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arxiv: 2606.25577 · v1 · pith:ARR4E7MZnew · submitted 2026-06-24 · 🌌 astro-ph.GA

The OTELO Survey: The main sequence of low-mass galaxies

Bernab\'e Cedr\'es , Jordi Cepa , Carmen P. Padilla--Torres , \'Angel Bongiovanni , Miguel Cervi\~no , Jos\'e A. de Diego , Jakub Nadolny , Simon B. De Daniloff
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Mauro Gonz\'alez--Otero Monica I. Rodr\'iguez Jes\'us Gallego Mirjana Povi\'c Maritza A. Lara--L\'opez J. Ignacio Gonz\'alez--Serrano Miguel S\'anchez--Portal Ana Mar\'ia P\'erez--Garc\'ia Ricardo P\'erez--Mart\'inez Emilio J. Alfaro
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Pith reviewed 2026-06-25 20:47 UTC · model grok-4.3

classification 🌌 astro-ph.GA
keywords main sequencelow-mass galaxiesstar formation ratestellar massemission line galaxiesspectral energy distribution fittingredshift
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The pith

The main sequence of star formation rate and stellar mass for low-mass galaxies agrees with literature values except for a higher turnover mass at all redshifts.

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

This paper investigates the main sequence relating star formation rate to stellar mass in low-mass emission-line galaxies at redshifts of approximately 0.38, 0.83, and 1.43. Stellar masses and star formation rates are obtained through spectral energy distribution fitting, and the sequence is constructed both for the full sample and in mass bins. The derived main sequence matches previous results well in the low-mass regime, suggesting the relation is consistent even in this less-explored domain, although the turnover mass is higher than reported elsewhere, possibly owing to differences in selection and fitting approaches.

Core claim

When comparing the main sequence obtained for the sample of low-mass emission line galaxies with those from the bibliography, very good agreement is found in general. The main sequence can be considered almost the same for the relatively unexplored regime of low-mass galaxies, although the turnover mass is higher for all redshifts compared with the ones from the literature, an effect suggested to arise from the different methods and samples used.

What carries the argument

The main sequence parameterized by a turnover mass and the slope of the low-mass regime, derived from fitting spectral energy distributions of emission line galaxies to obtain stellar masses and total infrared luminosities as proxies for star formation rates.

If this is right

  • 100 percent of H-alpha emitters and about 90 percent of [OIII] and [OII] emitters are low-mass galaxies below 10^10 solar masses.
  • The main sequence holds similarly across the three redshift regimes for low-mass galaxies.
  • The color-magnitude selection method leaves out a significant number of emission line galaxies.
  • The sample contains few luminous infrared galaxies and no ultra-luminous infrared galaxies.

Where Pith is reading between the lines

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

  • The higher turnover mass may indicate that low-mass galaxies have different dust attenuation or star formation properties not captured in prior samples.
  • Improving infrared constraints could refine the star formation rates and potentially adjust the main sequence parameters.
  • Broader application of the color-magnitude selection might reveal a more complete main sequence at these redshifts.

Load-bearing premise

The total infrared luminosity, and therefore the star formation rate, can be reliably recovered from spectral energy distribution fits that lack direct infrared constraints.

What would settle it

Independent measurements of infrared emission from the same set of galaxies that produce star formation rates differing from the SED-derived values would show whether the main sequence parameters are accurate.

Figures

Figures reproduced from arXiv: 2606.25577 by Ana Mar\'ia P\'erez--Garc\'ia, \'Angel Bongiovanni, Bernab\'e Cedr\'es, Carmen P. Padilla--Torres, Emilio J. Alfaro, Jakub Nadolny, Jes\'us Gallego, J. Ignacio Gonz\'alez--Serrano, Jordi Cepa, Jos\'e A. de Diego, Maritza A. Lara--L\'opez, Mauro Gonz\'alez--Otero, Miguel Cervi\~no, Miguel S\'anchez--Portal, Mirjana Povi\'c, Monica I. Rodr\'iguez, Ricardo P\'erez--Mart\'inez, Simon B. De Daniloff.

