Day 428

Tuesday.  Actually, Thursday.

1305.0824
The observed squeezed limit of cosmological three-point functions
Pajer, Schmidt, Zaldarriaga

The squeezed limit of 3pt function of cosmo perturbations is a powerful discriminant of different models of the early Universe.  Present a conceptually simple and complete framework to relate any primordial bispectrum in this limit to late time observables, such as CMB temperature bispectrum and the scale-dependent halo bias.  Employ a series of convenient coordinate transformations to capture the leading NL effects of cosmological perturbation theory on these observables.  This makes crucial use of Fermi Normal Coordinates and their conformal generalization.  Apply this formalism to standard slow-roll single-field inflation; show explicitly that Maldacena's results for the squeezed limits of the scalar bispectrum [proportional to (ns-1) in comoving gauge] and the tensor-scalar-scalar bispectrum lead to no deviations from a Gaussian universe, except for projection effects [so the early universe is Gaussian then, for slow-roll inflationary scenario?].  In particular, the primordial contributions to the squeezed CMB bispectrum and scale dependent halo bias vanish, and there are no "fossil" correlations between long-wavelength tensor perturbations and small-scale perturbations.  The contributions to observed correlations are then only due to projection effects such as gravitational lensing and redshift perturbations.

1305.0826
Morphology with light profile fitting of confirmed cluster galaxies at z=0.84
Nantais, ... Jee, et al

Morphological study of 124 spectroscopically confirmed cluster galaxies in the z=0.84 galaxy cluster.  Classify by color, morphology, 1- and 2-component light profile fitting from HST riz imaging.  Classification of field galaxies correlated with kinematic features of these galaxies; compare cluster galaxy morphology to those of field galaxies at similar redshift.  Also compare galaxy morphologies in regions of the cluster with different DM density as determined by WL maps.  Find an early-type fraction for the cluster population as a whole of 47%, about 2.8x higher than the field, and similar to the dynamically young cluster MS 1054 at similar redshift.  [what is the early-type fraction for local galaxy clusters?]  Find the most drastic change in morphology distribution between the low and intermediate DM density regions within the cluster, with the early type fraction doubling and the peculiar fraction dropping by nearly half.  The peculiar fraction drops more drastically than the spiral fraction going from the outskirts to the intermediate-density regions.  Suggests that many galaxies falling into clusters at z~0.8 may evolve directly from peculiar, merging , and compact systems into early-type galaxies, without having the chance to first evolve into a regular spiral galaxy.

1305.0828
Constrained simulations of the Antennae galaxies: comparison with Herschel-PACS observations
Karl, et al

A set of hydro-sims of Antennae galaxies, to understand the origin of the central overlap SB.  Good match to observed nuclear and overlap SF, especially when using a range of rather inefficient stellar feedback efficiencies (0.01<q_EoS<0.1).  In this case, a simple conversion of local SF to molecular H surface density motivated by observations accounts well for the observed distribution of CO.  Using radiative transfer post-processing, model synthetic FIR SEDs and 2d emission maps for direct comparison with Herschel-PACS data.  For gas-to-dust ratio of 62:1 and the best matching range of stellar feedback efficiencies, the synthetic FIR SEDs of the central SF region peak at values of ~65-81Jy at 99-116 um, similar to a 3-component modified BB fit to IR observations.  Also the spatial distribution of the FIR emission at 70/100/160 um compares well with the observations: >50% (>35%) of the emission in each band is concentrated in the overlap regions while only <30% (<15%) is distributed to the combined emission from the 2 galactic nuclei in the simulations (observations).  Parameter variations in the feedback model result in unambiguous changes both in the global and in the spatially resolved observable FIR properties of Antennae galaxy models.  Results strengthen the importance of direct, spatially resolved comparative studies of matched galaxy merger sims as a valuable tool to constraint the fundamental SF and feedback physics.

