Colloquia Archives

Reka Winslow (University of British Columbia)
Thursday, October 31, 2013
3:45 p.m.
LGRT 1033
Title:
Investigation of Mercury's magnetospheric and surface magnetic
Abstract:
Mercury’s proximity to the Sun and its low magnetic field strength lead to dynamic interactions of the solar wind with the magnetosphere as well as with the planet’s surface, which are unique in the solar system. MESSENGER, having been in orbit about Mercury since March 2011, has made important discoveries of this exciting magnetospheric environment. In this talk, I will discuss some aspects of Mercury’s magnetosphere, paying special attention to the bow shock, magnetopause, and cusp regions as well as to the planet’s internal magnetic field. I will discuss how we characterized the time-averaged shape and location of Mercury’s magnetopause and bow shock, as well as established these boundaries’ responses to the solar wind and interplanetary magnetic field. I will also describe the first observations of Mercury’s northern cusp region using Magnetometer data, and our estimates of the flux of precipitating particles to the surface. Finally, I will discuss a novel adaptation of the electron reflectometry technique in which we use protons precipitating to the surface (observed by the Fast Imaging Plasma Spectrometer onboard MESSENGER) to acquire the first measurements of Mercury’s surface magnetic field strength.
Marc Postman (STScI)
Thursday, October 24, 2013
3:45 p.m.
LGRT 1033
Title:
The Cluster Lensing And Supernova survey with Hubble (CLASH)
Abstract:
The Cluster Lensing And Supernova survey with Hubble (CLASH), a 524-orbit Multi-Cycle Treasury Program, completed its observations this past July. CLASH uses the gravitational lensing properties of 25 galaxy clusters to address at least 4 key science objectives: (1) Map the dark matter distribution in clusters with unprecedented accuracy, (2) Detect type Ia supernova out to z~2 to constrain their rates, the time evolution of the dark energy equation of state and the evolution of SN Ia themselves, (3) Detect and characterize some of the most distant galaxies (z > 7), and (4) study the internal structure and evolution of the galaxies in and behind the clusters. The survey obtained broadband images of the clusters in 16 passbands, providing remarkable panchromatic coverage from 0.2 - 1.6 microns, all with HST-quality resolution. I will present highlights from each of the 4 main science objectives.
Roman Shchebarkov (Univ. of Maryland)
Thursday, October 17, 2013
3:45 p.m.
LGRT 1033
Title:
Feeding and Feedback in Nearby Low-luminosity AGNs.
Abstract:
Most galaxies in the Universe host low-luminosity AGNs. These systems exhibit a vast range of dynamical and radiative effects, which require high sensitivity and high angular resolution to study. The closest objects with the largest central supermassive black holes are revealing their secrets with the improvement of instrumentation. I will review recent progress on observing with Chandra and modeling of the accretion flow onset regions in Sgr A* and NGC3115. The hot accretion flow in these sources is shaped by the combined effects of (1) radius-dependent mass injection by stellar winds, (2) galactic gravitational potential, (3) small-scale feedback such as conduction, and (4) supernova feedback. The natural outcomes of modeling are the virial/supervirial gas temperature and inhibited accretion with shallow density profile.
Massimo Stiavelli (STScI)
Thursday, October 10, 2013
3:45 p.m.
LGRT 1033
Title:
Reionization and first light studies using space telescopes: an
Abstract:
I will discuss what existing data tell us about the reionization of the Universe and the role played by faint galaxies including some new results derived by constraining the faint end of the luminosity function at redshift 6 using a form of surface brightness fluctuations analysis. I will also discuss expectations for the JWST contribution in this field. Moving to higher redshift I will discuss how JWST will study the first galaxies and the constraints it could place on the first stars by studying their supernovae.
Laura Cadonati (UMass)
Thursday, October 3, 2013
3:45 p.m.
