 |
Event
Presentations
|
|
|
Listing of Talk Abstracts
| The Role of Dwarf Galaxy Interactions in Shaping the Magellanic System and Implications for Magellanic Irregulars and Dwarf Spheroidals |
| Gurtina Besla (Columbia University) |
|
I will present a new numerical model of the evolution of the Milky Way's largest satellite galaxies, the Large and Small Magellanic Clouds (LMC/SMC), in which their current internal structure and kinematics and large-scale gas morphology are dictated by their mutual tidal interactions, rather than interactions with the Milky Way. This picture is consistent with the recent HST proper motions of the LMC (Kallivayalil et al. 2006) - using cosmologically motivated models for the Milky Way, these new proper motions imply that the Clouds have not made multiple passages about the Milky Way.
In particular, the LMC's peculiar off-center bar and one-armed spiral morphology is a natural by-product of a recent direct collision with the SMC. This scenario may shed light on the dynamical state of a class of dwarf galaxies known as Magellanic Irregulars (de Vaucouleurs & Freeman 1972), which, like the LMC, are asymmetric spirals with off-center bars, but are rarely associated with massive spirals.
As a result of its collision with the LMC, the simulated SMC is left in a highly disturbed state where its older stellar population does not display a pronounced rotation curve, as observed. The SMC may thus represent an object in transition from a dwarf Irregular galaxy to a dwarf Spheroidal. This process is expected to occur ubiquitously in small groups of low mass galaxies and may represent a generic mode of dwarf galaxy evolution that is independent of proximity to a massive host. |
|
| New Observational Constraints on the Formation of the Milky Way's Disk(s) |
| Jo Bovy (Institute for Advanced Study) |
| Observations of the structure and kinematics of different stellar populations in the Milky Way's disk provide a unique perspective on disk formation and evolution. I will discuss how current and future data sets that provide detailed kinematics and elemental abundances
beyond the Solar neighborhood lead to qualitatively new tests of internal and external disk evolution models. In particular, I will show recent results from a dissection into mono-abundance components of the Galactic disk based on SDSS/SEGUE data. These results show that the individual components are simple, but exhibit very different spatial structure, and they lend direct observational support for inside-out formation models for galactic disks. |
|
| Fundamental Properties of Main-sequence Stars |
| Tabetha Boyajian (Georgia State University) |
| This presentation will review the recent results from a survey to measure the fundamental properties of nearby, main-sequence stars. Direct measurements of the stellar angular diameter are obtained through interferometry. This information coupled with the distance and bolometric flux, provides a direct way to determine the stellar linear radius, effective temperature and luminosity. I will highlight the challenges these data bring to current stellar atmospheric and evolutionary models, as well as newly defined empirically based relations to the stellar effective temperature and radius.
|
|
| Photometric Detection of Transiting Planets with Highly Nonlinear Ephemerides |
| Joshua Carter (Smithsonian Astrophysical Observatory) |
| To date, the tools to find transiting exoplanets in photometric data are identical with respect to a single assumption: the transits are strictly periodic. This is strictly not true when more than two bodies are gravitationally bound (e.g., multi-planet systems, circumbinary planets or transiting exomoons). The scale of nonlinearity depends on the mass ratios and separations in the system but the timing variations can be small (e.g., Kepler-18), medium (e.g., Kepler-11) or large (e.g., Kepler-16 – which has 9 day variations). The combination of large timing variations and small transit signal-to-noise ratios render strictly periodic search algorithms ineffective at finding these valuable targets. We present a new solution for detecting these planets, the Quasiperiodic Automated Transit Search (QATS) algorithm. The QATS algorithm is a maximum likelihood search that requires that the interval between any two successive, equivalently shaped box-like events be bounded between a minimum and maximum value. We will motivate the importance of such an algorithm, present example applications to real and simulated Kepler data, discuss the false alarm probability, and show initial detection results. |
|
| The Importance of Dusty Starbursts to the Cosmic Star Formation History of the Universe |
| Caitlin Casey (IfA Hawaii) |
| Whether most of the Universe's stars are formed in galaxy mergers or quiescent, secular processes is fiercely debated. Recently, the importance of infrared-bright, dusty galaxies to the cosmic star formation rate density has become evident, shifting many galaxy evolution studies to longer wavelength regimes where dust emits. I will present recent results on a large ongoing redshift survey of Herschel-SPIRE selected galaxies, and implications on the star formation history of the Universe from 0
|
|
| The Role of Environment in the Size Evolution of Massive Early-type Galaxies at Intermediate Redshift |
| Mike Cooper (UC Irvine) |
| Highly-complete spectroscopic redshift surveys in fields imaged by HST enable both the morphology and the local environment of a galaxy to be measured out to intermediate redshift. In this talk, I will present a summary of recent spectroscopic efforts in deep HST imaging fields, including those currently being surveyed as part of the CANDELS Multi-Cycle Treasury Program. In addition, I will discuss recent results regarding the role of environment in driving the size evolution of the massive early-type population, investigating the role of minor mergers in puffing up the sizes of compact red galaxies at z < 2.
