The 8.2m Subaru Telescope features a very stiff structure, enabling us to mount instruments at the prime focus and achieve an unprecedentedly wide field-of-view among the largest optical/near-IR telescopes. Subaru has played a leading role particularly in survey-type observations, e.g., an extensive study of Lyman-alpha emitters in the epoch of reionization. In the past 10 years, we have been...
The discovery and study of high-redshift quasars (z > 6) provides crucial insights into the first billion years of the Universe, particularly in relation to cosmic reionization, black hole growth, and galaxy formation. In the era of the JWST and Euclid, our ability to detect and characterize these distant quasars has significantly advanced. In this talk, I will summarize the efforts of the...
Luminous high-z quasars provide direct probes of the buildup of supermassive black holes, the primeval massive galaxies hosting them, and the intergalactic medium during the epoch of reionization. Despite its extraordinary capabilities, a significant challenge remains: the lack of quasar samples at redshift larger than 7. The Euclid space telescope offers a promising avenue to enrich our...
The study of high-redshift (z>6) quasars is a fundamental key to the understanding of the formation and evolution of the first supermassive black holes (SMBHs) and the history of Reionization. We present the proximity zone size analysis performed on optical and near-infrared spectroscopic observations for a sample of 45 quasars at 6.50 < z ≤ 7.64. This represents the largest...
Bolometric luminosity is a fundamental property that enables us to resolve the central supermassive black hole (SMBH) accretion history. A common method to quantify bolometric luminosity is based on only one monochromatic luminosity. To take advantage of multi-band data, we explore the mid-infrared through ultraviolet spectral energy distributions of ~30,000 SDSS broad-lined quasars with 0.5 <...
AGN spectral energy distributions (SED) are often described by a standard template, but broadband multiwavelength data clearly show a systematic change, with the bolometric luminosity being increasingly dominated by an EUV component at higher L/LEdd while the X-ray spectra become steeper. I will discuss models of the accretion flow which can follow this behaviour, and draw comparisons to the...
The possibility of forming black holes in the early universe was mentioned more than half a century ago. But it had not been seriously studied until recently. Thanks to the rapid progress in gravitational wave astronomy/cosmology, that situation has drastically changed. In this talk, I will review the current understanding and future issues of primordial black holes from my personal perspective.
Primordial Black Holes (PBHs) may be produced by gravitational collapse in regions with a large amplitude of density contrasts in the early Universe. They may provide the seeds for galaxy formation, account for a population of the LIGO-Virgo events, and the candidates of cold dark matter. The main purpose of our study is to develop a more accurate estimation for PBH abundance. We will address...
"Stars in the early universe were likely massive. This talk provides an overview of their formation processes and characteristics, then examine the potential for supermassive star formation and the subsequent emergence of direct collapse black holes (DCBHs) in some environments, e.g., characterized by strong far-ultraviolet (FUV) radiation, dense shocks, or dynamic heating from mergers....
The origin of high-redshift supermassive black holes (SMBHs) has been an intriguing mystery in astronomy and cosmology. Recent observations from James Webb Space Telescope further challenged our previous understanding about their formation mechanism. A promising solution to this problem is the direct collapse black holes from primordial metal-free clouds, which often requires stringent...
von Neumann of (thermal) quantum entropy fame purportedly responded to Shannon asking what his novel classical information content measure should be called: paraphrasing, entropy, nobody understands it anyway. Nowadays thermal entropy, gravitational entropy and information entropy have merged as ideas, and expanded to encompass phase info as well as counting info, into quantum information aka...
One of the more surprising results from JWST has been the discovery of faint, broad-line AGN at z > 5 with luminosities that are 2-3 dex below those of bright quasars found from the ground. I will discuss recent AGN-related results from the CEERS Survey and what they tell us about the growth of SMBHs in the early universe. This includes the discovery of an actively accreting SMBH at z=8.67,...
One of the most surprising results from JWST has been the discovery of a large population of compact red sources at z>4, with very red rest-frame optical colors, blue UV slopes, and broad Balmer lines. The compact sizes and luminous broad lines strongly suggest that these objects are powered by accreting supermassive black holes, but their lack of evidence for X-ray emission or hot dust in the...
