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Ken Mawatari

Publications and source records attributed to Ken Mawatari.

At least 37 records · Page 2Linked to original sources
arXiv2024

Detection of the [O I] 63 $μ$m emission line from the $z = 6.04$ quasar J2054-0005

We report the highest-redshift detection of [O I] 63 $μ$m from a luminous quasar, J2054-0005, at $z=6.04$ based on the Atacama Large Millimeter/sub-millimeter Array Band 9 observations. The [O I] 63 $μ$m line luminosity is $(4.5\pm1.5) \times 10^{9}~L_{\rm \odot}$, corresponding to the [O I] 63 $μ$m-to-far-infrared luminosity ratio of $\approx 6.7\times10^{-4}$, which is consistent with the value obtained in the local universe. Remarkably, [O I] 63 $μ$m is as bright as [C II] 158 $μ$m, resulting in the [O I]-to-[C II] line luminosity ratio of $1.3\pm0.5$. Based on a careful comparison of the luminosity ratios of [O I] 63 $μ$m, [C II] 158 $μ$m, and dust continuum emission to models of photo-dissociation regions, we find that J2054-0005 has a gas density log($n_{\rm H}$/cm$^{-3}$)$=3.7\pm0.3$ and an incident far-ultraviolet radiation field of log($G/G_{\rm 0}$)$= 3.0\pm0.1$, showing that [O I] 63 $μ$m serves as an important coolant of the dense and warm gas in J2054-0005. A close examination of the [O I] and [C II] line profiles suggests that the [O I] line may be partially self-absorbed, however deeper observations are needed to verify this conclusion. Regardless, the gas density and incident radiation field are in a broad agreement with the values obtained in nearby star-forming galaxies and objects with [O I] 63 $μ$m observations at $z=1-3$ with the Herschel Space Observatory. These results demonstrate the power of ALMA high-frequency observations targeting [O I] 63 $μ$m to examine the properties of photo-dissociation regions in high-redshift galaxies.

astro-ph.GA↗
arXiv2024

EMPRESS. X. Spatially resolved mass-metallicity relation in extremely metal-poor galaxies: evidence of episodic star-formation fueled by a metal-poor gas infall

Using the Subaru/FOCAS IFU capability, we examine the spatially resolved relationships between gas-phase metallicity, stellar mass, and star-formation rate surface densities (Sigma_* and Sigma_SFR, respectively) in extremely metal-poor galaxies (EMPGs) in the local universe. Our analysis includes 24 EMPGs, comprising 9,177 spaxels, which span a unique parameter space of local metallicity (12+log(O/H) = 6.9 to 7.9) and stellar mass surface density (Sigma_* ~ 10^5 to 10^7 Msun/kpc^2), extending beyond the range of existing large integral-field spectroscopic surveys. Through spatially resolved emission line diagnostics based on the [NII] BPT-diagram, we verify the absence of evolved active galactic nuclei in these EMPGs. Our findings reveal that, while the resolved mass-metallicity relation exhibits significant scatter in the low-mass regime, this scatter is closely correlated with local star-formation surface density. Specifically, metallicity decreases as Sigma_SFR increases for a given Sigma_*. Notably, half of the EMPGs show a distinct metal-poor horizontal branch on the resolved mass-metallicity relation. This feature typically appears at the peak clump with the highest Sigma_* and Sigma_SFR and is surrounded by a relatively metal-enriched ambient region. These findings support a scenario in which metal-poor gas infall fuels episodic star formation in EMPGs, consistent with the kinematic properties observed in these systems. In addition, we identify four EMPGs with exceptionally low central metallicities (12+log(O/H) <~ 7.2), which display only a metal-poor clump without a surrounding metal-rich region. This suggests that such ultra-low metallicity EMPGs, at less than a few percent of the solar metallicity, may serve as valuable analogs for galaxies in the early stages of galaxy evolution.

astro-ph.GA↗
arXiv2024

JWST, ALMA, and Keck Spectroscopic Constraints on the UV Luminosity Functions at z~7-14: Clumpiness and Compactness of the Brightest Galaxies in the Early Universe

