Euclid and Roman with JWST Could Reveal Quasars at up to $z \sim$ 15

Muhammad A. Latif, Daniel J. Whalen

First listed 2025-06-26 | Last updated 2025-08-29

Abstract

Although supermassive black holes (SMBHs) are found at the centers of most galaxies today, over 300 have now been discovered at $z >$ 6, including UHZ1 at $z = 10.1$ and GHZ9 at $z =$ 10.4. They are thought to form when 10$^4$ - 10$^5$ M$_{\odot}$ primordial stars die as direct-collapse black holes (DCBHs) at $z \sim$ 20 - 25. While studies have shown that DCBHs should be visible at birth at $z \gtrsim$ 20 in the near infrared (NIR) to the James Webb Space Telescope (JWST), none have considered SMBH detections at later stages growth down to $z \sim$ 6 - 7. Here, we present continuum NIR luminosities for a BH like ULAS J1120+0641, a $1.35 \times 10^9$ M$_{\odot}$ quasar at $z =$ 7.1, from a cosmological simulation for Euclid, the Roman Space Telescope (RST) and JWST bands from $z =$ 6 - 15. We find that Euclid and RST could detect such BHs, including others like UHZ1 and GHZ9, at much earlier stages of evolution, out to $z \sim$ 14 - 15, and that their redshifts could be confirmed spectroscopically with JWST. Synergies between these three telescopes could thus reveal the numbers of SMBHs at much higher redshifts and discriminate between their evolution pathways because Euclid and RST can capture large numbers of them in wide-field surveys for further study by JWST.

Short digest

Normalizing a thin-disk+corona spectrum to a J1120-like quasar grown in the Smidt et al. (2018) simulation, the authors predict continuum NIR AB magnitudes from z = 6–15 in Euclid, Roman, and JWST bands. They find Euclid can photometrically select such SMBHs to z ≈ 11 (Wide), z ≈ 13 (Deep), and z ≈ 14 (Ultra Deep), while Roman reaches z ≈ 14.5 in Y/J/H and its F213 band extends selection to z ≈ 18. JWST’s sensitivity enables spectroscopic redshift confirmation to z ≈ 15 and even detects ≳10^6 M⊙ BHs accreting near Eddington. This Euclid/Roman discovery plus JWST follow-up pipeline could inventory early SMBHs (including analogs of UHZ1 and GHZ9) and discriminate their growth channels beyond z > 10.

Key figures to inspect

• Figure 1: Trace the bolometric luminosity versus redshift from the J1120-like simulation to see the 0.2–0.8 Eddington phases that set the normalization of the disk+corona SED used for all detectability forecasts.
• Figure 2 (Euclid panel): Read where the H/J AB-magnitude curves intersect WS/DS/EUDS limits (24.5/26.0/27.7) to get z ≈ 11/13/14 reach; note why earlier times are cut off by the Lyman-limit absorption entering these filters.
• Figure 2 (Roman panel): Compare Y/J/H curves to the HLSS 28 mag line to see Roman’s z ≈ 14.5 advantage and large-area yield; keep in mind the seven-filter coverage and F213 to 2.3 µm that supports z > 15 dropouts.
• Figure 3: JWST NIRCam (2.5, 3.65, 4.44, 4.60 µm) AB magnitudes lie well above the m_AB ≈ 32 imaging limit, illustrating comfortable margins for NIRSpec confirmation and viability down to ~10^6 M⊙ at z ≈ 15.