Observations with the James Webb Space Telescope (JWST) have revealed active galactic nuclei (AGN) powered by supermassive black holes with estimated masses of 10^7−10^8 M⊙ at redshifts z∼7−9. Some reside in overmassive systems with higher AGN to stellar mass ratios than locally. Understanding how massive black holes could form so early in cosmic history and affect their environment to...
JWST has uncovered a substantial population of high-z (z>4) galaxies exhibiting broad Hα emission line with a Full Width at Half Maximum exceeding 1,000 km/s. This population includes a subset known as 'Little Red Dots', characterized by their compact morphology and extremely red rest-frame optical colors. If all of these broad Hα emitters were attributed to type 1−1.9 Active Galactic Nuclei...
The James Webb Space Telescope (JWST) observations have revolutionized extragalactic research, particularly with the discovery of little red dots (LRD), which have been discovered as a popula- tion of dust-reddened broad-line active galactic nuclei. Their unique v-shape spectral feature, which appears blue in the rest-frame UV and red in the optical, as observed through JWST/NIRCam, challenges...
The advent of the James Webb Space Telescope (JWST) has revealed a wealth of new galaxies, among which are ’little red dots’ (LRDs) at z ∼ 4 - 11, a population of previously-hidden, dust-obscured active galactic nuclei (AGNs) powered by 10^6 -10^8 M_⊙ black holes (BHs). In this talk, I will discuss results from 3D cosmological simulation which show that black holes of 10^3-10^5 solar masses...
The James Webb Space Telescope (JWST) observations have revolutionized extragalactic research, particularly with the discovery of low-luminosity active galactic nuclei (AGNs) at high redshifts, powered by accreting black holes (BHs) with masses of 10^6-8 Msun. These AGN populations are crucial for understanding early BH assembly and coevolution with their host galaxies. Several remarkable...
James Webb Space Telescope (JWST) has discovered many faint AGNs at high-z by detecting their broad Balmer lines. However, some of their characteristics are quite different from general type-1 AGN features, such as ~2-3 dex higher number density compared with the extrapolated quasar luminosity function, hosting a very massive SMBH, and no detection in X-rays. Are AGNs newly discovered by JWST...
Clustering measurements have always been foundational in building our understanding of the properties of quasars and galaxies, as well as their (co-)evolution with redshift. Recently, thanks to the advent of the James Webb Space Telescope (JWST), we have pushed the study of clustering well into the era of reionization: several JWST NIRCam/WFSS surveys, such as EIGER and ASPIRE, are measuring...
Growth of massive black holes (BHs) in the galactic centers are regulated by the environment. Modern cosmological galaxy-formation simulations suggest that supernova (SN) feedback evacuates the gas in galactic center, suppressing the BH growth until the host galaxies have grown sufficiently to develop a deep gravitational potential, leading to under-massive growth track relative to the local...
The origin and evolution of supermassive black holes as well as their interaction with their host galaxies still holds many unanswered questions such as the uncertainty surrounding the seeding and growth of the first supermassive balck holes embedded in first galaxies. The launch of JWST was expected to shed more light on this domain by probing the low mass, low luminosity end of the active...
JWST is now detecting early black holes (BHs) as they transition from seeds to supermassive BHs. I will present our recent results harnessing the power of the JWST UNCOVER survey combined with Chandra X-ray observations to identify UHZ-1, the first X-ray luminous massive BH at z=10.1. Placing UHZ-1 into context with other z=8-10 luminous active galactic nuclei, we are purportedly now...
Observational constraints on the evolution of active galactic nuclei (AGN) are key for constraining the origins and evolution of supermassive black holes (BHs) across cosmic time. In this talk, I present a sample of 50 H-alpha detected broad-line AGN (BLAGN) at redshifts 3.5<z<6.8 using data from the CEERS and RUBIES JWST/NIRSpec Surveys. I compute rest-frame ultraviolet and optical spectral...
The unprecedented sensitivity and resolution of the James Webb Space Telescope (JWST) have enabled us to uncover faint galaxies and AGNs in the early universe. Using their special colors shown in the JWST/NIRCam bands and compactness measurements, we report the discovery of 261 Hbeta+[O III] and Halpha dual-line emitters, including 58 AGN candidates (22%) which have compact morphology at...
