Spatially resolved broad line region in a quasar at z=4: Dynamical black hole mass and prominent outflow
GRAVITY+ Collaboration, K. Abd El Dayem, N. Aimar, A. Berdeu, J. -P. Berger, G. Bourdarot, P. Bourget, W. Brandner, Y. Cao, C. Correia, S. Cuevas Cardona, R. Davies, D. Defrère, A. Drescher, A. Eckart, F. Eisenhauer, M. Fabricius, A. Farah, H. Feuchtgruber, N. M. Förster Schreiber, A. Foschi, P. Garcia, R. Garcia Lopez, R. Genzel, S. Gillessen, T. Gomes, F. Gonté, V. Gopinath, J. Graf, M. Hartl, X. Haubois, F. Haußmann, L. C. Ho, S. Hönig, M. Houllé, S. Joharle, C. Keiman, P. Kervella, J. Kolb, L. Kreidberg, A. Labdon, S. Lacour, O. Lai, S. Lai, R. Laugier, J. -B. Le Bouquin, J. Leftley, R. Li, B. Lopez, D. Lutz, F. Mang, A. Mérand, F. Millour, M. Montargès, N. More, N. Morujão, H. Nowacki, M. Nowak, S. Oberti, C. Onken, J. Osorno, T. Ott, T. Paumard, K. Perraut, G. Perrin, R. Petrov, P. -O. Petrucci, N. Pourré, S. Rabien, C. Rau, D. Ribeiro, S. Robbe-Dubois, M. Sadun Bordoni, M. Salman, J. Sanchez-Bermudez, D. Santos, J. Sauter, M. Scialpi, J. Scigliuto, J. Shangguan, P. Shchekaturov, T. Shimizu, F. Soulez, C. Straubmeier, E. Sturm, M. Subroweit, C. Sykes, L. J. Tacconi, H. Übler, G. Ulbricht, F. Vincent, R. Webster, E. Wieprecht, J. Woillez, C. Wolf
Published: 2025/9/17
Abstract
We present the first near-infrared interferometric data of a QSO at z=4. The K-band observations were performed with GRAVITY+ on the VLTI using all 4 UTs, detecting a differential phase signal that traces the spatially resolved kinematics for both the H$\beta$ and H$\gamma$ lines in the broad line region. We fit the two lines simultaneously with an updated model that includes distinct rotating and conical outflowing components. We find that more than 80\% of the HI line emission from the BLR originates in an outflow with a velocity up to $10^4$ km s$^{-1}$. This is oriented so that our line of sight is along an edge of the conical structure, which produces the prominent blue wing on the line profile. A combination of anisotropic line emission and mid-plane opacity lead to the single-sided phase signal. The model is able to qualitatively match both the outflowing CIV line profile and the systemic OI fluorescent emission. The derived black hole mass of $8\times10^8$ M$_\odot$ is the highest redshift black hole mass measurement to date obtained directly from BLR dynamics. It is an order of magnitude lower than that inferred from various single epoch scaling relations, and implies that the accretion is highly super-Eddington. With reference to recent simulations, the data suggest that this QSO is emitting close to its radiative limit in a regime where strong outflows are expected around a polar conical region.