Yoshiki Toba

We report the discovery of 31 new high- z quasars in the redshift range 6.6 < z < 7.8. These quasars were selected from approximately 3000 deg ² of sky covered during the first 1.5 years of the Euclid Wide Survey, representing the initial results of the Euclid high- z quasar search. Our candidate selection employed multiple machine-learning and probabilistic techniques applied to the EuclidI _E , Y _E , J _E , and H _E images, supplemented by ancillary z -band data when available. Spectroscopic follow-up observations were carried out with Keck, Magellan, and the Large Binocular Telescope (LBT). Among the new discoveries, there are 12 quasars at z ≥ 7, more than doubling the number of previously known quasars at z ≥ 7. The newly discovered quasars exhibit 21.2 < J _E < 23.2 (−25.5 < M ₁₄₅₀ < −23.6), extending quasar studies to the faint end of the quasar luminosity function (QLF) at z ≳ 7. The quasar with the highest- z , EUCL J172902.75+641018.1 at z ≈ 7.77, sets the new redshift record for the most distant quasar ever reported. These discoveries demonstrate Euclid ’s transformative role in high- z quasar discovery and set the stage for future follow-up studies of the early galaxies hosting quasars, supermassive black hole growth, and the intergalactic medium in the epoch of reionisation.

Hard-X-ray-selected Compton-thick active galactic nuclei (AGNs) provide a relatively obscuration-resistant census of accretion, but optical line diagnostics can be strongly shaped by extinction and geometry. Spatially resolved integral-field spectroscopy can mitigate these effects and provide direct constraints on outflow kinematics and ionization state on kiloparsec scales. We present Kyoto Okayama Optical Low-dispersion Spectrograph fiber integral field unit (IFU) instrument optical integral-field spectroscopy of NGC 6552 obtained on the 3.8 m Seimei Telescope. Using spatially resolved emission-line ratios and nonparametric [O iii ] λ 5007 kinematics over the central ∼2 kpc, we test whether ionized-gas kinematics are locally coupled to excitation. The [O iii ] λ 5007 width W ₈₀ is broadly elevated across the inner region (∼530–830 km s ⁻¹ ) and declines monotonically with projected galactocentric distance, consistent with a centrally concentrated outflow that decelerates at larger radii. Despite this clear kinematic structure, neither W ₈₀ nor the velocity asymmetry parameter Δ v shows a statistically significant correlation with [O iii ] λ 5007/H β . Order-of-magnitude outflow energetics yield E ̇ K / L bol ≈ 0.01 % –0.28% (for assumed n _e = 50–1000 cm ⁻³ ), consistent with [O iii ]-based estimates tracing only the ionized phase of a multiphase outflow. We conclude that in NGC 6552, both the total line broadening traced by W ₈₀ and Δ v are consistent with being governed primarily by spatial dynamical structure and line-of-sight superposition of multiple kinematic components, with no statistically significant coupling to excitation-driven processes detected at our sensitivity level. A positive W ₈₀ –[O iii ] λ 5007/H β coupling does emerge in the small subset of bins for which the two-component fit is most strongly favored statistically, and deeper observations will be needed to confirm.

Active galactic nuclei (AGN) are an important phase in galaxy evolution. However, they can be difficult to identify due to their varied observational signatures. Furthermore, to understand the impact of an AGN on its host galaxy, it is important to quantify the strength of the AGN with respect to the host galaxy. We developed a deep learning (DL) model to identify AGN in imaging data by deriving the contribution of the central point source. The model was trained with Euclidised mock galaxy images in which we artificially injected different levels of AGN, in the form of varying contributions of the point spread function (PSF). Our DL-based method can precisely and accurately recover the injected AGN contribution fraction, f _PSF , with a mean difference between the predicted and true f _PSF of −0.0078 and an overall root mean square error of 0.051. With this new method, we move beyond the simplistic AGN versus non-AGN classification and are able to precisely quantify the AGN contribution and study galaxy evolution across a continuous spectrum of AGN activity. We applied our method to a stellar-mass-limited sample (with M _* ≥ 10 ^9.8 M _⊙ and 0.5 ≤ z ≤ 2.0 ) selected from the first Euclid quick data release (Q1) and, using a threshold of f _PSF > 0.2, we identified 61 432 ± 70 AGN over 63.1 deg ² (9.8 ± 0.1% of our sample). We compared these DL-selected AGN with AGN selected in the X-ray, mid-infrared (MIR), and via optical spectroscopy and investigated their overlapping fractions depending on different thresholds on the PSF contribution. We find that the overlap increases with increasing X-ray or bolometric AGN luminosity. We observe a positive correlation between the luminosity in the I _E filter of the AGN and the host galaxy stellar mass, suggesting that supermassive black holes (SMBHs) generally grow faster (in absolute terms, i.e. the luminosity of the PSF component is larger) in more massive galaxies. Moreover, the mean relative contribution of the AGN is higher in the quiescent galaxy population than in the star-forming population. In terms of absolute power, starburst galaxies, as well as the most massive galaxies (across the star-formation main sequence), tend to host the most luminous AGN, indicating concomitant assembly of the SMBH and the host galaxy.

