arXiv subjects

Masami Ouchi

Publications and source records attributed to Masami Ouchi.

At least 91 records · Page 5Linked to original sources

arXiv2023

Redshift Evolution of the Electron Density in the ISM at $z\sim 0-9$ Uncovered with JWST/NIRSpec Spectra and Line-Spread Function Determinations

We present electron densities $n_{\rm e}$ in the inter-stellar medium (ISM) of star-forming galaxies at $z=4-9$ observed by the JWST/NIRSpec GLASS, ERO, and CEERS programs. We carefully evaluate line-spread functions of the NIRSpec instrument as a function of wavelength with the calibration data of a planetary nebula taken onboard, and obtain secure [OII]$λλ$3726,3729 doublet fluxes for 14 galaxies at $z=4.02-8.68$ falling on the star-formation main sequence with the NIRSpec high and medium resolution spectra. We thus derive the electron densities of singly-ionized oxygen nebulae with the standard $n_{\rm e}$ indicator of [OII] doublet, and find that the electron densities of the $z=4-9$ galaxies are $n_{\rm e}\gtrsim 300$ cm$^{-3}$ significantly higher than those of low-$z$ galaxies at a given stellar mass, star-formation rate (SFR), and specific SFR. Interestingly, typical electron densities of singly ionized nebulae increase from $z=0$ to $z=1-3$ and $z=4-9$, which is approximated by the evolutionary relation of $n_{\rm e}\propto(1+z)^{p}$ with $p\sim 1-2$. Although it is not obvious that the ISM property of $n_{\rm e}$ is influenced by global galaxy properties, these results may suggest that nebula densities of high-$z$ galaxies are generally high due to the compact morphologies of high-$z$ galaxies evolving by $r_{\rm e}$ approximately proportional to $(1+z)^{-1}$ ($r_{\rm vir} \propto (1+z)^{-1}$) for a given stellar (halo) mass whose inverse square corresponds to the $p\sim 2$ evolutionary relation. The $p\sim 1-2$ evolutionary relation can be explained by a combination of the compact morphology and the reduction of $n_{\rm e}$ due to the high electron temperature of the high-$z$ metal poor nebulae.

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arXiv2023

SILVERRUSH. XIII. A Catalog of 20,567 Ly$α$ Emitters at $z=2-7$ Identified in the Full-depth Data of the Subaru/HSC-SSP and CHORUS Surveys

We present 20,567 Ly$α$ emitters (LAEs) at $z=2.2-7.3$ that are photometrically identified by the SILVERRUSH program in a large survey area up to 25 deg$^2$ with deep images of five broadband filters (grizy) and seven narrowband filters targeting Ly$α$ lines at $z=2.2$, $3.3$, $4.9$, $5.7$, $6.6$, $7.0$, and $7.3$ taken by the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) and the Cosmic HydrOgen Reionization Unveiled with Subaru (CHORUS) survey. We select secure $>5σ$ sources showing narrowband color excesses via Ly$α$ break screening, taking into account the spatial inhomogeneity of limiting magnitudes. After removing spurious sources by careful masking and visual inspection of coadded and multi-epoch images obtained over the 7 yr of the surveys, we construct LAE samples consisting of 6995, 4641, 726, 6124, 2058, 18, and 5 LAEs at $z=2.2$, 3.3, 4.9, 5.7, 6.6, 7.0, and 7.3, respectively, although the $z=7.3$ candidates are tentative. Our LAE catalogs contain 241 spectroscopically confirmed LAEs at the expected redshifts from previous work. We demonstrate that the number counts of our LAEs are consistent with previous studies with similar LAE selection criteria. The LAE catalogs will be made public on our project webpage with detailed descriptions of the content and ancillary information about the masks and limiting magnitudes.

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arXiv2023

ALMA FIR View of Ultra High-redshift Galaxy Candidates at $z\sim$ 11-17: Blue Monsters or Low-$z$ Red Interlopers?

