REVIEW
The buildup of stellar mass and the 3.6 micron luminosity function in clusters from z=1.25 to z=0.2
Astrophysics · Submitted 27 Feb 2006 · 49 references
Pith's verdict: Careful, useful 3.6 micron cluster LF measurement whose strongest abstract claim outruns its five-track GRASIL grid; worth referee time with a softened conclusion.
T0 · AI review
Why Pith says this
Highlight any text to comment on it.
Referee report
The paper
The paper claims
Using 3.6 micron photometry of about 1000 galaxies in 32 clusters, this paper argues that cluster galaxies formed their stars early and did not grow in stellar mass after z≈1.25.
The reading
What carries the argument
The central machinery is a joint fit of unbinned galaxy counts in cluster and background directions, using an extended likelihood (following the APG method), so that the background, the Schechter luminosity function, and its redshift evolution are solved for simultaneously rather than assumed. The evolution is parameterized by replacing the Schechter characteristic magnitude with $m^*_z = m^*_{z=0.5} + \Delta m_{\rm model} - Q(z-0.5)$, where $\Delta m_{\rm model}$ comes from one of five GRASIL stellar-mass-growth tracks (E, Sa, Sb, Sc, SB) and $Q$ allows extra linear redshift dependence. Model selection by BIC and likelihood-ratio tests then decides which growth history, and whether $Q=0$, the data require; a split of the sample at the median redshift provides a visual cross-check that the chosen track makes the two halves share a common $m^*_{0.5}$.
Extended reading notes
Core claim
On its own terms, the paper establishes that the [3.6]-band luminosity function of cluster galaxies evolves as an old and passively evolving population formed at high redshift. The characteristic magnitude at z=0.5 is $m^* = 16.30 \pm 0.10$ mag, and the best-fit model has zero additional redshift-dependent evolution ($Q=0$); the Bayesian Information Criterion strongly prefers the early-formation (E) track over later-type star-formation histories, and it rejects the unphysical model in which stars have the same age at all redshifts. Converted to a mass scale, the characteristic stellar mass is $M_* \approx 1.1$–$1.2 \times 10^{11} M_\odot$ and is constant from $z\approx 1.1$ to $z\approx 0.3$, over the last two-thirds of cosmic time. The paper reads this as evidence that the population of cluster galaxies was completely assembled at high redshift, not just that its stars are old.
Load-bearing premise
The conclusion that stellar mass growth is ruled out relies on the assumption that the five GRASIL tracks (E, Sa, Sb, Sc, SB) span the range of plausible star-formation histories; the paper itself notes a degeneracy in which an older, longer star-formation episode could mimic the same luminosity evolution as a younger, shorter one.
Editorial extensions
If this is right
- Cluster galaxy stellar mass was largely in place by $z \approx 1.25$; therefore late-time mergers and star formation add little to the total stellar mass budget of present-day cluster galaxies.
- The $3.6\,\mu$m band can serve as a nearly dust-free, single-estimator ruler for measuring $m^*$ and $M_*$ evolution over $0.2 < z < 1.25$ without binning artifacts.
- Galaxy-formation models in which cluster galaxies grow substantially in stellar mass below $z \approx 1$ are ruled out at high confidence and must assemble these galaxies at $z > 1.25$.
- The constancy of $M_* \approx 1.1$–$1.2 \times 10^{11} M_\odot$ sets a quantitative target that galaxy-formation simulations must reproduce.
- The rejection of both prolonged mass growth and the same-age-at-all-redshifts model narrows the allowed star-formation histories to an early, short episode.
Reading between the lines
- My inference: the same simultaneous-fit strategy could be applied to the 4.5 micron IRAC band, where dust is even less important; a detection of $Q \neq 0$ there would challenge the passive-formation conclusion.
- My inference: the paper's population-level constancy does not by itself prove each galaxy stopped assembling; a cleaner test is the number density of very massive ($M > 10^{11.5} M_\odot$) cluster galaxies at $z>1.25$, which the paper mentions but does not measure.
- My inference: if the E-track result is correct, field galaxies may behave differently; predicting a steeper decline of massive field galaxies at high redshift would be a testable extension of the method to another environment.