|
|
| The Dependence of the Neutrino Mechanism of Core-Collapse Supernovae on the Equation of State |
| Sean Couch (University of Chicago) |
| Numerical simulations of core-collapse supernovae suggest that the critical neutrino luminosity necessary to cause explosions is dependent on dimensionality. The lower threshold for explosion in 2D versus 1D has been well-documented, but recently Nordhaus et al. (2010) have found that going to 3D simulations further reduces the critical neutrino luminosity by around 20% as compared with 2D simulations. This result may reflect the fundamental difference in the development of turbulence between 2D and 3D simulations and may indicate that 3D simulations are critically necessary to study core-collapse supernovae. The conclusion that the critical neutrino luminosity is reduced in 3D simulations is not yet well-established, however. Hanke et al. (2011) conducted a study similar to that of Nordhaus et al. and find that, while the critical luminosity in 2D is lower than in 1D, going to 3D does not result in a significantly lowered critical neutrino luminosity for explosion. This leaves open the question of the importance of 3D simulations and what physical mechanisms reduce the critical neutrino luminosity in simulations of core-collapse supernovae. I will discuss my recent effort to simulate core-collapse supernovae using the FLASH code. I will discuss in particular the dependence of the neutrino mechanism on the equation of state employed. I have conducted a parameter study in 1D and 2D in which the EOS is varied as well as the driving neutrino luminosity. I will present my results for the commonly used Shen et al. (1998) and Latter & Swesty (1991) EOS that show the neutrino mechanism is significantly dependent on the EOS used.
|
|
| Peeking into the Crust of a Neutron Star |
| Nathalie Degenaar (University of Michigan) |
| Neutron stars are the densest, directly observable stellar objects in our Universe. As such, they provide a gateway to study the behavior of matter under extreme physical conditions and serve as outstanding probes to test theories of gravity. Understanding the structure and composition of neutron stars is a key element of such challenges. I will explore how we can employ observations of accreting neutron stars to track their thermal evolution and how this yields us important insight into their interior properties. |
|
| New Probes of Substellar Evolution from Infrared Parallax Programs |
| Trent Dupuy (CfA/SAO) |
| A broad-brush view of the evolution of photometric and spectroscopic properties of brown dwarfs has been in place for nearly a decade, largely thanks to the first parallax programs that enabled modest samples of brown dwarfs to be placed on color-magnitude diagrams (CMDs). However, these previous samples were not populous enough to probe some significant physical effects such as the impact of cloud clearing on evolution and the role of "second parameters" such as metallicity and surface gravity in shaping the emergent spectra of ultracool dwarfs. I will present large sample of parallaxes from our high-precision astrometric monitoring campaign using CFHT/WIRCam that has now enabled some of these next generation tests of substellar evolution. We discover a "gap" in near-IR CMDs at the L/T transition, where the dominant source of photospheric opacity changes from dust clouds to molecular absorption bands. This implies that the last stages of cloud clearing occur very rapidly, and this L/T gap may also be linked to an earlier slowing of brown dwarf evolution as predicted by the latest evolutionary models that incorporate a realistic treatment of dust in ultracool photospheres for the first time. We also find that the latest type T dwarfs show an unanticipated amount of scatter in near-IR absolute magnitudes at a given spectral type, suggesting that metallicity and/or surface gravity variations have a much strong effect at such low temperatures than previously realized. Finally, I will discuss the future directions of this work: pushing out to the larger distances of young moving groups to measure distances for planetary-mass objects; and using Spitzer parallaxes to establish the temperature scale for the newly discovered Y dwarf spectral class. |
|
| Multiply-Transiting Planetary Systems from Kepler
|
| Daniel Fabrycky (University of California Santa Cruz) |
| NASA's Kepler Space Telescope uses photometry to detect dimming due to transits of small planets in front of their stars. It has found ~2300 planet candidates and ~365 systems of more than one candidate, an extraordinary dataset for studying the orbital architectures and dynamics of planetary systems. Regarding their architecture, we find their orbits to be nearly coplanar and the logarithm of their orbital periods to be even spaced, traits shared with the Solar System. Regarding their dynamics, we are confirming these candidate systems by showing how the observed changes in orbital periods result from interplanetary gravitational perturbations. |