1305.0830
Pulsars cannot account for the inner galaxy's GeV excess
Hooper, Cholis, Linden, Siegal-Gaskins, Slatyer

As the title says.  Based on Fermi spectra, and the extent (~3kpc from Galactic center, instead of being confined to the innermost hundreds of pc's) of the gamma-ray source.  Cannot be millisecond pulsars.

1305.0882
The importance of major mergers in the build up of stellar mass in brightest cluster galaxies at z=1
Lidman et al

Sims and observations show that BCGs have increased their M* by a factor of almost two between z~0.9 and 0.2.  Sims further suggest that more than half this mass is accreted through major mergers.  Use 18 galaxy clusters with 600 spectra-confirmed cluster members between them; search for obaservational evidence that major mergers do play a significant role.  Find a major merger rate of 0.38pm0.14 mergers per Gyr at z~1.  While the uncertainties, which stem from the small size of the sample, are relatively large, the rate is consistent with the results that are derived from numerical simulations.  Assume that this rate continues to the present day and that half of the mass of the companion is accreted onto the BCG during these mergers, then this rate can explain the growth in the stellar mass of the BCGs that is observed and predicted by simulations.  Major mergers therefore appear to be playing an important role, perhaps even the dominant one, in the build up of stellar mass in these extraordinary galaxies.

1305.0930
Statistical ages and the cooling rate of X-ray dim isolated neutron stars
Gill, Heyl

Cooling theory of NSs is corroborated by its comparison with observations of thermally emitting isolated NSs.  Important is the age of the object, which typically is obtained from the spin-down history.  This age is highly uncertain if the object's B-field varies appreciably over time.  Other age estimators, such as SNe remnant ages and kinematic agnes, only apply to a few handful of NSs.  Conduct a population synthesis study of the nearby isolated thermal emitters and obtain their ages statistically from the observed luminosity function of these objects.  Argue that a more sensitive blind scan of the galactic disk with the upcoming space telescopes can help to constrain the ages to higher accuracy.

1305.0934
Redshift-space distortions from the cross-correlation of photometric populations
Asorey, Crocce, Gastanaga

Possibility of measuring z-space distortions from angular auto-correlations of galaxies in photo-z bins: extend this idea to include the cross-correations between z-bins, as an additional way of measuring radial information.  Show that this extra information allows to reduce the recovered error in the growth rate index gamma by a factor of ~2.  Although the final error in gamma depends on the bias and the mean photometric accuracy of the galaxy sample, the improvement from adding X-correlations is robust on different settings.  Another factor of 2-3 improvement in the determination of gamma can be achieved by considering two galaxy populations over the same photometric sky area but with different biases.  This additional gain is shown to be much larger than the one from the same populations when observed over different areas of the sky (with twice the combined area).  The total improvement of ~5 implies that a photometric survey such as DES should be able to recover gamma at the 5-10% from the angular clustering in linear scales of two different tracers.  It can also constrain the evolution of f(z)*sigma_8(z) in few bins beyond z~0.8-0.9 at the 10% level per-bin, compatible with recent constraints from lower-z spectroscopic surveys.  Also show how further improvement can be achieved by reducing the photometric redshift error.

1305.1297
Detectability of small-scale magnetic fields in early-type stars
Kochukhov, Sudnik

Strong, globally-organized B-fields are found for a small fraction of O, B, and A stars; many theoretical and indirect observational studies suggested ubiquitous presence of weak localized B-fields at the surfaces of massive stars.  However, no direct detections of such fields have been reported yet.  Have carried out the first comprehensive theoretical investigation of the spectropolarimetric observational signatures of the structured B-fields.  Calculations applied to interpret null results of the recent magnetic surveys of massive stars. Use detailed polarized radiative transfer calculations with LTE model atmospheres.  Similar to observational analysis, the mean Stokes I and V line profiles are obtained by applying a multi-line averaging technique.  Different spectropolarimetric observables are examined for multiple realization of randomly distributed radial B-field spots with different spatial scales.  Characterize the amplitude of the circular polarization profiles and the mean longitudinal B-field as a function of magnetic spot sizes.  The dependence of these observables on the effective temperature, projected rotational velocity, and inclination angle is also investigated.  Using results of the recently completed Magnetism in Massive Stars (MiMeS) survey, derive upper limits on the small-scale B-fields compatible with the MiMeS non-detections.  According to simulations, existing spectropolarimetric observations of sharp-lined massive stars rule out the presence of the small-scale fields stronger than 50-250G, depending on the typical spot sizes.  For broad-lined stars, the observations constrain such fields to be below approximately 1kG.  

