Day 1291

Monday.  Tuesday.  Wednesday. 

1707.06755

Reanalysis of the BICEP2, Keck and Planck Data: no evidence for gravitational radiation

Gott, Colley

A joint analysis of data collected by the Planck and BICEP2+Keck teams has previously given r=0.09±0.05 for BICEP2 and r=0.02±0.03 for Keck.  Analyzing BICEP2 using its published noise estimate, Colley+Gott(2015) found r=0.09±0.04, agreeing with the final joint results for BICEP2.  With the Keck data now available, they have done something the joint analysis did not: a correlation study of the BICEP2 vs. Keck B-mode maps.  Knowing the correlation coefficient between the two and their amplitudes allows us to determine the noise in each map (which is checked using the E-modes).  Find the noise power in the BICEP2 map to be twice the original BICEP2 published estimate, explaining the anomalously high r value obtained by BICEP2.  Now find r=0.004±0.04 for BICEP2 and r=-0.01±0.04 for Keck.  Since r>=0 by definition, this implies a maximum likelihood value of r=0, or no evidence for gravitational waves.  Starobinsky Inflation (r=0.0036) is not ruled out, however.  Krauss+Wilzcek (2014) have already argued that "measurement of polarization of the CMB due to a long-wavelength stochastic background of gravitational waves from Inflation in the early Universe would firmly establish the quantization of gravity," and, therefore, the existence of gravitons.  Argue it would also constitute a detection of gravitational Hawking radiation (explicitly from the causal horizons due to Inflation).

1707.07003

Witnessing galaxy assembly in an extended z~3 structure

Fumagalli, et al

Present new observations acquired with the Multi Unit Spectroscopic Explorer instrument on the VLT in a quasar field that hosts a high column-density damped Lya absorber (DLA) at z~3.25. Detect Lya emission from a nebula at the redshift of the DLA with line luminosity (27±1)e41 erg/s, which extends over 37±1 kpc above a surface brightness limit of 6e-19 erg/s/cm2/arcsec2 at a projected distance of 30.5±0.5 kpc from the quasar sightline.  Two clumps lie inside this nebula, both with Lya rest-frame equivalent width >50A and with relative line-of-sight velocities aligned with two main absorption components seen in the DLA spectrum.  In addition, identify a compact galaxy at a projected distance of 19.1±0.05 kpc from the quasar sightline.  The galaxy spectrum is noisy but consistent with that of a star-forming galaxy at the DLA redshift.  Argue that the Lya nebula is ionized by radiation from SF inside the two clumps, or by radiation from the compact galaxy.  In either case, these data imply the presence of a structure with size >>50 kpc inside which galaxies are assembling, a picture consistent with galaxy formation in groups and filaments as predicted by cosmological simulations such as the EAGLE simulations.

1707.07535

Probing superfoods with weak lensing

Higuchi, Inoue

CMB has non-Gaussian features in the temperature fluctuations.  An anomalous cold spot surrounded with a hot ring, called the Cold Spot, is one such feature.  If a large underdense region (super void) resides towards the Cold Spot, a systematic shape distortion in the images of BG source galaxies via WL should be detected.  In order to estimate the detectability of such signals, use N-body sims to simulate full-sky ray-tracing of source galaxies.  Search for a most prominent underdense region using the simulated convergence maps smoothed at a scale of 20 degree and obtained tangential shears around it.  The lensing signal expected in a concordant LCDM model can be detected at a signal-to-noiseratio S/N~3.  If a super void with a radius of ~200 Mpc/h and a density contrast delta0~-0.3 at the centre resides at a redshift z~0.2, on-going and near-future WL surveys would detect a lensing signal with S/N~5 without resorting to stacking.


1707.07693
What sets the central structure of dark matter haloes?
Ogiya, Hahn

DM haloes forming near the thermal cut-off scale of the density perturbations are unique, since they are the smallest objects and form through monolithic gravitational collapse, while larger haloes contrastingly have experienced mergers.  While standard CDM sims readily produce haloes that follow the universal NFW density profile with an inner slope, rho~r^-alpha with alpha=1, recent simulations have found that when the free-streaming cut-off is resolved, the resulting haloes follow nearly power-law density profiles of alpha~1.5.  In this paper, study the formation of density cusps in haloes using idealized N-body sims of the collapse of proto-haloes.  When the proto-halo profile is initially cored due to particle free-streaming at high z, universally find ~r^-1.5 profiles irrespective of the proto-halo profile slope outside the core and large-scale non-spherical perturbations.  Quite in contrast, when the proto-halo has a power-law profile, then obtain profiles compatible with the NFW shape when the density slope of the porto-halo patch is shallower than a critical value, alpha_ini~0.3, while the final slope can be steeper for alpha_ini>~0.3.  Further demonstrate that the r^-1.5 profiles are sensitive to small scale noise, which gradually drives them towards an inner slope of -1, where they become resilient to such perturbations.  Demonstrate that the r^-1.5 solutions are in hydrostatic equilibrium, largely consistent with a simple analytic model, and provide arguments that angular momentum appears to determine the inner slope.