Thursday, May 26, 2011, 8:30 AM - 9:20 AM 400 Invited Session America Ballroom
400.01
The Least Luminous Galaxies in the Universe
Beth Willman1
1Haverford College.
8:30 AM - 9:20 AM
America Ballroom
In the past six years, more than two dozen dwarf galaxies have been discovered around the Milky Way and M31. Many of these discoveries are 100 times less luminous than any galaxy previously known, and a million times less luminous than the Milky Way itself. These discoveries have made astronomers question the very meaning of the word "galaxy", and hint that such ultra-faint dwarf galaxies may be the most numerous type of galaxy in the universe. This talk will highlight i. how we can see galaxies that are effectively invisible in images of the sky, ii. the brewing controversy over the definition of the term "galaxy", and iii. what ultra-faint galaxies can reveal about the distribution of dark matter in our Universe.
Thursday, May 26, 2011, 10:00 AM - 11:30 AM 401 Particle Physics III: Variations of Fundamental Constants and Dark Matter Searches Meeting-in-a-Meeting America North
401.01
An Overview in Variations in the Fundamental Constants
Keith Olive1
1University of Minnesota.
10:00 AM - 10:30 AM
America North
In many theories of unified interactions, there are additional degrees of freedom which may allow for the variation of the fundamental constants of nature. I will review the motivation for and theoretical relations between such variations. I will then review the various astrophysical and experimental constraints on the variations of constants.
401.02
Results from the XENON100 Dark Matter Search
Rafael F. Lang1
1Columbia University.
10:30 AM - 11:00 AM
America North
The XENON project searches for direct interactions of non-baryonic Dark Matter with a laboratory-scale detector. The XENON100 detector uses 64kg of pure liquid xenon as a target for Dark Matter interactions. The target volume is instrumented as a liquid/gas time-projection chamber with two arrays of photomultipliers. This allows to reconstruct the vertex of each particle interaction with millimeter resolution in all three dimensions. Additional information about the interacting particle as well as its energy are extracted. This allows for an excellent discrimination of dominant background from the expected Dark Matter signal. Major results from the recent analysis of data from this detector will be be presented.
401.03
Testing the Time Stability of the Fundamental "Constants" of Physics
Steve Lamoreaux1
1Yale University.
11:00 AM - 11:30 AM
America North
The time stabilities of the masses of particles and the strengths of the various interactions between them are assumptions that can be tested. These tests can be observational, archeological, or performed in the laboratory. An overview of the current state of our knowledge on the stability of the fine structure constant and other dimensionless parameters will be presented. The prospects of possible new methods to improve detection sensitivity will also be discussed.
402 Oral Session America Central
402.01
Carbon-rich Planets: Atmospheric Spectra, Thermal Inversions, And Formation Conditions
Nikku Madhusudhan1, O. Mousis2, J. Lunine3, T. Johnson4
1Princeton University, 2UTINAM, CNRS/INSU, France, 3University of Arizona, 4NASA JPL.
10:00 AM - 10:10 AM
America Central
Carbon-rich planets (CRPs) are the exotic new members in the repertoire of extrasolar planets. The first CRP atmosphere was discovered recently, for the extremely irradiated hot Jupiter WASP-12b. In this work, we report several candidate carbon-rich planets amongst the known sample of transiting exoplanets, along with follow-up theoretical and observational efforts that aim at confirming these candidates. We also discuss the atmospheric chemistry and temperature structure of carbon-rich giant planets, their formation via core accretion, and the chemistry and apportionment of ices, rock, and volatiles in their envelopes.
Our results show that CRP atmospheres probe a unique region in composition space, especially at high T. For C/O ≥ 1, most of the oxygen is occupied by CO for T > 1400 K and P < 1bar, causing a substantial depletion in water vapor, and an overabundance of methane compared to equilibrium chemistry with solar abundances. Adopting gas phase elemental abundances in the disk similar to those estimated in the star gives a C/O ratio in planetesimals and then in the envelope of WASP-12b similar to or below the solar C/O. Under these conditions, a C/O ratio of 1 in WASP-12b would require that the oxygen abundance in the disk is depleted by a factor of 0.41.
