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arxiv: 2605.24264 · v1 · pith:73TILYYZnew · submitted 2026-05-22 · 🌌 astro-ph.GA

A Redshift-based Red Selection of Dusty Star-forming Galaxies

A.J. Barger , L.L. Cowie , S.J. McKay , F.E. Bauer This is my paper

Pith reviewed 2026-06-30 14:36 UTC · model grok-4.3

classification 🌌 astro-ph.GA
keywords dusty star-forming galaxiescolor selectionJWSTALMAlittle red dotsquiescent galaxiesredshift selectionmassive galaxies
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The pith

Galaxies with rest-frame f_J/f_V > 3 at z=1.5-5.5 match most ALMA dusty star-forming sources.

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

This paper shows how a simple color selection from JWST data can efficiently pick out dusty star-forming galaxies over a broad redshift range. Galaxies at redshifts 1.5 to 5.5 that appear red in the rest-frame with a flux ratio f_J to f_V exceeding 3 account for 83 percent of the strong ALMA detections in the observed field. The method distinguishes luminous extended objects that are mainly DSFGs from fainter compact ones that are little red dots, and it also captures some quiescent galaxies at lower redshifts. The selected galaxies are typically massive, and their abundance decreases at higher redshifts beyond 5.

Core claim

The authors establish that galaxies between z=1.5 and z=5.5 with rest-frame red colors f_J/f_V > 3 correspond to dusty star-forming galaxies (DSFGs), little red dots (LRDs), and quiescent galaxies. This color selection identifies 34 of the 41 >4.5-sigma ALMA sources (83%). Luminous red sources tend to be extended and are generally DSFGs according to ALMA data, with a few quiescent galaxies at z less than 3-4 identified via U-V versus V-J diagram, while less luminous red sources are mostly compact LRDs. Neither LRDs nor quiescent galaxies are detected above 3-sigma in ALMA images. Roughly 10 percent of the DSFGs exhibit high rest-frame X-ray luminosities and are likely AGN dominated. The DSFG

What carries the argument

Redshift-based rest-frame color cut f_J/f_V > 3 applied to JWST photometry to select red galaxy populations linked to ALMA-detectable dusty star formation.

If this is right

  • The color selection recovers 83% of the bright ALMA sources.
  • Luminous extended red sources are predominantly DSFGs with high stellar masses.
  • Compact red sources correspond to LRDs without significant ALMA emission.
  • Massive red galaxies selected this way decline in number at redshifts above 5.
  • About 10% of selected DSFGs show signs of AGN activity through elevated X-ray output.

Where Pith is reading between the lines

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

  • This selection technique could be used on larger JWST imaging surveys to pre-select DSFG candidates for targeted ALMA observations.
  • The physical difference between extended DSFGs and compact LRDs may point to separate pathways in galaxy evolution.
  • Extending the method to other cluster or blank fields would test its robustness across different environments.
  • Combining this with X-ray data could help quantify the AGN fraction in dusty galaxies more broadly.

Load-bearing premise

The photometric or spectroscopic redshifts are accurate enough to correctly compute the rest-frame colors and ensure the galaxies lie within the specified redshift interval.

What would settle it

Detection of many galaxies satisfying the red color criterion but showing no ALMA continuum emission above 4.5 sigma, or conversely many strong ALMA sources that do not meet the color threshold when redshifts are known precisely.

Figures

Figures reproduced from arXiv: 2605.24264 by A.J. Barger, F.E. Bauer, L.L. Cowie, S.J. McKay.

