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arxiv: 2604.04794 · v1 · submitted 2026-04-06 · 🌌 astro-ph.GA

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Galaxy Populations in Groups and Clusters: II. Conditional Luminosity Functions at Redshifts from z ~ 1 to z ~ 0

Ce Gao , Cheng Li , Houjun Mo , Jiacheng Meng , Qinglin Ma , Xiaohu Yang , Yizhou Gu , Qingyang Li
Authors on Pith no claims yet

Pith reviewed 2026-05-10 19:22 UTC · model grok-4.3

classification 🌌 astro-ph.GA
keywords conditional luminosity functionsatellite galaxiesred sequencegalaxy quenchingdark matter halosredshift evolutiongroup galaxiescluster galaxies
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The pith

The low-mass end of the red galaxy sequence in groups and clusters was already established by redshift one.

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

This work measures how the number of galaxies at different brightnesses inside dark matter halos changes from redshift one to the present, distinguishing central galaxies from satellites and red from blue populations. The satellite populations show surprisingly little change over this interval, with blue satellites following a consistent power-law slope at the faint end and red satellites displaying a persistent upturn in numbers at low luminosities. Central galaxies grow fainter over time, with red centrals evolving as if they have stopped forming stars while blue ones continue to do so. Satellites change brightness faster than expected from stellar aging alone, pointing to the added role of their dense surroundings. The fraction of satellites that have stopped forming stars dips to a minimum at a fixed stellar mass near one billion solar masses, regardless of the host halo mass or the cosmic epoch.

Core claim

The conditional luminosity functions of satellite galaxies exhibit weak evolution over 0 < z < 1. Blue satellites are described by a single Schechter function with faint-end slope between -1.25 and -1.2 across all halo masses and redshifts, while red satellites show a pronounced faint-end upturn with slope -1.8 to -1.7 that remains stable. This pattern indicates that the low-mass end of the red sequence in groups and clusters was already in place by z ~ 1. Satellite characteristic magnitudes and central luminosities both fade with decreasing redshift, red centrals consistent with passive evolution and blue centrals driven by ongoing star formation. Satellite galaxies evolve more rapidly than

What carries the argument

The conditional luminosity function (CLF), which counts galaxies per unit luminosity within fixed halo mass bins and is measured separately for central versus satellite galaxies and for red versus blue color.

If this is right

  • Red satellite galaxies maintain a steep faint-end upturn with slope between -1.8 and -1.7 across all halo masses and the full redshift range.
  • Blue satellite galaxies follow a single Schechter function whose faint-end slope stays near -1.2 with little dependence on halo mass or time.
  • Red central galaxies dim in a manner consistent with passive aging after star formation ceases, while blue centrals continue to brighten from ongoing star formation.
  • Satellite galaxies dim faster than predicted by aging stellar populations alone, requiring additional environmental processes.
  • The fraction of quenched satellites reaches a minimum at stellar mass around 10^9 solar masses independent of halo mass and redshift.

Where Pith is reading between the lines

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

  • Efficient environmental quenching must operate on low-mass galaxies inside groups and clusters already at redshift one to produce the stable faint red population.
  • The stellar-mass location of the quenched-fraction minimum may mark a transition scale where internal galaxy processes and external stripping balance in a characteristic way.
  • Extending the same CLF measurements beyond redshift one would test whether the red-sequence faint end builds even earlier or changes at higher redshift.
  • Galaxy formation models must add strong environmental effects at early times to reproduce the observed lack of evolution in the red satellite faint end.

Load-bearing premise

The group catalog accurately separates centrals from satellites and assigns correct halo masses without redshift-dependent errors that would distort the faint-end measurements.

What would settle it

An independent measurement at z greater than 1 that finds either a much shallower faint-end slope for red satellites or strong evolution in that slope between z=1 and z=0.

Figures

Figures reproduced from arXiv: 2604.04794 by Ce Gao, Cheng Li, Houjun Mo, Jiacheng Meng, Qinglin Ma, Qingyang Li, Xiaohu Yang, Yizhou Gu.

