Showing papers by "Ryan Cooke published in 2017"
TL;DR: In this paper, a near-pristine absorption system, located at a redshift z_abs=2.52564 toward the quasar Q1243+307, based on the combination of archival and new data obtained with the HIRES echelle spectrograph on the Keck telescope was analyzed.
Abstract: We report a reanalysis of a near-pristine absorption system, located at a redshift z_abs=2.52564 toward the quasar Q1243+307, based on the combination of archival and new data obtained with the HIRES echelle spectrograph on the Keck telescope. This absorption system, which has an oxygen abundance [O/H]=-2.769+/-0.028 (~1/600 of the Solar abundance), is among the lowest metallicity systems currently known where a precise measurement of the deuterium abundance is afforded. Our detailed analysis of this system concludes, on the basis of eight D I absorption lines, that the deuterium abundance of this gas cloud is log_10(D/H) = -4.622+/-0.015, which is in very good agreement with the results previously reported by Kirkman et al. (2003), but with an improvement on the precision of this single measurement by a factor of ~3.5. Combining this new estimate with our previous sample of six high precision and homogeneously analyzed D/H measurements, we deduce that the primordial deuterium abundance is log_10(D/H)_P = -4.5974+/-0.0052 or, expressed as a linear quantity, (D/H)_P = (2.527+/-0.030)x10^-5; this value corresponds to a one percent determination of the primordial deuterium abundance. Combining our result with a BBN calculation that uses the latest nuclear physics input, we find that the baryon density derived from BBN agrees to within 2 sigma of the latest results from the Planck CMB data.
367 citations
TL;DR: In this paper, the discovery and analysis of the most metal-poor damped Lyman α (DLA) system currently known was reported, based on observations made with the Keck HIRES spectrograph.
Abstract: We report the discovery and analysis of the most metal-poor damped Lyman α (DLA) system currently known, based on observations made with the Keck HIRES spectrograph. The metal paucity of this system has only permitted the determination of three element abundances: [C/H] = −3.43 ± 0.06, [O/H] = −3.05 ± 0.05 and [Si/H] = −3.21 ± 0.05, as well as an upper limit on the abundance of iron: [Fe/H] ≤ −2.81. This DLA is among the most carbon-poor environment currently known with detectable metals. By comparing the abundance pattern of this DLA to detailed models of metal-free nucleosynthesis, we find that the chemistry of the gas is consistent with the yields of a 20.5 M_⊙ metal-free star that ended its life as a core-collapse supernova; the abundances we measure are inconsistent with the yields of pair-instability supernovae. Such a tight constraint on the mass of the progenitor Population III star is afforded by the well-determined C/O ratio, which we show depends almost monotonically on the progenitor mass when the kinetic energy of the supernova explosion is Eexp ≳ 1.5 × 10^(51) erg. We find that the DLA presented here has just crossed the critical ‘transition discriminant’ threshold, rendering the DLA gas now suitable for low mass star formation. We also discuss the chemistry of this system in the context of recent models that suggest some of the most metal-poor DLAs are the precursors of the ‘first galaxies’, and are the antecedents of the ultrafaint dwarf galaxies.
50 citations
TL;DR: The discovery of the Little Cub, an extremely metal-poor star-forming galaxy in the local universe, found in the constellation Ursa Major (a.k.a. the Great Bear) is reported in this article.
Abstract: We report the discovery of the Little Cub, an extremely metal-poor star-forming galaxy in the local universe, found
in the constellation Ursa Major (a.k.a. the Great Bear). We first identified the Little Cub as a candidate metal-poor
galaxy based on its Sloan Digital Sky Survey photometric colors, combined with spectroscopy using the Kast
spectrograph on the Shane 3 m telescope at Lick Observatory. In this Letter, we present high-quality spectroscopic
data taken with the Low Resolution Imaging Spectrometer at Keck Observatory, which confirm the extremely
metal-poor nature of this galaxy. Based on the weak [O III] λ4363 A emission line, we estimate a direct oxygen
abundance of 12 + log(O/H) = 7.13 ± 0.08, making the Little Cub one of the lowest-metallicity star-forming
galaxies currently known in the local universe. The Little Cub appears to be a companion of the spiral galaxy NGC
3359 and shows evidence of gas stripping. We may therefore be witnessing the quenching of a near-pristine galaxy
as it makes its first passage about a Milky Way–like galaxy.
33 citations
TL;DR: The discovery of the Little Cub, an extremely metal-poor star-forming galaxy in the local universe, found in the constellation Ursa Major (a.k.a. the Great Bear) was reported in this paper.
Abstract: We report the discovery of the Little Cub, an extremely metal-poor star-forming galaxy in the local Universe, found in the constellation Ursa Major (a.k.a. the Great Bear). We first identified the Little Cub as a candidate metal-poor galaxy based on its Sloan Digital Sky Survey photometric colors, combined with spectroscopy using the Kast spectrograph on the Shane 3-m telescope at Lick Observatory. In this letter, we present high-quality spectroscopic data taken with the Low Resolution Imaging Spectrometer at Keck Observatory, which confirm the extremely metal-poor nature of this galaxy. Based on the weak [O III] 4363 Angstrom emission line, we estimate a direct oxygen abundance of 12 + log(O/H) = 7.13 +/- 0.08, making the Little Cub one of the lowest metallicity star-forming galaxies currently known in the local Universe. The Little Cub appears to be a companion of the spiral galaxy NGC 3359 and shows evidence of gas stripping. We may therefore be witnessing the quenching of a near-pristine galaxy as it makes its first passage about a Milky Way-like galaxy.
5 citations