We present the number densities and physical properties of the bright galaxies spectroscopically confirmed at $z\sim7-14$. Our sample is composed of 60 galaxies at $z_\mathrm{spec}\sim7-14$, including recently-confirmed galaxies at $z_\mathrm{spec}=12.34-14.32$ with JWST, as well as new confirmations at $z_\mathrm{spec}=6.583-7.643$ with $-24< M_\mathrm{UV}< -21$ mag using ALMA and Keck. Our JWST/NIRSpec observations have also revealed that very bright galaxy candidates at $z\sim10-13$ identified from ground-based telescope images before JWST are passive galaxies at $z\sim3-4$, emphasizing the necessity of strict screening and spectroscopy in the selection of the brightest galaxies at $z>10$. The UV luminosity functions derived from these spectroscopic results are consistent with a double power-law function, showing tensions with theoretical models at the bright end. To understand the origin of the overabundance of bright galaxies, we investigate their morphologies using JWST/NIRCam high-resolution images obtained in various surveys including PRIMER and COSMOS-Web. We find that $\sim70\%$ of the bright galaxies at $z\sim7$ exhibit clumpy morphologies with multiple sub-components, suggesting merger-induced starburst activity, which is consistent with SED fitting results showing bursty star formation histories. At $z\gtrsim10$, bright galaxies are classified into two types of galaxies; extended ones with weak high-ionization emission lines, and compact ones with strong high-ionization lines including NIV]$λ$1486, indicating that at least two different processes (e.g., merger-induced starburst and compact star formation/AGN) are shaping the physical properties of the brightest galaxies at $z\gtrsim10$ and are responsible for their overabundance.

astro-ph.GA↗
arXiv2024

Point Cloud Novelty Detection Based on Latent Representations of a General Feature Extractor

We propose an effective unsupervised 3D point cloud novelty detection approach, leveraging a general point cloud feature extractor and a one-class classifier. The general feature extractor consists of a graph-based autoencoder and is trained once on a point cloud dataset such as a mathematically generated fractal 3D point cloud dataset that is independent of normal/abnormal categories. The input point clouds are first converted into latent vectors by the general feature extractor, and then one-class classification is performed on the latent vectors. Compared to existing methods measuring the reconstruction error in 3D coordinate space, our approach utilizes latent representations where the shape information is condensed, which allows more direct and effective novelty detection. We confirm that our general feature extractor can extract shape features of unseen categories, eliminating the need for autoencoder re-training and reducing the computational burden. We validate the performance of our method through experiments on several subsets of the ShapeNet dataset and demonstrate that our latent-based approach outperforms the existing methods.

cs.CV↗
arXiv2024

JWST/NIRSpec spectroscopy of intermediate-mass quiescent galaxies at $z \sim 3-4$

We present the analysis of three intermediate-mass quiescent galaxies (QGs) with stellar masses of $\sim10^{10}M_{\rm \odot}$ at redshifts $z\sim 3 - 4$ using NIRSpec low-resolution spectroscopy. Utilising the SED fitting code BAGPIPES, we confirm these target galaxies are consistent with quiescent population, with their specific star formation rates (sSFR) falling below 2-dex the star-forming main sequence at the same redshifts. Additionally, we identify these QGs to be less massive than those discovered in previous works, particularly prior to the JWST era. Two of our target galaxies exhibit the potentially-blended H$α$+[NII] emission line within their spectra with $S/N>5$. We discuss whether this feature comes from an Active Galactic Nucleus (AGN) or star formation although future high-resolution spectroscopy is required to reach a conclusion. One of the target galaxies is covered by JWST/NIRCam imaging of the PRIMER survey. Using the 2D profile fitting code Galfit, we examine its morphology, revealing a disc-like profile with a Sérsic index of $n=1.1 \pm 0.1$. On the size-mass relation, we find a potential distinction between less-massive ($\log_{10}{(M_*/M_\odot)}<10.3$) and massive ($\log_{10}{(M_*/M_\odot)}>10.3$) QGs in their evolutionary pathways. The derived quenching timescales for our targets are less than 1 Gyr. This may result from these galaxies being quenched by AGN feedback, supporting the AGN scenario of the emission line features.