"The CSTACK Tool (http://lambic.astrosen.unam.mx/cstack/) is a public tool for X-ray stacking analysis on several deep fields observed with Chandra for probing the average X-ray flux of populations of sources. As JWST data in deep fields are becoming available, we notice a recent increase in CSTACK. use. In this poster, we introduce the tool and explain its functions and usages,
As an...
"In this project, we present preliminary results from a systematic X‐ray analysis combined with multiwavelength photometric and spectroscopic data to identify and characterize obscured and highly obscured (Compton‐Thick or CT) AGNs in the XMM‐Newton 1.75 Ms Ultra Narrow Deep Field (XMM175UNDF) survey, one of the deepest XMM‐Newton survey to date.
We analyzed a sample of 118 X-ray AGNs...
Detection of supermassive black hole seeds and the first AGNs in the Universe are some of the key questions at the frontier of galaxy evolution. With the launch of JWST, we are now able to observe the rest-frame optical and UV lines at z>8. These tracers are necessary to detect emission coming from these first AGNs in the Universe, constraining the theoretical models on the origin of...
"Deep spectroscopic JWST observations have recently unveiled an emerging population of faint z>5 active galactic nuclei (AGN) with supermassive black hole (SMBH) masses of 10^6-10^8 solar masses. Their often compact, red appearance in JWST/NIRCam imaging earned them the nick name “little red dots” and is likely due to large amounts of intrinsic dust-reddening. First estimates of their number...
Deep IR observations by JWST have discovered a large number of high-z, red, and compact objects called “little red dots” (LRDs). Based on the detection and analysis of broad emission lines, previous studies have argued that LRDs are low-luminosity AGNs hosting overmassive black holes. However, previous LRDs selection is mainly based on color and compactness criteria, potentially biasing...
"Deep X-ray surveys have long been the most effective method for uncovering obscured Active Galactic Nuclei (AGN) in the distant Universe, revealing that the growth of supermassive black holes (SMBHs) becomes increasingly shrouded in obscuration at earlier cosmic times. However, even the most extensive X-ray surveys to date struggle to uncover and thoroughly understand the physics and...
"In this talk, I will present key results on the selection of high-redshift AGN and their peculiar properties. Specifically, I will introduce three new narrow-line AGN diagnostic diagrams, leveraging the [OIII]4363 auroral line, which has been detected in several JWST spectra. These diagnostics effectively differentiate much of the AGN population from Star-Forming Galaxies (SFGs) and have...
Twenty or more narrow-line (FWHM<500 km/s) quasars have been discovered through the high-z quasar search project SHELLQs, based on the Subaru HSC Survey. Their narrow but luminous Ly_alpha make them good candidates of obscured quasars at z > 6, that are expected to be abundant. Besides the discovery spectra in the rest-frame UV band, JWST-NIRSpec data of 9 objects have been acquired during the...
Tracing the buildup of supermassive black hole (SMBH) mass across cosmic time requires a full census of the active SMBH population, including obscured type-2 quasars. Active galactic nuclei unification predicts similar number counts of type-1 and type-2 quasars. The JWST discovery of LRDs indicates the obscured fraction may be much higher than we expected. However, to date only dozens of...
Heavily obscured AGN in the early universe are an important population that represent an early, violent growth phase of SMBHs and their host spheroidal components. We performed a MIPS 24um search for z>3 heavily obscured AGN in the XMM-LSS and COSMOS fields, focusing on their strong rest-frame NIR emission originating from AGN hot dust. As a result of the selection, approximately 90% of the...
Quasars discovered at the highest redshift provide a unique opportunity to study the early growth of the first supermassive black holes (SMBHs) and their host galaxies at the reionization epoch. Extensive observations were conducted out using large submillimeter/millimeter/radio telescopes and interferometer arrays to investigate the dust continuum, molecular CO, and fine structure line...
The co-evolution of AGN/SMBHs and their host galaxies is one of the main topics in the field of galaxy evolution. The key is to understand the relation between the masses of SMBHs and the properties of their hosts. For quasars where AGN are in the most active phase, their brightness prevents us from directly probing their host galaxies in the optical. Previous studies usually rely on two...
The environments of high-redshift quasars are a key probe of the formation and growth of supermassive black holes in the early Universe. With JWST, we can study their local kpc-scale environments in great detail. Here I will present our latest work using the NIRSpec IFU to study high-z quasars and their host galaxies. In the GA-NIFS program, we have discovered a large number of interacting...
