James Webb Space Telescope Feed Post

Overmassive black holes at cosmic noon: linking the local and the high-redshift Universe

One of the 12 cosmic noon low-mass galaxies hosting an overmassive BH. Top left: Spectral energy distribution fitting of the rest-frame observed ultraviolet, optical, and infrared (when available) photometry (black points) with the best-fit model (black curve), including a combination of the galaxy template (green), an AGN accretion disk component (blue) and an AGN dust torus model (yellow). Top right: PDF for the stellar mass taking into account all possible fractions of AGN emission and providing an upper limit on the stellar mass. So the most probable value (MsPDF, blue dashed line) has a higher value than the best-fit stellar mass (MsBEST, red solid line). The 16 and 84 percentile intervals (gray shades) are also indicated. Middle: Emission line fitting of the VIPERS spectrum including the continuum emission (in yellow, top panel), and the broad lines (in blue) decomposed into broad (in red) and narrow (in green) components (zoom-in in the bottom panels). Bottom: Subaru Hyper Suprime-Cam image in the i-band. Abstract: We report for the first time a sample of 12 supermassive black holes (SMBHs) hosted by low-mass galaxies at cosmic noon, i.e., in a redshift range consistent with the peak of star formation history: z~1-3. These black holes are two orders of magnitude too massive for the stellar content of their hosts when compared with the local relation for active galaxies. These overmassive systems at cosmic noon share similar properties with the high-z sources found ubiquitously in recent \textit{James Webb Space Telescope} (\textit{JWST}) surveys (same range of black hole-to-stellar mass ratio, bolometric luminosity, and Eddington ratio). We argue that black hole feedback processes, for which there is possible evidence in five of the sources, and the differing environments in galactic nuclei at these respective epochs play a key role in these overmassive systems. These findings contribute to our understanding of the growth and co-evolution of SMBHs and their host galaxies across cosmic time, offering a link between the early Universe (z > 4) observed by \textit{JWST} and observations of the present-day Universe (z <= 1).