Colloquia Archives

Kaitlin Kratter (University of Arizona)
Thursday, December 11, 2014
3:45 p.m.
LGRT 1033
Title:
What can we learn from planets in binary systems?
Abstract:
Exoplanet surveys have revealed a surprising array of planetary systems hosted by binary stars. The diversity and architecture of these systems provide insight into the fundamentals of planet formation for a wide range of systems. Moreover, these planets provide an important final boundary condition for our models of star formation, and especially binary formation. I will review the statistics of these surprisingly un-exotic systems, describe the theoretical implications, and discuss the prospects for progress with observational facilities of the future.
Stephanie LaMassa (Yale University)
Thursday, December 4, 2014
3:45 p.m.
LGRT 1033
Title:
Discovering Rare AGN with the Stripe 82X X-ray Survey
Abstract:
Supermassive black holes (SMBHs) grow by accreting matter in a phase where they are observed as active galactic nuclei (AGN). In order to track the evolution of rare objects, such as AGN at high luminosity, which signal when the majority of black hole growth occurred, a large volume of the Universe has to be explored through wide area surveys. Until recently, no large area X-ray survey has existed, meaning that a key phase in SMBH growth and SMBH/galaxy co-evolution is missing: luminous obscured SMBH growth. To rectify this gap, I have begun a wide area X-ray survey in the Sloan Digital Sky Survey region Stripe 82 which contains a veritable treasure trove of multi-wavelength coverage, expediting follow-up of identified X-ray sources. In this talk, I will review the highlights of our first release of "Stripe 82X" which covers ~16.5 deg^2 with ~3300 X-ray sources identified. I will discuss our current ground-based follow-up campaigns to target interesting classes of AGN and will comment on what we expect to learn with the addition of 20 deg^2 awarded to our team in the current XMM-Newton observing cycle.
Mike Dunham (CfA)
Thursday, November 20, 2014
3:45 p.m.
LGRT 1033
Title:
The Evolution of Protostars: Assembling Stars from Dense Cores
Abstract:
Stars form from the gravitational collapse of dense molecular cloud cores. In the protostellar phase, mass accretes from the core onto a protostar, likely through an accretion disk, and it is during this phase that the initial masses of stars and the initial conditions for planet formation are set. Over the past decade, new observational capabilities have provided wide-field infrared and (sub)millimeter surveys of entire star-forming clouds along with interferometric images at very high angular resolution, giving an unprecedented view of the star formation process. In this talk I will review resulting advances in the field of protostellar evolution, focusing on observational constraints on the problem of how mass is transferred from dense cores to stars.
Nick Cowan (Amherst College)
Thursday, November 13, 2014
3:45 p.m.
LGRT 1033
Title:
Balancing the Radiation Budget of Short-Period Planets
Abstract:
What started as a trickle in the mid 1990’s is now a torrent, with over one thousand extrasolar planets currently known, and thousands of candidates awaiting confirmation. The study of exoplanets has already revolutionized our view of planet formation, and will soon do the same to our understanding of planetary atmospheres and interiors. Since we view them from the top-down, one of the first aspects of exoplanet atmospheres to be constrained is their thermal emission. By combining infrared emission measurements at a variety of orbital phases, we can infer a planet's Bond albedo, the efficiency of its day-night heat transport, and, in the case of planets subject to eccentricity seasons, its thermal inertia. Multi-wavelength emission measurements can also constrain a planetary atmosphere's composition and vertical temperature structure. Such inferences are particularly sensitive to the uncertainty in emission measurements, however, and the accuracy of eclipse measurements has typically been over-stated. Fortunately, improved analysis techniques and next-generation instruments should allow us to resolve outstanding questions about hot Jupiters, and to extend our methods to temperate terrestrial planets.
Houjun Mo (UMass)
Friday, November 7, 2014
3:45 p.m.
LGRT 1033
Title:
Star formation and stellar mass assembly histories in dark matte
Abstract:
TBA
Erik Tollerud (Yale University)
Thursday, November 6, 2014
3:45 p.m.
