Day 408

Wednesday.

1304.2391
The assembly of Milky Way-like galaxies since z~2.5
van Dokkum et al

Using data from 3D-HST and CANDELS, study progenitors of MW-like galaxies, which dominate the stellar mass density of the Universe today.  Find: galaxies with present-day stellar masses of log(M)~10.7 Msun built ~90% of their stellar mass since z~2.5, with most of the SF occurring before z~1.  In marked contrast to the assembly history of massive elliptical galaxies, the centers and outer parts of the [MW-like] galaxies built up at roughly the same rate between z~2.5 and z~1.  Conclude that a "standard" model for the formation of spiral galaxies, with the bulge assembling first and the disk building around it, is probably not correct.  Instead, bulges (and BHs) likely formed in lockstep with disks, through bar instabilities, clump migration or other processes.  Find that after z~1 the growth in the central regions gradually stopped and the disk continued to build, consistent with recent studies of the gas distributions in z~1 galaxies and the properties of many spiral galaxies today.

1304.2393
Enabling non-parametric strong lensing models to derive reliable cluster mass distributions.  WSLAP+
Sendra, Diego, Broadhurst, Lazkoz

In the SL regime, non-parametric lens models struggle to achieve sufficient angular resolution for a meaningful derivation of the central cluster mass distribution.  The problem lies mainly with cluster members which perturb lensed images and generate additional images, requiring high resolution modeling, even though one mainly wishes to understand the relatively smooth cluster component.  The required resolution is not achievable because the separation between lensed images is several times larger than the deflection angles by member galaxies, even for the deepest data.  Bypass this limitation by incorporating a simple physical prior for member galaxies, using their observed positions and their luminosity scaled masses [is it still non-parametric, though, if you assume physical prior (model?) for member galaxies?].  This galaxy contribution is added to a relatively coarse Gaussian pixel grid for modeling the cluster mass distribution, extending the established WSLAP code.  Test this new code with a simulation based on A1689, using the pixels belonging to multiply-lensed images and the observed member galaxies.  Dealing with the cluster members this way leads to convergent solutions, without resorting to regularization, reproducing well the input cluster and substructures.  Highlight the ability of this method to recover dark sub-components of the cluster, unrelated to member galaxies.  Such anomalies can provide clues to the nature of invisible DM, but are hard to discover using parameterized models where substructures are defined by the visible data.  With the increased resolution and stability, show that non-parametric models can be made sufficiently precise to locate multiply-lensed systems, thereby achieving fully self-consistent solutions without reliance on input systems from less objective means.

1304.2395
The structural evolution of Milky Way-like star forming galaxies since z~1.3
Patel, ... Franx, van Dokkum, ... Rix et al

Follow structural evolution of SFGs like the MW by selecting progenitors to z~1.3 based on the stellar mass growth inferred fro the evolution of the SF sequence.  Select sample from 3D-HST, which utilizes spectroscopy NIR grism, and enables precise redshift measurements for the SFG sample.  Structural properties obtained from CANDELS WFC3 imaging.  Progenitors of z=0 SFGs with stellar mass M=1e10.5 Msun are ~2x less massive at z~1.  This late-time stellar mass assembly is consistent with recent studies that employ abundance matching techniques.  The descendant SFGs at z~0 have grown in half-light radius by a factor of ~1.4 since z~1.  The half-light radius grows with stellar mass at r_e M^0.29.  While most of the stellar mass is clearly assembling at large radii, the mass surface density profiles reveal ongoing mass growth also in the central regions where bulges and pseudo-bulges are common features in present day late-type galaxies.  Some portion of this growth in the central regions is due to SF as recent observations of H-alpha maps for SFGs at z~1 are found to be extended but centrally peaked.  Connecting the lookback study with galactic archeology, find the stellar mass surface density at R=8 kpc to have increased by ~2x since z~1, in good agreement with measurements derived for the solar neighborhood of the MW.

1304.2399
Subaru weak-lensing survey of dark matter subhaloes in coma cluster : subhalo mass function and statistical properties
Okabe, Futamase et al

4 sq deg survey of Coma cluster subhaloes. Detect 32 subhalos down to 1e-3 of the virial mass of the cluster.  WL measurement of shear-selected subhaloes allows investigation of subhalo properties and the correlation between subhalo masses and galaxy luminosities.  The mean distortion profiles stacked over subhaloes show a sharply truncated feature which is well-fitted by NFW mass model with the truncation radius, as expected by the tidal destruction by the main cluster.  Found that subhalo masses, truncation radii and M/L ratios decrease toward the cluster center.  Subhalo MF, dn/dlnM_sub, in the range of two orders of magnitude in mass, is well described by a single power law or a Schechter function.  Best-fit power indices of 1.11 for the former model and 0.94 for the latter one are in remarkable agreement with slopes of ~0.9-1.0 predicted by the CDM paradigm.  The tangential distortion signals in the radial range of 0.02-2Mpc/h from the cluster center show a complex structure which is well described by a composition of 3 mass components of sub haloes, NFW mass distribution as a smooth component of the main cluster, and lensing model from LSS behind the cluster.  Although the lensing signals are one order lower than those for clusters at z~0.2, the total S/N=13.3, is comparable to or higher because a large number of BG source galaxies compensate low lensing efficiency of the nearby cluster.

1304.2406
The warm DM halo mass function below the cut-off scale
Angulo, Hahn, Abel

An accurate scrutiny of WDM predictions with N-body sims difficult due to numerical artifacts.  Report on cosmological simulations that, for the first time, are devoid of these problems, and thus, are able to accurately resolve the WDM halo MF well below the cut-off.  Discover a complex picture, with perturbations at different evolutionary stages populating different ranges in the halo MF.  On the smallest mass scales resolved, identified objects are typically centers of filaments that are staring to collapse.  On intermediate mass scales, objects typically correspond to fluctuations that have collapsed and are in the process of relaxation whereas the high mass end is dominated by objects similar to haloes identified in CDM simulations.  When explicitly show how the formation of low-mass haloes is suppressed, which translates into a strong cut-off in the halo MF.  This disfavors some analytic formulations that predict a halo MF that would extend well below the free streaming mass.  Argue for a more detailed exploration of the formation of the smallest structures expected to form in a given cosmology, which is foreseen to advance overall understanding of structure formation.


1304.2593
Simulation covariance error
Dodelson, Schneider

Extracting parameter constraints from cosmological observations requires accurate determination of the covariance matrix for use in the likelihood function.  We show here that uncertainties in the elements of the covariance matrix propagate directly to increased uncertainties in cosmological parameters.  When the covariance matrix is determined by simulations, the resulting variance of each parameter increases by a factor of order 1+N_b/N_s where N_b is the number of bands in the measurement and N_s is the number of simulations.