402.02
Kepler Super-Earths And Constraints To The High-density Limit On Radius
Dimitar D. Sasselov1, Kepler Team
1Harvard-Smithsonian CfA.
10:10 AM - 10:20 AM
America Central
The minimum radius for super-Earths of a given mass could be determined by planet formation history, high-density mineral phases, and evaporation. I will discuss theoretical models and constraints imposed on them by Kepler mission observations.
402.03
The Low Density Limit of the Mass-Radius Relation for Exo-Neptunes
Leslie Rogers1, P. Bodenheimer2, J. Lissauer3, S. Seager1
1Massachusetts Institute of Technology, 2University of California Santa Cruz, 3NASA-Ames Research Center.
10:20 AM - 10:30 AM
America Central
Kepler has found hundreds of Neptune-size (2-6 REarth) planet candidates. The masses of most of these candidates will be difficult to measure. Using theoretical models of planet formation, evolution and structure, we endeavor to estimate the minimum plausible mass as a function of planet radius and equilibrium temperature. We explore both core nucleated accretion and outgassing of H2 as two separate formation pathways for low-mass planets with voluminous atmospheres of light gases.
402.04
The Dynamics of Stellar Coronae Harboring Close-in Planets
Ofer Cohen1, J. J. Drake1, V. L. Kashyap1, I. V. Sokolov2, C. Garraffo1, T. I. Gombosi2
1Harvard-Smithsonian Center for Astrophysics, 2University of Michigan.
10:30 AM - 10:40 AM
America Central
We carry out the first full 3D, time-dependent numerical MagnetoHydroDynamic modeling of the interplanetary environment of close-in planets, as well as a space weather event on close-in planet. In the simulations, we use observed parameters of the HD189733 system. Our simulations reveal a unique interaction between the planet and the corona, as well as unique CME-magnetosphere interaction that can deposit large amount of energy in the planetary atmosphere. We discuss the consequences of such interaction in the context of planetary magnetic shielding, planetary atmosphere erosion, as well as planet habitability.
402.05
The Role of Binary Planetesimals in Planet Formation
Hagai Perets1
1Harvard Smithsonian Center for Astrophysics.
10:40 AM - 10:50 AM
America Central
One of the main evolutionary stages of planet formation is the dynamical evolution of planetesimal disks. These disks are thought to evolve through gravitational encounters and physical collisions between single planetesimals. In recent years, many binary planetesimals (BPs) have been observed in the solar system, indicating that the binarity of planetesimals is high. However, current studies of planetesimal disk formation and evolution do not account for the role of binaries. We point out (Perets 2011) that gravitational encounters of BPs can have an important role in the evolution of planetesimal disks. BPs catalyze close encounters between planetesimals and can strongly enhance their collision rate. Binaries may also serve as an additional heating source of the planetesimal disk, through the exchange of the binaries gravitational potential energy into the kinetic energy of planetesimals in the disk.
402.06
Wind-Shearing Between Planetesimals in Gaseous Protoplanetary Disks
Ruth Murray-Clay1, H. Perets1
1Harvard-Smithsonian Center for Astrophysics.
10:50 AM - 11:00 AM
America Central
Planetesimals, the building blocks of planetary embryos, must grow before gas is dispersed from their natal protoplanetary disks. Due to their different aerodynamic properties, planetesimals of varying sizes and shapes experience different drag forces from the gas during this time. Such differential forces produce a wind-shearing effect, which generates an effective acceleration between nearby planetesimals of different sizes. For any two planetesimals, a wind-shearing radius can be considered, at which the differential acceleration due to the wind becomes greater than the mutual gravitational pull between the planetesimals. We demonstrate that this wind-shearing radius can be much smaller than the gravitational shearing radius by the star (the Hill radius). We then discuss the role of wind-shearing for the stability and survival of binary planetesimals, and provide stability criteria for binary planetesimals embedded in a gaseous disk.