We present ALMA Band~7 observations of a remarkably bright galaxy candidate at $z_{\rm phot}$=$16.7^{+1.9}_{-0.3}$ ($M_{\rm UV}$=$-21.6$), S5-z17-1, identified in JWST Early Release Observation data of Stephen's Quintet. We do not detect the dust continuum at 866~$μ$m, ruling out the possibility that \targb\ is a low-$z$ dusty starburst with a star-formation rate of $\gtrsim 30$~$M_{\odot}$~yr$^{-1}$. We detect a 5.1$σ$ line feature at $338.726\pm0.007$~GHz exactly coinciding with the JWST source position, with a 2\% likelihood of the signal being spurious. The most likely line identification would be [OIII]52$μ$m at $z=16.01$ or [CII]158$μ$m at $z=4.61$, whose line luminosities do not violate the non-detection of the dust continuum in both cases. Together with three other $z\gtrsim$ 11--13 candidate galaxies recently observed with ALMA, we conduct a joint ALMA and JWST spectral energy distribution (SED) analysis and find that the high-$z$ solution at $z\sim$11--17 is favored in every candidate as a very blue (UV continuum slope of $\simeq-2.3$) and luminous ($M_{\rm UV}\simeq[-$24:$-21]$) system. Still, we find in several candidates that reasonable SED fits ($Δ$ $χ^{2}\lesssim4$) are reproduced by type-II quasar and/or quiescent galaxy templates with strong emission lines at $z\sim3$--5, where such populations predicted from their luminosity functions and EW([OIII]+H$β$) distributions are abundant in survey volumes used for the identification of the $z\sim$11--17 candidates. While these recent ALMA observation results have strengthened the likelihood of the high-$z$ solutions, lower-$z$ possibilities are not completely ruled out in several of the $z\sim$11--17 candidates, indicating the need to consider the relative surface densities of the lower-$z$ contaminants in the ultra high-$z$ galaxy search.

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arXiv2023

Roman CCS White Paper: Identifying high-redshift pair-instability supernovae by adding sparse F213 filter observations

Pair-instability supernovae (PISNe) are explosions of very massive stars that may have played a critical role in the chemical evolution and reionization of the early Universe. In order to quantify their roles, it is required to know the PISN event rate at z > 6. Although Roman Space Telescope has a capability to discover PISNe at z > 6, identifying rare high-redshift PISN candidates among many other transients is challenging. In order to efficiently identify PISN candidates at z > 6, we propose to add sparse F213 observations reaching 26.5 mag (or deeper) every half year in the High Latitude Time Domain Survey. By adding the F213 information, PISNe at z > 6 can be efficiently identified in the color-magnitude diagram.

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arXiv2023

The Spitzer Coverage of HSC-Deep with IRAC for Z studies (SHIRAZ) I: IRAC mosaics

We present new Spitzer Infrared Array Camera (IRAC) 3.6 and 4.5μm mosaics of three fields, E-COSMOS, DEEP2-F3, and ELAIS-N1. Our mosaics include both new IRAC observations as well as re-processed archival data in these fields. These fields are part of the HSC-Deep grizy survey and have a wealth of additional ancillary data. The addition of these new IRAC mosaics is critical in allowing for improved photometric redshifts and stellar population parameters at cosmic noon and earlier epochs. The total area mapped by this work is {\sim} 17 deg2 with a mean integration time of {\sim}1200s, providing a median 5σ depth of 23.7(23.3) at 3.6(4.5)μm in AB. We perform SExtractor photometry both on the combined mosaics as well as the single-epoch mosaics taken {\sim}6 months apart. The resultant IRAC number counts show good agreement with previous studies. In combination with the wealth of existing and upcoming spectro-photometric data in these fields, our IRAC mosaics will enable a wide range of galactic evolution and AGN studies. With that goal in mind, we make the combined IRAC mosaics and coverage maps of these three fields publicly available. counts show good agreement with previous studies.