Original abstract
We have measured the 3.6 micron luminosity evolution of about 1000 galaxies in 32 clusters at 0.2<z<1.25, without any a priori assumption about luminosity evolution, i.e. in a logically rigorous way. We find that the luminosity of our galaxies evolves as an old and passively evolving population formed at high redshift without any need for additional redshift-dependent evolution. Models with a prolonged stellar mass growth are rejected by the data with high confidence. The data also reject models in which the age of the stars is the same at all redshifts. Similarly, the characteristic stellar mass evolves, in the last two thirds of the universe age, as expected for a stellar population formed at high redshift. Together with the old age of stellar populations derived from fundamental plane studies, our data seems to suggest that early-type cluster galaxies have been completely assembled at high redshift, and not only that their stars are old. The quality of the data allows us to derive the LF and mass evolution homogeneously over the whole redshift range, using a single estimator. The Schechter function describes the galaxy luminosity function well. The characteristic luminosity at z=0.5 is is found to be 16.30 mag, with an uncertainty of 10 per cent.
The compiled record
The paper's own sentences, arranged, kept beside the review and separate from it. Each label is drawn from a closed vocabulary; the number beside it is the probability the classifier gave that label. Numbers in the tables are the authors', checked by code. No sentence in this record was written by a model.
The abstract, sentence by sentence
We have measured the 3.6 micron luminosity evolution of about 1000 galaxies in 32 clusters at 0.2<z<1.25, without any a priori assumption about luminosity evolution, i.e. in a logically rigorous way. We find that the luminosity of our galaxies evolves as an old and passively evolving population formed at high redshift without any need for additional redshift-dependent evolution. Models with a prolonged stellar mass growth are rejected by the data with high confidence. The data also reject models in which the age of the stars is the same at all redshifts. Similarly, the characteristic stellar mass evolves, in the last two thirds of the universe age, as expected for a stellar population formed at high redshift. Together with the old age of stellar populations derived from fundamental plane studies, our data seems to suggest that early-type cluster galaxies have been completely assembled at high redshift, and not only that their stars are old. The quality of the data allows us to derive the LF and mass evolution homogeneously over the whole redshift range, using a single estimator. The Schechter function describes the galaxy luminosity function well. The characteristic luminosity at z=0.5 is is found to be 16.30 mag, with an uncertainty of 10 per cent.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We have measured the 3.6 micron luminosity evolution of about 1000 galaxies in 32 clusters at 0.2<z<1.25, without any a priori assumption about luminosity evolution, i.e. in a logically rigorous way. | method 0.51 | 0.98 | 0.06 | asserted 1.00 |
| s1 | We find that the luminosity of our galaxies evolves as an old and passively evolving population formed at high redshift without any need for additional redshift-dependent evolution. | result 0.98 | 0.97 | 0.62 | asserted 1.00 |
| s2 | Models with a prolonged stellar mass growth are rejected by the data with high confidence. | result 0.98 | 0.85 | 0.27 | asserted 1.00 |
| s3 | The data also reject models in which the age of the stars is the same at all redshifts. | result 0.99 | 0.88 | 0.07 | asserted 1.00 |
| s4 | Similarly, the characteristic stellar mass evolves, in the last two thirds of the universe age, as expected for a stellar population formed at high redshift. | result 0.99 | 0.89 | 0.14 | asserted 0.98 |
| s5 | Together with the old age of stellar populations derived from fundamental plane studies, our data seems to suggest that early-type cluster galaxies have been completely assembled at high redshift, and not only that their stars are old. | interpretation 1.00 | 0.68 | 0.71 | hedged possibility 1.00 |
| s6 | The quality of the data allows us to derive the LF and mass evolution homogeneously over the whole redshift range, using a single estimator. | method 0.80 | 0.94 | 0.05 | asserted 0.99 |
| s7 | The Schechter function describes the galaxy luminosity function well. | result 0.99 | 0.79 | 0.04 | asserted 1.00 |
| s8 | The characteristic luminosity at z=0.5 is is found to be 16.30 mag, with an uncertainty of 10 per cent. | result 1.00 | 0.96 | 0.03 | asserted 1.00 |
What was examined, and what was not
- arXiv listing abstract v1
- full text
- figures and tables
- references and citing sentences
- relations to other papers
- P abstract
- S sections
- T body sentences
- C citations
- R cross-paper relations
Figures
Showing 6 of the paper's 7 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:astro-ph/0602576 by the authors.
References
How the literature uses it
Papers whose main result relates to this one's
States the same result 1 paper
-
Together with the old age of stellar populations derived from fundamental plane studies, our data seems to suggest that massive early-type cluster galaxies have been completely assembled at high redshift, and not only that their stars are old.
Discussion
Disagree with the review, or know something it missed? Leave a comment, highlight any passage above to comment on it, or challenge this review formally.