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2014 Astronomy Talks

UNAB-UDP Seminar Series

Other Talks at UDP

UNAB-UDP Seminar Series

Date Speaker Title/Abstract Location
Friday
14/03

11:30am
Gaspar Galaz
Instituto de Astrofisica, PUC
The Hidden Universe
In this talk I summarize the most important features of low surface brightness galaxies, in particular those populating the faint end of the galaxy luminosity function, dominate the volume number density of extragalactic objects in the universe and also are the astronomical reservoirs of dark matter. I discuss new discoveries and finish with the possible use of new instruments to boost the research on these objects.
UNAB
Edificio R5, Sala 304, Republica 399
Friday
28/03

11:30am
Ricardo Demarco
Universidad de Concepcion
Early-type galaxy formation: understanding the role of the environment
One of the most characteristic features of galaxy clusters is the so-called “red sequence” (RS) that early-type galaxies form in the color-magnitude space of filters chosen to straddle the rest-frame 4000 A-break feature in galaxy spectra. Since these galaxies are, in general, devoid of gas and dust, their red colors are mainly a consequence of their passive nature. The denser cluster core is dominated by these “red-and-dead” galaxies, some of them the most massive galaxies known. However, the physical mechanisms responsible for quenching their star formation, thus originating the RS, are poorly understood. Environmental effects should play a significant role in the formation of the RS by transforming the observed galaxy properties from late to early-type ones. However, the details of how this actually happens are still unclear. I will present part of the work in progress that our team at UdeC is carrying out to better understand whether nature or nurture dominates in the formation of the RS. In this respect, I will briefly present our KMOS program aimed at studying the kinematical structure of cluster galaxies at 0.8
UDP
Auditorio Facultad de Ingenieria, Av. Ejercito 441
Friday
11/04

11:30am
Dimitri Mawet
ESO, JPL and University of Liege
Planetary system formation and evolution in the golden age of high contrast imaging
In this talk, I first briefly review the approaches used so far to tackle open questions about the formation and evolution of extra-solar planetary systems: the ‘top-down’ brown dwarf and the ‘bottom-up’ disk studies, both bracketing exoplanet detection and characterization efforts. As examples of direct imaging applications, I present the status of an ambitious survey of Spitzer/WISE debris disk stars at Keck, VLT, and Palomar, and recent results on famous brown dwarf and disk-bearing systems using innovative high contrast imaging techniques, polarimetry, and data mining in the VLT and HST archives. Despite vigorous efforts, direct imaging has only scratched the surface of a huge parameter space, complementary to the very successful, yet indirect methods. With modern coronagraphic and wavefront control technologies on the ground and in space, facilities such as GPI, SPHERE, P3K, SCExAO, and later on JWST and WFIRST-AFTA, are poised to break through the current contrast and inner working angle (IWA) limits. However, first-generation ground-based instruments and the HST still have a lot of untapped potential that savvy hardware and data reduction upgrades can unleash. As a case in point, I present the development, deployment, and science results of small IWA vector vortex coronagraphs (VVC) at Palomar, VLT, and LBT, and the status of on-going Palomar and Keck upgrades, paving the way towards future (extremely) large ground and space-based on-axis and/or segmented telescopes. Finally, I discuss the results and implications of the successful 2-year VVC test campaign on the JPL high contrast imaging testbed performed within NASA’s technology demonstration for exoplanet missions program.
UNAB
Sala 304, Edificio R5, Republica 399
Friday
25/04

11:30am
Nelson Padilla
Instituto de Astrofisica, PUC
Effects of the stochastic growth of angular momentum in the evolution of galaxies
Dark matter (DM) haloes, the cradles where galaxies form and evolve, acquire angular momentum in a stochastic way which results in a final non-zero DM adimensional spin parameter. We will see how this process translates into the ability of the galaxy, living in this DM halo, to form stars. To do this we will first measure this stochasticity from the Millennium II simulation, and then see how it affects the properties of the disc of baryons that forms in the center of a DM halo. We will see that the smooth infall of matter comes in chunks with almost, but not quite, random angular momenta, which affects the ability of a disc to form stars and also the frequency of instabilities in the disc leading to the formation of bars and pseudo-bulges, constituting discs more episodic in nature.
UDP
Auditorio Facultad de Ingenieria, Av. Ejercito Libertador 441
Friday
09/05

