Discovery of a high-z protocluster with tunable filters: the case of 6C0140+326 at z=4.4

TL;DR

This study uses a tunable narrowband filter on the Gran Telescopio Canarias to identify a high-redshift protocluster around the radio galaxy 6C0140+326 at z=4.4, revealing a significant overdensity of Lya emitters.

Contribution

First application of a tunable filter for high-z protocluster detection, demonstrating its effectiveness in identifying overdensities at z>4.

Findings

Detected 27 candidate Lya emitters in the protocluster field.

Found the protocluster to be denser by a factor of 9±5 compared to blank fields.

Observed spatial and redshift distributions indicating a real overdensity.

Abstract

We present the first results obtained using a tunable narrowband filter in the search for high-z protoclusters. Using the recently commissioned red tunable filter on the Gran Telescopio Canarias we have searched for Lya emitters in a 75 arcmin^2 field centered on the z=4.413 radio galaxy 6C0140+326. With three different wavelength tunings we find a total of 27 unique candidate Lya emitters. The availability of three different wavelength tunings allows us to make estimates of the redshifts for each of the objects. It also allows us to separate a possible protocluster from structure in the immediate foreground. This division shows that the foreground region contains significantly fewer Lya emitters. Also, the spatial distribution of the objects in the protocluster field deviates from a random distribution at the 2.5 sigma level. The observed redshift distribution of the emitters is different from the expected distribution of a blank field at the ~3 sigma level, with the Lya emitters concentrated near the radio galaxy at z>4.38. The 6C0140+326 field is denser by a factor of 9+/-5 than a blank field, and the number density of Lya emitters close to the radio galaxy is similar to that of the z~4.1 protocluster around TNJ1338-1942. We thus conclude that there is an overdensity of Lya emitters around the radio galaxy 6C0140+326. This is one of few known overdensities at such a high redshift.