|
| The Evolution of Galaxy Colors and their Contribution to Reionization at 4 < z < 8 |
| Steven Finkelstein (The University of Texas at Austin) |
| We present recent results from the CANDELS project on the evolution of the rest-frame UV colors from galaxies, as well as their contribution to the reionization of the intergalactic medium, in the crucial epoch of 4 < z < 8. With the much larger volume probed by CANDELS, we have now placed stronger limits on the likelihood of very metal-poor stars at high redshift, finding that even the faintest galaxies at z ~ 7 have colors consistent with local blue galaxies. In general, galaxies at z~7 are consistent with being dust-free, while by z~4 the typical galaxy has 0.3-0.4 mag of dust attenuation. However, when examining this trend as a function of stellar mass, we find that the most massive galaxies are dusty at all redshifts. It thus appears likely that star-formation-related feedback (i.e., supernovae) are preferentially removing dust from the highest mass galaxies, which is a manifestation of the mass-metallicity relation seen at lower redshift. The lower mass galaxies do not begin to build up their dust reservoirs until low-mass stars pass through their AGB phase, which implies a formation epoch for these galaxies of z > 10. Finally, we examine the specific luminosity density of our sample of galaxies, and we find that the galaxies we see can sustain reionization at z = 6, if the average galaxy has an ionizing escape fraction > 50%. If reionization concludes at z > 6, then it requires a near-unity escape fraction and/or a significant contribution from galaxies much fainter than our detection limit. |
|
| Galactic Outflows and Photoionization Heating During the Reionization Epoch
|
| Kristian Finlator (University of California Santa Barbara) |
| What were the feedback processes that modulated star formation at early times, and what signatures did they leave for us to study? The current decade will bring a windfall of observations of the structures that formed during the first billion years of cosmic history. A complete understanding of what these observations can teach us hinges on theoretical insight into the nature of likely feedback processes and their observational signatures. Observations and models of the post-reionization epoch indicate that galaxies constantly exchange metals, mass, and energy with their environment. These processes grow stronger as observations push into the reionization epoch, when the dominant galaxy population was both vigorous and fragile. Complicating interpretation, numerical experiments indicate that the likely-dominant feedback processes coupled to each other, with the implication that a complete understanding of their impact requires models to treat them simultaneously. To this end, I discuss recent progress toward the key theoretical goal of understanding observations of galaxies, the intergalactic medium, and its impact on the cosmic microwave background within a single model for structure formation. Simulations now indicate that early galaxies accreted their gas predominantly via cold flows, leading to smoothly-rising star formation histories and long duty cycles. I will compare this scenario's predictions with current observations. I will also consider whether observations already indicate the impact of photoionization heating and galactic outflows during the first billion
years as well as how feedback may have further impacted the luminosity function of galaxies at early times. Finally, I will discuss recent efforts to interpret joint reionization-epoch constraints on galaxies, the cosmic microwave background, and the Lyman-alpha forest within a self-consistent model for structure formation. |
|
| Stellar Halo Formation in a Hierarchical Universe: Lessons from our Sister Galaxy Andromeda |
| Karoline Gilbert (University of Washington) |
| In the paradigm of hierarchical galaxy formation, massive galaxies are built
through a series of major and minor merger events. Stellar halos provide
low density environments where the detritus of hierarchical structure formation
can remain visible for billions of years in the form of tidal debris features. In fact,
simulations imply that galactic stellar halos are likely composed primarily
of tidal debris from past accretion events, providing a record of the galaxy's
merger history. In order to increase observational constraints on theories of stellar halo
formation, we have undertaken a large Keck/DEIMOS spectroscopic survey of
individual red giants in Andromeda's stellar halo. I will review what we
have learned from stellar kinematics about M31's extended stellar halo and
merger history, and compare our observations of the structure and substructure
of M31's stellar halo with predictions from simulations of stellar halo formation
via accretion.
