-
Jo Bovy,
Carlos Allende Prieto,
Timothy C. Beers,
Dmitry Bizyaev,
Luiz N. da Costa,
Katia Cunha,
Garrett L. Ebelke,
Daniel J. Eisenstein,
Peter M. Frinchaboy,
Ana Elia García Pérez, [......],
Kaike Pan,
Helio J. Rocha-Pinto,
Ricardo P. Schiavon,
Donald P. Schneider,
Mathias Schultheis,
Michael Skrutskie,
Verne V. Smith,
David H. Weinberg,
John C. Wilson,
Gail Zasowski
[show abstract]
[hide abstract]
ABSTRACT: We measure the Milky Way's rotation curve over the Galactocentric range 4 kpc
<~ R <~ 14 kpc from the first year of data from the Apache Point Observatory
Galactic Evolution Experiment (APOGEE). We model the line-of-sight velocities
of 3,365 stars in fourteen fields with b = 0 deg between 30 deg < l < 210 deg
out to distances of 10 kpc using an axisymmetric kinematical model that
includes a correction for the asymmetric drift of the warm tracer population
(\sigma_R ~ 35 km/s). We determine the local value of the circular velocity to
be V_c(R_0) = 218 +/- 6 km/s and find that the rotation curve is approximately
flat with a local derivative between -3.0 km/s/kpc and 0.4 km/s/kpc. We also
measure the Sun's position and velocity in the Galactocentric rest frame,
finding the distance to the Galactic center to be 8 kpc < R_0 < 9 kpc, radial
velocity V_{R,sun} = -10 +/- 1 km/s, and rotational velocity V_{\phi,sun} =
242^{+10}_{-3} km/s, in good agreement with local measurements of the Sun's
radial velocity and with the observed proper motion of Sgr A*. We investigate
various systematic uncertainties and find that these are limited to offsets at
the percent level, ~2 km/s in V_c. Marginalizing over all the systematics that
we consider, we find that V_c(R_0) < 235 km/s at >99% confidence. We find an
offset between the Sun's rotational velocity and the local circular velocity of
26 +/- 3 km/s, which is larger than the locally-measured solar motion of 12
km/s. This larger offset reconciles our value for V_c with recent claims that
V_c >~ 240 km/s. Combining our results with other data, we find that the Milky
Way's dark-halo mass within the virial radius is ~8x10^{11} M_sun.
09/2012;
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[show abstract]
[hide abstract]
ABSTRACT: We present ultraviolet (UV) integrated colors of 44 Galactic globular
clusters (GGCs) observed with the Galaxy Evolution Explorer (GALEX) in both FUV
and NUV bands. This data-base is the largest homogeneous catalog of UV colors
ever published for stellar systems in our Galaxy. The proximity of GGCs makes
it possible to resolve many individual stars even with the somewhat low spatial
resolution of GALEX. This allows us to determine how the integrated UV colors
are driven by hot stellar populations, primarily horizontal branch stars and
their progeny. The UV colors are found to be correlated with various parameters
commonly used to define the horizontal branch morphology. We also investigate
how the UV colors vary with parameters like metallicity, age, helium abundance
and concentration. We find for the first time that GCs associated with the
Sagittarius dwarf galaxy have (FUV-V) colors systematically redder than GGCs
with the same metallicity. Finally, we speculate about the presence of an
interesting trend, suggesting that the UV color of GCs may be correlated with
the mass of the host galaxy, in the sense that more massive galaxies possess
bluer clusters.
