as 10^17.8. Please clarify whether the quoted limit is the first bin center, the bin edge, or the median N_HI,lim, and define the binning consistently.

Circularity Check

0 steps flagged

No significant circularity: central f(N_HI) is an image-based measurement weighted by an external HIMF.

full rationale

The central derivation, Eq. (1), sums pixel areas from HI images weighted by the external Guo et al. (2023) HIMF. The HIMF is not derived from the target f(N_HI) and is independently measured from ALFALFA; the paper even quantifies the sensitivity by re-deriving f with the Zwaan et al. (2003) HIMF, finding a constant 0.075 dex offset (Sec. 4.3.4). No equation reduces to its own input. The length-incidence and f_cov numbers are integrals/ratios of the measured f and external LLS compilations, not fits to those compilations. The TNG50 comparison uses an external simulation with mock-observation post-processing (Lin et al. 2025); even though the mock pipeline is from the same team, the simulation prediction is not an input to the f(N_HI) construction. Self-citations to prior FEASTS papers (Wang et al. 2024a, 2025; Huang et al. 2025) provide imaging/calibration procedures and scaling relations; none of them assumes the z=0 f(N_HI) being derived. The acknowledged limitations — HI-rich sample bias (Sec. 2.4), 50% completeness at log N=17.8 (Sec. 4.1), and the assumption that HI-poor MW-like galaxies follow the same N_HI distribution (Sec. 6.3.3) — are accuracy/robustness concerns, not circularity. Therefore no load-bearing step reduces by construction; score 0.

Axiom & Free-Parameter Ledger

5 free parameters · 8 axioms · 0 invented entities

No new physical entities are introduced. The central result is an observational measurement whose normalization depends on the externally fitted HIMF and on the assumption that the HI-rich sample is representative within M_HI bins. The Schechter fit parameters are additional fitted quantities used for extrapolation and for the derived length incidence and covering fraction.

free parameters (5)
  • Schechter function normalization log f* = -1.754 (+0.036/-0.037)
    Fitted to the measured f(N_HI) over log N_HI 17.8-22 (Section 5, Table 1); used to compute integrated length incidence and covering fraction.
  • Schechter function slope beta = 1.150 (+0.016/-0.016)
    Fitted to the measured f(N_HI) and used for the extrapolated length incidence below 17.8 in Section 6.2.
  • Schechter break column density log N*_HI = 21.26 (+0.02/-0.02)
    Fitted to the measured f(N_HI) at the high-column-density turnover.
  • Variance-underestimation parameter log f = -5.49 (+0.13/-0.12)
    Fitted in the emcee likelihood to absorb underestimated data variance; not physically meaningful but part of the model.
  • Adopted HIMF normalization/shape (Guo et al. 2023) = External fit to ALFALFA data
    The absolute normalization of f(N_HI) is proportional to the assumed HI mass function. The paper shows switching to the Zwaan et al. (2003) HIMF shifts f(N_HI) by ~0.075 dex (Section 4.3.4).
axioms (8)
  • domain assumption Within each 0.3-dex M_HI bin, the observed galaxies are representative of the full galaxy population at that M_HI; the psi/omega weighting recovers the cosmic f(N_HI).
    Stated as a bias in Section 2.4 ('Both samples are biased toward highly star-forming and HI-rich galaxies') and discussed as upper limits in Section 4.4.1; the weighting only corrects between bins, not within bins.
  • domain assumption 21-cm emission is optically thin for log N_HI < 21, so column densities derived from moment-0 images are accurate in the LLS regime.
    Adopted in Section 4.3.3 with a 'sandwich' model sanity check showing <0.03 dex effects below log N_HI=21.
  • domain assumption The 1-kpc smoothed column-density distribution can be compared to pc-scale quasar absorption statistics only after accounting for the sub-kpc cloud covering fraction f_cloud <= 1.
    Explicitly used in Sections 6.1 and 6.2.1 to interpret the z=0 vs z>=3 comparison and to infer f_cloud~0.7.
  • domain assumption The NUM HIMF predictions (Guo et al. 2023) describe the z>0 galaxy population used to extrapolate the z=0 length incidence.
    Section 6.2.1 uses NUM HIMFs at different redshifts; the paper acknowledges this as one of three possible explanations for the 1.48x discrepancy.
  • domain assumption The stellar-mass-to-halo-mass relation of Behroozi et al. (2019) provides unbiased r200 estimates for Milky-Way-like galaxies.
    Used in Section 6.3.2 to normalize impact parameters and to derive the covering fraction within the virial radius; uncertainty quoted as ~0.1 dex.
  • domain assumption The r001-M_HI relation (Wang et al. 2025) holds for HI-poor galaxies when the MW-like covering fraction is corrected from HI-rich FEASTS galaxies to the general population.
    Section 6.3.3 uses this relation to shift f_cov by ~0.8 dex; the paper explicitly awaits expansion to low-HI-richness systems to confirm.
  • ad hoc to paper The FAST beam model and observing simulator used in the new full-HI combination procedure faithfully reproduce the true beam response.
    Section 3.1.3 and Appendix B rely on mock tests rather than direct ground-truth observations; residual uncertainties are quoted as ~0.04 dex.
  • ad hoc to paper Extrapolating the best-fit Schechter function below the reliable limit to log N_HI=17.5 is valid for computing ell(>17.5).
    Section 6.2.1 extrapolates the fit below the 50% completeness limit and notes that forcing flattening at 17.8 reduces the inferred gap by only 16%.

