Friday. Monday.
1601.03391
Galaxy and mass assembly (GAMA): stellar mass growth of spiral galaxies in the cosmic web
Alpaslan et al
Look for correlated changes in stellar mass and SFR along filaments in the cosmic web by examining the stellar masses and UV-derived SFR of 1799 ungrouped and unpaired spiral galaxies that reside in filaments. Devise multiple distance metrics to characterize the complex geometry of filaments, and find that galaxies closer to the cylindrical centre of a filament have higher stellar masses than their counterparts near the periphery of filaments, on the edges of voids. In addition, these peripheral spiral galaxies have higher sSFR at a given mass. Complementing the sample of filament spiral galaxies with spiral galaxies in tendrils and voids, find that the average SFR of these objects in different large scale environments are similar to each other with the primary discriminant in SFR being stellar mass, in line with previous works. However, the distributions of SFRs are found to vary with LS environment. Results thus suggest a model in which in addition to stellar mass as the primary discriminant, the LS environment is imprinted in the SFR as a second order effect. Furthermore, the detailed results for filament galaxies suggest a model in which gas accretion from voids onto filaments is primarily in an orthogonal direction. Overall, find the results to be in line with theoretical expectations of the thermodynamic properties of the IGM in different LS environments.
1601.03455
Globular clusters as cradles of life and advanced civilizations
Stefano, Ray
Globular clusters are ancient stellar populations with no SF or core-collapse SNe. Several lines of evidence suggest that globular clusters are rich in planets. If so, and if advanced civilizations can develop there, then the distances between these civilizations and other stars would be far smaller than typical distances between stars in the Galactic disk. The relative proximity would facilitate interstellar communication and travel. However, the vary proximity that promotes interstellar travel also beings danger, wince stellar interactions can destroy planetary systems. However, by molding globular clusters and their stellar populations, find that large regions of many globular clusters can be thought of as "sweet spots" where habitable-zone planetary orbits can be stable for long times. Also compute the ambient densities and fluxes in the regions within which habitable-zone planets can survive. Globular clusters are among the best targets for searches for extraterrestrial intelligence (SETI). Use the Drake equation to compare globular clusters to the Galactic disk, in terms of the likelihood of housing advanced communicating civilizations. Also consider free-floating planets, since wide-orbit planets can be ejected and travel freely through the clusters. A civilization spawned in a globular cluster may have opportunities to establish self-sustaining outposts, thereby reducing the probability that a single catastrophic event will destroy the civilization or its descendants. Although individual civilizations within a cluster may follow different evolutionary paths, or even be destroyed, the cluster may always host some advanced civilization, once a small number of them have managed to jump across interstellar space.
1601.03740
Turnaround overdensity as cosmological observable: the case for a local measurement of $\Lambda$
Tanoglidis et al
Demonstrate that, in the context of the LCDM model, it is in principle possible to measure the value of the cosmological constant by tracing, across cosmic time, the evolution of the turnaround radius of cosmic structures. The novelty of the presented method is that it is local, in the sense that it uses the effect of the cosmo constant on the relatively short scales of cosmic structures and not on the dynamics of the universe at its largest scales. In this way, it can provide an important consistency check for the standard cosmological model and can give signs of new physics, beyond LCDM.
1601.03741
Probing dark energy via galaxy cluster outskirts
Morandi, Sun
Present a Bayesian approach to combine Planck data and the X-ray physical properties of the intracluster medium in the virialization region of a sample of 320 galaxy clusters (0.056<z<1.24, kT>3 keV) observed with Chandra. Exploit the high-level of similarity of the emission measure in the cluster outskirts as cosmo proxy. The cosmo parameters are thus constrained assuming that the emission measure profiles at different redshift are weakly self-similar, that is their shape is universal, explicitly allowing for temperature and redshift dependences of the gas fraction. This cosmo test, in combination with Planck+SNIa data, allows putting a tight constraint on the DE models. For a constant-w model, have w=-1.010±0.030 and Omegam=0.311±0.014, while for a time-evolving EoS DE w(z), have Omega_m=0.308±).017, w0=-0.993±0.046 and wa=-0.123±0.400. Constraints on the cosmology are further improved by adding priors on the gas fraction evolution from hydrodynamic sims. Current data favor the cosmo constant with w=-1, with no evidence for dynamic DE. Checked that the method is robust towards different sources of systematics, including background modeling, outlier measurements, selection effects, inhomogeneities of the gas distribution and cosmic filaments. Also provided for the first time constraints on which definition of cluster boundary radius is more tenable, namely based on a fixed overdensity with respect to the critical density of the Universe. This novel cosmo test has the capacity to provide a generational leap forward in the understanding of the EoS of DE.
1601.03947
SKA weak lensing I: cosmological forecasts and the power of radio-optical cross-correlations
Harrison Camera, Zuntz, Brown
Construct forecasts for cosmo prometter constraints from WL surveys involving SKA. Considering matter content, DE and modified gravity parameters, show that the first phase of the SKA can be competitive with other Stage III experiments such as DES, and full SKA can potentially form tighter constraints than Stage IV optical WL experiments, such as those that will be constructed with LSST or Euclid-like facilities. Using WL alone, going from SKA1 to SKA2 represents improvements by factors of ~10 in matter, ~8 in DE and ~5 in modified gravity parameters. Also show, for the first time, the powerful result that comparably tight constrains (within ~5%) for both Stage III and IV experiments, can be gained from cross-correlating shear maps between the optical and radio wavebands, a process which will also eliminate a number of potential sources of systematic errors which can otherwise greatly limit the utility of WL cosmology.
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