LGRT 1033
Title:
Local Dwarf Galaxies and Near-Field Cosmology in ΛCDM
Abstract:
Dwarf galaxies are a frontier for new discoveries in both galaxy formation and cosmology. I discuss work centered around connecting LCDM and its predictions to observations of dwarf galaxies at three different scales of "dwarf". I will discuss the Milky Way's satellites and both solutions and lingering troubles with their abundances and scalings. The strangest of these puzzles manifest in the bright dSphs, which seem to be under-dense relative to LCDM expectations. With this in mind, I describe results from a large spectroscopic survey of M31's dSph satellites searching for signs of similar puzzles. Finally, I describe searches for comparable satellites beyond the Local Group, and compare their abundances and properties to straightforward LCDM expectations.
Scott Chapman (Dalhousie University)
Thursday, October 30, 2014
3:45 p.m.
LGRT 1033
Title:
The role of ultra-luminous galaxies in galaxy formation and evol
Abstract:
I will provide an overview of ultra-luminous galaxies (L_IR>1012 Lsun) at high redshift, and the different roles and properties they appear to exhibit as a function of their luminosity. I will focus on the molecular gas properties of the galaxies as the crucial fuel available for star formation, emphasizing our recent work with ALMA and the IRAM Plateau-de-Bure, where we have studied galaxies preselected at various wavelengths, and conducted blind surveys for CO gas. I will conclude with very wide field surveys (SPT) that are uncovering the most extreme specimens of star forming galaxies in the universe, and point to future facilities like CCAT which will push the field to a new level of understanding.
Greg Stinson (MPIA)
Thursday, October 23, 2014
3:45 p.m.
LGRT 1033
Title:
A Critical Phase in Galaxy Formation
Abstract:
As galaxies grow and evolve, they go through a violent phase of their evolution where intense star formation drives outflows. I will examine this phase using cosmological galaxy formation simulations. The simulations show that starbursts and outflows have implications for many observed properties of galaxies including their gaseous halos, morphology, potential, and star formation history.
Laura Lopez (MIT)
Thursday, October 16, 2014
3:45 p.m.
LGRT 1033
Title:
Observational Assessment of Stellar Feedback in Star-Forming Reg
Abstract:
Stellar feedback has a profound influence in many astrophysical phenomena, yet it is often cited as one of the biggest uncertainties in star and galaxy formation models today. This uncertainty stems from a dearth of observational constraints as well as the great dynamic range between the small scales (<1 pc) over which feedback occurs and the large scales (>1 kpc) on which galaxies are shaped by that feedback. In this talk, I will show how multiwavelength observations can be used to overcome these challenges to assess the role of many stellar feedback mechanisms, including radiation, stellar winds, supernovae, and cosmic rays. I will present results from the application of these approaches to a variety of sources and discuss the implications regarding the dynamics of star-forming regions and the launching of galactic winds. Finally, I will highlight the exciting prospects of using current and upcoming facilities to explore feedback in diverse conditions.
Mario Livio (STScl)
Thursday, October 9, 2014
3:45 p.m.
LGRT 1033
Title:
Brilliant Blunders
Abstract:
Even the greatest scientists have made some serious blunders. "Brilliant Blunders" concerns the evolution of life on Earth, of the Earth itself, of stars, and of the universe as a whole. In this talk, I shall concentrate on and analyze major errors committed by such luminaries as Charles Darwin, Linus Pauling, and Albert Einstein. I will also scrutinize the various types of blunders and attempt to identify their causes. Most importantly, however, I'll argue that blunders are not only inevitable, ­but rather part and parcel of progress in science and other creative enterprises.
Andrew West (Boston University)
Thursday, October 2, 2014
3:45 p.m.
