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Astronomy Talks

2018 UDP Seminar Series


Next seminar

December 6, 11AM
Lauranne Lanz (Dartmouth, USA): Black Hole Feedback in Action? Understanding the role of AGN in Transitioning Galaxies

In past several decades, we have made great progress in developing a consistent paradigm for the formation and evolution of galaxies, seeking to answer the basic question of where galaxies like our Milky Way come from and where we are headed on cosmic timescales. However, many details of this picture remain unclear. One particularly interesting question regards the role that active supermassive black holes play in the transition from a gas-rich, actively star forming state to gas-poor quiescence. I will describe a recently discovered type of galaxies at an earlier stage of transition that the classical post-starburst galaxies, and present new X-ray observations of these galaxies, which provide a crucial window into the role of AGN in the early phases of transformation.

Forthcoming seminars

♦ December 7, 3PM (joint UDP-UNAB)

Andreas Morlok (University of Münster, Germany): Cosmic Petrology: the composition of bodies in young solar systems and infrared spectroscopy of circumstellar dust and meteorites

Over the last 20 years, infrared astronomy allowed for the first time to determine the mineralogical composition of the dust material observed around young stars in the circumstellar and debris disk stage. For our Solar System, we have material left over from this stage in the form of meteorites and various other planetary materials. So the infrared spectroscopic study of these materials can help to link the detailed (forensic) knowledge we have of our, early Solar System with the observations of similar systems forming right now. I will give an overview of my work in this field in the past – comparison of astronomical data with lab studies with e.g. primitive meterorites, the influence of impact shock, as well as of current work.

♦ December 18, 3PM
Kohei Ichikawa (Columbia University, USA; Tohoku University, Japan)

 

For other talks in Santiago see the SOCHIAS calendar


Previous seminars

 December 4, 3PM
Peter Boorman (Southampton University, UK): A Census of Growing Supermassive Black Holes – First Results from the NuLANDS Survey

Very little is known about how black holes at the centres of galaxies grow to become “super” massive. Sensitive X-ray observations have enabled studies of the closest regions to growing supermassive black holes (aka Active Galactic Nuclei – AGN), and have revealed the majority are obscured by gas. Unfortunately though, the most obscured AGN are typically too faint to be detected in wide-field X-ray surveys. This has led to estimates of the fraction of heavily obscured AGN relative to the total population varying drastically between ~20-70%, yet a determination of this fraction is essential to understand the evolution and demographics of all supermassive black holes. The NuSTAR Local AGN N(H) Distribution Survey (NuLANDS) is one of the largest legacy surveys of AGN currently underway with the X-ray space telescopes NuSTAR, XMM-Newton and the Neil Gehrels Swift Observatory (> 4 million seconds of total exposure) aimed at resolving this issue. Via multiwavelength techniques, NuLANDS is targetting AGN representatively of the underlying population, and has thus already led to the discovery and classification of multiple heavily obscured AGN previously hidden at X-ray wavelengths. The initial results from the survey indicate that > 30% of all AGN in the local Universe are heavily obscured, and that high-energy X-ray selection alone preferentially selects less-obscured AGN. As such, NuLANDS marks a major step in completing the local census of supermassive black hole growth, and will pave the way in quantifying how many AGN, on average, are heavily obscured in the local Universe.

♦ November 23, 3PM
Ghina Halabi (Institute of Astronomy, University of Cambridge): Confronting challenges in stellar structure and evolution

Our knowledge of the structure and evolution of stars has significantly improved in the past few decades. This improvement has been largely due to our increased understanding of the properties of stellar matter in the energy regimes characteristic of different evolutionary stages. However, stellar models still face significant uncertainties which are often manifest as discrepancies between theory and observations. I will discuss some of the most infamous uncertainties, particularly convection, rotation and mass transfer in close binary systems. I will present some of my research endeavours that confront all three of them, one at a time.