Figure 1
Figure 1. Figure 1: Z-OTELOAB colour–magnitude diagram. The filled grey contours represent the density of all the OTELO sources. The Hα, [O iii], and [O ii] emitters are presented by green, blue, and orange dots, respectively. The dash-dotted black line is the 2Σ isoline of colour significance from Bongiovanni et al. (2019). to a starburst or a star-forming galaxy. Taking all this into ac￾count, we may assume that all subsets… view at source ↗
Figure 4
Figure 4. Figure 4: Histogram of the logarithm of the stellar mass obtained [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Difference between the logarithm of S FRinstantaneous and the logarithm of S FRLTIR as a function of the logarithm of S FRLTIR for all the emitters in the sample. forbidden lines have, as in [O ii] (e.g. Kewley et al. 2004) or [O iii] (e.g. Suzuki et al. 2016), been proposed as a SFR esti￾mate, although, since such lines do not scale linearly with the ionizing flux of OB stars (Villaverde et al. 2010), ext… view at source ↗
Figure 7
Figure 7. Figure 7: Histogram of the logarithm of the SFR from CIGALE for [PITH_FULL_IMAGE:figures/full_fig_p005_7.png] view at source ↗
Figure 9
Figure 9. Figure 9: Fitted MS for the different emitters in the sample fol￾lowing eq. 1. The dotted green line, dashed blue line, and solid orange line represent the fit for Hα, [O iii], and [O ii] emitters, respectively. The shaded areas represents the propagation of 1σ uncertainties [PITH_FULL_IMAGE:figures/full_fig_p006_9.png] view at source ↗
Figure 10
Figure 10. Figure 10: Slope of the low-mass regime, γ, as a function of the age of the Universe. Symbols are indicated in the legend. (2023). The results are summarised in table 3, where we have also included the value of the age of the Universe used in each subsample. In [PITH_FULL_IMAGE:figures/full_fig_p006_10.png] view at source ↗
Figure 11
Figure 11. Figure 11: Turnover mass as a function of the age of the Universe. [PITH_FULL_IMAGE:figures/full_fig_p007_11.png] view at source ↗
Figure 12
Figure 12. Figure 12: Reduced χ 2 of the fit as a function of the number of bins for each emitter. Symbols are indicated in the legend. The horizontal dash-dotted line represents a value of χ 2 = 1 [PITH_FULL_IMAGE:figures/full_fig_p008_12.png] view at source ↗
Figure 13
Figure 13. Figure 13: Binned MS for the emitters. Symbols are indicated in [PITH_FULL_IMAGE:figures/full_fig_p008_13.png] view at source ↗
read the original abstract

This paper describes the relationship between the star formation rate and the stellar mass, the so-called main sequence (MS), of low-mass galaxies at three different redshifts from the OTELO survey. In particular, we study Halpha at z=0.38, [OIII] at z=0.83, and [OII] at z=1.43 emission line galaxies (ELGs). This is done to characterise the properties of low-mass ELGs. We fitted the spectral energy distribution (SED) of each emitter and obtained the stellar masses, the total infrared luminosity, and the star formation rate. We found that 100% of the Halpha emitters and about 90% of the [OIII] and [OII] emitters are low-mass galaxies (< 1E10M_sun). We generated a MS for each redshift regime, employing all galaxies and binning them in stellar mass. We obtained the parameters of the fit (turnover mass and slope of the low-mass regime) and compared them to results from the literature. We found that the colour-magnitude method employed to select ELGs leaves out a significant number of them. We also found that the whole sample contains few luminous infrared galaxies and no ultra-luminous infrared galaxies. We also found that the lack of infrared constraints in the input SEDs may generate problems when determining the total infrared luminosity. When comparing the MS obtained for our sample of low-mass ELGs with those from the bibliography, we found, in general, very good agreement. We can consider the MS to be almost the same for the relatively unexplored regime of low-mass galaxies. However, the turnover mass obtained by this work is higher for all redshifts compared with the ones from the literature. We suggest that this is an effect of the different methods and samples used in the generation of the MS compared to those of the bibliography.

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

3 major / 2 minor

Summary. This manuscript analyzes the star-formation main sequence (MS) for low-mass emission-line galaxies (ELGs) selected via the OTELO survey at three redshift slices (Hα at z=0.38, [OIII] at z=0.83, [OII] at z=1.43). SED fits without direct IR photometry yield stellar masses and total IR luminosities (hence SFRs); the authors report that 90–100% of the sample lies below 10^10 M⊙, construct binned MS relations, and fit for turnover mass and low-mass slope. They claim general agreement with literature MS relations in the low-mass regime but systematically higher turnover masses at all redshifts, attributing the offset to differences in methods and samples.

Significance. The work targets the sparsely sampled low-mass end of the MS, which is relevant for galaxy evolution models. If the higher turnover masses prove robust after addressing SFR uncertainties, the result would highlight possible selection or methodological effects in prior studies. The manuscript already notes the absence of luminous/ultra-luminous IR galaxies and incompleteness from the colour-magnitude selection, which are useful contextual findings.