LGRT 1033
Title:
Stellar Underdogs: the Comeback of Low-mass Stars in the Era of
Abstract:
My primary goal of this colloquium is to demonstrate that we can do big science with little stars. M and L dwarfs are the smallest, coolest and least massive (main sequence) stars in the Galaxy. Yet despite their diminutive physical properties, low-mass stars make up ~70% of all of the stars in the Milky Way galaxy and have lifetimes that exceed trillions of years. Their dominance in the Galaxy make low-mass stars excellent tracers of both the structure and evolution of the local Milky Way. In addition, low-mass stars have intense stellar flares and strong magnetic fields that allow us to probe their interiors and may have important consequences for their space weather environments and the habitability of planets that orbit them. I will present results from the largest samples of low-mass stars ever assembled. The advent of large surveys such as the Sloan Digital Sky Survey (SDSS) has yielded photometric and spectroscopic catalogs of more than 100 million and 70,000 stars respectively. Specifically, I will highlight work that has used the unprecedented statistical power of surveys to examine the nature of stellar magnetic fields (and subsequent "magnetic activity") and stellar age, and how large samples of wide low-mass binaries can help us constrain evolutionary models of stars. In addition, I will highlight the confirmation of an age-rotation-activity relation that has come from a collaboration with the MEarth planet hunting team, show how IR excesses around low-mass dwarfs may give us insights into planet formation/evolution, and demonstrate how a large sample of M dwarfs has helped us map the three-dimensional distribution of dust in the local Galaxy.
Debra Fischer (Yale University)
Thursday, September 25, 2014
3:45 p.m.
LGRT 1033
Title:
The Search for 100 Earths
Abstract:
The search for exoplanets is motivated by the question of whether life exists elsewhere. This drives our interest in the detection of planets that are similar to our own world: rocky planets with the potential for liquid surface water and plate tectonics; worlds that might harbor life that we can recognize. Importantly, we will need to discover not just a few, but hundreds of these worlds to eventually gain a statistical understanding of whether life is rare, common, or ubiquitous and ground-based telescopes offer an ideal platform for carrying out decade-long surveys. It is critical for follow-up studies (imaging, atmospheric studies) that these planets orbit nearby stars. In this talk, I will discuss how we plan to take what we've learned and push on to the next frontier: our plans for a next generation spectrograph, EXPRES, to carry out a search 100 Earths with the Discovery Channel Telescope.
Jeff Wagg (SKA)
Thursday, September 11, 2014
3:45 p.m.
LGRT 1033
Title:
From Exoplanets to Cosmic Dawn with the Square Kilometre Array
Abstract:
Building on the major scientific advances made by the current generation of cm and metre-wavelength telescopes, phase 1 of the Square Kilometre Array (SKA) will be the next global radio astronomy observatory. The SKA is being designed by more than 350 engineers and scientists from around the world, with the aim to begin early science operations in 2020. The SKA will answer fundamental questions related to the evolution of atomic Hydrogen in the Universe, from the present day back to the Cosmic Dawn, when the first galaxies began to form less than 200 Myr after the Big Bang. It will also conduct key tests of general relativity through surveys and timing of pulsars in our galaxy, and beyond. I will give an overview of some of the science drivers for the SKA, along with a description of the planned SKA telescopes and the sites that will host them.
Thaisa Storchi-Bergmann (Universidade Federal do Rio Grando do Sul)
Thursday, September 4, 2014
3:45 p.m.
LGRT 1033
Title:
Feeding & Feedback of Supermassive Black Holes tracing Co-evolut
Abstract:
A fundamental role is attributed to supermassive black holes (SMBH) and the feedback they generate in the evolution of galaxies. Cosmologial models that do not consider these feedback effects end up producing over-massive galaxies. I will present and discuss astronomical observations of feeding and feedback processes around SMBHs that occur when the SMBH is being fed in Active Galactic Nuclei (AGN). These observations comprise optical and near-infrared Integral Field Spectroscopy of the inner few hundred parsecs of nearby AGN host galaxies, and are intended to provide constraints to the feeding and feedback processes. I will discuss in particular results obtained by my group that reveal gas inflows along nuclear spirals and disks. The inflow rates are much larger than the AGN accretion rate, suggesting that the excess gas is depleted via formation of new stars that are indeed observed in many casas and can be interpreted as signatures of co-evolution of the host galaxy and its AGN. Gas outflows are prevalent among the highest luminosity AGN, with velocities ranging from a few up to ~1000 km/s and mass outflow rates of a few solar masses per year.
