Federica Loiacono

We present three outliers on the quasar main sequence at z > 6, as revealed by JWST/NIRSpec integral field unit (IFU) observations from the Aether survey, a program targeting ∼200 quasars at cosmic dawn. The quasars, J0216−5226, J0320−3521, and J1429+5447, exhibit exceptionally strong Fe ii emission and weak H β and [O iii ] lines, indicating rapid chemical enrichment within the first Gyr of cosmic history. Their Fe ii strengths ( R _{Fe II, λ 4570} ≡ EW _{Fe II} /EW _{H β} ) range between ∼2.5 and 3.6, placing them among the top ∼3% of Sloan Digital Sky Survey quasars at (0 ≲ z ≲ 1). The H α emission lines of J0216−5226 and J1429+5447 imply black hole masses of ∼1–7 × 10 ⁹ M _⊙ with λ _Edd ∼ 0.1–0.6, comparable to typical high- z quasars, although virial black hole masses may be systematically overestimated in strong Fe ii emitters. In contrast, J0320−3521 hosts a lower-mass black hole of ∼0.2–2 × 10 ⁹ M _⊙ , suggesting possible super-Eddington rate accretion with λ _Edd ∼ 0.5–6.0. The IFU data of J0320−3521 reveal a distinct emission-line region at a projected distance of ∼1.5 kpc, consistent with either an interacting companion or ionized gas associated to the quasar. We further identify a complex environment around J1429+5447, including two candidate companion galaxies or extended ionized gas structures. These quasars with bright emission-line regions, J0320−3521 and J1429+5447, are radio-loud sources, while J0216−5226 remains undetected in radio ( R _{5GHz, 3 σ} ≲ 4). Together, these results confirm previous findings that highly enriched, rapidly growing black holes were already in place at cosmic dawn. Despite the small sample size, our results further highlight the diversity in environment and radio-jet properties among quasars that otherwise share the same extreme region of the quasar fundamental plane.

We report JWST/NIRSpec integral field unit (IFU) observations of the quasar J1512+4422 at z ∼ 6.2 from the Aether survey. At ∼900 Myr after the Big Bang, this object already lies on the M _BH – σ _* relation found in the local Universe, with an M _BH ≃ 8.9 × 10 ⁸ M _⊙ and a stellar velocity dispersion σ _* ≃ 288 km s ⁻¹ . We detect an outflow with a velocity of ∼478 km s ⁻¹ in the nuclear region, which likely extends to ∼3.2 kpc in projection and has a median velocity of ∼352 km s ⁻¹ . The outflow dynamical timescale (∼9 Myr) is consistent with the timescale of the current quenching process based on the star formation history as reported previously. The total mass outflow rate (92.6 − 74.1 + 92.6 M _⊙ yr ⁻¹ ) is larger than the current star formation rate (0.9 − 0.8 + 3.8 or 4.3 − 3.7 + 5.8 M _⊙ yr ⁻¹ ), and the total kinetic energy outflow rate (0.6% − 0.5 % + 0.6 % of quasar luminosity) meets the threshold for negative quasar feedback as suggested by simulations. These results suggest that the outflow is capable of suppressing or quenching the star formation activity within the host galaxy. Furthermore, J1512+4422 exhibits σ _* , stellar mass, and size similar to those of z ≳ 3 quiescent and poststarburst galaxies, implying a link between the two. Overall, for objects like J1512+4422, the evolution of their supermassive black holes and host galaxies appears to be tightly coupled within the first billion years. The quasar feedback likely plays a critical role in both placing them on the M _BH – σ _* relation and quenching.

