First Results from Z -FOURGE: Discovery of a Candidate Cluster at z = 2.2 in COSMOS
Abstract
We report the first results from the Z -FOURGE survey: the discovery of a candidate galaxy cluster at z = 2.2 consisting of two compact overdensities with red galaxies detected at >~ 20σ above the mean surface density. The discovery was made possible by a new deep (Ks <~ 24.8 AB 5σ) Magellan/FOURSTAR near-IR imaging survey with five custom medium-bandwidth filters. The filters pinpoint the location of the Balmer/4000 Å break in evolved stellar populations at 1.5 < z < 3.5, yielding significantly more accurate photometric redshifts than possible with broadband imaging alone. The overdensities are within 1' of each other in the COSMOS field and appear to be embedded in a larger structure that contains at least one additional overdensity (~10σ). Considering the global properties of the overdensities, the z = 2.2 system appears to be the most distant example of a galaxy cluster with a population of red galaxies. A comparison to a large ΛCDM simulation suggests that the system may consist of merging subclusters, with properties in between those of z > 2 protoclusters with more diffuse distributions of blue galaxies and the lower-redshift galaxy clusters with prominent red sequences. The structure is completely absent in public optical catalogs in COSMOS and only weakly visible in a shallower near-IR survey. The discovery showcases the potential of deep near-IR surveys with medium-band filters to advance the understanding of environment and galaxy evolution at z > 1.5.
This Letter includes data gathered with the 6.5 m Magellan Telescopes located at Las Campanas Observatory, Chile.- Publication:
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The Astrophysical Journal
- Pub Date:
- April 2012
- DOI:
- 10.1088/2041-8205/748/2/L21
- arXiv:
- arXiv:1112.2691
- Bibcode:
- 2012ApJ...748L..21S
- Keywords:
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- galaxies: clusters: general;
- galaxies: high-redshift;
- large-scale structure of universe;
- Astrophysics - Cosmology and Nongalactic Astrophysics
- E-Print:
- final version accepted by ApJL, see http://z-fourge.strw.leidenuniv.nl for more details