REVIEW 3 major objections 5 minor 57 references
The VIMOS Public Extragalactic Redshift Survey (VIPERS) -- Environment-size relation of massive passive galaxies at 0.5 < z < 0.8
T0 review · 3 major / 5 minor · reviewed 2026-08-14 · deepseek-v4-flash
Pith's one-line read Below $2\times10^{11}M_\odot$, massive passive galaxies have the same compactness in every environment quartile; only the densest-region giants show merger-driven growth.
desk verdict Worth reading for the low-mass null result; the high-mass 'factor ~10' deficit claim is softer than the text implies. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing object is the surface stellar mass density $\Sigma = M_\star/(2\pi R_e^2)$, which combines stellar masses from spectral-energy-distribution fitting with circularized effective radii from two-dimensional Sérsic profile fits. The environment axis is the galaxy density contrast $\delta$, computed with a cylinder $\pm1000$ km/s deep whose radius is the distance to the fifth nearest galaxy in a volume-limited tracer sample; the sample is then split into four quartiles of $1+\delta$ (D1 through D4). To prevent the well-known correlation between stellar mass and density from masquerading as a size–environment trend, the authors construct 100 mass-matched resamplings of the four density bins and compare low- and high-$\Sigma$ counts using $\chi^2$ and Kolmogorov-Smirnov tests.
What would settle it
Repeat the same $\Sigma$-$\delta$ analysis on the same VIPERS galaxies but select passive systems by morphology (Sérsic index $n>2$) instead of NUVrK colours: a significant excess of low-$\Sigma$ over high-$\Sigma$ galaxies at $M_\star\le 2\times10^{11}M_\odot$ in the densest quartile would overturn the paper's central claim, while a flat trend would confirm it.
Extended reading notes
Core claim
The paper's claim is that the $\Sigma$-$\delta$ relation of massive passive galaxies is mass-dependent. For $10^{11} M_\odot \le M_\star \le 2\times10^{11} M_\odot$, the counts of low-$\Sigma$ ($\Sigma \le 1000 M_\odot\,\mathrm{pc}^{-2}$) and high-$\Sigma$ ($\Sigma > 2000 M_\odot\,\mathrm{pc}^{-2}$) galaxies are statistically indistinguishable across the four density quartiles (Kolmogorov-Smirnov median probability $p \sim 0.3$), meaning environment plays no detectable role in setting their size. For $M_\star > 2\times10^{11} M_\odot$, the densest quartile contains about twice as many low-$\Sigma$ galaxies and about ten times fewer high-$\Sigma$ galaxies as the other quartiles ($p = 5\times10^{-3}$); the mean effective radius in that bin is $8.73\pm0.08$ kpc versus about $6.2$ kpc elsewhere. The authors interpret this as a late-time migration of some compact galaxies to larger sizes through mergers or cannibalism, not as environment-dependent formation. The paper also shows that low-$\Sigma$ massive star-forming galaxies at $0.8\le z\le1.0$ have the same $\Sigma$-$\delta$ trend as low-$\Sigma$ massive passive galaxies at $z<0.8$, adding an environmental match to the number-density match already established for this progenitor relation.
Load-bearing premise
Everything rests on the assumption that the local crowding measure used here—counting the nearest few galaxies within a few million light-years—truly captures the environment that drives satellite capture; if this measure is noisy or samples the wrong scale, the four environment bins may not represent physically distinct neighbourhoods.
Editorial extensions
If this is right
- For most massive passive galaxies ($10^{11} \le M_\star/M_\odot \le 2\times10^{11}$), dry satellite accretion is not required to explain their size growth at $0.5<z<0.8$.
- The environmental consistency between star-forming galaxies at $z\ge0.8$ and low-$\Sigma$ passive galaxies at $z<0.8$ reinforces the number-density argument that most large passive galaxies are simply quenched star-forming galaxies.
- Environment-driven size growth, if real, is confined to the most massive passive galaxies ($M_\star > 2\times10^{11} M_\odot$) in the densest regions, where the mean effective radius is about 1.4 times larger than elsewhere.
- The inferred migration of high-$\Sigma$ to low-$\Sigma$ galaxies in dense regions involves fewer than about 10 out of 902 galaxies, bounding the cosmic importance of merger-driven growth in this population.
Reading between the lines
- A clean morphological selection (e.g., Sérsic index $n>2$) applied to the same sample would test whether the 20–30% disk contamination of NUVrK colour selection hides a real size–environment trend among ellipticals.
- Extending the same $\Sigma$-$\delta$ measurement to $M_\star>2\times10^{11}M_\odot$ galaxies at $z>0.9$ would discriminate the two scenarios the paper leaves open: a flat trend would confirm delayed merger-driven migration, while an already-present excess of low-$\Sigma$ galaxies would indicate environment-dependent formation.