LGRT 1033
Title:
Progress towards gravitational wave astronomy
Abstract:
The quest for gravitational waves is reaching a key milestone as Advanced LIGO is approaching completion and science runs are scheduled to begin in 2015. In this talk, I will review the status and timelines of second generation gravitational wave detectors and the prospected observing scenarios over the next decade, with focus on searches for gravitational wave transients, the ability to localize gravitational wave sources and the ongoing efforts towards coincident searches of gravitational wave and electromagnetic signatures.
Kate Whitaker (GSFC)
Thursday, September 26, 2013
3:45 p.m.
LGRT 1033
Title:
The Quenching of Star Formation in Massive Galaxies
Abstract:
Nearby galaxies exhibit a bimodal color distribution, where actively star-forming galaxies have blue colors and quiescent galaxies have red colors. It is generally thought that red galaxies arise from blue galaxies when star formation is quenched. However, the origin of this color bimodality remains unknown. Furthermore, it is not well understood how actively star-forming galaxies quench and migrate to form the well-defined color-mass relation, known as the “red sequence”. In this talk, direct evidence is presented that the massive end of the red sequence is most-rapidly building up when the universe was only 3 billion years old, with an influx of young recently quenched galaxies that are almost non-existent over the past 8 billion years. Presenting recent results from the 3D-HST Survey, I will discuss the properties of these massive galaxies in the context of current galaxy formation and evolution theories.
Jason Kalirai (STScI)
Thursday, September 19, 2013
3:45 p.m.
LGRT 1033
Title:
Exploring the Stellar Graveyard of the Milky Way
Abstract:
Abstract: 98% of all stars will end their lives as white dwarfs. In old stellar populations, such as globular clusters and stellar halos, the bulk of the progenitor stellar mass function above the present day turnoff is therefore now populated on the white dwarf cooling sequence. These remnants have remarkable properties and can be studied in exquisite detail to reveal their temperatures, gravities, and masses. In this talk, I will describe unprecedented HST imaging and Keck spectroscopic observations of these stars in old stellar populations. This work has led to the first global constraints on the mapping between initial stellar mass and final mass, and therefore has broad applications for understanding stellar evolution theory, mass loss, and chemical enrichment of the interstellar medium. Additionally, through a new technique, I will describe how we can invert the process of stellar evolution to establish a relation between the remnant mass in an old stellar population and the parent age. By applying this technique to nearby Milky Way halo stars, we measure the age of the inner halo of the Milky Way to be 11.4 ± 0.7 Gyr.
Daniela Calzetti (UMass)
Thursday, September 12, 2013
3:45 p.m.
LGRT 1033
Title:
KINGFISH, or Key Insights on Nearby Galaxies: a Far-Infrared Su
Abstract:
TBABy targeting the far-infrared and sub-millimeter regime with unprecedented sensitivity and angular resolution, the Herschel Space Telescope has provided new insights into both the phenomenology and the physics of dust emission from galaxies. I review the results obtained so far by KINGFISH (Key Insights on Nearby Galaxies: a Far-Infrared Survey with Herschel), an Herschel Open Time Key Project, and by similar projects on galaxies within the local ~30 Mpc, where Herchel affords a spatial resolution better than ~ 0.8-5 kpc, and can thus probe the variety of environments within galaxies.
William Irvine (UMass)
Thursday, May 2, 2013
3:45 p.m.
LGRT 1033
Title:
The Development of Astronomy & Astrobiology in the Five College
Abstract:
The last 180 years of astronomy at the institutions now known as the Five Colleges include: students arriving at college by stage coach; an observatory built as an octagon; a famous poet; an infamous, illicit love affair; pioneering observations from the Chilean desert; early astrobiology; the first SETI, more than 100 years ago; the first astronomical observations from an artificial platform above the earth’s surface; an innovative way to augment department budgets; discrimination against women in astronomy; the Layzer-Irvine equation; the Hapke-Irvine Law; a 100-ft long absorption cell for infrared spectroscopy; telescopes built with telephone poles and chicken wire; a Nobel prize; the Rydbeck factor; the Five College Radio Astronomy Observatory; new interstellar molecules; viruses from space and a new physical/biological measurement unit; a phony press release picked up by the media; giving the International Halley Watch FITS; and, after 800 years, a Scottish coat-of-arms with a comet (Halley’s, of course).
