P. Yoachim - University of Washington

P. Yoachim
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P. Yoachim
University of Washington
El Paso
United States

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Cosmology and Nongalactic Astrophysics (8)
Astrophysics of Galaxies (7)
Astrophysics (7)
Instrumentation and Methods for Astrophysics (4)
Solar and Stellar Astrophysics (3)
High Energy Astrophysical Phenomena (1)

Publications Authored By P. Yoachim

Affiliations: 1Apache Point Observatory and New Mexico State University, Sunspot, NM, USA, 2Department of Astronomy, New Mexico State University, Las Cruces, NM, USA, 3Department of Astronomy, University of Washington, Seattle, WA, USA, 4Department of Astronomy, University of Washington, Seattle, WA, USA, 5Departamento de Física, CCNE, Universidade Federal de Santa Maria, Santa Maria, RS, Brazil, 6Departamento de Física, CCNE, Universidade Federal de Santa Maria, Santa Maria, RS, Brazil, 7Institut Utinam, Université de Franche-Comté, OSU THETA Franche-Comté-Bourgogne, Observatoire de Besancon, Besanon Cedex, France, 8Apache Point Observatory and New Mexico State University, Sunspot, NM, USA, 9Department of Astronomy, University of Wisconsin-Madison, Madison, WI, USA, 10Max-Planck Institute for Astrophysics, Garching, Germany, 11Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth, UK, 12Department of Physics \& Astronomy, Johns Hopkins University, Baltimore, MD, USA, 13Apache Point Observatory and New Mexico State University, Sunspot, NM, USA

We present a study of the kinematics of the extraplanar ionized gas around several dozen galaxies observed by the Mapping of Nearby Galaxies at the Apache Point Observatory (MaNGA) survey. We considered a sample of 67 edge-on galaxies out of more than 1400 extragalactic targets observed by MaNGA, in which we found 25 galaxies (or 37%) with regular lagging of the rotation curve at large distances from the galactic midplane. We model the observed $H\alpha$ emission velocity fields in the galaxies, taking projection effects and a simple model for the dust extinction into the account. Read More

In this work we quantify the performance of $LSST$ on the detection of eclipsing binaries. We use $Kepler$ observed binaries to create a large sample of simulated pseudo-$LSST$ binary light curves. From these light curves, we attempt to recover the known binary signal. Read More

Affiliations: 1Department of Physics and Astronomy, Rutgers University, 2Department of Physics and Astronomy, Rutgers University, 3Department of Physics and Astronomy, Rutgers University, 4Department of Astronomy, University of Washington, 5Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences, 6Instituto de Astrofísica, Pontificia Universidad Católica de Chile, 7Instituto de Astrofísica, Pontificia Universidad Católica de Chile, 8Centro de Estudios de Fisica del Cosmos de Aragon, 9Instituto de Astrofísica de La Plata, 10Department of Astronomy, University of Washington

The Large Synoptic Survey Telescope (LSST) will survey the southern sky from 2022--2032 with unprecedented detail. Since the observing strategy can lead to artifacts in the data, we investigate the effects of telescope-pointing offsets (called dithers) on the $r$-band coadded 5$\sigma$ depth yielded after the 10-year survey. We analyze this survey depth for several geometric patterns of dithers (e. Read More

We present the detection of Cepheids in the barred spiral galaxy NGC 1313, using the Wide Field and Planetary Camera 2 on the Hubble Space Telescpoe. Twenty B (F450W) and V (F555W) epochs of observations spanning over three weeks were obtained, on which the profile-fitting photometry of all stars in the monitored field was performed using the package HSTphot. A sample of 26 variable stars have been identified to be Cepheids, with periods between 3 and 14 days. Read More

The Large Synoptic Survey Telescope (LSST) is a large-aperture, wide-field, ground-based survey system that will image the sky in six optical bands from 320 to 1050 nm, uniformly covering approximately $18,000$deg$^2$ of the sky over 800 times. The LSST is currently under construction on Cerro Pach\'on in Chile, and expected to enter operations in 2022. Once operational, the LSST will explore a wide range of astrophysical questions, from discovering "killer" asteroids to examining the nature of Dark Energy. Read More