Luminous quasars at z > 6 are key probes of early supermassive black hole (SMBH) growth, massive galaxy evolution, and intergalactic medium properties during cosmic reionization. However, their discovery is very challenging due to their scarcity and overwhelming contamination. Foreground ultracool dwarfs (UCDs) outnumber z > 6 quasars by 2–4 orders of magnitude. In this work, we leveraged the extensive coverage of DESI Legacy Survey DR10 to conduct a self-supervised search for quasars at z > 6, directly analyzing multiband optical images and minimizing the biases of the traditional catalog-driven color-color selection criteria. By applying a contrastive learning (CL) method followed by spectral energy distribution (SED) fitting prioritization, we identified 1139 high-priority quasar candidates, for which we expect a competitive 1:1 quasar-to-UCD ratio based on the literature samples. We spectroscopically confirm 16 new quasars at z = 5.94 − 6.45, achieving a 45% success rate. Remarkably, all 16 objects are relatively bright ( M ₁₄₅₀ < −25.5) quasars, including several with unusual properties such as narrow Ly [[INLINE10]] emission (FWHM ≲ 2600 km s ⁻¹ ), strong Ly [[INLINE13]] +N V emission with an equivalent width > 100 Å, and a mild observed-frame red near-infrared (NIR) continua ( z − J > 0.4). Notably, three of them would have been missed by traditional color–color selections. These results highlight the power of self-supervised machine learning, combined with SED fitting prioritization, to uncover rare, distant sources beyond the limitations of conventional techniques. Our approach offers a scalable and robust framework for data mining and can be readily extended to forthcoming wide-field surveys such as Rubin/LSST, 4MOST, Euclid , and Roman. These applications will advance the census of high-redshift quasars, potentially extend the redshift frontier, and improve constraints on SMBH formation and evolution in the first billion years of the Universe.

Luminous quasars at the redshift frontier z > 7 serve as stringent probes of super-massive black hole (SMBH) formation and they are thought to undergo much of their growth obscured by dense gas and dust in their host galaxies. Fully characterizing the symbiotic evolution of SMBHs and hosts requires rest-frame optical observations that span spatial scales from the broad-line region (BLR) to the interstellar and circumgalactic medium (ISM and CGM). The James Webb Space Telescope (JWST) now provides the necessary spatially resolved spectroscopy to do so. However, the physical conditions that regulate the interplay between SMBHs and their hosts at the highest redshifts, especially the nature of early feedback phases, remain unclear. We present JWST/NIRSpec integral field unit (IFU) observations of J0313−1806 at z = 7.64, the most distant luminous quasar known. From the rest-frame optical spectrum of the unresolved quasar, we derived a black hole mass of M _BH = (1.63 ± 0.10)×10 ⁹ M _⊙ based on H βλ 4861 (H β ) and an Eddington rate of λ = L / L _Edd = 0.80 ± 0.05, consistent with previous Mg II λ 2800-based estimates. J0313–1806 exhibits no detectable [O III ] λλ 4959, 5007 emission on nuclear scales (3 σ upper limit equivalent width of [O III ] λ 5007 < 1.42 Å). Most remarkably, we did detect an ionized gas shell extending out to ∼1.8 kpc traced by H β emission that also lacks any significant [O III ] λλ 4959, 5007, with a 3 σ upper limit on the [O III ] λ 5007 to H β flux ratio of log ₁₀ ( F ([O III ])/ F (H β )) = −1.15. Through photoionization modeling, we demonstrate that the extended emission is consistent with a thin, clumpy outflowing shell where [O III ] is collisionally de-excited by dense gas. We interpret this structure as a fossil remnant of a recent blowout phase, providing evidence for episodic feedback cycles in one of the earliest quasars. These findings suggest that dense ISM phases may play a crucial role in shaping the spectral properties of quasars across cosmic time.

