1901.05005
Phenotypic redshifts with self-organizing maps: a novel method to characterize redshift distributions of source galaxies for weak lensing
Buchs, et al
Wide-field imaging surveys such as DES rely on coarse measurements of spectral energy distributions in a few filters to estimate the redshift distribution of source galaxies. In this regime, cosmic variance, shot noise, and selection effects limit the attainable accuracy of redshift calibration and thus of cosmological constraints. Present a new method to combine wide-field, few-filter measurements with catalogs from deep fields with additional filters and sufficiently low photometric noise to break degeneracies in photometric redshifts. The multi-band deep field is used as an intermediary between wide-field observations and accurate redshifts, greatly reducing cosmic variance, shot noise, and selection effects. The implementation of the method uses self-organizing maps to group galaxies into phenotypes based on their observed fluxes, and is tested using a mock DES catalog created from N-body sims. It yields a typical uncertainty on the mean redshift in each of five tomographic bins for a simulation of the DES Year 3 WL tomographic analysis of Delta z=0.007, which is a 60% improvement compared to the Y1 analysis. Although the implementation of the method is tailored to DES, its formalism can be applied to other large photometric surveys with a similar observing strategy.
1901.05007
Does radiative feedback make faint z>6 galaxies look small?
Ploeckinger, Schaye, et al
Recent observations of lensed sources have shown that the faintest M_UV~ -15 mag galaxies observed at z=6-8 appear to be extremely compact. Some of them have inferred sizes of less than 40 pc for stellar masses between 1e6 and1e7 Msun, comparable to individual super star clusters or star cluster complexes at low redshift. High-z, low mass galaxies are expected to show a clumpy, irregular morphology and if star clusters form in each of these well-separated clumps, the observed galaxy size would be much larger than the size of an individual star forming region. As supernova explosions impact the galaxy with a minimum delay time that exceeds the time required to form a massive star cluster, other processes are required to explain the absence of additional massive SF regions. In this work, investigate whether the radiation of a young massive star cluster can suppress the formation of other detectable clusters within the same galaxy already before SN feedback can affect the galaxy. Find that in low-mass (M_200 <~1e10 Msun) haloes, the radiation from a compact star forming region with an initial mass of 1e7 Msun can keep gas clumps with Jeans masses larger than ~1e7 Msun warm and ionized throughout the galaxy. In this picture, the small intrinsic sizes measured in the faintest z=6-8 galaxies are a natural consequence of the strong radiation field that stabilizes massive gas clumps. A prediction of this mechanism is that the escape fraction for ionizing radiation is high for the extremely compact, high-z sources.
A mass-dependent slope of the galaxy size-mass relation out to z~3: further evidence for a direct relation between median galaxy size and median halo mass
Mowla, et al
Reassess the galaxy size-mass relation out to z~3 using a new definition of size and a sample of >29000 galaxies from the 3D-HST, CANDELS, and COSMOS-DASH surveys. Instead of the half-light radius r_50, use r_80, the radius containing 80% of the stellar light. Find that the r_80 -- M* relation has the form of a broken power law, with a clear change of slope at a pivot mass M_p. Below the pivot mass the relation is shallow (r_80 ~ M*^0.15) and above it it is steep (r_80~M*^0.6). The pivot mass increases with redshift, from log(M_p/M_sun)~10.2 at z=0.4 to log(M_p/Msun)~10.9 at z=1.7-3. Compare these r_80--M* relations to the M_halo--M* relations derived from gg lensing, clustering analyses, and abundance matching techniques. Remarkably, the pivot stellar masses of both relations are consistent with each other at all redshifts, and the slopes are very similar both above and below the pivot when assuming M_halo~r_80^3. The implied scaling factor to relate galaxy size to halo size is r_80/r_vir=0.047, independent of stellar mass and redshift. From redshift 0 to 1.5, the pivot mass also coincides with the mass where the fraction of SF galaxies is 50%, suggesting that the pivot mass reflects a transition from dissipation to dissipation less galaxy growth. Finally, the results imply that the scatter in the stellar-to-halo mass ratio is relatively small for massive haloes (~0.2 dec for M_halo>1e12.5 Msun).
1901.05017
A new view of the size-mass distribution of galaxies: using r_20 and r_80 instead of r_50
Miller, van Dokkum, Mowla, van der Wel
When investigating the sizes of galaxies it is standard practice to use the half-light radius, r_50. Here, explore the effects of the size definition on the distribution of galaxies in the size -- stellar mass plane. Specifically, consider r_20 and r_80, the radii that contain 20% and 80% of a galaxy's total luminosity, as determined from a Service profile fit, for galaxies in the 3D-HST/CANDELS and COSMOS-DASH surveys. These radii are calculated form size catalogs based on a simple calculation assuming a Service profile. Find that the size-mass distributions for r_20 and r_80 are markedly different from each other and also from the canonical r_50 distribution. The most striking difference is in the relative sizes of SF and quiescent galaxies at fixed stellar mass. Whereas quiescent galaxies are smaller than SF galaxies in r_50, this difference nearly vanishes for r_80. By contrast, the distance between the two populations increases for r_20. Considering all galaxies in a given stellar mass and redshift bin, detect a significance bimodality in the distribution of r_20, with one peak corresponding to SF galaxies and the other to quiescent galaxies. Suggest that different measures of the size are tracing different physical processes within galaxies; r_20 is closely related to processes controlling the SFR of galaxies and r_80 may be sensitive to accretion processes and the relation of galaxies with their haloes.
