8 research outputs found

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

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    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 ZZ_\odot by deep Magellan/MagE spectroscopy for faint {\sc[Oiii]}λ\lambda4363 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 (107.0108.4M10^{7.0}-10^{8.4} M_\odot), we find no significant (>1σ>1\sigma) difference between these two CCFs. We also compare mass-metallicity relations (MZRs) of the EMPGs and those of galaxies at zz\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-zz EMPG search, we select 17 candidates of zz\sim 4--5 EMPGs with the deep (30\simeq30 mag) near-infrared JWST/NIRCam images obtained by ERO and ERS programs. We find galaxy candidates with negligible {\sc[Oiii]}λλ\lambda\lambda4959,5007 emission weaker than the local EMPGs and known high-zz galaxies, suggesting that some of these candidates may fall in 0--0.01 ZZ_\odot, which potentially break the lowest metallicity limit known to date

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

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    We present kinematics of 6 local extremely metal-poor galaxies (EMPGs) with low metallicities (0.0160.098 Z0.016-0.098\ Z_{\odot}) and low stellar masses (104.7107.6M10^{4.7}-10^{7.6} M_{\odot}). Taking deep medium-high resolution (R7500R\sim7500) integral-field spectra with 8.2-m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with Hα\alpha emission. Carefully masking out sub-structures originated by inflow and/or outflow, we fit 3-dimensional disk models to the observed Hα\alpha flux, velocity, and velocity-dispersion maps. All the EMPGs show rotational velocities (vrotv_{\rm rot}) of 5--23 km s1^{-1} smaller than the velocity dispersions (σ0\sigma_{0}) of 17--31 km s1^{-1}, indicating dispersion-dominated (vrot/σ0=0.290.80<1v_{\rm rot}/\sigma_{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 fgas0.91.0f_{\rm gas}\simeq 0.9-1.0. Comparing our results with other Hα\alpha kinematics studies, we find that vrot/σ0v_{\rm rot}/\sigma_{0} decreases and fgasf_{\rm gas} increases with decreasing metallicity, decreasing stellar mass, and increasing specific star-formation rate. We also find that simulated high-zz (z7z\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 z7z\sim 7.Comment: Submitted to ApJ; After revisio

    Classification of cosmic structures for galaxies with deep learning : connecting cosmological simulations with observations

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    We explore the capability of deep learning to classify cosmic structures. In cosmological simulations, cosmic volumes are segmented into voids, sheets, filaments, and knots, according to distribution and kinematics of dark matter (DM), and galaxies are also classified according to the segmentation. However, observational studies cannot adopt this classification method using DM. In this study, we demonstrate that deep learning can bridge the gap between the simulations and observations. Our models are based on 3D convolutional neural networks and trained with data of distribution of galaxies in a simulation to deduce the structure classes from the galaxies rather than DM. Our model can predict the class labels as accurate as a previous study using DM distribution for the training and prediction. This means that galaxy distribution can be a substitution for DM for the cosmic-structure classification, and our models using galaxies can be directly applied to wide-field survey observations. When observational restrictions are ignored, our model can classify simulated galaxies into the four classes with an accuracy (macro-averaged F1-score) of 64 per cent. If restrictions such as limiting magnitude are considered, our model can classify SDSS galaxies at ∼100 Mpc with an accuracy of 60 per cent. In the binary classification distinguishing void galaxies from the others, our model can achieve an accuracy of 88 per cent

    EMPRESS. V. Metallicity Diagnostics of Galaxies over 12+log(O/H)=~6.9-8.9 Established by a Local Galaxy Census: Preparing for JWST Spectroscopy

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    We present optical-line gas metallicity diagnostics established by the combination of local SDSS galaxies and the largest compilation of extremely metal-poor galaxies (EMPGs) including new EMPGs identified by the Subaru EMPRESS survey. A total of 103 EMPGs are included that cover a large parameter space of magnitude (Mi=-19 to -7) and H-beta equivalent width (10-600 Ang), i.e., wide ranges of stellar mass and star-formation rate. Using reliable metallicity measurements of the direct method for these galaxies, we derive the relationships between strong optical-line ratios and gas-phase metallicity over the range of 12+log(O/H)=~6.9-8.9 corresponding to 0.02-2 solar metallicity Zsun. We confirm that R23-index, ([OIII]+[OII])/H-beta, is the most accurate metallicity indicator with the metallicity uncertainty of 0.14 dex over the range among various popular metallicity indicators. The other metallicity indicators show large scatters in the metal-poor range (<0.1 Zsun). It is explained by our CLOUDY photoionization modeling that, unlike R23-index, the other metallicity indicators do not use a sum of singly and doubly ionized lines and cannot trace both low and high ionization gas. We find that the accuracy of the metallicity indicators is significantly improved, if one uses H-beta equivalent width measurements that tightly correlate with ionization states. In this work, we also present the relation of physical properties with UV-continuum slope beta and ionization production rate xi_ion derived with GALEX data for the EMPGs, and provide local anchors of galaxy properties together with the optical-line metallicity indicators that are available in the form of ASCII table and useful for forthcoming JWST spectroscopic studies.Comment: 33 pages, 14 figures. Accepted for publication in ApJ Supplement Series. Visit https://sci.nao.ac.jp/MEMBER/ouchi/members/nakajima.html for the publicly available table of EMPGs (Table 6