John O'Meara (Saint Michael's College)
Thursday, April 25, 2013
3:45 p.m.
LGRT 1033
Title:
Rediscovering the Universe at Redshift 3
Abstract:
The 1990's saw revolution of our understanding of the high redshift universe through the advent of 10 meter class telescopes and the application of large scale computer simulations to cosmology. Since that time, new advances in instrumentation and simulation have pushed the techniques from high redshift to more recent epochs. In this talk, I will discuss how we have returned to the universe at z~3 with new technologies, theories, and techniques, and how these advances can re-revolutionize our understanding of the universe over all cosmic times.
Debra Elmegreen (Vassar College)
Thursday, April 11, 2013
3:45 p.m.
LGRT 1033
Title:
Local Analogs of Early Universe Galaxies
Abstract:
The Hubble Ultra Deep Field in the redshift range z=1 to 5 is dominated by clumpy galaxies, whose kiloparsec-scale star-forming complexes have masses 100x greater than similar complexes in local spirals. The clumps evidently form from gravitational instabilities following gas accretion, and the galaxies transform into the familiar disk morphologies of nearby spirals after a Gyr. Though rare, there are UV-bright local analogs of these distant clumpy galaxies that appear to be at an early evolutionary stage. I will compare star formation properties of local and distant galaxies based on photometry and spectroscopy, and present recent observations of local tadpole galaxies that show evidence for accretion of metal-poor gas.
Jeff Bary (Colgate )
Thursday, March 28, 2013
3:45 p.m.
LGRT 1033
Title:
The Importance of Being Duplicitous: Why Binarity Matters
Abstract:
In spite of the depiction of Luke Skywalker's home planet of Tatooine as orbiting two suns, astronomers have long assumed that such systems would be difficult if not impossible to form and remain stable. Recently, the Kepler space telescope has discovered several exoplanetary systems (Kepler 16-b, 34-b, 35-b, 47-b, and 47-c) in which the planet(s) orbit(s) both of the host stars. These recent detections highlight the importance of binary and higher order multiple systems to our overall understanding of the processes that lead to the formation of planets. In this talk, recent observational studies comprised of multi-epoch spectroscopic monitoring and high-spatial resolution spectral imaging of two distinctly different young binary systems will be presented. With both observational programs we seek to reveal the underlying dynamical complexity of such systems and the interactions between the stellar cores, the circumstellar disks, and circumbinary disk.
Helen Kirk (McMaster University)
Thursday, March 14, 2013
3:45 p.m.
LGRT 1033
Title:
Filamentary Flows and Clustered Star Formation
Abstract:
Most stars, including our Sun, are thought to have formed within a stellar cluster, yet much of the star formation process within this type of environment is poorly constrained. Recent results from the Herschel Space Telescope hint that dense filaments of gas and dust are intimately linked with star formation, for both isolated stars and clustered systems. Several models also predict the importance of filaments in cluster formation, but observations of the key predicted processes are limited. I will present results from a Mopra survey of the Serpens South system which addresses this lack of observations. Serpens South is a recently discovered young cluster forming deeply embedded within a prominent dense filament. As such, it provides an ideal testbed for the scenario of significant mass accretion onto clusters via filaments. I will finish by discussing ways in which numerical simulations of star formation can be used to gain a deeper understanding of the processes involved, highlighting ongoing efforts of the group at McMaster University.
B-G Anderson (SOFIA)
Thursday, March 7, 2013
3:45 p.m.
