Recent Talks

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 stellar initial mass function (IMF) is usually assumed to be a probability density distribution function. Recent data appear to question this interpretation though, and I will discuss alternative applications and results concerning the possibly true nature of the IMF. Empirical evidence has emerged that the IMF becomes top-heavy in intense star bursts and at low metallicity. Related to the IMF are binary star distribution functions, and these evolve through dynamical processes in embedded star clusters. The insights gained from these considerations lead to a mathematically computable method for calculating stellar populations in galaxies, with possibly important implications for the matter cycle in galaxies. It turns out that the galaxy-wide IMF, the IGIMF, becomes increasingly top-heavy with increasing galaxy-wide star formation rate, while at the same time the binary fraction in the galactic field decreases.

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.

The standard model of cosmology is based on the Friedmann-Robertson-Walker (FRW) metric. Often written in terms of co-moving coordinates, this elegant and highly practical solution to Einstein's equations is based on the Cosmological principal and Weyl's postulate. But not all of the physics behind such symmetries has yet been recognized. We invoke the fact that the co-moving frame also happens to be in free fall to demonstrate that the FRW metric is apparently valid only for a medium with zero active mass. In other words, the application of FRW appears to require an equation-of-state rho+3p = 0, in terms of the total energy density rho and total pressure p. Though the standard model is not framed in these terms, the optimization of its parameters brings it ever closer to this constraint as the precision of the observations continues to improve. For example, the latest high-precision BAO measurements rule out the standard model at better than the 99.34% C.L. if the zero active mass condition is ignored.

 A comprehensive understanding of sub-stellar objects (brown dwarfs and extrasolar giant planets) and their population characteristics (e.g. IMF, formation history) is only possible through the robust interpretation of ultra-cool objects spectroscopy. However, the physics of ultra-cool atmospheres is complicated by a variety of challenging ingredients (dust properties, non-equilibrium chemistry, molecular opacities). Moreover, while hydrogen-burning stars stabilize on the stellar main-sequence, sub-stellar objects continuously cool down (since they lack an internal source of energy) and evolve towards later spectral types. Their atmospheric parameters are a strong function of age. In this talk I will present the spectroscopic analysis of a large sample of L and T dwarfs, complementing the spectroscopic data with astrometry from the PARSEC program, in order to constrain the sub-stellar initial mass function and formation history. I will then describe our new effort to identify and characterize a large sample of benchmark systems, combining Gaia capabilities with large area near-infrared surveys such as UKIDSS, SDSS, and VVV, in order to calibrate effectively the theoretical models.
    

I will talk about our current understanding of globular cluster (GC) formation and what we have yet to learn about them. I will particularly focus on the chemical and dynamical properties of the neglected GC NGC4372, which I studied for the first time with  high-resolution spectroscopic observations.
Its chemical abundances revealed it as a typical representative of the old, metal-poor halo group. More interesting, however, are its structural and kinematic properties as the cluster has an unusually high intrinsic rotation for its metallicity and appears to be rotationally flattened. I will discuss what
rotating GCs tell us about their early evolution.

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.

The Sun is a magnetic star, not as magnetic as some stars, or as it was when it
was younger, but nonetheless magnetic fields dominate and even construct its
atmosphere. There would be no corona without magnetic fields. The surface is
also dappled with small scale magnetic field associated with surface convection
cells, granules and supergranules. But sometimes we also see much larger and
more powerful Active Regions containing sunspots. These are wounds in the
surface of the Sun that allow waves and oscillations in the solar interior and
atmosphere to be coupled much more directly than they usually are. In
particular, they allow the Sun's internal seismology (the p-modes) to drive a
variety of waves through the Active Region atmosphere, and conversely, the
atmospheres to pollute the internal seismology. This makes active region
helioseismology a very challenging field.

The importance of Luminous and Ultraluminous infrared galaxies (U/LIRGs) in the context of the cosmological evolution of the star-formation has been well established in the last decades. They have been detected in large numbers at high-z (z>1) in deep surveys with Spitzer and Herschel, and they seem to be the dominant component to the star formation rate (SFR) density of the Universe beyond z~2. Although rare locally, nearby U/LIRGs are valuable candidates to study extreme cases of compact star-formation and coeval AGN. In particular, the study of local U/LIRGs using near-IR integral field spectroscopic techniques allows us to disentangle the 2D distribution of the gas and the star-formation using high spatial resolution, and characterise dust-enshrouded, spatially-resolved star-forming regions with great amount of detail. In that context, we are carrying on a comprehensive 2D IFS near-IR survey of local 10 LIRGs and 12 ULIRGs, based on VLT-SINFONI observations. I will review different topics on the spatially resolved study of the ISM and the star-formation at different spatial scales. I will focus on the analysis of the multi-phase gas morphology and kinematics, and on the study of the spatially-resolved distribution of the extinction-corrected star-formation rate (SFR) and star-formation rate surface density (ΣSFR). In particular, I will present some recent results on the characterization of individual star-forming regions, in terms of their sizes and Paα luminosities.

The extragalactic background light (EBL) is the second most energetic diffuse background that fills our Universe. It is produced by star formation processes and supermassive black hole accretion over the history of the  Universe. Thus, it contains fundamental information about galaxy evolution and cosmology. Interestingly, it brings together classical astronomy and high energy astrophysics since gamma-rays from extragalactic sources such as blazars and gamma-ray bursts interact by pair-production with EBL photons. Therefore, it is also essential for extragalactic gamma-ray astronomy to understand precisely and accurately the EBL in order to interpret correctly high energy observations. In this talk, I will review the present EBL knowledge, and describe how we can extract information, such as the value of the expansion rate of the Universe, from the EBL. Finally, the latest all-sky Fermi-LAT catalog of hard sources (E>50 GeV), called 2FHL, and future directions of EBL research will also be discussed.