Saved in:
| Main Authors: | , , , |
|---|---|
| Format: | Preprint |
| Published: |
2025
|
| Subjects: | |
| Online Access: | https://arxiv.org/abs/2503.22130 |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
Table of Contents:
- JWST reveals numerous high-z galaxies and Supermassive Black Holes (SMBHs), suggesting that stars and SMBH seeds formation at $z \gtrsim 10$ may be more efficient than previously derived. One popular SMBH seed scenario is the Direct Collapse Black Holes (DCBHs) formed in pristine atomic-cooling halos irradiated by nearby galaxies. Therefore, the efficient star formation likely facilitates the formation of DCBH. We calculate the first critical $k_{\rm H_2}-k_{\rm H^-}$ curves for DCBH formation under the influence of X-ray radiation using the one-zone model. We then build the UV luminosity function consistent with JWST observations and incorporate it into the model that calculates the DCBH-triggering probability. We confirm that enhanced star formation promotes the DCBH formation. However, the DCBH abundance $n_{\rm DCBH}$ is significantly influenced by the X-ray radiation that is also related to star formation. Since the 21 cm global spectrum is also X-ray dependent, the 21 cm absorption depth $δT_b^{\rm trough}$ at Cosmic Dawn encodes the DCBH abundance information. We provide a tentative trend in the $n_{\rm DCBH}$ - $δT^{\rm trough}_{\rm b}$ relation, which could be a useful guide. In our fiducial model, if $δT_b^{\rm trough}\gtrsim -100$ mK, then the DCBH is rather rare; if $-150~{\rm mK} \lesssim δT_b^{\rm trough}\lesssim -100$ mK, $ n_{\rm DCBH} \sim \mathcal{O}(10^{-2}-10^{-3})$ cMpc$^{-3}$ (comoving $\rm Mpc^{-3}$), consistent with the HST/JWST observed SMBHs abundance at $z\gtrsim 6$; if $δT_b^{\rm trough}\lesssim -150$ mK, $n_{\rm DCBH}$ can largely exceed $\mathcal{O}(10^{-2})$ cMpc$^{-3}$. The 21 cm global spectrum observations will help to constrain the DCBH abundance.