astro-ph.GA↗
arXiv2024

FINER: Far-Infrared Nebular Emission Receiver for the Large Millimeter Telescope

Unveiling the emergence and prevalence of massive/bright galaxies during the epoch of reionization and beyond, within the first 600 million years of the Universe, stands as a pivotal pursuit in astronomy. Remarkable progress has been made by JWST in identifying an immense population of bright galaxies, which hints at exceptionally efficient galaxy assembly processes. However, the underlying physical mechanisms propelling their rapid growth remain unclear. With this in mind, millimeter and submillimeter-wave spectroscopic observations of redshifted far-infrared spectral lines, particularly the [O III] 88 micron and [C II] 158 micron lines, offers a crucial pathway to address this fundamental query. To this end, we develop a dual-polarization sideband-separating superconductor-insulator-superconductor (SIS) mixer receiver, FINER, for the Large Millimeter Telescope (LMT) situated in Mexico. Harnessing advancements from ALMA's wideband sensitivity upgrade (WSU) technology, FINER covers radio frequencies spanning 120-360 GHz, delivering an instantaneous intermediate frequency (IF) of 3-21 GHz per sideband per polarization, which is followed by a set of 10.24 GHz-wide digital spectrometers. At 40% of ALMA's light-collecting area, the LMT's similar atmospheric transmittance and FINER's 5 times wider bandwidth compared to ALMA culminate in an unparalleled spectral scanning capability in the northern hemisphere, paving the way for finer spectral-resolution detection of distant galaxies.

astro-ph.IM↗
arXiv2024

EMPRESS. XII. Statistics on the Dynamics and Gas Mass Fraction of Extremely-Metal Poor Galaxies

We present demography of the dynamics and gas-mass fraction of 33 extremely metal-poor galaxies (EMPGs) with metallicities of $0.015-0.195~Z_\odot$ and low stellar masses of $10^4-10^8~M_\odot$ in the local universe. We conduct deep optical integral-field spectroscopy (IFS) for the low-mass EMPGs with the medium high resolution ($R=7500$) grism of the 8m-Subaru FOCAS IFU instrument by the EMPRESS 3D survey, and investigate H$α$ emission of the EMPGs. Exploiting the resolution high enough for the low-mass galaxies, we derive gas dynamics with the H$α$ lines by the fitting of 3-dimensional disk models. We obtain an average maximum rotation velocity ($v_\mathrm{rot}$) of $15\pm3~\mathrm{km~s^{-1}}$ and an average intrinsic velocity dispersion ($σ_0$) of $27\pm10~\mathrm{km~s^{-1}}$ for 15 spatially resolved EMPGs out of the 33 EMPGs, and find that all of the 15 EMPGs have $v_\mathrm{rot}/σ_0<1$ suggesting dispersion dominated systems. There is a clear decreasing trend of $v_\mathrm{rot}/σ_0$ with the decreasing stellar mass and metallicity. We derive the gas mass fraction ($f_\mathrm{gas}$) for all of the 33 EMPGs, and find no clear dependence on stellar mass and metallicity. These $v_\mathrm{rot}/σ_0$ and $f_\mathrm{gas}$ trends should be compared with young high-$z$ galaxies observed by the forthcoming JWST IFS programs to understand the physical origins of the EMPGs in the local universe.

astro-ph.GA↗
arXiv2023

Reionization and the ISM/Stellar Origins with JWST and ALMA (RIOJA): The core of the highest redshift galaxy overdensity at $z = 7.88$ confirmed by NIRSpec/JWST

