Regina A. Jorgenson

Precision measures of the primordial abundance of deuterium

We report the discovery of deuterium absorption in the very metal-poor ([Fe/H] = –2.88) damped Lyα system at z_abs = 3.06726 toward the QSO SDSS J1358+6522. On the basis of 13 resolved D I absorption lines and the damping wings of the H I Lyα transition, we have obtained a new, precise measure of the primordial abundance of deuterium. Furthermore, to bolster the present statistics of precision D/H measures, we have reanalyzed all of the known deuterium absorption-line systems that satisfy a set of strict criteria. We have adopted a blind analysis strategy (to remove human bias) and developed a software package that is specifically designed for precision D/H abundance measurements. For this reanalyzed sample of systems, we obtain a weighted mean of (D/H)_p = (2.53 ± 0.04) × 10^–5, corresponding to a universal baryon density 100 Ω_b, 0 h^2 = 2.202 ± 0.046 for the standard model of big bang nucleosynthesis (BBN). By combining our measure of (D/H)p with observations of the cosmic microwave background (CMB), we derive the effective number of light fermion species, N eff = 3.28 ± 0.28. We therefore rule out the existence of an additional (sterile) neutrino (i.e., N_eff = 4.046) at 99.3% confidence (2.7σ), provided that the values of N eff and of the baryon-to-photon ratio (η_10) did not change between BBN and recombination. We also place a strong bound on the neutrino degeneracy parameter, independent of the 4He primordial mass fraction, Y P: ξD = +0.05 ± 0.13 based only on the CMB+(D/H)_p observations. Combining this value of ξD with the current best literature measure of Y P, we find a 2σ upper bound on the neutrino degeneracy parameter, |ξ| ≤ +0.062.

A carbon-enhanced metal-poor damped Lyα system: probing gas from Population III nucleosynthesis?

We present high-resolution observations of an extremely metal-poor damped Lyα system (DLA), at z_(abs) = 2.340 0972 in the spectrum of the QSO J0035−0918, exhibiting an abundance pattern consistent with model predictions for the supernova yields of Population III stars. Specifically, this DLA has [Fe/H]≃−3, shows a clear ‘odd–even’ effect, and is C-rich with [C/Fe]=+1.53, a factor of ∼20 greater than reported in any other DLA. In analogy to the carbon-enhanced metal-poor stars in the Galactic halo (with [C/Fe] > +1.0), this is the first known case of a carbon-enhanced DLA. We determine an upper limit to the mass of ^(12)C, M(^(12)C) ≤ 200 M_⊙, which depends on the unknown gas density n(H); if n(H) > 1 cm^(−3) (which is quite likely for this DLA given its low velocity dispersion), then M(^(12)C) ≤ 2 M_⊙, consistent with pollution by only a few prior supernovae. We speculate that DLAs such as the one discovered here may represent the ‘missing link’ between the yields of Population III stars and their later incorporation in the class of carbon-enhanced metal-poor stars which show no enhancement of neutron-capture elements (CEMP-no stars).

The Transitional Stripped-Envelope SN 2008ax: Spectral Evolution and Evidence for Large Asphericity

Supernova (SN) 2008ax in NGC 4490 was discovered within hours after shock breakout, presenting the rare opportunity to study a core-collapse SN beginning with the initial envelope-cooling phase immediately following shock breakout. We present an extensive sequence of optical and near-infrared spectra, as well as three epochs of optical spectropolarimetry. Our initial spectra, taken two days after shock breakout, are dominated by hydrogen Balmer lines at high velocity. However, by maximum light, He I lines dominated the optical and near-infrared spectra, which closely resembled those of normal Type Ib supernovae (SNe Ib) such as SN 1999ex. This spectroscopic transition defines Type IIb SNe, but the strong similarity of SN 2008ax to normal SNe Ib beginning near maximum light, including an absorption feature near 6270 A due to Hα at high velocities, suggests that many objects classified as SNe Ib in the literature may have ejected similar amounts of hydrogen as SN 2008ax, roughly a few × 0.01 M ☉. Only the unusually early discovery of SN 2008ax allowed us to observe the spectroscopic signatures of the hydrogen-rich outer ejecta. Early-time spectropolarimetry (six and nine days after shock breakout) revealed strong line polarization modulations of 3.4% across Hα, indicating the presence of large asphericities in the outer ejecta and possibly that the spectrum of SN 2008ax could be dependent on the viewing angle. After removal of interstellar polarization, the continuum shares a common polarization angle with the hydrogen, helium, and oxygen lines, while the calcium and iron absorptions are oriented at different angles. This is clear evidence of deviations from axisymmetry even in the outer ejecta. Intrinsic continuum polarization of 0.64% only nine days after shock breakout shows that the outer layers of the ejecta were quite aspherical. A single epoch of late-time spectropolarimetry as well as the shapes of the nebular line profiles demonstrate that asphericities extended from the outermost layers all the way down to the center of this core-collapse SN. SN 2008ax may in some ways be an extragalactic analog of the explosion giving rise to Cassiopeia A, which has recently been determined to be a remnant of an SN IIb.

