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2015 Astronomy Talks

2015 UNAB-UDP Seminar Series

2014 UNAB-UDP Seminar Series

Other Talks at UDP

2015 UNAB-UDP Seminar Series

Date Speaker Title/Abstract Location
Monday
09/03

10:30am
Richard de Grijs
Kavli Institute for Astronomy and Astrophysics, Peking University, China
Not-so-simple stellar populations in resolved massive star clusters
Until about a decade ago, star clusters were considered “simple” stellar populations: all stars in a cluster were thought to have similar ages and the same metallicity. Only the individual stellar masses were thought to vary, in essence conforming to a “universal” initial mass function. Over the past decade, this situation has changed dramatically. Yet, at the same time, star clusters are among the brightest stellar population components and, as such, they are visible out to much greater distances than individual stars, even the brightest, so that understanding the intricacies of star cluster composition and their evolution is imperative for understanding stellar populations and the evolution of galaxies as a whole. I will discuss my group’s recent progress in this context, with particular emphasis on the properties and importance of binary systems, the effects of rapid stellar rotation, and the presence of multiple populations in Local Group star clusters across the full age range. Our very recent results imply a reverse paradigm shift, back to the old simple stellar population picture for at least some intermediate- age (~2 Gyr-old) star clusters, which opens up exciting avenues for future research directions.
UNAB
Casona de Las Condes, Main Auditorium
Monday
23/03

11:30am
Roberta Paladini
IPAC/Caltech
The submillimiter properties of regions of high-mass star formation from Planck and Herschel observations
Massive star formation occurs inside Giant Molecular Clouds (GMC) and proceeds through many stages, each involving different physical scales. Intermediate scales, represented by coherent structures of gravitationally bound material, are difficult to study, mainly due to observational biases which characterize ground-based instruments. Investigating how star formation varies as a function of Galactocentric radius is also challenging, as the outer Galaxy is not very well explored. To address these issues, we have selected a complete sample of candidate Massive Young Stellar Objects (MYSOs) and UCHII regions from the Red MSX Source (RMS) survey. By combining Planck HFI data with IRIS data, we have built the SED for these clumps and derived their dust temperatures. With the distance information provided by the RMS survey, we have also estimated luminosities and masses, and searched for variations of the distance-independent L/M ratio as a function of Galactocentric radius. Finally, we have computed bolometric luminosities for the candidate MYSOs and UCHII regions with ancillary MSX, WISE and Herschel data, and compare these to the bolometric luminosities of their Planck counterparts. We have found that, while star formation is a rare phenomenon in the outer Galaxy, it is extremely efficient, even more than in the inner Galaxy. In addition, our analysis shows that the clump luminosity is correlated with the luminosity of the embedded MYSOs/UCHIIs, with potentially important implications for star formation theories.
UDP
Núcleo de Astronomía, Av Ejército 441
Friday
17/04

3:00pm
Aaron Romanowsky
San José State University
Mapping galaxy assembly histories with the chemodynamics of substructure
In the modern cosmological paradigm of cold dark matter, all galaxies should be experiencing continual bombardment from smaller, infalling dark matter halos. These have a natural correspondence with the satellite galaxies, stellar streams, shells, and other substructures observed around the Milky Way and other galaxies. There is a major industry in studying satellite infall and streams in the Local Group, with accompanying controversies about the consistency with the standard paradigm. However, a full picture requires expansion to a larger sample of galaxies and a broader range of morphological types and environments. This goal is very challenging observationally, but is now possible through a combination of techniques for probing low-surface brightness features with resolved stars, integrated light spectroscopy, globular clusters, and planetary nebulae. I will present results from ongoing surveys using these techniques to map out the chemodynamics of galaxy halo substructures beyond the Local Group.
UNAB
Auditorio Campus Casona Las Condes, Fernández Concha 700
Friday
24/04

