662 research outputs found
Concurrent panel session 1: Challenges of economic growth & diversification & labor preparation in Las Vegas
Moderator: Dr. Mel Jameson, UNLV College of Business Scribe: Angela Moor, UNLV Department of History Conference white paper & Full summary of panel session, 6 page
Was the Progenitor of the Sagittarius Stream a Disc Galaxy?
We use N-body simulations to explore the possibility that the Sagittarius
(Sgr) dwarf galaxy was originally a late-type, rotating disc galaxy, rather
than a non-rotating, pressure-supported dwarf spheroidal galaxy, as previously
thought. We find that bifurcations in the leading tail of the Sgr stream,
similar to those detected by the SDSS survey, naturally arise in models where
the Sgr disc is misaligned with respect to the orbital plane. Moreover, we show
that the internal rotation of the progenitor may strongly alter the location of
the leading tail projected on the sky, and thus affect the constraints on the
shape of the Milky Way dark matter halo that may be derived from modelling the
Sgr stream. Our models provide a clear, easily-tested prediction: although
tidal mass stripping removes a large fraction of the original angular momentum
in the progenitor dwarf galaxy, the remnant core should still rotate with a
velocity amplitude ~20 km/s that could be readily detected in future,
wide-field kinematic surveys of the Sgr dwarf.Comment: Letter accepted by MNRAS. N-body model animations can be downloaded
from http://www.ast.cam.ac.uk/~jorpega/files/sgr
PAndAS' cubs: discovery of two new dwarf galaxies in the surroundings of the Andromeda and Triangulum galaxies
We present the discovery of two new dwarf galaxies, Andromeda XXI and
Andromeda XXII, located in the surroundings of the Andromeda and Triangulum
galaxies (M31 and M33). These discoveries stem from the first year data of the
Pan-Andromeda Archaeological Survey (PAndAS), a photometric survey of the
M31/M33 group conducted with the Megaprime/MegaCam wide-field camera mounted on
the Canada-France-Hawaii Telescope. Both satellites appear as spatial
overdensities of stars which, when plotted in a color-magnitude diagram, follow
metal-poor, [Fe/H]=-1.8, red giant branches at the distance of M31/M33.
Andromeda XXI is a moderately bright dwarf galaxy (M_V=-9.9+/-0.6), albeit with
low surface brightness, emphasizing again that many relatively luminous M31
satellites still remain to be discovered. It is also a large satellite, with a
half-light radius close to 1 kpc, making it the fourth largest Local Group
dwarf spheroidal galaxy after the recently discovered Andromeda XIX, Andromeda
II and Sagittarius around the Milky Way, and supports the trend that M31
satellites are larger than their Milky Way counterparts. Andromeda XXII is much
fainter (M_V=-6.5+/-0.8) and lies a lot closer in projection to M33 than it
does to M31 (42 vs. 224 kpc), suggesting that it could be the first Triangulum
satellite to be discovered. Although this is a very exciting possibility in the
context of a past interaction of M33 with M31 and the fate of its satellite
system, a confirmation will have to await a good distance estimate to confirm
its physical proximity to M33. Along with the dwarf galaxies found in previous
surveys of the M31 surroundings, these two new satellites bring the number of
dwarf spheroidal galaxies in this region to 20.Comment: 10 pages, 6 figures, accepted for publication in ApJ; v2: minor
typographical correction
A Catalog of Chandra X-ray Sources in the Carina Nebula
We present a catalog of ~14,000 X-ray sources observed by the ACIS instrument
on the Chandra X-ray Observatory within a 1.42 square degree survey of the
Great Nebula in Carina, known as the Chandra Carina Complex Project (CCCP).
This study appears in a Special Issue of the ApJS devoted to the CCCP. Here, we
describe the data reduction and analysis procedures performed on the X-ray
observations, including calibration and cleaning of the X-ray event data, point
source detection, and source extraction. The catalog appears to be complete
across most of the field to an absorption-corrected total-band luminosity of
~10^{30.7} erg/s for a typical low-mass pre-main sequence star. Counterparts to
the X-ray sources are identified in a variety of visual, near-infrared, and
mid-infrared surveys. The X-ray and infrared source properties presented here
form the basis of many CCCP studies of the young stellar populations in Carina.Comment: Accepted for the ApJS Special Issue on the Chandra Carina Complex
Project (CCCP), scheduled for publication in May 2011. All 16 CCCP Special
Issue papers are available at
http://cochise.astro.psu.edu/Carina_public/special_issue.html through 2011 at
least. 29 pages, 11 figure
Strong RR Lyrae excess in the Hercules-Aquila Cloud
We map the large-scale sub-structure in the Galactic stellar halo using
accurate 3D positions of ~14,000 RR Lyrae reported by the Catalina Sky Survey.
