The impact of protocluster environments atz= 1.6

Abstract

We investigate the effects of dense environments on galaxy evolution by examining how the properties of galaxies in the z = 1.6 protocluster Cl 0218.3−0510 depend on their location. We determine galaxy properties using spectral energy distribution fitting to 14-band photometry, including data at three wavelengths that tightly bracket the Balmer and 4000Å breaks of the protocluster galaxies. We find that two-thirds of the protocluster galaxies, which lie between several compact groups, are indistinguishable from field galaxies. The other third, which reside within the groups, differ significantly from the intergroup galaxies in both colour and specific star formation rate. We find that the fraction of red galaxies within the massive protocluster groups is twice that of the intergroup region. These excess red galaxies are due to enhanced fractions of both passive galaxies (1.7 times that of the intergroup region) and dusty star-forming galaxies (3 times that of the intergroup region). We infer that some protocluster galaxies are processed in the groups before the cluster collapses. These processes act to suppress star formation and change the mode of star formation from unobscured to obscured.

MAHALO Deep Cluster Survey I. Accelerated and enhanced galaxy formation in the densest regions of a protocluster at z = 2.5

“…4). Such higher dust obscuration of galaxies in local overdensities for a given stellar mass range is consistent with the results of past studies (Koyama et al 2013b;Hatch et al 2017) that have investigated the environmental dependence of dust reddening of galaxies on a more global scale. However, our measurement of the dust reddening is based on the SED-fitting under the assumption of fixed stellar metallicity and limited star formation history.…”

Enhancement of AGN in a protocluster at z = 1.6

“…This is consistent with the 8 AGN found using the "Goldilocks" sample in Section 2.2. Therefore, we conclude that our result of the AGN enhancement in the protocluster is robust to the protocluster member selection technique used in Hatch et al (2017).…”

“…We also find that the AGN picked out as part of the test protocluster sample, and not the "Goldilocks" sample, are either massive and red, or blue. They all lie within the region of the colour-mass diagram where > 75% of protocluster members would be correctly identified (Hatch et al 2017). It is therefore unlikely that we are missing any protocluster AGN due to the protocluster membership selection criterion.…”

ALMA Pinpoints a Strong Overdensity of U/LIRGs in the Massive Cluster XCS J2215 at z = 1.46

“…Of particular relevance here is the SCUBA-2 survey of the clusters by Ma15, which discovered an overdensity of submillimeter galaxies (SMGs) in its core. Unlike other (proto-)clusters studied at high redshifts (e.g., CLG J0218; Rudnick et al 2012;Lotz et al 2013;Hatch et al 2016), XCS J2215 appears structurally well-developed. By combining XMM-Newton and Chandra observations, Hilton et al (2010, hereafter H10) Carlberg et al (1997;where R 200 is the radius from the cluster center within which the mean density is 200 times the critical density at the redshift of the cluster), H10 used an iterative method to estimate a line-of-sight velocity dispersion of σ v =720±110 km s −1 from the 31 galaxies with spectroscopic redshifts within R 200 =0.8±0.1 Mpc or 100″.…”