The Formation of Direct Collapse Black Holes at Cosmic Dawn and 21 cm Global Spectrum
JWST reveals numerous high- z galaxies and supermassive black holes (SMBHs), suggesting that stars and SMBH seeds formation at z ≳ 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 irrad...
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| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
| Subjects: | |
| Online Access: | https://doi.org/10.3847/1538-4357/adc730 |
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| Summary: | JWST reveals numerous high- z galaxies and supermassive black holes (SMBHs), suggesting that stars and SMBH seeds formation at z ≳ 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 ${k}_{{{\rm{H}}}_{2}}\unicode{8210}{k}_{{{\rm{H}}}^{-}}$ 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 _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 $\delta {T}_{b}^{{\rm{trough}}}$ at Cosmic Dawn encodes the DCBH abundance information. We provide a tentative trend in the n _DCBH – $\delta {T}_{{\rm{b}}}^{{\rm{trough}}}$ relation, which could be a useful guide. In our fiducial model, if $\delta {T}_{b}^{{\rm{trough}}}\gtrsim -100$ mK, then the DCBH is rather rare; if $-150\,\mathrm{mK}\lesssim \delta {T}_{b}^{\mathrm{trough}}\lesssim -100$ mK, ${n}_{{\rm{DCBH}}}\sim { \mathcal O }(1{0}^{-2}-1{0}^{-3})$ cMpc ^−3 (comoving Mpc ^−3 ), consistent with the HST/JWST observed SMBHs abundance at z ≳ 6; if $\delta {T}_{b}^{{\rm{trough}}}\lesssim -150$ mK, n _DCBH can largely exceed ${ \mathcal O }(1{0}^{-2})$ cMpc ^−3 . The 21 cm global spectrum observations will help to constrain the DCBH abundance. |
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| ISSN: | 1538-4357 |