# Warm dark matter constraints from high-$z$ Direct Collapse Black Holes using the JWST

## TL;DR

This study models the formation and evolution of direct collapse black holes at high redshifts under different dark matter scenarios, predicting their abundance, redshift distribution, and observable signatures with JWST to constrain dark matter properties.

## Contribution

It introduces a semi-analytic model that combines dark matter and baryonic processes to compare DCBH formation in CDM and WDM cosmologies, providing new insights into their redshift evolution and observability.

## Key findings

- DCBH number density increases from 10^{-6.1} to 10^{-3.5} cMpc^{-3} from z~17.5 to 8 in CDM.
- WDM delays structure formation, allowing DCBHs to persist down to z~5, unlike in CDM.
- JWST NIRCam colors can help identify DCBHs and constrain WDM particle mass.

## Abstract

We use a semi-analytic model, ${\it Delphi}$, that jointly tracks the dark matter and baryonic assembly of high-redshift ($z \simeq 4-20$) galaxies to gain insight on the number density of Direct Collapse Black Hole (DCBH) hosts in three different cosmologies: the standard Cold Dark Matter (CDM) model and two Warm Dark Matter (WDM) models with particle masses of 3.5 and 1.5 keV. Obtaining the Lyman-Werner (LW) luminosity of each galaxy from ${\it Delphi}$, we use a clustering bias analysis to identify all, pristine halos with a virial temperature $T_{vir}>=10^4$ K that are irradiated by a LW background above a critical value as, DCBH hosts. In good agreement with previous studies, we find the DCBH number density rises from $\sim10^{-6.1}$ to $\sim 10^{-3.5}\, \mathrm{cMpc^{-3}}$ from $z\simeq 17.5$ to $8$ in the CDM model using a critical LW background value of $30 J_{21}$ (where $J_{21}= 10^{-21} \, {\rm erg\, s^{-1}\, Hz^{-1} \, cm^{-2} \, sr^{-1}}$). We find that a combination of delayed structure formation and an accelerated assembly of galaxies results in a later metal-enrichment and an accelerated build-up of the LW background in the 1.5 keV WDM model, resulting in DCBH hosts persisting down to much lower redshifts ($z \simeq 5$) as compared to CDM where DCBH hosts only exist down to $z \simeq 8$. We end by showing how the expected colours in three different bands of the Near Infrared Camera (NIRCam) onboard the forthcoming James Webb Space Telescope (${\it JWST}$) can be used to hunt for potential $z \simeq 5-9$ DCBHs, allowing hints on the WDM particle mass.