|
|
| Discovery of Main-Belt Comet P/2006 VW139 by Pan-STARRS1 |
| Henry Hsieh (Univ. of Hawaii - IfA) |
| Main-belt comets exhibit cometary activity indicative of ice sublimation yet are dynamically indistinguishable from main-belt asteroids and appear to have formed in situ. Much of the current interest in studying these objects lies in the possible role of icy main-belt objects in the primordial delivery of terrestrial water. On 2011 November 5, main-belt asteroid (300163) 2006 VW139 (later designated comet P/2006 VW139) was discovered to exhibit comet-like activity by the Pan-STARRS1 survey telescope, and now appears to be just the sixth main-belt comet to be discovered to date. I will describe the methods used to discover this new main-belt comet, detail the follow-up analyses used to conclude that its activity is in fact driven by ice sublimation (and not by a recent impact), and discuss other recent and ongoing work in the study of these rare and still poorly understood objects.
|
|
| Understanding Fomalhaut |
| Markus Janson (Princeton University) |
| Fomalhaut is a nearby A4-type star surrounded by a dust ring that appears to be dynamically sculpted by an unseen giant planet. In 2004 and 2006, a point source was detected at visible wavelengths near the inner edge of the ring with the Hubble Space Telescope, which was interpreted as a direct image of this planet. However, the collected body of observational evidence that exists for the system render any direct connection between the observed point source and the dynamically inferred planet unlikely. In this talk, I will discuss the various constraints that can be placed on the system from various observations, including recently reported Spitzer observations, and what they imply for the underlying physics of the point source. I will also discuss some possible ways forward for further improving our understanding of the Fomalhaut system. |
|
| Physical Properties of Spectroscopically Confirmed Galaxies at 5.6 < z < 7 |
| Linhua Jiang (Arizona State University) |
| In this talk I will present a systematic study of the physical properties of spectroscopically
confirmed galaxies at 5.6 < z < 7. Our initial sample contains more than 30 LAEs and LBGs. They represent the most luminous galaxies in this redshift range. Their rest-frame UV properties are measured from our deep HST near-IR and Spitzer mid-IR imaging data as well as a series of ground-based optical images. These galaxies generally have very steep UV slopes (alpha < -2). They show a wide range of morphology in the HST images, from compact features to multiple component systems. One third of them, among the brightest in the sample, appear to be interacting/merging systems. There are also a variety of SEDs among these galaxies, from young and small galaxies to mature and massive galaxies. In addition, I will discuss our improved measurements of Lya luminosities and their implications for the Lya luminosity functions at z > 6. |
|
| The Role of Galaxy Mergers Among High Redshift ULIRGs |
| Jeyhan Kartaltepe (NOAO) |
| In the local universe, Ultraluminous Infrared Galaxies (ULIRGs, L_IR>10^12 L_sun) are all interacting and merging galaxies. To date, studies of ULIRGs at high redshift have found a variety of results due to their varying selection effects, small sample sizes, and the variety of morphological classifications used. Some studies have found that mergers still dominate the galaxy morphology while others have found a high fraction of morphologically normal or clumpy star forming disks. Near-infrared imaging is crucial for interpreting galaxy structure at high redshift since it probes the rest frame optical light of a galaxy and thus we can compare directly to studies in the local universe. Here, we present the results of a morphological analysis of a sample of high redshift (z~1-3) ULIRGs. These galaxies are selected based on their infrared luminosities measured using 100 and 160 micron data from the GOODS-Herschel coverage of GOODS-S. We visually classified all of the ULIRGs as well as a comparison sample with the same redshift and H band magnitude range using ACS and WFC3 data from the GOODS and CANDELS surveys. The high resolution and increased sensitivity of WFC3 over NICMOS for this large sample of objects allows us to investigate the role of galaxy mergers among high redshift ULIRGs consistently for the first time.