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arXiv2023

Quasar Luminosity Function at z = 7

We present the quasar luminosity function (LF) at $z = 7$, measured with 35 spectroscopically confirmed quasars at $6.55 < z < 7.15$. The sample of 22 quasars from the Subaru High-$z$ Exploration of Low-Luminosity Quasars (SHELLQs) project, combined with 13 brighter quasars in the literature, covers an unprecedentedly wide range of rest-frame ultraviolet magnitudes over $-28 < M_{1450} < -23$. We found that the binned LF flattens significantly toward the faint end populated by the SHELLQs quasars. A maximum likelihood fit to a double power-law model has a break magnitude $M^*_{1450} = -25.60^{+0.40}_{-0.30}$, a characteristic density $Φ^* = 1.35^{+0.47}_{-0.30}$ Gpc$^{-3}$ mag$^{-1}$, and a bright-end slope $β= -3.34^{+0.49}_{-0.57}$, when the faint-end slope is fixed to $α= -1.2$ as observed at $z \le 6$. The overall LF shape remains remarkably similar from $z = 4$ to $7$, while the amplitude decreases substantially toward higher redshifts, with a clear indication of an accelerating decline at $z \ge 6$. The estimated ionizing photon density, $10^{48.2 \pm 0.1}$ s$^{-1}$ Mpc$^{-3}$, is less than 1 % of the critical rate to keep the intergalactic medium ionized at $z = 7$, and thus indicates that quasars are not a major contributor to cosmic reionization.

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arXiv2023

Morphologies of Galaxies at $z \gtrsim 9$ Uncovered by JWST/NIRCam Imaging: Cosmic Size Evolution and an Identification of an Extremely Compact Bright Galaxy at $z\sim 12$

We present morphologies of galaxies at $z \gtrsim 9$ resolved by JWST/NIRCam $2$-$5μ$m imaging. Our sample consists of $22$ galaxy candidates identified by stringent dropout and photo-$z$ criteria in GLASS, CEERS, SMACS J0723, and Stephan's Quintet flanking fields, one of which has been spectroscopically identified at $z=11.44$. We perform surface brightness (SB) profile fitting with GALFIT for $6$ bright galaxies with S/N $=10$-$40$ on an individual basis and for stacked faint galaxies with secure point-spread functions (PSFs) of the NIRCam real data, carefully evaluating systematics by Monte-Carlo simulations. We compare our results with those of previous JWST studies, and confirm that effective radii $r_{\rm e}$ of our measurements are consistent with those of previous measurements at $z\sim 9$. We obtain $r_{\rm e}\simeq 200$-$300$ pc with the exponential-like profiles, Sérsic indexes of $n\simeq 1$-$1.5$, for galaxies at $z\sim 12$-$16$, indicating that the relation of $r_{\rm e}\propto (1+z)^s$ for $s=-1.22^{+0.17}_{-0.16}$ explains cosmic evolution over $z\sim 0$-$16$ for $\sim L^*_{z=3}$ galaxies. One bright ($M_{\rm UV}=-21$ mag) galaxy at $z\sim 12$, GL-z12-1, has an extremely compact profile with $r_{\rm e}=39 \pm 11$ pc that is surely extended over the PSF. Even in the case that the GL-z12-1 SB is fit by AGN$+$galaxy composite profiles, the best-fit galaxy component is again compact, $r_{\rm e}=48^{+38}_{-15}$ pc that is significantly ($>5σ$) smaller than the typical $r_{\rm e}$ value at $z\sim 12$. Comparing with numerical simulations, we find that such a compact galaxy naturally forms at $z\gtrsim 10$, and that frequent mergers at the early epoch produce more extended galaxies following the $r_{\rm e}\propto (1+z)^s$ relation.

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arXiv2023

JWST Census for the Mass-Metallicity Star-Formation Relations at z=4-10 with the Self-Consistent Flux Calibration and the Proper Metallicity Calibrators

We present the evolution of the mass-metallicity (MZ) relations at z=4-10 derived with 135 galaxies identified in the JWST/NIRSpec data taken from the three major public spectroscopy programs of ERO, GLASS, and CEERS. Because there are many discrepancies between flux measurements reported by early ERO studies, we first establish our NIRSpec data reduction procedure for reliable emission-line flux measurements and errors successfully explaining Balmer decrements with no statistical tensions via thorough comparisons of the early ERO studies. Applying the reduction procedure to the 135 galaxies, we obtain emission-line fluxes for physical property measurements. We confirm that 10 out of the 135 galaxies with [OIII]4363-lines have electron temperatures of (1.1-2.3)*10^4K, similar to lower-z star-forming galaxies, that can be explained by heating of young massive stars. We derive metallicities of the 10 galaxies by the direct method and the rest of the galaxies with strong lines by the metallicity calibrations of Nakajima et al. (2022) applicable for these low-mass metal-poor galaxies, anchoring the metallicities with the direct-method measurements. We thus obtain MZ relations and star-formation rate (SFR)-MZ relations over z=4-10. We find that there is a small evolution of the MZ relation from z~2-3 to z=4-10, while interestingly that the SFR-MZ relation shows no evolution up to z~8 but a significant decrease at z>8 beyond the error. This SFR-MZ relation decrease at z>8 may suggest a break of the metallicity equilibrium state via star-formation, inflow, and outflow, while further statistical and local-baseline studies are needed for a conclusion.

