Found 217 talks archived in Galaxies

Understanding the stellar initial mass function (IMF) is a key aspect to obtain a complete picture of galaxy formation and evolution. In the past years, we have carried out a systematic census of the IMF in the unresolved stellar populations of (massive) early-type galaxies (ETGs), using optical and NIR spectroscopy from different surveys (e.g.  SDSS, CALIFA) and dedicated observing programmes (OSIRIS@GTC, XSHOOTER@VLT).  I will present results on a non-universal IMF in ETGs - pointing to an excess of low-mass stars in high-, relative to low-, mass galaxies - and current constraints on the physical driver behind the IMF variations.

Models of galaxy formation predict that gas accretion from the cosmic web is a primary driver of star formation over cosmic history. Except in very dense environments where galaxy mergers are also important, model galaxies feed from cold streams of gas from the web that penetrate their dark matter haloes. Although these predictions are unambiguous, the observational support has been indirect so far. I will report spectroscopic evidence for this process in extremely metal-poor galaxies (XMPs) of the local Universe, taking the form of localized starbursts associated with gas having low metallicity. Because gas mixes azimuthally in a rotation timescale (a few hundred Myr),  the observed metallicity inhomogeneities are only possible if the metal-poor gas producing stars fell onto the disk recently. I will analyze several possibilities for the origin of the metal-poor gas, favoring the metal-poor gas infall predicted by numerical models. In addition, I will show model galaxies in cosmological numerical simulations with starbursts of low metallicity like to the star-forming regions in XMPs.

The realism of hydrodynamical simulations of the formation and evolution of galaxies has improved considerably in recent years. I will try to give some insight into the reasons behind this success, focusing in particular on the importance of subgrid models and the associated limitations. I will also present recent results from the cosmological EAGLE simulations as well as from higher-resolution simulations of individual galaxies.

The epoch of reionization has been predicted to leave an imprint on the star formation histories of dwarf galaxies. I will briefly review theoretical ideas and observational constraints on reionization. I will then discuss the predicted effects on the evolution of dwarf galaxies.
This will be followed by a discussion of tests using star formation histories of nearby dwarf galaxies.

The World Health Organization’s International Agency for Research on Cancer (IARC) on May 31st 2011 classified mobile phone use and other radio-frequency electromagnetic fields as a possible carcinogen (group 2B). This is neither new research nor at odds with previous findings. It does, however, underline the need for further research and precautionary measures to be taken now.
In continuation with the microwave theme the tone is set for a more serious talk about the everyday use of microwave devices and in particular mobile phones. The information that Roger will pass on about the dangers of microwave devices (in a semi-digested state) is important for everyone and will probably be cause for much debate.
There are many opinions filling the internet on this subject. It really is difficult to get a fact based opinion. Either you believe that microwaves are so dangerous we should not be using them at all or you can be led to believe that there is No risk at all.
In this talk Dr Roger Hoyland will present the facts and helpful information that he has found from the most up-to-date research results. He will attempt to give a more rational view of this hot topic!

In this talk I will present my view on what we know and what we don't know about the so-called secular evolution processes in galaxies. I will focus on the processes that lead to the building of main stellar components in the centre of disc galaxies, and explore how these processes fit in the current cosmological paradigm of galaxy formation and evolution. I will also make an attempt at clarifying misconceptions and discussing outstanding open questions.

The presence of Dark Matter (DM) is required in the universe regulated by the standard general relativistic theory of gravitation. The nature of DM is however still elusive to any experimental search. We discuss here the process of accumulation of evidence for the presence of DM in the universe, the astrophysical constraints for the leading DM scenarios that can be obtained through a multi-frequency analysis of cosmic structures on large scales, and a new strategy related to the search for the nature of the DM with the Square Kilometer Array (SKA).

Major tests of cosmological and galaxy formation models can be constructed through dynamical and structural parameters of galaxies. Towards this end, we present the SHIVir (Spectroscopic and H-band Imaging of Virgo cluster galaxies) survey, which provides dynamical information and stellar population diagnostics for hundreds of galaxies. We construct scaling relations and dynamical profiles within the optical radius of most galaxies, paying close attention to the baryon-to-dark matter transition region and selected metrics which reduce scatter in fundamental scaling relations. Salient results include bimodal mass and surface brightness distributions for Virgo galaxies, a possible bifurcation in the stellar-to-halo mass relation for low-mass galaxies, and the need for deep velocity dispersions to extract meaningful science. Once complete, ours should be the most extensive mass catalogue ever assembled for a galaxy cluster.

The fueling of black holes occurring in active galactic nuclei (AGN) is fundamental to the evolution of galaxies. AGN themselves are largely explained in the context of a unified theory, by which a geometrically and optically thick torus of gas and dust obscures the AGN central engine. The torus intercepts a substantial amount of flux from the central engine and and reradiates it in the infrared. In this talk I will present our CanariCam ESO/GTC large programme which is aimed at understanding the properties of the obscuring material around AGN, including the torus, and the role of nuclear (< 100 pc) starbursts in feeding and/or obscuring AGNs. The CanariCam nearly diffraction limited observations (median 0.3arcsecond), which were finished recently, include imaging and spectroscopy of 45 local AGN, and polarimetry for selected AGN. I will first present an overview of the spectroscopic properties of the sample. Then I will discuss results on the torus properties of different types of AGN from the modelling of the unresolved infrared emission with the CLUMPY torus models. Finally I will also show that we can use the 11.3micron PAH feature to trace star formation activity in the nuclear regions of AGN.

Stars, the most fundamental building blocks of galaxies, are born within the clouds of gas and dust and and during their lives they enrich the gas and the interstellar medium (ISM) with heavy elements, magnetic fields, and cosmic rays all of which strongly affects the subsequent formation of stars and their host galaxy. To understand the evolution and appearance of galaxies it is therefore crucial to study the interplay between stars and the ISM. Putting together the infrared, submm, and radio observations of nearby galaxies, we have studied the physical properties of the dusty and magnetized ISM in nearby galaxies to address the pressing questions: How the ISM components are inter-connected and how their physical properties change in different galactic environments e.g. star forming regions, spiral arms, nucleus and outer disks? In what extent the star formation influences the physical properties and structure of the ISM in a galaxy? I will show the effect of star formation on the dust emission properties, interstellar magnetic fields, cosmic ray electron energy index and further discuss the important factors in the energy balance of the ISM at different scales in M33, M31, NGC6946, and other nearby galaxies.