|
|
| Elusive Explosions in the Local Universe |
| Mansi Kasliwal (Carnegie Institution for Science) |
| Until recently, the venerable field of cosmic explosions was plagued with a glaring six-magnitude luminosity "gap" between the brightest novae and faintest supernovae. Systematic surveys, serendipitous discoveries and archival searches have started uncovering transients fainter, faster and rarer than supernovae only in the past few years. Theorists predict a variety of mechanisms to produce transients in the gap and observers have the best chance of finding them in the local universe. Here I will present discoveries and unique physics of cosmic explosions that bridge this gap between novae and supernovae. There is now evidence of multiple, distinct populations of rare transients in this gap. |
|
| Measurements of Gravitational Lensing of the CMB |
| Ryan Keisler (University of Chicago) |
| The paths of CMB photons are distorted by the gravity of intervening matter as they travel to us from z~1000. This process encodes into the CMB information about the large-scale distribution of matter at intermediate redshifts, 0.5 < z < 5. This is a rapidly evolving field, and I will present two robust detections of this effect made in the past year using data from the South Pole Telescope (SPT). I will also describe SPTpol, a new camera recently installed on the SPT that aims to detect, for the first time, the ``B-mode'' polarization pattern in the CMB, another signature of gravitational lensing. |
|
| Moving Mesh Cosmology: Characteristics of Galaxies and Halos |
| Dusan Keres (UC Berkeley) |
| We present cosmological hydrodynamic simulations of galaxy formation with the new moving-mesh code AREPO, which promises higher accuracy compared with the traditional SPH technique that has been widely employed for this problem. We use the same initial conditions, set of physics and gravity solver to compare these results to the ones with well-tested SPH code GADGET-3 which enables us to cleanly test the differences in hydrodynamics. We find that AREPO leads to significantly higher star formation rates for galaxies in massive halos enabled by a more efficient cooling of the hot halo gas. Furthermore, galaxies in AREPO show more extended gaseous disks, which also feature a thinner and smoother morphology than their GADGET counterparts. Consequently, galaxies formed in AREPO have higher specific angular momentum than their SPH correspondents.
We discuss the causes of these differences which can be connected to shortcomings of the standard SPH implementation. We point out that AREPO can be readily applied to simulations of galaxy formation in a cosmological context where, for a given mass resolution, it requires similar runtimes but offers much higher accuracy than GADGET-3. Our findings also raise questions about some of the previous galaxy formation studies using traditional SPH implementations. |
|
| Metal Outflows from Dwarf Galaxies |
| Evan Kirby (Caltech) |
| Galaxies have one job to do: Turn gas into stars. The dwarf spheroidal satellite galaxies (dSphs) of the Milky Way--especially the ultra-faint dwarfs--are very bad at their jobs. They are significantly more metal-poor than would be expected from a closed box model of chemical evolution. Gas outflows likely carried away most of the metals produced by the dSphs and kept star formation rates low. Based on Keck/DEIMOS observations and chemical evolution models, we calculated the mass in Mg, Si, Ca, and Fe expelled from dSphs. The largest dwarfs lost 96% the metals their stars manufactured, and the ultra-faint galaxies lost >99% of their metals. |
|
| ``Giant Planets'' in Ultra-Wide Orbits |
| Adam Kraus (Univ. of Hawaii - IfA) |
| Over the past decade, direct imaging surveys for extrasolar planets have discovered a small, but significant number of planetary-mass companions that orbit more than 100 AU from their host stars. It is still unclear whether these objects should be regarded as the widest orbiting gas giant planets or the least massive binary companions, as they pose a significant challenge to models of both planet and binary formation.
The first step in addressing this question is to obtain better measurements of their temperatures and luminosities, as well as search for ongoing processes like accretion and chromospheric activity. I will summarize some preliminary results from a WFC3 optical imaging campaign for these potential planets, including the first measurement of their optical colors (and hence their corresponding temperatures and luminosities) and apparent indications of ongoing accretion out of circum(planetary?) disks. |
|
| Chemical Imaging of Protoplanetary Disks |
| Karin Oberg (Harvard-Smithsonian CfA) |
| The disks around pre-main-sequence stars provide the reservoirs of raw material and initial conditions for the formation of planetary systems. Disk chemistry thus sets the stage for the composition of planetesimals and eventually planets. Imaging how specific molecules are distributed in disks provides direct constraints on the chemistry present in different disk regions. In this talk I will look at observations that test predictions on that specific density structures are anticipated for molecules whose formation depend on deuterium fractionation, on ice chemistry on grain surfaces, or on UV photodissociation. In the first case, the common view is that deuterium fractionation is mainly efficient at low temperatures (T<30 K), which should correspond to outer disk regions, and the deuterium enhancement in Earth's seawater has been used as an argument for comet delivery of volatiles. Second, ice chemistry products