1:00pm
Alvaro Orsi
Instituto de Astrofisica, PUC
The cosmic evolution of star-forming galaxies revealed by nebular emission
Emission lines in the spectra of star-forming galaxies are typically regarded as an astrophysical tool to derive the physical properties of their stellar and gaseous components. In recent years, a new era of large surveys of high redshift galaxies is aiming at using emission-line galaxies (ELGs) as a cosmological tool. Despite the successful strategies developed to detect these galaxies in a wide range of redshifts, a robust interpretation of their different line fluxes is far from trivial. Hence, a theoretical understanding of ELGs is currently needed for an optimal utilization of current and forthcoming data and its galaxy formation and cosmological value. In this talk I will review our current understanding of ELGs in a cosmological context. Theoretical models coupling radiative transfer codes with galaxy formation models have successfully reproduced a number of statistical properties of the ELG population, hence unveiling the link between emission lines and the physical processes driving galaxy formation. Finally, I will discuss how we characterize ELGs as biased tracers of the underlying dark matter density distribution, and how these calculations can help the interpretation of ongoing and future large area galaxy surveys such as HETDEX, EUCLID, J-PAS and others.
UNAB
Sala 304, Edificio R5, Republica 399
Friday
23/05

11:30am
Mario Riquelme
Universidad de Chile
Dissipation in weakly collisional astrophysical plasmas
Weakly collisional plasmas are ubiquitous in astrophysics, especially in the interstellar and intergalactic media. In these environments the plasma density is so low that particle collisions are very infrequent. Under these conditions, the mechanism by which the plasma bulk motion is dissipated into heat is a mistery. I will mention some astrophysical phenomena where this problem is relevant (for instance, for the thermal evolution of some accretion disks and galaxy clusters). I will describe recent progresses in the study of these weakly collisional plasmas (most of them making use of numerical simulations), and I will emphasize those questions that remain to be answered.
UNAB
Sala 304, Edificio R5, Republica 399
Friday
06/06

11:30am
Carlos De Breuck
ESO Garching
ALMA resolves turbulent, rotating emission in a young starburst galaxy at z=4.8
I will present spatially resolved Atacama Large Millimeter/submillimeter Array (ALMA) observations of the z=4.7555 submillimetre galaxy, ALESS 73.1. Our 0.5″ FWHM map resolves the emitting gas which is centred close to the active galactic nucleus (AGN). The gas kinematics are dominated by rotation but with high turbulence, v_rot/sigma_int~3.1, and a Toomre Q parameter <1 throughout the disk. By fitting three independent thin rotating disk models to our data, we derive a total dynamical mass of 3+-2x10^10 M_sol. This is close molecular gas derived from previous CO(2-1) observations, and implies CO H_2 conversion factor alpha_CO<2.3M_sol(K km>~0.4. The diameter of the dust continuum emission is <2 kpc, while the star-formation rate is as high 1000 M_sol>80 Gyr^{-1}, especially since there are no clear indications of recent merger activity. Finally, our high signal-to-noise measurement revises the observed / ratio, which suggests a close to solar metallicity, unless the flux contains significant contributions from HII regions. Our observations suggest that ALESS73.1 is a nascent galaxy undergoing its first major burst of star formation, embedded within an unstable but metal-rich gas disk.
UDP
Auditorio Facultad de Ingenieria, Av. Ejercito Libertador 441
Friday
13/06

11:30am
Alberto Bolatto
University of Maryland
The ALMA view of one of the nearest starburst galaxies
In the context of galaxy evolution, it is particularly interesting to understand better the mechanisms that regulate starburst activity in galaxies. In this talk I will present an analysis of the molecular ISM properties in the prototypical circumnuclear starburst galaxy, NGC 253, derived from ALMA observations. I will discuss the evidence for a molecular superwind, our measurements of the mass loss rate, and the possible gas entraining mechanisms. I will show our measurement of the properties of giant molecular clouds in the starbust, in an effort to better understand the conditions in this region. Finally, I will present and discuss some of the chemical complexity we see in the data. The extremely rich spectroscopy, a common feature in many ALMA datasets, opens new windows for the study of physical conditions in extragalactic systems.
UDP
Auditorio Facultad de Ingenieria, Av. Ejercito Libertador 441
Friday
04/07

