Now showing items 1-20 of 4209

    • IGRINS Spectral Library

      Park, Sunkyung; Lee, Jeong-Eun; Kang, Wonseok; Lee, Sang-Gak; Chun, Moo-Young; Kim, Kang-Min; Yuk, In-Soo; Lee, Jae-Joon; Mace, Gregory N.; Kim, Hwihyun; Kaplan, Kyle F.; Park, Chan; Sok Oh, Jae; Lee, Sungho; Jaffe, Daniel T.; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2018-10)
      We present a library of high-resolution (R lambda/Delta lambda similar to 45,000) and high signal-to-noise ratio (S/N >= 200) near-infrared spectra for stars of a wide range of spectral types and luminosity classes. The spectra were obtained with the Immersion GRating INfrared Spectrograph covering the full range of the H (1.496-1.780 mu m) and K (2.080-2.460 mu m) atmospheric windows. The targets were primarily selected for being MK standard stars covering a wide range of effective temperatures and surface gravities, with metallicities close to the solar value. Currently, the library includes flux-calibrated and telluric-absorption-corrected spectra of 84 stars, with prospects for expansion to provide denser coverage of the parametric space. Throughout the H and K atmospheric windows, we identified spectral lines that are sensitive to T-eff or log g and defined corresponding spectral indices. We also provide their equivalent widths (EWs). For those indices, we derive empirical relations between the measured EWs and the stellar atmospheric parameters. Therefore, the derived empirical equations can be used to calculate the T-eff and log g of a star without requiring stellar atmospheric models.
    • The Arizona Radio Observatory CO Mapping Survey of Galactic Molecular Clouds. VI. The Cep OB3 Cloud (Cepheus B and C) in CO J=2-1, (CO)-C-13 J=2-1, and CO J=3-2

      Bieging, John H.; Patel, Saahil; Hofmann, Ryan; Peters, William L.; Kainulainen, Jouni; Zhang, Miaomiao; Stutz, Amelia M.; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2018-10)
      We present (1) new fully sampled maps of CO and (CO)-C-13 J = 2-1 emission and CO J = 3-2 emission toward the molecular clouds Cep B and C, associated with the Cep OB3 association; (2) a map of extinction, A(V), derived from IR colors of background stars; and (3) the distribution of young stellar objects (YSOs) over the same field as the molecular maps. An LTE analysis of the CO and (CO)-C-13. maps yields the distribution of molecular column densities and temperatures. Substantial variations are evident across the clouds; smaller subregions show correlations between molecular properties and dust extinction, consistent with a picture of outer photodissociation regions with a layer of CO-dark molecular gas, a CO self-shielded interior, and an inner cold dense region where CO is largely depleted onto grains. Comparing the distribution of YSOs with molecular gas surface density shows a power-law relation very similar in slope to that for the giant molecular cloud associated with the H II region Sh2-235 from a previous paper in this series that employed the same methodology. We note the presence of several compact, isolated CO emission sources in the J = 3-2 maps. The gas temperature and (CO)-C-13. velocity dispersion yield a map of the sonic Mach number, which varies across the cloud but always exceeds unity, confirming the pervasiveness of supersonic turbulence over length scales greater than or similar to 0.1 pc (the map resolution). We also compute a J = 2-1 CO X-factor that varies with position but is, on average, within. 20% of the Galactic average derived from CO J = 1-0 observations.
    • Emission Line Ratios for the Circumgalactic Medium and the “Bimodal” Nature of Galaxies

      Zhang, Huanian; Zaritsky, Dennis; Werk, Jessica; Behroozi, Peter; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2018-10-10)
      We find significantly different diagnostic emission line ratios for the circumgalactic gas associated with galaxies of stellar masses above and below 10(10.4)M(circle dot) using Sloan Digital Sky Survey spectroscopy. Specifically, in a sample of 17,393 galaxies, intersected by 18,535 lines of sight at projected radii between 10 and 50 kpc, we stack measured fluxes for nebular strong emission lines, [O III] lambda 5007, H alpha, and [N II] lambda 6583, and find that the gas surrounding the lower-mass galaxies exhibits similar line ratios to those of gas ionized by star formation and that surrounding the higher-mass galaxies similar to those of gas ionized by active galactic nucleus or shocks. This finding highlights yet another characteristic of galaxies that is distinctly different above and below this stellar mass threshold, but one that is more closely connected to the gas accretion behavior hypothesized to be responsible for this dichotomy.
    • Evidence for Ultra-diffuse Galaxy “Formation” through Galaxy Interactions