LGRT 1033
Title:
Status of the Stratospheric Observatory for Infrared Astronomy
Abstract:
The Stratospheric Observatory for Infrared Astronomy (SOFIA) is now performing scientific observations and the Call for Proposals for the second open observing cycle is about to be released (late April). With an available wavelength coverage from the visual to sub-mm wavelengths and a long life time - including planned instrument upgrades, SOFIA will provide critical resource for the astronomical community for the next decade and beyond. Current and expected SOFIA instruments provide heterodyne spectroscopy in the THz band, including the line of [O I], [C II] and [N II] as well as OH, HD and many other hydrides, at high spectral resolution. Echelle spectroscopy in the Mid-infrared (MIR) which will allow observations of e.g. fine-structure lines of and H2 pure rotational lines. These will help address questions of interstellar chemistry and physics in star forming regions, PDRs and galaxies. Mid-infrared (MIR) grism spectroscopy, of e.g. dust and ices, can be used to address questions of the freeze-out of molecules from the gas phase to better understand the formation, destruction and characteristics of interstellar ices. Imaging in the MIR and FIR and FIR polarimetry can provide a more complete picture of the temperature, density and magnetic field structure of e.g. star forming cores. I will highlight the current and expected capabilities of SOFIA and some of the early science results achieved.
Robert Feldman (University of California, Berkeley)
Thursday, February 28, 2013
3:45 p.m.
LGRT 1033
Title:
It's the law - The role of star formation laws for galaxy evolut
Abstract:
Empirical relations connecting star formation and the interstellar medium form the basis of many theoretical models of galaxy evolution. After reviewing the current observational status (and its limitations) of star formation laws, I will show what role they play for the evolution of various global galaxy properties. Observations of the mass-metallicity relation and of the cosmic star formation history, in particular, put stringent constraints on the actual functional relationship between star formation and the gas reservoir of galaxies. These results point towards a very simple and essentially time-independent star formation law that encapsulates most aspects of star formation relevant for the evolution of average galaxy properties across cosmic history.
Aaron Dutton (Max Planck Institute for Astronomy, Heidelberg)
Thursday, February 21, 2013
3:45 p.m.
LGRT 1033
Title:
Star Formation, Galaxy Formation and the Nature of Dark Matter
Abstract:
The distribution of dark matter in galaxies provides a non-linear scale cosmological test of dark matter models. However, the utility of this test is at present limited by our lack of knowledge about how dark matter haloes respond to galaxy formation, and form of the stellar initial mass function. I will discuss recent progress in constraining these unknowns, including methods based on galaxy scaling relations and strong gravitational lensing. Finally, I will describe how the relation between stellar mass and galaxy rotation velocity (also known as the Tully-Fisher relation) together with the stellar mass function can be used to place constraints on the temperature of warm dark matter candidates.
Michael Boylan-Kolchin (University of California, Irvine)
Thursday, February 14, 2013
3:45 p.m.
LGRT 1033
Title:
Near-Field Cosmology: Big Science From Small Galaxies
Abstract:
Near-Field Cosmology: Big Science From Small Galaxies
Stella Offner (Yale)
Thursday, February 7, 2013
3:45 p.m.
LGRT 1033
Title:
Symbiotic Star Formation: Modeling the Complex Ecology of Molecu
Abstract:
The details of star formation are intimately related to the natal molecular cloud environment. This environment is in turn shaped by radiative and kinematic feedback from embedded forming stars. In this talk, I will present gravito-radiation-hydrodynamic simulations of clustered star formation. I will explore how protostellar radiation and mass outflows impact the stellar initial mass function, multiplicity, and molecular cloud evolution. I will discuss the importance of producing "synthetic observations", for example by modeling dust and CO line emission, in order to connect numerical results directly to observables.
Smadar Naoz (CfA)
Tuesday, February 5, 2013
3:45 p.m.
