Discovery of a Large Number of Candidate Protoclusters Traced by ~15 Mpc-scale Galaxy Overdensities in COSMOS
Abstract
To demonstrate the feasibility of studying the epoch of massive galaxy cluster formation in a more systematic manner using current and future galaxy surveys, we report the discovery of a large sample of protocluster candidates in the 1.62 deg2 COSMOS/UltraVISTA field traced by optical/infrared selected galaxies using photometric redshifts. By comparing properly smoothed three-dimensional galaxy density maps of the observations and a set of matched simulations incorporating the dominant observational effects (galaxy selection and photometric redshift uncertainties), we first confirm that the observed ~15 comoving Mpc-scale galaxy clustering is consistent with ΛCDM models. Using further the relation between high-z overdensity and the present day cluster mass calibrated in these matched simulations, we found 36 candidate structures at 1.6 < z < 3.1, showing overdensities consistent with the progenitors of M z = 0 ~ 1015 M ⊙ clusters. Taking into account the significant upward scattering of lower mass structures, the probabilities for the candidates to have at least M z = 0 ~ 1014 M ⊙ are ~70%. For each structure, about 15%-40% of photometric galaxy candidates are expected to be true protocluster members that will merge into a cluster-scale halo by z = 0. With solely photometric redshifts, we successfully rediscover two spectroscopically confirmed structures in this field, suggesting that our algorithm is robust. This work generates a large sample of uniformly selected protocluster candidates, providing rich targets for spectroscopic follow-up and subsequent studies of cluster formation. Meanwhile, it demonstrates the potential for probing early cluster formation with upcoming redshift surveys such as the Hobby-Eberly Telescope Dark Energy Experiment and the Subaru Prime Focus Spectrograph survey.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- February 2014
- DOI:
- 10.1088/2041-8205/782/1/L3
- arXiv:
- arXiv:1312.4747
- Bibcode:
- 2014ApJ...782L...3C
- Keywords:
-
- cosmology: observations;
- galaxies: clusters: general;
- galaxies: evolution;
- galaxies: high-redshift;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- 6 pages, 3 figures, 1 table