11:30am
Guillermo Blanc
Universidad de Chile
A Characteristic Transition Mass Scale in the Gas Phase Mass-Metallicity Relation of Local Star Forming Galaxies
I will discuss the results of re-measuring the mass-metallicity relation (MZR) of local star forming galaxies using IZI, a recently developed Bayesian code that measures the physical properties of ionized nebulae using photo-ionization models. I will make the argument for the existence of a characteristic transition mass sale in the MZR at which star forming galaxies suffer a significant enhancement in their level of chemical enrichment. Using simple chemical evolution models that include the flow of baryons in and out of galaxies I will show how the MZR can be used to constrain the efficiency of star formation, the magnitude of gas outflows, and the physics of gas accretion into dark matter halos.
UDP
Núcleo de Astronomía, Av Ejército 441
Friday
08/05

11:30am
Alexander Scholz
University of St. Andrews, UK
Young brown dwarfs: testing star and planet formation
Brown dwarfs – objects intermediate in mass between stars and planets – are ideal benchmark objects to test theories of star and planet formation. In particular, we hope to contribute to the understanding of the Initial Mass Function, the evolution of disks, and the physics of accretion. In this talk I will present results from a variety of observational studies focused on young brown dwarfs. I will show recent findings from our brown dwarf survey SONYC (Substellar Objects in Nearby Young Cluster), from IR and submm/mm observations of brown dwarf disks, and from variability studies aimed to constrain magnetic activity and accretion.
UNAB
Auditorio Campus Casona Las Condes, Fernández Concha 700
Friday
22/05

11:30am
Jenny Greene
Princeton
Supermassive Black Holes at the Low-mass End
We still do not know the origin of supermassive black holes. I will discuss our efforts to find the lowest-mass supermassive black holes known, as a way of putting constraints on seeding mechanisms. I will also discuss megamaser disk galaxies and the scaling between black hole mass and galaxy properties in spiral galaxies in general that they reveal.
UDP
Sala de Titulación, Núcleo de Astronomía, Av Ejército 441
Friday
12/06

11:30am
Mark Phillips
Carnegie
Near-Infrared Observations of Type Ia Supernovae
Type Ia supernovae (SNe Ia) are one of the most effective observational tools for measuring the expansion history of the Universe. Their successful use in cosmology is due to the discovery of empirical relations that dramatically decrease the dispersion in peak luminosities at optical wavelengths. The first of these is the well-known correlation of absolute magnitude with light curve shape, and the second is a strong dependence of peak luminosity on color that is in the same sense as dust reddening, but with an average value of the ratio of total-to-selective extinction, Rv, that is significantly less than what is typically observed for interstellar dust in the Milky Way. Recent work indicates that there is an additional dependence of both Rv and the optical luminosity of SNe Ia on the mass (and, presumably, the metallicity) of the host galaxies. These complications can largely be avoided by working in the near-infrared, where dust extinction corrections are much smaller than in the optical, and where the luminosity-light curve shape dependence can also largely be ignored. The combination of optical + near-infrared photometry shows that SNe Ia have Rv values that span the range from ~1.5-3 that may be a function of the amount of reddening itself. The application of individual values of Rv rather than a global average leads to significant improvements in the dispersion of the Hubble diagram, both at optical and near-IR wavelengths. Further improvements should be possible through near-infrared spectroscopy since K-corrections are still only approximately understood at these wavelengths. Near-infrared spectroscopy also offers a new tool for probing the progenitors and explosion physics of SNe Ia.
UNAB
Auditorio Aznar Campus Casona Las Condes, Fernández Concha 700
Friday
26/06

11:30am
Timo Anguita
Universidad Andrés Bello
Measuring small scale structure with Quasar Microlensing
Quasar microlensing refers to the uncorrelated dynamical brightness fluctuations observed in the multiple images of lensed quasars due to compact objects in lensing galaxies. This phenomenon is present in most, if not all, gravitationally lensed quasars to different extents. In the typical scenario, the projected size of the Einstein radii of stars in lensing galaxies closely match the scales of the background AGN. Thus, the observed microlensing signal not only depends on the projected distribution of compact objects on top of the lensed quasar images, but also on the internal geometry of the source quasar. In this talk I will review the phenomenon and its use as a tool to i) probe the compact (baryonic) matter to smoothly distributed (dark) matter ratio in intermediate redshift lensing galaxies, as well as to ii) measure the inner structure of high redshift quasars: from the accretion disk to the line emitting regions.
UNAB
Sala 301, Edificio R1, República 330
Friday
10/07