♦ November 16, 3PM
Tanio Diaz (UDP): The Interstellar Medium of the Most Luminous Galaxies, Near and Far

Room: Sala Titulacion, Facultad Ingenieria y Ciencias, UDP

Galaxies spend most of their lives inhabiting what is called a main-sequence (MS) of star-formation, a peaceful and gentle state in which galaxies form stars and feed their central black holes in a steady manner. Most of the energy in the Universe at any cosmic epoch is generated within these galaxies. However, there is also a “obscured” galaxy population that, while very small in number (a few percent), still accounts for a significant fraction of the total energy production (up to 30%). The study of these incredibly luminous sources is therefore fundamental to our understanding of all the main physical processes that drive galaxy evolution. In this talk I will present results obtained from far-infrared observations of two samples of nearby and high-redshift luminous infrared galaxies, for which in-depth studies of their interstellar medium have only been made possible during the last years by the advent of state-of-the-art observatories such as Herschel or ALMA.

♦ November 9, 3PM (joint UDP-UNAB)
Claudia Paladini (ESO): A tale of giants and how they start losing mass
Location: UNAB

Mass loss is one of the most important factors in the post main sequence evolution, making low- and intermediate- mass stars crucial contributors to the chemical enrichment of the Universe. Although the mass-loss process on the Asymptotic Giant Branch (AGB) has been studied for over 40 years, many basic aspects are still not understood. This is especially the case for the geometry of the process and how it influences the following phase of stellar evolution when the star expels its envelope as a planetary nebula (PN). Although ≈ 70% of the observed PNe are not spherically symmetric, and neither are the winds of post-AGB objects, the AGB wind morphology is widely regarded as such.
With the advancement in the instrumentation and with the increasing amount of apertures available, the new generation of interferometers allows today to reconstruct images of the very inner spatial scales of the atmosphere of AGB stars, thus opening a unique view on the onset of the mass-loss process. Convective patterns and asymmetric ejections of the size of the astronomical unit can be fully characterised. 3D models are slowly catching up, and are now ready to be challenged by these new observations. In this presentation I will discuss the implications of the recently obtained images of AGB surfaces. I will highlight the potential of the second generation VLTI instruments, and conclude with the advantages of the synergy between VLTI and other imaging and high angular resolution facilities (e.g., VLT/SPHERE, VLT/VISIR, and ALMA).

♦ October 26, 3PM
Stefano Bovino (Universidad de Concepción): A timeline for massive star-forming regions via astrochemical studies
Room: Sala Titulacion, Facultad Ingenieria y Ciencias, UDP

Stars form in dense and cold regions within molecular clouds, and this process is regulated by different physical phenomena that act at small scales. In fact, magnetic pressure, turbulence, and rotation can delay the collapse, inducing long timescales for stars to form. These processes are particularly relevant for determining timescales for the formation of massive stars. Despite their fundamental astrophysical importance, the pathways of high-mass star formation remain highly controversial (see Zinnecker & Yorke 2007). In particular, do they form through slow collapse supported by magnetic pressure and/or turbulence (McKee & Tan 2003), or during a fast global collapse process (Bonnell et al. 2001)? That is, the timescales of the process remain elusive to date. Chemistry, and in particular deuteration chemistry, provides a tool with which to measure these timescales (Fontani et al. 2011). In this talk I will introduce the basic processes which regulate the deuterium enrichment in star-forming regions and show some of our recent results from state-of-the-art hydrodynamical simulations of collapsing clumps and filaments where, for the first time, we have followed the evolution of deuterated tracers (e.g. H2D+) along with magnetic fields, turbulence, hydrodynamics, and gravity. I will also present some recent observations and future work.

♦ October 19, 2PM
Leopoldo Infante (Carnegies): Carnegie and Las Campanas Observatory; science and instrumentation highlights

In this talk, I will give a brief description of the role played by the Carnegie Institution for Science (former Carnegie Institution of Washington) in the history of astronomy during the last century and the need to establish an observatory in the southern hemisphere at the end 1960, which became Las Campanas Observatory. I will discuss the current and future availability of telescopes and instrumentation in LCO, as well as the most recent scientific discoveries made in LCO and the opportunities that open up for the Chilean astronomical community.

