Bulletin of the American Physical Society
APS April Meeting 2014
Volume 59, Number 5
Saturday–Tuesday, April 5–8, 2014; Savannah, Georgia
Session C9: Galaxies and Clusters |
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Sponsoring Units: DAP Chair: Tonia Venters, NASA Goddard Space Flight Center Room: 203 |
Saturday, April 5, 2014 1:30PM - 1:42PM |
C9.00001: The deceleration of nebular shells in evolved planetary nebulae Margarita Pereyra, Michael Gerard Richer, Jose Alberto Lopez We have selected a group of 100 evolved planetary nebulae (PNe) and study their kinematics based upon spatially-resolved, long-slit, echelle spectroscopy. The data have been drawn from the San Pedro Martir Kinematic Catalogue of PNe (Lopez et al. 2012). The aim is to characterize in detail the global kinematics of PNe at advanced stages of evolution with the largest sample of homogenous data used to date for this purpose. The results reveal two groups that share kinematics, morphology, and photo-ionization characteristics of the nebular shell and central star luminosities at the different late stages under study. The typical flow velocities we measure are usually larger than seen in earlier evolutionary stages, with the largest velocities occurring in objects with very weak or absent [NII]6584 line emission, by all indications the least evolved objects in our sample. The most evolved objects expand more slowly. This apparent deceleration during the final stage of PNe evolution is predicted by hydrodynamical models, but other explanations are also possible. These results provide a template for comparison with the predictions of theoretical models. [Preview Abstract] |
Saturday, April 5, 2014 1:42PM - 1:54PM |
C9.00002: Evolution of dwarf galaxies simulated in the cosmological LCDM scenario Alejandro Gonzalez, Pedro Colin, Vladimir Avila-Reese, Aldo Rodriguez-Puebla, Octavio Valenzuela We present results from numerical simulations of low-mass galaxies with the aim to explore the way their stellar masses are assembled. We analyze how the mass assembly histories of the parent halo determine the growth of their host galaxy and its implications on the current paradigm of formation and evolution of low-mass structures in the LCDM scenario. We have found that low-mass galaxies simulated in this scenario assemble their stellar masses following roughly the dark matter halo assembly, which seems to be in tension with the downsizing trend suggested by current observational inferences. We show that there is no more room to increase the strength of feedback from astrophysical processes in order to deviate strongly the stellar mass assembly from the dark halo one, as has been recently invoked to solve some of the potential issues faced by CDM-based simulations of dwarf galaxies. [Preview Abstract] |
Saturday, April 5, 2014 1:54PM - 2:06PM |
C9.00003: Broadband Spectral Modeling of NGC 253 from Hard X-rays to TeV Gamma Rays Tonia Venters, Daniel Wik, Bret Lehmer, Mihoko Yukita, Ann Hornschemeier, Andrew Ptak, Andreas Zezas, Keith Bechtol, Megan Argo, Vallia Antoniou, Fiona Harrison, Roman Krivonos, Jean-Christophe Leyder, Thomas Maccarone, Daniel Stern, William Zhang We present the latest results from detailed broadband spectral modeling of the nearby starburst galaxy NGC 253 from keV to TeV energies. The mechanism for producing the gamma-ray emission in starburst galaxies is difficult to determine solely from Fermi-LAT and HESS data. NuSTAR observations of NGC 253 in the hard X-ray band (10--30 keV) provide the most sensitive observations to date of the non-thermal emission in that bandpass, which in turn may constrain the role of hadronic and leptonic interactions in producing the GeV emission. [Preview Abstract] |
Saturday, April 5, 2014 2:06PM - 2:18PM |
C9.00004: Spectral Energy Distributions and X-ray Variability of the Blazar PKS 2155-304 Paul Wiita, Jai Bhagwan, Alok Gupta, Iossif Papadakis PKS 2155-304 is a BL Lac object that is variable across the entire EM spectrum and is the brightest object in UV to gamma-ray bands in the southern hemisphere. It is a high synchrotron peak blazar and is frequently observed by the XMM-Newton satellite in the X-ray, UV and optical. We present spectral energy distributions (SEDs) resulting from 20 pointings of XMM-Newton. We focused on the changes in the synchrotron peak with optical/UV and X-ray flux variations and also analyzed the X-ray spectral variations in more detail for 1 pointing. We modeled the observed SEDs of PKS 2155-304 from the optical to X-ray bands using a synchrotron self-Compton model in which electron energies have log-parabolic distributions. In our analysis, we found a significant anti-correlation between the spectral slope parameter, a, and the peak frequency. All SEDs are fitted well with log-parabolic curves and we considered how each model parameter would change the SED curve. We did not find any significant correlation of magnetic field intensity, electron density, and the bulk Lorentz factor with the peak frequency. One observation analyzed in more detail showed a significant anti-correlation between the X-ray spectral slope and the flux, indicating some X-rays arise from inverse Compton scattering. [Preview Abstract] |
Saturday, April 5, 2014 2:18PM - 2:30PM |
C9.00005: Abell 2146: A unique bullet cluster system Lindsay King, Jacob White, Rebecca Canning, Helen Russell, Joseph Coleman Abell 2146 is a unique post-merger cluster system, where two clusters have merged about 0.2 Gyr ago. Such systems provide a direct test of dark matter, and our understanding of gravity on large scales. Massive objects in the universe distort space-time and act as gravitational lenses, and we harness this property in our study of the system. We report on our campaign to better understand the dynamics of this system, using spectroscopic data, primarily from the Gemini telescope. This data allows us to determine redshifts for galaxies in the field, and so identify and study cluster members. We also discuss our gravitational lensing analysis of Hubble Space Telescope data, which reveals numerous strongly lensed arcs. This is compared with Chandra X-ray images, which map the distribution and properties of the hot gas in the system. [Preview Abstract] |
Saturday, April 5, 2014 2:30PM - 2:42PM |
C9.00006: Evolution of the outer planets and planetesimals due to gas drag in transition disks Samuel Navarro, Mauricio Reyes-Ruiz, H\'ector Aveves, Carlos Chavez, Santiago Torres We study the effect of aerodynamic drag due to the gaseous component of a transition protoplanetary disk, on the process of giant planet migration due to the interaction with a disk of planetesimals. We present a series of numerical simulations of the dynamics of the four outer planets in our Solar System and a disk of planetesimals exterior to these; planets are arranged in a compact, multiresonant configuration as that proposed in the so-called Nice model. We model the gaseous component of the protoplanetary disk as both a minimum mass solar nebula and a viscous accretion disk model, both truncated out to a disc radius of approximately 20 AU, following recent observations. We find that aerodynamic drag has important consequences on the early evolution of the compact Solar System. As pointed out previously by other authors, gas drag leads to planetesimal trapping in low order resonances, particularly for kilometer size bodies. In our case, since planetesimals are all located initially outwards of Neptune, these are trapped in outer resonances with such planet on typical timescales of a few million years. This effect leads to an accelerated migration scenario, with the system becoming dynamically unstable on a very short timescale, in comparison to gas free scenarios. [Preview Abstract] |
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