Day 599

Friday.

1402.6695
In hot bubble: why super bubble feedback works and isolated supernovae do not?
Sharma, Roy, Nath, Shchekinov

Most massive stars form in star clusters extending over just few 10s of pc.  Fast winds from massive stars and the first SNe are expected to create a hot, dilute bubble which encompasses the whole star cluster.  Thus subsequent SNe going off within the hot bubble maintains a strong termination shock, which keeps the super bubble over-pressured and drives the outer shock well after it becomes radiative.  Isolated SNe, in contrast, do not have further energy injection, become radiatively quite early (<0.1 Myr, 10s of pc), and stalls at scales <100 pc because of radiative and adiabatic losses.  While isolated SNe lose almost all of their mechanical energy by a Myr, super bubbles can retain up to ~40% of the input energy in form of mechanical energy over the lifetime of the star cluster (few 10s of Myr).  Thus, super bubbles are expected to be more effective feedback agents compared to isolated SNe.  These conclusions are likely to hold even in presence of realistic B-fields and thermal conduction.  Compare various recipes for implementing SN feedback in numerical simulations.  Show that the SN energy needs to be deposited over a small volume in order for it to couple to the ISM.  Important: thermalization of SN energy, which forms the basis of the analytic estimates.  Verify analytic scalings with numerical simulations.  Individual SN ejecta needs to thermalize within the termination shock for the appearance of a simple CC85 thermal wind within the hot bubble.  A steady thermal wind appears only for a large number (>1e4) of SNe.

1402.6697
A 10 deg$^2$ Lyman-$\alpha$ survey at z=8.8 with spectroscopic follow-up: strong constraints on the LF and implications for other surveys
Matthee et al

CF-HiZELS survey: large area, medium depth NIR narrow-band survey targeted at z=8.8 Lya emitters (LAE), and covering 10 deg sq with CFHT.  Comoving volume of 4.7e6 Mpc^3 to Lya luminosity limit of 6.3e43 erg/s.  Search for i) clear emission line source, ii) no optical detections (ugriz from CFHTLS), iii) no visible detection in the optical stack (ugriz>27), iv) visually checked reliable NB_J and J detections, and v) J-K<0.  Compute photo-z and remove a significant amount of dustily lower z line-emitters at z~1.4 or 2.2.  A total of 13 lay candidates found, of which two are marked as strong candidates, bu the majority have very weak constraints on their SEDs.  Using follow-up observations with SINFONI/VLT, able to exclude the most robust candidates as Lya emitters.  Put a strong constraint on the Lya LF at z~9 and make realistic predictions for ongoing and future surveys.  Results show that surveys for the highest-z LAEs are susceptible of multiple contaminations and that spectroscopic follow-up is absolutely necessary.

1402.6706
Airships: a new horizon for science
Miller … Rhodes, … et al

Investigate the potential of a variety of airships to surge as observatories and science instrumentation platforms for a range of space, atmospheric, and Earth science.  The participants represent a diverse cross-section of the aerospace sector, NASA, and academia.  Development interest in high altitude, stratospheric lighter-than-air (LTA) airship that could maneuver and remain in a desired geographic position ("station-keeping") for weeks, months or even years.  Study found considerable scientific value in both low altitude (<40 kft) [why don't they use meters?] and high altitude (>60 kft) airships across a wide spectrum of space, atmospheric, and Earth science programs.  Over the course of the study period, identify stratospheric tethered aerostats and a viable alternative to airships where station-keeping was valued over maneuverability.  By opening up the sky and Earth's stratospheric horizon in affordable ways with long-term flexibility, airships allow us to push technology and science forward in a project-rich environment that complements existing space observatories as well as aircraft and high-altitude balloon missions.

1402.6980
Inflationary schism after Planck2013
Ijjas, Steinhardt, Loeb

Classic inflation, the theory described in textbooks, is based on the idea that beginning from typical initial conditions and assuming a simple inflation potential with a minimum of fine-tuning, inflation can create exponentially large volumes of space that are generically homogeneous, isotropic and flat, with nearly scale-inveriant spectra of density and gravitational wave fluctuations that are adiabatic, Gaussian and have generic predictable properties.  In a recent paper, show that in addition to having certain conceptual problems known for decades, classic inflation is for the first time also disfavored by data, specifically the most recent data from WMAP, ACT and Planck2013.  Guth, Kaiser and Nomura and Linde have each recently published critiques of "our paper", agree about one thing: the problematic state of classic inflation.  Instead, they describe an alternative inflationary paradigm that revises the assumptions and goals of inflation, and perhaps of science generally.

1402.6983
Estimating cosmological parameter covariance
Taylor, Joachimi

Investigate the bias and error in estimates of the cosmological parameter covariance matrix, due to sampling or modeling the data covariance matrix, for likelihood width and peak scatter estimators.  Show that these estimators do not coincide unless the data covariance is exactly known.  For sampled data covariances, with Gaussian distributed data and parameters, the parameter covariance matrix estimated from the width of the likelihood has a Wishart distribution, from which the mean and covariance is derived.  This mean is biased; propose an unbiased estimator of the parameter covariance matrix.  Comparing analytic results to a numerical Wishart sampler of the data covariance matrix, find excellent agreement.  An accurate ansatz for the man parameter covariance for the pan scatter estimator is found, and fit covariance to numerical analysis.  The mean is again biased and propose an unbiased estimator for the peak partaker covariance.  For sampled data covariances, the width estimator is more accurate that the peak scatter estimator.  Investigate modeling the data covariance, or equivalently data compression, and shown that the peak scatter estimator is less sensitive to biases in the model data covariance matrix than the width estimator, but requires independent realizations of the data to reduce the statistical error.  If the model bias on the peak estimator is sufficiently low this is promising, otherwise the sampled width estimator is preferable.