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arXiv2023

Photometric IGM tomography with Subaru/HSC: the large-scale structure of Ly$α$ emitters and IGM transmission in the COSMOS field at $z\sim5$

We present a novel technique called "photometric IGM tomography" to map the intergalactic medium (IGM) at $z\simeq4.9$ in the COSMOS field. It utilizes deep narrow-band (NB) imaging to photometrically detect faint Ly$α$ forest transmission in background galaxies across the Subaru/Hyper-Suprime Cam (HSC)'s $1.8\rm\,sq.\,deg$ field of view and locate Ly$α$ emitters (LAEs) in the same cosmic volume. Using ultra-deep HSC images and Bayesian spectral energy distribution fitting, we measure the Ly$α$ forest transmission at $z\simeq4.9$ along a large number ($140$) of background galaxies selected from the DEIMOS10k spectroscopic catalogue at $4.98<z<5.89$ and the SILVERRUSH LAEs at $z\simeq5.7$. We photometrically measure the mean Ly$α$ forest transmission and achieve a result consistent with previous measurements based on quasar spectra. We also measure the angular LAE-Ly$α$ forest cross-correlation and Ly$α$ forest auto-correlation functions and place an observational constraint on the large-scale fluctuations of the IGM around LAEs at $z\simeq4.9$. Finally, we present the reconstructed 2D tomographic map of the IGM, co-spatial with the large-scale structure of LAEs, at a transverse resolution of $11 \,h^{-1}\rm cMpc$ across $140\,h^{-1}\rm cMpc$ in the COSMOS field at $z\simeq4.9$. We discuss the observational requirements and the potential applications of this new technique for understanding the sources of reionization, quasar radiative history, and galaxy-IGM correlations across $z\sim3-6$. Our results represent the first proof-of-concept of photometric IGM tomography, offering a new route to examining early galaxy evolution in the context of the large-scale cosmic web from the epoch of reionization to cosmic noon.

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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.

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arXiv2023

EMPRESS. XI. SDSS and JWST Search for Local and z~4-5 Extremely Metal-Poor Galaxies (EMPGs): Clustering and Chemical Properties of Local EMPGs

We search for local extremely metal-poor galaxies (EMPGs), selecting photometric candidates by broadband color excess and machine-learning techniques with the SDSS photometric data. After removing stellar contaminants by shallow spectroscopy with Seimei and Nayuta telescopes, we confirm that three candidates are EMPGs with 0.05--0.1 $Z_\odot$ by deep Magellan/MagE spectroscopy for faint {\sc[Oiii]}$λ$4363 lines. Using a statistical sample consisting of 105 spectroscopically-confirmed EMPGs taken from our study and the literature, we calculate cross-correlation function (CCF) of the EMPGs and all SDSS galaxies to quantify environments of EMPGs. Comparing another CCF of all SDSS galaxies and comparison SDSS galaxies in the same stellar mass range ($10^{7.0}-10^{8.4} M_\odot$), we find no significant ($>1σ$) difference between these two CCFs. We also compare mass-metallicity relations (MZRs) of the EMPGs and those of galaxies at $z\sim$ 0--4 with a steady chemical evolution model and find that the EMPG MZR is comparable with the model prediction on average. These clustering and chemical properties of EMPGs are explained by a scenario of stochastic metal-poor gas accretion on metal-rich galaxies showing metal-poor star formation. Extending the broadband color-excess technique to a high-$z$ EMPG search, we select 17 candidates of $z\sim$ 4--5 EMPGs with the deep ($\simeq30$ mag) near-infrared JWST/NIRCam images obtained by ERO and ERS programs. We find galaxy candidates with negligible {\sc[Oiii]}$λλ$4959,5007 emission weaker than the local EMPGs and known high-$z$ galaxies, suggesting that some of these candidates may fall in 0--0.01 $Z_\odot$, which potentially break the lowest metallicity limit known to date.