are only expected to form outside of the condensation front, or snowline, of the parent molecule. Two key prebiotic molecules, CH3OH and H2CO, are proposed to form from CO ice and may thus only be present in outer disk regions, where the temperature is low enough for CO ice to form (~20 K). Finally, photochemical products should be centrally concentrated if the star is the main UV source. To address these chemistry predictions we have 1) combined Submillimeter-Array (SMA) observations of HCO+, DCO+ and HCN, and ALMA observations of DCN to image deuterium fraction, 2) used SMA observations of CO and H2CO to investigate the latter's dependence on the CO snowline, and 3) acquired SMA observations on photochemistry products. All observations show resolved structures and together they demonstrate the potential power of chemical disk imaging as a tool for constraining the prebiotic evolution during planet formation. |
|
| The First 700 Myr Seen with the HST |
| Pascal Oesch (UC Santa Cruz) |
| The installation of WFC3/IR on the HST has allowed us to push the current observational frontier of galaxies into the heart of cosmic reionization out to z~8-10. We are now able to directly trace the build-up of galaxies in the first few 100 Myr of cosmic time and to derive their contribution to reionization. I will present our current results on z>=7 galaxy searches in the 160 arcmin^2 of WFC3/IR data around GOODS-South, including the deepest IR images ever taken as part of the HUDF09 survey. The recent addition of F105W imaging from the CANDELS survey has allowed for a reliable measurement of the z~8 UV luminosity function across almost two orders of magnitude in luminosity, with 70 candidate z~8 galaxies identified to date. In the same data set, we identified only one single robust z~10 candidate. Nevertheless, these data are sensitive enough to derive stringent upper limits on the UV LF at z~10. By comparison with the trends in the relatively well-measured UV LF at z~4-8, we find that the galaxy population undergoes faster growth than expected, as the SFR density drops by more than an order of magnitude from z~8 to z~10 above our detection limit. We are thus witnessing a rapid build-up of the first generations of galaxies at these epochs, indicating that fainter dwarf galaxies below our current detection limits must have caused the bulk of cosmic reionization. |
|
| How do Planets Become Large? |
| Chris Ormel (UC Berkeley) |
| In the core accretion paradigm of giant planet formation, the first critical step is the formation of a solid core -- massive enough to gravitationally bind the nebular gas. But how do cores acquire their mass in the first place? Traditionally, it is believed that the building blocks of giant plants are bodies in the ~km-size range: planetesimals. However, mm-wavelength observations of disks suggests that the mass reservoir resides in (small) particles of mm--cm in size. Therefore, the scenario where fragments play the dominant role in the accretion process must be investigated. This requires a
rethinking of the use of the proper gravitational cross section, since gas drag forces will compete with the gravitational (2-body) force.
|
|
| The Host Galaxies of Dark Gamma-Ray Bursts |
| Daniel Perley (Caltech) |
| If gamma-ray bursts can serve as tracers of overall cosmic star-formation, then a significant number of these events should occur within luminous, dust-enshrouded galaxies. This anticipated host population has historically been elusive, but earlier work relied primarily on optical afterglow positions to identify the host galaxy and was therefore biased against events in dusty environments. I will present multiwavelength observations from Spitzer, HST, and ground-based facilities targeting the hosts of over 20 Swift GRBs with highly dust-suppressed afterglows, and show that the majority of these objects are indeed found within red, IR-luminous galaxies. This suggests that GRBs can indeed form in massive, metal-enriched systems after all, bolstering their utility as a cosmic SFR probe and providing additional constraints on the progenitor. Many other dark GRB hosts are actually quite blue and have low stellar masses, confirming that even ordinary and seemingly dust-free systems can host significant obscured star formation. |
|
| Core-Collapse Supernovae in Dwarf Galaxies |
| Jose Prieto (Princeton University) |
| We are using the All-Sky Automated Survey for Supernovae (ASAS-SN), small 7-15cm telescopes with a large field of view, to find and study bright supernovae explosions and other variable sources all-sky. I will discuss nearby core-collapse supernovae found in dwarf
galaxies, studied in part using ASAS-SN, and show why they might be important for understanding stellar evolution and star-formation. |
|
| Constraining the Processes that Drive the Evolution of the Galaxy Stellar Mass Function |
| Ryan Quadri (Carnegie Observatories) |
| The stellar mass function is perhaps the most fundamental statistic of the evolving galaxy population. Investigating how the mass function varies as a function of galaxy type, environment, and redshift provides necessary information about how these variables interact in shaping the galaxy population. I will present new results that give clues to the physical processes that drive the evolution of the mass function, and point out some interesting challenges for both observers and modelers. I will also describe two new surveys, CSI and ZFOURGE, which will yield new constraints by providing accurate redshift information for unbiased galaxy samples over a wide area out to z~1 and down to the lowest the stellar masses to z~3.