08/2012;
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David L. Nidever,
Gail Zasowski,
Steven R. Majewski,
Jonathan Bird,
Annie C. Robin,
Inma Martinez-Valpuesta,
Rachael L. Beaton,
Ralph Schoenrich,
Mathias Schultheis,
John C. Wilson, [......],
Jon Holtzman,
Fred R. Hearty,
Elena Malanushenko,
Viktor Malanushenko,
Demitri Muna,
Daniel Oravetz,
Kaike Pan,
Audrey Simmons,
Stephanie Snedden,
Benjamin A. Weaver
[show abstract]
[hide abstract]
ABSTRACT: Commissioning observations with the Apache Point Observatory Galactic
Evolution Experiment (APOGEE), part of the Sloan Digital Sky Survey III, have
produced radial velocities (RVs) for ~4700 K/M-giant stars in the Milky Way
bulge. These high-resolution (R \sim 22,500), high-S/N (>100 per resolution
element), near-infrared (1.51-1.70 um; NIR) spectra provide accurate RVs
(epsilon_v~0.2 km/s) for the sample of stars in 18 Galactic bulge fields
spanning -1<l<20 deg, |b|<20 deg, and dec>-32 deg. This represents the largest
NIR high-resolution spectroscopic sample of giant stars ever assembled in this
region of the Galaxy. A cold (sigma_v~30 km/s), high-velocity peak (V_GSR \sim
+200 km/s) is found to comprise a significant fraction (~10%) of stars in many
of these fields. These high RVs have not been detected in previous MW surveys
and are not expected for a simple, circularly rotating disk. Preliminary
distance estimates rule out an origin from the background Sagittarius tidal
stream or a new stream in the MW disk. Comparison to various Galactic models
suggests that these high RVs are best explained by stars in orbits of the
Galactic bar potential, although some observational features remain
unexplained.
07/2012;
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Hwihyun Kim,
Bradley C. Whitmore,
Rupali Chandar,
Abhijit Saha,
Catherine C. Kaleida,
Max Mutchler,
Seth H. Cohen,
Daniela Calzetti, Robert W. O'Connell,
Rogier A. Windhorst, [......],
Jay A. Frogel,
Donald N. B. Hall,
Jon A. Holtzman,
Randy A. Kimble,
Patrick J. McCarthy,
Francesco Paresce,
Joe I. Silk,
John T. Trauger,
Alistair R. Walker,
Erick T. Young
[show abstract]
[hide abstract]
ABSTRACT: We present a multi-wavelength photometric study of ~15,000 resolved stars in
the nearby spiral galaxy M83 (NGC5236, D=4.61Mpc) based on Hubble Space
Telescope Wide Field Camera 3 observations using four filters: F336W, F438W,
F555W, and F814W. We select 50 regions (an average size of 260 pc by 280 pc) in
the spiral arm and inter-arm areas of M83, and determine the age distribution
of the luminous stellar populations in each region. This is accomplished by
correcting for extinction towards each individual star by comparing its colors
with predictions from stellar isochrones. We compare the resulting luminosity
weighted mean ages of the luminous stars in the 50 regions with those
determined from several independent methods, including the number ratio of
red-to-blue supergiants, morphological appearance of the regions, surface
brightness fluctuations, and the ages of clusters in the regions. We find
reasonably good agreement between these methods. We also find that young stars
are much more likely to be found in concentrated aggregates along spiral arms,
while older stars are more dispersed. These results are consistent with the
scenario that star formation is associated with the spiral arms, and stars form
primarily in star clusters and then disperse on short timescales to form the
field population. The locations of Wolf-Rayet stars are found to correlate with
the positions of many of the youngest regions, providing additional support for
our ability to accurately estimate ages. We address the effects of spatial
resolution on the measured colors, magnitudes, and age estimates. While
individual stars can occasionally show measurable differences in the colors and
magnitudes, the age estimates for entire regions are only slightly affected.
04/2012;
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Ricardo P. Schiavon,
Emanuele Dalessandro,
Sangmo T. Sohn,
Robert T. Rood, Robert W. O'Connell,
Francesco R. Ferraro,
Barbara Lanzoni,
Giacomo Beccari,
Soo-Chang Rey,
Jaehyon Rhee,
R. Michael Rich,
Suk-Jin Yoon,
Young-Wook Lee
[show abstract]
[hide abstract]
ABSTRACT: We present GALEX data for 44 Galactic globular clusters obtained during 3
GALEX observing cycles between 2004 and 2008. This is the largest homogeneous
data set on the UV photometric properties of Galactic globular clusters ever
collected. The sample selection and photometric analysis are discussed, and
color-magnitude diagrams are presented. The blue and intermediate-blue
horizontal branch is the dominant feature of the UV color-magnitude diagrams of
old Galactic globular clusters. Our sample is large enough to display the
remarkable variety of horizontal branch shapes found in old stellar
populations. Other stellar types that are obviously detected are blue
stragglers and post core-He burning stars. The main features of UV
color-magnitude diagrams of Galactic globular clusters are briefly discussed.
