Day 945

Friday.


1508.03042
Reactivity and survivability of Glycolaldehyde in simulated meteorite impact experiments
McCaffrey, et al

Sugars of extraterrestrial origin have been observed in the ISM, in at least one comet spectrum, and in several carbonaceous chondritic meteorites that have been recovered from the surface of the Earth.  To explore the possibility that sugars could be generated during shock events, this paper reports on the results of the first laboratory impact experiments wherein glycolaldehyde, found in the ISM, as well as glycolaldehyde mixed with montmorillonite clay, have been subjected to reverberated shocks from ~5 to >25 GPa.  New biologically relevant molecules, including threes, erythrose and ethylene glycol, where identified in the resulting samples.  These results show that sugar molecules can not only survive but also become more complex during impact delivery to planetary bodies.


1508.03043
SETI via leakage from light sails in exoplanetary systems
Guillochon, Loeb

The primary challenge of rocket propulsion is the burden of needing to accelerate the spacecraft's own fuel, resulting in only a logarithmic gain in maximum speed as propellant is added to the spacecraft.  Light sails offer an attractive alternative in which fuel is not carried by the spacecraft, with acceleration being provided by an external source of light.  By artificially illuminating the spacecraft with beamed radiation, speeds are only limited by the area of the sail, heat resistance of its material, and power use of the accelerating apparatus.  In this paper, show that leakage from a light sail propulsion apparatus in operation around a solar system analogue would be detectable.  To demonstrate this, model the launch and arrival of a microwave beam-driven light sail constructed for transit between planets in orbit around a single star, and find an optimal beam frequency on the order of tens of GHz.  Leakage from these beams yields transients with flux densities of 0.1 Jy and durations of seconds at 100 pc. Because most travel within a planetary system would be conducted between the habitable worlds within that system, multiply-transiting explanatory systems offer the greatest chance of detection, especially when the planets are in projected conjunction as viewed from Earth.  If interplanetary travel via beam-driven light sails is commonly employed in our galaxy, this activity could be revealed by radio follow-up of nearby transiting explanatory systems.  The expected signal properties define a new strategy in the search for extraterrestrial intelligence (SETI).


1508.03046
Exploring the 2MASS extended and point source catalogs with clustering redshifts
Rahman, Ménard, Scranton

2MASS has mapped out the low-z Universe down to K_S~14 mag.  As its NIR photometry primarily probes the featureless Rayleigh-Jeans tail of galaxy spectral energy distributions, color-based redshift estimation is rather uninformative.  Until now, redshift estimates for this dataset have relied on optical follow-up suffering from selection biases. Here, use the newly-developed technique of clustering-based redshift estimation to infer the redshift distribution of the 2MASS sources regardless of their optical properties.  Characterize redshift distributions of objects from the Extended Source Catalog as a function of NIR colors and brightness and report some observed trends.  Also apply the clustering redshift technique to dropout populations, sources with non-detections in one or more NIR bands, and present their redshift distributions.  Combining all extended sources, show that the z distribution of the sample extends up to z~0.3.  Perform a similar analysis with the PSC and show that it can be separated into stellar and extragalactic contributions with galaxies reaching z~0.7.  Estimate that the PSC contains 1.6 M extragalactic objects: as many as in the ESC but probing a cosmic volume ten times larger.


1508.03162
Improving the precision matrix for precision cosmology
Paz, Sanchez

The estimation of cosmo constraints from observations of the LSS of the universe, such as the power spectrum or the correlation function, requires the knowledge of the inverse of the associated covariance matrix, namely the precision matrix, Psi.  In most analyses, Psi is estimated from a limited set of mock catalogues.  Depending on how many mocks are used, this estimation has an associated error which must be propagated into the final cosmo constraints.  For future surveys such as Euclid and DESI, the control of this additional uncertainty requires a prohibitively larger number of mock catalogues.  In this work, test a novel technique for the estimation of the precision matrix, the covariance tapering method, in the context of BAO measurements.  Even though this technique was originally devised as a way to speed up maximum likelihood estimations, our results show that it also reduces the impact of noisy precision matrix estimates on the derived confidence intervals, without introducing biases on the target parameters.  The application of this technique can help future surveys to reach their true constraining power using a significantly smaller number of mock catalogues.