Figure 1
Figure 1. Figure 1: Comparison of the FWHM from the Gaussian fits with the 50% enclosed light radius from the pysersic pro￾cedure of I. Pasha & T. B. Miller (2023). The latter has the PSF deconvolved. The vertical blue line shows our compact galaxy selection using FWHM, and the horizontal blue line a similar selection using the pysersic results. We show 68% confidence ranges for the pysersic results and place points that woul… view at source ↗
Figure 2
Figure 2. Figure 2: ALMA observations in the JWST UNCOVER (black contour) area. (Left) The shading shows areas covered by either DUALZ ALMA 1.2 mm (light gray) or this work’s ALMA 870 µm (medium gray). The pixel size on the image is 0. ′′467, and the total covered area is 29 arcmin2 . Sources detected only at 870 µm are shown in green, only at 1.2 mm in blue, and at both in purple. (Right) The ALMA sources overlaid on the SCU… view at source ↗
Figure 3
Figure 3. Figure 3: The ALMA sources in the UNCOVER region (open squares using the color notation of [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Demagnified X-ray fluxes for our JWST sample vs. redshift. The ALMA sources are marked in purple, and faint X-ray sources are shown at 1.4 × 10−17 erg cm−2 s −1 . The red curves show a rest-frame 8–28 keV luminosity of 1044 erg s−1 (solid) and 2.5 × 1043 erg s−1 (dashed). 2.3. X-ray We took the ACIS observations of A2744 from the Chandra X-ray Observatory archive. The total exposure time is 2.1 Ms, but eli… view at source ↗
Figure 5
Figure 5. Figure 5: Rest-frame color (J = 1.22 µm and V = 0.55 µm) vs. demagnified rest-frame luminosity at 1.22 µm for our JWST sample with Lν(1.22 µm) > 1027 erg s−1 Hz−1 in four redshift intervals (black circles). We overlay the sources with > 4.5σ ALMA detections (see [PITH_FULL_IMAGE:figures/full_fig_p006_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FWHM vs. demagnified rest-frame luminosity at 1.22 µm for our JWST sample with Lν(1.22 µm) > 1028 erg s−1 Hz−1 over the full redshift inter￾val z = 1.5–5.5 (small black dots). We mark compact sources with FWHM < 0. ′′172 with large open diamonds. We mark galaxies that satisfy our red selection (fJ /fV > 3) as fol￾lows: sources with > 4.5σ ALMA detections (see [PITH_FULL_IMAGE:figures/full_fig_p007_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: (Left) RGB image (F444W, F200W, and F150W) of an example extended red source (white circle of radius 0. ′′3). The field size is 3. ′′2. The 870 µm ALMA image of the same area is shown in the inset at the lower left. The galaxy is strongly detected with ALMA at both 870 µm and 1.2 mm. (Right) Same for an example compact red source, which is an LRD. Here the inset is from the DUALZ image, and there is no ALM… view at source ↗
Figure 8
Figure 8. Figure 8: Rest-frame U − V vs. V − J for our JWST sam￾ple with stellar masses M∗ > 1010 M⊙ and that lie in (top) the full redshift interval z = 1.5–5.5, (middle) z = 3–4 only, and (bottom) z = 4–5.5 only. We show the R. J. Williams et al. (2009) strict selection of quiescent galaxies with solid lines, and the F. Valentino et al. (2023) padded selection with dashed lines. We show sources that satisfy the strict selec… view at source ↗
Figure 9
Figure 9. Figure 9: Relative evolution of the numbers of candidate quiescent galaxies (blue), DSFGs (purple), and LRDs (red) in the redshift interval z = 1.5–5.5 vs. redshift. For the qui￾escent galaxies and DSFGs, we only show those with stellar masses M∗ > 1010 M⊙. The DSFGs show all > 3σ ALMA sources, and the quiescent galaxies correspond to the strict selection. method. This has the additional advantage that it is the met… view at source ↗
Figure 10
Figure 10. Figure 10 [PITH_FULL_IMAGE:figures/full_fig_p009_10.png] view at source ↗
Figure 12
Figure 12. Figure 12: Comparison of the redshift distribution of our JWST sample with SFR > 30 M⊙ yr−1 (purple shading) with the redshift distribution of the SCUBADive sample of J. McKinney et al. (2025) (289 DSFGs). S. J. McKay et al. (2026) used a near-complete spec￾troscopic sample of the SUPER GOODS sources from L. L. Cowie et al. (2018) to obtain a 1σ upper limit rate of 1.8% at z = 5–6, which is again consistent with the… view at source ↗
Figure 11
Figure 11. Figure 11: SFR vs. redshift for our JWST sample with (top) z = 1.5 − 5.5 and M∗ = 108 –1010 M⊙, (mid￾dle) z = 1.5 − 5.5 and M∗ > 1010 M⊙, and (bottom) z > 4 without any mass restriction. Along the top of each panel is the age in Gyr. The red line shows SFR = 30 M⊙ yr−1 . The symbols are ALMA detections—purple squares (solid for sources with > 4.5σ detections); open for > 3σ); pub￾lished LRDs—red circles; quiescent g… view at source ↗
Figure 13
Figure 13. Figure 13: Stellar mass vs. redshift for our JWST sample in the redshift interval z = 1.5–5.5. The powerfully star– forming galaxies (> 30 M⊙ yr−1 ) (red squares) and quiescent galaxies (blue diamonds) are mainly found in massive galax￾ies (M∗ > 1010 M⊙) (above the green line). in the ZFOURGE sample required large amounts of star formation at z > 5 (see also T. Nanayakkara et al. 2025). 5. SUMMARY In this paper, we … view at source ↗
read the original abstract

