REVIEW
The Clustering Evolution of Distant Red Galaxies in the GOODS-MUSIC Sample
Astrophysics · Submitted 3 Mar 2006 · 54 references
Pith's verdict: Solid new clustering measurement for DRGs in GOODS-South, but the claimed low-z versus high-z distinction rests on overlapping error bars and model curves normalized to the same uncertain point.
T0 · AI review
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Referee report
The paper
The paper claims
This paper argues that distant red galaxies at different redshifts form two distinct populations with different descendants, not one population seen at two ages.
The reading
What carries the argument
The central machinery is the $J-K_s$ colour cut defining Distant Red Galaxies, combined with the angular two-point correlation function and its Limber inversion. The cut is designed to catch galaxies with a strong 4000 Å break at $z>2$, but template colour–redshift tracks show that dusty star-forming galaxies at $z\sim1.5$ also satisfy it; that heterogeneity is what the clustering analysis then separates. The Landy–Szalay estimator measures $w(\theta)$, and the Limber equation converts it to a spatial scale $r_0$ using the observed redshift distribution. Closing the argument are two simplified clustering-evolution models, object-conserving and merging, whose predictions bracket the descendant clustering expected from a single evolving population; the low-redshift measurement falls outside that bracket.
Extended reading notes
Core claim
On the paper's own terms, the discovery is a clustering dichotomy inside the DRG population. Using 179 galaxies with $J-K_s\ge1.3$ (AB) in a 135 square arcminute field with colour-estimated redshifts accurate to about $\sigma_z=0.06$–$0.08$, the angular two-point correlation function corresponds to a spatial correlation length $r_0=9.78\,h^{-1}\,\mathrm{Mpc}$ for the whole sample. Splitting at $z=2$ gives $r_0=7.41\,h^{-1}\,\mathrm{Mpc}$ for the $1<z<2$ subsample and $r_0=13.36\,h^{-1}\,\mathrm{Mpc}$ for the $2<z<4$ subsample. When the integrated clustering amplitude within $20\,h^{-1}\,\mathrm{Mpc}$ is compared with the range allowed by object-conserving and merging evolution models, the low-redshift value falls outside the band predicted from the high-redshift sample. The paper concludes that it is unlikely that the two samples are the same population at different evolutionary stages: high-redshift DRGs are the likely progenitors of massive local ellipticals and group-scale structures, while low-redshift DRGs are dusty starbursts headed toward less massive field galaxies.
Load-bearing premise
The load-bearing premise is that colour-estimated redshifts with typical scatter of 0.06–0.08 correctly sort galaxies on either side of $z=2$, since the paper does not quantify how much of the measured clustering difference could be blurred or created by redshift scatter across that boundary.
Editorial extensions
If this is right
- Colour-selected DRG samples that mix $z\sim1.5$ and $z\sim2.7$ galaxies will show an intermediate clustering amplitude, so redshift binning is necessary before interpreting clustering evolution.
- The high-redshift DRG clustering amplitude implies their likely descendants are among the most strongly clustered local populations, giant ellipticals and radio galaxies.
- The low-redshift DRG descendants should be less massive field galaxies, with clustering near that of $L^*$ ellipticals rather than cluster members.
- The large-scale excess in the DRG angular correlation function means small pencil-beam surveys systematically underestimate DRG number density because of cosmic variance.
Reading between the lines
- The same redshift-dependent contamination probably affects other colour-selected high-redshift samples, such as BzK or ERO selections, so part of the clustering evolution reported for those populations may also be a selection effect rather than purely physical evolution.
- If high-redshift DRGs mark the sites of future groups and clusters, their descendant halos should be identifiable in local group and cluster catalogs; a quantitative cross-match of simulated descendants with observed massive ellipticals would test the progenitor link directly.
- A natural extension is to repeat the Limber inversion using the full photometric-redshift probability distribution of each galaxy rather than a single best estimate, turning the paper's main uncertainty into a measured error bar.