11:10am
Matthieu Bethermin
ESO Garching
Understanding the High-z, Dusty, Star-Forming Galaxy Populations
The star formation rate (SFR) density was more than 10 times higher at z=2 than nowadays. In addition, the star formation was dominated by objects forming ~100Msun/yr. This strong evolution is very difficult to explain with physical models. Observations and phenomenological models can thus provide crucial insights to explain this. I will review the new results obtain using a new modeling approach called 2SFM (2 star-formation mode). This modeling approach is based on the existence of a strong correlation between the stellar mass and the SFR, so-called main sequence, suggesting that the bulk of the star formation in the galaxies is driven by secular processes. However, a second population of major-merger-driven starburst, with a boosted star formation efficiency, is necessary to explain the most extreme objects. This approach is very efficient to reproduce a large number of statistical observables as the infrared luminosity functions and the number counts of galaxies from the mid-IR to the radio assuming just a set of observed scaling laws. With few extra assumptions concerning the relation between the dust attenuation and the stellar mass, we are also able to reproduce the UV luminosity functions. We also extended this model to predict the link between the dark matter halos and the star-forming galaxies using a technique of abundance matching, and managed to reproduce the fluctuations of the cosmic infrared background, measured by Planck and Herschel and caused by the fact that star-forming galaxies follow the large-scale structures. In this paradigm, the strong evolution of star-forming galaxies can be explained by an universal halo mass where the star-formation is the most efficient and the evolution of the accretion into halos at this mass. This model also agrees well with our new extensive study of the clustering of UV- and FIR-selected at z~2 as a function of their physical properties, which also provide interesting constraints on the nature of starbursts and the mechanisms of quenching of galaxies at high redshift and. Finally, I will present new results on the evolution of the mean infrared SEDs of main-sequence galaxies and starbursts up to z=4 and the consequences on their dust and gas content. These results suggest that the main causes of the evolution of the star formation at high redshift is the presence of massive reservoirs of gas, rather than an evolution of the star formation efficiency.
UNAB
Sala 304, Edificio R5, Republica 399
Friday
18/07

11:30am
James Jenkins
Universidad de Chile
The Search for Rocky Exoplanets
In this talk I will discuss some of the latest results from our radial velocity surveys of nearby stars to search for low-mass exoplanets. In the first half of the talk I will introduce the Calan-Hertfordshire Extrasolar Planet Search (CHEPS) and discuss some of the results from this survey. In the second half of the talk I will discuss our latest studies of the nearest stars to determine the fraction of super-Earth planets orbiting M-dwarfs, the fraction of those that are orbiting in the Habitable Zone, and finally, our steps to answer these questions for more massive Sun-like stars.
UDP
Auditorio Facultad de Ingenieria, Av. Ejército Libertador 441
Friday
01/08

11:30am
Giovanni Carraro
ESO Chile
Morphological transformations of Dwarf Galaxies in the Local Group
In the Local Group there are three main types of dwarf galaxies: Dwarf Irregulars, Dwarf Spheroidals, and Dwarf Ellipticals. Intermediate/transitional types are present as well. This contribution reviews the idea that the present day variety of dwarf galaxy morphologies in the Local Group might reveal the existence of a transformation chain of events, of which any particular dwarf galaxy represents a manifestation of a particular stage. In other words, all dwarf galaxies that now are part of the Local Group would have formed identically in the early universe, but then evolved differently because of morphological transformations induced by dynamical processes like galaxy harassment, ram pressure stripping, photo-evaporation, and so forth. We start describing the population of dwarf galaxies and their spatial distribution in the LG. Then, we describe those phenomena that can alter the morphology of a dwarf galaxies, essentially by removing, partially or completely, their gas content. Lastly, we discuss morphological signatures in the Local Group Dwarf Galaxies that can be attributed to different dynamical phenomena. While it is difficult to identify a unique and continuous transformation sequence, we have now a reasonable understanding of the basic evolutionary paths that lead to the various dwarf galaxy types.
UNAB
Sala 401, Edificio R2, Republica 252
Friday
08/08