      Bennet, P.; Sand, D. J.; Zaritsky, D.; Crnojević, D.; Spekkens, K.; Karunakaran, A.; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2018-10-10)
      We report the discovery of two ultra-diffuse galaxies (UDGs) that show clear evidence of an association with tidal material and an interaction with a larger galaxy halo, found during a search of the Wide portion of the Canada-France-Hawaii Telescope Legacy Survey. The two new UDGs, NGC 2708-Dw1 and NGC 5631-Dw1, are faint (M-g = -13.7 and -11.8 mag), extended (r(h) = 2.60 and 2.15 kpc), and have low central surface brightness (mu(g, 0) = 24.9 and 27.3 mag arcsec(-2)), while the stellar stream associated with each has a surface brightness mu(g) greater than or similar to 28.2 mag arcsec(-2). These observations provide evidence that the origin of some UDGs may connect to galaxy interactions, either by transforming normal dwarf galaxies by expanding them, or because UDGs can collapse out of tidal material (i.e., they are tidal dwarf galaxies). Further work is needed to understand the fraction of the UDG population "formed" through galaxy interactions, and wide field searches for diffuse dwarf galaxies will provide further clues to the origin of these enigmatic stellar systems.
    • Resolved Kinematics of Runaway and Field OB Stars in the Small Magellanic Cloud

      Oey, M. S.; Jones, J. Dorigo; Castro, N.; Zivick, P.; Besla, G.; Januszewski, H. C.; Moe, M.; Kallivayalil, N.; Lennon, D. J.; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2018-11-01)
      We use Gaia Data Release 2 proper motions of field OB stars from the Runaways and Isolated O-Type Star Spectroscopic Survey of the Small Magellanic Cloud (SMC) to study the kinematics of runaway stars. The data reveal that the SMC Wing has a systemic peculiar motion relative to the SMC Bar of (v(alpha), v(delta)) = (62 +/- 7, -18 +/- 5) km s(-1) and relative radial velocity +4.5 +/- 5.0 km s(-1). This unambiguously demonstrates that these two regions are kinematically distinct: the Wing is moving away from the Bar, and towards the Large Magellanic Cloud with a 3D velocity of 64 +/- 10 km s(-1). This is consistent with models for a recent, direct collision between the Clouds. We present transverse velocity distributions for our field OB stars, confirming that unbound runaways comprise on the order of half our sample, possibly more. Using eclipsing binaries and double-lined spectroscopic binaries as tracers of dynamically ejected runaways, and high-mass X-ray binaries (HMXBs) as tracers of runaways accelerated by supernova kicks, we find significant contributions from both populations. The data suggest that HMXBs have lower velocity dispersion relative to dynamically ejected binaries, consistent with the former group corresponding to less energetic supernova kicks that failed to unbind the components. Evidence suggests that our fast runaways are dominated by dynamical, rather than supernova, ejections.
    • Global-mean Vertical Tracer Mixing in Planetary Atmospheres. I. Theory and Fast-rotating Planets

      Zhang, Xi; Showman, Adam P.; Univ Arizona, Dept Planetary Sci; Univ Arizona, Lunar & Planetary Lab (IOP PUBLISHING LTD, 2018-10-10)
      Most chemistry and cloud formation models for planetary atmospheres adopt a one-dimensional (1D) diffusion approach to approximate the global-mean vertical tracer transport. The physical underpinning of the key parameter in this framework, eddy diffusivity K-zz, is usually obscure. Here we analytically and numerically investigate vertical tracer transport in a 3D stratified atmosphere and predict K-zz as a function of the large-scale circulation strength, horizontal mixing due to eddies and waves and local tracer sources and sinks We find that K-zz increases with tracer chemical lifetime and circulation strength but decreases with horizontal eddy mixing efficiency. We demarcated three K-zz regimes in planetary atmospheres. In the first regime where the tracer lifetime is short compared with the transport timescale and horizontal tracer distribution under chemical equilibrium (chi(0)) is uniformly distributed across the globe, global-mean vertical tracer mixing behaves diffusively. But the traditional assumption in current 1D models that all chemical species are transported via the same eddy diffusivity generally breaks down. We show that different chemical species in a single atmosphere should in principle have different eddy diffusion profiles. In the second regime where the tracer is short-lived but chi(0) is non-uniformly distributed, a significant non-diffusive component might lead to a negative K-zz under the diffusive assumption. In the third regime where the tracer is long-lived, global-mean vertical tracer transport is also largely influenced by non-diffusive effects. Numerical simulations of 2D tracer transport on fast-rotating zonally symmetric planets validate our analytical K-zz theory over a wide parameter space.
    • Global-mean Vertical Tracer Mixing in Planetary Atmospheres. II. Tidally Locked Planets

