LARGE-SCALE STRUCTURE AROUND A z = 2.1 CLUSTER

Abstract

The most prodigious starburst galaxies are absent in massive galaxy clusters today, but their connection with largescale environments is less clear at  z 2. We present a search of large-scale structure around a galaxy cluster core at z = 2.095 using a set of spectroscopically confirmed galaxies. We find that both color-selected star-forming galaxies (SFGs) and dusty star-forming galaxies (DSFGs) show significant overdensities around the z = 2.095 cluster. A total of eight DSFGs (including three X-ray luminous active galactic nuclei, AGNs) and 34 SFGs are found within a 10′ radius (corresponds to ∼15 cMpc atz 2.1) from the cluster center and within a redshift range of D = z 0.02, which leads to galaxy overdensities of d~12.3 DSFG and d~2.8 SFG . The cluster core and the extended DSFG-and SFG-rich structures together demonstrate an active cluster formation phase, in which the cluster is accreting a significant amount of material from large-scale structure while the more mature core may begin to virialize. Our finding of this DSFG-rich structure, along with a number of other protoclusters with excess DSFGs and AGNs found to date, suggest that the overdensities of these rare sources indeed trace significant mass overdensities. However, it remains puzzling how these intense star formers are triggered concurrently. Although an increased probability of galaxy interactions and/or enhanced gas supply can trigger the excess of DSFGs, our stacking analysis based on 850 μm images and morphological analysis based on rest-frame optical imaging do not show such enhancements of merger fraction and gas content in this structure.

On the Gas Content, Star Formation Efficiency, and Environmental Quenching of Massive Galaxies in Protoclusters at z ≈ 2.0–2.5

“…Steinhauser et al 2016). In line with these findings, Casey et al (2015) and Hung et al (2016) found slightly higher fractions of irregular and interacting galaxies in the z = 2.47 and 2.10 structures than in their control samples (although with a low statistical significance of ∼ 1.5σ), supporting the influence of galaxy mergers in the evolution of galaxies in overdense environments.…”

“…Previous studies probing the gas content of galaxies in high density environments suffer from small samples of extreme sources like DSFGs or AGN. In contrast, our study benefits from a relatively large sample of massive galaxies which are spectroscopically-confirmed to be proto-cluster members (drawn from Casey et al 2015;Casey 2016;and Hung et al 2016). As described in detail in the aforementioned references, the targets were selected from several redshift surveys, which followed up cluster candidates from large near-infrared (NIR)-selected catalogs (mostly K-band selected galaxies) in the COSMOS field (e.g.…”

“…This active formation phase is further support by the high number of extreme galaxies within the proto-clusters. The z = 2.10 structure contains 9 rare DSFGs and 4 AGNs, has a total star formation rate (SFR) of ∼ 5300 M ⊙ yr −1 , total stellar mass of ∼ 2 × 10 12 M ⊙ , a galaxy overdensy of δ gal ∼ 8, and an estimated total halo mass of ∼ 2 × 10 14 M ⊙ (Spitler et al 2012;Yuan et al 2014;Hung et al 2016;Casey 2016). Similarly, the z = 2.47 structure contains at least 7 rare DSFGs and 5 AGNs, implying an overdensity of δ gal ∼ 10, a total SFR of ∼ 4500 M ⊙ yr −1 , total stellar mass of ∼ 1 × 10 12 M ⊙ , and halo mass of ∼ 8×10 13 M ⊙ (Casey et al 2015;Casey 2016).…”

SCUBA-2 observations of candidate starbursting protoclusters selected by Planck and Herschel-SPIRE

“…We also apply our MCMC χ 2 -minimisation method to SCUBA-2 maps of a known DSFG-rich protocluster at z ∼2, PCL1002 (Casey et al 2015;Hung et al 2016), and 256 sources distributed in the COSMOS field in the S2CLS survey. The original COSMOS map is cropped to the central 1 deg × 1 deg region in order to exclude the lower sensitivity edges.…”

ALMA Deep Field in SSA22: Source Catalog and Number Counts

“…Furthermore, there are other z = 3.09 ALMA SMGs outside the AzTEC beam across the entire field of ADF22 ( Figure 7, Table 2). This suggests that intense dusty star formation may also be enhanced by the environment on a large-scale (Umehata et al 2015; see also Blain et al 2004;Tamura et al 2009;Umehata et al 2014;Casey et al 2015;Casey 2016;Hung et al 2016). …”