The James Webb Space Telescope (JWST) has revolutionized our understanding of the early universe, particularly in the study of quasars (QSOs) at redshifts beyond 6. In this talk, I will present groundbreaking results from our Cycle 1 JWST program, which targeted 12 QSOs from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP). Our analysis has successfully detected host galaxies for the...
JWST is revealing a remarkable new population of high-redshift (z>4), low-luminosity Active Galactic Nuclei (AGNs) in deep surveys and detecting the host galaxy's stellar light in the most luminous and massive quasars at z~6 for the first time. Recent findings claim that SMBHs in these systems are significantly more massive than predicted by the local MBH-M* relation and that this is not due...
We present JWST/NIRSpec fixed slit spectra of 12 z~6 low-luminosity quasars and their host galaxies from the HSC SHELLQs sample. By modelling and subtracting the point-source quasar profiles from the 2D spectra, we reveal emission from the quasar's host galaxy extending at least 3 kpc. Of the 12 extracted spectra, at least seven show extended emission from the [OIII] 4959/5007 doublet and/or...
The unprecedented sensitivity of the JWST has led to the discovery of numerous supermassive black holes (SMBHs) with high black hole (BH)-to-galaxy mass ratios. This elevated mass ratio is thought to arise from the massive nature of seed BHs, which are believed to dominate the host galaxy’s mass at the time of their formation. However, as seed BHs undergo different growth trajectories, the...
We discuss the relationship between black hole and galaxy growth, as inferred from observations using the TRINITY empirical model. Key findings include: 1) the ratio between cosmic SMBH accretion rate and galaxy star formation rate stays constant at ~0.002 from z=0–4, and decreases at z>4; 2) the average SMBH Eddington ratio increases towards higher redshifts, nearly reaching η=1 at z~10; 3)...
Quasars are among the most active sources emerging in the early universe (z > 6). Their host galaxies have stellar masses and star formation rates orders of magnitude higher than what is observed in typical galaxies at the same redshifts. Investigating these sources is thus necessary if we want to unveil how the first massive galaxies formed. Here we present the rest-frame optical spectrum of...
With the advent of the James Webb Space Telescope (JWST), the study of supermassive black hole (SMBH) and host galaxy co-evolution has entered an unprecedented era, pushing the quasar redshift frontier to z~7.6. In this talk, I will present the first detailed kinematic analysis of the extended rest-frame optical emission in J0313-1806, the most distant luminous quasar currently known, using...
The large-scale environment is one of the key drivers of galaxy evolution, but the link with SMBH growth, especially at high redshift, is so far poorly understood. Massive SMBHs are thought to form in the peaks of the dark matter distribution of the early Universe, and dense and gas-rich regions at later cosmic times can provide the conditions for efficient SMBH growth. This scenario can be...
Understanding the interplay between galaxies and SMBHs has become a central theme in the latest research on galaxy formation and evolution. AGN feedback is thought to be the most reasonable solution to regulate star formation and match current observations in the modern hydrodynamic simulations. The hydrodynamic simulations report that studying solely luminous AGNs would not contribute to...
In this talk I will give an overview of some of the exciting research in quasar-galaxy co-evolution that will be enabled by future wide-field imaging and spectroscopic surveys including the Vera C. Rubin Observatory Legacy Survey of Space Time (LSST), the Euclid mission as well as wide-field spectroscopic surveys with new facilities such as 4MOST and VLT-MOONS. The focus will be on...
High-redshift (z > 5) quasars provide effective probes for the study of galaxy evolution and cosmology, hence it is critical to obtain a large sample of high-redshift quasars to study the intergalactic medium, circumgalactic medium and the co-evolution of supermassive black holes and their host galaxies. Here we present a machine learning search for high-redshift (5.0 < z < 6.5) quasars using...
NEXUS is a JWST Multi-Cycle (Cycles 3–5; 368 primary hrs) GO Treasury imaging and spectroscopic survey around the North Ecliptic Pole. It contains two overlapping tiers. The Wide tier
(~400 arcmin2) performs NIRCam/WFSS 2.4–5 μm grism spectroscopy with three epochs over 3 years (final continuum sensitivity of 22.2 at F444W). The Deep tier (~50 arcmin2) performs high-multiplexing NIRSpec...