      Zhang, Xi; Showman, Adam P.; Univ Arizona, Dept Planetary Sci; Univ Arizona, Lunar & Planetary Lab (IOP PUBLISHING LTD, 2018-10-10)
      In Zhang & Showman, we developed an analytical theory of 1D eddy diffusivity K-zz for global-mean vertical tracer transport in a 3D atmosphere. We also presented 2D numerical simulations on fast-rotating planets to validate our theory. On a slowly rotating planet such as Venus or a tidally locked planet (not necessarily a slow-rotator) such as a hot Jupiter, the tracer distribution could exhibit significant longitudinal inhomogeneity and tracer transport is intrinsically 3D. Here we study the global-mean vertical tracer transport on tidally locked planets using 3D tracer-transport simulations. We find that our analytical K-zz theory in Zhang & Showman is validated on tidally locked planets over a wide parameter space. K-zz strongly depends on the large-scale circulation strength, horizontal mixing due to eddies, and waves, and local tracer sources and sinks due to chemistry and microphysics. As our analytical theory predicted, K-zz on tidally locked planets also exhibit three regimes. In Regime I where the chemical and microphysical processes are uniformly distributed across the globe, different chemical species should be transported via different eddy diffusivity. In Regime II where the chemical and microphysical processes are nonuniform-for example, photochemistry or cloud formation that exhibits strong day-night contrast-the global-mean vertical tracer mixing does not always behave diffusively. In the third regime where the tracer is long-lived, non-diffusive effects are significant. Using species-dependent eddy diffusivity, we provide a new analytical theory of the dynamical quench points for disequilibrium tracers on tidally locked planets from first principles.
    • Extremely Irradiated Hot Jupiters: Non-oxide Inversions, H- Opacity, and Thermal Dissociation of Molecules

      Lothringer, Joshua D.; Barman, Travis; Koskinen, Tommi; Univ Arizona, Lunar & Planetary Lab (IOP PUBLISHING LTD, 2018-10-10)
      Extremely irradiated hot Jupiters, exoplanets reaching dayside temperatures >2000 K, stretch our understanding of planetary atmospheres and the models we use to interpret observations. While these objects are planets in every other sense, their atmospheres reach temperatures at low pressures comparable only to stellar atmospheres. In order to understand our a priori theoretical expectations for the nature of these objects, we self-consistently model a number of extreme hot Jupiter scenarios with the PHOENIX model atmosphere code. PHOENIX is well-tested on objects from cool brown dwarfs to expanding supernovae shells, and its expansive opacity database from the UV to far-IR make PHOENIX well-suited to understanding extremely irradiated hot Jupiters. We find several fundamental differences between hot Jupiters at temperatures >2500 K and their cooler counterparts. First, absorption by atomic metals like Fe and Mg, molecules including SiO and metal hydrides, and continuous opacity sources like H-, all combined with the short-wavelength output of early-type host stars, result in strong thermal inversions, without the need for TiO or VO. Second, many molecular species, including H2O, TiO, and VO are thermally dissociated at pressures probed by transit and eclipse observations, potentially biasing retrieval algorithms that assume uniform vertical abundances. We discuss other interesting properties of these objects, as well as future prospects and predictions for observing and characterizing this unique class of astrophysical object, including the first self-consistent model of the hottest known Jovian planet, KELT-9b.
    • The MOSDEF Survey: The Nature of Mid-infrared Excess Galaxies and a Comparison of IR and UV Star Formation Tracers at z ∼ 2

