Wednesday Colloquium


"Eclipsing binaries as a unique tool for measuring the Hubble Constant with a precision of 1 %"

Grzegorz Pietrzyński (Astronomical Observatory, Warsaw University)


"Cosmology with the largest all-sky surveys: 2MPZ, WISE and beyond"

Maciej Bilicki (Department of Astronomy, University of Cape Town and Kepler Institute of Astronomy, University of Zielona Góra)

Our view of the low-redshift Cosmic Web has been revolutionized by various wide-angle galaxy redshift surveys such as the Sloan Digital Sky Survey. However, the trade-off between depth and sky coverage limits a systematic three-dimensional account of the entire sky beyond the Local Volume. In order to reliably map the Universe to cosmologically significant depths over the whole sky, one must draw on multiwavelength datasets and state-of-the-art photometric redshift techniques. I have been leading a dedicated programme of employing the largest photometric all-sky surveys – 2MASS, WISE and SuperCOSMOS – to obtain accurate redshift estimates of millions of galaxies. The first outcome of these efforts – the 2MASS Photometric Redshift catalogue (2MPZ) – was publicly released in 2013 and includes almost 1 million galaxies with a median depth over 300 Mpc. In this talk I will detail how this catalogue was constructed and how using the WISE mid-infrared survey together with SuperCOSMOS optical data allows us to push to depths over 1 Gpc on unprecedented angular scales. These photometric redshift samples, with about 20 million sources in total, provide access to volumes large enough to verify observationally the Copernican Principle of universal homogeneity and isotropy, as well as to study various properties of dark energy and dark matter through cross-correlations with other data such as the cosmic microwave or gamma-ray background.


"Stellar Populations and Kinematics of the Fornax dSph Galaxy"

Andrés del Pino (NCAC, Warsaw)

We present a comprehensive and detailed study of the stellar populations of the Fornax dwarf spheroidal galaxy. We will show its detailed star formation history (SFH), together with the spatial distribution and the chemo-dynamics of its stellar populations. This work is based on the deepest ground based Color-Magnitude Diagrams up to date, obtained from FORS1@VLT photometry (I~25); wide field photometry (~2 square degrees, V ~ 24), and spectroscopy of more than 2500 stars. Our results show that Fornax is a complex system. It has a long standing star formation from ~12 Gyr ago to ~0.5 Gyr or even more recent. Young populations concentrate in the central region of the galaxy, where the most intense star formation burst occurred ~8 Gyr ago. This was delayed ~2 Gyr with respect to the main peak of star formation. The spatial distribution of the stellar populations is irregular and only in the case of older stars it follows an elliptical distribution. We confirm the detection of shell-like structures and clumps of stars not aligned with the optical major-axis of the system stars younger than 3 Gyr. The later strongly suggest accretion of material with different angular momentum. We also detect a non negligible rotation signal (~12 kms -1) about the main optical axes of the galaxy as an important change in the preferred rotation direction of the galaxy at 8 Gyr (z~1). These results lead us to propose an scenario in which Fornax had suffered a major merger at z~1.