402.07
Can Hydrogen Sulfide Gas Be a Biosignature in a Habitable Exoplanet?
Renyu Hu1, S. Seager1, W. Bains2
1MIT, 2Rufus Scientific, United Kingdom.
11:00 AM - 11:10 AM
America Central
A group of microorganisms can disproportionate sulfite and elemental sulfur into sulfide and sulfate to obtain energy for a living. We explore if the sulfide produced by microorganisms can alter the atmospheric composition to manifest in the spectrum of a habitable exoplanet. We consider a dry (i.e., limited ocean cover) habitable planet of Earth size and mass, orbiting a Sun-like star. As on Earth, volcanoes release sulfur as sulfur dioxide and hydrogen sulfide, but the volcanic production of hydrogen sulfide is limited by the scarcity of water. In the meantime, in our scenario, microbes can flourish in the ocean and effectively make use of the energy gained from the sulfur disproportion and release sulfide as the metabolic byproduct. The metabolic sulfur disproportion can enhance the overall outgassing rate of hydrogen sulfide by nearly one order of magnitude over the non-biological emission. To study the atmospheric response to this enhancement, we build a one-dimensional chemical transport model that treats all O, H and S bearing species and the relevant photochemical and chemical reactions. The vertical transport is approximated with the eddy diffusion. We also consider the formation and the sedimentation of elemental sulfur aerosols and sulfate aerosols in the atmosphere and explore the effect of aerosol particle size on the chemistry and the radiative transfer. To establish hydrogen sulfide as a biosignature, we need to understand the atmospheric response to the sulfide outgassing, the spectral features of hydrogen sulfide and its photochemical products, and the volcanic release of H2S. The current work will address the first two problems, and the main uncertainty will remain at the possible false positives due to the volcanism.
402.08
Obliquity Variations of a Moonless Earth
Jack J. Lissauer1, J. W. Barnes2, J. E. Chambers3
1NASA Ames Research Center, 2University of Idaho, 3Carnegie Institution.
11:10 AM - 11:20 AM
America Central
We numerically explore the obliquity (axial tilt) variations of a hypothetical moonless Earth. Previous work has shown that the Earth's Moon stabilizes Earth's obliquity such that it remains within a narrow range, between $22.1^\circ$ and $24.5^\circ$. Without lunar influence, a frequency map analysis by Laskar et al. (1993 Nature 361, 615) showed that the obliquity could vary between $0^\circ$ and $85^\circ$. Using a modified version of the orbital integrator {\tt mercury}, we calculate the obliquity
evolution for moonless Earths with various initial conditions for up to 4 billion years. We find many configurations in which obliquity variations are small. This implies that moonless extrasolar planets may
well have the climate stability thought to be required for the development of advanced life.
403 Evolution of Galaxies II Oral Session America South
403.01
Extended Lyman-alpha Emission From Interacting Galaxies At High Redshifts
Hidenobu Yajima1, Q. Zhu1, Y. Li1
1Pennsylvania State University.
10:00 AM - 10:10 AM
America South
We investigate Lyman-alpha emission from high-redshift galaxies, by combining hydrodynamic simulations with three dimensional radiative transfer calculations. We focus on a set of major mergers of galaxies in the redshift range of z~3 -7, with a mass range of 2-5*10^{12} Msun. The hydrodynamic simulations include star formation, black hole growth, and feedback processes. The radiative transfer includes continuum emission, dust absorption and re-emission, ionization of neutral hydrogen, and Lyman-alpha emission from both recombination and collisional excitation.