      Azadi, Mojegan; Coil, Alison; Aird, James; Shivaei, Irene; Reddy, Naveen; Shapley, Alice; Kriek, Mariska; Freeman, William R.; Leung, Gene C. K.; Mobasher, Bahram; Price, Sedona H.; Sanders, Ryan L.; Siana, Brian; Zick, Tom; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2018-10-10)
      We present an analysis using the MOSFIRE Deep Evolution Field (MOSDEF) survey on the nature of "MIR-excess" galaxies, which have star formation rates (SFRs) inferred from mid-infrared (MIR) data that are substantially elevated relative to those estimated from dust-corrected UV data. We use a sample of similar to 200 galaxies and active galactic nuclei (AGNs) at 1.40 < z < 2.61 with 24 mu m detections (rest-frame 8 mu m) from MIPS/Spitzer. We find that the identification of MIR-excess galaxies strongly depends on the methodologies used to estimate IR luminosity (L-IR) and to correct the UV light for dust attenuation. We find that extrapolations of the SFR from the observed 24 mu m flux, using luminosity-dependent templates based on local galaxies, substantially overestimate L-IR in z similar to 2 galaxies. By including Herschel observations and using a stellar-mass-dependent, luminosity-independent L-IR, we obtain more reliable estimates of the SFR and a lower fraction of MIR-excess galaxies. Once stellar-mass selection biases are taken into account, we identify similar to 24% of our galaxies as MIR excess. However, SFRH alpha is not elevated in MIR-excess galaxies compared to MIR-normal galaxies, indicating that the intrinsic fraction of MIR excess may be lower. Using X-ray-, IR-, and optically selected AGNs in MOSDEF, we do not find a higher prevalence for AGNs in MIR-excess galaxies relative to MIR-normal galaxies. A stacking analysis of X-ray-undetected galaxies does not reveal a harder spectrum in MIR-excess galaxies relative to MIR-normal galaxies. Our analysis indicates that AGN activity does not contribute substantially to the MIR excess and instead implies that it is likely due to the enhanced polycyclic aromatic hydrocarbon emission.
    • Dust Emission in an Accretion-rate-limited Sample of z ≳ 6 Quasars

      Venemans, Bram P.; Decarli, Roberto; Walter, Fabian; Bañados, Eduardo; Bertoldi, Frank; Fan, Xiaohui; Farina, Emanuele Paolo; Mazzucchelli, Chiara; Riechers, Dominik; Rix, Hans-Walter; Wang, Ran; Yang, Yujin; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2018-10-20)
      We present Atacama Large Millimeter Array 1 mm observations of the rest-frame far-infrared (FIR) dust continuum in 27 quasars at redshifts 6.0 less than or similar to z < 6.7. We detect FIR emission at greater than or similar to 3 sigma in all quasar host galaxies with flux densities at similar to 1900 GHz in the rest-frame of 0.12 < S-rest,S- (1900) (GHz) < 5.9 mJy, with a median (mean) flux density of 0.88 mJy (1.59 mJy). The implied FIR luminosities range from L-FIR = (0.27-13) x 10(12) L-circle dot, with 74% of our quasar hosts having L-FIR > 10(12) L-circle dot The estimated dust masses are M-dust = 10(7)-10(9) M-circle dot. If the dust is heated only by star formation, then the star formation rates in the quasar host galaxies are between 50 and 2700 M-circle dot yr(-1). In the framework of the host galaxy-black hole coevolution model a correlation between ongoing black hole growth and star formation in the quasar host galaxy would be expected. However, combined with results from the literature to create a luminosity-limited quasar sample, we do not find a strong correlation between quasar UV luminosity (a proxy for ongoing black hole growth) and FIR luminosity (star formation in the host galaxy). The absence of such a correlation in our data does not necessarily rule out the coevolution model, and could be due to a variety of effects (including different timescales for black hole accretion and FIR emission).
    • The VLA Nascent Disk and Multiplicity Survey of Perseus Protostars (VANDAM). V. 18 Candidate Disks around Class 0 and I Protostars in the Perseus Molecular Cloud

      Segura-Cox, Dominique M.; Looney, Leslie W.; Tobin, John J.; Li, Zhi-Yun; Harris, Robert J.; Sadavoy, Sarah; Dunham, Michael M.; Chandler, Claire; Kratter, Kaitlin; Pérez, Laura; Melis, Carl; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2018-10-20)
      We present the full disk-fit results VANDAM survey of all Class 0 and I protostars in the Perseus molecular cloud. We have 18 new protostellar disk candidates around Class 0 and I sources, which are well described by a simple, parametrized disk model fit to the 8 mm VLA dust continuum observations. 33% of Class 0 protostars and just 11% of Class I protostars have candidate disks, while 78% of Class 0 and I protostars do not have signs of disks within our 12 au disk diameter resolution limit, indicating that at 8 mm most disks in the Class 0 and I phases are <10 au in radius. These small radii may be a result of surface brightness sensitivity limits. Modeled 8 mm radii are similar to the radii of known Class 0 disks with detected Keplerian rotation. Since our 8 mm data trace a population of larger dust grains that radially drift toward the protostar and are lower limits on true disk sizes, large disks at early times do not seem to be particularly rare. We find statistical evidence that Class 0 and I disks are likely drawn from the same distribution, meaning disk properties may be defined early in the Class 0 phase and do not undergo large changes through the Class I phase. By combining our candidate disk properties with previous polarization observations, we find a qualitative indication that misalignment between inferred envelope-scale magnetic fields and outflows may indicate disks on smaller scales in Class 0 sources.
    • Polar Dust, Nuclear Obscuration, and IR SED Diversity in Type-1 AGNs

