Day 836

Wednesday.  Thursday.

1502.04710
The influence of wavelength, flux, and lensing selection effects on the redshift distribution of dusty, star-forming galaxies
Béthermin, De Breudk, Sargent, Daddi

Interpret the large variety of z distributions of galaxies found by FIR and (sub-)mm deep surveys depending on their depth and wavelength using a phenomenological model of galaxy evolution.  This model reproduces without any new parameter tuning the observed z distributions from 100um to 1.4mm, and especially the increase of the median z with survey wavelength.  This median redshift varies also significantly with the depth of the surveys, and deeper surveys do necessarily not probe higher redshifts.  Paradoxically, at fixed wavelength and flux limit, the lensed sources are not always at higher z.  Found that the higher z of 1.4mm-selected SPT sources compared to other SMG surveys is not only caused by the lensing selection, but also by the longer wavelength.  This SPT sample is expected to be dominated by a population of lensed MS galaxies and a minor contribution (~10%) of unlensed extreme starbursts.


1502.04984
Predictions for the abundance and colors of galaxies in high redshift clusters in hierarchical models
Merson, Baugh, Abdalla, et al

High-z galaxy clusters allows examination of galaxy formation in extreme environments.  Compile data for z>1 galaxy clusters to test the predictions from one of the latest semi-analytical models of galaxy formation.  The model gives a good match to the slope and zero-point of the cluster red sequence.  The model is able to match the cluster galaxy luminosity function at faint and bright magnitudes, but underestimates the number of galaxies around the break in the LF.  Find that simply assuming a weaker dust attenuation improves the model predictions for the cluster galaxy LF, but worsened the predictions for the red sequence at bright magnitudes.  Examination of the properties of the bright cluster galaxies suggests that the default dust attenuation is very large due to these galaxies having large reservoirs of cold gas as well as small radii.  Find that matching the LF and colors of high z cluster galaxies, whilst remaining consistent with local observations, poses a challenge for galaxy formation models.  Results highlight the need to consider observations beyond the local Universe, as well as for different environments, when calibrating the parameters of galaxy formation models.


1502.05043
Connecting dark matter halos with the galaxy center and the supermassive black hole
Bogdan, Goulding

Correlation between central SMBHs and properties of the host galaxies (i.e., stellar bulge mass or central stellar velocity dispersion) observed; models of BH and bulge co-evolution emerged.  Coevolution challenged by observational and theoretical studies, hinted that the fundamental connection may be between BHs and DM halos, and not necessarily their host galaxies.  Based on a study of 3130 elliptical galaxies -- selected from SDSS and ROSAT All Sky Surveys -- demonstrate that the central stellar velocity dispersion exhibits a significantly tighter correlation with the total gravitating mass, traced by the X-ray luminosity of the hot gas, than with the stellar mass.  This hints that the central stellar velocity dispersion, and hence the central gravitational potential, may be the fundamental property of elliptical galaxies that is most tightly connected to the larger-scale DM halo.  Furthermore, using the central stellar velocity dispersion as a surrogate for the BH mass, find that in elliptical galaxies the inferred BH mass and inferred total gravitating mass within the viral radius (or within 5 effective radii) can be expressed as M_BH propto M_tot^1.6 (or M_5r_eff^1.8).  These results are consistent with a picture in which the BH mass is directly set by the central stellar velocity dispersion, which, in turn, is determined by the total gravitating mass of the system.


1502.05356
Delousing the CMB with the cosmic infrared background
Sherwin, Schmittfull

Robust delensing of CMB polarization will help with search of B-mode polarization.  Investigate in detail the possibility of delensing the CMB with CIB, emission from dusty SF galaxies that is an excellent tracer of the CMB lensing signal, in order to improve constraints on the tensor-to-scalar ratio r.  Find that the maps of the CIB, such as current Planck satellite maps at 545 GHz, can be used to remove more than half of the lensing B-mode power.  Calculating optimal combinations of different large-scale-structure tracers for delensing, find that co-adding CIB data and external arcminute-resolution CMB lensing reconstruction can lead to significant additional improvements in delensing performance.  Investigate whether measurement uncertainty in the CIB spectra will degrade the delensing performance if no model of the CIB spectra is assumed, and instead the CIB spectra are marginalized over, when constraining r.  Find that such uncertainty does not significantly affect B-mode surveys smaller than a few thousand degrees.  Even for larger surveys, it causes only a moderate reduction in CIB delousing performance, especially if the surveys have high (arcmin) resolution, which allows self-calibration of the delensing procedure.  Though further work on the impact of FG residuals is required, the overall conclusions for delensing with current CIB data are optimistic: this delensing method can tighten constraints on r by a factor up to ~2.2, and by a factor up to ~4 when combined with external ~3uK-arcmin lensing reconstruction, without requiring the modeling of CIB properties.  CIB delensing is thus a promising method for the upcoming generation of CMB polarization surveys.