The Herschel view of the environment of the radio galaxy 4C+41.17 at z = 3.8

TL;DR

This study uses Herschel and Spitzer data to analyze the environment of the high-redshift radio galaxy 4C+41.17, identifying potential protocluster members and demonstrating the importance of multi-wavelength observations for such analyses.

Contribution

First detailed multi-wavelength analysis of 4C+41.17's environment, highlighting the rarity of a nearby galaxy at the same redshift and emphasizing the role of spectral energy distribution data.

Findings

Most Herschel sources are foreground objects.

The closest source to 4C+41.17 is likely at the same redshift.

Multi-wavelength data helps confirm or exclude protocluster candidates.

Abstract

We present Herschel observations at 70, 160, 250, 350 and 500 micron of the environment of the radio galaxy 4C+41.17 at z = 3.792. About 65% of the extracted sources are securely identified with mid-IR sources observed with the Spitzer Space Telescope at 3.6, 4.5, 5.8, 8 and 24 micron. We derive simple photometric redshifts, also including existing 850 micron and 1200 micron data, using templates of AGN, starburst-dominated systems and evolved stellar populations. We find that most of the Herschel sources are foreground to the radio galaxy and therefore do not belong to a structure associated with 4C+41.17. We do, however, find that the SED of the closest (~ 25" offset) source to the radio galaxy is fully consistent with being at the same redshift as 4C+41.17. We show that finding such a bright source that close to the radio galaxy at the same redshift is a very unlikely event, making the environment of 4C+41.17 a special case. We demonstrate that multi-wavelength data, in particular on the Rayleigh-Jeans side of the spectral energy distribution, allow us to confirm or rule out the presence of protocluster candidates that were previously selected by single wavelength data sets.