Dark ages bounds on non-accreting massive compact halo objects

TL;DR

This paper uses the cosmic dawn and dark ages 21-cm signal to place new upper bounds on the fraction of dark matter in massive compact halo objects, especially for masses above 10^3 solar masses.

Contribution

It introduces a cosmological method to constrain MACHO dark matter using 21-cm signals, avoiding astrophysical uncertainties and considering various mass distributions.

Findings

Constraints on MACHO fraction are tighter using dark ages data.

Extended mass distributions yield more stringent bounds than monochromatic models.

Critical collapse models provide the strongest constraints at intermediate masses.

Abstract

We derive a complementary cosmological upper bound on the fraction of dark matter residing inside massive compact halo objects (MACHOs) using the cosmic dawn and dark ages global 21-cm signal $(T_{21})$. MACHOs of masses $M\gtrsim 10^3~M_\odot$ moving through the post-recombination baryonic fluid transfer kinetic energy to the intergalactic medium via dynamical friction, raising the gas temperature and distorting the 21-cm signal from the $\Lambda$CDM prediction. We consider both a monochromatic and two extended MACHO mass distributions: log normal and critical collapse. Imposing the conditions that the deviation in the global 21-cm signal $\Delta T_{21}$ does not exceed $50~\rm mK$ at $z\sim 17$ or $15~\rm mK$ at $z\sim 89$, and that no emission signal appears at $z \gtrsim 300$, we derive upper bounds on the MACHO fraction $f_M$ across the mass range $10^3 \lesssim M_c/M_\odot \lesssim 10^7$. The dark ages criterion yields constraints that are both tighter and free from astrophysical uncertainties associated with star formation, providing a complementary cosmological window. Extended distributions produce bounds that are generally more stringent than their monochromatic counterpart, with the critical collapse models yielding the strongest constraints at intermediate masses.