ORCID Profile
0000-0001-6401-723X
Current Organisation
University of Tokyo
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Publisher: Oxford University Press (OUP)
Date: 09-02-2011
DOI: 10.1093/PASJ/PSX046
Publisher: American Astronomical Society
Date: 28-09-2022
Abstract: The search for Population III stars has fascinated and eluded astrophysicists for decades. One promising place for capturing evidence of their presence must be high-redshift objects signatures should be recorded in their characteristic chemical abundances. We deduce the Fe and Mg abundances of the broadline region (BLR) from the intensities of ultraviolet Mg ii and Fe ii emission lines in the near-infrared spectrum of UKIDSS Large Area Survey (ULAS) J1342+0928 at z = 7.54, by advancing our novel flux-to-abundance conversion method developed for quasars up to z ∼ 3. We find that the BLR of this quasar is extremely enriched, by a factor of 20 relative to the solar Fe abundance, together with a very low Mg/Fe abundance ratio: [Fe/H] = +1.36 ± 0.19 and [Mg/Fe] =−1.11 ± 0.12, only 700 million years after the Big Bang. We conclude that such an unusual abundance feature cannot be explained by the standard view of chemical evolution that considers only the contributions from canonical supernovae. While there remains uncertainty in the high-mass end of the Population III initial mass function, here we propose that the larger amount of iron in ULAS J1342+0928 was supplied by a pair-instability supernova (PISN) caused by the explosion of a massive Population III star in the high-mass end of the possible range of 150–300 M ⊙ . Chemical evolution models based on initial PISN enrichment well explain the trend in [Mg/Fe]- z all the way from z 3 to z = 7.54. We predict that stars with very low [Mg/Fe] at all metallicities are hidden in the galaxy, and they will be efficiently discovered by ongoing new-generation photometric surveys.
Publisher: American Astronomical Society
Date: 26-03-2013
Publisher: American Astronomical Society
Date: 10-2019
Abstract: We report the discovery of 28 quasars and 7 luminous galaxies at 5.7 ≤ z ≤ 7.0. This is the tenth in a series of papers from the Subaru High- z Exploration of Low-Luminosity Quasars (SHELLQs) project, which exploits the deep multiband imaging data produced by the Hyper Suprime-Cam (HSC) Subaru Strategic Program survey. The total number of spectroscopically identified objects in SHELLQs has now grown to 93 high- z quasars, 31 high- z luminous galaxies, 16 [O iii ] emitters at z ∼ 0.8, and 65 Galactic cool dwarfs (low-mass stars and brown dwarfs). These objects were found over 900 deg 2 , surveyed by HSC between 2014 March and 2018 January. The full quasar s le includes 18 objects with very strong and narrow Ly α emission, whose stacked spectrum is clearly different from that of other quasars or galaxies. While the stacked spectrum shows N v λ 1240 emission and resembles that of lower- z narrow-line quasars, the small Ly α width may suggest a significant contribution from the host galaxies. Thus, these objects may be composites of quasars and star-forming galaxies.
Publisher: American Astronomical Society
Date: 20-12-2018
Publisher: American Astronomical Society
Date: 25-08-2016
Publisher: American Astronomical Society
Date: 06-02-2019
Publisher: American Astronomical Society
Date: 03-07-2018
Publisher: American Astronomical Society
Date: 06-03-2018
No related grants have been discovered for Hiroaki Sameshima.