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Porter L.A.,University of California at Santa Cruz | Somerville R.S.,Rutgers University | Primack J.R.,University of California at Santa Cruz | Croton D.J.,Swinburne University of Technology | And 4 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2014

Recent observations have probed the formation histories of nearby elliptical galaxies by tracking correlations between the stellar population parameters, age and metallicity, and the structural parameters that enter the Fundamental Plane, size Re, and velocity dispersion σ. These studies have found intriguing correlations between these four parameters. In this work, we make use of a semi-analytic model, based on halo merger trees extracted from the Bolshoi cosmological simulation, that predicts the structural properties of spheroid-dominated galaxies based on an analytic model that has been tested and calibrated against an extensive suite of hydrodynamic+N-body binary merger simulations. We predict the Re, σ, luminosity, age, and metallicity of spheroid-dominated galaxies, enabling us to compare directly to observations. Our model predicts a strong correlation between age and σ for early-type galaxies, and no significant correlation between age and radius, in agreement with observations. In addition, we predict a strong correlation between metallicity and σ, and a weak correlation between metallicity and Re, in qualitative agreement with observations. We find that the correlations with σ arise as a result of the strong link between σ and the galaxy's assembly time. Minor mergers produce a large change in radius while leaving σ nearly the same, which explains the weaker trends with radius. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Perryman M.,Peyton Hall | Perryman M.,University College Dublin | Spergel D.N.,Peyton Hall | Lindegren L.,Lund Observatory
Astrophysical Journal | Year: 2014

While the precise relationship between theMilkyWay disk and the symmetry planes of the darkmatter halo remains somewhat uncertain, a time-varying disk orientation with respect to an inertial reference frame seems probable. Hierarchical structure formation models predict that the dark matter halo is triaxial and tumbles with a characteristic rate of ∼2 rad H -1 0 (∼30μas yr-1). These models also predict a time-dependent accretion of gas, such that the angular momentum vector of the disk should be misaligned with that of the halo. These effects, as well as tidal effects of the LMC, will result in the rotation of the angular momentum vector of the disk population with respect to the quasar reference frame. We assess the accuracy with which the positions and proper motions from Gaia can be referred to a kinematically non-rotating system, and show that the spin vector of the transformation from any rigid self-consistent catalog frame to the quasi-inertial system defined by quasars should be defined to better than 1μas yr-1. Determination of this inertial frame by Gaia will reveal any signature of the disk orientation varying with time, improve models of the potential and dynamics of the Milky Way, test theories of gravity, and provide new insights into the orbital evolution of the Sagittarius dwarf galaxy and the Magellanic Clouds. © 2014 The American Astronomical Society. All rights reserved.

Perryman M.,Peyton Hall | Perryman M.,University College Dublin | Hartman J.,Peyton Hall | Bakos G.A.,Peyton Hall | Lindegren L.,Lund Observatory
Astrophysical Journal | Year: 2014

We provide a revised assessment of the number of exoplanets that should be discovered by Gaia astrometry, extending previous studies to a broader range of spectral types, distances, and magnitudes. Our assessment is based on a large representative sample of host stars from the TRILEGAL Galaxy population synthesis model, recent estimates of the exoplanet frequency distributions as a function of stellar type, and detailed simulation of the Gaia observations using the updated instrument performance and scanning law. We use two approaches to estimate detectable planetary systems: one based on the signal-to-noise ratio of the astrometric signature per field crossing, easily reproducible and allowing comparisons with previous estimates, and a new and more robust metric based on orbit fitting to the simulated satellite data. With some plausible assumptions on planet occurrences, we find that some 21,000 (±6000) high-mass (∼1-15MJ) long-period planets should be discovered out to distances of ∼500 pc for the nominal 5 yr mission (including at least 1000-1500 around M dwarfs out to 100 pc), rising to some 70,000 (±20,000) for a 10 yr mission. We indicate some of the expected features of this exoplanet population, amongst them ∼25-50 intermediate-period (P ∼ 2-3 yr) transiting systems. © 2014. The American Astronomical Society. All rights reserved.