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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 $z\sim 7$.

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arXiv2023

Stellar Initial Mass Function (IMF) Probed with Supernova Rates and Neutrino Background: Cosmic Average IMF Slope is $\simeq 2-3$ Similar to the Salpeter IMF

The stellar initial mass function (IMF) is expressed by $ϕ(m) \propto m^{-α}$ with the slope $α$, and known as the poorly-constrained but very important function in studies of star and galaxy formation. There are no sensible observational constraints on the IMF slopes beyond Milky Way and nearby galaxies. Here we combine two sets of observational results, 1) cosmic densities of core-collapse supernova explosion (CCSNe) rates and 2) cosmic far ultraviolet radiation (and infrared re-radiation) densities, which are sensitive to massive ($\simeq 8-50 \,{\rm M}_\odot$) and moderately massive ($\simeq 2.5-7 \,{\rm M}_\odot$) stars, respectively, and constrain the IMF slope at $m>1\,{\rm M}_\odot$ with a freedom of redshift evolution. Although no redshift evolution is identified beyond the uncertainties, we find that the cosmic average IMF slope at $z=0$ is $α=1.8-3.2$ at the 95 % confidence level that is comparable with the Salpeter IMF, $α=2.35$, which marks the first constraint on the cosmic average IMF. We show a forecast for the Nancy Grace Roman Space Telescope supernova survey that will provide significantly strong constraints on the IMF slope with $δα\simeq 0.5$ over $z=0-2$. Moreover, as for an independent IMF probe instead of 1), we suggest to use diffuse supernovae neutrino background (DSNB), relic neutrinos from CCSNe. We expect that the Hyper-Kamiokande neutrino observations over 20 years will improve the constraints on the IMF slope and the redshift evolution significantly better than those obtained today, if the systematic uncertainties of DSNB production physics are reduced in the future numerical simulations.

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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.

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arXiv2023

The Stellar Mass - Black Hole Mass Relation at $z\sim2$ Down to $\mathcal{M}_\mathrm{BH}\sim10^7 M_\odot$ Determined by HETDEX

We investigate the stellar mass - black hole mass ($\mathcal{M}_*-\mathcal{M}_\mathrm{BH}$) relation with type 1 AGN down to $\mathcal{M}_\mathrm{BH}=10^7 M_\odot$, corresponding to a $\simeq -21$ absolute magnitude in rest-frame ultraviolet (UV), at $z = 2-2.5$. Exploiting the deep and large-area spectroscopic survey of the Hobby-Eberly Telescope Dark Energy Experiment (HETDEX), we identify 66 type 1 AGN with $\mathcal{M}_\mathrm{BH}$ ranging from $10^7$ to $10^{10} M_\odot$ that are measured with single-epoch virial method using C{\sc iv} emission lines detected in the HETDEX spectra. $\mathcal{M}_*$ of the host galaxies are estimated from optical to near-infrared photometric data taken with Spitzer, WISE, and ground-based 4-8m class telescopes by CIGALE SED fitting. We further assess the validity of SED fitting in two cases by host-nuclear decomposition performed through surface brightness profile fitting on spatially-resolved host galaxies with JWST/NIRCam CEERS data. We obtain the $\mathcal{M}_*-\mathcal{M}_\mathrm{BH}$ relation covering the unexplored low-mass ranges of $\mathcal{M}_\mathrm{BH}~\sim~10^7-10^8~M_\odot$, and conduct forward modelling to fully account for the selection biases and observational uncertainties. The intrinsic $\mathcal{M}_*-\mathcal{M}_\mathrm{BH}$ relation at $z\sim 2$ has a moderate positive offset of $0.52\pm0.14$~dex from the local relation, suggestive of more efficient black hole growth at higher redshift even in the low-mass regime of $\mathcal{M}_\mathrm{BH}~\sim~10^7-10^8~M_\odot$. Our $\mathcal{M}_*-\mathcal{M}_\mathrm{BH}$ relation is inconsistent with the $\mathcal{M}_\mathrm{BH}$ suppression at the low-$\mathcal{M}_*$ regime predicted by recent hydrodynamic simulations at a $98\%$ confidence level, suggesting that feedback in the low-mass systems may be weaker than those produced in hydrodynamic simulations.