Original abstract
We use the GOODS-MUSIC sample, a catalog of ~3000 Ks-selected galaxies based on VLT and HST observation of the GOODS-South field with extended multi-wavelength coverage (from 0.3 to 8 micron) and accurate estimates of the photometric redshifts to select 179 DRGs with J-Ks>1.3 in an area of 135 sq. arcmin. We first show that the J-Ks>1.3 criterion selects a rather heterogeneous sample of galaxies, going from the targeted high-redshift luminous evolved systems, to a significant fraction of lower redshift (1<z<2) and less luminous dusty starbursts. These low-redshift DRGs are significantly less clustered than higher-z DRGs. With the aid of extreme and simplified theoretical models of clustering evolution we show that it is unlikely that the two samples are drawn from the same population observed at two different stages of evolution. High-z DRGs likely represent the progenitors of the more massive and more luminous galaxies in the local Universe and might mark the regions that will later evolve into structures of intermediate mass, like groups or small galaxy clusters. Low-z DRGs, on the other hand, will likely evolve into slightly less massive field galaxies.
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 use the GOODS-MUSIC sample, a catalog of ~3000 Ks-selected galaxies based on VLT and HST observation of the GOODS-South field with extended multi-wavelength coverage (from 0.3 to 8 micron) and accurate estimates of the photometric redshifts to select 179 DRGs with J-Ks>1.3 in an area of 135 sq. arcmin. We first show that the J-Ks>1.3 criterion selects a rather heterogeneous sample of galaxies, going from the targeted high-redshift luminous evolved systems, to a significant fraction of lower redshift (1<z<2) and less luminous dusty starbursts. These low-redshift DRGs are significantly less clustered than higher-z DRGs. With the aid of extreme and simplified theoretical models of clustering evolution we show that it is unlikely that the two samples are drawn from the same population observed at two different stages of evolution. High-z DRGs likely represent the progenitors of the more massive and more luminous galaxies in the local Universe and might mark the regions that will later evolve into structures of intermediate mass, like groups or small galaxy clusters. Low-z DRGs, on the other hand, will likely evolve into slightly less massive field galaxies.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | We use the GOODS-MUSIC sample, a catalog of ~3000 Ks-selected galaxies based on VLT and HST observation of the GOODS-South field with extended multi-wavelength coverage (from 0.3 to 8 micron) and accurate estimates of the photometric redshifts to select 179 DRGs with J-Ks>1.3 in an area of 135 sq. arcmin. | method 0.99 | 0.90 | 0.03 | asserted 0.99 |
| s1 | We first show that the J-Ks>1.3 criterion selects a rather heterogeneous sample of galaxies, going from the targeted high-redshift luminous evolved systems, to a significant fraction of lower redshift (1<z<2) and less luminous dusty starbursts. | result 0.96 | 0.93 | 0.06 | asserted 1.00 |
| s2 | These low-redshift DRGs are significantly less clustered than higher-z DRGs. | result 1.00 | 0.87 | 0.21 | asserted 1.00 |
| s3 | With the aid of extreme and simplified theoretical models of clustering evolution we show that it is unlikely that the two samples are drawn from the same population observed at two different stages of evolution. | result 0.56 | 0.88 | 0.33 | asserted 0.66 |
| s4 | High-z DRGs likely represent the progenitors of the more massive and more luminous galaxies in the local Universe and might mark the regions that will later evolve into structures of intermediate mass, like groups or small galaxy clusters. | interpretation 1.00 | 0.46 | 0.45 | hedged possibility 0.84 |
| s5 | Low-z DRGs, on the other hand, will likely evolve into slightly less massive field galaxies. | interpretation 1.00 | 0.33 | 0.10 | hedged possibility 0.99 |
What was examined, and what was not
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Figures
Showing 8 of the paper's 10 figures. See all figures in the PDF ↗ Figures reproduced from arXiv:astro-ph/0603095 by the authors.
References
Discussion
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