major comments (3)
  1. [Abstract] Abstract: turnover masses are reported as 'higher for all redshifts' with no numerical values, uncertainties, or tabulated comparison to specific literature fits (e.g., no error bars or baseline sample listed), preventing quantitative assessment of the central claim.
  2. [SED fitting and SFR derivation] The section describing SED fitting and SFR derivation: the text explicitly states that 'the lack of infrared constraints in the input SEDs may generate problems when determining the total infrared luminosity,' yet no quantitative test (e.g., comparison of TIR-derived SFRs against any available IR photometry or mock tests) is provided. Because the turnover mass is the bend point fitted to the high-mass SFRs, any systematic offset or scatter in these SFRs directly shifts the fitted turnover location and undermines the claim that the turnover is higher than literature values.
  3. [MS fitting and comparison] The MS fitting and comparison section: no explicit baseline comparison sample is defined, and the binned MS fits lack reported uncertainties on the turnover mass or low-mass slope parameters, making it impossible to judge whether the reported offset is statistically significant or driven by the acknowledged selection incompleteness.
minor comments (2)
  1. [Abstract] The abstract states 'We also found that the colour-magnitude method employed to select ELGs leaves out a significant number of them' without quantifying the fraction or showing the impact on the MS parameters.
  2. [Methods] Notation for turnover mass and low-mass slope should be defined once with symbols and units when first introduced in the fitting description.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for their constructive comments. We address each major comment below and will revise the manuscript to strengthen quantitative aspects and clarify limitations.

read point-by-point responses

  1. Referee: [Abstract] Abstract: turnover masses are reported as 'higher for all redshifts' with no numerical values, uncertainties, or tabulated comparison to specific literature fits (e.g., no error bars or baseline sample listed), preventing quantitative assessment of the central claim.

    Authors: We agree that the abstract would benefit from including specific numerical values for the turnover masses, their uncertainties, and explicit comparisons to literature fits. We will revise the abstract to incorporate these details for quantitative assessment. revision: yes

  2. Referee: [SED fitting and SFR derivation] The section describing SED fitting and SFR derivation: the text explicitly states that 'the lack of infrared constraints in the input SEDs may generate problems when determining the total infrared luminosity,' yet no quantitative test (e.g., comparison of TIR-derived SFRs against any available IR photometry or mock tests) is provided. Because the turnover mass is the bend point fitted to the high-mass SFRs, any systematic offset or scatter in these SFRs directly shifts the fitted turnover location and undermines the claim that the turnover is higher than literature values.

    Authors: We acknowledge this limitation, which is already noted in the manuscript. No IR photometry is available for the sample, so quantitative tests or mocks cannot be performed. The emission-line selected, low-mass sample may reduce the impact, but we recognize the potential effect on high-mass SFRs. We will expand the discussion to address possible systematics on the turnover mass as a caveat. revision: partial

  3. Referee: [MS fitting and comparison] The MS fitting and comparison section: no explicit baseline comparison sample is defined, and the binned MS fits lack reported uncertainties on the turnover mass or low-mass slope parameters, making it impossible to judge whether the reported offset is statistically significant or driven by the acknowledged selection incompleteness.

    Authors: We agree and will revise the section to explicitly define the comparison literature samples and report uncertainties on the turnover mass and slope parameters. We already discuss selection incompleteness and will add further evaluation of its potential effect on the results. revision: yes

Circularity Check

0 steps flagged

No significant circularity in MS parameter derivation or literature comparison

full rationale

The paper derives MS parameters (turnover mass, low-mass slope) by direct fitting to OTELO SED-derived stellar masses and SFRs at each redshift, then compares the resulting curves to external literature values. No load-bearing self-citations appear in the provided text, and the higher-turnover claim is presented as an empirical outcome of the new sample rather than a quantity forced by prior fits or definitions. The derivation chain remains independent of its own inputs and does not reduce by construction to any fitted parameter or self-referential premise.

Axiom & Free-Parameter Ledger

2 free parameters · 2 axioms · 0 invented entities

The central claim rests on standard assumptions of SED fitting (IMF, dust attenuation law, template libraries) and on the completeness of the color-magnitude emission-line selection; the turnover mass and slope are free parameters fitted to the binned data.

free parameters (2)
  • turnover mass (per redshift bin)
    Fitted parameter of the broken power-law or similar functional form used to describe the main sequence; reported as higher than literature values.
  • low-mass slope (per redshift bin)
    Fitted parameter describing the relation below the turnover; compared to literature but no numerical values given in abstract.
axioms (2)
  • domain assumption SED fitting yields reliable stellar masses and SFRs even without direct IR photometry
    Invoked when deriving SFR from total IR luminosity; the paper itself flags that lack of IR constraints may generate problems.
  • domain assumption Color-magnitude selection of ELGs is sufficiently complete for the low-mass regime
    The paper notes that this method leaves out a significant number of emitters, yet still uses the selected sample to define the MS.

pith-pipeline@v0.9.1-grok · 6010 in / 1702 out tokens · 30299 ms · 2026-06-25T20:47:27.111895+00:00 · methodology

discussion (0)

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