11:30am
Yara Jaffe
Universidad De Concepcion
Understanding galaxy quenching in clusters though their orbital histories
We investigate the effect of environment in the quenching of galaxies in 2 very different clusters at z~0.2 from the Blind Ultra Deep HI Environmental Survey (BUDHIES). We use simulations of galaxies in and around clusters to infer the orbital histories of the observed cluster galaxies. We do this as a function of their relative position and velocity with respect to the cluster (phase-space). We further exploit our multi-wavelength data to distinguish between the different physical processes that affect galaxies in clusters. Our results strongly support a scenario in which ram-pressure by the intra-cluster medium stripps away the HI gas in disk galaxies as they first fall into the cluster. After complete gas removal, the galaxy eventually ceases to form stars and becomes red.
UDP
Auditorio Facultad de Ingenieria, Av. Ejercito Libertador 441
Friday
22/08

11:30am
Nicolas Tejos
University of California, Santa Cruz
The Intergalactic Medium in the Cosmic Web
I will present observational results on the properties and distribution of the intergalactic medium (IGM) in the cosmic web. I use proprietary and public data from HST/COS UV spectroscopy of background QSOs to observe the IGM in absorption, together with galaxies mapped in emission from optical spectroscopy. By cross-matching the position of individual HI absorption line systems to those of different large scale structures (LSS) traced by galaxy distributions (e.g. voids, filaments, clusters), I characterize the IGM in different cosmic environments. I will present results on the properties of the IGM: (i) around normal star-forming and non-star-forming galaxies; (ii) within and around galaxy voids at z<0.1, that trace low- and mean-density environments respectively; and (iii) high-density environments traced by galaxy cluster pairs (cosmological filaments). With these datasets, we can directly test the modern paradigm for the cosmic web developed from
UDP
Auditorio Facultad de Ingenieria Av. Ejército Libertador 441
Friday
05/09

11:30am
Franz Bauer
Instituto de Astrofisica, PUC
Reconciling IR Constraints on AGN Tori using X-rays
Interferometric mid-IR observations of nearby AGN have provided us with a mixed picture of how the material around AGN is distributed. In some cases, a classical “torus” is seen, while in others diffuse clouds, and still others display multiple structures. Such findings can at times appear at odds with observations at other wavelengths, where obscuration is clearly present. X-ray observations provide an alternate method for probing the structure of the AGN, as transmitted X-rays can penetrate column densities up to many times 1e24 cm-2 directly, while above this value, Compton-reflected X-rays from different lines of sight can still be seen. I will present new results from NuSTAR and Chandra that help us understand where these Compton-reflected X-rays come from and how this relates to what we know from the mid-IR.
UNAB
Sala 302, Edificio R5, Republica 399
Thursday
11/09

12pm
Rob Ivison
ESO Garching
“ESO in 2014” and “Dusty, high-redshift starbursts – the genesis of the massive local population?”

UDP
Auditorio Facultad de Ingenieria, Av. Ejercito Libertador 441
Friday
26/09

11:30am
Monica Rubio
Universidad de Chile
Molecular Gas and Star Formation in the The Small Magellanic Cloud
The Small Magellanic Cloud is the nearest galaxy in which we can study the gas, dust and star formation at low metallicities (1/10), resembling the early phases of galaxy formation in the Universe. The SMC has been studied in CO line emission but most of the molecular gas is likely to be in moderate extinction regions where CO is faint and photo dissociated. Dust emission is potentially a better molecular tracer because of its independence of photo-chemistry and density structures of the molecular clouds, allowing for a more complete census of the cold dense star forming gas distribution and its relationship to star formation. We present results of sub-mm observations which combined with Spitzer and Herschel confirm dust emission excess from the molecular gas and sets important constraint to use the dust emission at sub-millimeter as an alternative method to derive the amount of H2 gas in which star formation takes place. We discuss these results and its impact in to other low metallicity system in the Local Group.
UNAB
Sala 302, Edificio R5, Republica 399
Friday
10/10

