2024A&A...689A.170L

Context. Green pea galaxies (GPs) are renowned for their compact sizes, low masses, strong emission lines, high star formation rates (SFRs), and being analogs to high-z Lyα-emitting galaxies.
Aims. This investigation focuses on a curated sample of six GPs with X-ray detections, sourced from XMM-Newton, Swift, Chandra and eROSITA, with the aim to elucidate the origin of their X-ray luminosity.
Methods. We determined the GPs' physical properties, including the SFRs, stellar masses, and metallicities, based on multiwavelength photometry and LAMOST spectra analysis.
Results. Within the L_X-SFR relation, GPs predominantly occupy the high specific SFR domain, where high-mass X-ray binaries (HMXBs) dominate, leading to an excess in X-ray luminosity compared to the sole contributions from HMXBs ($ L_X^{\rm HMXB} $ ). Moreover, GPs exhibit a noticeable excess in X-ray luminosity within the L_X-SFR-metallicity relationship. The cumulative input from X-ray binaries, hot gas, hot interstellar medium, and young stellar objects falls short in accounting for the X-ray luminosity observed in GPs. The presence of active galactic nucleus (AGNs) surfaces is suggested based on mid-infrared color-color criteria. Furthermore, based on the M_BH derived from LAMOST optical spectra, GPs conform to the M_BH-M_⋆ scaling relation.
Conclusions. The origin of the X-ray excess likely stems from the combined contributions of HMXBs and AGNs, although further scrutiny via X-ray spectra and spatially resolved imaging using forthcoming facilities is needed to confirm this.