We establish the locus of post-core He burning stars in the UV color-magnitude
diagram and present a catalog of candidate AGB-manqu \'e, post early-AGB, and
post-AGB stars within our cluster sample.
01/2012;
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Daniel J. Eisenstein,
David H. Weinberg,
Eric Agol,
Hiroaki Aihara,
Carlos Allende Prieto,
Scott F. Anderson,
James A. Arns,
Éric Aubourg,
Stephen Bailey,
Eduardo Balbinot, [......],
John P. Wisniewski,
W. Michael Wood-Vasey,
Brian Yanny,
Naoki Yasuda,
Christophe Yèche,
Donald G. York,
Erick Young,
Gail Zasowski,
Idit Zehavi,
and Bo Zhao
[show abstract]
[hide abstract]
ABSTRACT: Building on the legacy of the Sloan Digital Sky Survey (SDSS-I and II), SDSS-III is a program of four spectroscopic surveys on three scientific themes: dark energy and cosmological parameters, the history and structure of the Milky Way, and the population of giant planets around other stars. In keeping with SDSS tradition, SDSS-III will provide regular public releases of all its data, beginning with SDSS Data Release 8 (DR8), which was made public in 2011 January and includes SDSS-I and SDSS-II images and spectra reprocessed with the latest pipelines and calibrations produced for the SDSS-III investigations. This paper presents an overview of the four surveys that comprise SDSS-III. The Baryon Oscillation Spectroscopic Survey will measure redshifts of 1.5 million massive galaxies and Lyα forest spectra of 150,000 quasars, using the baryon acoustic oscillation feature of large-scale structure to obtain percent-level determinations of the distance scale and Hubble expansion rate at z < 0.7 and at z 2.5. SEGUE-2, an already completed SDSS-III survey that is the continuation of the SDSS-II Sloan Extension for Galactic Understanding and Exploration (SEGUE), measured medium-resolution (R = λ/Δλ 1800) optical spectra of 118,000 stars in a variety of target categories, probing chemical evolution, stellar kinematics and substructure, and the mass profile of the dark matter halo from the solar neighborhood to distances of 100 kpc. APOGEE, the Apache Point Observatory Galactic Evolution Experiment, will obtain high-resolution (R 30,000), high signal-to-noise ratio (S/N ≥ 100 per resolution element), H-band (1.51 μm < λ < 1.70 μm) spectra of 105 evolved, late-type stars, measuring separate abundances for ~15 elements per star and creating the first high-precision spectroscopic survey of all Galactic stellar populations (bulge, bar, disks, halo) with a uniform set of stellar tracers and spectral diagnostics. The Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS) will monitor radial velocities of more than 8000 FGK stars with the sensitivity and cadence (10-40 m s–1, ~24 visits per star) needed to detect giant planets with periods up to two years, providing an unprecedented data set for understanding the formation and dynamical evolution of giant planet systems. As of 2011 January, SDSS-III has obtained spectra of more than 240,000 galaxies, 29,000 z ≥ 2.2 quasars, and 140,000 stars, including 74,000 velocity measurements of 2580 stars for MARVELS.
