Day 678

Friday.

1406.3020
Exoplanet population inference and the abundance of Earth analogs from noisy, incomplete catalogs
Foreman-Mackey, Hogg, Morton

No true extrasolar Earth analog is known.  Hundreds of planets have been found around Sun-like stars that are either Earth-sized by on shorter periods, or else on year-long orbits but somewhat larger.  Under strong assumptions, exoplanet catalogs have been used to make an extrapolated estimate of the rate at which Sun-like stars host Earth analogs.  These studies are complicated by the fact that every catalog is censored by non-trivial selection effects and detection efficiencies, and every property (period, radius, etc.) is measured nosily.  Present a general hierarchical probabilistic framework for making justified inferences about the population of exoplanets, taking into account survey completeness and, for the first time, observational uncertainties.  Able to make fewer assumptions about the distribution than previous studies; it only requires that the occurrence rate density be a smooth function of period and radius (employing a Gaussian process).  By applying method to synthetic catalogs, demonstrate that it produces more accurate estimates of the whole population than standard procedures based on weighting by inverse detection efficiency.  Apply the method to an existing catalog of small planet candidates around G dwarf stars (Petigura+2013).  Confirm a previous result that the radius distribution changes slope near Earth's radius.  Find that the rate density of Earth analogs is about 0.02 (per star per natural log bin in period and radius) with large uncertainty.  This number is much smaller than previous estimates made with the same data but stronger assumptions.

1406.3023
Driving the growth of the earliest supermassive black holes with major mergers of host galaxies
Tanaka

The formation mechanism of SMBHs in general, and of ~1e9 Msun SMBHs observed as luminous quasars at z>6 in particular, remains an open fundamental question.  The presence of such massive BHs at such early times, when the Universe was less than a billion years old, implies that they grew few either super-Eddington accretion, or nearly uninterrupted gas accretion near the Eddington limit; the latter, at first glance, is at odds with empirical trends at lower redshifts, where quasar episodes associated with rapid BH growth are rare and brief.  In this work, examine whether and to what extend the growth of the z>6 quasar SMBHs can be explained within the standard quasar paradigm, in which major mergers of host galaxies trigger episodes of rapid gas accretion below or near the Eddington limit.  Using a suite of Monte Carlo merger tree simulations of the assembly histories of the likely hosts of the z>6 quasars, investigate (i) their growth and major merger rates out to z~40, and (ii) how long the feeding episodes induced by host mergers must last in order to explain the observed z>6 quasar population without super-Eddington accretion.  The halo major merger rate scales roughly as (1+z)^5/2, with quasar hosts typically experiencing >10 major mergers between 15>z>6 (~650 Myr), compared to ~1 for typical massive galaxies at 3>z>0 (~11Gyr).  An example of a viable sub-Eddignton SMBH growth model is one where a host merger triggers feeding for a duration comparable to the halo dynamical time.  These findings suggest that the growth mechanisms of the earliest quasar SMBHs need not have been drastically different from their counterparts at lower redshifts.

1406.3025
Detecting industrial pollution in the atmospheres of earth-like exoplanets
Lin, Abad, Loeb

Detecting biomarker, such as molecular oxygen, in the atmospheres of transiting exoplanets has been am nor focus in the search for alien life.  Point out that in addition to these generic indicators, anthropogenic pollution could be used as a novel biomarker for intelligent life.  To this end, identify pollutants in the Earth's atmosphere that have significant absorption features in the spectral range covered by JWST.  Estimate that for an Earth-mass planet i the habitable zone of a white dwarf, methane (CH4) and nitrous oxide (N2O) can be detected at earth-like concentrations with an integration time of ~1.5 hrs and 12 hrs respectively.  Detecting pollutants that are produced nearly exclusively by anthropogenic activities will be sugfniciantly more challenging.  Of these pollutants, focus on tetrafluoromethane (CF4) and trichlorofluoromethane (CCl3F), which will be the easiest to detect.  Estimate that ~1.5 days (~3 days) of total integration time will be sufficient to detect or constrain the concentration of CCl3F (CF4) to ~100 times the current terrestrial level.