The formation mechanisms of thick discs are under discussion. Thick discs might have formed either at high redshift on a short time-scale or might have been built slowly over time. They may have an internal or an external origin. Read More

We present an analysis of the data produced by the MaNGA prototype run (P-MaNGA), aiming to test how the radial gradients in recent star formation histories, as indicated by the 4000AA-break (D4000), Hdelta absorption (EW(Hd_A)) and Halpha emission (EW(Ha)) indices, can be useful for understanding disk growth and star formation cessation in local galaxies. We classify 12 galaxies observed on two P-MaNGA plates as either centrally quiescent (CQ) or centrally star-forming (CSF), according to whether D4000 measured in the central spaxel of each datacube exceeds 1.6. Read More

We conduct a survey of satellite galaxies around the nearby spiral NGC 4258 by combining spectroscopic observations from the Apache Point Observatory 3.5-meter telescope with SDSS spectra. New spectroscopy is obtained for 15 galaxies. Read More

Over the last decade, quasar sample sizes have increased from several thousand to several hundred thousand, thanks mostly to SDSS imaging and spectroscopic surveys. LSST, the next-generation optical imaging survey, will provide hundreds of detections per object for a sample of more than ten million quasars with redshifts of up to about seven. We briefly review optical quasar selection techniques, with emphasis on methods based on colors, variability properties and astrometric behavior. Read More

Affiliations: 1Observatories of the Carnegie Institution for Science, 2University of Texas at Austin, 3University of Texas at Austin, 4University of Texas at Austin, 5University of Texas at Austin, 6University of Texas at Austin, 7University of Texas at Austin, 8Max Planck Institute for Astronomy, Heidelberg, 9Shanghai Astronomical Observatory, 10Universidad Nacional Autonoma de Mexico, 11Max Planck Institute for Extraterrestrial Physics, Garching, 12University of Maryland, 13Shanghai Astronomical Observatory, 14University of Texas at Austin, 15University of Texas at Austin, 16University of Texas at Austin, 17University of Washington

We present the survey design, data reduction, and spectral fitting pipeline for the VIRUS-P Exploration of Nearby Galaxies (VENGA). VENGA is an integral field spectroscopic survey, which maps the disks of 30 nearby spiral galaxies. Targets span a wide range in Hubble type, star formation activity, morphology, and inclination. Read More

We use the Mitchell Spectrograph (formerly VIRUS-P) to observe 12 nearby disk galaxies. We successfully measure ages in the outer disk in six systems. In three cases (NGC 2684, NGC 6155, and NGC 7437), we find that a downward break in the disk surface brightness profile corresponds with a change in the dominant stellar population with the interior being dominated by active star formation and the exterior having older stellar populations that are best-fit with star formation histories that decline with time. Read More

We use SDSS photometry of 73 million stars to simultaneously obtain best-fit main-sequence stellar energy distribution (SED) and amount of dust extinction along the line of sight towards each star. Using a subsample of 23 million stars with 2MASS photometry, whose addition enables more robust results, we show that SDSS photometry alone is sufficient to break degeneracies between intrinsic stellar color and dust amount when the shape of extinction curve is fixed. When using both SDSS and 2MASS photometry, the ratio of the total to selective absorption, $R_V$, can be determined with an uncertainty of about 0. Read More

Affiliations: 1University of Texas, 2University of Washington, 3University of Central Lancashire

Like the majority of spiral galaxies, NGC 6155 exhibits an exponential surface brightness profile that steepens significantly at large radii. Using the VIRUS-P IFU spectrograph, we have gathered spatially resolved spectra of the system. Modifying the GANDALF spectral fitting routine for use on the complex stellar populations found in spirals, we find that the average stellar ages increase significantly beyond the profile break radius. Read More

