ODIN: Clustering Properties of Ly$\alpha$ Blobs at $z$ $\sim$ 2.4 and 3.1

TL;DR

This study uses clustering analysis of Ly$ ext{alpha}$ blobs from the ODIN survey to estimate their dark matter halo properties at redshifts 2.4 and 3.1, revealing their association with proto-group environments and massive halos.

Contribution

First clustering-based estimation of dark matter halo masses for Ly$ ext{alpha}$ blobs at these redshifts, linking them to proto-group environments and galaxy evolution.

Findings

LABs inhabit massive dark matter halos (~10^{12} M_ ext{sun})

LABs trace proto-group environments evolving into present-day massive halos

LABs occupy a small but significant fraction of halos above certain mass thresholds

Abstract

Spatially extended Ly$\alpha$ nebulae, known as Ly$\alpha$ blobs (LABs), are a rare population at $z > 2$ that are thought to trace proto-groups or the progenitors of massive galaxies in the present-day universe. However, their dark matter halo properties (e.g., halo mass) are still uncertain due to their rarity and strong field-to-field variation. The One-hundred-deg$^2$ DECam Imaging in Narrowbands (ODIN) survey has discovered 103 and 112 LABs in the extended ($\sim$9~\sqdeg) COSMOS field at $z\sim2.4$ and 3.1, respectively, enabling estimation of their bias and host halo masses through clustering analysis. We measure the angular auto-correlation functions (ACFs) of LABs and derive galaxy bias factors of $b$ = $4.0\pm0.8$ and $3.8\pm0.7$, corresponding to minimum halo masses of $2.8^{+3.0}_{-1.8}$ and $0.7^{+0.8}_{-0.5}\times10^{12}~M_\odot$ and median halo masses of $4.2^{+3.8}_{-2.5}$ and $1.1^{+1.1}_{-0.7}\times10^{12}~M_\odot$ at $z\sim2.4$ and 3.1, respectively. LABs occupy $\sim$11$^{+39}_{-8}$\% and $\sim$3$^{+9}_{-2}$\% of all dark matter halos above these minimum halo masses. These findings suggest that LABs inhabit massive dark matter halos, likely tracing proto-group environments that evolve into present-day massive halos ($\sim$10$^{13}~M_\odot$), where massive elliptical galaxies or galaxy groups reside, by $z=0$.