X-Ray View of Little Red Dots: Do They Host Supermassive Black Holes?

The discovery of Little Red Dots (LRDs)-a population of compact, high-redshift, dust-reddened galaxies-is one of the most surprising results from JWST. However, the nature of LRDs is still debated: does the near-infrared emission originate from accreting supermassive black holes (SMBHs), or intense star formation? In this work, we utilize ultra-deep Chandra observations and study LRDs residing behind the lensing galaxy cluster, A2744. We probe the X-ray emission from individual galaxies but find that they remain undetected and provide SMBH mass upper limits of less than or similar to(1.5-16) x 106 M circle dot assuming Eddington limited accretion. To increase the signal-to-noise ratios, we conduct a stacking analysis of the full sample with a total lensed exposure time of approximate to 87 Ms. We also bin the galaxies based on their stellar mass, lensing magnification, and detected broad-line H alpha emission. For the LRDs exhibiting broad-line H alpha emission, there is a hint of a stacked signal (similar to 2.6 sigma), corresponding to an SMBH mass of similar to 3.2 x 106 M circle dot. Assuming unobscured, Eddington-limited accretion, this black hole (BH) mass is at least 1.5 orders of magnitude lower than that inferred from virial mass estimates using JWST spectra. Given galaxy-dominated stellar mass estimates, our results imply that LRDs do not host overmassive SMBHs and/or accrete at a few percent of their Eddington limit. However, alternative stellar mass estimates may still support that LRDs host overmassive BHs. The significant discrepancy between the JWST and Chandra data hints that the scaling relations used to infer the SMBH mass from the H alpha line and virial relations may not be applicable for high-redshift LRDs.