Seminarium Zakładu Astrofizyki

A new graph-theory based FOF group finder and its application to the updated 2MRS

We present the galaxy group catalog for the newly completed 2MASS Redshift Survey up to a magnitude limit of K < 11.75. Consisting of ~ 45 000 redshifts, including 1 041 previously unpublished
redshifts mostly distributed along the Zone of Avoidance. The galaxy group catalog is generated by using a novel, graph theory based, modified version of the friends-of-friends algorithm. The results and

Co-evolution of galaxies and the multi-scale cosmic web at high redshift: from predictions to observations

The multi-scale cosmic web is the environment in which galaxies form and evolve. Gas flows along walls and filaments, penetrates within dark matter haloes and brings to the galaxies both angular momentum and fuel for star formation. Recent observational studies at low and intermediate redshifts have shown evidence that the cosmic web environment (e.g. proximity to cosmic filaments, or number of filaments connected to the galaxies sitting at the “nodes”) modulates galaxy mass assembly and morphology beyond the mere effect of halo mass and local density.

Knocking on giants’ doors: the evolution of dust-to-stellar mass ratio in distant galaxies

Recent advent of millimetre arrays such as ALMA and NOEMA helps unveiling the long redshift tail (2<z<7) of dusty galaxies, transforming our view of massive star-formation in the very distant Universe. Despite such progress, the dust-to-stellar mass ratio, one of the most important quantities, remains poorly constrained, which prevents us from knowing the complexity of physical processes involved in the production of dust, metals and stars in galaxy evolution.

Star formation and black hole growth: driven by mergers, or not?

Most massive galaxies host a supermassive black hole (SMBH) at their centre. When the central SMBH goes through a phase of rapid accretion, it is known as an Active Galactic Nucleus (Nuclei for plural - AGN). Cold, dense gas is the main fuel that is consumed in feeding the SMBH leading to its growth. Mergers between gas-rich galaxies constitute  a potential mechanism for transferring cold gas to the central sub-kpc regions of galaxies.

Numerical studies of Neutron Star atmospheres

Neutron stars are very complicated to study due to the extreme conditions occurring there. Mean densities are comparable to the atomic density. The magnetic fields strength on the surface ranges from 104 up to 1011 Tesla. Gravity is strong enough that it acts as a gravitational lens and bends the radiation emitted by the neutron star that the areas normally invisible become visible. The interaction between matter and radiation is very complicated. We must consider scattering processes, absorption, emission and illumination.

News from O3, LIGO-Virgo detector network's third observing run

Currently ongoing observing run O3 (1st April 2019 - 30th April 2020) of three interferometric detectors (LIGO Livingston and Hanford, Virgo) surveys the largest volume of the Universe till date, and has already delivered more than 40 significant signal candidates. Here I will discuss the current status of the detectors, talk about the interesting signal cases (in particular the recently published GW190425), as well as plans for the future.

Galaxies and their dark matter halos

In the standard cosmological model (ΛCDM) baryonic components of galaxies, in form of stars, gas and dust, are thought to be embedded inside the dark matter (DM) haloes. This dark matter component is dominant and as such drives the evolution of the large-scale structure of the Universe.

Unfortunately, as for now, we can't directly observe dark matter, and we have to relay on models/simulations describing dark matter halo shapes and distribution. These models are based upon assumptions and some of them are known to be oversimplified.

Identifying galaxy mergers and their effect on star formation rates

Galaxy mergers underpin our current understanding of how galaxies grow and evolve. In the current CDM models, dark matter halos merge hierarchically resulting in the collision between their baryonic counterparts. During these mergers the galaxies are disrupted, with the tidal forces twisting and distorting them, moving the stars, dust and gas and changing morphologies. This movement of material can also trigger extreme events, with gas pushed into the centre of the galaxies triggering active galactic nuclei and the compression of the gas triggering periods of intense star formation.