    EMPRESS. IV. Extremely Metal-poor Galaxies Including Very Low-mass Primordial Systems with M <SUB>*</SUB> = 10<SUP>4</SUP>-10<SUP>5</SUP> M <SUB>⊙</SUB> and 2%-3% (O/H): High (Fe/O) Suggestive of Metal Enrichment by Hypernovae/Pair-instability Supernovae

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    International audienceWe present Keck/LRIS follow-up spectroscopy for 13 photometric candidates of extremely metal-poor galaxies (EMPGs) selected by a machine-learning technique applied to the deep (~26 AB mag) optical and wide-area (~500 deg2) Subaru imaging data in the EMPRESS survey. Nine out of the 13 candidates are EMPGs with an oxygen abundance (O/H) less than ~10% solar value (O/H)⊙, and four sources are contaminants of moderately metal-rich galaxies or no emission-line objects. Notably, two out of the nine EMPGs have extremely low stellar masses and oxygen abundances of 5 × 104-7 × 105 M ⊙ and 2%-3% (O/H)⊙, respectively. With a sample of five EMPGs with (Fe/O) measurements, two (three) of which are taken from this study (the literature), we confirm that two EMPGs with the lowest (O/H) ratios of ~2% (O/H)⊙ show high (Fe/O) ratios of ~0.1, close to the solar abundance ratio. Comparing galaxy chemical enrichment models, we find that the two EMPGs cannot be explained by a scenario of metal-poor gas accretion/episodic star formation history due to their low (N/O) ratios. We conclude that the two EMPGs can be reproduced by the inclusion of bright hypernovae and/or hypothetical pair-instability supernovae (SNe) preferentially produced in a metal-poor environment. This conclusion implies that primordial galaxies at z ~ 10 could have a high abundance of Fe that did not originate from Type Ia SNe with delays and that Fe may not serve as a cosmic clock for primordial galaxies

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

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    Submitted to ApJWe present kinematics of 6 local extremely metal-poor galaxies (EMPGs) with low metallicities (0.0160.098 Z0.016-0.098\ Z_{\odot}) and low stellar masses (104.7107.6M10^{4.7}-10^{7.6} M_{\odot}). Taking deep medium-high resolution (R7500R\sim7500) integral-field spectra with 8.2-m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with Hα\alpha emission. Carefully masking out sub-structures originated by inflow and/or outflow, we fit 3-dimensional disk models to the observed Hα\alpha flux, velocity, and velocity-dispersion maps. All the EMPGs show rotational velocities (vrotv_{\rm rot}) of 5--23 km s1^{-1} smaller than the velocity dispersions (σ0\sigma_{0}) of 17--31 km s1^{-1}, indicating dispersion-dominated (vrot/σ0=0.290.80<1v_{\rm rot}/\sigma_{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 fgas0.91.0f_{\rm gas}\simeq 0.9-1.0. Comparing our results with other Hα\alpha kinematics studies, we find that vrot/σ0v_{\rm rot}/\sigma_{0} decreases and fgasf_{\rm gas} increases with decreasing metallicity, decreasing stellar mass, and increasing specific star-formation rate. We also find that simulated high-zz (z7z\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 z7z\sim 7

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

    No full text
    Submitted to ApJWe present kinematics of 6 local extremely metal-poor galaxies (EMPGs) with low metallicities (0.0160.098 Z0.016-0.098\ Z_{\odot}) and low stellar masses (104.7107.6M10^{4.7}-10^{7.6} M_{\odot}). Taking deep medium-high resolution (R7500R\sim7500) integral-field spectra with 8.2-m Subaru, we resolve the small inner velocity gradients and dispersions of the EMPGs with Hα\alpha emission. Carefully masking out sub-structures originated by inflow and/or outflow, we fit 3-dimensional disk models to the observed Hα\alpha flux, velocity, and velocity-dispersion maps. All the EMPGs show rotational velocities (vrotv_{\rm rot}) of 5--23 km s1^{-1} smaller than the velocity dispersions (σ0\sigma_{0}) of 17--31 km s1^{-1}, indicating dispersion-dominated (vrot/σ0=0.290.80<1v_{\rm rot}/\sigma_{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 fgas0.91.0f_{\rm gas}\simeq 0.9-1.0. Comparing our results with other Hα\alpha kinematics studies, we find that vrot/σ0v_{\rm rot}/\sigma_{0} decreases and fgasf_{\rm gas} increases with decreasing metallicity, decreasing stellar mass, and increasing specific star-formation rate. We also find that simulated high-zz (z7z\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 z7z\sim 7
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