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Featured submissions

January 2019 

  • 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.

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