1406.3026
Maintaining low star formation rates in early-type galaxies with AGB heating
Conroy, van Dokkum, Kravtsov

Revisit previous suggestions that the heating provided by the winds of dying low-mass stars is capable of suppressing SF in quiescent galaxies.  At the end of the asymptotic giant branch, intermediate and low-mass stars eject their envelopes rapidly in a super-wind phase, usually giving rise to planetary nebular.  In galaxies with high stellar velocity dispersions, the interaction of these ejected envelopes with the ambient diffuse gas can lead to significant, isotropic and steady-state heating that scales as M_* sigma^2_*.  Show that cooling of the central regions of the hot diffuse halo gas can be delayed for a Hubble time for haloes more massive than ~1e12.5 Msun at 0<z<2.  This mechanism provides a natural explanation for the strong trend of galaxy quiescence with stellar surface density and velocity dispersion [what trend?], and may obviate the need for other proposed mechanisms that maintain the low observed SFRs of quiescent galaxies.

1406.3036
LensExplorer, a tool for the visualization of the gravitational lensing effect n the Hubble Frontiers Fields clusters
Diego

LensExplorer is an IDL GUI code that can be used to visualize the lensing deflection field derived in the HFF clusters.  The code can be used for both research and educational purposes as it offers an intuitive way to explore the solutions in the different clusters.  LensExplorer can be used to predict the magnifications at different redshifts of background sources and for a given location.  Present in this document a quick guide to get started with LensExplorer.  The code and lens models for A2744 and MACSJ0416.1-2403 are publicly available from a website where the new solutions ( and new versions of the code) will be also uploaded as they become available.

1406.3057
In what sense is the early universe fine-tuned?
Carroll

It is commonplace in discussions of modern cosmology to assert that the early universe began in a special state.  Conventionally, cosmologists characterize the fine-tuning in terms of the horizon and flatness problems.  Argue that the fine-tuning is real, but these problems aren't the best way to think about it: causal disconnection of separated regions isn't the real problem, and flatness isn't a problem at all.  Fine-tuning is better understood in terms of a measure on the space of trajectories: given reasonable conditions in the late universe, the fraction of cosmological histories that were smooth at early times is incredibly tiny.  This discussion helps clarify what is required by a complete theory of cosmological initial conditions.

1406.3102
Search for strong gravitational lensing effect in the current GRB data of BATSE
Li, Li

Because GRBs trace high-z Universe, there is an appreciable probability for a GRB to be gravitationally lensed by galaxies in the universe.  Consider the gravitational lensing effect of GRBs contributed by the DM haloes in galaxies.  Assuming that all halos have the SIS mass profile in the mass range 1e10 Msun/h < M < 2e13 Msun/h and all GRB samples follow the intrinsic redshift distribution and luminosity function derived from the Swift LGRBs sample, calculated the gravitational lensing probability in BATSE, Swift/BAT and Fermi/GBM GRBs, respectively.  With a derived probability result in BATSE GRBs, searched for lensed GRB pairs in the BATSE 5B GRB Spectral catalog.  The search did not find any convincing gravitationally lensed events.  Discuss result and future observations for GRB lensing observation.

1406.3330
Joint likelihood function of cluster counts and $n$-point correlation functions: improving their power through including halo sample variance
Schaan, Takada, Spergel

Naive estimates of the statistics of LSS and WL PS measurements that include only Gaussian errors exaggerate their scientific impact.  NL evolution and finite volume effects are both significant sources of non-Gaussian covariance that reduce the ability of PS measurements to constrain cosmological parameters.  Using a halo model formalism, derive an intuitive understanding of the various contributions to the covariance and show that the analytical treatment agrees with simulations.  This approach enables an approximate derivation of a joint likelihood for the cluster number counts, the WL PS and the bispectrum.  Show that this likelihood is a good description of the ray-tracing simulation.  Since all of these observables are sensitive to the same finite volume effects and contain information about the NL evolution, a combined analysis recovers much of the "lost" information and obviates the non-Gaussian covariance.  For upcoming WL surveys, estimate that a joint analysis of PS, number counts and bispectrum will produce an improvement of about 30-40% in determinations of the matter density and scalar amplitude.  This improvement is equivalent to doubling the survey area.

1406.3044
Astronomy of two Indian tribes: Banjaras and Kolams
Vahia et al

As the title says.  ...Show that apart from the absolute importance of the data on human perception of the sky, the data also reveal subtle aspects of interactions between physically co-located but otherwise isolated communities as well as their own lifestyles.  Also show that there is a strong relationship between profession and perspective of the sky.