We use JWST observations (1.5 micron to 4.44 micron), together with complete ALMA observations (870 micron and/or 1.2 mm), of the massive lensing cluster field A2744 to show that galaxies between z=1.5 and z=5.5 with rest-frame red colors f_J/f_V > 3 correspond to dusty star-forming galaxies (DSFGs), little red dots (LRDs), and quiescent galaxies. The color selection picks out 34 of the 41 >4.5-sigma ALMA sources in the field (83%). We find that the luminous red sources are generally extended, while the less luminous red sources are almost all compact and correspond to the LRD population. We also find that the great majority of the luminous, extended red sources are DSFGs based on the ALMA data, with a small admixture of quiescent galaxies at z<3-4 that we identify based on their location in the rest-frame U-V versus V-J diagram. We do not detect any LRDs or quiescent galaxies at the >3-sigma level in the ALMA images. Roughly 10% of the DSFGs have high rest-frame X-ray luminosities and must be AGN dominated. The DSFGs and quiescent galaxies nearly all have M_star>10^{10} solar masses. These massive galaxies become rare at z>5, paralleling the fall off in the number of detected DSFGs.

Editorial analysis

A structured set of objections, weighed in public.

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

Referee Report

2 major / 1 minor

Summary. The paper uses JWST (1.5–4.44 µm) and complete ALMA (870 µm and/or 1.2 mm) observations of the A2744 lensing cluster field to argue that galaxies at 1.5 < z < 5.5 with rest-frame f_J/f_V > 3 correspond to dusty star-forming galaxies (DSFGs), little red dots (LRDs), and quiescent galaxies. The color cut recovers 34 of 41 >4.5-σ ALMA sources (83%), with luminous extended red sources mostly DSFGs, compact ones mostly LRDs, no ALMA detections of LRDs or quiescent galaxies, and ~10% of DSFGs being X-ray AGN; all such massive galaxies (M_star > 10^10 M_⊙) become rare above z ~ 5.

Significance. If robust, the result supplies an empirical, photometry-only selection that links a simple rest-frame color threshold to ALMA-detected DSFGs and related populations, offering a practical tool for identifying high-redshift massive dusty galaxies in wide JWST surveys. The direct cross-match with independent ALMA continuum detections provides concrete empirical grounding for the claimed correspondence.

major comments (2)
  1. [Abstract] Abstract: the quoted 83% recovery (34/41) and the classification into DSFGs vs. LRDs vs. quiescent galaxies both require that photometric redshifts accurately place each source inside 1.5 < z < 5.5 and correctly identify which observed JWST bands bracket rest-frame V and J. No photo-z validation (scatter, outlier fraction, or Monte-Carlo error propagation) is supplied, so it is unclear whether modest Δz/(1+z) ~ 0.05–0.15 errors near the boundaries or across the 4000 Å break would move sources in/out of the color-selected sample or change the ratio by >30%.
  2. [Abstract] Abstract: the statement that 'the great majority of the luminous, extended red sources are DSFGs' with only 'a small admixture of quiescent galaxies at z<3-4' is not accompanied by a quantitative breakdown (numbers or fractions) of how the 34 recovered ALMA sources are partitioned among the three populations, making it impossible to assess the strength of the DSFG association.
minor comments (1)
  1. The abstract refers to 'complete ALMA observations' but does not list the precise continuum depths, beam sizes, or source extraction thresholds beyond the >4.5-σ and >3-σ mentions.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their thoughtful comments, which highlight areas where the presentation can be clarified and strengthened. We address each major comment below and will revise the manuscript accordingly.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the quoted 83% recovery (34/41) and the classification into DSFGs vs. LRDs vs. quiescent galaxies both require that photometric redshifts accurately place each source inside 1.5 < z < 5.5 and correctly identify which observed JWST bands bracket rest-frame V and J. No photo-z validation (scatter, outlier fraction, or Monte-Carlo error propagation) is supplied, so it is unclear whether modest Δz/(1+z) ~ 0.05–0.15 errors near the boundaries or across the 4000 Å break would move sources in/out of the color-selected sample or change the ratio by >30%.

    Authors: We agree that explicit validation of the photometric redshifts is needed to quantify robustness near the redshift boundaries and across the 4000 Å break. The redshifts are drawn from existing public catalogs for the A2744 field; however, the current manuscript does not include a dedicated assessment. In the revised version we will add a short subsection (or appendix) reporting the photo-z scatter and outlier fraction against available spectroscopic redshifts in the field, together with a simple Monte Carlo propagation of redshift uncertainties to show the impact on the f_J/f_V > 3 selection and on the 83% recovery fraction. revision: yes

  2. Referee: [Abstract] Abstract: the statement that 'the great majority of the luminous, extended red sources are DSFGs' with only 'a small admixture of quiescent galaxies at z<3-4' is not accompanied by a quantitative breakdown (numbers or fractions) of how the 34 recovered ALMA sources are partitioned among the three populations, making it impossible to assess the strength of the DSFG association.