In the heliocentric distance range of 10-25 kpc, in the region of the sky
approximately bounded by 30{\deg} < l < 55{\deg} and -45{\deg} < b < -25{\deg},
there appears to be a strong excess of RRab stars. This overdensity, peaking at
18 kpc, is most likely associated with the so-called Hercules-Aquila Cloud,
previously detected using Main Sequence tracers at similar distances in the
Sloan Digital Sky Survey data. Our analysis of the period-amplitude
distribution of RR Lyrae in this region indicates that the HAC is dominated by
the Oosterhoff I type population. By comparing the measured RR Lyrae number
density to models of a smooth stellar halo, we estimate the significance of the
observed excess and provide an updated estimate of the total luminosity of the
Cloud's progenitor.Comment: 12 pages, 9 figures, 3 tables. Accepted for publication in MNRA
A spectroscopic confirmation of the Bootes II dwarf spheroidal
We present a new suite of photometric and spectroscopic data for the faint
Bootes II dwarf spheroidal galaxy candidate. Our deep photometry, obtained with
the INT/WFC, suggests a distance of 46 kpc and a small half-light radius of 4.0
arcmin (56 pc), consistent with previous estimates. Follow-up spectroscopy
obtained with the Gemini/GMOS instrument yielded radial velocities and
metallicities. While the majority of our targets covers a broad range in
velocities and metallicities, we find five stars which share very similar
velocities and metallicities and which are all compatible with the colors and
magnitudes of the galaxy's likely red giant branch. We interpret these as a
spectroscopic detection of the Bootes II system. These stars have a mean
velocity of -117 km/s, a velocity dispersion of (10.5+-7.4) km/s and a mean
[Fe/H] of -1.79 dex, with a dispersion of 0.14 dex. At this metallicity, Boo II
is not consistent with the stellar-mass-metallicity relation for the more
luminous dwarf galaxies. Coupled with our distance estimate, its high negative
systemic velocity rules out any physical connection with its projected
neighbor, the Bootes I dwarf spheroidal, which has a velocity of ~+100 km/s.
The velocity and distance of Bootes II coincide with those of the leading arm
of Sagittarius, which passes through this region of the sky, so that it is
possible that Bootes II may be a stellar system associated with the Sagittarius
stream. Finally, we note that the properties of Bootes II are consistent with
being the surviving remnant of a previously larger and more luminous dSph
galaxy.Comment: 10 pages, 8 figures, accepted for publication in the Astrophysical
Journa
The Milky Way Tomography With SDSS. III. Stellar Kinematics
We study Milky Way kinematics using a sample of 18.8 million main-sequence stars with r 20 degrees). We find that in the region defined by 1 kpc < Z < 5 kpc and 3 kpc < R < 13 kpc, the rotational velocity for disk stars smoothly decreases, and all three components of the velocity dispersion increase, with distance from the Galactic plane. In contrast, the velocity ellipsoid for halo stars is aligned with a spherical coordinate system and appears to be spatially invariant within the probed volume. The velocity distribution of nearby (Z < 1 kpc) K/M stars is complex, and cannot be described by a standard Schwarzschild ellipsoid. For stars in a distance-limited subsample of stars (< 100 pc), we detect a multi-modal velocity distribution consistent with that seen by HIPPARCOS. This strong non-Gaussianity significantly affects the measurements of the velocity-ellipsoid tilt and vertex deviation when using the Schwarzschild approximation. We develop and test a simple descriptive model for the overall kinematic behavior that captures these features over most of the probed volume, and can be used to search for substructure in kinematic and metallicity space. We use this model to predict further improvements in kinematic mapping of the Galaxy expected from Gaia and the Large Synoptic Survey Telescope.NSF AST-615991, AST-0707901, AST-0551161, AST-02-38683, AST-06-07634, AST-0807444, PHY05-51164NASA NAG5-13057, NAG5-13147, NNXO-8AH83GPhysics Frontier Center/Joint Institute for Nuclear Astrophysics (JINA) PHY 08-22648U.S. National Science FoundationMarie Curie Research Training Network ELSA (European Leadership in Space Astrometry) MRTN-CT-2006-033481Fermi Research Alliance, LLC, United States Department of Energy DE-AC02-07CH11359Alfred P. Sloan FoundationParticipating InstitutionsJapanese MonbukagakushoMax Planck SocietyHigher Education Funding Council for EnglandMcDonald Observator
The INT/WFC survey of the Monoceros Ring: Accretion origin or Galactic Anomaly?