LGRT 1033
Title:
The Origin of Retrograde Hot Jupiters
Abstract:
The search for extra-solar planets has led to the surprising discovery of many Jupiter-like planets in very close proximity to their host star, the so-called ``hot Jupiters'' (HJs). Even more surprising, many of these HJs have orbits that are eccentric or highly inclined with respect to the equator of the star, and some (about 25%) even orbiting counter to the spin direction of the star. This poses a unique challenge to all planet formation models. We show that secular interactions between Jupiter-like planet and another perturber in the system can easily produce retrograde HJ orbits. We show that in the frame of work of secular hierarchical triple system (the so-called Kozai mechanism) the inner orbit's angular momentum component parallel to the total angular momentum (i.e., the z-component of the inner orbit angular momentum) need not be constant. In fact, it can even change sign, leading to a retrograde orbit. A brief excursion to very high eccentricity during the chaotic evolution of the inner orbit allows planet- star tidal interactions to rapidly circularize that orbit, decoupling the planets and forming a retrograde hot Jupiter. We estimate the relative frequencies of retrograde orbits and counter to the stellar spin orbits using Monte Carlo simulations, and find that the they are consistent with the observations. The high observed incidence of planets orbiting counter to the stellar spin direction may suggest that three body secular interactions are an important part of their dynamical history.
Catherine Espaillat (CfA)
Thursday, January 31, 2013
3:45 p.m.
LGRT 1033
Title:
Characterizing Planet-Forming Disks Around Young Stars
Abstract:
Theoretical simulations predict that a young planet will interact with the accretion disk surrounding its host star, clearing the material around itself and leaving behind an observational signature in the form of a clearing in the disk. Circumstellar disks with large, inner holes have been detected and are known as "transitional disks." A few years ago, Spitzer identified a new class of "pre-transitional disks" which have gaps rather than holes - they have an inner disk, a gap, and an outer disk. These gapped disks are the strongest evidence to date for disk clearing by planets and serve as signposts to guide young planet searches in the ALMA era.
Kristian Finlator (University of California Santa Barbara)
Tuesday, January 29, 2013
3:45 p.m.
LGRT 1033
Title:
Galaxy Formation and Feedback During the Cosmic Dark Ages
Abstract:
The study of structure formation during the first billion years is advancing rapidly, driven by pathfinding discoveries with the Hubble Space Telescope and motivated by anticipated studies that will wield next-generation facilities including ALMA, JWST, and LOFAR. I will show how detailed comparisons between numerical simulations and observations such as these inform our understanding of galaxy growth well into the cosmic dark ages. I will discuss observational and theoretical arguments that constrain how young galaxies ionized and heated the intergalactic medium. I will describe how the intergalactic medium's structure regulated the progress of cosmological reionization. Finally, I will show how a new class of cosmological radiation hydrodynamic simulations can be used to interpret existing observations of low-ionization metal absorbers that trace the earliest stages of structure formation.
Viviana Acquaviva (New York City College of Technology)
Thursday, January 24, 2013
3:45 p.m.
LGRT 1033
Title:
From galaxies to cosmic acceleration
Abstract:
The accelerated expansion of the Universe could be due either to Dark Energy filling space, or to General Relativity failing on large scales. By studying the evolution and clustering of galaxies, we can probe both the expansion history and the linear growth of structure, thereby testing these two scenarios across cosmic time. I will present my efforts at improving our understanding of galaxy properties through Spectral Energy Distribution (SED) fitting, the process of comparing theoretical templates to observations in order to find which models best resemble the data. I will introduce GalMC, our publicly available Markov Chain Monte Carlo algorithm for SED fitting, and show how it can be used to recover the age, mass, dust content, metallicity and star formation history of galaxies, with reduced systematics. I will also present SpeedyMC, the fast kin of GalMC optimized for very large surveys, and describe our ongoing work as a joint analysis of photometric redshifts and SED fitting parameters. Finally, I will describe the science goals of the Hobby Eberly Telescope Dark Energy eXperiment (HETDEX), which will discover about a million Lyman Alpha Emitting galaxies at 2 < z < 3.5 and use them to shed light on the behavior of dark energy and gravity in this largely unexplored redshift range.