Figure 1
Figure 1. Figure 1: CLF measurements for total, red and blue populations are shown for 0.2 ⩽ 𝑧 < 0.5 and 0.5 ⩽ 𝑧 < 1.0, respectively. Black/red/blue and grey/pink/cyan error bars represent our measurements of CLF of satellite and central galaxies respectively. Errors are calculated from bootstrap resamplings of groups for 200 times. Green and purple dashed lines represent our fitting results for CLF of satellites and centrals… view at source ↗
Figure 2
Figure 2. Figure 2: The upper panels show the 𝑀c versus 𝑀h relation, while the lower panels show the 𝜎c versus 𝑀h relation of central galaxies in three different redshift ranges, for total (the left panels), red (the middle panels) and blue (the right panels) populations. After fitting the CLFs of central galaxies with a Gaussian distribution, here each data point with error bar represents the mean value (the upper panels) an… view at source ↗
Figure 3
Figure 3. Figure 3: The upper panels show the luminosity versus halo mass relation of central galaxies for total, red and blue populations, from left to right. In each sub-panel, the circle, triangle, diamond data points with error bars represent the observed results with three successive redshift bins, after accounting for the correction of halo mass growth from higher redshift to 𝑧 ∼ 0. The shaded regions bounded by solid l… view at source ↗
Figure 4
Figure 4. Figure 4: Here we show CLF measurements of different halo masses at three redshift ranges in three different colors. For total/red/blue satellites shown in the left/middle/right column, the green/orange/green represents results using SDSS groups and DESI photometric galaxies at 0.01 ⩽ 𝑧 ⩽ 0.08, taken from Paper I, the orange/purple/cyan represents this work using SV3 groups and HSC imaging catalog at 0.2 ⩽ 𝑧 < 0.5, … view at source ↗
Figure 5
Figure 5. Figure 5: MCMC best-fitting model parameters as a function of halo mass, for total (top panel), red (middle panel) and blue (bottom panel) satellites. In the top panel, green, orange and purple data points represent results at 0.01 ⩽ 𝑧 ⩽ 0.08 (directly taken from Paper I), 0.2 ⩽ 𝑧 < 0.5 and 0.5 ⩽ 𝑧 < 1.0, respectively. In the middle/bottom panel, our results are shown as orange/green, purple/cyan and red/blue data p… view at source ↗
Figure 6
Figure 6. Figure 6: Same as [PITH_FULL_IMAGE:figures/full_fig_p010_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: The green data points with error bars, orange and purple lines with shaded regions show the old fraction of satellite galaxies as a function of absolute magnitude 𝑀r , at three redshift ranges 0.01 ⩽ 𝑧 ⩽ 0.08, 0.2 ⩽ 𝑧 < 0.5, 0.5 ⩽ 𝑧 < 1.0, measured from DESI (the first one, taken from Paper I) or HSC (the latter two) photometric galaxies. Error bars or shaded regions represent 16% – 84% percentiles obtaine… view at source ↗
Figure 8
Figure 8. Figure 8: Same as [PITH_FULL_IMAGE:figures/full_fig_p011_8.png] view at source ↗
read the original abstract

Using DESI SV3 spectroscopic group centrals together with deep HSC photometric data, we measure the conditional luminosity functions (CLFs) of central and satellite galaxies, separately for red and blue populations, in dark matter halos spanning $M_h\sim10^{12}- 10^{15}M_{\odot}$ and $0<z<1$. The depth of the HSC imaging enables CLFs to be measured to unprecedentedly faint limits, reaching $M_r \approx -15$ at $0.2 \leqslant z < 0.5$ and $M_r \approx -17$ at $0.5 \leqslant z < 1.0$. We find a remarkably weak evolution in the CLF of satellite galaxies over $0<z<1$. The Blue satellite CLFs are well described by a single Schechter function across all halo masses and redshifts, with a nearly constant slope of $-1.25\lesssim \alpha\lesssim -1.2$. In contrast, red satellite CLFs exhibit a pronounced and ubiquitous faint-end upturn in all halo mass and redshift bins, with little evolution in the faint-end slope ($-1.8\lesssim \alpha_f\lesssim -1.7$). These results indicate that the low-mass end of the red sequence in clusters/groups was already established by $z\sim1$. Both satellite characteristic magnitudes and central galaxy luminosities fade with time. Red central galaxies are consistent with passive evolution, whereas the luminosity evolution of blue centrals is dominated by ongoing star formation. Satellite galaxies evolve more rapidly than predicted by simple stellar population models, highlighting the importance of environmental effects. The quenched fraction of satellite galaxies as a function of stellar mass exhibits a universal minimum at $M_{\ast} \sim 10^9M_{\odot}$, independent of halo mass and redshift. We discuss possible interpretations of these results and their implications for galaxy formation and evolution.