Calabrese E.,University of Oxford | Hlozek R.,Peyton Hall | Battaglia N.,Carnegie Mellon University | Bond J.R.,University of Toronto | And 21 more authors.
Journal of Cosmology and Astroparticle Physics | Year: 2014

Future arcminute resolution polarization data from ground-based Cosmic Microwave Background (CMB) observations can be used to estimate the contribution to the temperature power spectrum from the primary anisotropies and to uncover the signature of reionization near ℓ=1500 in the small angular-scale temperature measurements. Our projections are based on combining expected small-scale E-mode polarization measurements from Advanced ACTPol in the range 300<ℓ<3000 with simulated temperature data from the full Planck mission in the low and intermediate ℓ region, 2<ℓ<2000. We show that the six basic cosmological parameters determined from this combination of data will predict the underlying primordial temperature spectrum at high multipoles to better than 1% accuracy. Assuming an efficient cleaning from multi-frequency channels of most foregrounds in the temperature data, we investigate the sensitivity to the only residual secondary component, the kinematic Sunyaev-Zel'dovich (kSZ) term. The CMB polarization is used to break degeneracies between primordial and secondary terms present in temperature and, in effect, to remove from the temperature data all but the residual kSZ term. We estimate a 15σ detection of the diffuse homogeneous kSZ signal from expected AdvACT temperature data at ℓ>1500, leading to a measurement of the amplitude of matter density fluctuations, σ8, at 1% precision. Alternatively, by exploring the reionization signal encoded in the patchy kSZ measurements, we bound the time and duration of the reionization with σ(zre)=1.1 and σ(Δzre)=0.2. We find that these constraints degrade rapidly with large beam sizes, which highlights the importance of arcminute-scale resolution for future CMB surveys. © 2014 IOP Publishing Ltd and Sissa Medialab srl .

Johansson P.H.,University of Helsinki | Johansson P.H.,University of Turku | Naab T.,Max Planck Insitut fur Astrophysik | Ostriker J.P.,Peyton Hall
Astrophysical Journal | Year: 2012

We present a sample of nine high-resolution cosmological simulations in the mass range of M vir = 7 × 1011-4 × 10 12 M starting from ΛCDM initial conditions. Our simulations include primordial radiative cooling, photoionization, star formation, supernova II feedback, but exclude supernova-driven winds and active galactic nucleus feedback. The simulated galaxies assemble in two phases, with the initial growth dominated by compact (r < r eff) in situ star formation fueled by cold, low-entropy gas streams resulting in a very similar mean assembly redshift of z f, ins 2.5 for the in situ stellar component in all galaxies. The late growth is dominated by accretion of old stars formed in subunits outside the main galaxy (r > r eff) resulting in an assembly redshift of z f, acc 0.5-1.5 with much larger scatter. We find a positive correlation between the fraction of accreted stars and the final mass of our galaxies. We show that gravitational feedback strongly suppresses late star formation in massive galaxies contributing to the observed galaxy color bimodality. The accretion of stellar material is also responsible for the observed size growth of early-type galaxies. In addition, we find that the dark matter fractions within the stellar half-mass radii continuously increase toward lower redshift from about f DM 0.05 at z 3 to f DM 0.1-0.3 at z = 0. Furthermore, the logarithmic slope of the total density profile is nearly isothermal at the present day (γ′ 1.9-2.2). Finally, the input of gravitational heating lowers the central dark matter densities in the galaxies, with the effect being smaller compared to simulations without supernova feedback. © 2012. The American Astronomical Society. All rights reserved.

