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1. Euclid : A UV-faint quasar in a highly luminous star-forming host galaxy at z  ≈ 7.7

   https://doi.org/10.1051/0004-6361/202659319  

   Belladitta, S; Decarli, R; Bañados, E; Walter, F; Yang, D; Guarneri, F; Jahnke, K; Bisogni, S; Bosman, S_E I; Fan, X; et al (July 2026, Astronomy & Astrophysics)

   Constraining the co-evolution of supermassive black holes and their host galaxies in the first billion years after the Big Bang is essential for understanding the formation of the earliest cosmic structures. Here, we present IRAM/NOrthern Extended Millimeter Array (NOEMA) observations of thez ≈ 7.7 quasar EUCL J125308.55+705432.3, recently discovered in the first data release of the Euclid Wide Survey. We report the most distant detections of [C II]158 μm and cold dust emission in a quasar host to date. The [C II]emission line sets the systemic redshift atz = 7.6980 ± 0.0004. The source exhibits luminosities ofL_FIR = 3.6 × 10¹² L_⊙andL_[C II]= 2 × 10⁹L_⊙, respectively, a dust mass of 1.4 × 10⁸ M_⊙, and a dynamical mass in the range 0.33 − 1.3 × 10¹⁰ M_⊙. Remarkably, despite being nearly two magnitudes fainter in the rest-frame UV (M₁₄₅₀ = −24.06) than previously knownz ≈ 7.5 quasars (⟨M₁₄₅₀⟩ ∼ − 26.5), EUCL J125308.55+705432.3 exhibits the brightest [C II]emission among them. This indicates that the host galaxy is actively star-forming, with a star-formation rate > 250M_⊙yr⁻¹, consistent with recent findings that UV-faint quasars atz > 6 preferentially reside in [C II]-luminous galaxies. The UV-faintness likely reflects dust obscuration or sub-Eddington accretion, rather than lower host mass, suggesting these systems are at a different stage in their evolution compared to UV-bright quasars. These IRAM/NOEMA observations highlight the power of combiningEuclid’s wide-area quasar discovery potential with submillimetre follow-up observations to characterise the host galaxies of early supermassive black holes across a broader redshift and luminosity range than previously accessible. 

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2. A first look at quasar-galaxy clustering at z   ≃  7.3

   https://doi.org/10.1051/0004-6361/202557623  

   Schindler, Jan-Torge; Hennawi, Joseph F; Davies, Frederick B; Bosman, Sarah_E I; Wang, Feige; Yang, Jinyi; Eilers, Anna-Christina; Fan, Xiaohui; Kakiichi, Koki; Pizzati, Elia; et al (April 2026, Astronomy & Astrophysics)

   Linking quasars to their dark matter environments provides critical insights into the formation and early growth of supermassive black holes (SMBHs). We present JWST observations of the environments surrounding two high-redshift quasars, J0252−0503 atz = 7.0 and J1007+2115 atz = 7.5, which enable the first constraints on quasar–galaxy clustering atz ≃ 7.3. Galaxies in the vicinity of the quasars were selected through ground-based and JWST/NIRCam imaging and were then spectroscopically confirmed with JWST/NIRSpec using the multi-shutter assembly (MSA). Over both fields, we identified 51z > 5 galaxies, of which eight are found within a Δv_LOS= ± 1500 km s⁻¹line-of-sight velocity window from the quasars and another eight in the background. The galaxy J0252_8713, located just 7 pkpc and Δv_LOS≈ 360 km s⁻¹from quasar J0252−0503, emerges as a compelling candidate for one of the most distant quasar-galaxy mergers. Combining the galaxy discoveries over the two fields, we measured the quasar-galaxy cross-correlation and obtain a correlation length ofr₀^QG≈ 7.6^+1.7_−1.6h⁻¹cMpc, based on a power-law model with a fixed slope ofγ_QG = 2.0. Under the assumption that quasars and galaxies trace the same underlying dark matter density fluctuations, we infer a minimum dark matter halo mass forz ≃ 7.3 quasars of log₁₀(M_halo,min/M_⊙) = 11.6^+0.6_−0.7in a halo model framework. Compared to measurements from EIGER at ⟨z⟩ = 6.25 and ASPIRE at ⟨z⟩ = 6.7 (where log₁₀(M_halo, min/M_⊙)≳12.1), our clustering results provide tentative evidence for a nonmonotonic redshift evolution of quasar clustering properties. We further estimate a quasar duty cycle off_duty ≈ 0.05%, consistent with constraints from quasar proximity zones and intergalactic medium (IGM) damping wings. However, this implies very short phases of quasar activity, exacerbating the challenge to build billion solar mass SMBHs in only 700 Myr of cosmic time. 