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 / 2 minor

Summary. The manuscript measures conditional luminosity functions (CLFs) of central and satellite galaxies, split into red and blue populations, in halos spanning 10^12 to 10^15 M_⊙ over 0 < z < 1. Using DESI SV3 spectroscopic centrals to define groups and deep HSC photometry to reach M_r ≈ -17 at 0.5 ≤ z < 1, the authors report weak evolution in satellite CLFs: blue satellites follow a single Schechter function with α ≈ -1.25 to -1.2, while red satellites show a stable faint-end upturn with α_f ≈ -1.8 to -1.7 across all halo masses and redshifts. They conclude that the low-mass end of the red sequence in groups/clusters was already established by z ∼ 1, with additional results on luminosity fading, faster satellite evolution than simple stellar population models, and a universal minimum in the quenched fraction at M_* ∼ 10^9 M_⊙.

Significance. If the completeness and membership assignments hold, the work supplies valuable observational benchmarks for galaxy formation models by demonstrating early assembly of the faint red sequence and the importance of environmental processes. The depth of the HSC data to unprecedented faint limits at z ∼ 1 is a clear strength, enabling direct constraints on low-mass satellites that are otherwise inaccessible. The separation by color and central/satellite status facilitates targeted comparisons with quenching models.

major comments (2)
  1. [§2] §2 (Data and sample construction): The central claim of little evolution in the red satellite faint-end slope (abstract and §4) depends on the assumption that DESI SV3 group catalogs and HSC photometry yield redshift-independent completeness and purity for faint red satellites. The manuscript must provide quantitative tests (e.g., recovery fractions from mocks or depth maps) showing that photometric redshift scatter, varying HSC depth relative to the red-sequence locus, and field contamination do not preferentially suppress or enhance faint red objects at 0.5 ≤ z < 1 relative to lower redshifts.
  2. [§4] §4 (CLF measurements and fits): The reported constancy of α_f ≈ −1.8 to −1.7 for red satellites across redshift bins requires a full error budget that includes systematic uncertainties from color classification, membership assignment, and completeness corrections. Without explicit demonstration that these systematics are subdominant and do not correlate with redshift at the faint end, the conclusion that the low-mass red sequence was established by z ∼ 1 remains vulnerable to bias.
minor comments (2)
  1. [Figures 5–8] Figure captions and text should explicitly state the magnitude limits used for each redshift bin when comparing CLF shapes, to allow readers to assess the impact of the differing depth cuts (M_r ≈ −15 at z < 0.5 vs. −17 at z ≥ 0.5).
  2. [Abstract and §5] The abstract states that satellite galaxies 'evolve more rapidly than predicted by simple stellar population models' but does not cite the specific models or quantify the discrepancy; adding a brief reference in the discussion would improve clarity.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful and constructive review. The comments correctly identify areas where additional quantitative validation would strengthen the robustness of our conclusions regarding the weak evolution of satellite CLFs. We have revised the manuscript to incorporate the requested tests and expanded error analysis, as detailed below.

read point-by-point responses

  1. Referee: [§2] §2 (Data and sample construction): The central claim of little evolution in the red satellite faint-end slope (abstract and §4) depends on the assumption that DESI SV3 group catalogs and HSC photometry yield redshift-independent completeness and purity for faint red satellites. The manuscript must provide quantitative tests (e.g., recovery fractions from mocks or depth maps) showing that photometric redshift scatter, varying HSC depth relative to the red-sequence locus, and field contamination do not preferentially suppress or enhance faint red objects at 0.5 ≤ z < 1 relative to lower redshifts.

    Authors: We agree that explicit validation of redshift-independent completeness is essential for the central claim. In the revised manuscript we have added a new subsection (§2.4) presenting recovery fractions derived from mock catalogs injected into the HSC imaging, as well as HSC depth maps relative to the red-sequence locus. These tests demonstrate that completeness for faint red satellites (Mr ≳ −18) remains >80% and shows no significant redshift-dependent decline between 0.2 < z < 1.0 once the varying depth and photo-z scatter are accounted for. Field contamination is controlled via statistical background subtraction calibrated on random fields; the residual bias on the faint-end slope α_f is <0.05, well below the statistical uncertainty. revision: yes

  2. Referee: [§4] §4 (CLF measurements and fits): The reported constancy of α_f ≈ −1.8 to −1.7 for red satellites across redshift bins requires a full error budget that includes systematic uncertainties from color classification, membership assignment, and completeness corrections. Without explicit demonstration that these systematics are subdominant and do not correlate with redshift at the faint end, the conclusion that the low-mass red sequence was established by z ∼ 1 remains vulnerable to bias.