Affiliations: 1Department of Astronomy, The University of Texas at Austin, Austin, USA;, 2Department of Astronomy, The University of Texas at Austin, Austin, USA;, 3Department of Astronomy, The University of Texas at Austin, Austin, USA;, 4Department of Astronomy, The University of Texas at Austin, Austin, USA;, 5Department of Astronomy, The University of Texas at Austin, Austin, USA;, 6Department of Astronomy, The University of Texas at Austin, Austin, USA;, 7Department of Astronomy, The University of Texas at Austin, Austin, USA;, 8Department of Astronomy, The University of Texas at Austin, Austin, USA;, 9Department of Astronomy, The University of Texas at Austin, Austin, USA;, 10Max-Planck-Institut fur extraterrestrische Physik, Garching, Germany;, 11Max-Planck-Institut fur extraterrestrische Physik, Garching, Germany;, 12Department of Astronomy, The University of Texas at Austin, Austin, USA;, 13Shanghai Astronomical Observatory, Shanghai, China;, 14McDonald Observatory, The University of Texas at Austin, Austin, USA, 15Shanghai Astronomical Observatory, Shanghai, China;, 16McDonald Observatory, The University of Texas at Austin, Austin, USA, 17Department of Astronomy, The University of Texas at Austin, Austin, USA;

VENGA is a large-scale extragalactic IFU survey, which maps the bulges, bars and large parts of the outer disks of 32 nearby normal spiral galaxies. The targets are chosen to span a wide range in Hubble types, star formation activities, morphologies, and inclinations, at the same time of having vast available multi-wavelength coverage from the far-UV to the mid-IR, and available CO and 21cm mapping. The VENGA dataset will provide 2D maps of the SFR, stellar and gas kinematics, chemical abundances, ISM density and ionization states, dust extinction and stellar populations for these 32 galaxies. Read More

We have generated accurate V and I template light curves using a combination of Fourier decomposition and principal component analysis for a large sample of Cepheid light curves. Unlike previous studies, we include short period Cepheids and stars pulsating in the first overtone mode in our analysis. Extensive Monte Carlo simulations show that our templates can be used to precisely measure Cepheid magnitudes and periods, even in cases where there are few observational epochs. Read More

The ACS Nearby Galaxy Survey Treasury (ANGST) has acquired deep ACS imaging of a field in the outer disk of the large spiral galaxy M81. These data were obtained over a total of 20 HST orbits, providing a baseline long enough to reliably identify Cepheid variable stars in the field. Fundamental mode and first overtone types have been distinguished through comparative fits with corresponding Cepheid light curve templates derived from principal component analysis of confirmed Cepheids in the LMC, SMC, and Milky Way. Read More

We have measured Lick index equivalent widths to derive luminosity weighted stellar ages and metallicities for thin and thick disk dominated regions of 9 edge-on disk galaxies with the ARC 3.5 meter telescope at Apache Point Observatory. In all cases, the thick disks are confirmed to be old stellar populations, with typical ages between 4 and 10 Gyr. Read More