1305.1299
Cosmic clocks
Jeong, Schmidt

In a perturbed Universe, comoving tracers on a 2-d surface of constant observed z are at different proper time since BB.  For tracers whose age is known independently, one can measure these perturbations of the proper time.  Examples of such sources include cosmic events which only happen during a short period of cosmic history, as well as evolving standard candles and standard rulers.  In this paper, derive a general gauge-invariant linear expression for this perturbation i terms of space-time perturbations.  As an example, show that the observed temperature perturbations of CMB on large scales are exactly given by these proper time perturbations.  Together with the 6 ruler perturbations derived in Schmidt and Jeong (2012), this compeltes the set of independent observables which can be measured with standard rulers and candles.

1305.1305
Evolution of star formation in the UKIDSS ultra deep survey field - I. Luminosity functions and cosmic star formation rate out to z=1.6
Drake, et al

Compile narrow-band data from Subaru and VISTA, in conjunction with broad-band data from SXDS and UDS, to make a selection of 5735 emission-line galaxies in 12 z slices, spanning 10 Gyr of cosmic time.  Determine photo-z for the sample using 11-band photometry, and use a spectroscopically confirmed subset to fine-tune the resultant z distribution.  Use the maximum-likelihood technique to determine luminosity functions in each redshift slice and model the selection effects inherent in any narrow-band selection statistically, to obviate the retrospective corrections ordinarily required.  The deep narrow-band data are sensitive to very low SFRs, and allow an accurate evaluation of the fain end slope of the Schechter function alpha.  Find that alpha is particularly sensitive to the assumed faintest broadband magnitude of galaxy capable of hosting an emission line, and propose that this limit should be empirically motivated.  For this analysis, base the threshold on the limiting observed equivalent widths of emission lines in the local Universe.  Compute the characteristic SFR of galaxies in each redshift slice, and the integrated SFR density, rho_SFR.  Find results to be in good agreement with the literature and parameterize the evolution of the SFR density as rho_SFR proportional to (1+z)^4.6 confirming a steep decline in SF activity since z=1.6.

1305.1308
Spot the difference.  Impact of different selection criteria on early-type galaxies observed properties in zCOSMOS 20-k sample
Moresco et al

Select 6 different samples of early-type galaxies with different selection criteria based on photometric, spectroscopic and morphological properties, (morphology, optical colors, sSFR, SED, combination of morphology, spectroscopic and photometric informations) up to z=1.  The "morphological" sample has the higher percentage of contamination in colors, sSFR and presence of emission lines, while the "pure passive" sample is the purest, with properties mostly compatible with no SF activity; however, it is also the less economic criterion in terms of information used.  The best performing among the other criteria are the "photometric type" and the "sSFR", providing a percentage of contamination only slightly higher than the "pure passive" criterion (on average of a factor of ~2) but with absolute values of the properties of contaminants still compatible with a red, passively evolving population.  Also provided two revised definitions of early type galaxies based on restframe color-color and color-mass criteria, that better reproduce the observed bimodalities.  The analysis of the number densities shows evidences of mass-assembly downsizeing, with galaxies at 10.25<log(M/Msun)<10.75 increasing their number by a factor ~2-4 from z=0.6 to z=0.2, by a factor ~2-3 from z=1 to 0.2 at 1e10.75 to 1e11, and by only ~10-50% from z=1 to z=0.2 at 1e11 to 1e11.5.  [what are the properties of early-types that are affected by the criteria differences besides downsizing?  are early-types defined by their sSFR/presence of emission lines/color?  How exactly do they define pure?]