- Because the fifth-nearest-neighbour cylinder averages over group and cluster-outskirt scales, a finer environmental probe such as projected distance to the brightest group galaxy could reveal whether the surplus low-$\Sigma$ galaxies are preferentially central galaxies that have cannibalised satellites.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper uses the VIPERS spectroscopic survey to measure the relation between the mean surface stellar mass density Sigma and environment, defined through a fifth-nearest-neighbor density contrast delta, for about 900 massive passive galaxies (MPGs) at 0.5<z<0.8. The sample is split by stellar mass and by Sigma, and counts in four density quartiles are corrected for survey incompleteness and mass-matched through resampling. The authors find no significant Sigma-delta trend for MPGs with Mstar<=2e11 Msun, which they interpret as evidence that satellite accretion is not the main mass-assembly channel for most MPGs. For Mstar>2e11 Msun, they report an excess of low-Sigma MPGs and a deficit of high-Sigma MPGs in the densest quartile, with a median KS probability p=5e-3, and interpret this as migration of a small fraction (<1%) of high-Sigma MPGs into low-Sigma MPGs through mergers or cannibalism. They also compare the Sigma-delta trend of low-Sigma MPGs with that of massive star-forming galaxies at higher redshift and conclude that the two are consistent.
Significance. If the low-mass null result holds, it is an important observational constraint on dry-merger-driven size growth: at Mstar<2e11 Msun, the local environment does not measurably change the surface stellar mass density of massive passive galaxies. The analysis is carefully executed in several respects: explicit completeness weights (TSR, SSR, CSR) are applied, mass-matching across density quartiles is performed with 100 resamplings, and appendices B and E test the sensitivity to the density-field definition and to the quartile cuts. The high-mass branch, however, is much less secure: it is based on a very small number of raw counts and the strongest quantitative claim, a factor of about 10 drop, is not reproducible from the tabulated data. The paper's central qualitative conclusion for the majority of MPGs is credible, but the quantitative interpretation of the high-mass signal needs to be brought in line with what the data and the tables actually support.
major comments (3)
- [3.2, Table 1, Summary] In Section 3.2 the authors state that in the densest bin the number of high-Sigma MPGs with M>2e11 Msun "drastically drops by a factor ~10". This is not supported by the published raw counts in Table 1, which list 12, 9, 10, and 3 high-Sigma objects in D1-D4; the D1-D3 mean is 10.3, so the drop relative to that mean is a factor of 3.4, not 10. The mass-matched and completeness-corrected counts used for Fig. 6 are not tabulated, so the quoted factor cannot be checked. The Summary uses the same approximate "10" inconsistently: it says "10 is the difference between the mean value ... and the value in the D4 bin", but 10.3 - 3 = 7.3, not 10. Please tabulate the corrected counts in an appendix and revise the quantitative statements in the text and abstract accordingly.
- [Fig. 6, Fig. 7, Table 1] The entire high-mass signal for a deficit of high-Sigma objects rests on three raw counts in the D4 bin. With such small numbers, the median KS probability p=5e-3 reported in Fig. 7 and the mean radius Re=8.73 +/- 0.08 kpc quoted in Section 3.2 are fragile: removing or reclassifying one or two galaxies, or perturbing Re within the quoted 12% error tail, could plausibly change the result. Please add a leave-one-out or bootstrap analysis of the high-mass trends, report the distribution of p-values over the 100 mass-matched samples, and state how many individual objects drive the signal.
- [4, Fig. 8] The progenitor-consistency test in Section 4 is presented in the abstract as showing that MSFGs at z>0.8 are consistent with being the progenitors of low-Sigma MPGs at z<0.8. The actual test is a 1-sigma consistency between two populations drawn from the same survey, with only 56 high-mass MSFGs in total. This is a consistency check with limited statistical power, not a detection; a flat/null trend in the upper panel of Fig. 8 would also be formally consistent with the data. Please quantify the statistical power of this comparison and temper the abstract's wording from "consistent" to "consistent within the limited precision of this test".
minor comments (5)
- [Abstract] There is a typographical error: "rapidily" should be "rapidly". The same LaTeX-rendering issue appears in the abstract of the full text.
- [Fig. 1 caption] The phrase "The solid blue dashed histogram" is confusing; it should probably be "the blue dashed histogram" or "the solid blue histogram", depending on the intended line style.
- [3.2] The sentence "accretion of satellites could be a viable mechanisms" has a subject-verb disagreement; "mechanisms" should be "mechanism".
- [5] There are several residual LaTeX artifacts such as "M /geqslant", which should be cleaned up before final publication.
- [3.1] The comparison with Kelkar et al. (2015), which cites raw counts of 9 cluster versus 4 field low-Sigma galaxies, should be explicitly described as a small-number, qualitative consistency check.