      Lyu, Jianwei; Rieke, George H.; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2018-10-20)
      Despite the hypothesized similar face-on viewing angles, the infrared emission of type-1 active galactic nuclei (AGNs) has diverse spectral energy distribution (SED) shapes that deviate substantially from the well-characterized quasar templates. Motivated by the commonly seen UV-optical obscuration and the discovery of parsec-scale mid-IR polar dust emission in some nearby AGNs, we develop semi-empirical SED libraries for reddened type-1 AGNs built on quasar intrinsic templates, assuming low-level extinction caused by an extended distribution of large dust grains. We demonstrate that this model can reproduce the nuclear UV to IR SED and the strong mid-IR polar dust emission of NGC 3783, the type-1 AGN with the most relevant and robust observational constraints. In addition, we compile 64 low-z Seyfert-1 nuclei with negligible mid-IR star formation contamination and satisfactorily fit the individual IR SEDs as well as the composite UV to mid-IR composite SEDs. Given the success of these fits, we characterize the possible infrared SED of AGN polar dust emission and utilize a simple but effective strategy to infer its prevalence among type-1 AGNs. The SEDs of high-z peculiar AGNs, including the extremely red quasars, mid-IR warm-excess AGNs, and hot dust-obscured galaxies, can be also reproduced by our model. These results indicate that the IR SEDs of most AGNs, regardless of redshift or luminosity, arise from similar circumnuclear torus properties but differ mainly due to the optical depths of extended obscuring dust components.
    • Velocity-resolved Reverberation Mapping of Five Bright Seyfert 1 Galaxies

      De Rosa, G.; Fausnaugh, M. M.; Grier, C. J.; Peterson, B. M.; Denney, K. D.; Horne, Keith; Bentz, M. C.; Ciroi, S.; Bontà, E. Dalla; Joner, M. D.; Kaspi, S.; Kochanek, C. S.; Pogge, R. W.; Sergeev, S. G.; Vestergaard, M.; Adams, S. M.; Antognini, J.; Salvo, C. Araya; Armstrong, E.; Bae, J.; Barth, A. J.; Beatty, T. G.; Bhattacharjee, A.; Borman, G. A.; Boroson, T. A.; Bottorff, M. C.; Brown, J. E.; Brown, J. S.; Brotherton, M. S.; Coker, C. T.; Clanton, C.; Cracco, V.; Crawford, S. M.; Croxall, K. V.; Eftekharzadeh, S.; Eracleous, M.; Fiorenza, S. L.; Frassati, A.; Hawkins, K.; Henderson, C. B.; Holoien, T. W.-S.; Hutchison, T.; Kellar, J.; Kilerci-Eser, E.; Kim, S.; King, A. L.; Mura, G. La; Laney, C. D.; Li, M.; Lochhaas, C.; Ma, Z.; MacInnis, F.; Manne-Nicholas, E. R.; Mason, M.; McGraw, S. M.; Mogren, K.; Montouri, C.; Moody, J. W.; Mosquera, A. M.; Mudd, D.; Musso, R.; Nazarov, S. V.; Nguyen, M. L.; Ochner, P.; Okhmat, D. N.; Onken, C. A.; Ou-Yang, B.; Pancoast, A.; Pei, L.; Penny, M.; Poleski, R.; Portaluri, E.; Prieto, J.-L.; Price-Whelan, A. M.; Pulatova, N. G.; Rafter, S.; Roettenbacher, R. M.; Romero-Colmenero, E.; Runnoe, J.; Schimoia, J. S.; Shappee, B. J.; Sherf, N.; Simonian, G. V.; Siviero, A.; Skowron, D. M.; Skowron, J.; Somers, G.; Spencer, M.; Starkey, D. A.; Stevens, D. J.; Stoll, R.; Tamajo, E.; Tayar, J.; Saders, J. L. van; Valenti, S.; Villanueva, Jr., S.; Villforth, C.; Weiss, Y.; Winkler, H.; Zastrow, J.; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2018-10-20)
      We present the first results from a reverberation-mapping campaign undertaken during the first half of 2012, with additional data on one active galactic nucleus (AGN) (NGC 3227) from a 2014 campaign. Our main goals are (1) to determine the black hole masses from continuum-H beta reverberation signatures, and (2) to look for velocity-dependent time delays that might be indicators of the gross kinematics of the broad-line region. We successfully measure H beta time delays and black hole masses for five AGNs, four of which have previous reverberation mass measurements. The values measured here are in agreement with earlier estimates, though there is some intrinsic scatter beyond the formal measurement errors. We observe velocity-dependent H beta lags in each case, and find that the patterns have changed in the intervening five years for three AGNs that were also observed in 2007.
    • SMASHing the LMC: A Tidally Induced Warp in the Outer LMC and a Large-scale Reddening Map