1305.1325Population III stars and remnants in high redshift galaxies
Xu, Wise, Norman

Sims show some fraction of Pop III stars form in binaries, in addition to being massive (tens of Msun).  Deaths of metal-free stars result in the initial chemical enrichment of the universe and the production of the first stellar-mass BHs.  AMR sims, form 1e9 Msun haloes and >13k Pop III stars by z~15.  Most halos do not form Pop III stars until they reach Mvir~1e7 Msun because this biased region is quickly enriched from both Pop III and galaxies, which also produce high levels of UV radiation that suppress H2 formation.  Nevertheless, Pop III stars continue to form, albeit in more massive halos, at a rate of 1e-4 Msun/yr/Mpc^3 at z=15.  The most massive starless halo has a mass of 7e7 Msun, which could host massive BH formation through the direct gaseous collapse scenario.  Show that the multiplicity of Pop III remnants grows with halo mass above 1e8 Msun, culminating in 50 remnants located in 1e9 Msun haloes on average.  This has implications that high mass X-ray binaries and intermediate mass BHs that originate from metal-free stars may be abundant in high-z galaxies.

1305.1357
UVUDF: Ultraviolet imaging of the Hubble ultradeep field with wide-field camera 3
Teplitz, ... Grogin, Koekemoer, ... Gawaiser, Coe, et al

Overview of a 90-orbit HST treasuring program of UV imaging of HUDF using WFC3 UVIS detector with F225W, F275W and F336W filters.  Survey is designed to (i) investigate the episode of peak SF activity in galaxies at 1<z<2.5, (ii) probe the evolution of massive galaxies by resolving sub-galactic units (clumps), (iii) examine the escape fraction of ionizing radiation from galaxies at z~2-3, (iv) greatly improve the reliability of photoz estimates, and (v) measure the SFR efficiency of neutral atomic-dominated H gas at z~1-3.  In this overview paper, describe the survey details and data reduction challenges, including both the necessity of specialized calibration and the effects of CTI (which has stark effects).  STScI recommendation of adding BG light "post-flash" for very sensitive measurements with UVIS. Find: number density of UV dropouts at z=1.7, 2.1 and 2.7 is largely consistent with the number predicted by published LFs.  Also confirm that the image mosaics have sufficient sensitivity and resolution to support the analysis of the evolution of SF clumps, reaching 28-29th magnitude depth at 5 sigma in a 0.2 arcsecond radius aperture depending on filter and observing epoch.

1305.1485
Extreme value statistics of the weak lensing convergence: 1. primordial non-Gaussianities
Capranico, Kalovidouris, Schaefer

From the observation of single extreme values in the EUCLID WL survey it is possible to place constraints on fnl and gnl of the order 1e2 and 1e5, respectively, while tnl can not be constrained in a meaningful way.

1305.1629
Ringing the initial universe: the response of overdensity and transformed-density power spectra to initial spikes
Neyrinck, Yang

An experiment: 'ring' a set of cosmo N-body sim ICs, placing spikes in its initial PS at different wavenumber bins.  Then measure where these spikes end up in the final conditions.  In the usual, overdensity PS, most sensitive to contracting and collapsing dense regions, initial power on slightly NL scales (k~0.3 h/Mpc) smears to smaller scales, coming to dominate the initial power once there.  In log-density and Gaussianized-density power spectra, the sensitivity to low-density (expanding) as well as high-density regions produces a different response: initial spikes spread symmetrically in scale, both upward and downward.  Also test the difference between a crude approximation of the Lya flux field, and its Gaussianized form.  In the PS of the reciprocal density, 1/(1+delta), spikes migrate to larger scales, indicating the magnifying effect voids have on small-scale modes.  Give a toy model that qualitatively explains the symmetric power spreading in Gaussianized-density PS.  Discuss how to use this framework to estimate PS covariance matrices.  This can be used to track the fate of information in the Universe, that takes the form of initial degrees of freedom, one random spike per initial mode.