James Webb Space Telescope Feed Post

GA-NIFS: JWST discovers an offset AGN 740 million years after the Big Bang

Top left: Color-composite image of ZS7 and its immediate environment created using public NIRCam data from the PRIMER program (PI: James Dunlop). The approximate NIRCam PSF is indicated by the white filled (F200W, ~ 0.06'') and open (F444W, ~ 0.14'') circles. The effective NIRSpec-IFU field of view (FOV) is indicated by the dashed white box. Top right: Zoom-in on the environment of ZS7, as indicated by the rectangular solid white box in the top left panel. The color scale shows a line map integrated over 90 Å around the [O iii]?5007 position, where we indicate the positions of two faint companions detected spectrally at the same redshift with dashed grey circles. The centroids of the [O iii]?5007 emission and the BLR emission are indicated by a white plus and a golden star, respectively, where the small white circles on top of the symbols indicate five times the fitting errors on the centroid positions. The approximate NIRSpec PSF at 4??m is indicated by the white circle. The centroid of the [O iii]?5007 emission coincides with the NIRCam F200W emission, while the BLR location coincides with the F444W emission, reflected in the color gradient in the NIRCam false-color image. Abstract: A surprising finding of recent studies is the large number of Active Galactic Nuclei (AGN) associated with moderately massive black holes (log(M·/M?)~6-8), in the first billion years after the Big Bang (z>5). In this context, a relevant finding has been the large fraction of candidate dual AGN, both at large separations (several kpc) and in close pairs (less than a kpc), likely in the process of merging. Frequent black hole merging may be a route for black hole growth in the early Universe; however, previous findings are still tentative and indirect. We present JWST/NIRSpec-IFU observations of a galaxy at z=7.15 in which we find evidence for a log(M·/M?)~7.7 accreting black hole, as traced by a broad component of Hß emission, associated with the Broad Line Region (BLR) around the black hole. This BLR is offset by 620 pc in projection from the centroid of strong rest-frame optical emission, with a velocity offset of ~40 km/s. The latter region is also characterized by (narrow) nebular emission features typical of AGN, hence also likely hosting another accreting black hole, although obscured (type 2, narrow-line AGN). We exclude that the offset BLR is associated with Supernovae or massive stars, and we interpret these results as two black holes in the process of merging. This finding may be relevant for estimates of the rate and properties of gravitational wave signals from the early Universe that will be detected by future observatories like LISA.