Wednesday Colloquium


"Galaxy clustering using photometric redshifts"

Andrzej Sołtan (NCAC, Warsaw)

We investigated the evolution of the galaxy two point correlation function (CF) over a wide redshift range, 0.2 < z < 3. For the first time the systematic analysis covers the redshifts above 1 - 1.5. The catalogue of ~250000 galaxies with i+ < 25 and known photometric redshifts in the Subaru Deep field is used. First, the 2D CF is determined for several distance bins. Calculations are based on the quantitative differences between the surface distributions of galaxy pairs with comparable and distinctly different photometric redshifts. The power law approximation for the CF is used. Then, the 3D functions for all the selected luminosities and distances are calculated. The power-law parameters of the CF, the slope and the correlation length, are determined. Both parameters do not show strong variations over the whole investigated redshift range. The slope of the luminous galaxies appears to be consistently steeper than that for the fainter ones. The linear bias factor, b(z), grows systematically with redshift; assuming the local normalization b(0) = 1.1-1.2, the bias reaches 3 - 3.5 at the high redshift limit.


"Hyperons in neutron stars"

Morgane Fortin (NCAC, Warsaw)

The existence two-solar-mass neutron stars (NSs) puts strong constraints on the properties of matter at high density and in particular questions the existence of hyperons (baryons containing at least one strange quark) in the core of massive NSs. I will present ongoing projects which examine the consequences of the presence of hyperons inside NSs on the macrophysical properties of NSs (radius, thermal evolution, ...) and on the nuclear properties of matter. Their consistency with astrophysical observations and nuclear experiments will be assessed.


"Accretion Disks, Elevated"

Mitch Begelman (JILA, Boulder, CO)

In addition to driving the turbulence that transfers angular momentum and permits accretion disks to accrete, the magnetorotational instability also creates a strong, highly organized magnetic field parallel to the disk plane. Although this field is buoyant and continuously escapes, under certain conditions it can build up to the point where it dominates other forms of pressure in supporting the disk vertically against gravity. I will discuss the properties of such "magnetically elevated" disks and show that their existence can resolve several longstanding problems in accretion disk theory.


"Blue stragglers in globular clusters"

Michał Różyczka (NCAC, Warsaw)

My talk is divided into three parts. The introduction comprises a bit of history, some basic information about blue stragglers (BSs), an outline of procedures employed to select BSs from among cluster members, and an outline of hypotheses proposed to explain their nature. The second part is devoted to correlations between cluster parameters and BSs distribution, and to links these correlations imply between the dynamical evolution of globular clusters and characteristics of BSs population. In the third part the CASE project is briefly introduced, and some of its results are presented (in particular – several detailed portraits of blue stragglers).