      Choi, Yumi; Nidever, David L.; Olsen, Knut; Blum, Robert D.; Besla, Gurtina; Zaritsky, Dennis; van der Marel, Roeland P.; Bell, Eric F.; Gallart, Carme; Cioni, Maria-Rosa L.; Clifton Johnson, L.; Katherina Vivas, A.; Saha, Abhijit; de Boer, Thomas J. L.; Noël, Noelia E. D.; Monachesi, Antonela; Massana, Pol; Conn, Blair C.; Martinez-Delgado, David; Muñoz, Ricardo R.; Stringfellow, Guy S.; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2018-10-20)
      We present a study of the three-dimensional (3D) structure of the Large Magellanic Cloud (LMC) using similar to 2.2 million red clump (RC) stars selected from the Survey of the MAgellanic Stellar History. To correct for line-of-sight dust extinction, the intrinsic RC color and magnitude and their radial dependence are carefully measured by using internal nearly dust-free regions. These are then used to construct an accurate 2D reddening map (165 deg(2) area with similar to 10' resolution) of the LMC disk and the 3D spatial distribution of RC stars. An inclined disk model is fit to the 2D distance map, yielding a best-fit inclination angle i = 25.86(-1.39)(+0.73) degrees with random errors of +/- 0 degrees.19 and line-of-nodes position angle 149.23(-8.35)(+6.43) degrees with random errors of +/- 0 degrees.49. These angles vary with galactic radius, indicating that the LMC disk is warped and twisted likely due to the repeated tidal interactions with the Small Magellanic Cloud (SMC). For the first time, our data reveal a significant warp in the southwestern part of the outer disk starting at rho similar to 7 degrees that departs from the defined LMC plane up to similar to 4 kpc toward the SMC, suggesting that it originated from a strong interaction with the SMC. In addition, the inner disk encompassing the off-centered bar appears to be tilted up to 5 degrees-15 degrees relative to the rest of the LMC disk. These findings on the outer warp and the tilted bar are consistent with the predictions from the Besla et al. simulation of a recent direct collision with the SMC.
    • The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Perseus Protostars. VI. Characterizing the Formation Mechanism for Close Multiple Systems

      Tobin, John J.; Looney, Leslie W.; Li, Zhi-Yun; Sadavoy, Sarah I.; Dunham, Michael M.; Segura-Cox, Dominique; Kratter, Kaitlin; Chandler, Claire J.; Melis, Carl; Harris, Robert J.; Perez, Laura; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2018-11-01)
      We present Atacama Large Millimeter/submillimeter Array observations of multiple protostar systems in the Perseus molecular cloud, previously detected by the Karl G. Jansky Very Large Array. We observe 17 close (<600 au separation) multiple systems at 1.3 mm in continuum and five molecular lines (i.e., (CO)-C-12, (CO)-O-18, (CO)-C-13, H2CO, SO) to characterize the circum-multiple environments in which these systems are forming. We detect at least one component in the continuum for the 17 multiple systems. In three systems one companion is not detected, and for two systems the companions are unresolved at our observed resolution. We also detect circum-multiple dust emission toward eight out of nine Class 0 multiples. Circum-multiple dust emission is not detected toward any of the eight Class I multiples. Twelve systems are detected in the dense gas tracers toward their disks/inner envelopes. For these 12 systems, we use the dense gas observations to characterize their formation mechanism. The velocity gradients in the circum-multiple gas are clearly orthogonal to the outflow directions in eight out of the 12 systems, consistent with disk fragmentation. Moreover, only two systems with separations <200 au are inconsistent with disk fragmentation, in addition to the two widest systems (>500 au). Our results suggest that disk fragmentation via gravitational instability is an important formation mechanism for close multiple systems, but further statistics are needed to better determine the relative fraction formed via this method.
    • Mapping Lyman Continuum Escape in Tololo 1247–232