Andy Fruchter (STScI)
Thursday, May 1, 2014
3:45 p.m.
LGRT 1033
Title:
Refusing to Go Quietly: Gamma-Ray Bursts and their Progenitors
Abstract:
Gamma-ray bursts (GRBs) are the most brilliant objects in the universe. Some are initially bright enough to be seen by the unaided eye across a distance of billions of light years. Yet the majority of GRBs which are detected, the so-called long-soft GRBs (LGRBs) are, like most supernovae, produced by the collapse of a massive star. I will discuss the environmental conditions that appear to produce LGRBs, and what this tells us about their progenitor stars. I will also speak about the less frequently detected and even more poorly understood, "short-hard" GRBs (SGRBs), and present recent observations which appear to show a "kilonova" associated with SGRB 130603B. If this interpretation of the data is also supported by observations of future bursts, it will provide direct evidence that SGRBs are formed by the merger of compact objects, and give us an electromagnetic signature that could help locate sources of gravitational waves in the advanced-LIGO era.
Claudia Scarlata (Univ. of Minnesota)
Thursday, April 17, 2014
3:45 p.m.
LGRT 1033
Title:
The WISP survey: overview of recent results for galaxies in the
Abstract:
The WFC3 Infrared Spectroscopic Parallel Survey (WISP) is a large ( ~1000 orbits) HST program that uses WFC3 slitless spectroscopy to detect thousands of galaxies across a wide redshift range 0.3 < z < 2.3. I will present an overview of recent results on emission line galaxies, including a statistical determination of their dust extinction properties, the discovery of a new population of extremely strong emission-line dwarf galaxies, and the implication of the observed number counts for the EUCLID mission. I will also discuss the properties of passive galaxies at z∼1.5 derived from the combination of the WISP spectra with broad-band photometry from HST-UVIS and Spitzer images.
Arjun Dey (NOAO)
Thursday, April 10, 2014
3:45 p.m.
LGRT 1033
Title:
Lyman Alpha Emission and Galaxy Formation: An Observer's Perspec
Abstract:
Lyman alpha has long been used as a signpost of young galaxies in the distant Universe. My collaborators and I are engaged in ongoing searches for Lyman alpha emission at a range of redshifts (z~2-4), discovering both Lyman alpha "blobs" (giant, 100-kpc clouds of glowing, galaxy-forming gas) and much lower mass Lyman alpha emitters, which may be the building blocks of larger galaxies. I will also discuss some of the properties of the new blobs (one of which is a good candidate for an extremely low-metallicity galaxy forming environment) and report on using Lyman alpha as a tracer of protocluster environments at high redshift.I will also talk briefly about the DESI project planned for the Mayall telescope, a cost-effective dark energy project for this decade. I will describe the main scientific goals, the technical plan and the current status of this project.
Jeff Newman (University of Pittsburgh)
Thursday, April 3, 2014
3:45 p.m.
LGRT 1033
Title:
Exploring the Milky Way and the Universe with Extragalactic Surv
Abstract:
Determining the global properties of the Milky Way presents unique challenges, primarily due to our position embedded within its disk. As a result our knowledge of many basic properties of the Galaxy, including itscolor and luminosity, has remained limited. In this talk, I will describe how we have developed improved determinations of the total stellar mass (M) and star formation rate (SFR) of the Milky Way using Hierarchical Bayesian statistical techniques. We then use the results, in combination with data from SDSS, to better determine the Galaxy's luminosity and integrated color. We exploit the close relationship between galaxies' photometric properties and their total stellar mass and star formation rate. We thus select a sample of Milky Way analog galaxies designed to match the best Galactic M and SFR measurements, including measurement uncertainties. Applying the Copernican assumption that the Milky Way should not be special amongst galaxies of similar properties, the color and luminosity distribution of these Galactic analogs then constrains the properties of our own Galaxy much more tightly than previous measurements. In the remaining time, I will describe the next steps in large spectroscopic surveys of the distant universe. I will provide an overview of the eBOSS project, a component of the next-generation SDSS-IV survey beginning observations this summer; eBOSS will obtain redshifts of ~650,000 galaxies and ~850,000 QSOs at 0.6 < z < 3.5 in order to study dark energy via the Baryon Acoustic Oscillations (BAO) technique. I will also describe plans for DESI, the Dark Energy Spectroscopic Instrument, which may be used for a survey of >20 million galaxies and QSOs, placing strong constraints on dark energy models via BAO early in the next decade.