The recent discovery of five massive stellar clusters at z = 9.625 in the Cosmic Gems galaxy has raised the question about the formation mechanism of star clusters in the first 500 Myr after the Big Bang. We inferred the total stellar mass in clusters by normalizing and integrating the stellar cluster mass function (SCMF, d n ( M )/d M = n ₀ M ^β ), assuming three different slopes ( β = −1.5, −2.0, and −2.5) and different lower-mass limits between 10 ² and 10 ⁵ M _⊙ . We compared the total integrated cluster stellar mass to the stellar mass inferred from the counter image of the Cosmic Gems, which provides the best modestly magnified ( μ = 1.84 ± 0.05) representation of the entire galaxy. The delensed stellar mass of the Cosmic Gems galaxy was estimated as 3.5 _−1.8 ^+3.3 × 10 ⁷ M _⊙ , with an effective radius of R _eff = 103 ₋₁₅ ⁺¹³ parsecs and a stellar surface mass density of Σ _mass = 520 ₋₂₂₅ ⁺³⁴⁰ M _⊙ pc ⁻² . Accounting for normalization uncertainties – including different lensing magnification scenarios for the arc – a modified SCMF, combined with a significantly high star cluster formation efficiency (approaching 100%), appears to be a necessary condition to explain the relatively short formation timescale of both the star clusters and the counter image, without exceeding the galaxy’s stellar mass. By extrapolating the physical properties at the peak of the burst, we found that in its recent past (≲30 Myr) the Cosmic Gems galaxy likely experienced a specific star formation rate exceeding 25 Gyr ⁻¹ and luminosity approaching the “blue monster” regime ( M _UV < −20). Our study provides insights into the extreme clustered nature of star formation in early galaxies and sheds light on the formation of bound star clusters that might survive to z = 0 as globular clusters older than 13 Gyr.

We present JWST/NIRSpec integral field spectroscopy of the Cosmic Gems arc, strongly magnified by the galaxy cluster SPT-CL J0615−5746. Six-hour integration using NIRSpec prism spectroscopy (resolution R ≃ 30 − 300), covering the spectral range 0.8 − 5.3 μm, reveals a pronounced Ly α -continuum break at λ ≃ 1.3 μm, as well as weak optical H β and [O III ] λ 4959 emission lines at z = 9.625 ± 0.002, located in the reddest part of the spectrum ( λ > 5.1 μm). No additional ultraviolet or optical emission lines are reliably detected. A weak Balmer break is measured alongside a very blue ultraviolet slope ( β ≤ −2.5, F _λ ∼ λ ^β ). Spectral fitting with Bagpipes suggests that the Cosmic Gems galaxy is in a post-starburst phase, making it the highest-redshift system currently observed in a mini-quenched state. Spatially resolved spectroscopy at tens of parsecs shows relatively uniform features across subcomponents of the arc. These findings align well with the physical properties previously derived from JWST/NIRCam photometry of the stellar clusters, now corroborated by spectroscopic evidence. In particular, five observed star clusters exhibit ages of 7 − 30 Myr. An updated lens model constrains the intrinsic sizes and masses of these clusters, confirming they are extremely compact and denser than typical star clusters in local star-forming galaxies (Σ M _★ = 10 ⁵ − 10 ⁶ M _⊙ ). Additionally, four compact stellar systems consistent with star clusters (≲10 pc) are identified along the extended tail of the arc. A sub-parsec line-emitting H II 1.2ex region straddling the critical line, lacking a NIRCam counterpart, is also serendipitously detected. The Cosmic Gems arc thus offers a rare opportunity to investigate, at parsec scales, the aftermath of a star formation burst in the early Universe.

We report the discovery of a faint (M ₁₇₀₀ ≃ −12.2), oxygen-deficient, strongly lensed ionizing source – dubbed Lensed And Pristine 2 (LAP2) – at a spectroscopic redshift of z = 4.19. LAP2 appears to be isolated and lies very close to the caustic produced by the lensing galaxy cluster Abell 2744. It was observed with the James Webb Space Telescope (JWST) NIRSpec MSA in prism mode as part of the UNCOVER program. The NIRSpec spectrum reveals prominent Ly α (7.1 σ ), clear H α (6.2 σ ), tentative H β (≃2.8 σ ) emissions and no detectable [O/ III ] λλ 4959,5007 (∼7 times fainter than H α ). The inferred [O III ] 2 σ upper limit corresponds to an R3 index < 0.85 (assuming the H α /H β = 2.86 case B recombination ratio), which, under high-ionization conditions, implies a metallicity of Z < 6 × 10 ⁻³ Z _⊙ . The combination of faint ultraviolet luminosity, a large rest-frame H α equivalent width (≃650 Å), and an extremely compact size (< 10 pc) suggests that LAP2 is being caught in an early, pristine formation phase consistent with an instantaneous-burst scenario, with an estimated stellar mass of at most a few ×10 ⁴ M _⊙ . Deep VLT/MUSE observations further reveal copious Ly α emission forming an arclet that straddles the critical line. LAP2 joins the rare class of extremely metal-poor star-forming complexes that the JWST has started to unveil at redshifts 3–7, and it provides a glimpse into a still very poorly explored low-luminosity regime.

