Day 738

Friday.

1409.1218
Why z>1 radio-loud galaxies are commonly located in proto-clusters
Hatch et al

Distant powerful radio-loud AGN (RLAGN) tend to reside in dense environments and are commonly found in proto-clusters at z>1.3.  Examine whether this occurs because RLAGN are hosted by massive galaxies, which preferentially reside in rich environments.  Compare environments of powerful RLAGN at 1.3<z<3.2 from the CARLA survey to a sample of radio-quiet galaxies matched in mass and redshift.  Find the environment s of RLAGN are significantly denser than those of radio-quiet galaxies, implying that not more than 50% of massive galaxies in this epoch can host powerful radio-loud jets.  This is not an observational selection effect as we find no evidence to suggest it is easier to observe the radio emission when the galaxy resides in a dense environment.  Therefore suggest that the dense Mpc-scale environment fosters the formation of a radio jet from an AGN.  Show that the number density of potent RLAGN host galaxies is consistent with every >1e14 Msun cluster having experienced powerful radio-loud feedback of duration ~60Myr during 1.3<z<3.2. This feedback could heat the interacluster medium to the extent of 0.5-1 KeV per gas particle, which could limit the amount of gas available for further star formation in the proto-cluster galaxies.

1409.1225
Redshift space distortions in the effective field theory of large scale structures
Senatore, Zaldarriaga

Introduce a formalism, valid both for DM and collapsed objects, that allows description of z-space distortions in the context of EFT of LSS.  Expressing density perturbations in z-space corresponds to performing a change of coordinates and the resulting expressions contain products of density perturbations and velocity fields evaluated at the same location.  These terms are sensitive to non-perturbative short-distance physics and in order to correctly treat them, they need to be renormalized by adding suitable counter terms.  Therefore more counter terms are required in z-space expressions compared to their real space analogs.  In particular in the expression for the one-loop matter PS there are two new counter terms.  Just as in real space, long wavelength displacements affect correlation functions in z-space and need to be resumed.  Generalize the real space formulas for IR resumption to this case: the final expressions are conceptually similar but are more challenging to compute numerically due to their reduced symmetry.

1409.1228
First frontier field constraints on the cosmic star-formation rate density at z~10 - The impact of lensing shear on completeness of high-redshift galaxy samples
Oesch, ... van Dokkum, et al

Search HFF dataset of A2744 and its parallel field for z~10 sources to further refine the evolution of the cosmic SFR density at z>8.  Independently confirm two images of the recently discovered triply-imated z~9.8 source by Zitrin+2014, and set an upper limit for similar z~10 galaxies with red colors of J_125-H_160>1.2 in the parallel field of A2744.  Utilize extensive simulations to derive the effective selection volume of Lyman-break galaxies at z~10, both in the lensed cluster field and in the adjacent parallel field.  Particular care is taken to include position-dependent lensing shear to accurately account for the expected sizes and morphologies of highly-magnified sources.  Show that both source blending and shear reduce the completeness at a given observed magnitude in the cluster, particularly near the critical curves.  These effects have a significant, but largely overlooked, impact on the detectability of high-z sources behind clusters, and substantially reduce the expected number of highly-magnified sources.  The detections and limits from both pointings result in a SFRD which is higher by 0.4pm0.4 dex than previous estimates at z~10 from blank fields.  Nevertheless, the combination of these new results with all other estimates remain consistent with a rapidly declining SFRD in the 170 Myr from z~8 to z~10 as predicted by cosmological simulations and DM halo evolution in LCDM.  Once biases introduced by magnification dependent completeness are accounted for, the full six cluster and parallel FF program will be an extremely powerful new dataset to probe the evolution of the galaxy population at z>8 before the advent of JWST.

1409.1232
A size-duration trend for gamma-ray burst progenitors
Barnacka, Loeb

GRBs show a bimodal distribution of durations, separated at a duration of ~2s.  Observations have confirmed the association of long GRBs with the collapse of massive stars.  The origin of short GRBs is still being explored.  Examine constraints on the emission region size in short and log GRBs detected by Fermi/GBM.  Find that the emission region size during the prompt emission, R, and the burst duration, T_90, are consistent wit the relation R~c * T_90, for both long and short GRBs.  Find the characteristic size for the prompt emission region to be ~2e10 cm ,and ~4e11 cm for short and long GRBs, respectively.

1409.1239
The triggering of starbursts in low-mass galaxies
Lelli, et al

Results suggest that the starburst is triggered either by past interactions/mergers between gas-rich dwarfs or bay direct gas infall from the IGM.

1409.1240
Stability of small-scale baryon perturbations during cosmological recombination
Venumadhav, Hirata

Study small-scale fluctuations (baryon pressure sound waves) in the baryon fluid during recombination.  In particular, look at their evolution in the presence of relative velocities between baryons and photons on large scales (k~1e-1 /Mpc), which are naturally present during the era of decoupling.  Previous work concluded that the fluctuations grow due to an instability of sound waves in a recombining plasma, but that the growth factor is small for typical cosmological models.  These analyses model recombination in an inhomogeneous universe as a perturbation to the parameters of the homogenous solution.  Show that for relevant wave numbers k>1e3 /Mpc, the dynamics are significantly altered by the transport of both ionizing continuum (h nu > 13.6 eV) and Lyman-alpha photons between crests and troughs of the density perturbations.  Solve the radiative transfer of photons in both these frequency ranges and incorporate the results in a perturbed 3-level atom model.  Conclude that the instability persists at intermediate scales.  Use the results to estimate a distribution of growth rates in 1e7 random realizations of large-scale relative velocities.  Results indicate that there is no appreciable growth; out of these 1e7 realizations, the maximum growth factor we find is less than ~1.2 at wave numbers of k~1e3 /Mpc.

1409.1254
Strong lens time delay challenge: II. results of TDC1
Liao, Treu, Marshall, et al

Present the results of the first SL TDC.  Present the main challenge, TDC1, consisting in analyzing thousands of simulated light curves blindly.  Observational properties of the light curves cover the range in quality obtained for current targeted efforts (e.g. COSMOGRAIL) and expected from future synoptic surveys (LSST), and include "evilness" in the form of simulated systematic errors.  7 teams participated in TDC1, submitting results from 78 different method variants.  After describing each method, compute and analyze basic statistics measuring accuracy (or bias) A, goodness of fit chisq, precision P, and success rate f.  For some methods, identify outliers as an important issue.  Other methods show that outliers can be controlled via visual inspection or conservative quality control.  Several methods are competitive, i.e. give |A|<0.03, P<0.03, and chisq<1.5, with some of the methods already reaching sub-percent accuracy.  The fraction of light curves yielding a time delay measurement is typically in the range f=20-40%.  It depends strongly on the quality of the data: COSMOGRAIL-quality cadence and light curve lengths yield significantly higher f than does sparser sampling.  Estimate that LSST should provide around 400 robust time-delay measurements, each with P<0.03 and |A|<0.01, comparable to current lens modeling uncertainties.  In terms of observing strategies, find that A and f depend mostly on season length, while P depends mostly on cadence and campaign duration.