GA-NIFS: The highly overdense system BR1202-0725 at z $\sim$ 4.7. A double AGN with fast outflows plus eight companion galaxies

Abstract

Distant quasars (QSOs) in galaxy overdensities are considered key actors in the evolution of the early Universe. In this work, we studied the kinematic and physical properties of the BR1202-0725 system at z=4.7, one of the most overdense fields known in the early Universe, consisting of a QSO, a submillimeter galaxy (SMG), and three Lyman-$α$ emitters. We used data from the JWST/NIRSpec Integral Field Unit (IFU) to analyze the rest-frame optical emission of each source in the system. We estimated a bolometric luminosity of log($L_{\rm bol}/$[erg/s]) = 47.2 $\pm$ 0.4 and a black hole mass of log($M_{\rm BH}/M_\odot$) = 10.1 $\pm$ 0.5 for the QSO, which are consistent with previous measurements obtained with ground-based observations. The NIRSpec spectra of the SMG revealed instead unexpected [OIII] and H$α$+[NII] profiles. The overall [OIII] line profile is blue-shifted by more than 700 km/s relative to the systemic velocity of the galaxy. Additionally, both the [OIII] and H$α$+[NII] lines show prominent broad (1300 km/s), blueshifted wings associated with outflowing ionized gas. The analysis of NIRSpec and X-ray observations indicates that the SMG likely hosts an accreting supermassive black hole as supported by the following results: (i) the excitation diagnostic diagram is consistent with ionization from an active galactic nucleus (AGN); (ii) the X-ray luminosity is higher than $10^{44}$ erg/s; and (iii) it hosts a fast outflow ($v_{\rm out}$ = 5000 km/s), comparable to those observed in luminous QSOs. Therefore, the QSO-SMG pair represents one of the highest-redshift double AGN to date, with a projected separation of 24 kpc. Finally, we investigated the environment of this system and found four new galaxies at the same redshift of the QSO and within a projected distance of 5 kpc from it. This overdense system includes at least ten galaxies in only 980 kpc$^2$.

Figures (19)

• Figure 1: HST ACS F775W filter ($i$-band; left) and JWST NIRSpec IFU H$\alpha$ ($3.74~{\rm \mu m}<\lambda<3.75~{\rm \mu m}$; right) image of BR1202-0725. Dust continuum emission from ALMA in Band 7 is shown as black contours. Star symbols illustrate the position of the three Lyman-$\alpha$ emitters. North is up, east is left. A logarithmic color scale is used.
• Figure 2: Original (left) and PSF-subtracted (right) maps of the QSO at the wavelength corresponding to the H$\beta$ emission line.
• Figure 3: JWST/NIRSpec rest-frame optical spectrum of the QSO in the two gratings/filters G235H/F170LP and G395H/F290LP (green and purple lines, respectively), extracted from an aperture of $R = 0.5\arcsec$. The brightest nebular lines are marked and the Fe ii multiplet bands are highlighted in gray. The green dashed line shows the broken power-law continuum model fitted to reproduce the featureless continuum emission. The gray line in the bottom panel shows the residuals of the fitting.
• Figure 4: QSO rest-frame optical continuum-subtracted spectrum (gray line) in the spectral region 4700 -- 5400 Å. The emission lines H$\beta$ and [O iii]$\lambda \lambda$4959,5007 Å (marked with vertical lines) are blended with the Fe ii emission, which can be clearly seen at $\sim$3 $\mu$m. The following fitted Fe ii templates are shown: veron-cetty2004, boroson1992 and tsuzuki2006. The lines in the bottom panel shows the different residuals of the fitting.
• Figure 5: Continuum-subtracted JWST NIRSpec spectrum of the QSO. The best-fit model is shown with a black solid line, while the results of the individual components are reported with different colors: the blue dashed line shows the Narrow + Outflow components, and the purple dotted line corresponds to the BLR component. The fitted veron-cetty2004 Fe ii template (VC+04) is shown with the orange dash-dotted line.