The protoclusters in the epoch of reionization, traced by galaxies overdensity regions, are ideal laboratories for studying the process of stellar assembly and cosmic reionization. We present the spectroscopic confirmation of the core of the most distant protocluster at $z = 7.88$, A2744-z7p9OD, with the James Webb Space Telescope NIRSpec integral field unit spectroscopy. The core region includes as many as 4 galaxies detected in [OIII] 4960 Å and 5008 Å in a small area of $\sim 3\arcsec \times 3\arcsec$, corresponding to $\sim$ 11 kpc $\times$ 11 kpc, after the lensing magnification correction. Three member galaxies are also tentatively detected in dust continuum in Atacama Large Millimeter/submillimeter Array Band 6, which is consistent with their red ultraviolet continuum slopes, $β\sim -1.3$. The member galaxies have stellar masses in the range of log($M_{*}/M_{\rm \odot}$) $\sim 7.6-9.2$ and star formation rates of $\sim 3-50$ $M_{\rm \odot}$ yr$^{-1}$, showing a diversity in their properties. FirstLight cosmological simulations reproduce the physical properties of the member galaxies including the stellar mass, [OIII] luminosity, and dust-to-stellar mass ratio, and predict that the member galaxies are on the verge of merging in a few to several tens Myr to become a large galaxy with $M_{\rm *}\sim 6\times10^{9} M_{\rm \odot}$. The presence of a multiple merger and evolved galaxies in the core region of A2744-z7p9OD indicates that environmental effects are already at work 650 Myr after the Big Bang.

astro-ph.GA↗
arXiv2023

Characterizing CO Emitters in the SSA22-AzTEC26 Field

We report the physical characterization of four CO emitters detected near the bright submillimeter galaxy (SMG) SSA22-AzTEC26. We analyze the data from Atacama Large Millimeter/submillileter Array band 3, 4, and 7 observations of the SSA22-AzTEC26 field. In addition to the targeted SMG, we detect four line emitters with a signal-to-noise ratio $>5.2$ in the cube smoothed with 300 km s$^{-1}$ FWHM Gaussian filter. All four sources have NIR counterparts within 1$\arcsec$. We perform UV-to-FIR spectral energy distribution modeling to derive the photometric redshifts and physical properties. Based on the photometric redshifts, we reveal that two of them are CO(2-1) at redshifts of 1.113 and 1.146 and one is CO(3-2) at $z=2.124$. The three sources are massive galaxies with a stellar mass $\gtrsim10^{10.5}M_\odot$, but have different levels of star formation. Two lie within the scatter of the main sequence (MS) of star-forming galaxies at $z\sim1-2$, and the most massive galaxy lies significantly below the MS. However, all three sources have a gas fraction within the scatter of the MS scaling relation. This shows that a blind CO line search can detect massive galaxies with low specific star formation rates that still host large gas reservoirs and that it also complements targeted surveys, suggesting later gas acquisition and the need for other mechanisms in addition to gas consumption to suppress star formation.

astro-ph.GA↗
arXiv2023

GREX-PLUS Science Book

GREX-PLUS (Galaxy Reionization EXplorer and PLanetary Universe Spectrometer) is a mission candidate for a JAXA's strategic L-class mission to be launched in the 2030s. Its primary sciences are two-fold: galaxy formation and evolution and planetary system formation and evolution. The GREX-PLUS spacecraft will carry a 1.2 m primary mirror aperture telescope cooled down to 50 K. The two science instruments will be onboard: a wide-field camera in the 2-8 $μ$m wavelength band and a high resolution spectrometer with a wavelength resolution of 30,000 in the 10-18 $μ$m band. The GREX-PLUS wide-field camera aims to detect the first generation of galaxies at redshift $z>15$. The GREX-PLUS high resolution spectrometer aims to identify the location of the water ``snow line'' in proto-planetary disks. Both instruments will provide unique data sets for a broad range of scientific topics including galaxy mass assembly, origin of supermassive blackholes, infrared background radiation, molecular spectroscopy in the interstellar medium, transit spectroscopy for exoplanet atmosphere, planetary atmosphere in the Solar system, and so on.