We find that the intense star formation and enhanced cooling induced by gravitational interaction produce strong Lyman-alpha emission from these merging galaxies. The Lyman-alpha emission appear to be extended due to the extended distribution of sources and gas. Moreover, the presence of AGN in the system significantly increases the Lyman-alpha emission. During the close encounter of galaxy progenitors when the star formation rate peaks at ~10^2 Msun/yr, our model produces a Lyman-alpha luminosity of L~10^{43} ergs/s and a size of D~20 kpc at z>6, while at z~3, L~10^{44} ergs/s and D~50 kpc. These results are in broad agreement with observations of Lyman-alpha blobs from redshifts z~3 - 6.6. Our model suggests that merging galaxies may produce the Lyman-alpha blobs observed at high redshifts.
403.02
The Average Physical Properties and Star Formation Histories of the UV-Brightest Star-forming Galaxies at z~3.7
Kyoung-Soo Lee1, A. Dey2, N. Reddy2, M. J. I. Brown3, A. H. Gonzalez4, B. T. Jannuzi2, M. C. Cooper5, X. Fan6, F. Bian6, E. Glikman1, D. Stern7, M. Brodwin8, A. Cooray5
1Yale University, 2NOAO, 3Monash University, Australia, 4University of Florida, 5University of California, Irvine, 6University of Arizona, 7JPL, 8CfA.
10:10 AM - 10:20 AM
America South
We investigate the average physical properties and star formation histories (SFHs) of the most UV-luminous star-forming galaxies at z~3.7. Our results are based on the average spectral energy distributions (SEDs), constructed from stacked optical to infrared photometry, of a sample of the 1,913 most UV-luminous star-forming galaxies found in 5.3 square degrees of the NOAO Deep Wide-Field Survey. We find that the shape of the average SED in the rest-optical and infrared is fairly constant with UV luminosity: i.e., more UV luminous galaxies are, on average, also more luminous at longer wavelengths. In the rest-UV, however, the spectral slope beta; measured at 0.13 -0.28 um rises steeply with the median UV luminosity from -1.8 at L~L* to -1.2 (L~4-5L*). We use population synthesis analyses to derive their average physical properties and find that: (1) L_UV, and thus star-formation rates (SFRs), scale closely with stellar mass such that more UV-luminous galaxies are more massive; (2) The median ages indicate that the stellar populations are relatively young (200-400 Myr) and show little correlation with UV luminosity; and (3) More UV-luminous galaxies are dustier than their less-luminous counterparts, such that L~4-5L* galaxies are extincted up to A(1600)=2 mag while L~L* galaxies have A(1600)=0.7-1.5 mag. We argue that the average SFHs of UV-luminous galaxies are better described by models in which SFR increases with time in order to simultaneously reproduce the tight correlation between the UV-derived SFR and stellar mass, and their universally young ages. We demonstrate the potential of measurements of the SFR-M* relation at multiple redshifts to discriminate between simple models of SFHs. Finally, we discuss the fate of these UV-brightest galaxies in the next 1-2 Gyr and their possible connection to the most massive galaxies at z~2.
403.03D
Optical and Infrared Backgrounds from HST and Beyond
Timothy Dolch1, H. C. Ferguson2, R. Chary3, A. R. Cooray4, A. M. Koekemoer2, S. Ravindranath5, T. Sukhbold6
1Johns Hopkins Univ., 2Space Telescope Science Institute, 3California Institute of Technology, 4University of California, Irvine, 5Inter-University Center for Astronomy and Astrophysics, India, 6Univeristy of Arizona.