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3. Predicting the Yields of z > 6.5 Quasar Surveys in the Era of Roman and Rubin

   https://doi.org/10.3847/1538-4357/acf12d  

   Tee, Wei Leong; Fan, Xiaohui; Wang, Feige; Yang, Jinyi; Malhotra, Sangeeta; Rhoads, James E. (October 2023, The Astrophysical Journal)

   Abstract About 70 luminous quasars discovered atz> 6.5 are strongly biased toward the bright end, thus not providing a comprehensive view of quasar abundance beyond the cosmic dawn. We present the predicted results of the Roman/Rubin high-redshift quasar survey, yielding 3 times more, 2–4 mag deeper quasar samples, probing high-redshift quasars across a broad range of luminosities, especially faint quasars atL_bol∼ 10¹⁰L_⊙orM₁₄₅₀∼ −22, which are currently poorly explored. We include high-zquasars, galactic dwarfs, and low-zcompact galaxies with similar colors as quasar candidates. We create mock catalogs based on population models to evaluate selection completeness and efficiency. We utilize the classical color dropout method in thezandYbands to select primary quasar candidates, followed up with the Bayesian selection method to identify quasars. We show that overall selection completeness >80% and efficiency ∼10% at 6.5 <z< 9, with 180 quasars atz> 6.5, 20 atz> 7.5, and 2 atz> 8.5. The quasar yields depend sensitively on the assumed quasar luminosity shape and redshift evolution. Brown dwarf rejection through proper motion up to 50% can be made for stars brighter than 25 mag, low-zgalaxies dominate at fainter magnitude. Our results show that Roman/Rubin are able to discover a statistical sample of the earliest and faintest quasars in the Universe. The new valuable data sets are worth follow-up studies with JWST and Extremely Large Telescopes to determine the quasar luminosity function faint end slope and constraint the supermassive black holes growth in the early Universe. 

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4. Paving the way for Euclid and JWST via probabilistic selection of high-redshift quasars

   https://doi.org/10.1093/mnras/stac1944  

   Nanni, Riccardo; Hennawi, Joseph F; Wang, Feige; Yang, Jinyi; Schindler, Jan-Torge; Fan, Xiaohui (August 2022, Monthly Notices of the Royal Astronomical Society)

   ABSTRACT We introduce a probabilistic approach to select 6 ≤ $$z$$ ≤ 8 quasar candidates for spectroscopic follow-up, which is based on density estimation in the high-dimensional space inhabited by the optical and near-infrared photometry. Densities are modelled as Gaussian mixtures with principled accounting of errors using the extreme deconvolution (XD) technique, generalizing an approach successfully used to select lower redshift ($$z$$ ≤ 3) quasars. We train the probability density of contaminants on 1902 071 7-d flux measurements from the 1076 deg2 overlapping area from the Dark Energy Camera Legacy Survey (DECaLS) ($$z$$), VIKING (YJHKs), and unWISE (W1W2) imaging surveys, after requiring they dropout of DECaLS g and r, whereas the distribution of high-$$z$$ quasars are trained on synthetic model photometry. Extensive simulations based on these density distributions and current estimates of the quasar luminosity function indicate that this method achieves a completeness of $$\ge 56{{\ \rm per\ cent}}$$ and an efficiency of $$\ge 5{{\ \rm per\ cent}}$$ for selecting quasars at 6 < $$z$$ < 8 with JAB < 21.5. Among the classified sources are 8 known 6 < $$z$$ < 7 quasars, of which 2/8 are selected suggesting a completeness $$\simeq 25{{\ \rm per\ cent}}$$, whereas classifying the 6 known (JAB < 21.5) quasars at $$z$$ > 7 from the entire sky, we select 5/6 or a completeness of $$\simeq 80{{\ \rm per\ cent}}$$. The failure to select the majority of 6 < $$z$$ < 7 quasars arises because our quasar density model is based on an empirical quasar spectral energy distribution model that underestimates the scatter in the distribution of fluxes. This new approach to quasar selection paves the way for efficient spectroscopic follow-up of Euclid quasar candidates with ground-based telescopes and James Webb Space Telescope. 

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5. The Pan-STARRS1 z > 5.6 Quasar Survey. II. Discovery of 55 Quasars at 5.6 < z < 6.5

   https://doi.org/10.3847/1538-4365/acb3c7  

   Bañados, Eduardo; Schindler, Jan-Torge; Venemans, Bram P.; Connor, Thomas; Decarli, Roberto; Farina, Emanuele Paolo; Mazzucchelli, Chiara; Meyer, Romain A.; Stern, Daniel; Walter, Fabian; et al (March 2023, The Astrophysical Journal Supplement Series)

   Abstract The identification of bright quasars atz≳ 6 enables detailed studies of supermassive black holes, massive galaxies, structure formation, and the state of the intergalactic medium within the first billion years after the Big Bang. We present the spectroscopic confirmation of 55 quasars at redshifts 5.6 <z< 6.5 and UV magnitudes −24.5 <M₁₄₅₀< −28.5 identified in the optical Pan-STARRS1 and near-IR VIKING surveys (48 and 7, respectively). Five of these quasars have independently been discovered in other studies. The quasar sample shows an extensive range of physical properties, including 17 objects with weak emission lines, 10 broad absorption line quasars, and 5 objects with strong radio emission (radio-loud quasars). There are also a few notable sources in the sample, including a blazar candidate atz= 6.23, a likely gravitationally lensed quasar atz= 6.41, and az= 5.84 quasar in the outskirts of the nearby (D∼ 3 Mpc) spiral galaxy M81. The blazar candidate remains undetected in NOEMA observations of the [Cii]and underlying emission, implying a star formation rate <30–70M_⊙yr⁻¹. A significant fraction of the quasars presented here lies at the foundation of the first measurement of thez∼ 6 quasar luminosity function from Pan-STARRS1 (introduced in a companion paper). These quasars will enable further studies of the high-redshift quasar population with current and future facilities. 

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