Aaron Evans (NRAO)
Thursday, April 26, 2012
3:45 p.m.
LGRT 1033
Title:
GOALS: The Great Observatories All-sky LIRG Survey
Abstract:
Luminous Infrared Galaxies (LIRGs) are observed primarily to be interacting and merging galaxies. They are the sites of rampant star formation and active galactic nuclei (AGN), which are fed by abundant supplies of molecular gas. However, the very property that led to their initial discovery as a significant population - their high infrared luminosity - also makes them difficult to study; the majority of the UV and optical light from young, massive stars and AGN is absorbed by obscuring dust and re-emitted in the infrared. The Great Observatories All-sky LIRGs Survey thus makes use of the diversity in wavelength coverage of the present space-based telescopes to probe the activity in a large (~ 100 - 200), flux-limited sample of LIRGs from the Revised Bright Galaxy Sample (RBGS). The majority of the talk will be devoted to discussing the survey as a whole. The latter part of the talk will be focussed specifically on a GOALS analysis of NGC 2623.
Stella Offner (CfA)
Thursday, April 12, 2012
3:45 p.m.
LGRT 1033
Title:
The Role of Episodic Accretion in Star Formation
Abstract:
A number of young stars, like FU Orionis, have been observed to experience short abrupt changes in their luminosity of an order of magnitude or more. These changes are commonly attributed to episodic fluctuations in the accretion rate onto the star. However, the characteristics, frequency and importance of these bursts in the star formation process are poorly constrained. Recently, episodic accretion has been proposed as the origin of the stellar age spread in low-mass stars inferred in young clusters. Episodic accretion has also been suggested as a solution for the protostellar "luminosity problem," wherein protostars are observed to be dimmer than predicted by star formation models. In this talk, I will give an overview of each of these issues and evaluate whether episodic accretion could provide a solution. I will also discuss some current and future observational programs that may help to constrain protostellar accretion histories.
Bruce Draine (Princeton)
Thursday, April 5, 2012
3:45 p.m.
LGRT 1033
Title:
Infrared, Submm, and Microwave Emission from Interstellar Dust
Abstract:
Interstellar dust radiates most powerfully in the far-infrared, typically peaking in the 100-200um region. However, the emission at longer wavelengths is often unexpectedly strong. This is particularly true at microwave frequencies (~cm wavelengths), where sensitive studies of the CMB revealed emission that was far stronger than expected. This "anomalous microwave emission" is almost certainly produced in part by dust grains (PAHs) spinning at tens of GHz, although other processes may also contribute. The emission at mm- and submm wavelengths has also been problematic. Some galaxies (e.g., the SMC) show much stronger emission near ~1 mm than expected from "normal" dust models. This is sometimes attributed to large masses of very cold dust, but more likely it is telling us about new emission processes. I will argue that much of the submm excess in the SMC may be magnetic dipole emission from iron nanoparticles. If true for the SMC, this may presumably apply to other low-metallicity galaxies as well.
Daniel Eisenstein (CfA)
Thursday, March 29, 2012
3:45 p.m.
LGRT 1033
Title:
Dark Energy and Cosmic Sound
Abstract:
I will discuss how the acoustic oscillations that propagate in the photon-baryon fluid during the first million years of the Universe provide a robust method for measuring the cosmological distance scale. The distance that the sound can travel can be computed to high precision and creates a signature in the late-time clustering of matter that serves as a standard ruler. Galaxy clustering results from the Sloan Digital Sky Survey reveal this feature, giving a geometric distance to a redshift of 0.35 and an accurate measurement of Omega_matter. I will review our recent work on the theory and practice of the acoustic oscillation method and our latest cosmology results from SDSS-II. I will then present SDSS-III, which will use the acoustic method to produce 1% distance measurements in order to map the curvature and expansion history of the Universe and measure the evolution of dark energy.
