Wednesday.
1409.0859
Evolution of central dark matter of early-type galaxies up to z~0.8
Tortora et al
Investigate the evolution of dark and luminous matter in the central regions of ETGs up to z~0.8. Use a spectroscopically selected sample of 154 cluster and field galaxies from the EDisCS survey, covering a wide range in redshifts (z~0.4-0.8), stellar masses (log M*/Msun~10.5-1.5 dex) and velocity dispersions (sigma_*~100-300 km/s). Obtain central DM fractions by determining the dynamical masses from Jeans modeling of galaxy aperture velocity dispersions and the M* from galaxy colors, and compare the results with local samples. Discuss how the correlations of central DM with galaxy size (i.e., the effective radius, Re), M* and sigma* evolve as a function of z, finding clear indications with z can be only partially interpreted as a consequence of the size-redshift evolution. Discuss results within galaxy formation scenarios, and conclude that the growth in size and DM content which is measured within the last 7 Gyr is incompatible with passive evolution, while it is well reproduced in the multiple minor merger scenario. Also discuss the impact of the IMF on the DM inferences and argue that this can be non-universal with the loopback time. In particular, find the Salpeter IMF can better accommodated by low z systems, while producing stellar masses at high-z which are unphysically larger than the estimated dynamical masses (particularly for lower-sigma* systems).
1409.0860
Effects of large-scale environment on the assembly history of central galaxies
Jun, Lee, Yi
Construct DM halo merger trees from N-body sims and calculate the formation and evolution of galaxies using SAM. Confirm earlier results that smaller haloes show a notable difference in formation time with a mild dependence on large-scale environment. However, using SAM, find that on average the growth rate of the stellar mass of central galaxies is largely insensitive to large-scale environment. Although results show that the SFR and the stellar mass of central galaxies in smaller haloes are slightly affected by the assembly bias of haloes, those galaxies are faint, and the difference in the SFR is minute, and therefore it is challenging to detect it in real galaxies given the current observational accuracy. Future galaxy surveys (BigBOSS and LSST) are expected to provide observational data for fainter objects, providing a chance to test model predictions.
1409.0863
A new data compression method and its application to cosmic shear analysis
Asgari, Schneider
Future large scale cosmo surveys will provide huge data sets whose analysis requires efficient data compression. Calculating accurate covariances is extremely challenging with increasing number of statistics used. Introduce a formalism for achieving efficient data compression, based on a local expansion of statistical measures around a fiducial cosmological model. Specifically apply and test this approach for the case of cosmic shear statistics. Demonstrate the performance of the approach, using a Fisher analysis on cosmic shear tomography described in terms of COSEBIs. Show that data compression is highly effective in extracting essentially the full cosmological information from a strongly reduced number of observables. Specifically, the number of statistics needed decreases by at least one order of magnitude relative to the COSEBIs, which already compress the data substantially compared to the shear 2pt correlation functions. The efficiency appears to be affected only slightly if a highly inaccurate covariance is used for defining the compressed statistics, showing the robustness of the method. Conclude that an efficient data compression is achievable and that the number of compressed statistics depends on the number of model parameters. In addition, study how well band powers can be obtained from measuring shear correlation functions over a finite interval of separations. Show the strong limitations on the possibility to construct top-hat filters in Fourier space, for which the real-space analog has a finite support, yielding strong bounds on the accuracy of band power estimates. The error on an estimated band-power is larger for a narrow filter and a smaller angular range which for relevant cases can be as large as 10%.
1409.1028
The population of early-type galaxies: how it evolves with time and how it differed from passive and late-type galaxies
Tamburri et al
Are ETGs morphologically selected differ from a sample of a passive galaxies? How does the relative abundance of galaxies, the number density and the stellar mass density for different morphological types change over the redshift 0.6<z<2.5? From the 1302 galaxies brighter than Ks=22, classify ETGs on the basis of their morphology and the passive galaxies on the basis of their sSFR. Prove how the definition of passive galaxy depends on the IMF adopted in the models and on the assumed sSFR threshold. Find that ETGs cannot be distinguished from the other morphological classes on the basis of their low sSFR, irrespective of the IMF adopted in the models. Using the sample of 1302 galaxies morphologically classified into spheroidal galaxies (ETGs) and not spheroidal galaxies (LTGs), find that their fractions are constant over 0.6<z<2.5 (20-30% ETGs vs 70-80% LTGs). However, at z<1 these fractions change among the population of the most massive (M*>=1e11 Msun) galaxies, with the fraction of massive ETGs rising up to 40% and the fraction of massive LTGs decreasing down to 60%. Moreover, find that the number density and the stellar mass density of the whole population of massive galaxies increase almost by a factor of ~10 between 0.6<z<2.5, with a faster increase of these densities for the ETGs than for the LTGs. Finally, find that the number density of the highest-mass galaxies (M*>3-4e11 Msun) both ETGs and LTGs do not increase since z~2.5, contrary to the lower mass galaxies. This suggests that the population of the most massive galaxies formed at z>2.5-3 and that the assembly of such high-mass galaxies is not effective at lower redshift.
No comments:
Post a Comment