|
|
| Measuring the Growth of Structure and the Expansion Rate at z=0.6 in the SDSS-III Baryon Oscillation Spectroscopic Survey |
| Beth Reid (Lawrence Berkeley National Lab) |
| While the underlying clustering of galaxies is believed to be isotropic, two distinct effects change the relative amplitude of clustering along and perpendicular to the line of sight. The Alcock-Pacyznski effect allows a geometric test to measure the product of the angular diameter distance and Hubble expansion rate at the galaxy sample's redshift. Peculiar velocities of galaxies also amplify the apparent clustering along the line-of-sight. We demonstrate our ability to distinguish these effects in the data through their scale-dependence, and present preliminary measurements of both the growth of structure and the expansion rate at z=0.6 using data from the SDSS-III Baryon Oscillation Spectroscopic Survey. |
|
| Some Simple considerations on Galactic Structure and Rotation |
| Ralph Schönrich (OSU) |
| The recent development of tools to analyze average distances to stars as well as progress in more realistic descriptions of disc kinematics spurs the examination of Galactic structure with large stellar samples. I will outline the use of these methods to assess claims of a dual halo, to the determination of the local standard of rest and to measurements of Galactic rotation. |
|
| Feeding and Accretion in Low Luminosity AGNs. |
| Roman Shcherbakov (University of Maryland) |
| Supermassive black holes in the galactic centers, while having short quasar phases, spend most of their time in a low-luminosity AGN state. The most famous LLAGN is the black hole (BH) Sgr A* in the center of the Milky Way. Sub-mm peak of its peculiar spectrum is produced close to the event horizon, which allows determination of BH spin and inclination as well as the properties of the infalling gas. I will present the results of self-consistent general relativistic polarized radiative transfer performed over 3D GRMHD simulation and discuss the uncertainties in the determined parameters.
Very long baseline interferometry enables imaging the infalling gas and spotting the BH shadow. The improvement of observation would allow the observation of a shadow by 2014-2015. However, gas from the molecular cloud, now on the way to Sgr A*, may reach the event horizon by 2014, increasing the accretion rate and output luminosity. The BH shadow might become unobservable.
Another important question is feeding of low-luminosity AGNs. The ongoing Chandra observations of Sgr A* and NGC 3115 within X-ray visionary projects (XVPs) will produce precise radius-dependent spectra. This will allow determination of outflow velocities as well as density and temperature profiles. Then 2D models of BH feeding from stellar winds and the onset of the accretion flow will be extensively tested. |
|
| Moving Mesh Cosmology: The Hydrodynamics of Galaxy Formation |
| Debora Sijacki (HCO, Harvard University) |
| As already established in Frenk et al. 1999, entropy profiles of galaxy clusters are systematically different when simulated with SPH versus Eulerian mesh codes. This systematic difference has persisted until now, casting doubts on the ability of hydrodynamical schemes to follow complex hydrodynamical flows in full cosmological settings reliably. I will present a detailed comparison between the well-known SPH code GADGET and the new moving-mesh code AREPO on a number of hydrodynamical test problems. Through a variety of numerical experiments with increasing complexity I will establish a clear link
between simple test problems with known analytic solutions and systematic numerical effects seen in cosmological simulations of galaxy formation. These tests demonstrate deficiencies of the SPH method in several sectors. An inadequate treatment of fluid instabilities in GADGET suppresses entropy generation by mixing, underestimates vorticity generation in curved shocks and prevents efficient gas stripping from infalling substructures. These accuracy
problems not only manifest themselves in idealized hydrodynamical tests, but also propagate to more realistic simulation setups of galaxy formation, ultimately affecting local and global gas properties in the full cosmological framework. |
|
| The Contribution of Galaxies to Reionization |
| Dan Stark (University of Arizona) |
| Over the last several years, deep infrared imaging campaigns have provided our first reliable census of star formation activity in what is thought to be the reionization era. One of the most important goals of these studies is to determine whether galaxies are the primary ionizing agents responsible for reionization. Yet these efforts have been stunted by limitations in our understanding of radiative feedback in early galaxies and the redshift window over which reionization occurs. I will discuss new insight into these topics stemming from a series of ongoing spectroscopic surveys.
|
|
|
