Radio observations of water maser emission in Keplerian rotation around the black hole in galaxy NGC4258 allow the determination of both the black hole mass and a geometrical distance to the host galaxy. The former quantity can be compared to the mass and velocity dispersion of the host's galactic bulge as measured by NIR and optical observation to see if it fits the established Black Hole - Bulge Mass correlation. The existence of this correlation strongly suggests an intimate link between star-formation and black hole growth in the early universe.
The water maser determined distance to this galaxy is also important for calibrating Cepheid variable star distance estimates and hence a vital step on the cosmic distance ladder.
In this project students will use Onsala 20m telescope observations to determine the rate of acceleration of water maser features and reduce archival VLBI data to determine the maser disk radius and structure; these observations together give the black hole mass and source distance. NIR imaging optical spectroscopy observations with NOT will be used to determine galactic bulge properties to compare with the black hole properties.
The Nobel prize in Physics 2006 was given to Dr. John Mather and Prof. George Smooth for their detection of the very first structures in the universe. The measurements were taken by a NASA-funded satellite called COBE (COsmic Background Explorer), and in particular by the Differential Microwave Radiometer (DMR) instrument, which mapped the CMB sky at 31, 53 and 90 GHz with an angular resolution of 7 degrees.
In this project, you will repeat the 4-year COBE-DMR likelihood analysis, and estimate the amplitude of the initial perturbations. If you only had been 20 years earlier obtaining this result, this would have won you a Nobel prize instead of Mather and Smooth!
Most quasars are found using various colour-selections in optical bands (as an example this is how quasars are found in the SDSS survey). An interesting question is how many quasars we miss in these optically selected surveys.
In this project we will perform ALFOSC spectroscopy of a number of candidate dust reddened quasars selected using near-infrared colour-selection. If possible we can also study the most dust obscured quasars we find using the Onsala radio telescope.
The Cosmic Microwave Background (CMB) is one of the strongest pillars of the Big Bang theory. The CMB fills up the entire sky and is the relic of the epoch when matter and light decoupled at a redshift ~1100, when the Universe was about 3000 K. With the expansion of the Universe, the CMB photons have cooled down to 2.73 K at present day.
Measurements of the CMB temperature at high redshift allows us to trace the evolution of the CMB temperature with time (i.e. with redshift). This provides constraints on cosmological models.
The goal of this project is to determine the temperature of the Cosmic Microwave Background at a redshift z=0.89. For this, you will use molecules seen in absorption in front of a background quasar and perform multi-transition excitation analysis.
The standard cosmological model is based on the assumption that about 95% of the total energy density of the Universe consists of dark matter and dark energy. While successful on very large scales, the model is still to be tested on relatively smaller scales. Cosmological simulations in conjunction with observations provided by galaxy surveys are today one of the main tools used to perform these tests. On the one hand, simulations give the ability to make theoretical predictions about individual astrophysical objects in the non-linear regime. On the other hand, the increasing amount of high-quality data from the existing and upcoming galaxy surveys provides enough statistical power to verify these predictions.
Clusters of galaxies, as the largest known gravitationally bound objects in the Universe, are of particular interest in this regard. As their dynamics are not dominated by baryonic physics, they can be modeled in a much simpler way compared to individual galaxies and thus, predictions can be obtained with much simpler calculations. Two particularly interesting properties of galaxy clusters are their mass and velocity dispersion distributions, which can be used as sensitive probes of cosmological parameters for a given model.
In this project you will take the first step in using galaxy clusters to test the standard cosmological model by obtaining the distribution of their velocity dispersion both from theoretical simulations of structure formation and from real data provided by the Sloan Digital Sky Survey (SDSS). The comparison between the results of the two approaches is a starting point for more sophisticated tests based for instance on the statistical estimations of the cosmological parameters. In addition, you will learn how an N-body simulation code works in practice and how one can read particularly interesting data from huge astrophysical data sets such as the SDSS.