The Astronomical Journal 08/2011; 142(3):72. · 4.03 Impact Factor
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Sugata Kaviraj,
R. Mark Crockett,
Bradley C. Whitmore,
Joseph Silk, Robert W. O'Connell,
Rogier A. Windhorst,
Max Mutchler,
Marina Rejkuba,
Sukyoung Yi,
Jay A. Frogel,
Daniela Calzetti
[show abstract]
[hide abstract]
ABSTRACT: We combine near-ultraviolet (NUV; 2250 {\AA}) and optical (U, B, V, I)
imaging from the Wide Field Camera 3 (WFC3), on board the Hubble Space
Telescope (HST), to study the globular cluster (GC) population in NGC 4150, a
sub-L* (M_B ~ -18.48 mag) early-type minor-merger remnant in the Coma I cloud.
We use broadband NUV-optical photometry from the WFC3 to estimate individual
ages, metallicities, masses and line-of-sight extinctions [E_(B-V)] for 63
bright (M_V < -5 mag) GCs in this galaxy. In addition to a small GC population
with ages greater than 10 Gyr, we find a dominant population of clusters with
ages centred around 6 Gyr, consistent with the expected peak of stellar mass
assembly in faint early-types residing in low-density environments. The old and
intermediate-age GCs in NGC 4150 are metal-poor, with metallicities less than
0.1 ZSun, and reside in regions of low extinction (E_(B-V) < 0.05 mag). We also
find a population of young, metal-rich (Z > 0.3 ZSun) clusters that have formed
within the last Gyr and reside in relatively dusty (E_(B-V) > 0.3 mag) regions
that are coincident with the part of the galaxy core that hosts significant
recent star formation. Cluster disruption models (in which ~80-90% of objects
younger than a few 10^8 yr dissolve every dex in time) suggest that the bulk of
these young clusters are a transient population.
07/2011;
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Guido De Marchi,
Francesco Paresce,
Nino Panagia,
Giacomo Beccari,
Loredana Spezzi,
Marco Sirianni,
Morten Andersen,
Max Mutchler,
Bruce Balick,
Michael A. Dopita, [......],
Jon A. Holtzman,
Randy A. Kimble,
Patrick J. McCarthy, Robert W. O'Connell,
Abhijit Saha,
Joseph I. Silk,
John T. Trauger,
Alistair R. Walker,
Rogier A. Windhorst,
Erick T. Young
[show abstract]
[hide abstract]
ABSTRACT: Using observations obtained with the Wide Field Camera 3 (WFC3) on board the
Hubble Space Telescope (HST), we have studied the properties of the stellar
populations in the central regions of 30 Dor, in the Large Magellanic Cloud.
The observations clearly reveal the presence of considerable differential
extinction across the field. We characterise and quantify this effect using
young massive main sequence stars to derive a statistical reddening correction
for most objects in the field. We then search for pre-main sequence (PMS) stars
by looking for objects with a strong (> 4 sigma) Halpha excess emission and
find about 1150 of them over the entire field. Comparison of their location in
the Hertzsprung-Russell diagram with theoretical PMS evolutionary tracks for
the appropriate metallicity reveals that about one third of these objects are
younger than ~4Myr, compatible with the age of the massive stars in the central
ionising cluster R136, whereas the rest have ages up to ~30Myr, with a median
age of ~12Myr. This indicates that star formation has proceeded over an
extended period of time, although we cannot discriminate between an extended
episode and a series of short and frequent bursts that are not resolved in
time. While the younger PMS population preferentially occupies the central
regions of the cluster, older PMS objects are more uniformly distributed across
the field and are remarkably few at the very centre of the cluster. We
attribute this latter effect to photoevaporation of the older circumstellar
discs caused by the massive ionising members of R136.