12:30pm
Guido Garay
Universidad de Chile
The formation of high-mass stars
I will review the current status of our knowledge about the formation process of high-mass stars, drawn mainly from moderate (~10″) angular resolution observations, and discuss the key questions that will be addressed with ALMA. A summary of the recent results derived from ALMA observations will be presented.
UNAB
Auditorio C6-401, Campus Casona Las Condes, Fernández Concha 700
Friday
24/07

11:30am
Nancy Levenson
Gemini Observatory
Highlights and Innovations at Gemini Observatory
I will present some of the recent science highlights from Gemini users and provide an update on recent developments and new initiatives that are coming at the observatory. These include new instrument capabilities such as high-resolution optical spectroscopy and collaborative approaches toward procuring new capabilities. Gemini is also introducing new ways of proposing and observing, such as fast turnaround programs and priority visitor mode. Gemini aims to be the flexible observatory that responds to your needs to fulfill your science goals, so I welcome your input and suggestions.
UDP
Núcleo de Astronomía, Av Ejército 441
Friday
14/08

11:30am
Rodrigo Reeves
Universidad de Concepcion
CePIA-UdeC, Status, activities and future opportunities
Astronomical instrumentation is seen as a mean for the percolation of state-of-the-art technology and associated techniques into society. The proliferation of instrumentation labs materializes the previous statement and with time, the largely awaited appearance of technology related industry, spearheaded by these lab members, should happen. In this talk we present CePIA, an instrumentation nucleus under development at Astronomy/UdeC. We introduce some of the academic activities being hosted by the lab and will review the status of current development projects. Prominent scientific activities in the discipline of radioastronomy will be also discussed and will finish by sharing opportunities and views for the future of the instrumentation community.
UNAB
Sala TEAL/FIAC (302), Edificio R2, Echaurren 250
Friday
28/08

11:30am
Kelly Denney
The Ohio State University
(Reverberation) Mapping the Universe 1 or 1000 Quasars at a Time
Reverberation mapping is a method that uses the time domain to probe size scales deep within the gravitational potential of the accreting supermassive black hole in the center of an active galactic nucleus (AGN), or quasar. By studying the time variability characteristics of what are effectively light echoes arising from various emission regions near the black hole, we can probe the geometry, kinematics, and physics of material on scales that are spatially unresolvable with even the largest telescopes. I will discuss how this method works, some basic physical properties of the systems that we are able to obtain, and the broader applications of these measurements. I’ll also present some of the newest observational campaigns/experiments recently finished or still underway that are using a multi-directional approach to expand and extend the current state of the field.
UDP
Sala de Titulación, Facultad de Ingeniería, Av. Ejército 441
Friday
11/09

11:30am
Mario Soto
STScI
Proper motions in the Galactic Bulge and Multiple Stellar Populations in Globular Clusters using HST
I will report on two projects currently being carried out at the Space Telescope Science Institute (STScI). The first project studies the proper motions in several low foreground extinction windows of the Galactic bulge. Ten fields have been strategically placed on both ends of the Galactic bar and the Galactic minor-axis allowing for a wide coverage of the kinematics of bulge stars. The second project attempts to characterize the multiple stellar populations patterns in a sample of 55 globular clusters by observing them in the UV/blue WFC3 UVIS filters F275W, F336W, and F438W. A detailed account of both project motivations and techniques will be presented, as well as their respective current status, including new results.
UNAB
Auditorio Campus Casona Las Condes, Fernández Concha 700
Friday
25/09

11:30am
Jason Kalirai
STScI
Stellar Astrophysics: 100 Years after Russell
Since the pioneering work of Henry Norris Russell 100 years ago, the study of nearby stellar populations has served as a foundation for our quest to understand the nature of galaxies. Today, studies of resolved stellar populations constrain fundamental relations — such as the initial mass function of stars, the time scales of stellar evolution, the timing of mass loss and amount of energetic feedback, the color-magnitude relation and its dependency on age and metallicity — that represent key ingredients in our prescription to interpret light from the Universe and to measure the physical state of galaxies. In this presentation, I’ll describe new, high-precision measurements of some of the most important relations that provide this mapping between resolved and unresolved light, and discuss new opportunities for stellar population studies given an unprecedented suite of astronomical tools that are now on our horizon – GAIA, JWST, LSST, WFIRST, 30-meter telescopes.
UDP
Sala de Titulación, Facultad de Ingeniería, Av. Ejército 441
Friday
9/10

