A Large-Scale Structure at Redshift 1.71 in the Lockman Hole

Abstract

We previously identified LH146, a diffuse X-ray source in the Lockman Hole, as a galaxy cluster at redshift 1.753. The redshift was based on one spectroscopic value, buttressed by seven additional photometric redshifts. We here confirm the previous spectroscopic redshift and present concordant spectroscopic redshifts for an additional eight galaxies. The average of these nine redshifts is 1.714 ± 0.012 (error on mean). Scrutiny of the galaxy distribution in redshift and the plane of the sky shows that there are two concentrations of galaxies near the X-ray source. In addition there are three diffuse X-ray sources spread along the axis connecting the galaxy concentrations. LH146 is one of these three and lies approximately at the center of the two galaxy concentrations and the outer two diffuse X-ray sources. We thus conclude that LH146 is at the redshift initially reported but it is not a single virialized galaxy cluster as previously assumed. Rather it appears to mark the approximate center of a larger region containing more objects. For brevity we term all these objects and their alignments as large scale structure. The exact nature of LH146 itself remains unclear.

Faint polarised sources in the Lockman Hole field at 1.4 GHz

“…11 and 15), which show peaks at z ≈ 0.6 and z ≈ 1.5. Henry et al (2014) also suggest that such an over-dense structure is present in the Lockman Hole at z = 1.71, which could also contribute to our observations. Due to the lack of faint sources it might be necessary to distinguish between the bright sources, where our source counts fit the simulations of O' Sullivan et al (2008), and faint sources, where the loss of FR I sources becomes dominant.…”

Mapping the large-scale structure around a z = 1.46 galaxy cluster in 3D using two adjacent narrow-band filters

“…Observational studies through wide-field imaging surveys of distant clusters at z < 1 have also supported the hierarchical formation by finding large-scale structures around galaxy clusters (e.g., Kodama et al 2005;Gal et al 2008;Tanaka et al 2009;Koyama et al 2010). Now, the discovery of large-scale structures around galaxy clusters and protoclusters is being extended to z ∼ 3 (e.g., Tanaka et al 2011;Tadaki et al 2012;Hayashi et al 2012;Koyama et al 2013;Erb et al 2011;Yamada et al 2012;Galametz et al 2013;Henry et al 2014). One interesting finding suggested by such observational studies is that cluster galaxies seem to follow an inside-out evolution in the sense that the environment where galaxies are active shifts from the densest regions at high redshifts (z ≈ 2-3) towards less dense regions at lower redshifts (z ≪ 1).…”

“…Now, the discovery of large-scale structures around galaxy clusters and protoclusters is being extended to z ∼ 3 (e.g. Erb, Bogosavljević & Steidel 2011;Tanaka et al 2011;Hayashi et al 2012;Tadaki et al 2012;Yamada et al 2012;Galametz et al 2013;Koyama et al 2013a;Henry et al 2014). One interesting finding suggested by such observational studies is that cluster galaxies seem to follow an inside-out evolution in the sense that the environment where galaxies are active shifts from the densest regions at high redshifts (z ≈ 2-3) towards less dense regions at lower redshifts (z 1).…”

KECK/MOSFIRE SPECTROSCOPIC CONFIRMATION OF A VIRGO-LIKE CLUSTER ANCESTOR AT z = 2.095

“…However, it is largely unknown whether and how these correlations would hold up at higher redshifts of z 2, when the mean star formation activities of the universe peaked and clusters were formed (e.g., Hopkins & Beacom 2006;Rettura et al 2010). Studying dense galaxy groups and clusters at z 2 provides crucial knowledge of the star formation history of high-mass galaxies and the hierarchical growth of massive structures (e.g., McCarthy et al 2007;Tran et al 2010;Brodwin et al 2013;Strazzullo et al 2013;Henry et al 2014).…”