Circularity Check
No significant circularity: the Sigma-delta analysis is an empirical comparison, and the cited Paper I result is separate evidence rather than a fitted input.
full rationale
I find no circular step in this paper. The central analysis compares counts of low- and high-Sigma MPGs across environment quartiles, where the quartiles are defined from the MPG (1+delta) distribution; this self-referential binning is a deliberate null-hypothesis construction, but the quantities compared (low- vs high-Sigma counts, KS probabilities, mean effective radii) are independent observables and are not algebraically forced to produce the reported trend. The mass-matching procedure in Appendix C removes the M-delta correlation by resampling the stellar mass distributions; it does not fit a parameter to the Sigma-delta trend, so the high-mass deficit of high-Sigma galaxies in D4 is not a fitted input renamed as a prediction. The consistency test between low-Sigma MSFGs at z>0.8 and low-Sigma MPGs at z<0.8 (Fig. 8) is a cross-redshift comparison of independent samples and is reported as a 1-sigma agreement, not imposed by construction. Paper I (Gargiulo et al. 2017) is a self-citation for the number-density evolution of MPGs and MSFGs, but that is a separate, falsifiable measurement based on its own data; the present paper adds the environment channel as an independent test rather than relying on Paper I to define its outcome. Concerns that the quoted factor-of-10 drop in high-Sigma MPGs is not directly reproducible from Table 1 and depends on small counts are statistical robustness and correctness issues, not circularity. Therefore the appropriate circularity score is 0.
Assumptions & free parameters
free parameters (3)
- Sigma thresholds for low/high samples =
1000 and 2000 Msun pc^-2
- Stellar mass split =
2x10^11 Msun
- Density quartile cuts =
25th, 50th, 75th percentiles of 1+delta in four z-bins
assumptions (5)
- domain assumption Stellar masses and effective radii derived from SED fitting and GALFIT are accurate to the quoted errors (Re error <4.4% for 68% of sample).
- domain assumption NUVrK color selection isolates passive galaxies; contamination by dusty star-forming or disk galaxies is small or does not bias the Sigma-delta trends.
- domain assumption The fifth-nearest-neighbor density contrast from a volume-limited tracer sample (MB<=-20.4-z) traces the local environment relevant to galaxy interactions.
- domain assumption The completeness weights (TSR, SSR, CSR) and mass-matched resampling remove the mass-density correlation and selection biases.
- standard math Flat LCDM cosmology with the stated parameters and Chabrier IMF.
Cite this review
Pith. "Pith review of The VIMOS Public Extragalactic Redshift Survey (VIPERS) -- Environment-size relation of massive passive galaxies at 0.5 < z < 0.8." pith.science (2026). https://pith.science/paper/MPHPO5KA
@misc{pith2026190905094,
author = {Pith},
title = {Pith review of: The VIMOS Public Extragalactic Redshift Survey (VIPERS) -- Environment-size relation of massive passive galaxies at 0.5 < z < 0.8},
year = {2026},
howpublished = {\url{https://pith.science/paper/MPHPO5KA}},
note = {Machine review of arXiv:1909.05094}
}
read the original abstract
We use the statistics of the VIPERS survey to investigate the relation between the surface mean stellar mass density Sigma=Mstar/(2*pi*Re^2) of massive passive galaxies (MPGs, Mstar>10^11 Msun) and their environment in the redshift range 0.5<z<0.8. Passive galaxies were selected on the basis of their NUVrK colors (~900 objects), and the environment was defined as the galaxy density contrast, delta, using the fifth nearest-neighbor approach. The analysis of Sigma vs. delta was carried out in two stellar mass bins. In galaxies with Mstar<2*10^11 Msun, no correlation between Sigma and delta is observed. This implies that the accretion of satellite galaxies, which is more frequent in denser environments and efficient in reducing the galaxy Sigma, is not relevant in the formation and evolution of these systems. Conversely, in galaxies with Mstar>2*10^11 Msun, we find an excess of MPGs with low Sigma and a deficit of high-Sigma MPGs in the densest regions wrt other environments. We interpret this result as due to the migration of some high-Sigma MPGs (<1% of the total population of MPGs) into low-Sigma MPGs, probably through mergers or cannibalism of small satellites. In summary, our results imply that the accretion of satellite galaxies has a marginal role in the mass-assembly history of most MPGs. We have previously found that the number density of VIPERS massive star-forming galaxies (MSFGs) declines rapidily from z=0.8 to z=0.5, which mirrors the rapid increase in the number density of MPGs. This indicates that the MSFGs at z>0.8 migrate to the MPG population. Here, we investigate the Sigma-delta relation of MSFGs at z>0.8 and find that it is consistent within 1 sigma with that of low-Sigma MPGs at z<0.8. Thus, the results of this and our previous paper show that MSFGs at z>0.8 are consistent in terms of number and environment with being the progenitors of low-Sigma MPGs at z<0.8.
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Reviewed August 14, 2026 · model on record in the stance chip above.
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