Alexey Vikhlinin (CfA)
Thursday, March 15, 2012
3:45 p.m.
LGRT 1033
Title:
On the long-term future of X-ray astronomy
Abstract:
Chandra has revolutionized X-ray astronomy by being a versatile observatory for studying objects ranging in scale from the inner structure of the Crab pulsar nebula to high-redshift AGNs, clusters of galaxies, and cosmology. Chandra is operating well and is expected to last into 2020's. In the next few years, we expect a launch of an array of smaller missions, which will open new areas of X-ray astronomy such as polarimetry, imaging at E>10 keV, sensitive surveys, high-resolution X-ray spectroscopy, ensuring a continues short-term vibrancy of the field. However, in the post-Chandra era, X-ray astronomy cannot be sustained by small-scale experiments, and there are no concrete plans for a powerful, observatory-class mission. What an X-ray observatory for the 2020's can look like? We are developing a concept, SMART-X, for a next-generation X-ray observatory with large-area, 0.5" resolution grazing incidence adjustable X-ray mirrors, high-throuput critical transmission gratings, and X-ray microcalorimeter and CMOS-based imager in the focal plane. High angular resolution is enabled by new technology based on controlling the shape of mirror segments using thin film piezo actuators deposited on the back surface. Science application include observations of growth of supermassive black holes sinse redshifts of ~10, ultra-deep surveys overs 10's of square degrees, galaxy assembly at z=2-3, as well as new opportunities in the high-resolution X-ray spectroscopy and time domain.
Caleb Scharf (Columbia)
Thursday, March 8, 2012
3:45 p.m.
LGRT 1033
Title:
Outstanding questions for exoplanetary science
Abstract:
Exoplanetary science has gone from non-existence to a burgeoning field in less than 20 years. I'll present an overview of where it stands now, from the extraordinary abundance of exoplanets to the remarkable diversity of system architectures and planetary characteristics. Many huge questions remain, and I'll discuss some work on planet formation and the nature of terrestrial-like worlds, including the application of new computer technology to planet discovery and system simulation.
David Hogg (NYU)
Thursday, March 1, 2012
3:45 p.m.
LGRT 1033
Title:
Finding the dark matter
Abstract:
One of the principal goals of Gaia and surveys like it is to infer the density map and formation history of the Milky Way. I present a few toy problems in which we use phase-space information for a snapshot of tracer particles to infer the matter density within the system. All known methods for performing this inference make multiple assumptions that are known to be false for the Galaxy, and few have made proper use of the observational noise model. I will express some optimism for methods that make use of cold phase-space structures and other kinds of rare but informative tracers.
Michael Kuhlen (UC Berkeley)
Tuesday, February 28, 2012
3:45 p.m.
LGRT 1033
Title:
Computational Cosmology and Galaxy Formation
Abstract:
Fueled by continuing advances in numerical methods and computational capabilities, the future of galaxy formation theory is going to be driven by numerical simulations. Yet computational galaxy formation is extremely challenging, owing to the multitude of important physical processes and the wide range of scales over which they operate. Much of the galaxy formation simulation work to date has relied on simple, and often ad-hoc, subgrid models for star formation and feedback. In this talk I will describe my recent efforts to improve this situation by including more realistic and physics-driven treatments of some of the relevant processes. As one example, I will discuss cosmological adaptive mesh refinement simulations in which star formation is regulated by the local abundance of molecular hydrogen. These simulations reproduce much of the observational phenomenology of star formation rates as a function of atomic and molecular gas content and metallicity. At the same time this new piece of physics leads to a suppression of the stellar content of low mass dark matter halos, thereby helping to explain the vexing dwarf galaxy problem.

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