Scott Chapman (Dalhousie University)
Thursday, March 27, 2014
3:45 p.m.
LGRT 1033
Title:
The role of ultra-luminous galaxies in galaxy formation and evo
Abstract:
I will provide an overview of ultra-luminous galaxies (L_IR>1012 Lsun) at high redshift, and the different roles and properties they appear to exhibit as a function of their luminosity. I will focus on the molecular gas properties of the galaxies as the crucial fuel available for star formation, emphasizing our recent work with ALMA and the IRAM Plateau-de-Bure, where we have studied galaxies preselected at various wavelengths, and conducted blind surveys for CO gas. I will conclude with very wide field surveys (SPT) that are uncovering the most extreme specimens of star forming galaxies in the universe, and point to future facilities like CCAT which will push the field to a new level of understanding.
Pete Schloerb (UMass)
Thursday, March 13, 2014
3:45 p.m.
LGRT 1033
Title:
Update on the Large Millimeter Telescope
Abstract:
I will provide an update on the status of the Large Millimeter Telescope. The LMT has begun a second season of "Early Science" observations with its new active surface system in place. The telescope and instruments are working well, and our understanding of the system and its performance have improved greatly over the past year. All in all, things are in good shape, and we have a millimeter-wave telescope that is very competitive with the world's other large millimeter-wave single dish telescopes. I will review the technical performance of the LMT and present some examples of scientific data obtained with the telescope. Then we will turn our attention to the future and present an overview of the completion plan for the full 50m telescope. Finally we will consider the long term future of LMT Observatory and the participation of astronomers from UMass and the US community in this endeavor.
Ranga-Ram Chary (Caltech)
Thursday, March 6, 2014
3:45 p.m.
LGRT 1033
Title:
CSI-Los Angeles: The Growth of Distant Galaxies and Reionization
Abstract:
The discovery of an unusual population of galaxies with extremely strong nebular line emission has come as a panacea to several problems in galaxy evolution. These objects, classified as Halpha emitters, were first detected in the z>5 Universe in deep Spitzer imaging, where they dominate the spectroscopically confirmed star-forming galaxy population. Since then, they have been re-discovered in the local Universe in the Sloan Digital Sky Survey where they constitute 0.04% of the spectroscopic sample, and at intermediate redshifts using Hubble/WFC3 grism surveys. Their ubiquity in the distant Universe and the unusual properties of their stellar population make them strong candidates for being progenitors of massive galaxies at z~2 and for being the primary sources responsible for reionization. I will present our work in identifying these galaxies, insights into the mechanism for fueling star-formation in these objects and the resultant reionization history of the Universe. The merits of using multiwavelength observations in obtaining an improved understanding of high redshift galaxy populations will in particular be highlighted.
Junko Ueda (University of Tokyo and CfA)
Thursday, February 27, 2014
3:45 p.m.
LGRT 1033
Title:
Probing the evolution of merger remnants through formation of c
Abstract:
It has been long predicted from numerical simulations that a major merger of two disk galaxies results in a formation of the spheroid-dominated early-type galaxy. Contrary to this classical scenario of galaxy merger evolution, recent simulations with more realistic gas physics have shown that not all of the major mergers will become an early-type galaxy, but some will reemerge as a disk dominated late-type galaxy. In order to check this scenario and look for observational evidence of a forming molecular disk, we investigate new and archival interferometric CO maps of 37 optically selected merger remnants in the local universe. The new maps are obtained toward 27 sources with ALMA, CARMA, and SMA. We find that 65 % (24/37) of the sample show kinematical signatures of the molecular gas disk in their velocity fields. However, the majority of the merger remnants except for a few shows a compact molecular gas disk relative to the stellar spheroidal component. Unless the disks grow significantly, for example from the return of ejected molecular gas or tidal HI gas, the majority will likely evolve into spheroid dominated early-type galaxies. We tentatively suggest that a few sources with extended gas disks may evolve into disk dominated late-type galaxies, if there are no further mechanism to transport the molecular gas toward the central region.