06/2011;
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Steven L. Finkelstein,
Seth H. Cohen,
Rogier A. Windhorst,
Russell E. Ryan,
Nimish P. Hathi,
Keely D. Finkelstein,
Jay Anderson,
Norman A. Grogin,
Anton M. Koekemoer,
Sangeeta Malhotra, [......],
Jon A. Holtzman,
Randy A. Kimble,
Gerard Luppino,
Francesco Paresce,
Abhijit Saha,
Joseph I. Silk,
John T. Trauger,
Alistair R. Walker,
Bradley C. Whitmore,
and Erick T. Young
[show abstract]
[hide abstract]
ABSTRACT: We present the highest redshift detections of resolved Lyα emission, using Hubble Space Telescope (HST)/Advanced Camera for Surveys F658N narrowband-imaging data taken in parallel with the Wide Field Camera 3 Early Release Science program in the GOODS Chandra Deep Field-South. We detect Lyα emission from three spectroscopically confirmed z = 4.4 Lyα emitting galaxies (LAEs), more than doubling the sample of LAEs with resolved Lyα emission. Comparing the light distribution between the rest-frame ultraviolet continuum and narrowband images, we investigate the escape of Lyα photons at high redshift. While our data do not support a positional offset between the Lyα and rest-frame ultraviolet (UV) continuum emission, the half-light radius in one out of the three galaxies is significantly (>1σ) larger in Lyα than in the rest-frame UV continuum. Stacking the three LAEs in both the narrowband and UV continuum images, we find that the Lyα light appears larger than the rest-frame UV at 4.2σ significance. This Lyα flux detected with HST is a factor of 4-10 less than observed in similar filters from the ground. These results together imply that the Lyα emission is not strictly confined to its indigenous star-forming regions. Rather, for at least one object the Lyα emission is more extended, with the missing HST flux possibly existing in a diffuse outer halo. This suggests that the radiative transfer of Lyα photons in high-redshift LAEs is complicated, with the interstellar-medium geometry and/or outflows playing a significant role in galaxies at these redshifts.
The Astrophysical Journal 06/2011; 735(1):5. · 6.02 Impact Factor
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Sungryong Hong,
Daniela Calzetti,
Michael A. Dopita,
William P. Blair,
Bradley C. Whitmore,
Bruce Balick,
Howard E. Bond,
Marcella Carollo,
Michael J. Disney,
Jay A. Frogel, [......],
Patrick J. McCarthy, Robert W. O'Connell,
Francesco Paresce,
Abhijit Saha,
Joseph I. Silk,
John T. Trauger,
Alistair R. Walker,
Rogier A. Windhorst,
Erick T. Young,
and Max Mutchler
[show abstract]
[hide abstract]
ABSTRACT: We investigate the ionization structure of the nebular gas in M83 using the line diagnostic diagram, [O III](5007 Å)/Hβ versus [S II](6716 Å+6731 Å)/Hα, with the newly available narrowband images from the Wide Field Camera 3 (WFC3) of the Hubble Space Telescope (HST). We produce the diagnostic diagram on a pixel-by-pixel (02 × 02) basis and compare it with several photo- and shock-ionization models. We select four regions from the center to the outer spiral arm and compare them in the diagnostic diagram. For the photoionized gas, we observe a gradual increase of the log ([O III]/Hβ) ratios from the center to the spiral arm, consistent with the metallicity gradient, as the H II regions go from super-solar abundance to roughly solar abundance from the center out. Using the diagnostic diagram, we separate the photoionized from the shock-ionized component of the gas. We find that the shock-ionized Hα emission ranges from ~2% to about 15%-33% of the total, depending on the separation criteria used. An interesting feature in the diagnostic diagram is a horizontal distribution around log ([O III]/Hβ) 0. This feature is well fit by a shock-ionization model with 2.0 Z ☉ metallicity and shock velocities in the range of 250-350 km s–1. A low-velocity shock component, <200 km s–1, is also detected and is spatially located at the boundary between the outer ring and the spiral arm. The low-velocity shock component can be due to (1) supernova remnants located nearby, (2) dynamical interaction between the outer ring and the spiral arm, and (3) abnormal line ratios from extreme local dust extinction. The current data do not enable us to distinguish among those three possible interpretations. Our main conclusion is that, even at the HST resolution, the shocked gas represents a small fraction of the total ionized gas emission at less than 33% of the total. However, it accounts for virtually all of the mechanical energy produced by the central starburst in M83.