Roediger J.C.,Queen's University | Roediger J.C.,University of California at Santa Cruz | Courteau S.,Queen's University | Graves G.,Peyton Hall | And 2 more authors.
Astrophysical Journal, Supplement Series | Year: 2014

We present an extensive literature compilation of age, metallicity, and chemical abundance pattern information for the 41 Galactic globular clusters (GGCs) studied by Schiavon et al. Our compilation constitutes a notable improvement over previous similar work, particularly in terms of chemical abundances. Its primary purpose is to enable detailed evaluations of and refinements to stellar population synthesis models designed to recover the above information for unresolved stellar systems based on their integrated spectra. However, since the Schiavon sample spans a wide range of the known GGC parameter space, our compilation may also benefit investigations related to a variety of astrophysical endeavors, such as the early formation of the Milky Way, the chemical evolution of GGCs, and stellar evolution and nucleosynthesis. For instance, we confirm with our compiled data that the GGC system has a bimodal metallicity distribution and is uniformly enhanced in the α elements. When paired with the ages of our clusters, we find evidence that supports a scenario whereby the Milky Way obtained its globular clusters through two channels: in situ formation and accretion of satellite galaxies. The distributions of C, N, O, and Na abundances and the dispersions thereof per cluster corroborate the known fact that all GGCs studied so far with respect to multiple stellar populations have been found to harbor them. Finally, using data on individual stars, we verify that stellar atmospheres become progressively polluted by CN(O)-processed material after they leave the main sequence. We also uncover evidence which suggests that the α elements Mg and Ca may originate from more than one nucleosynthetic production site. We estimate that our compilation incorporates all relevant analyses from the literature up to mid-2012. As an aid to investigators in the fields named above, we provide detailed electronic tables of the data upon which our work is based at people/Stephane-Courteau/roediger2013/index.html. © 2014. The American Astronomical Society. All rights reserved..

Fressin F.,Harvard - Smithsonian Center for Astrophysics | Knutson H.A.,Harvard - Smithsonian Center for Astrophysics | Charbonneau D.,Harvard - Smithsonian Center for Astrophysics | O'Donovan F.T.,Harvard - Smithsonian Center for Astrophysics | And 4 more authors.
Astrophysical Journal | Year: 2010

We use the Spitzer Space Telescope to estimate the dayside thermal emission of the exoplanet TrES-3 integrated in the 3.6, 4.5, 5.8, and 8.0 μm bandpasses of the Infrared Array Camera (IRAC) instrument. We observe two secondary eclipses and find relative eclipse depths of 0.00346 ± 0.00035, 0.00372 ± 0.00054, 0.00449 ± 0.00097, and 0.00475 ± 0.00046, respectively, in the four IRAC bandpasses. We combine our results with the earlier K-band measurement of De Mooij etal., and compare them with models of the planetary emission. We find that the planet does not require the presence of an inversion layer in the high atmosphere. This is the first very strongly irradiated planet that does not have a temperature inversion, which indicates that stellar or planetary characteristics other than temperature have an important impact on temperature inversion. De Mooij & Snellen also detected a possible slight offset in the timing of the secondary eclipse in the K band. However, based on our four Spitzer channels, we place a 3σ upper limit of |ecos(ω)| < 0.0056, where e is the planet's orbital eccentricity and ω is the longitude of the periastron. This result strongly indicates that the orbit is circular, as expected from tidal circularization theory.

Bai X.-N.,Peyton Hall | Bai X.-N.,Harvard - Smithsonian Center for Astrophysics | Stone J.M.,Peyton Hall
Proceedings of the International Astronomical Union | Year: 2012

Protoplanetary disks (PPDs) are widely believed to be turbulent as a result of the magnetorotational instability (MRI). We perform magnetohydrodynamical simulations of PPDs that for the first time, take into account both Ohmic resistivity and ambipolar diffusion in a self-consistent manner. We show that in the inner region of PPDs that corresponds the habitable zone, the MRI is completely suppressed due to the interplay between magnetic field and ambipolar diffusion. The gas in this region is laminar throughout the entire vertical extent of the disk. Instead of MRI-driven accretion, a strong magnetocentrifugal wind is launched that efficiently carries away disk angular momentum. A physical wind geometry requires the presence of a strong current layer that is offset from the disk midplane where horizontal magnetic fields flip. We show that the entire accretion flow proceeds through this strong current layer. The non-turbulent nature of the gas flow strongly favors the habitable zone as the site for planetesimal formation, and has important implications for their subsequent growth into terrestrial planets. Copyright © International Astronomical Union 2014.