The Euclid Quick Data Release (Q1) is a powerful dataset to study active galactic nuclei (AGN) and their host galaxies. Deriving their physical properties through multi-component spectral energy distribution (SED) fitting is a challenging task for AGN, but it is greatly aided by the Euclid near-infrared photometry. Here we present a new method of quantifying the reliability of SED-derived parameters, such as AGN bolometric and monochromatic luminosities, host's stellar mass (M_⋆), star-formation rate (SFR), and specific star-formation rate (sSFR), by using mock SEDs of AGN built by combining observed SEDs of QSOs and galaxies. We applied this methodology to the ∼1 million Q1 AGN candidates, constructing a catalogue of AGN and host galaxy properties, alongside their respective reliability values. With a reliability threshold at 0.5, we find 88% of sources to have robust stellar masses and 76% to have reliable AGN luminosities. Moreover, through SED fitting we also measured the AGN fraction (f_ > 0.075 threshold yields 85% completeness and purity. Comparable to colour-colour AGN selections, this method has the advantage of being less affected by redshift evolution and exploring fainter magnitudes. Additionally, by comparing the AGN and host galaxy parameters across different identification methods, we find that the probed range in stellar mass and AGN luminosity can be quite different. This highlights the importance of combining different approaches and accounting for their selection biases when studying AGN and their role in galaxy evolution. Finally, for the X-ray detected sample, we present the X-ray to mid-IR luminosity relation, and the correlation between stellar mass and bolometric luminosity as a function of redshift, in good agreement with previous results. AGN) of the total mid-infrared flux and we used its lower-limit to select AGN. A f_ AGN, , low

JWST surveys have identified a new class of active galactic nuclei (AGNs) called little red dots (LRDs). Their observational properties challenge the canonical AGN paradigm and provide key insights into the early growth phase of the supermassive black holes (SMBHs). We report Subaru/PFS spectroscopic follow-up of a radio-loud quasar at z = 1.715 from the UNVEIL radio AGN catalog, including X-ray detections. The spectrum displays broad C iii ] λ 1909 and Mg ii λ 2800 emission lines with FWHM ≳4000 km s ⁻¹ , accompanied by narrow absorption features. The spectrum reveals a characteristic Λ-shape over the rest-frame wavelength ranging ∼1500–3500 Å. The underlying continuum cannot be reproduced by simply applying dust extinction to typical unobscured quasars. Alternatively, it is well described by a blackbody spectrum with a temperature of T ∼ 10 ⁴ K. This result agrees well with its UV to MIR photometry, which can be well modeled by three blackbody components representing the BH envelope ( T ≈ 9700 K), dust torus ( T ≈ 1500 K), and host galaxy dust ( T ∼ 80 K). The source is marginally detected in the GALEX NUV, revealing a potential V-shaped spectral energy distribution around 1400 Å, reminiscent of the spectral feature reported for LRDs whose V-shapes occur around 3000–4000 Å. This wavelength shift is broadly consistent with the temperature contrast between our blackbody component ( T ∼ 10 ⁴ K) and the lower effective temperature of T ∼ 5000 K expected for the BH envelope of LRDs. These properties suggest that this source might be caught in an evolutionary phase in which the dense gas envelope characteristic of LRD has begun to fragment, allowing us to witness the emergence of a quasar from an LRD-like state.

We present an analysis of the rest-frame optical JWST NIRSpec Fixed Slit spectra of extended host galaxy emission in 12 moderate luminosity quasars from the Subaru High- z Exploration of Low-Luminosity Quasars sample at redshifts 6.0 < z < 6.4. We fit and subtract a point-spread model based on observations of a calibration star and use it to remove the quasar from the 2D spectra, leaving only extended emission, which we analyze. Ten of 12 systems show spatially extended line emission, and six of 12 systems show an extended stellar continuum. From the extended [O III ] λ 5008 emission line, we measure a 132 ± 22 km s ⁻¹ ionized outflow in one system and 52 ± 12 km s ⁻¹ rotation, suggesting a coherent disk, in another. From the extended narrow H α emission, which we hypothesize is ionized by star-forming regions rather than the quasar, we measure star formation rates ranging from ∼7 to 111 M _⊙ yr ⁻¹ , the majority of which are consistent with the star-forming main sequence (SFMS) at z ≈ 6. The positions of our host galaxies on the log 10 [ O III ] λ 5008 / H β versus log 10 [ NII ] 6584 / H α (R3N2) Baldwin–Phillips–Terlevich diagram indicate ionization rates typical of active galactic nucleus (AGN) activity in the low-redshift Universe, but are consistent with the placement of other z ≈ 6 quasar host galaxies, suggesting that the R3N2 line ratios cannot distinguish AGN- and star-formation-powered line emission at high redshifts. We conclude from the consistency between our quasar host sample with z ∼ 6 galaxies that the presence of a low-luminosity AGN causes little significant change in the properties of galaxies at z ≈ 6 on 10 Myr timescales.

We present our discovery of a complex ionized outflow in SDSS J101034.28+372514.7 (J1010+3725), a dust-obscured galaxy (DOG) at z = 0.282. The Sloan Digital Sky Survey optical spectrum of J1010+3725 shows five narrow components with one broad component in [O iii ] λ 5007, which represents one of the most complex outflow structures observed among dusty active galactic nuclei. Spectrum fitting shows that the five narrow components have a wide range of velocity shifts (from −1475 to +507 km s ⁻¹ ). The possible multiple peaks are also observed in [O iii ] λ 4363 and [Ne iii ] λ 3868, which allows us to investigate the physical condition of the outflowing gas by comparing the measured emission-line flux ratios with photoionization models. The comparison suggests that the five outflowing components are characterized by high hydrogen densities (≳10 ⁵ cm ⁻³ ). Our results imply that the five highly dense gas components may be outflowing with multiple bulk velocities at the innermost part of the narrow-line region in J1010+3725.