pith-pipeline@v1.3.0-alltime-deepseek · 38605 in / 16234 out tokens · 153279 ms · 2026-08-02T19:17:37.592080+00:00 · methodology

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read the original abstract

We present the first $z=0$ HI column density distribution function, $f(N_\mathrm{HI})$, extending down to $\log (N_\mathrm{HI}/\mathrm{cm}^{-2})=17.8$. This was derived from high-sensitivity 21-cm emission-line imaging at $\sim$1 kpc resolution. At high-column-densities (19.8$< \log (N_\mathrm{HI}/\mathrm{cm}^{-2}) <$21.3), our results align with earlier $z=0$ studies but benefit from 100 times greater sensitivity. Comparisons with $z\sim3$ quasar absorption-line studies reveal that $f(N_\mathrm{HI})$ at $z=0$ is systematically lower by 0.1-0.4 dex for $19.2< \log (N_\mathrm{HI}/\mathrm{cm}^{-2}) <21$. However, the distributions become comparable at $17.8< \log (N_\mathrm{HI}/\mathrm{cm}^{-2}) <19.2$, suggesting weak evolution in this regime. Extrapolating the length incidence ($\mathrm{d}N/\mathrm{d}X$) for $\log (N_\mathrm{HI}/\mathrm{cm}^{-2}) >17.5$ implies a covering fraction ($f_\mathrm{cov}$) of $\sim0.7$ within 1-kpc-scale HI-detected pixels at $z=0$. Notably, for $17.8< \log (N_\mathrm{HI}/\mathrm{cm}^{-2}) <20$, impact parameters at a given $N_\mathrm{HI}$ are significantly lower than previous $z\sim0$ absorption-line results and TNG50 simulation predictions. This discrepancy indicates challenges in identifying galaxy counterparts for absorbers and in recovering low-column-density HI within cosmological simulations. Finally, we derive a covering fraction of 0.006 for $\log (N_\mathrm{HI}/\mathrm{cm}^{-2}) >17.8$ gas within the virial radius around Milky-Way-like galaxies. These findings provide new constraints on the baryonic flows and gaseous dynamics governing galaxy evolution.

Figures

Figures reproduced from arXiv: 2603.02670 by C\'eline P\'eroux, Claudia del P. Lagos, Di Li, D. Kleiner, Dong Yang, Fabian Walter, Fangxiong Zhong, F. M. Maccagni, Freeke van de Voort, George Heald, Hong Guo, J. Healy, Jing Wang, Kentaro Nagamine, Lister Staveley-Smith, Luis C. Ho, Peter Kamphuis, Qifeng Huang, Simon Weng, Siqi Liu, Siwei Zou, W.J.G. de Blok, Xinkai Chen, Xuchen Lin, Ze-zhong Liang, Zherong Su, Zhijie Qu.