11:30am
Eduardo Ibar
Universidad de Valparaiso
A multi-wavelength exploration of the deficit in H -ATLAS/GAMA galaxies out to z = 0.2
We explore the behaviour of λ157.74 μm forbidden fine-structure line observed in a sample of 28 galaxies selected from ∼ 160 deg^2 of the H-ATLAS survey. The sample is primarily constructed using galaxies with 160 μm flux densities higher than 150 mJy and optical spectra from the GAMA survey. Far-IR spectra centred on this redshifted line were taken with the Photodetector Array Camera and Spectrometer (PACS) on-board the Herschel Space Observatory. The galaxies span 0.02 < z < 0.2, with 10 < log(L_IR /L_⊙ ) < 12 (where L_IR ≡ L_IR ) and 7.2 < log(L_ /L_⊙ ) < 9.4, covering a variety of dust-emitting galaxy morphologies, including face- and edge-on disks, ellipticals and irregulars. The sample exhibits the so-called deficit at high IR luminosities (L_IR ), i.e. L_ /L_IR (hereafter /IR) decreases at high L_IR. We find significant differences between those galaxies presenting /IR > 2.5 × 10^−3 with respect to those showing lower ratios. We suggest that the main parameter responsible for controlling the /IR ratio is the strength of the radiation fields. In particular, we find that galaxies with high ratios tend to have: (1) L_IR < 10^11 L_⊙ ; (2) colder dust temperatures, often T_d < 30 K; (3) the presence of disk-like morphologies in SDSS r-band images; (4) WISE colours in the range 0.5 < S_12μm /S_22μm < 1.0; (5) low surface brightness Σ_IR ≈ 10 8−9 L_⊙ kpc^−2 , (6) and a wide range of specific star- formation rates, sSFR ≈ 0.01 − 3 Gyr^−1 . Our analyses suggest that for galaxies with L_IR < 10^11 L_⊙, the /IR luminosity ratio is controlled by the diffuse cold neutral (rather than warm ionised) media, and the dominant emitter is insensitive to the star-formation efficiency of the ISM. We find that within the brighter IR population, 11 < log(L_IR /L_⊙) < 12, the deficit is unlikely to be produced by line self absorption or controlled by the presence of an AGN (identified via the BPT diagram).
UDP
Auditorio Facultad de Ingenieria, Av. Ejercito Libertador 441
Friday
24/10

11:30am
Koraljka Muzic
ESO Chile
Low-mass end of the Initial Mass Function: Insights from the SONYC survey
The origin of the objects populating the substellar tail of the Initial Mass Function (IMF) is one of the major unsolved questions in star formation. A fundamental prerequisite to test the various competing theories is to establish a census of brown dwarfs in nearby young star forming regions. Such a census allows us to probe the shape of the IMF, and yields large and homogeneous samples required to study disks, multiplicity, and accretion in the substellar regime. SONYC (Substellar Objects in Nearby Young Clusters) is a survey program to provide a census of the substellar population in nearby star forming regions. The survey is based on deep imaging, combined with proper motions, and followed with extensive spectroscopic campaigns that have resulted in more than 700 spectra of candidate objects in NGC1333, Rho-Ophiuchi, Chamaeleon-I, Upper-Sco, and Lupus-3. We have identified and characterized more than 60 new young brown dwarfs, including a handful with masses close to, or below the Deuterium-burning limit. Thanks to the SONYC survey and the efforts of other groups, the mass function in young star forming regions is now well characterized down to about 10 Jupiter masses. Below this mass, however, the situation is less clear – the frequencies of the free-floating brown dwarfs with planetary masses are still debated. In this talk, I will give an overview of our current understanding of the IMF at its low-mass end, discuss possible environmental differences, and outline the impact on our understanding of star formation.
UNAB
Sala 310, Edificio R3, Republica 239
Friday
07/11

11:30am
Julio Chaname
Instituto de Astrofisica, PUC
Very Wide Binaries in the Galaxy and Beyond
Wide binaries, with semi-major axes of hundreds of AU and larger, are objects useful for a variety of applications on many areas, ranging from the determination of fundamental parameters of single field stars (metallicities, ages, etc.) to the study of the clustering properties of dark matter in Galactic and extragalactic environments. Wide binaries might also be responsible for a fraction of supernovae type Ia, under a recently proposed scenario for this type of explosion. I will provide an overview of what is currently known about wide binaries in the Galaxy, their formation and evolution, detection, and will focus on some of their applications to current problems. The upcoming reality of surveys such as Gaia and LSST promises an explosion of the available grid of wide binaries that not only will allow us to improve on all of the above but will also open new frontiers for the exploration of the Galaxy and astrophysical processes.
UDP
Auditorio Facultad de Ingenieria, Av. Ejercito 441
Friday
21/11

