2019/10/31 by Takashi Kojima, Masami Ouchi, Michael Rauch +18
Physics and Astronomy · #Astronomy and Astrophysical Research #Classifier (UML) #Galaxies: Formation, Evolution, Phenomena #Galaxy #Hubble Deep Field #Metallicity #Photometry (optics) #Sky #Spectroscopy #Stellar, planetary, and galactic studies #astro-ph.GA
paper · pdf · doi:10.3847/1538-4357/aba047
published as The Astrophysical Journal, Volume 898, Number 2, 142 pp. (2020) · 30 pages, 26 figures, and 8 tables; (Revision: metallicities changed due to the use of a more pricise dust correction method, but conclusion does not change, Minor: a table, some figures, and sentences are added for a clear explanation.)
arxiv created 2020/06/07 · openalex created_date 2020/06/12 · openalex publication_date 2020/08/01 · arxiv updated 2021/03/23 · openalex updated_date 2026/08/06
Abstract We have initiated a new survey for local extremely metal-poor galaxies (EMPGs) with Subaru/Hyper Suprime-Cam (HSC) large-area (∼500 deg 2 ) optical images reaching a 5 σ limit of ∼26 mag, about 100 times deeper than the Sloan Digital Sky Survey (SDSS). To select Z / Z ⊙ < 0.1 EMPGs from ∼40 million sources detected in the Subaru images, we first develop a machine-learning (ML) classifier based on a deep neural network algorithm with a training data set consisting of optical photometry of galaxy, star, and QSO models. We test our ML classifier with SDSS objects having spectroscopic metallicity measurements and confirm that our ML classifier accomplishes 86% completeness and 46% purity EMPG classifications with photometric data. Applying our ML classifier to the photometric data of the Subaru sources, as well as faint SDSS objects with no spectroscopic data, we obtain 27 and 86 EMPG candidates from the Subaru and SDSS photometric data, respectively. We conduct optical follow-up spectroscopy for 10 of our EMPG candidates with Magellan/LDSS-3+MagE, Keck/DEIMOS, and Subaru/FOCAS and find that the 10 EMPG candidates are star-forming galaxies at z = 0.007–0.03 with large H β equivalent widths of 104–265 Å, stellar masses of log( / ) = 5.0–7.1, and high specific star formation rates of ∼300 Gyr −1 , which are similar to those of early galaxies at z ≳ 6 reported recently. We spectroscopically confirm that 3 out of 10 candidates are truly EMPGs with Z / Z ⊙ < 0.1, one of which is HSC J1631+4426, the most metal-poor galaxy, with Z / Z ⊙ = 0.016, ever reported.