Sep 5

"A Systematic Approach to Studying Galaxy Cluster Formation in the Early Universe"
Yi-Kuan Chiang, University of Texas at Austin

Observations of massive galaxy clusters have shown that the overall cluster properties evolved very little since z < 1-2. Stellar populations of the cluster red sequence are old, with implied formation redshifts of z ~ 2-4. To understand how these galaxy clusters form and how their overdense environments influence galaxy evolution, it is crucial to probe the epoch of cluster formation at 2 < z < 5. With the ultimate goal of building a roadmap for interpreting future surveys like HETDEX, we are performing a statistical, simulations-assisted study of (proto-)cluster evolution. We use the LCDM predictions for dark matter and accurate semi-analytic models for galaxies to quantify the relations between galaxy clusters and overdensities in the distributions of the dark matter, halos, and galaxies as a function of, e.g., redshift and galaxy type. We model the selection and projection effects as found in observational surveys even more accurately by using lightcones and simulated data. We use our simulations predictions to interpret observations of a range of structures found at z > 2, and to make feasibility predictions for future experiments.

Nov 7

"A Systematic Approach to Studying Galaxy Cluster Formation in the Early Universe"
Chiara Spiniello, Rijksuniversiteit, Groningen, Netherlands

In this talk I present the first results from The X-Shooter Lens Survey (X-LENS).

The X-Shooter Lens Survey (X-LENS) aims to study the internal structure and mass profiles of a sample of massive early type lens galaxies (ETGs) with Sigma > 250 km/s using the VLT X-Shooter spectrograph. The combination of gravitational lensing, stellar kinematics and spectroscopic tracers of low-mass stars has proven to be a powerful tool to disentangle between the luminous and dark matter. Separate the two mass components and understand their interaction is a "conditio-sine-qua-non" to study their impact on galaxies assembly and evolution in the hierarchical galaxy formation framework. In this context, characterizing the slope of the IMF and assess whether it is universal or if it depends on galaxy mass, on epoch of formation or on local density, is critical.

Recent observations indicate that the internal dark-matter fraction increases rapidly with galaxy mass in very massive ETGs, although some hints for a varying initial mass function (IMF) have also been suggested where the low-mass end of the stellar IMF steepens with galaxy mass.

With X-LENS we are able, for the first time ever, to probe directly the structure and dynamical evolution of ETGs and simultaneously to constrain the low mass end of the IMF normalization and slope. By combining precise lensing and dynamical constraints on the mass distribution (few % accuracy) with high signal-to-noise spectroscopy in the entire rest-frame visible to the NIR, and mass-to-light ratios with 10-20% absolute accuracy, we are able to obtain the most precise dark-matter mass fractions to date. I will present the first X-LENS cases showing the power of our survey for understanding the interplay of stellar and dark mass in massive ETGs focusing on constrain the low-mass end of the IMF directly from galaxy spectra.

Nov 28

"Scalar Fields as Dark Matter in the Universe"
Tonatiuh Matos, Department of Physics, CINVESTAV

In the last time the cold dark matter (CDM) model faces some difficulties to describe all the properties of nearby galaxies that can be observed in great detail as well as that it has some problems in the mechanism by which matter is more rapidly gathered into large-scale structure such as galaxies and clusters of galaxies. In this talk we review the scalar field dark matter (SFDM) model, which proposes that the galactic haloes form by condensation of a scalar field (SF) very early in the Universe, i.e., in this model the haloes of galaxies are astronomical Bose-Einstein Condensate drops of SF. On the other hand, large-scale structures like clusters or superclusters of galaxies form similar to the CDM model, by hierarchy, thus all the predictions of the CDM model at cosmological scales are reproduced by SFDM. This model predicts that all galaxy haloes must be very similar and exist for higher redshifts than in the CDM model.