Day 626

Friday.  Sunday.

1404.2599
Directly imaging damped Ly-alpha galaxies at z>2. II: imaging and spectroscopic observations of 32 quasar fields
Fumagalli … Prochaska, et al

DLAs are well-studied class of absorption line systems, and yet the properties of their host galaxies remain largely unknown.  To investigate the origin of these systems, conduct an imaging survey of 32 quasar fields with intervening DLAs between z~1.9-3.8, leveraging a technique that allows us to image galaxies at any small angular separation from the background quasars.  In this paper, present the properties of the targeted DLA sample, new imaging observations of the quasar fields, and at the analysis of new and archival spectra of the BG quasars.  In a companion paper, use these data to obtain an unbiased census of the DLA host galaxy population(s) and to directly measure the in-situ star formation rates of gas-rich galaxies at z>2. 

1404.2606
Planetesimal driven migration as an explanation for observations of high levels of warm, exozodiacal dust
Bonsor et al

High levels of exozodiacal dust have been observed in the inner regions of a large fraction of MS stars.  Given the short lifetime of the observed small dust grains, these 'exozoids' are difficult to explain, especially for old (>100 Myr) stars.  The exozodiacal dust may be observed as excess emission in the MIR, or using interferometry.  Hypothesize that exozodi are sustained by planetesimals scattered by planets inwards from an outer planetesimal belt, where collision timescales are long.  In this work, use N-body sims to show that the outward migration of a planet into a belt, driven by the scattering of planetesimals, can increase, or sustain, the rate at which planetesimals are scattered from the outer belt to the exozodi region.  Hypothesize that his increase is sufficient to sustain the observed exozodi on Gyr timescales.  No correlation between observations of an outer belt and an exozodi is required for this scenario to work, as the outer belt may be too faint to detect.  If planetesimal driven migration does explain the observed exozodi, this work suggest that the presence of an exozodi indicates the presence of outer planets and a planetesimal belt.

1404.2626
Galaxy and mass assembly (GAMA): autos spectral redshift measurements, confidence and errors
Baldry et al

GAMA has obtained spectra of >230k targets; to homogenize the redshift measurements and improve the reliability, a fully automatic z code was developed (autoz).  The measurements were made using a cross-correlation method for both absorption-line and emission-line spectra.  Large deviations in the high-pass filtered spectra are partially clipped in order to be robust against uncorrected artifacts and to reduce the weight given to single-line matches.  A single figure of merit (FOM) was developed that puts all template matches onto a similar confidence scale.  The z confidence as a function of the FOM was fitted with a tank function using a maximum likelihood method applied to repeat observations of targets.  The method could be adapted to provide robust automatic z for other large galaxy redshift surveys.  For the GAMA survey, there was a substantial improvement in the reliability of assigned redshifts and in the lowering of z uncertainties with a median velocity uncertainty of 33 km/s.

1404.2854
Fisher matrices for data with errors in both variables
Heavens et al

The Fisher information matrix formalism is extended to cases where both elements of each data pair have errors, with arbitrary correlations between points.  The analysis applies if all errors are gaussian, and if the errors in the independent variable are small, both in comparison with the scale over which the expected signal changes, and with the width of the prior distribution.  This generalizes the Fisher Matrix approach, which normally only considers errors in the ordinate.  In this work, include errors from observable data elements through marginalizing over latent variables, effectively employing a Bayesian hierarchical model, and deriving the Fisher Matrix for this more general case.  The methods here also extend to likelihood surfaces which are not gaussian in the parameter space, and so techniques such as DALI (Derivative Approximation for Likelihoods) can be generalized straightforwardly to include arbitrary gaussian data error covariances.  For simple mock data and theoretical models, compare to MCMC experiments, illustrating the method with cosmological SN data.  Also include the new method in the Fisher4Cast software.