♦ October 11, 2PM
Jhon Yana Galarza (IAG, USP Brazil): The effect of stellar activity on the stellar parameters of a young solar twin

Most spectroscopic surveys of stellar chemical composition assume that spectroscopic
equilibrium holds in solar-type stars, even for young spotted stars with high stellar activity.
However, it is known that there are important abundance anomalies in young open clusters,
which could be related to overexcitation and overionization effects, hence potentially affecting
the assumption of spectroscopic equilibrium. Furthermore, it is known that magnetic activity
causes radial velocity variability, hampering true detection of exoplanets.
In this work, we have tested for the first time variations in stellar parameters and chemical
abundances for the young solar twin HIP36515 (~0.6 Gyr, Prot ~ 5 days). This object has stellar
parameters well established and its activity cycle is estimated in ~7 years (from our previous
observations with HARPS at LaSilla/ESO). The stellar parameters of three different epochs in
the cycle (minimum, intermediate and maximum) were estimated using spectroscopic
equilibrium, achieving an extremely high precision (~5 K in effective temperature, ~0.01 dex in
surface gravity and metallicity). Surprisingly, we find a correlation between effective
temperature (-0.85, p-value=0.18) and microturbulence (+0.98, p-value=0.02) with stellar
activity.

♦October 5, 3PM (joint UDP-UNAB )
Laura Perez (U. Chile): The Role of Substructures in Protoplanetary Disks

During their formation, young pre-main sequence stars are generally surrounded by a gaseous accretion disk, which provides a large reservoir of material available for the eventual formation of planets. This process will leave an imprint on the distribution of solid particles at different locations in the disk, resulting in a variety of substructure (e.g. gaps, rings, spirals, vortices) over large and small scales. The role of these small-scale features is fundamental: theory predicts that without substructure large solids would be lost due to radial drift, impeding planetesimal and planet formation. In this talk, I will discuss results from our ALMA Large Program aimed at characterizing the underlying substructure of classical disks with superb spatial resolution, down to a radius of few au. I will introduce the main survey results and discuss our work in a misaligned disk system as well as in binary/multiple systems.

♦ October 1, 3PM
Rebecca McElroy (MPIA): Active galaxies in the local universe: triggering, variability, and feedback

This talk aims to investigate three important phenomena in the study of active galactic nuclei: how AGN are triggered, how they vary throughout their lifetimes, and how they can effect their host galaxies through feedback.
We search for evidence of triggering by mergers using MUSE-VLT data from the Close AGN Reference Survey (CARS). We compare stellar kinematics of our active galaxies and a comparison sample of inactive galaxies to measure the deviation from disk like rotation. We show that the AGN have a slight enhancement in large scale asymmetry. Many AGN are known to vary strongly throughout their lifetime. We observed known changing look AGN Mrk 1018 as part of CARS and found that the broad lines and continuum emission had dramatically changed for a second time. We attempt to explain the possible causes for this recent change, and discuss what such short timescale variability means for theories of AGN feedback. Finally, we show that outflows are prevalent in luminous local type 2 AGN using multiple component Gaussian emission line modelling to disentangle the kinematic and ionisation properties of emission lines. This allows us to show that shock-like emission is present in these galaxies, demonstrating that the outflows are directly impacting the surrounding ISM within the galaxies.

♦ September 28, 3PM
Julio Carballo-Bello (PUC):  Globular clusters and the hierarchical formation of the Milky Way

Globular clusters have played an important role in the study of the processes that led to the formation of our Galaxy. Moreover, the dual Galactic globular cluster system is considered a manifestation of its hierarchical formation in the context of the Lambda-CDM scenario. Wide-field imaging and spectroscopy, as the ones obtained for our project, are crucial tools to unveil the remnants of their progenitor dwarf galaxies, already assimilated by the Milky Way. In this talk, I will present some of the results obtained in this long-term project,  proving that globular clusters are still useful relics in the field of Near-Field cosmology.

♦ September 14, 11AM (special seminar)
Demian Arancibia (ASTROdata):Astroinformatics Program – Chile: An example initiative using astronomy for economic development in Chile

The Astroinformatics Program is funded by the Ministry of Economy. Its mission is to identify and initiate measures and investments to diversify and grow Chilean digital economy, using our natural resources for Astronomy and the field data-driven challenges.  According to the strategy of CORFO, the capacity to add data-driven value will be critical for competitive edges across industries over next decade, and a driver for diversification of the Chilean productive matrix.  We worked with scientific and industrial communities to facilitate multi-sector agreements about what are our opportunities to achieve this mission.  In our first year of work, we produced a high-level system concept that is potentially fit for increasing Chilean protagonism in Astronomy, digital capacity development, technology transfer and is sustainable from an economic point of view. This presentation is a progress report and an invitation to collaborate in the next steps of implementation.

