Day 594

Saturday.

1402.4803
Red or blue?  A potential kilo nova imprint of the delay until black hole formation flooding a neutron star merger
Metzger, Fernández

Mergers of binary NSs usually result in the formation of a hypermassive neutron star (HMNS).    Whether and when this remnant collapses to a BH depends primarily on the EoS and on angular momentum transport processes, both of which are uncertain.  Show that the lifetime of the merger remnant may be directly imprinted in the radioactively powered kilo nova emission following the merger.  Employ axisymmetric, time-dependent hydrodynamic simulations of remnant accretion disks orbiting a HMNS of variable lifetime, and characterize the effect of this delay to BH formation on the disk wind ejecta.  Models follow the system solution over several seconds, and include the effect of nuclear recombination, viscous heating, and neutrino irradiation by both the HMNS and the disk.  When BH formation is relatively prompt (<100 ms), outflows from the disk are sufficiently neutron rich to form heavy r-process elements with mass number A>140, resulting in ~week-long emission with a spectral peak in the NIR, similar to that produced by the dynamical ejecta.  In contrast, delayed BH formation allows neutrinos from the HMNS to raise the electron fraction in the polar direction to values such that potentially Lanthanide-free outflows (A<140) are generated.  The lower opacity would produce a brighter, bluer, and shorter-lived ~day-long emission (a `blue bump') prior to the late NIR peak from the dynamical ejecta and equatorial wind.  A long-lived HMNS also increases the eject mass significantly compared to the prompt BH case.  Work motivates effects to obtain early (~day) optical follow-up of mergers detected by Advanced LIG/Virgo.  This new diagnostic of BH formation should be useful for events with a signal to noise lower than that required for direct detection of gravitational waveform signatures.

1402.4812
Dust formation by failed supernovae
Kochanek

Consider dust formation during the ejection of the hydrogen envelope of a red supergiant during a failed supernova (SN) crating a black hole.  While the dense, slow moving eject are very efficient at forming dust, only the very last phases of the predicted visual transient will be obscured.  The net grain production consists of ~0.01 solar masses of very large grains (10 to 1000 microns).  This means that failed SNe could be the source of the very large extrasolar dust grains identified by Ulysses, Galileo and radar studies of meteoroid re-entry trails rather than their coming from an ejection process associated with protoplanetary or other disks.  

1402.4814
The green valley is a red herring: Galaxy Zoo reveals two evolutionary pathways towards quenching of star formation in early- and late-type galaxies
Schawinski et al

Use SDSS+GALEX+Galaxy Zoo data to study the quenching of SF in low-redshift galaxies.  Show that the green valley between the blue cloud of SF galaxies and the red sequence of quiescent galaxies in the color-mass diagram is not a single transitional state through which most blue galaxies evolve into red galaxies.  Rather, an analysis that takes morphology into account makes clear that only a small population of blue early-type galaxies move rapidly across the green valley after the morphologies are transformed from disk to spheroid and SF is quenched rapidly.  In contrast, the majority of blue SF galaxies have significant disks, and they retain their late-type morphologies as their SF rates decline very slowly.  Summarize a range of observations that lead to these conclusions, including UV-opitcal colors and halo masses, which both show a striking dependence on morphological type.  Interpret these results in terms of the evolution of cosmic gas supply and gas reservoirs.  Conclude that late-type galaxies are consistent with a scenario where the cosmic supply of gas is shut off, perhaps at a critical halo mass, followed by a slow exhaustion of the remaining gas over several Gyr, driven by secular and/or environmental processes.  In contrast, early-type galaxies require a scenario where the gas supply and gas reservoir are destroyed virtually instantaneously, which rapid quenching accompanied by a morphological transformation disk to spheroid.  This gas reservoir destruction could be the consequence of a major merger, which in most cases transforms galaxies from disk to elliptical morphology, and mergers could pay a role in inducing black hole accretion and possibly AGN feedback.

