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Turbulent velocity requirement for reproducing Balmer absorption in The Cliff

Determine whether a high turbulent velocity in the dense absorbing gas (v_turb ≈ 500 km s−1), as invoked in BH* Cloudy models to match Balmer absorption equivalent widths in MoM-BH*-1, is required to reproduce the Balmer absorption features observed in The Cliff by precisely constraining the absorber’s kinematics with deeper G395M spectroscopy.

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Background

BH* (black hole star) models posit dense, turbulent gas around a central ionizing source that can produce strong Balmer breaks and absorption features similar to stellar atmospheres.

In modeling MoM-BH*-1, a high turbulent velocity was necessary to reproduce Balmer absorption equivalent widths; however, the authors emphasize that the applicability of such a high v_turb to The Cliff remains to be established due to the current constraints on the absorption profile.

References

A high turbulent velocity ($v_{\rm turb}=500\,-1$) is needed to produce the EWs of the Balmer absorption features seen in MoM-BH*-1. Whether this is also needed for The Cliff is unclear, primarily due to the poorly constrained absorption feature in the G395M spectrum (Section~\ref{sec:elines}).

— A remarkable Ruby: Absorption in dense gas, rather than evolved stars, drives the extreme Balmer break of a Little Red Dot at $z=3.5$ (2503.16600 - Graaff et al., 20 Mar 2025) in Section 6.4 (A ‘Black hole star’?)