11:30am
Rubens Machado
UNAB
Chemical enrichment of the circumgalactic medium
Galaxies are surrounded by extended gaseous haloes. Simulations indicate that galactic outflows due to supernovae can transfer enriched gas to the circumgalactic medium. Observationally, this gas may be detected via oxygen absorption lines, but the details of this reservoir of metals are still uncertain. To link the simulation predictions to the current observational budgets of metals, we use cosmological hydrodynamical simulations of galaxy formation including supernova feedback. We analyse the gas properties of the most massive disc galaxies formed in these simulations, studying both the interstellar and the circumgalactic media (ISM and CGM). We find that the oxygen mass of the CGM is comparable to that of the ISM at low redshift. For the most massive galaxies, the CGM even exceeds the ISM in metal content, in agreement with observational claims. The masses of CGM metals measured in our simulations are in fair quantitative agreement with recent observational estimates, for galaxies of comparable stellar mass. The results are encouraging, considering that the feedback parameters had not deliberately tuned to reproduce these particular observations.
UNAB
Sala FIAC, República 252
Friday
16/10

11:30am
Eduardo Bañados
MPIE
The most distant quasars with Pan-STARRS1
High-redshift quasars provide unique information about the evolution of supermassive black holes, their host galaxies, and the intergalactic medium at early cosmic time. Numerous studies have established a sample of ~60 quasars at 5.55.5 quasars. The quasar sample spans a factor of ~20 in luminosity and shows a diverse range of properties, including a number of weak-line and radio-loud quasars. I will also discuss some of the surprises revealed by this quasar sample as well as our initial follow up studies, which are the first steps towards a statistical characterization of the high-redshift quasar population.
UDP
Sala de Titulación, Av. Ejército 441, Santiago
Friday
23/10

11:30am
Ezequiel Treister
Universidad de Concepción
The Cosmic History of Black Hole Growth
It is now clear that supermassive black holes (SMBHs; M>1e6 Msun) live in the center of most (all) galaxies, including our own Milky Way. Furthermore, it is also clear that the energy released during the growth of this black hole is a critical ingredient in understanding galaxy formation and evolution. There are significant open questions in our understanding of how SMBHs are formed and get most of their mass. In this talk I will review our observational efforts to understand how the first SMBH seeds formed using Chandra and the planned STAR-X observatory. I will also describe recent results using the NuSTAR satellite, the most sensitive hard X-ray, E>10 keV, observatory launched ~2 years ago and work being carried out in Chile to characterize these newly detected X-ray emitters and how they can be used to construct the most complete census of Black Hole Growth across the cosmic history to date. Finally, I will focus in the role of galaxy mergers in triggering black hole growth episodes and their connection to galaxy evolution. This work is being done as part of the EMBIGGEN Anillo project, which combines observations using Chandra, NuSTAR, ALMA and other ground-based telescopes installed in Chile with state-of-the-art simulations.
UNAB
Sala FIAC, República 252
Friday
13/11

11:30am
Manuel Aravena
UDP
Studying the evolution of star forming galaxies through cosmic time: An ALMA 1.2mm molecular deep field
In the last decade, significant progress has been achieved in the understanding the evolution of star formation in galaxies as a function of redshift. Its is now clear that the majority of galaxies at z<3 form a nearly linear correlation between their stellar mass and star formation rates and appear to create most of their stars in timescales of ~1 Gyr. At the highest luminosities, a significant fraction of galaxies deviate from this ‘main-sequence’, showing short duty cycles and thus producing most of their stars in a single burst of star formation (‘starburst’) within a few 100 Myr, being likely driven by major merger activity. Despite the large luminosities of starbursts, main-sequence galaxies appear to dominate the star formation density of the Universe at its peak. While progress has been impressive, a number of questions are still unanswered. In this talk, I will briefly review our current observational understanding of this ‘main-sequence’ vs ‘starburst’ galaxy paradigm, and will address how future deep field observations (e.g. with ALMA) will help us to have better insights into the fundamental properties of these galaxies. In particular, I will show recent attempts to conduct molecular deep field observations and preliminary results from ALMA molecular deep field spectroscopy of a region of the Hubble Ultra Deep Field.
UNAB
Sala FIAC, República 252
Friday
04/12