Figure 1
Figure 1. Figure 1: The location of the final sample in space of MHI or SFR versus M∗. The solid and dashed lines in the left panel are for the star forming main sequence (SFMS) and scatter (Saintonge et al. 2016), and those in the right are for the median relation and scatter of galaxies on the SFMS (Catinella et al. 2018). The squares, diamonds, and downward triangles plot the FEASTS sample for which the interferometric dat… view at source ↗
Figure 2
Figure 2. Figure 2: An atlas of column density maps for galaxies in the FEASTS sample. For each galaxy, from left to right, we display the column density maps from the FAST data, the interferometric data, the combined full-HI image, and the combined and deblended full-HI image, respectively. we smooth the higher-resolution image to the resolution of the lower-resolution one, and subtract it from the latter. This difference im… view at source ↗
Figure 3
Figure 3. Figure 3: An atlas of column density maps for galaxies in the MHONGOOSE sample. For each galaxy, we display the column density maps from the r10 t00 data and the combined full-HI im￾age. constructed with the main sample is 50%-complete down to 1017.8 cm−2 at ∼1-kpc resolution. In order to accurately construct f(NHI), the area counts of each NHI should be statistically large, the images should spa￾tially resolve the … view at source ↗
Figure 4
Figure 4. Figure 4: Properties of the main sample that are most relevant for f(NHI) constructions. Panels a to f show the number distributions of galaxies in properties including image physical resolution (beam major axis in unit of kpc), image HI column density limit, the number of beam elements for log(NHI/cm−2 ) > 18, the number of beam elements for log(NHI/cm−2 ) > 20, the HI mass, and the galactic axis ratio. The distrib… view at source ↗
Figure 6
Figure 6. Figure 6: Systematical shifts of f(NHI) due to different procedures of producing the full-HI images. Curves plot difference in f(NHI) between full-HI mock images produced with different procedures. The f(NHI) from images process with the fiducial procedure is com￾pared with true answer: Mock(measure)-Mock(true). The f(NHI) from FEASTS images processed with the old procedure is com￾pared with that of the new method: … view at source ↗
Figure 5
Figure 5. Figure 5: Systematic error estimation for f(NHI). Panel a: dif￾ferent errors as a function of log(NHI/cm−2 ). Three types of er￾rors are considered, due to the stochastic sampling of galaxies (blue upward triangles), due to stochastic inclusion of highly inclined galaxies (orange downward triangles), and distance errors (green crosses). The vertical line marks log(NHI/cm−2 ) = 21.3, above which the errors increase d… view at source ↗
Figure 7
Figure 7. Figure 7: Systematical uncertainties of f(NHI) related to 21-cm self-absorption and HIMF systematics. The blue curve plots the difference between assuming the Zwaan et al. (2003, Z03) HIMF and the fiducial Guo et al. (2023, G23) HIMF. The orange curve plots the difference between correcting and not correcting for self￾absorption of the HI 21-cm emission line. The error bars (shaded areas) are the propagation of f(NH… view at source ↗
Figure 8
Figure 8. Figure 8: Systematical shifts of f(NHI) due to different samples and resolutions. Curves plot difference in f(NHI) between different datasets, with details in section 4.4. The vertical dashed lines mark the median limiting log(NHI/cm−2 ) of 17.8. Panel a: differences in f(NHI) between different samples with the same resolution. The main sample (MS), the FEASTS sample (FST), and the MHON￾GOOSE sample (MGS) are compar… view at source ↗
Figure 9
Figure 9. Figure 9: The HI column density distribution function f(NHI) to the level of 1017.8 cm−2 for z = 0, and its comparison to literature results. In each set, the lower panel shows the f(NHI), and the upper panel the difference of best-fit models or literature results to the f(NHI) derived in this study; the vertical dashed line mark the median NHI,lim of the main sample. Panel a: the direct derivation of f(NHI) based o… view at source ↗
Figure 10
Figure 10. Figure 10: Length incidence for log(NHI/cm−2 ) > 17.5 (optical depth τ > 2). The red and blue dots are calculations based on z = 0 observations in this study. The direct z = 0 calculation (red dots) is based on cumulating the best-fit Schechter function of this study. The extrapolations (blue dots) are based on HI images in the main sample at z = 0, but HIMFs are the NUM predictions at different redshifts (Guo et al… view at source ↗
Figure 11
Figure 11. Figure 11: Probabilities of detecting HI in the space of NHI and impact parameter b. Panel a: the colored map and associated contours show 2D cumulative probabilities of detecting HI in the space of impact parameter b versus log(NHI/cm−2 ). Panel b: the colored map and associated contours show cumulative conditional probabilities of detecting HI below b as a function of NHI. The probabilities are evaluated along dif… view at source ↗
Figure 12
Figure 12. Figure 12: Panel a: the offsets in f(NHI) between TNG50 predictions and observations for MW-like galaxies. The MW-like galaxies are selected from the FEASTS sample, and the TNG50 sample is a property matched control sample for the FEASTS sample (Lin et al. 2025). Panels b and c: probabilities of HI detections in the 2D space of NHI and impact parameter b. Similar to [PITH_FULL_IMAGE:figures/full_fig_p020_12.png] view at source ↗
Figure 13
Figure 13. Figure 13: Cumulative conditional probabilities of impact parameters b given NHI, as a function of NHI in different normalizations of b . The probabilities are evaluated along b for a given NHI, and the accumulation starts from the highest probability density toward the lower ones. From panel a to c, the normalizations used are the physical unit kpc, the virial radius r200, the 0.01M⊙ pc−2 -HI radius r001, and the 1… view at source ↗
Figure 14
Figure 14. Figure 14: Depth and resolution of interferometry data for galaxies in the initial FEASTS+interferometric sample. The circles, upward triangles, and downward triangles are for data from the HALOGAS sample, the THINGS sample, and other VLA observed data. The left panel is a function of angular resolution; the right panel shows physical resolution. The two dashed vertical lines in the right panel enclose the range sel… view at source ↗
Figure 15
Figure 15. Figure 15: Example mock test galaxies, for which the input interferometric data are from the VLA. The left and right two columns are for two mock galaxies respectively. Please refer to Appendix B for detailed explanation of the image titles. Guo, H., Wang, J., Jones, M. G., & Behroozi, P. 2023, ApJ, 955, 57 Heald, G., Jozsa, G., Serra, P., et al. 2011, A&A, 526, A118 ´ Hoffman, G. L., Dowell, J., Haynes, M. P., & Gi… view at source ↗
Figure 16
Figure 16. Figure 16: Example mock test galaxies. Similar to [PITH_FULL_IMAGE:figures/full_fig_p028_16.png] view at source ↗
Figure 17
Figure 17. Figure 17: Schechter function fitting for the f(NHI) measurements. The parameters lgN ∗ HI, β and log f ∗ together form the Schechter function displayed in Eqation 2. The f of log f describes the fractional level of variance underestimation. It plots all the one and two dimensional projections of the posterior probability distributions of parameters, with prior distributions described in the main text (Section 5). T… view at source ↗

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