James Webb Space Telescope Feed Post

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

Top left: continuum flux density map at ?? = 2.9 - 3??m. Bottom left: continuum flux density map at ?? = 4.9 - 5??m. Top centre, bottom centre, and bottom right: integrated line flux maps with ??/?? = 5 from our spectral fitting for the narrow [O iii]?5007 component, the Hß BLR component, and the narrow [O iii]?4363 component, respectively. Top right: velocity map of the narrow [O iii]??4959,5007 emission. In each panel, the black cross and star indicate the centroid of the [O iii]?5007 emission and the BLR location as shown in Fig. 1, respectively. The black scale bar to the left indicates 0.2'' ~ 1 kpc, and the grey outline indicates the mask used for our full spectral fitting. There is a clear shift in the location of the continuum emission from bluer to redder wavelengths, aligning with the centroids of the [O iii]?5007 emission and the BLR position, reflecting the color gradient seen in the NIRCam image (Fig. 1). The flux of the auroral [O iii]?4363 line peaks at the BLR position, but covers also the [O iii]?5007 flux peak, indicating a clear gradient of the [O iii]?5007/[O iii]?4363 line ratio from the position of the AGN to the [O iii]?5007 emitter. 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.