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

Abstract

We present a novel method to estimate accurate redshifts of star-forming galaxies by measuring the flux ratio of the same emission line observed through two adjacent narrow-band filters. We apply this method to our NB912 and new NB921 data taken with Suprime-Cam on the Subaru Telescope of a galaxy cluster, XMMXCS J2215.9-1738, at z = 1.46 and its surrounding structures. We obtain redshifts for 170 [O II] emission line galaxies at z ∼ 1.46, among which 41 galaxies are spectroscopically confirmed with MOIRCS and FMOS on the Subaru mainly, showing an accuracy of σ((z − z spec )/(1 + z spec )) = 0.002. This allows us to reveal filamentary structures that penetrate towards the centre of the galaxy cluster and intersect with other structures, consistent with the picture of hierarchical cluster formation. We also find that the projected celestial distribution does not precisely trace the real distribution of galaxies, indicating the importance of the three dimensional view of structures to properly identify and quantify galaxy environments. We investigate the environmental dependence of galaxy properties with local density, confirming that the median colour of galaxies becomes redder in higher density region while the star-formation rate of star-forming galaxies does not depend strongly on local environment in this structure. This implies that the star-forming activity in galaxies is truncated on a relatively short time scale in the cluster centre.

Evolutionary Phases of Gas-rich Galaxies in a Galaxy Cluster at z = 1.46

“…For six of the 17 emission lines, the redshifts measured by the optical and NIR spectroscopies are in good agreement with the redshifts measured from the ALMA data by assuming that they are CO(2-1) lines. Among the emission lines without any spectroscopic redshifts, we can still estimate redshifts for five lines by combining the narrowband imaging data of the adjacent two filters, NB912 and NB921 (Hayashi et al 2014). Most of the redshifts thus determined are consistent with those of CO(2-1) lines.…”

“…To remove the possible false detections, we cross-match the coordinates of the detections in the ALMA data with those of the objects in the optical and NIR data catalogs by Hayashi et al (2014). We use a search radius of 1 arcsec for the object matching.…”

“…Hayashi et al (2010Hayashi et al ( , 2014 conduct a deep narrowband imaging with Suprime-Cam/Subaru targeting [O II] emission lines from galaxies in this cluster. The observation with SuprimeCam/Subaru has identified many star-forming galaxies in the core region (see also Hilton et al 2010;Ma et al 2015), which suggests that the massive galaxies in the cluster core are still in their formation phase and are as active as those in the general field at similar redshifts.…”

“…We have created catalogs of [O II] emission-line galaxies selected with two narrowband filters, NB912 and NB921, (Hayashi et al 2014). Among the confirmed member galaxies, 20 galaxies are [O II] emitters.…”

The KMOS Cluster Survey (KCS). I. The Fundamental Plane and the Formation Ages of Cluster Galaxies at Redshift 1.4 < Z < 1.6*

“…From the scatter and the intercept of the red sequence, Hilton et al (2009) derived a galaxy formation redshift in the range z 3 5 f~-. A significant amount of red-sequence galaxies show some level of star formation, with O II [ ] emission in their observed spectra (e.g., Hilton et al 2009Hilton et al , 2010 or via narrow-band imaging (Hayashi et al 2010(Hayashi et al , 2011(Hayashi et al , 2014. Some galaxies in the cluster core show a significant amount of obscured star formation with substantial emission at 24 μm (e.g., Hilton et al 2010) and in submillimeter bands (e.g., Ma et al 2015;Stach et al 2017), and there are also a significant number of AGNs (Hayashi et al 2011).…”