    Authors: We have expanded §4.3 to present a full systematic error budget. Systematic uncertainties on α_f arising from alternative color cuts, varying membership probability thresholds, and completeness corrections are quantified via bootstrap and mock realizations. These systematics are subdominant (Δα_f ≲ 0.08) to the statistical errors and exhibit no monotonic trend with redshift at the faint end. Consequently, the observed constancy of α_f across 0 < z < 1 remains robust, supporting the conclusion that the low-mass red sequence was already in place by z ∼ 1. We have also added a brief discussion of how these controls affect the interpretation. revision: yes

Circularity Check

0 steps flagged

No circularity: purely observational CLF measurements from survey data

full rationale

The paper performs direct measurements of conditional luminosity functions using DESI SV3 spectroscopic group centrals and HSC photometric data, fitting Schechter functions to the observed galaxy counts in halo mass and redshift bins. No load-bearing step reduces by construction to a fitted parameter or self-citation chain; the reported stability of the red satellite faint-end slope and conclusions about the red sequence at z~1 are direct outputs of the data analysis. The derivation chain is self-contained against external benchmarks (survey catalogs) with no renaming of known results or ansatz smuggling.

Axiom & Free-Parameter Ledger

1 free parameters · 2 axioms · 0 invented entities

The central claims rest on the accuracy of the DESI group catalog for halo mass assignment and central/satellite classification, plus standard assumptions in photometric luminosity measurements and Schechter function fitting; no independent verification of these steps is possible from the abstract alone.

free parameters (1)
  • Schechter function parameters (alpha, M*, phi)
    Fitted separately to red and blue CLFs in each halo mass and redshift bin.
axioms (2)
  • domain assumption DESI SV3 group catalog provides accurate halo masses and central/satellite labels across 0<z<1
    Invoked to bin galaxies by halo mass and separate centrals from satellites.
  • domain assumption HSC photometry is complete and unbiased down to the reported faint limits after corrections
    Required for the measured faint-end slopes to reflect true galaxy populations.

pith-pipeline@v0.9.0 · 5690 in / 1436 out tokens · 52406 ms · 2026-05-10T19:22:51.823869+00:00 · methodology

discussion (0)

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Reference graph

Works this paper leans on

4 extracted references · 1 canonical work pages · 1 internal anchor

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    The DESI Experiment Part I: Science,Targeting, and Survey Design

    Aihara H., et al., 2018, Publications of the Astronomical Society of Japan, 70, S4 Aihara H., et al., 2022, Publications of the Astronomical Society of Japan, 74, 247 ArnoutsS.,etal.,2002,MonthlyNoticesoftheRoyalAstronomicalSociety, 329, 355 Baldry I. K., Glazebrook K., Brinkmann J., Ivezić Ž., Lupton R. H., Nichol R. C., Szalay A. S., 2004, The Astrophys...

    work page internal anchor Pith review arXiv 2018

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    By applying a magnitude cut of𝑚r ⩽19.5, they achieved a spectro- scopic completeness of 46.4% for member galaxies and measured CLFs at𝑧⩽0.6using this so-called Y1-r19.5 sample

    lo- cated within the Year 1 (Y1) spectroscopic survey footprint. By applying a magnitude cut of𝑚r ⩽19.5, they achieved a spectro- scopic completeness of 46.4% for member galaxies and measured CLFs at𝑧⩽0.6using this so-called Y1-r19.5 sample. They also analyzed groups within the SV3 region under the same magnitude cut, where the completeness reaches 99.2%....

    2026

  3. [3]

    The COSMOS2020 catalog alsoprovidesstellarmassesestimatedusingLePhare(Arnoutsetal

    to perform spectral energy distribution (SED) fitting for each galaxy and derive stellar masses as the median values of their posterior probability distributions. The COSMOS2020 catalog alsoprovidesstellarmassesestimatedusingLePhare(Arnoutsetal. 2002;Ilbertetal.2006),basedonconfigurationsdifferentfromours. Our comparison between the two estimates shows no...

    2002

  4. [4]

    For reference, the stellar masses in Figure 11 of Paper I were derivedfromSDSSdata(Yangetal.2009)usingtherelationbetween stellar mass-to-light ratio and color from Bell et al. (2003). The differenceinstellarmassestimationmethodsintroducesasystematic MNRAS000, 1–21 (2026) Conditional luminosity functions from𝑧∼1to𝑧∼019 10 3 10 2 10 1 100 101 102 103 dN/dM ...

    2009