Massive starburst galaxies in a z = 2.16 proto-cluster unveiled by panoramic Hα mapping

Abstract

We present a panoramic narrow-band study of Hα emitters in the field of the z = 2.16 protocluster around PKS 1138−262 using MOIRCS on the Subaru Telescope. We find 83 Hα emitters down to a star formation rate of SFR (Hα) ∼ 10 M yr −1 across a ∼7 × 7 arcmin 2 region centred on the radio galaxy, and identify ∼10-Mpc scale filaments of emitters running across this region. By examining the properties of Hα emitters within the large-scale structure, we find that galaxies in the higher density environments at z = 2.16 tend to have redder colours and higher stellar masses compared to galaxies in more underdense regions. We also find a population of Hα emitters with red colours [(J − K s ) 1], which are much more frequent in the denser environments and which have apparently very high stellar masses with M * 10 11 M , implying that these cluster galaxies have already formed a large part of their stellar mass before z ∼ 2. Spitzer Space Telescope 24-µm data suggest that many of these red Hα emitters are bright, dusty starbursts (rather than quiescent sources). We also find that the proto-cluster galaxies follow the same correlation between SFR and M * (the 'main sequence') of z ∼ 2 field star-forming galaxies, but with an excess of massive galaxies. These very massive star-forming galaxies are not seen in our similar, previous study of z ∼ 1 clusters, suggesting that their star formation activity has been shut off at 1 z 2. We infer that the massive red (but active) galaxies in this rich proto-cluster are likely to be the products of environmental effects, and they represent the accelerated galaxy formation and evolution in a biased high-density region in the early Universe.

An excess of dusty starbursts related to the Spiderweb galaxy

“…In addition to this we find counterparts to several LABOCA sources in the Hα imaging data. This motivates us to test a new approach by applying the p-statistic method to the HAEs in the field of MRC1138−262 (Koyama et al 2013a); cf. with Smail et al (2014) who associated [OII] emitters successfully in the field and at the redshift of the cluster Cl0218.3−0510 with SMGs selected in this region.…”

“…In three cases, DKB01, DKB07 and DKB12, we find two, three and four HAEs within the search radius, respectively. Thirteen HAEs from Koyama et al (2013a) are LABOCA counterparts of which 10 are classified as robust counterparts and only three are tentative. Therefore, this seems to be a very promising approach in order to find SMG counterparts (with subarcsecond position accuracy) for a (proto)cluster with known redshift.…”

“…Rigby et al (2014) present Herschel SPIRE observations of a larger field (∼400 arcmin 2 ), centered on the HzRG. They report an excess of SPIRE 500 μm sources but found no filamentary structure in the far-infrared (FIR) as seen in the rest-frame optical (Kurk et al 2004a;Koyama et al 2013a). However, in both cases no counterpart identification was attempted for the individual sources.…”

Defying jet-gas alignment in two radio galaxies atz~ 2 with extended light profiles: Similarities to brightest cluster galaxies

“…Narrowband imaging is a standard way of identifying emissionline galaxies at high redshifts, and has been successfully used to identify over-densities of actively star-forming galaxies around high-redshift galaxies for almost two decades (e.g., Chambers et al 1996;Le Fevre et al 1996;Kurk et al 2004a;Venemans et al 2007;Hatch et al 2011;Koyama et al 2013;Hayashi et al 2012;Cooke et al 2014). Most of these observations were carried out for HzRGs at z 2, where Hα falls in the K band, which is relatively free from telluric night-sky lines.…”

Massive quiescent galaxies at z > 3 in the Millennium simulation populated by a semi-analytic galaxy formation model

“…Elbaz et al 2007;Tran et al 2010;Grützbauch et al 2011;Koyama et al 2013;Martini et al 2013;Bufanda et al 2017). The redshift z ∼ 2 marks an important epoch of galaxy evolution, encompassing both the peak of cosmic star formation rate (e.g.…”