JWST's PEARLS: A z=6 quasar in a train-wreck galaxy merger system

Madeline A. Marshall, Rogier A. Windhorst, Giovanni Ferrami, S. P. Willner, Maria Polletta, William C. Keel, Giovanni G. Fazio, Seth H. Cohen, Timothy Carleton, Rolf A. Jansen, Rachel Honor, Rafael Ortiz, Jake Summers, Jordan C. J. D'Silva, Anton M. Koekemoer, Dan Coe, Christopher J. Conselice, Jose M. Diego, Simon P. Driver, Brenda Frye, Norman A. Grogin, Nor Pirzkal, Aaron Robotham, Russell E. Ryan,, Christopher N. A. Willmer, Haojing Yan, Massimo Ricotti, Adi Zitrin, Nathan J. Adams, Cheng Cheng, J. Stuart B. Wyithe, Jeremy Lim, Michele Perna, Hannah Übler, Chris J. Willott, Gareth Jones, Jan Scholtz, Mira Mechtley

First listed 2025-02-27 | Last updated 2025-09-03

Abstract

We present JWST NIRSpec integral field spectroscopy observations of the z=5.89 quasar NDWFS J1425+3254 from 0.6-5.3 microns, covering the rest-frame ultraviolet and optical at a spectral resolution of R~100. The quasar has a black hole mass of $M_{\rm{BH}}=(1.4\substack{+3.1\\-1.0})\times10^9 M_\odot$ and an Eddington ratio of $L_{\rm{Bol}}/L_{\rm{Edd}}=0.3\substack{+0.6\\-0.2}$, as implied from the broad Balmer H$α$ and H$β$ lines. The quasar host has significant ongoing obscured star formation, as well as a quasar-driven outflow with velocity $6050\substack{+460\\-630}$ km/s and ionised outflow rate of $1650\substack{+130\\-1230}M_\odot$yr$^{-1}$. This is possibly one of the most extreme outflows in the early Universe. The data also reveal that two companion galaxies are merging with the quasar host. The north-eastern companion galaxy is relatively old and very massive, with a luminosity-weighted stellar age of $65\substack{+9\\-4}$ Myr, stellar mass of $(3.6\substack{+0.6\\-0.3})\times10^{11} M_\odot$, and star-formation rate (SFR) of ~15-30 $M_\odot$yr$^{-1}$. A bridge of gas connects this companion galaxy and the host, confirming their ongoing interaction. A second merger is occurring between the quasar host and a much younger companion galaxy to the south, with a stellar age of $6.7\pm1.8$ Myr, stellar mass of $(1.9\pm0.4)\times10^{10} M_\odot$, and SFR of ~40-65 $M_\odot$yr$^{-1}$. There is also another galaxy in the field, likely in the foreground at z=1.135, which could be gravitationally lensing the quasar with magnification $1<μ<2$, and, thus, <0.75 mag. Overall, the system is a 'train-wreck' merger of three galaxies, with star formation and extreme quasar activity that were likely triggered by these ongoing interactions.

Short digest

JWST/NIRSpec IFU prism data (0.6–5.3 μm, R≈100) on the z=5.89 quasar NDWFS J1425+3254 capture rest-UV/optical lines and spatially resolve its host environment. Broad Hα and Hβ yield MBH≈1.4×10^9 M⊙ and Lbol/LEdd≈0.3, while [O III] exposes a quasar-driven outflow with v≈6050 km s−1 and an ionized outflow rate ≈1650 M⊙ yr−1. The cube maps a “train-wreck” triple merger: an older, massive NE companion (M⋆≈3.6×10^11 M⊙, age≈65 Myr) linked to the host by a gas bridge, plus a very young SE companion (age≈6.7 Myr, M⋆≈1.9×10^10 M⊙) with ongoing star formation. These results argue for merger-triggered early SMBH growth; a likely foreground z=1.135 galaxy may modestly lens the quasar (1<μ<2; <0.75 mag).

Key figures to inspect

• Figure 1: Inspect the white-light and quasar-subtracted [O III] maps to see the four labeled regions, the gas bridge between the host and NE companion, and how the IFU [O III] morphology aligns with the HST F125W contours—key for confirming active interaction geometry.
• Figure 2: Use the full 0.82–5.2 μm spectrum to verify line identifications across rest-UV/optical, the Fe II pseudo-continuum zones, and continuum level used for luminosities feeding the mass and Eddington-ratio estimates.
• Figure 3: Examine the QubeSpec fits around Hβ–[O III] and Hα–[N II] to read off BLR FWHM for the virial MBH and the [O III] outflow wing parameters (velocity and flux), noting the stated aperture corrections applied to Hα and Hβ.
• Figure 4: Compare the MBH and Lbol/LEdd posteriors across multiple single-epoch calibrations (G05, V06, DB20/24, C23) to gauge systematic spread and the adopted combined estimate for this source.