MIGHTEE-HI: The star-forming properties of HI selected galaxies
Pith reviewed 2026-05-23 08:29 UTC · model grok-4.3
The pith
Galaxies with higher HI-to-stellar mass ratios form their stars later and deplete gas more slowly than massive galaxies.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
Analysis of the MIGHTEE-HI Early Science sample shows a strong positive correlation between HI-to-stellar mass ratio and time of formation together with an inverse correlation between stellar mass and time of formation, independent of the adopted star-formation history. Galaxies with lower stellar masses and higher HI-to-stellar mass ratios display longer gas depletion timescales, consistent with less efficient star formation in shallower potential wells. No significant link appears between peak star-formation activity and filament proximity, though the two galaxies within 1 Mpc of a filament exhibit short depletion times and misaligned spins.
What carries the argument
Correlations between HI-to-stellar mass ratio, formation timescale, stellar mass, and gas depletion time derived from photometric and HI data for the 187 galaxies.
If this is right
- Lower-mass, gas-rich galaxies require more time to convert their atomic gas into stars than higher-mass systems.
- Gas depletion proceeds more efficiently in galaxies that have already assembled larger stellar masses.
- Internal structural properties such as potential-well depth can set depletion timescales even when large-scale environment shows little direct influence.
- Spin-filament misalignment may appear only in the rare cases where a galaxy lies very close to a filament.
Where Pith is reading between the lines
- The mass-dependent depletion pattern could be tested by comparing depletion times measured in isolated versus group environments at fixed stellar mass.
- If the formation-time correlation survives in larger samples it would constrain the redshift at which low-mass galaxies begin to convert their HI reservoirs efficiently.
- Models that tie star-formation efficiency solely to total gas mass would need adjustment to reproduce longer depletion times at high HI fractions.
Load-bearing premise
The star-formation histories derived for the sample galaxies are not systematically biased by survey selection, dust effects, or the specific modeling choices used to convert photometry and HI measurements into formation parameters.
What would settle it
Deriving star-formation histories for an independent, volume-limited sample of HI-detected galaxies using an entirely different set of stellar-population models and finding no correlation between HI-to-stellar mass ratio and formation time.
read the original abstract
The interplay between atomic gas, the star-formation history of a galaxy and its environment are intrinsically linked, and we need to decouple these dependencies to understand their role in galaxy formation and evolution. In this paper, we analyse the star formation histories (SFHs) of 187 galaxies from the MIGHTEE-HI Survey Early Science Release data, focusing on the relationships between HI properties and star formation. A strong correlation emerges between a galaxy's HI-to-stellar mass ratio and the time of formation, alongside an inverse correlation between stellar mass and time of formation, regardless of the inferred SFH. Additionally, galaxies with lower stellar masses and higher HI-to-stellar mass ratios exhibit longer gas depletion times compared to more massive galaxies, which appear to have depleted their gas and formed stars more efficiently. This suggests that smaller, gas-rich galaxies have higher depletion times due to shallower potential wells and less efficient star formation. Furthermore, we explore the connection between spin-filament alignment and HI content. We find no significant correlation between peak star formation activity and proximity to filaments. However, we do find that the two galaxies in our sample within 1 Mpc of a filament have very low gas-depletion timescales and have their spin axis misaligned with the filament, suggestive of a link between the galaxy properties and proximity to a filament.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper analyzes star-formation histories (SFHs) of 187 HI-selected galaxies from the MIGHTEE-HI Early Science Release. It reports a strong correlation between HI-to-stellar mass ratio and galaxy formation time, an inverse correlation between stellar mass and formation time (independent of SFH parametrization), longer gas depletion times in lower-mass high-HI-ratio systems, and no significant link between peak star-formation activity and filament proximity (with two near-filament galaxies showing low depletion times and misaligned spins).
Significance. If the correlations prove robust after bias checks, the results would supply direct observational constraints on how atomic gas content modulates star-formation timing and efficiency as a function of stellar mass, offering testable inputs for semi-analytic models and hydrodynamical simulations of galaxy evolution.
major comments (3)
- [Abstract] Abstract: the headline correlations are presented without error bars, completeness corrections, or any statistical significance tests (e.g., Spearman rank or bootstrap p-values), so the strength of the claimed relationships cannot be evaluated from the provided information.
- [SFH inference] SFH inference section: the central claims rest on formation times derived from photometry plus HI data, yet no quantitative tests are described for sensitivity to the HI selection function, dust-attenuation assumptions, or SFH parametrization/priors; if low-mass high-HI-ratio galaxies are preferentially assigned later formation times under the adopted modeling, the reported trends may be partly artifactual.
- [Results (depletion times)] Results on depletion times: the interpretation that lower-mass galaxies exhibit longer depletion times 'due to shallower potential wells and less efficient star formation' is stated without supporting dynamical modeling or comparison to control samples that isolate the potential-well effect from other variables.
minor comments (1)
- [Abstract] Abstract: the phrase 'regardless of the inferred SFH' is used without stating how many distinct SFH parametrizations were tested or what the quantitative variation in formation times was across them.
Simulated Author's Rebuttal
We thank the referee for their constructive and detailed report. We respond point-by-point to the major comments below, indicating where revisions will be incorporated.
read point-by-point responses
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Referee: [Abstract] Abstract: the headline correlations are presented without error bars, completeness corrections, or any statistical significance tests (e.g., Spearman rank or bootstrap p-values), so the strength of the claimed relationships cannot be evaluated from the provided information.
Authors: We agree that the abstract would benefit from explicit statistical measures. The main text presents the correlations with uncertainties in the figures and discusses completeness in the sample section. In the revised version we will add the Spearman rank coefficients and p-values for the key relations to the abstract, along with a brief note on completeness. revision: yes
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Referee: [SFH inference] SFH inference section: the central claims rest on formation times derived from photometry plus HI data, yet no quantitative tests are described for sensitivity to the HI selection function, dust-attenuation assumptions, or SFH parametrization/priors; if low-mass high-HI-ratio galaxies are preferentially assigned later formation times under the adopted modeling, the reported trends may be partly artifactual.
Authors: The manuscript already shows that the stellar-mass versus formation-time trend is independent of SFH parametrization. We will add quantitative tests varying dust-attenuation assumptions and priors. The sample is defined by HI selection, and selection effects are discussed in the methods; a full end-to-end simulation of the selection function on formation times is beyond current scope and will be noted as a limitation. revision: partial
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Referee: [Results (depletion times)] Results on depletion times: the interpretation that lower-mass galaxies exhibit longer depletion times 'due to shallower potential wells and less efficient star formation' is stated without supporting dynamical modeling or comparison to control samples that isolate the potential-well effect from other variables.
Authors: We accept that the physical interpretation is qualitative. We will revise the relevant paragraph to present the explanation as a plausible interpretation consistent with the trends and with existing literature, rather than a direct result of new modeling, and will add references to supporting observational comparisons. revision: yes
Circularity Check
No circularity: paper reports direct observational correlations from survey data
full rationale
The manuscript presents empirical correlations (HI-to-stellar mass ratio vs. formation time; stellar mass vs. formation time; depletion time trends) derived from the MIGHTEE-HI Early Science sample of 187 galaxies. These are stated as observed relations 'regardless of the inferred SFH' with no model equations, fitted parameters renamed as predictions, self-definitional constructs, or load-bearing self-citations that reduce the central claims to inputs by construction. SFH parameters come from photometry+HI fitting against external benchmarks, but the reported results are direct data products rather than derived predictions. This matches the default expectation of a non-circular observational paper.
discussion (0)
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