We present the results of a wide-field camera survey of the stars in the
Monoceros Ring, thought to be an additional structure in the Milky Way of
unknown origin. Lying roughly in the plane of the Milky Way, this may represent
a unique equatorial accretion event which is contributing to the Thick Disk of
the Galaxy. Alternatively, the Monoceros Ring may be a natural part of the Disk
formation process. With ten pointings in symmetric pairs above and below the
plane of the Galaxy, this survey spans 90 degrees about the Milky Way's
equator. Signatures of the stream of stars were detected in three fields, ({\it
l},{\it b}) = (118,+16) and (150,+15) plus a more tentative
detection at (150,-15). Galactocentric distance estimates to these
structures gave 17, 17, and 13 kpc respectively. The
Monoceros Ring seems to be present on both sides of the Galactic plane, in a
form different to that of the Galactic suggestive of a tidal origin with
streams multiply wrapping the Galaxy. A new model of the stream has shown a
strong coincidence with our results and has also provided the opportunity to
make several more detections in fields in which the stream is less significant.
The confirmed detection at ({\it l},{\it b}) = (123,-19) at 14,
kpc from the Galactic centre allows a re-examination revealing a tentative new
detection with a Galactocentric distance of 21 kpc. (Abridged)Comment: 14 pages, figure resolution reduced. Accepted for publication in
MNRA
The Milky Way Tomography with SDSS: III. Stellar Kinematics
We study Milky Way kinematics using a sample of 18.8 million main-sequence
stars with r<20 and proper-motion measurements derived from SDSS and POSS
astrometry, including ~170,000 stars with radial-velocity measurements from the
SDSS spectroscopic survey. Distances to stars are determined using a
photometric parallax relation, covering a distance range from ~100 pc to 10 kpc
over a quarter of the sky at high Galactic latitudes (|b|>20 degrees). We find
that in the region defined by 1 kpc <Z< 5 kpc and 3 kpc <R< 13 kpc, the
rotational velocity for disk stars smoothly decreases, and all three components
of the velocity dispersion increase, with distance from the Galactic plane. In
contrast, the velocity ellipsoid for halo stars is aligned with a spherical
coordinate system and appears to be spatially invariant within the probed
volume. The velocity distribution of nearby ( kpc) K/M stars is complex,
and cannot be described by a standard Schwarzschild ellipsoid. For stars in a
distance-limited subsample of stars (<100 pc), we detect a multimodal velocity
distribution consistent with that seen by HIPPARCOS. This strong
non-Gaussianity significantly affects the measurements of the velocity
ellipsoid tilt and vertex deviation when using the Schwarzschild approximation.
We develop and test a simple descriptive model for the overall kinematic
behavior that captures these features over most of the probed volume, and can
be used to search for substructure in kinematic and metallicity space. We use
this model to predict further improvements in kinematic mapping of the Galaxy
expected from Gaia and LSST.Comment: 90 pages, 26 figures, submitted to Ap
The Fourteenth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the extended Baryon Oscillation Spectroscopic Survey and from the second phase of the Apache Point Observatory Galactic Evolution Experiment
The fourth generation of the Sloan Digital Sky Survey (SDSS-IV) has been in
operation since July 2014. This paper describes the second data release from
this phase, and the fourteenth from SDSS overall (making this, Data Release
Fourteen or DR14). This release makes public data taken by SDSS-IV in its first
two years of operation (July 2014-2016). Like all previous SDSS releases, DR14
is cumulative, including the most recent reductions and calibrations of all
data taken by SDSS since the first phase began operations in 2000. New in DR14
is the first public release of data from the extended Baryon Oscillation
Spectroscopic Survey (eBOSS); the first data from the second phase of the
Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE-2),
including stellar parameter estimates from an innovative data driven machine
learning algorithm known as "The Cannon"; and almost twice as many data cubes
from the Mapping Nearby Galaxies at APO (MaNGA) survey as were in the previous
release (N = 2812 in total). This paper describes the location and format of
the publicly available data from SDSS-IV surveys. We provide references to the
important technical papers describing how these data have been taken (both
targeting and observation details) and processed for scientific use. The SDSS
website (www.sdss.org) has been updated for this release, and provides links to
data downloads, as well as tutorials and examples of data use. SDSS-IV is
planning to continue to collect astronomical data until 2020, and will be
followed by SDSS-V.Comment: SDSS-IV collaboration alphabetical author data release paper. DR14
happened on 31st July 2017. 19 pages, 5 figures. Accepted by ApJS on 28th Nov
2017 (this is the "post-print" and "post-proofs" version; minor corrections
only from v1, and most of errors found in proofs corrected
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