Smith N.,University of Arizona | Mauerhan J.C.,University of Arizona | Prieto J.L.,Peyton Hall
Monthly Notices of the Royal Astronomical Society | Year: 2014

The recent supernova (SN) known as SN 2009ip had dramatic precursor eruptions followed by an even brighter explosion in 2012. Its pre-2012 observations make it the best documented SN progenitor in history, but have fuelled debate about the nature of its 2012 explosion - whether it was a true SN or some type of violent non-terminal event. Both could power shock interaction with circumstellar material (CSM), but only a core-collapse SN provides a self-consistent explanation. The persistent broad emission lines in the spectrum require a relatively large ejecta mass, and a corresponding kinetic energy of at least 1051 erg, while the faint 2012a event is consistent with published models of core-collapse SNe from compact (̃60 R⊙) blue supergiants. The light curves of SN 2009ip and another Type IIn, SN 2010mc, were nearly identical; we demonstrate that their spectra match as well, and that both are standard SNe IIn. Our observations contradict the recent claim that the late-time spectrum of SN 2009ip is returning to its progenitor's luminous blue variable-like state, and we show the that late-time spectra of SN 2009ip closely resemble the spectra of SN 1987A. Moreover, SN 2009ip's changing Hα equivalent width after explosion matches behaviour typically seen in core-collapse SNe IIn. Several key facts about SN 2009ip and SN 2010mc argue strongly in favour of a core-collapse interpretation, and make a non-terminal 1050 erg event implausible. The most straightforward and self-consistent interpretation is that SN 2009ip was an initially faint core-collapse explosion of a blue supergiant that produced about half as much 56Ni as SN 1987A, with most of the peak luminosity from CSM interaction. © 2013 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Bu D.-F.,Chinese Academy of Sciences | Yuan F.,Chinese Academy of Sciences | Stone J.M.,Peyton Hall
Monthly Notices of the Royal Astronomical Society | Year: 2011

In a hot, dilute, magnetized accretion flow, the electron mean-free path can be much greater than the Larmor radius, and thus thermal conduction is anisotropic and along the magnetic field lines. In this case, if the temperature decreases outward, the flow may be subject to a buoyancy instability - the magnetothermal instability (MTI). The MTI amplifies the magnetic field, and aligns the field lines with the radial direction. If the accretion flow is differentially rotating, a magnetorotational instability (MRI) may also be present. Using two-dimensional, time-dependent magnetohydrodynamic simulations, we investigate the interaction between these two instabilities. We use global simulations that span over two orders of magnitude in radius, centred on the region around the Bondi radius where the infall time of gas is longer than the growth time of both the MTI and MRI. A significant amplification of the magnetic field is produced by both instabilities, although we find that the MTI and MRI primarily amplify the radial and toroidal components of the field, respectively. Most importantly, we find that if the MTI and MRI can amplify the magnetic energy by factors of F t and F r, respectively, then when the MTI and MRI are both present, the magnetic energy can be amplified by a factor of F t·F r. Therefore, we conclude that the amplification of the magnetic energy by the MTI and MRI operates independently. We also find that the MTI contributes to the transport of angular momentum, because radial motions induced by the MTI increase the Maxwell (by amplifying the magnetic field) and Reynolds stresses. Finally, we find that thermal conduction decreases the slope of the radial temperature profile. The increased temperature near the Bondi radius decreases the mass accretion rate. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

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