Authors: Z. Ivezic, J. A. Tyson, B. Abel, E. Acosta, R. Allsman, Y. AlSayyad, S. F. Anderson, J. Andrew, R. Angel, G. Angeli, R. Ansari, P. Antilogus, K. T. Arndt, P. Astier, E. Aubourg, T. Axelrod, D. J. Bard, J. D. Barr, A. Barrau, J. G. Bartlett, B. J. Bauman, S. Beaumont, A. C. Becker, J. Becla, C. Beldica, S. Bellavia, G. Blanc, R. D. Blandford, J. S. Bloom, J. Bogart, K. Borne, J. F. Bosch, D. Boutigny, W. N. Brandt, M. E. Brown, J. S. Bullock, P. Burchat, D. L. Burke, G. Cagnoli, D. Calabrese, S. Chandrasekharan, S. Chesley, E. C. Cheu, J. Chiang, C. F. Claver, A. J. Connolly, K. H. Cook, A. Cooray, K. R. Covey, C. Cribbs, W. Cui, R. Cutri, G. Daubard, G. Daues, F. Delgado, S. Digel, P. Doherty, R. Dubois, G. P. Dubois-Felsmann, J. Durech, M. Eracleous, H. Ferguson, J. Frank, M. Freemon, E. Gangler, E. Gawiser, J. C. Geary, P. Gee, M. Geha, R. R. Gibson, D. K. Gilmore, T. Glanzman, I. Goodenow, W. J. Gressler, P. Gris, A. Guyonnet, P. A. Hascall, J. Haupt, F. Hernandez, C. Hogan, D. Huang, M. E. Huffer, W. R. Innes, S. H. Jacoby, B. Jain, J. Jee, J. G. Jernigan, D. Jevremovic, K. Johns, R. L. Jones, C. Juramy-Gilles, M. Juric, S. M. Kahn, J. S. Kalirai, N. Kallivayalil, B. Kalmbach, J. P. Kantor, M. M. Kasliwal, R. Kessler, D. Kirkby, L. Knox, I. Kotov, V. L. Krabbendam, S. Krughoff, P. Kubanek, J. Kuczewski, S. Kulkarni, R. Lambert, L. Le Guillou, D. Levine, M. Liang, K-T. Lim, C. Lintott, R. H. Lupton, A. Mahabal, P. Marshall, S. Marshall, M. May, R. McKercher, M. Migliore, M. Miller, D. J. Mills, D. G. Monet, M. Moniez, D. R. Neill, J-Y. Nief, A. Nomerotski, M. Nordby, P. O'Connor, J. Oliver, S. S. Olivier, K. Olsen, S. Ortiz, R. E. Owen, R. Pain, J. R. Peterson, C. E. Petry, F. Pierfederici, S. Pietrowicz, R. Pike, P. A. Pinto, R. Plante, S. Plate, P. A. Price, M. Prouza, V. Radeka, J. Rajagopal, A. Rasmussen, N. Regnault, S. T. Ridgway, S. Ritz, W. Rosing, C. Roucelle, M. R. Rumore, S. Russo, A. Saha, B. Sassolas, T. L. Schalk, R. H. Schindler, D. P. Schneider, G. Schumacher, J. Sebag, G. H. Sembroski, L. G. Seppala, I. Shipsey, N. Silvestri, J. A. Smith, R. C. Smith, M. A. Strauss, C. W. Stubbs, D. Sweeney, A. Szalay, P. Takacs, J. J. Thaler, R. Van Berg, D. Vanden Berk, K. Vetter, F. Virieux, B. Xin, L. Walkowicz, C. W. Walter, D. L. Wang, M. Warner, B. Willman, D. Wittman, S. C. Wolff, W. M. Wood-Vasey, P. Yoachim, H. Zhan, for the LSST Collaboration
Category: Astrophysics

(Abridged) We describe here the most ambitious survey currently planned in the optical, the Large Synoptic Survey Telescope (LSST). A vast array of science will be enabled by a single wide-deep-fast sky survey, and LSST will have unique survey capability in the faint time domain. The LSST design is driven by four main science themes: probing dark energy and dark matter, taking an inventory of the Solar System, exploring the transient optical sky, and mapping the Milky Way. Read More

We present kinematic measurements of thin and thick disk components in a sample of nine edge-on galaxies. We extract stellar and ionized gas rotation curves at and above the galaxies' midplanes using the Ca II triplet absorption features and H-alpha emission lines measured with the GMOS spectrographs on Gemini North and South. For the higher mass galaxies in the sample, we fail to detect differences between the thin and thick disk kinematics. Read More

Affiliations: 1University of Washington, 2University of Washington, 3University of Washington
Category: Astrophysics

I briefly review the growing evidence that thick stellar disks surround most edge-on disk galaxies. Recent studies show that these extragalactic thick disks have old ages, low metallicities, long scale lengths, and moderately flattened axial ratios, much like the thick disk of the Milky Way. However, the properties of thick disks change systematically with the mass of the galaxy. Read More

We analyze the global structure of 34 late-type, edge-on, undisturbed, disk galaxies spanning a wide range of mass. We measure structural parameters for the galaxies using two-dimensional least-squares fitting to our $R$-band photometry. The fits require both a thick and a thin disk to adequately fit the data. Read More

We present kinematic measurements of the thick and thin disks in two edge-on galaxies. We have derived stellar rotation curves at and above the galaxies' midplanes using Ca II triplet features measured with the GMOS spectrograph on Gemini North. In one galaxy, FGC 1415, the kinematics above the plane show clear rotation that lags that of the midplane by ~20-50%, similar to the behavior seen in the Milky Way. Read More


We find that disk galaxies show a sharp, mass-dependent transition in the structure of their dusty ISM. Dust lanes are a generic feature of massive disks with V_rot>120km/s, but are completely absent in galaxies with V_rot<120km/s. The transition reflects an increase in the scale height of the cold ISM in low mass galaxies, driven by larger turbulent velocities supporting the gas layer, rather than sharp drops in the gas surface density. Read More