21 cm forest constraints on primordial black holes

Primordial black holes (PBHs) as part of the Dark Matter (DM) would modify evolution large-scale structures and thermal history universe. Future 21 cm forest observations, sensitive to small scales state Inter Galactic Medium (IGM), could probe existence such PBHs. In this article, we show that shot noise isocurvature mode on induced by presence PBHs can enhance amount low mass halos, or minihalos, thus, number absorption lines. However, if is large $M_{\rm PBH}\gtrsim 10 \, M_\odot$, with an abundant enough fraction DM, $f_{\rm PBH}$, IGM heating due accretion onto counteracts enhancement mode, reducing lines instead. The concurrence both effects imprints distinctive signatures in absorbers, allowing bound abundance We compute prospects for constraining future finding achievable competitive upper limits PBH} \sim 10^{-3}$ at PBH}= 100 even lower larger masses, unexplored regions parameter space current probes. impact astrophysical X-ray sources temperature also studied, which potentially weaken bounds.