11:30am
Paulina Lira
Universidad de Chile
Accretion Disks of luminous high-z QSOs
I will present recent results on the use of classic Shakura-Sunyaev disk models to fit the observations of 30 luminous high-z QSOs obtained with the X-Shooter spectrograph. We show that in most cases the optically thick geometrically thin disk models perfectly represent the continuum emission in these AGN. Furthermore, for the first time it is also possible to infer the spin parameter for these sources and study their dependency with BH mass and accretion rate. I will finish with an ongoing investigation of the systematic spectral differences between radio loud and radio quiet QSOs and try to see whether these can be explained as intrinsic differences in the accretion flow or due to external factors.
UNAB
Sala 302, Edificio R5, Republica 399
Friday
16/01

11:30am
Felipe Barrientos
Instituto de Astrofisica, PUC
Exploiting large imaging surveys: The RCS case
The Red-Sequence Cluster Surveys are large imaging surveys that have been designed for identifying significant numbers of galaxy clusters for cosmology and cluster science. These surveys have also provided a rich and homogeneous dataset to enable a wider range of studies. In this talk I will present the main results in the photometric identification of QSOs, SNe and galaxy morphology using the RCSs.
UDP
Auditorio Facultad de Ingenieria, Av. Ejercito 441

 

Other Talks at UDP

Date Speaker Title/Abstract Location
Thursday
25/09

Alessandro Rettura
Infrared Processing and Analysis Center, California Institute of Technology
The most distant galaxy clusters: fundamental tools for cosmology and galaxy evolution.
Small temperature and density fluctuations in the early Universe have grown into the cosmic web of dark matter and barionic matter that we see today. Matter is distributed among large-scale filaments, punctuated by galaxy clusters at the intersection points of this web. Mapping the cosmic history of rich galaxy clusters provides fundamental information about both cosmology and galaxy formation. In this talk I will describe our panchromatic studies of X-ray and infrared-selected galaxy clusters at high redshift. These studies enable us to trace the first stages of galaxy evolution in high density environments. I will also discuss the role of the environment on both the structural and stellar populations properties in massive galaxies in rich, high-redshift environments.
UDP
Sala de Titulación, Facultad de Ingeniería, Av. Ejercito Libertador 441
Monday
05/01

11:30am
Loreto Barcos
University of Virginia
Peering into the Hearts of the Most Luminous Local Galaxies: The case of Arp 220
Many of the most luminous galaxies in the local universe are distant, compact, heavily dust-embedded merger-induced starbursts – properties that make them difficult to study in detail. Radio continuum produced by star formation and/or AGN activity offers a way to peer past the dust of these galaxies and still achieve very high spatial resolutions. My PhD. thesis mainly focuses on the study of new, high-resolution, multi-frequency (4-8 GHz and 29-36 GHz) radio continuum maps obtained with the recently upgraded Karl G. Jansky Very Large Array of 22 local luminous and ultraluminous infrared galaxies. The high resolution at 33 GHz (< 0.1" ~ 50 pc at 100 Mpc) and sensitivity to all spatial scales allows us to make the best measurements to date of the true size of the any nuclear starburst, and to determine the spectral energy distribution of the bright cores of these galaxies, which will allow us to constrain the nature of the central energy source. With the measurements of the sizes of the central regions of these galaxies, at a frequency range that it is optically thin to all the dust present in these systems, we are able to determine the surface brightnesses of their central parts. By comparing these quantities to the dusty Eddington limit, in which radiation pressure is balanced only by self-gravity, we are capable of determining whether radiation pressure on dust plays a major role in the physics of these systems. I will describe preliminary results from the previously mentioned survey and a detailed analysis of the observations of one of the most extreme star forming system in the local universe, Arp 220.
UDP
Núcleo de Astronomía, Av. Ejército 441