1402.4815
Measurement of the halo bias from stacked shear profiles of galaxy clusters
Covone, Sereno, Kilbinger, Cardone

Observational evidence of the 2-halo term in the stacked shear profile of a sample of ~1200 optically selected galaxy clusters based on imaging data and the public shear catalog from the CFHTLenS.  Find that the halo bias, a measure of the correlated distribution of matter around galaxy clusters, has amplitude and correlation with galaxy cluster mass in very good agreement with the predictions based on the LCDM standard cosmological model.  The mass-concentration relation is flat but higher than theoretical predictions.  Also confirm the close scaling relation between the optical richness of galaxy clusters and their mass.

1402.4828
The ages of stellar populations in a warm dark matter universe
Calura, Menci, Gallazzi

By SAM, show how the local observed relation between age and galactic stellar mass is affected by assuming a DM PS with a small-scale cutoff.  Compare results obtained by means of both a LCDM and LWDM PS -- suppressed with respect to the LCDM at scales below ~ 1Mpc.  Show that, within a LWDM cosmology with a thermal relic particle mass of 0.75 KeV, both the mass-weighted and the luminosity-weighted age-mass relations are steeper than those obtained within a LCDM universe, in better agreement with the observed relations.  Moreover, both the observed differential and cumulative age distributions are better reproduced within a LWDM cosmology.  In such a scenario, SF appears globally delayed with respect to the LCDM, in particular in low-mass galaxies.  The difficulty of obtaining a full agreement between model results and observations is to be ascribed to our present poor understanding of baryonic physics.  [the SAM used may not be correct either?]

1402.4856
A small, rapid optical-IR response gamma-ray burst space observatory
Grossan, Kumar, Perley, Smoot

Propose a new GRB mission: Next Generation rapid-response GRB observatory (NGRG).  GRB initial location determined from a coded-mask X-ray camera (similar to Swift).  Two new features above Swift: a beam steering system to begin optical observations within ~ 1s after location; second, a NIR camera viewing the same sky, for sensitivity to extinguished bursts.  These features allow measurement of the rise phase of GRB optical-NIR emission.  Thus far, the rise time and transition between prompt and afterglow in the optical and NIR are rarely measured.  Rapid-response measurements explore many science topics including optical emission mechanisms (synchrotron vs. SSC, photospheric emission) and jet characteristics (reverse vs. forward shock emission, baryon-dominated vs. magnetic dominated).  Rapid optical-NIR response can measure dynamic evolution of extinction due to vaporization of dust, and separate star system and galaxy dust extinction.  Discuss these measurements, giving reliable detection rate estimate from analysis of Swift data and scaled Swift performance.  Te NGRG will explore optical/NIR emission measured earlier than ever before, and potentially fainter, more extinguish GRBs than ever before.  Costs are important: the proposed modest NGRG can still produce new GRB science, while providing rapid GRB alerts for the entire community for post-Swift GRB science.  Show that an X-ray instrument barely 1/5 the area of Swift BAT will yield a significant fraction of Swift's detection rate: more than 65 X-ray, and with a 30cm optical-IR telescope and modern cameras, more than 19 NIR and 14 optical detections each year.  In addition, active feedback control of the beam-steering would remove the need for arc sec stabilization of the spacecraft, for a substantial cost saving.

1402.5101
Impact of chromatic effects on galaxy shape measurements
Meyers, Burchat

Current and future imaging surveys will measure cosmic shear with a statistical precision that demands a deeper understanding of potential systematic biases in galaxy shape measurements than has been achieved to date.  Investigate the effects of using the PSF measured with stars to determine the shape of a galaxy that has a different SED than the star.  Demonstrate that a wavelength dependent PSF size, for example as may originate from atmospheric seeing or the diffraction limit of the primary aperture, can introduce significant shape measurement biases.  This analysis shows that even small wavelength dependencies in the PSF may introduce biases, and hence that achieving the ultimate precision for WL from current and future imaging surveys will require a detailed understanding of the wavelength dependence of the PSF from all sources, including the CCD sensors.