astro-ph.CO↗
arXiv2023

Cosmological-Scale Lyman-alpha Forest Absorption Around Galaxies and AGN Probed with the HETDEX and SDSS Spectroscopic Data

We present cosmological-scale 3-dimensional (3D) neutral hydrogen ({\sc Hi}) tomographic maps at $z=2-3$ over a total of 837 deg$^2$ in two blank fields that are developed with Ly$α$ forest absorptions of 14,736 background Sloan Digital Sky Survey (SDSS) quasars at $z$=2.08-3.67. Using the tomographic maps, we investigate the large-scale ($\gtrsim 10$ $h^{-1}$cMpc) average {\sc Hi} radial profiles and two-direction profiles of the line-of-sight (LoS) and transverse (Trans) directions around galaxies and AGN at $z=2-3$ identified by the Hobby-Eberly Telescope Dark Energy eXperiment (HETDEX) and SDSS surveys, respectively. The peak of the {\sc Hi} radial profile around galaxies is lower than the one around AGN, suggesting that the dark-matter halos of galaxies are less massive on average than those of AGN. The LoS profile of AGN is narrower than the Trans profile, indicating the Kaiser effect. There exist weak absorption outskirts at $\gtrsim 30$ $h^{-1}$cMpc beyond {\sc Hi} structures of galaxies and AGN found in the LoS profiles that can be explained by the {\sc Hi} gas at $\gtrsim 30$ $h^{-1}$cMpc falls toward the source positions. Our findings indicate that the {\sc Hi} radial profile of AGN has transitions from proximity zones ($\lesssim$ a few $h^{-1}$cMpc) to the {\sc Hi} structures ($\sim 1-30$ $h^{-1}$cMpc) and the weak absorption outskirts ($\gtrsim 30$ $h^{-1}$cMpc). Although there is no significant dependence of AGN types (type-1 vs. type-2) on the {\sc Hi} profiles, the peaks of the radial profiles anti-correlate with AGN luminosities, suggesting that AGN's ionization effects are stronger than the gas mass differences.

astro-ph.GA↗
arXiv2023

EMPRESS. IX. Extremely Metal-Poor Galaxies are Very Gas-Rich Dispersion-Dominated Systems: Will JWST Witness Gaseous Turbulent High-z Primordial Galaxies?

We present kinematics of 6 local extremely metal-poor galaxies (EMPGs) with low metallicities ($0.016-0.098\ Z_{\odot}$) and low stellar masses ($10^{4.7}-10^{7.6} M_{\odot}$). Taking deep medium-high resolution ($R\sim7500$) integral-field spectra with 8.2-m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with H$α$ emission. Carefully masking out sub-structures originated by inflow and/or outflow, we fit 3-dimensional disk models to the observed H$α$ flux, velocity, and velocity-dispersion maps. All the EMPGs show rotational velocities ($v_{\rm rot}$) of 5--23 km s$^{-1}$ smaller than the velocity dispersions ($σ_{0}$) of 17--31 km s$^{-1}$, indicating dispersion-dominated ($v_{\rm rot}/σ_{0}=0.29-0.80<1$) systems affected by inflow and/or outflow. Except for two EMPGs with large uncertainties, we find that the EMPGs have very large gas-mass fractions of $f_{\rm gas}\simeq 0.9-1.0$. Comparing our results with other H$α$ kinematics studies, we find that $v_{\rm rot}/σ_{0}$ decreases and $f_{\rm gas}$ increases with decreasing metallicity, decreasing stellar mass, and increasing specific star-formation rate. We also find that simulated high-$z$ ($z\sim 7$) forming galaxies have gas fractions and dynamics similar to the observed EMPGs. Our EMPG observations and the simulations suggest that primordial galaxies are gas-rich dispersion-dominated systems, which would be identified by the forthcoming James Webb Space Telescope (JWST) observations at $z\sim 7$.

astro-ph.GA↗
arXiv2023

Detections of [C II] 158 $μ$m and [O III] 88 $μ$m in a Local Lyman Continuum Emitter, Mrk 54, and its Implications to High-redshift ALMA Studies