♦ September 7, 3PM (joint UDP-UNAB)
George Privon (U. Florida): Star Formation and Nuclear Activity: Dwarfs to ULIRGs

The stellar mass of star forming galaxies is thought to increase in a quasi-steady state, where the rate depends on the gas fraction and star formation efficiency. Galaxy mergers can lead to more rapid growth while active galactic nuclei have been argued to play an important role in halting star formation. These processes are tied together through the multiphase interstellar medium. I will discuss a program exploring so-called “dense gas” tracers, the use of dust emission as a probe of total molecular gas mass, and the behavior of starbursts in merging dwarf galaxies. This use of multiwavelength tracers and hydrodynamic simulations probes galaxy evolution along axes of nuclear activity, redshift, gas fraction, and metallicity. From these studies I will show new results on identification of heavily obscured AGN and intriguing differences in how mergers trigger starbursts in high gas fraction systems.

♦ August 31, 3PM
Ezequiel Treister (PUC): Physical Properties of the Gas in the Nuclear Regions of Nearby Dual AGN

Major galaxy mergers hosting two supermassive black holes (SMBHs) actively growing separated by less than 10 kpc, the so-called dual active galactic nuclei (AGNs) are ideal targets for understanding SMBH feeding, obscuration, and testing unification models and galaxy evolution. In this talk, I will present the main results from our program aimed to obtain optical and near-IR Integral Field Unit (IFU) spectroscopy and ALMA maps for a sample of confirmed nearby dual AGN. In addition to providing general properties of this population, I will focus on two remarkable systems, NGC6240 and Mrk 463.

At a distance of 210 Mpc, and a nuclear separation of ∼4 kpc, Mrk 463 is an excellent laboratory to study the gas dynamics, star formation processes and SMBH accretion in a late-stage gas-rich major galaxy merger. The optical data, which map the full extent of the merger, show evidence for a biconical outflow and material outflowing at >600 km/s, both associated with the east nucleus, along with large-scale gradients likely related to the ongoing galaxy merger. The ALMA observations of 12CO(2–1) and adjacent 1 mm continuum reveal the presence of ~1e9Mo in molecular gas in the system. The molecular gas shows velocity gradients of ~800 km/s and ~400 km/s around the Mrk 463E and 463W nuclei, respectively. We conclude that, in this system, the infall of ∼100s Mo/yr of molecular gas is in rough balance with the removal of ionized gas by a biconical outflow being fueled by a relatively small, <0.01% of accretion onto each SMBH.

We will further present the highest resolution maps of the merging galaxy system NGC6240, which hosts two SMBH growing simultaneously. At 0.03″ (15 pc), the ALMA 12CO(2-1) observations are a perfect match for existing Hubble optical and near-IR observations of this system. We find that most of the molecular gas is found in between the two nuclei but forming a clumpy stream and not a smooth rotating disk as it was previously assumed based on lower resolution data. A clear velocity gradient suggests that the molecular gas is getting ready for the next stage, in which will coalesce around each nuclei, being available significantly increase the amount of accretion onto each SMBH. We further detect the presence of significant high velocity, >500 km/s, outflows, responsible for the removal of a fraction of the material.

These results clearly show the importance of performing high resolution multi wavelength studies covering pc to kpc scales in order to understand the complex connection between black hole growth and galaxy evolution in this critical phase.

♦ August 17, 3PM at UDP
Stephane Blondin (CNRS, UMI-LFCA, PUC): Predicting the radiative display of Type Ia Supernovae: The case for multiple progenitor channels

Type Ia supernovae (SNe Ia) are amongst the most energetic stellar explosions. With typical luminosities several billion times that of the Sun, SNe Ia are visible across a large fraction of the observable universe, and enabled the discovery of its accelerated expansion. These events are thought to result from the thermonuclear disruption of a carbon-oxygen white dwarf (WD) star as it approaches the Chandrasekhar-mass limit, through accretion from a binary companion. However, the nature of this companion and the mechanisms by which the WD explodes are still debated. I will present the numerical setup developed with my collaborators to predict the light curves and spectra of SNe Ia, which provide support to the viability of the standard Chandrasekhar-mass model for most events. However, this standard model is difficult to reconcile with low-luminosity SNe Ia, making a strong case for the existence of multiple progenitor channels for these events.