1901.05019
Decorrelating the errors of the galaxy correlation function with compact transformation matrices
Yuan, Eisenstein
Covariance matrix estimation is a persistent challenge for cosmology, often requiring a large number of synthetic mock catalogues. The off-diagonal components of the covariance matrix also make it difficult to show representative error bars on the 2PCF, since errors computed from the diagonal values f the covariance matrix greatly underestimate the uncertainties. Develop a routine for decor relating the projected and anisotropic 2PCF wit simple and scale-compact transformations on the 2PCF. These transformation matrices are modeled after the Cholesky decomposition and the symmetric square root of the Fishder matrix. Using mock catalogues, show that the transformed projected and anisotropic 2PCF recover the same structure as the original 2PCF, while producing largely decor related error bars. Specifically, propose simple Cholesky based transformation matrices that suppress the off-diagonal covariances on the projected 2PCF by ~95% and that on the anisotropic 2PCF by ~87%. These transformations also serve as highly regularized models of the Fisher matrix, compressing the degrees of freedom so that one can fit for the Fisher matrix with a much smaller number of mocks.
1901.05289
On the tension between large scale structures and cosmic microwave background
Douspis, Salvati, Aghanim
Recent years have brought strong observational evidences for the standard LCDM cosmo model. CMB anisotropy and LSS probes do not favor any extensions of the standard model. Nevertheless, in this framework, the preferred cosmo parameters may differ from probe to probe, from experiment to experiment. This is the well known case of the tension between CMB and SZ GC from Planck. In 2013, the Planck team has shown that the preferred matter content Omega_m and density fluctuation PS amplitude sigma8 the two main cosmo params probed by the galaxy cluster number count ,are different n the CMB analyses and in the SZ cluster analyses at more than 2 sigmas (a result confirmed in subsequent analyses). Present the results of the new analysis using more recent measurements of the CMB, SZ clusters and SZ PS of 2016 and show that the tension on (Omega_m, sigma8) is mostly releaved. The lower value of the deionization optical depth and thus of sigma8 in the recent Planck studies is the main reason. Also show that basic extensions the standard model (massive neutrinos or non-lambda DE) do not help improving the agreement between the probes. In order to fully reconcile SZ clusters with CMB best model, the mass of the galaxy clusters should be 40% lower than derived from hydrostatic equilibrium estimates. While current numerical simulation and WL measurements agree for a mass bias of 20%, investigations are still going on to explain such disagreement on the mass bias. Show that considering a mass bias evolving with redshift or mass does not help in eliminating the discrepancy.
1901.05505
Testing emergent gravity on galaxy cluster scales
Tamosiunas, et al
Verlinde's theory of EG describes gravity as an emergent phenomenon rather than a fundamental source. Applying this reasoning de Sitter space leads to gravity behaving differently on galaxy and galaxy cluster scales; this excess gravity might offer an alternative to DM. Here, test these ideas using the data from the Coma cluster and from 58 stacked galaxy clusters. The X-ray surface brightness measurements of the clusters at 0.1<z<1.2 along with the WL data are used to test the theory. Find that the simultaneous EG fits of the X-ray and WL data sets are significantly worse than those provided by GR (with cold dark matter). For the Coma cluster, the predictions from Emergent Gravity and GR agree in the range of 250-700 Mpc, while at around 1 Mpc scales, EG total mass predictions are larger by a factor of 2. For the cluster stack the predictions are only in good agreement at around the 1-2 Mpc scales, white for r >~10 Mpc EG is in strong tension with the data. According to the Bayesian information criterion analysis, GR is preferred in all tested datasets; however, also discuss possible modifications of EG that greatly relax the tension with the data.
1901.05973
A second galaxy missing dark matter in the NGC1052 group
van Dokkum, et al
The ultra-diffuse galaxy NGC1052-DF2 has a very low velocity dispersion, indicating that it has little or no dark matter. Here, report the discovery of a second galaxy in this class, residing in the same group. NGC10052-DF4 closely resembles DF2 in terms of its size, surface brightness, and morphology; has a similar distance of D=19.9±2.8 Mpc; and has a similar population of luminous globular clusters extending out to 7 kpc from the center of the galaxy. Accurate radial velocities of seven clusters were obtained with the Low Resolution Imaging Spectrograph on the Keck I telescope. Their median velocity is <v>=1445 km/s, close to the central velocity of 22 galaxies in the NGC1052 group. The rms spread of the observed velocities is very small at sigma_obs=5.8 km/s. Taking observational uncertainties into account, determine an intrinsic velocity dispersion of sigma_intr=4.2+4.4-2.2 km/s, consistent with the expected value from the stars alone (sigma_stars~7 km/s) and lower than expected from a standard NFW halo (sigma_halo~30 km/s). Conclude that NGC1052-DF2 is not an isolated case but that a class of such objects exists. The origin of these large, faint galaxies with an excess of luminous globular clusters ad an apparent lack of DM is, at present, not understood.
1901.05978
Using the technical frontier: from overwhelmingly large data sets to machine learning
Acquaviva
This paper summarizes thoughts, given in an invited review at the IAU symposium 341 "Challenges in Panchromatic Galaxy Modeling with Next Generation Facilities", about how machine learning methods can help us solve some of the big data problems associated with current and upcoming large galaxy surveys.
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