We present integral field, far-infrared (FIR) spectroscopy of Mrk 54, a local Lyman Continuum Emitter (LCE), obtained with FIFI-LS on the Stratospheric Observatory for Infrared Astronomy. This is only the second time, after Haro 11, that [C II] 158 $μ$m and [O III] 88 $μ$m spectroscopy of the known LCEs have been obtained. We find that Mrk 54 has a strong [C II] emission that accounts for $\sim1$% of the total FIR luminosity, whereas it has only moderate [O III] emission, resulting in the low [O III]/[C II] luminosity ratio of $0.22\pm0.06$. In order to investigate whether [O III]/[C II] is a useful tracer of $f_{\rm esc}$ (LyC escape fraction), we examine the correlations of [O III]/[C II] and (i) the optical line ratio of $\rm O_{32} \equiv$ [O III] 5007 Å/[O II] 3727 Å, (ii) specific star formation rate, (iii) [O III] 88 $μ$m/[O I] 63 $μ$m ratio, (iv) gas phase metallicity, and (v) dust temperature based on a combined sample of Mrk 54 and the literature data from the Herschel Dwarf Galaxy Survey and the LITTLE THINGS Survey. We find that galaxies with high [O III]/[C II] luminosity ratios could be the result of high ionization (traced by $\rm O_{32}$), bursty star formation, high ionized-to-neutral gas volume filling factors (traced by [O III] 88 $μ$m/[O I] 63 $μ$m), and low gas-phase metallicities, which is in agreement with theoretical predictions. We present an empirical relation between the [O III]/[C II] ratio and $f_{\rm esc}$ based on the combination of the [O III]/[C II] and $\rm O_{32}$ correlation, and the known relation between $\rm O_{32}$ and $f_{\rm esc}$. The relation implies that high-redshift galaxies with high [O III]/[C II] ratios revealed by ALMA may have $f_{\rm esc}\gtrsim0.1$, significantly contributing to the cosmic reionization.

astro-ph.GA↗
arXiv2023

The SSA22 HI Tomography Survey (SSA22-HIT). I. Data Set and Compiled Redshift Catalog

We conducted a deep spectroscopic survey, named SSA22-HIT, in the SSA22 field with the DEep Imaging MultiObject Spectrograph (DEIMOS) on the Keck telescope, designed to tomographically map high-z HI gas through analysis of Lya absorption in background galaxies' spectra. In total, 198 galaxies were spectroscopically confirmed at 2.5 < z < 6 with a few low-z exceptions in the 26 x 15 arcmin^2 area, of which 148 were newly determined in this study. Our redshift measurements were merged with previously confirmed redshifts available in the 34 x 27 arcmin^2 area of the SSA22 field. This compiled catalog containing 730 galaxies of various types at z > 2 is useful for various applications, and it is made publicly available. Our SSA22-HIT survey has increased by approximately twice the number of spectroscopic redshifts of sources at z > 3.2 in the observed field. From a comparison with publicly available redshift catalogs, we show that our compiled redshift catalog in the SSA22 field is comparable to those among major extragalactic survey fields in terms of a combination of wide area and high surface number density of objects at z > 2. About 40 % of the spectroscopically confirmed objects in SSA22-HIT show reasonable quality of spectra in the wavelengths shorter than Lya when a sufficient amount of smoothing is adopted. Our data set enables us to make the HI tomographic map at z > 3, which we present in a parallel study.

astro-ph.GA↗
arXiv2023

HETDEX Public Source Catalog 1: 220K Sources Including Over 50K Lyman Alpha Emitters from an Untargeted Wide-area Spectroscopic Survey