      Micheva, Genoveva; Oey, M. S.; Keenan, Ryan P.; Jaskot, Anne E.; James, Bethan L.; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2018-11-01)
      Low-redshift, spatially resolved Lyman continuum (LyC) emitters allow us to clarify the processes for LyC escape from these starburst galaxies. We use Hubble Space Telescope (HST) WFC3 and ACS imaging of the confirmed low-redshift LyC emitter Tol 1247-232 to study the ionization structure of the gas and its relation to the ionizing star clusters. We perform ionization parameter mapping (IPM) using [O III] lambda lambda 4959, 5007 and [O II] lambda 3727 imaging as the high-and low-ionization tracers, revealing broad, large-scale, optically thin regions originating from the center and reaching the outskirts of the galaxy, consistent with LyC escape. We carry out stellar population synthesis modeling of the 26 brightest clusters using our HST photometry. Combining these data with the nebular photometry, we find a global LyC escape fraction of f(esc) = 0.12, with uncertainties also consistent with zero escape and all measured f(esc) values for this galaxy. Our analysis suggests that, similar to other candidate LyC emitters, a two-stage starburst has taken place in this galaxy, with a 12 Myr old, massive central cluster likely having precleared regions in and around the center and the second generation of 2-4 Myr old clusters dominating the current ionization, including some escape from the galaxy.
    • The Missing Satellites of the Magellanic Clouds? Gaia Proper Motions of the Recently Discovered Ultra-faint Galaxies

      Kallivayalil, Nitya; Sales, Laura V.; Zivick, Paul; Fritz, Tobias K.; Del Pino, Andrés; Sohn, Sangmo Tony; Besla, Gurtina; van der Marel, Roeland P.; Navarro, Julio F.; Sacchi, Elena; Univ Arizona, Steward Observ (IOP PUBLISHING LTD, 2018-11-01)
      According to LCDM theory, hierarchical evolution occurs on all mass scales, implying that satellites of the Milky Way should also have companions. The recent discovery of ultra-faint dwarf galaxy candidates in close proximity to the Magellanic Clouds provides an opportunity to test this theory. We present proper motion (PM) measurements for 13 of the 32 new dwarf galaxy candidates using Gaia data release 2. All 13 also have radial velocity measurements. We compare the measured 3D velocities of these dwarfs to those expected at the corresponding distance and location for the debris of a Large Magellanic Cloud (LMC) analog in a cosmological numerical simulation. We conclude that four of these galaxies (Hor1, Car2, Car3, and Hyi1) have come in with the Magellanic Clouds, constituting the first confirmation of the type of satellite infall predicted by LCDM. Ret2, Tuc2, and Gru1 have velocity components that are not consistent within 3 sigma of our predictions and are therefore less favorable. Hya2 and Dra2 could be associated with the LMC and merit further attention. We rule out Tuc3, Cra2, Tri2, and Aqu2 as potential members. Of the dwarfs without measured PMs, five of them are deemed unlikely on the basis of their positions and distances alone being too far from the orbital plane expected for LMC debris (Eri2, Ind2, Cet2, Cet3, and Vir1). For the remaining sample, we use the simulation to predict PMs and radial velocities, finding that Phx2 has an overdensity of stars in DR2 consistent with this PM prediction.
    • Structure of the heliosheath from HSTOF energetic neutral atoms measurements

      Czechowski, A.; Hilchenbach, M.; Hsieh, K. C.; Bzowski, M.; Grzedzielski, S.; Sokół, J. M.; Grygorczuk, J.; Univ Arizona, Dept Phys (EDP SCIENCES S A, 2018-10-09)
      Context. From the year 1996 until now, High energy Suprathermal Time Of Flight sensor (HSTOF) on board Solar and Heliospheric Observatory (SOHO) has been measuring the heliospheric energetic neutral atoms (ENA) flux between +/- 17 degrees from the ecliptic plane. At present it is the only ENA instrument with the energy range within that of Voyager LECP energetic ion measurements. The energetic ion density and thickness of the inner heliosheath along the Voyager 1 trajectory are now known, and the ENA flux in the HSTOF energy range coming from the Voyager 1 direction may be estimated. Aims. We use HSTOF ENA data and Voyager 1 energetic ion spectrum to compare the regions of the heliosheath observed by HSTOF and Voyager 1. Methods. We compared the HSTOF ENA flux data from the forward and flank sectors of the heliosphere observed in various time periods between the years 1996 and 2010 and calculated the predicted ENA flux from the Voyager 1 direction using the Voyager 1 LECP energetic ion spectrum and including the contributions of charge exchange with both neutral H and He atoms. Results. The ratio between the HSTOF ENA flux from the ecliptic longitude sector 210-300 degrees (the LISM apex sector) for the period 1996-1997 to the estimated ENA flux from the Voyager 1 direction is similar to 1.3, but decreases to similar to 0.6 for the period 1996 2005 and similar to 0.3 for 1998-2006. For the flank longitude sectors (120-210 degrees and 300-30 degrees), the ratio also tends to decrease with time from similar to 0.6 for 1996-2005 to similar to 0.2 for 2008 2010. We discuss implications of these results for the energetic ion distribution in the heliosheath and the structure of the heliosphere.
    • A collection of model stellar spectra for spectral types B to early-M