10:20 AM - 10:40 AM
America South
The sum total of the energy released by the earliest era of star formation should show up today within the diffuse extragalactic background light (EBL), its signature peaking in the near-infrared. There is considerable controversy over estimates of the average EBL per steradian at wavelengths longward of 1µm, over measurements of background fluctuations, and over the interpretation of the measurements. Resolving this controversy is important because the EBL constrains the history of galaxy evolution, and because the near-infrared fluctuations may contain important information about Population III stars and the earliest era of star formation. We compare number counts from recent galaxy surveys, correcting for their differing passbands. With some assumptions about galaxy sizes and surface-brightness profiles, we account for the light missed in standard photometric estimates, integrating the resulting corrected counts to estimate the total EBL due to resolved galaxies. We then present an analysis of background fluctuations in observations of the HUDF, the GOODS field, and the CANDELS fields obtained with WFC3. The fluctuation signal provides a constraint on the slope of galaxy counts fainter than the levels of individual detection. The color dependence of the fluctuations provides a constraint on the redshift distribution of these very faint sources. Fluctuations of the near-infrared EBL due to undetected sources help also constrain the nature of galaxies below current detection levels in other deep fields. The spatial and spectral information of these anisotropies provide valuable information about the EoR, as well as new populations of faint objects at lower redshifts. Via various analysis tools such as power spectra, P(D) fitting, and cross-correlations, best-fit models to faint sources can be obtained.
403.04
Hα Star Formation Rates for z>1 Galaxy Clusters in the IRAC Shallow Cluster Survey Using WFC3 IR Grism Spectroscopy
Gregory Zeimann1, A. Stanford2, M. Brodwin3, A. Dey4, D. Stern5, A. Gonzalez6
1UC Davis, 2UC Davis/LLNL, 3Harvard-Smithsonian Center for Astrophysics, 4NOAO, 5Jet Propulsion Laboratory, 6University of Florida.
10:40 AM - 10:50 AM
America South
We present new HST WFC3 grism data for 17 z>1 galaxy clusters in the IRAC Shallow Cluster Survey (ISCS). Using the G141 grism (λ = 1.10 − 1.65 μm, 46.5 A/pixel), we identified ∼5-15 new cluster members in each cluster candidate with a visual inspection of emission line galaxies in the reduced 1-d and 2-d spectral extractions. Given the redshift range of the cluster candidates and the wavelength coverage of the G141 grism, the emission line most identified was the blended Hα+NII. Correlations found in the literature between the EW of Hα+NII and the line ratio of NII to Hα were used to deblend the two fluxes. Hα emission was used as an indicator of star formation. Our program is sensitive to an unobscured star formation rate of 4 M⊙ / Year for z=1.5 and a nominal 1:4 ratio of NII to Hα. Concurrent MIPS 24μm data allows for the comparison of different SFR tracers. Whenever possible, we also use the ratio of Hβ/Hα to estimate dust obscuration and correct the SFRs. This dataset allows the study of a wide-range of star formation rates in dense cluster cores during the peak epoch of galaxy formation.
403.05
The Spitzer Interacting Galaxy Atlas
Lauranne Lanz1, N. Brassington2, A. Zezas3, H. A. Smith1, M. L. N. Ashby1, C. Klein4, P. Jonsson1, L. E. Hernquist1
1Harvard-Smithsonian Center for Astrophysics, 2University of Hertfordshire, United Kingdom, 3University of Crete, Greece, 4University of California, Berkeley.
10:50 AM - 11:00 AM
America South
The evolution of galaxies is greatly influenced by their interactions. The Spitzer Interacting Galaxy Survey sample was designed to probe a range of interaction parameters using infrared data complemented by a range of other observations. It is comprised of the Keel-Kennicutt (Keel et al. 1985) complete sample of interacting galaxies chosen on the basis of association likelihood. This selection criterion avoids the biases found in those chosen on the basis of morphology, infrared brightness, or optical line diagnostics. The resulting sample contains 111 galaxies in 50 systems, located with cz < 4000 km/s. We present a multiwavelength atlas of these data, which has complete Spitzer coverage and almost complete GALEX coverage. This atlas will be used to investigate the variation of star formation and AGN activity along the interaction sequence and the physical processes involved. Trends observed in this sample will also compared to those predicted by numerical simulations.
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