1710.11129
A one percent determination of the primordial deuterium abundance
Cooke, Pettini, Steidel
A reanalsys of a near-pristine absorption system at z_abs=2.52564 towards the quasar Q1243+307, based on observations on HIRES eschell spectrograph at Keck. The absorption system has oxygen abundance [O/H]=-2.769±0.028, which is among the lowest metallicity systems currently known where a precise measurement of the D abundance is afforded. Based on eight D I absorption lines, the D abundance of this gas cloud is log10(D/H)=-4.622±0.015, which is in very good agreement with the results previously reported by Kirkman+2003, but with an improvement on the precision of this single measurement by a factor of ~3.5. Combining this new estimate with the previous sample of 6 high precision and homogeneously analyzed D/H measurements, deduce that the primordial deuterium abundance is log10(D/H)_P=-4.5974±0.0052 or (D/H)_P=(2.527±0.030)e-5; this value corresponds to a one percent determination of the primordial D abundance. Combining the result with a BBN calculation that uses the latest nuclear physics input, find that the baryon density derived from BBN agrees to within 2 sigma of the latest results from the Planck CMB data.
1710.11131
The dearth of z~10 galaxies in all HST legacy fields -- the rapid evolution of the galaxy population in the first 500 Myr
Oesch, et al
HST legacy fields spanning >800 arcmin^2 in search of z~10 galaxy candidates and the study of their UV luminosity function (LF). New z~10 candidates selected from the full HFF (Hubble Frontier Field) data set. Despite the addition, find low abundance of z~10 candidates with only 9 reliable sources identified in all prime HST datasets that include HUDF09/12, HUDF/XDF, al the CANDELS fields, and HFF. Based on this comprehensive search, find that the UV LF decreases by one order of magnitude from z~8 to z~10 at all luminosities over a 4 magnitude range. This also implies that this accelerated evolution compared to lower z can entirely be explained by the fast build-up of the DM halo mass function at z>8. Consequently, the predicted UV LFs from several models of galaxy formation are in good agreement with this observed trend, even though the measured UV LF lies at the low end of model predictions. In particular, the number of only 9 observed candidate galaxies is lower, by ~50%, than predicted by galaxy evolution models. The difference is generally still consistent within the Poisson and cosmic variance uncertainties. However, essentially all models predict larger numbers than observed. Discuss the implications of these results in light of the upcoming JWST mission, which is poised to find much larger samples of z~10 galaxies as we as their progenitors at less than 400 Mir after the Big Bang.
1710.11134
Is life most likely around sun-like stars?
Lingam, Loeb
Consider the habiltability of Earth-analogs around stars of different masses, which is regulated by the stellar lifetime, stellar wind-induced atmospheric erosion, and biologically active UV irradiance. By estimating the timescales associated with each of these items, show that they collectively impose limits on the habitability of Earth-analogs. Conclude that planets orbiting most M-dwarfs are not likely to host life, and that the highest probability of complex biospheres is for planets around K- and G-type stars. The analysis suggests that the current existence of life near the Sun is slightly unusual, but not significantly anomalous.
1710.11136
Linear models for systematics and nuisances
Luger, Foreman-Mackey, Hogg
The target of many astronomical studies is the recovery of tiny astrophysical signals living in a sea of uninteresting (but usually dominant) noise In many contexts (i.e., stellar time series, or high-contrast imaging, or stellar spectroscopy), there are structured components in this noise caused by systematic effects in the astronomical source, the atmosphere, the telescope, or the detector. More often than not, evaluation of the true physical model for these nuisances is computationally intractable and dependent on too many (unknown) parameters to allow rigorous probability inference. Sometimes, housekeeping data --- and often the science themselves --- can be used as predictors of the systematic noise. Linear combinations of simple functions of these predictors are often used as computationally tractable models that can capture the nuisances. These models can be used to fit and subtract systematics prior to investigation of the signals of interest, or they can be used in a simultaneous fit of the systematics and the signals. In this Note, show that if a Gaussian prior is placed on the weights of the linear components, the weights can be marginalized out with an operation in pure linear algebra, which can (often) be made fast. Illustrate this model by demonstrating the applicability of a linear model for the non-linear systematics in K2 time-series data, where the dominant noise source for many stars is spacecraft motion and variability.
1710.11576
The complete ultraviolet, optical, and near-infrared light curves of the kilonova associated with the binary neutron star merger GW170817: Homogenized data set, analytic models, and physical implications
Villar, et al
The homogenized dataset includes 625 individual flux measurements spanning 0.45 yo 29.4 days post-merger, and thus has grater constrainer power for physical models than any single dataset. Find that the data are well modeled with a three-component kilonovamodel: a "blue" lanthanide-poor component with M~0.016 Msun and v~0.27c; an intermediate opacity "purple" component with M~0.04 Msun and a v~0.14c and a "red" lanthanide-rich component with M~0.009 Msun and v~0.08c. Further explore the possibility of eject asymmetry and its impact on the estimated parameters. From the inferred parameters, draw conclusions about the physical mechanisms responsible for the various ejecta components, the properties of the neutron stars, and, combined with an up-to-date merger rate, the implications for r-process enrichment via this channel. To facilitate future studies of this keystone even, make the homogenized dataset and the modeling code public.
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