We present the first publicly released catalog of sources obtained from the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX). HETDEX is an integral field spectroscopic survey designed to measure the Hubble expansion parameter and angular diameter distance at 1.88<z<3.52 by using the spatial distribution of more than a million Ly-alpha-emitting galaxies over a total target area of 540 deg^2. The catalog comes from contiguous fiber spectra coverage of 25 deg^2 of sky from January 2017 through June 2020, where object detection is performed through two complementary detection methods: one designed to search for line emission and the other a search for continuum emission. The HETDEX public release catalog is dominated by emission-line galaxies and includes 51,863 Lyα-emitting galaxy (LAE) identifications and 123,891 OII-emitting galaxies at z<0.5. Also included in the catalog are 37,916 stars, 5274 low-redshift (z<0.5) galaxies without emission lines, and 4976 active galactic nuclei. The catalog provides sky coordinates, redshifts, line identifications, classification information, line fluxes, OII and Ly-alpha line luminosities where applicable, and spectra for all identified sources processed by the HETDEX detection pipeline. Extensive testing demonstrates that HETDEX redshifts agree to within deltaz < 0.02, 96.1% of the time to those in external spectroscopic catalogs. We measure the photometric counterpart fraction in deep ancillary Hyper Suprime-Cam imaging and find that only 55.5% of the LAE sample has an r-band continuum counterpart down to a limiting magnitude of r~26.2 mag (AB) indicating that an LAE search of similar sensitivity with photometric pre-selection would miss nearly half of the HETDEX LAE catalog sample. Data access and details about the catalog can be found online at http://hetdex.org/.

astro-ph.GA↗
arXiv2022

A Comprehensive Study on Galaxies at z~9-16 Found in the Early JWST Data: UV Luminosity Functions and Cosmic Star-Formation History at the Pre-Reionization Epoch

We conduct a comprehensive study on dropout galaxy candidates at $z\sim9-16$ using the first 90 arcmin$^2$ JWST/NIRCam images taken by the early release observations (ERO) and early release science (ERS) programs. With the JWST simulation images, we find that a number of foreground interlopers are selected with a weak photo-$z$ determination ($Δχ^2>4$). We thus carefully apply a secure photo-$z$ selection criterion ($Δχ^2>9$) and conventional color criteria with confirmations of the ERO NIRSpec spectroscopic redshifts, and obtain a total of 23 dropout galaxies at $z\sim9-16$, including two candidates at $z_\mathrm{phot}=16.25_{-0.46}^{+0.24}$ and $16.41_{-0.55}^{+0.66}$. We perform thorough comparisons of dropout galaxies found in our work with recent JWST studies, and conclude that our galaxy sample is reliable enough for statistical analyses. We derive the UV luminosity functions at $z\sim9-16$, and confirm that our UV luminosity functions at $z\sim 9$ and $12$ agree with those determined by other HST and JWST studies. The cosmic star-formation rate density decreases from $z\sim9$ to $12$, and perhaps to $16$, but the densities at $z\sim12-16$ are higher than the constant star formation efficiency model. Interestingly, there are six bright galaxy candidates at $z\sim10-16$ with $M_\mathrm{UV}<-19.5$ mag and $M_*\sim10^{8-9} M_\odot$. Because a majority ($\sim80$\%) of these galaxies show no signatures of AGNs in their morphologies, the high cosmic star-formation rate densities and the existence of these UV-luminous galaxies are explained by no suppression of star-formation by the UV background radiation at the pre-reionization epoch and/or an efficient UV radiation production by a top-heavy IMF with Population III-like star formation.

astro-ph.GA↗
arXiv2022

EMPRESS. VIII. A New Determination of Primordial He Abundance with Extremely Metal-Poor Galaxies: A Suggestion of the Lepton Asymmetry and Implications for the Hubble Tension

