1507.05966
Can life survive Gamma-ray bursts in the high-redshift universe?
Li, Zhang
Nearby GRBs have been proposed as a possible cause of mass extinctions on Earth. Due to the higher event rate of GRBs at higher redshifts, it has been speculated that life as we know it may not survive above a certain redshift (z>0.5). Examine the duty cycle of lethal GRBs in the solar neighborhood, in the SDSS galaxies and GRB host galaxies, with the dependence of the long GRB rate on SF and metallicity properly taken into account. Find that the number of lethal GRBs attacking Earth within the past 500 Myr (~epoch of the Ordovician mass extinction) is 0.93. The number of lethal GRBs hitting a certain planet increases with redshift, thanks to the increasing SFR and decreasing metallicity in high-z galaxies. Taking 1 per 500 Myr as a conservative duty cycle for life to survive, as evidenced by the existence, find that there are still a good fraction of SDSS galaxies beyond z=0.5 where the GRB rate at high-mass radius is lower than this value. Derive the fraction of such benign galaxies as a function of redshift through MC simulations, and find that the fraction is ~50% at z~1.5 and ~10% even at z~3. The mass distribution of benign galaxies is dominated by MW-like ones, thanks to their commonness, relatively large mass, and low SFR. GRB host galaxies are among the most dangerous ones.
1507.05969
Estimates for the number of visible galaxy-spanning civilizations and the cosmological expansion of life
Olson
...the distance to the nearest visible Kardaschev type III (galaxy-spanning) civilizations is cosmological.
1507.05977
Cross-correlation cosmic shear with the SDSS and VLA FIRST surveys
Demetroullas, Brown
Measure the cosmic shear power spectrum on large angular scales by cross-correlating the shapes of ~9 million galaxies measure in the optical SDSS survey with the shapes of ~2.7e5 radio galaxies measured by the overlapping VLA-FIRST survey. The measurements span the multipole range 10<l<130, corresponding to angular scales 2deg<theta<20 deg. On these scales, the shear maps from both surveys suffer from significant systematic effects that prohibit a measurement of the shear power spectrum from either survey alone. Conversely, demonstrate that a power spectrum measured by cross-correlating the two surveys is unbiased. Measure an E-mode power spectrum from the data that is inconsistent with zero signal at the 99% CL (~2.7 sigma). The odd-parity B-mode signal and the EB cross-correlation are both found to be consistent with zero (within 1 sigma). These constraints are obtained after a careful error analysis that accounts for uncertainties due to cosmic variance, random galaxy shape noise and shape measurement errors, as well as additional errors associated with the observed large-scale systematic effects in the two surveys. Constraints are consistent wit the expected signal in the concordance cosmological model assuming recent estimates of the cosmological parameters from the Planck satellite, and literature values for the median redshifts of the SDSS and FIRST galaxy populations. The cross-power spectrum approach described in this paper represents a powerful technique for mitigating shear systematics and will be ideal for extracting robust results, with the exquisite control of systematics required, from further cosmic shear surveys wit the SKA, LSST, Euclid and WFIRST-AFTA.
1507.06140
How environment drives galaxy evolution: lessons learnt from satellite galaxies
Pasquali
Galaxy evolution is driven by intrinsic and environmental processes, bot contributing to shape the observed properties of galaxies. A number of early studies, both observational and theoretical, have shown that the SF activity of galaxies depends n their environmental local density and also on galaxy hierarchy, i.e. centrals vs. satellite. In fact, contrary to their central (most massive) galaxy of a group cluster, satellite galaxies are stripped of their gas and stars, and have their star formation quenched by their environment. Large galaxy surveys like SDSS now permit us to investigate in detail environment-driven transformation processes by comparing centrals and satellites. In this paper, summarize what have been learnt about environmental effects by analyzing the observed properties of local central and satellite galaxies in SDSS, as a function of their stellar mass and the DM matter mass of their host group/cluster.
1507.06270
At what distance ac the human eye detect a candle flame?
Krisciunas, Carona
Using CCD observations of a candle flame situated at a distance of 338m and calibrated with observations of Vega, show that a candle flame situated at ~2.6 km (1.6 miles) is comparable in brightness to a 6th magnitude star with the spectral energy distribution of Vega. The human eye cannot detect a candle flame at 10 miles or further, as some statements on the web suggest.
1507.06300
A quantitative criterion for defining planets
Margot
A simple metric can be used to determine whether a planet or exoplanet can clear its orbital zone during a characteristic time scale, such as the lifetime of the host star on the main sequence. This criterion requires only estimates of star mass, planet mass, and orbital period, making it possible to immediately classify 99% of all known exoplanets. All 8 planets and all classifiable exoplanets satisfy the criterion. This metric may be useful in generalizing and simplifying the definition of a planet.
1507.06639
SKA engineering change proposal: gridded visibilities to enable precision cosmology with radio weak lensing
Harrison, Brown
Submitted document as supporting material to an engineering change proposal (ECP) for the SKA. This ECP requests gridded visilbities as an extra imaging data product from the SKA, in order to enable bespoke analysis techniques to measure source morphologies to the carry necessary for precision cosmology with radio weak lensing. Also discuss the properties of an SKA weak lensing data set and potential overlaps with other cosmology science goals.
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