Joan Najita (NOAO, CfA)
Thursday, February 20, 2014
3:45 p.m.
LGRT 1033
Title:
From Planetesimals to Giant Planets: Chemical and Dynamical Pro
Abstract:
Work with the Spitzer Space Telescope revealed that emission from water and organic molecules is commonly present in the mid-infrared spectra of disks surrounding young stars. I will describe how these features might be used to help lift the veil on a very early stage of planet formation, the formation of planetesimals, those theoretically fundamental but observationally elusive building blocks of planets in core accretion theory. I will also describe some results from high resolution spectroscopy that suggest that forming high-mass giant planets may reveal themselves through non-axisymmetric signatures of their presence, e.g., circumplanetary disks and eccentric inner rims.
Bethany Ehlmann (Caltech (joint with Physics))
Wednesday, February 12, 2014
4 p.m.
Hasbrouck 124
Title:
Following the Water on Mars, Roving with Curiosity
Abstract:
The last decade of Mars exploration with orbiters and rovers has revealed that liquid water was common during the first billion years of the planet's history with diverse aqueous, potentially habitable environments varying in space and time. Curiosity's landing in 2012 provides the opportunity to explore one set of these environments up-close: sedimentary deposits in 150-km Gale Crater. The 10-instrument suite on Curiosity is the most advanced sent to a planetary surface to date, and results from the first year and a half of exploration will be described, along with a look ahead to the coming years as Curiosity's trek continues.
Jason Tumlinson (STScI)
Thursday, February 6, 2014
3:45 p.m.
LGRT 1033
Title:
The Circumgalactic Medium: A New Window on Galactic Fueling, Que
Abstract:
Why do some galaxies quench while others continue to form stars? Where is all the normal matter that galaxies should have, but don't? What happens to all the heavy elements that stars produce? The gas flows that feed galaxies and return their enriched products back to their environments are arguably the most important and least understood processes driving galaxy evolution. I will survey our group's results from Hubble's Cosmic Origins Spectrograph on the diffuse "Circumgalactic Medium" surrounding galaxies that reveal it to be a massive and richly structured medium with important roles as the mediator of galaxy accretion and feedback and a potential answer to some of these open questions about galaxies.
Christine Wilson (McMaster University)
Thursday, January 30, 2014
3:45 p.m.
LGRT 1033
Title:
Gas and Star Formation in Nearby Galaxies: New Results From the
Abstract:
The availability of new instruments and telescopes is making it possible to study large, well-selected samples of nearby galaxies at millimeter and submillimeter wavelengths. These observations trace the cold, dense gas and dust which is the fuel for star formation. I will discuss new results from the Herschel Space Observatory from the Very Nearby Galaxies Survey, which aims to observe the closest example of each major class of galaxy with all the photometric and spectroscopic modes that Herschel has available. Our results include evidence for the primary heating source of much of the dust emission in normal galaxies, an increase in the gas to dust ratio in the vicinity of the central engine in Centaurus A, and a component of very hot molecular gas seen via high frequency CO emission lines that dominates the CO luminosity of starburst and merging galaxies.
Kate Rubin (CfA)
Thursday, December 12, 2013
3:45 p.m.
