Recent Talks

The growth of astrophysical understanding typically results fromthe constructive interplay between theoretical ideas andobservational insights, with each mode of exploration drivingprogress at different times. The result is invariably a morecomplicated but richer picture of the phenomenon than initiallyenvisaged, as well as deeper appreciation of the behavior ofcomplex systems.In this talk, I will use the development of our understanding ofthe structure of outflows from massive O- and B-type stars toillustrate this collaborative “dance”. Starting from the smooth,spherically symmetric models for radiatively driven windsdeveloped in the late 1960s, our view of these outflows hasevolved to include the growth of inhomogeneities on a variety ofspatial scales. Explanations for the origin of this structure havein turn prompted the realization that non-radiative processesmust also shape the emergence of the wind from the stellarphotosphere. Consequently, O- and B-type stars are morecomplicated – and interesting! – objects than often thought.While many fruitful avenues of research remain to be explored,the current paradigm provides a (mostly) self-consistent pictureof massive stars and their outflows.

TBD

The bimodal distribution of red and blue galaxies can often be linked through a quenching mechanism that can attenuate the active star forming galaxies into passive ones. Both environment and the stellar mass play an important role in this transition. The ram pressure stripping (RPS) is an important environmental mechanism in dense environments that can severely change the properties and morphology of galaxies. The most extreme cases of galaxies undergoing RPS are known as jellyfish galaxies. Studying this transitioning piece is crucial to improve our understanding of the evolutionary path of galaxies and how quenching succeeds in galaxy clusters. However, jellyfish galaxies are not well characterised morphologically and finding them is still a complex task based mainly on visual inspection. We present the results of a comprehensive study on the properties of a large sample of jellyfish candidates in the multi-cluster system A901/2. We find evidence that the multi-cluster is triggering the effects of RPS in preferential regions in the system and that these galaxies show an enhancement in their star formation rates. We also use the software Morfometryka in order to analyse the unique morphometric features in jellyfish galaxies providing a better comprehension of their physical state and future. This can help unravel the physical processes behind such extreme morphologies as well as helping to automatise the search for jellyfish galaxy candidates in large surveys.

The collapse of the core and the associated supernova explosion mark the end of life of most massive stars, but the mechanism of explosion is poorly understood and perhaps even unknown. Some of its puzzling features were recently observed in the statistics of supernova progenitors, explosion energies, nickel yields, and in the remnant neutron star and black hole mass functions. I will describe my theoretical studies of the supernova explosion mechanism, its dependence on the progenitor star structure, and the connection with observables. I will argue that successful explosions are intertwined with failures in a complex but well-defined pattern that is tied to the pre-collapse structure of the progenitor star. I will also present a new method to extract the supernova parameters from light curves and expansion velocities, and illustrate how to constrain the explosion mechanism in the future.

Despite being some of the most abundant elements in the  Universe the determination and understanding of the chemical evolution  of C and N is still very uncertain.  One of the main limitations in understanding chemical evolution of C and N is the fact that C and N are altered as during the first dredge-up on the red giant branch.   We present old red giants at various metallicities and luminosities in a sample that is more than 100 times larger than the seminal work of Gratton et al. 2000. Using this we can see the impact of the first dredge-up as well as the on set of "extra" mixing at the bump in the luminosity function for giants more metal-poor than [Fe/H] < -0.4. These observations can be used to constrain future models of mixing.    At a fixed metallicity younger stars have a stronger mixing response during dredge-up.   This fact allows up to infer ages from the first dredge-up [C/N] ratio.   We demonstrate that we are able to interpret the DR14 [C/N]-[Fe/H] abundance distributions as trends in age-[Fe/H] space. Our results show that an anti-correlation between age and metallicity, which is predicted by simple chemical evolution models, is not present at any Galactic zone. Stars far from the plane (|Z| > 1 kpc) exhibit a radial gradient in [C/N]. The [C/N] dispersion increases toward the plane.  We measure a disk metallicity gradient for the youngest stars from 6 kpc to 12 kpc, which is in agreement with the gradient found from other surveys.  Older stars exhibit a flatter gradient, which is predicted by simulations in which stars migrate from their birth radii. We also find that radial migration is a plausible explanation for the observed upturn of the [C/N]-[Fe/H] abundance trends in the outer Galaxy, where the metal-rich stars are relatively enhanced in [C/N].

Thanks to its unique capabilities, the MUSE integral field spectrograph at ESO VLT has given us new insight of the Universe at high redshift. In this talk I will review some breakthrough in the observation of the Hubble Ultra Deep field with MUSE including the discovery of a new population of faint galaxies without HST counterpart in the UDF and the ubiquitous presence of extended Lyman-alpha haloes around galaxies.

In the past 10-15 years our view of AGN has significantly evolved thanks to the combination of new observations and models. X-ray, infrared and sub-mm data have been crucial to peer into the inner region of AGN and study the properties of the tori, circum-nuclear disks and nuclear outflows. In this talk I will summarize our current view of nuclear obscuration in AGN, focusing on the variations of the torus properties with gas phase. I will also present preliminary results from a new project aimed to characterize nuclear outflows in a sample of nearby quasars and study their impact in the stellar populations, on-going star formation and molecular gas reservoirs of the galaxies.

A young just married couple of Astrophysicist decided going to Kenya for they honeymoon. There, they meet Dr. Dismas Simiyu at Meru University, in Meru town, 240 km north from Nairobi. All of them together organised an Astrophysics Workshop in order to introduce both students and staff, into the Astrophysics and Computer Programming word. Follow the adventures in Kenya of this two young Astrophysicists next Thursday in the IAC seminar!