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arXiv2023

MAMMOTH-Subaru III. Ly$α$ Halo Extended to $\sim200$ kpc Identified by Stacking $\sim 3300$ Ly$α$ Emitters at $z=2.2-2.3$

In this paper, we present a Ly$α$ halo extended to $\sim200$ kpc identified by stacking $\sim 3300$ Ly$α$ emitters at $z=2.2-2.3$. We carry out imaging observations and data reduction with Subaru/Hyper Suprime-Cam (HSC). Our total survey area is $\sim12$ deg$^2$ and imaging depths are $25.5-27.0$ mag. Using the imaging data, we select 1,240 and 2,101 LAE candidates at $z=2.2$ and 2.3, respectively. We carry out spectroscopic observations of our LAE candidates and data reduction with Magellan/IMACS to estimate the contamination rate of our LAE candidates. We find that the contamination rate of our sample is low (8%). We stack our LAE candidates with a median stacking method to identify the Ly$α$ halo at $z=2$. We show that the Ly$α$ halo is extended to $\sim200$ kpc at a surface brightness level of $10^{-20}$ erg s$^{-1}$ cm$^{-2}$ arcsec$^{-2}$. Comparing to previous studies, our Ly$α$ halo is more extended at radii of $\sim25-100$ kpc, which is not likely caused by the contamination in our sample but by different redshifts and fields instead. To investigate how central galaxies affect surrounding LAHs, we divide our LAEs into subsamples based on the Ly$α$ luminosity ($L_{\rm Lyα}$), rest-frame Ly$α$ equivalent width (EW$_0$), and UV magnitude (M$_{\rm uv}$). We stack the subsamples and find that higher $L_{\rm Lyα}$, lower EW$_0$, and brighter M$_{\rm uv}$ cause more extended halos. Our results suggest that more massive LAEs generally have more extended Ly$α$ halos.

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arXiv2023

MAMMOTH-Subaru V. Effects of Cosmic Variance on Ly$α$ Luminosity Functions at $z=2.2-2.3$

Cosmic variance introduces significant uncertainties into galaxy number density properties when surveying the high-z Universe with a small volume, such uncertainties produce the field-to-field variance of galaxy number $σ_{g}$ in observational astronomy. This uncertainty significantly affects the Luminosity Functions (LF) measurement of Lya Emitters (LAEs). For most previous Lya LF studies, $σ_{g}$ is often adopted from predictions by cosmological simulations, but barely confirmed by observations. Measuring cosmic variance requires a huge sample over a large volume, exceeding the capabilities of most astronomical instruments. In this study, we demonstrate an observational approach for measuring the cosmic variance contribution for $z\approx2.2$ Lya LFs. The LAE candidates are observed using narrowband and broadband of the Subaru/Hyper Suprime-Cam (HSC), with 8 independent fields, making the total survey area $\simeq11.62$deg$^2$ and a comoving volume of $\simeq8.71\times10^6$Mpc$^3$. These eight fields are selected using the project of MAMMOTH. We report a best-fit Schechter function with parameters $α=-1.75$ (fixed), $L_{Lyα}^{*}=5.18_{-0.40}^{+0.43} \times 10^{42}$erg s$^{-1}$ and $ϕ_{Lya}^{*}=4.87_{-0.55}^{+0.54}\times10^{-4}$Mpc$^{-3}$ for the overall Lya LFs. After clipping out the regions that can bias the cosmic variance measurements, we calculate $σ_{g}$, by sampling LAEs within multiple pointings assigned on the field image. We investigate the relation between $σ_{g}$ and survey volume $V$, and fit a simple power law: $σ_g=k\times(\frac{V_{\rm eff}}{10^5 {\rm Mpc}^3})^β$. We find best-fit values of $-1.209_{-0.106}^{+0.106}$ for $β$ and $0.986_{-0.100}^{+0.108}$ for k. We compare our measurements with predictions from simulations and find that the cosmic variance of LAEs might be larger than that of general star-forming galaxies.

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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/.

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