11:30am
Krzysztof Stanek
The Ohio State University
All-Sky Automated Survey for SuperNovae: Big Science with Small Telescopes
Even in the modern era, only human eyes survey the entire optical sky for the violent, variable, and transient events that shape our universe. To change this, we have built and implemented the All-Sky Automated Survey for Supernovae (ASAS-SN or “Assassin”). This is a long-term project designed to monitor the entire sky down to V~17 mag every 2-3 days using multiple telescopes, hosted by Las Cumbres Observatory Global Telescope Network, in the northern and southern hemispheres. Our telescopes (currently eight) consist of commercially available telephoto lenses and CCD cameras, so further expansion, leading to a 1-day cadence, would be straightforward and relatively inexpensive. The primary focus of the survey is to find bright nearby supernovae (SNe) and other transient sources. We began running our real-time search for variable sources in late April 2013 with our first unit, “Brutus”, and in May 2014 we have deployed “Cassius” in Chile, expanded to four telescopes in July 2015. ASAS-SN has already discovered about 250 bright nearby SNe, including ASASSN-15lh, the most luminous supernova ever discovered. We also discovered 500+ new cataclysmic variable stars, dramatic M-dwarf flares and AGN outbursts, and three tidal disruption events, closest such events ever found in optical light. ASAS-SN is an ongoing survey which, judging by its success so far and likely future expansion, promises to be innovative and prolific, delivering a steady stream of interesting discoveries for years to come, at relatively low cost.
UDP
Sala de Titulación, Av. Ejército 441

 

Other Talks at UDP

Date Speaker Title/Abstract Location
Monday
16/03

11:30am
Vernesa Smolcic
University of Zagreb
Submillimeter galaxies: Insights from the COSMOS survey
With star formation rates (SFRs) of ∼100-1000 Msun/yr, submillimeter galaxies (SMGs) are acknowledged to be the most powerful starbursts in the universe. Their typical redshifts are ~2.5-3.5, and they are promising candidates for the progenitors of the most massive, non-star-forming elliptical galaxies seen in the present-day universe. In the past studies of SMGs were challenging given detections at low (10-30”) angular resolution that prohibited accurate counterpart association and, thus, redshift determination. With the upgrade of existing and the onset of new interferometers operating at (sub-)millimeter wavelengths (PdBI, VLA, ALMA) we have only recently overcome these challenges. This has yielded a wealth of new results related to the properties of SMGs and their role in galaxy formation and evolution. In this talk I will give an overview of the newest results on the redshift distribution, large-scale environment, and star-fomation sizes of SMGs in the COSMOS field. These are based on data taken with the PdBI, Jansky VLA and ALMA.
UDP
Núcleo de Astronomía, Av. Ejército 441
Friday
20/03

2:00pm
Chelsea Sharon
Cornell University
Probing Galaxy Evolution at High-z with CO Excitation
In order to understand the evolution of high-redshift galaxies, it is important to accurately characterize the molecular gas that fuels their star formation. Previous studies of molecular gas conditions in high-redshift galaxies found different CO line ratios in submillimeter galaxies and quasar host galaxies; observations of low-J rotational CO lines implied that submillimeter galaxies contain multi-phase molecular interstellar medium, including a substantial cold gas reservoir, and quasar host galaxies are consistent with a single phase of molecular gas. Since theoretical work has suggested that AGN may play an important role in quenching star formation in massive galaxies, this difference in gas excitation may be indicative of just such an evolutionary trend. However, this difference was observed in a small sample of high-redshift galaxies and was based on galaxy-wide averages of line ratios that may have hidden variation of molecular gas conditions on sub-galactic scales. I will present a new larger sample of CO(1-0) detections at z~2 from the Jansky Very Large Array that allow us to better evaluate the systematic difference in molecular gas excitation as a function of galaxy type. In addition, I will show a few detailed examples that illustrate how high spatial and spectral resolution mapping affects our characterization of the molecular ISM and enables analyses similar to those performed on low-redshift galaxies, like the resolved Schmidt-Kennicutt relation.
UDP
Auditorio Principal de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441