CLUSTERING OF LOW-REDSHIFT (<i>z</i>⩽ 2.2) QUASARS FROM THE SLOAN DIGITAL SKY SURVEY
Bibliographic record
Abstract
We present measurements of the quasar two-point correlation function, ξ Q , over the redshift range 0.3 ⩽ z ⩽ 2.2 based upon data from the Sloan Digital Sky Survey (SDSS). Using a homogeneous sample of 30,239 quasars with spectroscopic redshifts from the Data Release 5 Quasar Catalog, our study represents the largest sample used for this type of investigation to date. With this redshift range and an areal coverage of ≈4000 deg 2 , we sample over 25 h −3 Gpc 3 (comoving) of the universe in volume, assuming the current Lambda Cold Dark Matter (ΛCDM) cosmology. Over this redshift range, we find that the redshift-space correlation function, ξ( s ), is adequately fit by a single power law, with s 0 = 5.95 ± 0.45 h −1 Mpc and γ s = 1.16 +0.11 −0.16 when fit over 1.0 h −1 Mpc ⩽ s ⩽ 25.0 h −1 Mpc. We find no evidence for deviation from ξ( s ) = 0 at scales of s >100 h −1 Mpc, but do observe redshift-space distortions in the two-dimensional ξ( r p , π) measurement. Using the projected correlation function, w p ( r p ), we calculate the real-space correlation length, r 0 = 5.45 +0.35 −0.45 h −1 Mpc and γ = 1.90 +0.04 −0.03 , over scales of 1.0 h −1 Mpc ⩽ r p ⩽ 130.0 h −1 Mpc. Dividing the sample into redshift slices, we find very little, if any, evidence for the evolution of quasar clustering, with the redshift-space correlation length staying roughly constant at s 0 ∼ 6–7 h −1 Mpc at z ≲ 2.2 (and only increasing at redshifts greater than this). We do, however, see tentative evidence for evolution in the real-space correlation length, r 0 , at z >1.7. Our results are consistent with those from the 2dF QSO Redshift Survey and previous SDSS quasar measurements using photometric redshifts. Comparing our clustering measurements to those reported for X-ray selected active galactic nucleus at z ∼ 0.5–1, we find reasonable agreement in some cases but significantly lower correlation lengths in others. Assuming a standard ΛCDM cosmology, we find that the linear bias evolves from b ∼ 1.4 at z = 0.5 to b ∼ 3 at z = 2.2, with b ( z = 1.27) = 2.06 ± 0.03 for the full sample. We compare our data to analytical models and infer that quasars inhabit dark matter halos of constant mass M halo ∼ 2 × 10 12 h −1 M ☉ from redshifts z ∼ 2.5 (the peak of quasar activity) to z ∼ 0; therefore, the ratio of the halo mass for a typical quasar to the mean halo mass at the same epoch drops with decreasing redshift. The measured evolution of the clustering amplitude is in reasonable agreement with recent theoretical models, although measurements to fainter limits will be needed to distinguish different scenarios for quasar feeding and black hole growth.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".