      Allende Prieto, C.; Koesterke, L.; Hubeny, I.; Bautista, M. A.; Barklem, P. S.; Nahar, S. N.; Univ Arizona, Steward Observ (EDP SCIENCES S A, 2018-10-09)
      Context. Models of stellar spectra are necessary for interpreting light from individual stars, planets, integrated stellar populations, nebulae, and the interstellar medium. Aims. We provide a comprehensive and homogeneous collection of synthetic spectra for a wide range of atmospheric parameters and chemical compositions. Methods. We compile atomic and molecular data from the literature. We adopt the largest and most recent set of ATLAS9 model atmospheres, and use the radiative code ASS epsilon T. Results. The resulting collection of spectra is made publicly available at medium and high-resolution (R lambda/delta lambda = 10 000, 100 000 and 300 000) spectral grids, which include variations in effective temperature between 3500K and 30 000 K, surface gravity (0 <= log g <= 5), and metallicity (-5 <= [Fe/H] <= +0 : 5), spanning the wavelength interval 120-6500 nm. A second set of denser grids with additional dimensions, [alpha/ Fe] and micro-turbulence, are also provided (covering 200-2500 nm). We compare models with observations for a few representative cases.
    • AKARI mid-infrared slitless spectroscopic survey of star-forming galaxies at z ≲ 0.5

      Ohyama, Y.; Wada, T.; Matsuhara, H.; Takagi, T.; Malkan, M.; Goto, T.; Egami, E.; Lee, H.-M.; Im, M.; Kim, J.H.; Pearson, C.; Inami, H.; Oyabu, S.; Usui, F.; Burgarella, D.; Mazyed, F.; Imanishi, M.; Jeong, W.-S.; Miyaji, T.; Díaz Tello, J.; Nakagawa, T.; Serjeant, S.; Takeuchi, T. T.; Toba, Y.; White, G. J.; Hanami, H.; Ishigaki, T.; Univ Arizona, Steward Observ (EDP SCIENCES S A, 2018-10-18)
      Context. Deep mid-infrared (MIR) surveys have revealed numerous strongly star-forming galaxies at redshift z less than or similar to 2. Their MIR fluxes are produced by a combination of continuum and polycyclic aromatic hydrocarbon (PAH) emission features. The PAH features can dominate the total MIR flux, but are difficult to measure without spectroscopy. Aims. We aim to study star-forming galaxies by using a blind spectroscopic survey at MIR wavelengths to understand evolution of their star formation rate (SFR) and specific SFR (SFR per stellar mass) up to z similar or equal to 0.5, by paying particular attention to their PAH properties. Methods. We conducted a low-resolution (R similar or equal to 50) slitless spectroscopic survey at 5-13 mu m of 9 mu m flux-selected sources (> 0.3 mJy) around the north ecliptic pole with the infrared camera (IRC) onboard AKARI. After removing 11 AGN candidates by using the IRC photometry, we identify 48 PAH galaxies with PAH 6.2, 7.7, and 8.6 mu m features at z < 0.5. The rest-frame optical-MIR spectral energy distributions (SEDs) based on CFHT and IRC imaging covering 0.37-18 mu m were produced, and analysed in conjunction with the PAH spectroscopy. We defined the PAH enhancement by using the luminosity ratio of the 7.7 mu m PAH feature over the 3.5 mu m stellar component of the SEDs. Results. The rest-frame SEDs of all PAH galaxies have a universal shape with stellar and 7.7 mu m bumps, except that the PAH enhancement significantly varies as a function of the PAH luminosities. We identify a PAH-enhanced population at z greater than or similar to 0.35, whose SEDs and luminosities are typical of luminous infrared galaxies. They show particularly larger PAH enhancement at high luminosity, implying that they are vigorous star-forming galaxies with elevated specific SFR. Our composite starburst model that combines a very young and optically very thick starburst with a very old population can successfully reproduce most of their SED characteristics, although we cannot confirm this optically think component from our spectral analysis.