Bright submillimeter galaxies do trace galaxy protoclusters

TL;DR

This study demonstrates that bright submillimeter galaxies are effective tracers of galaxy protoclusters across a wide redshift range, revealing complex morphologies and evolving galaxy populations in dense environments.

Contribution

First systematic search confirming that submillimeter galaxies reliably trace galaxy protoclusters from redshift 1.2 to 5.3, including new protocluster detections and insights into their morphology and galaxy content.

Findings

92% of SMGs are associated with galaxy overdensities.

Protoclusters show complex core morphologies, including filamentary and clumpy structures.

High-redshift ($z ightarrow5$) protoclusters are dominated by Lyman-alpha emitters and Lyman break galaxies.

Abstract

There is controversy whether dusty starbursts selected at submillimeter wavelengths can trace galaxy overdensities. We perform the first systematic search for protoclusters around a homogeneously selected sample of 12 spectroscopically confirmed submillimeter galaxies (SMGs) at $z\sim1.2-5.3$ in the GOODS-N field. We applied the Poisson Probability Method (PPM) to search for Mpc scale overdensities around these SMGs using three photometric redshift catalogs. We detect galaxy overdensities for 11 out of the 12 SMGs ($92\%\pm8$\%), distributed over eight protoclusters. We confirm three previously discovered protoclusters, and we detect five new ones around the SMGs SMMJ123634 ($z=1.225$), ID.19 ($z=2.047$), SMMJ123607 ($z=2.487$), SMMJ123606 ($z=2.505$), and GN10 ($z=5.303$). A wavelet-based analysis shows that the SMGs live in protocluster cores with a complex morphology (compact, filamentary, or clumpy) and an average size of $\sim(0.4-1)$Mpc. By comparing the PPM results obtained using independently the three redshift catalogs, we possibly witness a transitioning phase at $z\gtrsim4$ for the galaxy populations. While $z\lesssim4$ protoclusters appear to be populated by dusty galaxies, those at highest redshifts $z\sim5$ are detected as overdensities of Lyman$\alpha$ emitters or Lyman break galaxies. We also find a good correlation between the molecular (H$_2$) gas mass of the SMG and the overdensity significance. To explain the overall phenomenology, we suggest that galaxy interactions in dense environments likely triggered the starburst and gas-rich phase of the SMGs. Altogether, we support the scenario that SMGs are excellent tracers of distant protoclusters. Those presented in this work are excellent targets for the {\it James Webb Space Telescope.} Surveys with forthcoming facilities (e.g., {\it Euclid}, LSST) can be tuned to detect even larger samples of distant protoclusters.