To fully characterize the formation and evolution of galaxies, we need to observe their stars, gas, and dust on resolved spatial scales. We present the ALPINE-CRISTAL-JWST survey, which combines kiloparsec-resolved imaging and spectroscopy from the Hubble Space Telescope, JWST, and Atacama Large Millimeter/submillimeter Array for 18 representative main-sequence galaxies at z = 4–6 and log ( M * / M ⊙ ) > 9.5 to study their star formation, chemical properties, and extended gas reservoirs. The cospatial measurements resolving the ionized gas, molecular gas, stars, and dust on 1–2 kpc scales make this a unique benchmark sample for the study of galaxy formation and evolution at z ∼ 5, connecting the Epoch of Reionization with the cosmic noon. In this paper, we outline the survey goals and sample selection, and present a summary of the available data for the 18 galaxies. In addition, we measure spatially integrated quantities (such as global gas metallicity), test different star formation rate indicators, and quantify the presence of H α halos. Our targeted galaxies are relatively metal rich (10%–70% solar), complementary to JWST samples at lower stellar mass, and there is broad agreement between different star formation indicators. One galaxy has the signature of an active galactic nuclei (AGN) based on its emission-line ratios. Six show broad H α emission suggesting type 1 AGN candidates. We conclude with an outlook on the exciting science that will be pursued with this unique sample in forthcoming papers.

We report the discovery of a little red dot (LRD), dubbed BiRD (‘big red dot’), at z ∼ 2.33 in the field around the z ∼ 6.3 quasar SDSS J1030+0524. Using JWST/NIRCam images, we identified it as a bright outlier in the F 200 W − F 356 W color versus F 356 W magnitude diagram of point sources in the field. The NIRCam/WFSS spectrum reveals the emission from He I λ 10830 and Pa γ line, both displaying a narrow and a broad ( FWHM ≳ 2000 km s ⁻¹ ) component. The He I line is affected by an absorption feature, tracing dense gas with He I column density in the 2 ³ S level N (He I ) ∼ 0.5 − 1.2 × 10 ¹⁴ cm ⁻² , depending on the location of the absorber, which is outflowing at a speed of Δ _v = −830 ₋₁₄₈ ⁺¹³¹ km s ⁻¹ . As observed in the majority of LRDs, BiRD does not exhibit any X-ray or radio emission down to 3.7 × 10 ⁴² erg s ⁻¹ and 3 × 10 ³⁹ erg s ⁻¹ , respectively. The black hole mass and the bolometric luminosity, both inferred from the Pa γ broad component, amount to M _BH ∼ 10 ⁸ M _⊙ and L _bol ∼ 3 × 10 ⁴⁵ erg s ⁻¹ , respectively. Intriguingly, BiRD presents strict analogies with other two LRDs spectroscopically confirmed at cosmic noon, namely, GN-28074 (nicknamed Rosetta Stone) at z ∼ 2.26 and RUBIES-BLAGN-1 at z ∼ 3.1. The blueshifted He I absorption detected for all three sources suggests that gas outflows could be common in LRDs. We derived a first estimate of the space density of LRDs at z ∼ 2 − 3 based on JWST data, as a function of the bolometric luminosity and black hole mass. The space density Φ( L ) = 4.0 _−2.4 ^+4.0 × 10 ⁻⁶ Mpc ⁻³ dex ⁻¹ is only a factor of ∼2 − 3 lower than that of UV-selected quasars with comparable bolometric luminosity and redshift, meaning that the contribution of LRDs to the broader AGN population is also relevant at cosmic noon. A similar trend has also been observed with respect to black hole masses. As suggested by recent theories, if LRDs can indeed serves as probes of the very first and rapid growth of black hole seeds, our finding suggests that the formation of black hole seeds continues to be efficient at least up to cosmic noon.