The Magellan uniform survey of damped Lyman α systems – I. Cosmic metallicity evolution

We present the chemical abundance measurements of the first large, medium-resolution, uniformly selected damped Lyman- system (DLA) survey. The sample contains 99 DLAs towards 89 quasars selected from the SDSS DR5 DLA sample in a uniform way. We analyze the metallicities and kinematic diagnostics, including the velocity width of 90% of the optical depth, v90, and the equivalent widths of the Siii 1526 (W 1526), Civ 1548 and Mgii 2796 transitions. To avoid strong line-saturation e ects on the metallicities measured in medium-resolution spectra (FWHM 71 km s 1 ), we derived metallicities from metal transitions which absorbed at most 35 % of the quasar continuum flux. We find the evolution in cosmic mean metallicity of the sample,hZi = ( 0.04 0.13)z (1.06 0.36), consistent with no evolution over the redshift range z [2:2; 4:4], but note that the majority of our sample falls at z [2:2; 3:5]. The apparent lack of metallicity evolution with redshift is also seen in a lack of evolution in the median v90 and W 1526 values. While this result may seem to conflict with other large surveys that have detected significant metallicity evolution, such as Rafelski et al. (2012) who foundhZi = ( 0.22 0.03)z (0.65 0.09) over z [0; 5], several tests show that these surveys are not inconsistent with our new result. However, over the smaller redshift range covered by our uniformly-selected sample, the true evolution of the cosmic mean metallicity in DLAs may be somewhat flatter than the Rafelski et al. (2012) estimate.

THE MOST METAL-POOR DAMPED Lyα SYSTEMS: AN INSIGHT INTO DWARF GALAXIES AT HIGH-REDSHIFT

In this paper we analyze the kinematics, chemistry, and physical properties of a sample of the most metal-poor damped Ly? systems (DLAs), to uncover their links to modern-day galaxies. We present evidence that the DLA population as a whole exhibits a knee in the relative abundances of the ?-capture and Fe-peak elements when the metallicity is [Fe/H]? ?2.0, assuming that Zn traces the buildup of Fe-peak elements. In this respect, the chemical evolution of DLAs is clearly different from that experienced by Milky Way halo stars, but resembles that of dwarf spheroidal galaxies in the Local Group. We also find a close correspondence between the kinematics of Local Group dwarf galaxies and of high-redshift metal-poor DLAs, which further strengthens this connection. On the basis of such similarities, we propose that the most metal-poor DLAs provide us with a unique opportunity to directly study the dwarf galaxy population more than ten billion years in the past, at a time when many dwarf galaxies were forming the bulk of their stars. To this end, we have measured some of the key physical properties of the DLA gas, including their neutral gas mass, size, kinetic temperature, density, and turbulence. We find that metal-poor DLAs contain a warm neutral medium with T gas 9600 K predominantly held up by thermal pressure. Furthermore, all of the DLAs in our sample exhibit a subsonic turbulent Mach number, implying that the gas distribution is largely smooth. These results are among the first empirical descriptions of the environments where the first few generations of stars may have formed in the universe.

Spatially Resolved Emission of a High-redshift DLA Galaxy with the Keck/OSIRIS IFU

We present the first Keck/OSIRIS infrared IFU observations of a high redshift damped Lyman-alpha (DLA) galaxy detected in the line of sight to a background quasar. By utilizing the Laser Guide Star Adaptive Optics (LGSAO) to reduce the quasar PSF to FWHM~0.15 arcsec, we were able to search for and map the foreground DLA emission free from the quasar contamination. We present maps of the H-alpha and [OIII]

Cosmological Concordance or Chemical Coincidence? Deuterated Molecular Hydrogen Abundances at High Redshift

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The Magellan uniform survey of damped Lyman α systems-II. Paucity of strong molecular hydrogen absorption

5007, 4959 emission of DLA 2222-0946 at a redshift of z ~ 2.35. From the composite spectrum over the H-alpha emission region we measure a star formation rate of 9.5

A cold component and the complex velocity structure of DLA1331 + 170

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The explosion energy of early stellar populations: the Fe-peak element ratios in low-metallicity damped Lyα systems

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