The primordial He abundance $Y_\mathrm{P}$ is a powerful probe of cosmology. Currently, $Y_\mathrm{P}$ is best determined by observations of metal-poor galaxies, while there are only a few known local extremely metal-poor ($<0.1 Z_\odot$) galaxies (EMPGs) having reliable He/H measurements with HeI$λ$10830 near-infrared (NIR) emission. Here we present deep Subaru NIR spectroscopy for 10 EMPGs. Combining the existing optical data, He/H values of 5 out of the 10 EMPGs are reliably derived by the Markov chain Monte Carlo algorithm. Adding the existing 3 EMPGs and 51 moderately metal-poor ($0.1-0.4 Z_\odot$) galaxies with reliable He/H estimates, we obtain $Y_\mathrm{P}=0.2370^{+0.0034}_{-0.0033}$ by linear regression in the $\mathrm{(He/H)}-\mathrm{(O/H)}$ plane, where we increase the number of EMPGs from 3 to 8 anchoring He/H of the most metal-poor gas in galaxies. Although our $Y_\mathrm{P}$ measurement and previous measurements are consistent, our result is slightly ($\sim 1σ$) smaller due to our EMPGs. With our $Y_\mathrm{P}$ and the existing primordial deuterium $D_\mathrm{P}$ measurement, we constrain the effective number of neutrino species $N_\mathrm{eff}$ and the baryon-to-photon ratio $η$ showing $\gtrsim 1-2σ$ tensions with the Standard Model and Planck Collaboration et al. (2020). Motivated by the tensions, we allow the degeneracy parameter of electron-neutrino $ξ_e$ to vary as well as $N_\mathrm{eff}$ and $η$. We obtain $ξ_e = 0.05^{+0.03}_{-0.02}$, $N_\mathrm{eff}=3.11^{+0.34}_{-0.31}$, and $η\times10^{10}=6.08^{+0.06}_{-0.06}$ from the $Y_\mathrm{P}$ and $D_\mathrm{P}$ measurements with a prior of $η$ taken from Planck Collaboration et al. (2020). Our constraints suggest a lepton asymmetry and allow for a high value of $N_\mathrm{eff}$ within the $1σ$ level, which could mitigate the Hubble tension.

astro-ph.CO↗
arXiv2022

A Search for Massive Galaxy Population in a Protocluster of LAEs at $z = 2.39$ near the Radio Galaxy 53W002

We searched for massive galaxy population in the known large-scale high-density structure of Lyman$~α$ emitters (LAEs) at $z=2.39$ near the radio galaxy 53W002 by using $B,~V,~i^\prime,~J,~H,~{\rm{and}}~K_s$-bands imaging data taken with Suprime-Cam and MOIRCS on the Subaru telescope. We selected 62 protocluster member candidates by their $JHK_s$-band colors and Spectral Energy Distribution (SED) fitting analysis ($JHK_s$-selected galaxies) in our survey field of $70.2~{\rm{arcmin}}^{2}$, and compared their physical properties estimated from the SED fitting with a comparison sample in the COSMOS field. We found significant number density excesses for the $JHK_s$-selected galaxies in the 53W002 field at $K_s<22.25,~J-K_s>2,~{\rm{or}}~V-K_s>4$. In particular the number density of the $JHK_s$-selected galaxies with $K_s<22.25~{\rm{and}}~J-K_s>2$ in the 53W002 field is nine times higher than the comparison sample. Most of those with $K_s<22.25~{\rm{and}}~J-K_s>2$ are massive galaxies with $M_s>10^{11}~M_\odot$, and their sSFRs of $10^{-11}$--$10^{-10}~\rm{yr^{-1}}$ suggest that the star formation has not yet stopped completely. We also found a density excess of quiescent galaxies with $M_s=5\times10^{10}$--$10^{11}~M_\odot~{\rm{and}}~{\rm{sSFR}}<10^{-11}~\rm{yr^{-1}}$ as well as that of low-mass galaxies with $M_s=10^{9.75}$--$10^{10}~M_\odot$ and various sSFRs. The massive galaxies with $M_s>10^{11}~M_\odot$ are not located at the density peaks of LAEs, but widely distributed along the similar direction with the structure of LAEs over $\sim15$--$20$ comoving Mpc. On the other hand, the quiescent galaxies with ${\rm{sSFR}}<10^{-11}~\rm{yr^{-1}}$ clearly avoid the structure of LAEs. Our results suggest that massive galaxies also exist in this protocluster discovered by the moderate overdensity of LAEs and their star formation activities depend on location in the protocluster.

astro-ph.GA↗