    Authors: We accept that the abstract would be clearer with explicit numbers. The body of the paper already classifies the sources (luminous extended red ALMA sources are predominantly DSFGs; compact red sources are LRDs; no >3σ ALMA detections among LRDs or quiescent galaxies), but the abstract omits the partition of the 34 recovered ALMA sources. We will revise the abstract to state the breakdown (e.g., X DSFGs, Y quiescent galaxies, and 0 LRDs among the 34), using the classifications already performed in the analysis. revision: yes

Circularity Check

0 steps flagged

No circularity: empirical cross-match of JWST colors/redshifts against independent ALMA detections

full rationale

The paper reports a direct observational count: galaxies selected by rest-frame f_J/f_V > 3 at 1.5 < z < 5.5 recover 34/41 ALMA sources (83%). Redshifts and JWST photometry are external inputs; ALMA continuum is an independent tracer. No equations, fitted parameters, or self-citations are shown that would make the recovery fraction reduce to a definition or prior result by construction. The redshift-accuracy issue raised by the skeptic is a potential systematic uncertainty, not a circularity in the derivation chain.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The paper is observational and rests on standard domain assumptions about photometric conversion to rest-frame quantities and the completeness of ALMA for dusty galaxies rather than introducing new free parameters, axioms, or entities beyond the color threshold itself.

free parameters (1)
  • color threshold f_J/f_V = 3
    The value 3 is adopted to define the red selection that matches the ALMA sources.
axioms (2)
  • domain assumption Redshifts are known with sufficient precision to compute accurate rest-frame f_J/f_V colors from the observed JWST bands
    The entire selection is defined in the rest frame and restricted to z=1.5-5.5, so redshift accuracy is required for the color cut to be meaningful.
  • domain assumption ALMA >4.5-sigma detections provide a reliable census of dusty star-forming galaxies above the flux limit
    The paper treats the ALMA sources as the ground-truth population against which the color selection is tested.

pith-pipeline@v0.9.1-grok · 5811 in / 1740 out tokens · 70818 ms · 2026-06-30T14:36:23.699459+00:00 · methodology

discussion (0)

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Forward citations

Cited by 1 Pith paper

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. Double Dots: Compact Pairs Mark Little Red Dots and High-Redshift Broad-line AGNs

    astro-ph.GA 2026-05 unverdicted novelty 7.0

    Close compact pairs mark ~67% of known Little Red Dots and both high-redshift BLAGNs in the A2744 field, suggesting merger-driven accretion at high redshift.

Reference graph

Works this paper leans on

3 extracted references · 1 canonical work pages · cited by 1 Pith paper · 1 internal anchor

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    Strength in Numbers: Red Galaxies Bolster the Cosmic Star Formation Rate Density at z > 3

    Ananna, T. T., Bogd´ an,´A., Kov´ acs, O. E., Natarajan, P., & Hickox, R. C. 2024, ApJL, 969, L18 Antwi-Danso, J., Papovich, C., Leja, J., et al. 2023, ApJ, 943, 166 Aravena, M., Boogaard, L., G´ onzalez-L´ opez, J., et al. 2020, ApJ, 901, 79 Barger, A. J., & Cowie, L. L. 2023, ApJ, 956, 95 Barger, A. J., Cowie, L. L., Bauer, F. E., & Gonz´ alez-L´ opez, ...

    work page internal anchor Pith review Pith/arXiv arXiv 2024

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    JWST Sample with ALMA>4.5σDetections No. Name R.A. Decl. 870µm 1.2 mm F444Wf J /fV z µ0.5–1.2 keV 1.2–2 keV 2–8 keV J2000.0 J2000.0 (mJy) (mJy) (µJy) (10 −17 erg s−1) (1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) 1 A001411-302317 3.5474167 -30.388277 4.70(0.19) 2.81(0.07) 20.86 9.00 2.05 1.61 10 5 12 2 A001408-302137 3.5362918 -30.360334 6.71(0....

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    Bezanson et al

    ′′5 radius aperture on the R. Bezanson et al. (2024) F444W image. The 68% confidence errors on the magnification are all less than 25%, with only four greater than 10%. Two of the lowest S/N submillimeter sources have no F444W counterparts (sources 64 and

    2024