LGRT 1033
Title:
The Gaseous Environments of Low-Mass Galaxies at z~2
Abstract:
The environments extending several hundred kiloparsecs from galaxies both contain the fuel that feeds galactic star formation as well as act as the reservoir into which ejecta from stellar and AGN feedback are driven. Observations of the cool hydrogen and metal content of these regions (i.e., the circumgalactic medium, or CGM) can therefore provide incisive tests of our understanding of these processes. I will briefly discuss current constraints on the content of the CGM around massive Lyman Break Galaxies and QSO hosts at z~2. I will then describe a new technique that pinpoints much fainter, sub-luminous systems at this epoch, allowing us to probe the gas in their surroundings in absorption toward background QSOs for the first time. These measurements reveal the incidence and spatial distribution of the cool HI and metal enrichment in the lowest-mass halos at the peak of cosmic star formation activity.
Christine Chen (STScI)
Thursday, December 5, 2013
3:45 p.m.
LGRT 1033
Title:
The Origin and Evolution of Dust and Gas in Debris Disks
Abstract:
Debris disks are dusty, gas-poor disks around young stars, generated by collisions between parent bodies and/or sublimation of comets. The Spitzer Space Telescope has enabled photometric searches and detailed spectroscopic studies of thermal emission from dust in hundreds of debris disks at mid- to far-infrared wavelengths. These observations allow us: (1) to infer the spatial structure of dust in individual systems and determine how the dust grains are removed; (2) to measure the disk fraction (in young associations and moving groups) as a function of age to constrain the mechanism that triggers collisions; and (3) to place constraints on the mass of circumstellar molecular hydrogen and therefore models for giant planet formation. In this talk, I will discuss the spatial structure and removal mechanisms of dust in debris disks, and constraints on the models for the formation of gas giants and the late-stages of solar system evolution. I will also describe outstanding questions about debris disk evolution that will be addressed using future ground- and space-based instruments.
Dominik Riechers (Cornell)
Thursday, November 21, 2013
3:45 p.m.
LGRT 1033
Title:
Fueling Cosmic Star Formation: The Molecular Interstellar Medium
Abstract:
Submillimeter galaxies (SMGs) are thought to represent the link between high-redshift star-forming galaxies and passive early type galaxies, with the huge merger driven bursts consuming up most of the available gas and driving the morphological transition to a spheroid. These hyper-luminous high-z galaxies commonly trace regions of high galaxy overdensity, and may be directly related to the formation of galaxy clusters and their giant central ellipticals. Molecular gas plays a central role in our understanding of the nature of these often heavily obscured systems. It represents the material that stars form out of, and its mass, distribution, excitation, and dynamics provide crucial insight into the physical processes that support the ongoing star formation and stellar mass buildup. I will discuss the most recent progress in studies of gas-rich galaxies at high redshift through large submillimeter surveys with the Herschel Space Observatory and detailed follow-up studies of the molecular gas properties of SMGs with CARMA, the Jansky Very Large Array (JVLA), the Plateau de Bure interferometer, and the Atacama Large (sub)Millimeter Array (ALMA).
Chris Hayward (Heidelberg, Germany)
Thursday, November 14, 2013
3:45 p.m.
LGRT 1033
Title:
Advances in galaxy-formation simulations: calculating mock obser
Abstract:
Galaxy formation has been studied using idealized numerical simulations of isolated disk galaxies and galaxy mergers for decades, but most simulations performed to date have suffered from two potentially significant limitations: First, when comparing simulations with observations, physical quantities - rather than observables - from the simulations are used. Second, the most-commonly used techniques, smoothed-particle hydrodynamics (SPH) and adaptive mesh refinement, suffer from numerical inaccuracies that can potentially jeopardize the results of simulations performed with those techniques. I will discuss methods for solving both of these limitations. I address the first limitation by performing 3-D dust radiative transfer on hydrodynamical simulations to calculate spatially resolved UV-mm spectral energy distributions of simulated galaxies. I will present an application to submillimeter galaxies, for which a realistic comparison with observables yields results that are qualitatively different from those of more naive comparisons. I address the second limitation by using the more-accurate moving-mesh hydrodynamics code Arepo. I will discuss how merger simulations performed with the moving-mesh technique differ from otherwise identical simulations performed using SPH. Finally, based on this comparison and other work, I will outline the types of galaxy-formation simulations for which the traditional formulation of SPH is sufficiently accurate and describe when and why this is not the case.

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