The Astrophysical Journal 03/2011; 731(1):45. · 6.02 Impact Factor
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Loredana Spezzi,
Giacomo Beccari,
Guido De Marchi,
Erick T. Young,
Francesco Paresce,
Michael A. Dopita,
Morten Andersen,
Nino Panagia,
Bruce Balick,
Howard E. Bond, [......],
Randy A. Kimble,
Patrick J. McCarthy, Robert W. O'Connell,
Russell E. Ryan Jr,
Abhijit Saha,
Joseph I. Silk,
John T. Trauger,
Alistair R. Walker,
Bradley C. Whitmore,
and Rogier A. Windhorst
[show abstract]
[hide abstract]
ABSTRACT: We used near-infrared data obtained with the Wide Field Camera 3 on the Hubble Space Telescope to identify objects having the colors of brown dwarfs (BDs) in the field of the massive galactic cluster NGC 3603. These are identified through a combination of narrow- and medium-band filters which span the J and H bands and are particularly sensitive to the presence of the 1.3-1.5 μm H2O molecular band unique to BDs. We provide a calibration of the relationship between effective temperature and color for both field stars and BDs. This photometric method provides effective temperatures for BDs to an accuracy of ±350 K relative to spectroscopic techniques. This accuracy is shown to be not significantly affected by either stellar surface gravity or uncertainties in the interstellar extinction. We identify nine objects having effective temperatures between 1700 and 2200 K, typical of BDs, observed J-band magnitudes in the range 19.5-21.5, and that are strongly clustered toward the luminous core of NGC 3603. However, if these are located at the distance of the cluster, they are far too luminous to be normal BDs. We argue that it is unlikely that these objects are either artifacts of our data set, normal field BDs/M-type giants, or extragalactic contaminants and, therefore, might represent a new class of stars having the effective temperatures of BDs but with luminosities of more massive stars. We explore the interesting scenario in which these objects would be normal stars that have recently tidally ingested a hot Jupiter, the remnants of which are providing a short-lived extended photosphere to the central star. In this case, we would expect them to show the signature of fast rotation.
The Astrophysical Journal 03/2011; 731(1):1. · 6.02 Impact Factor
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Sungryong Hong,
Daniela Calzetti,
Michael A. Dopita,
William P. Blair,
Bradley C. Whitmore,
Bruce Balick,
Howard E. Bond,
Marcella Carollo,
Michael J. Disney,
Jay A. Frogel, [......],
Patrick J. McCarthy, Robert W. O'Connell,
Francesco Paresce,
Abhijit Saha,
Joseph I. Silk,
John T. Trauger,
Alistair R. Walker,
Rogier A. Windhorst,
Erick T. Young,
Max Mutchler
[show abstract]
[hide abstract]
ABSTRACT: We investigate the ionization structure of the nebular gas in M83 using the
line diagnostic diagram, [O III](5007 \degA)/H{\beta} vs. [S II](6716 \deg
A+6731 \deg A)/H{\alpha} with the newly available narrowband images from the
Wide Field Camera 3 (WFC3) of the Hubble Space Telescope (HST). We produce the
diagnostic diagram on a pixel-by-pixel (0.2" x 0.2") basis and compare it with
several photo- and shock-ionization models. For the photo-ionized gas, we
observe a gradual increase of the log([O III]/H{\beta}) ratios from the center
to the spiral arm, consistent with the metallicity gradient, as the H II
regions go from super solar abundance to roughly solar abundance from the
center out. Using the diagnostic diagram, we separate the photo-ionized from
the shock-ionized component of the gas. We find that the shock-ionized
H{\alpha} emission ranges from ~2% to about 15-33% of the total, depending on
the separation criteria used. An interesting feature in the diagnostic diagram
is an horizontal distribution around log([O III]/H{\beta}) ~ 0. This feature is
well fit by a shock-ionization model with 2.0 Z\odot metallicity and shock
velocities in the range of 250 km/s to 350 km/s. A low velocity shock
component, < 200 km/s, is also detected, and is spatially located at the
boundary between the outer ring and the spiral arm. The low velocity shock
component can be due to : 1) supernova remnants located nearby, 2) dynamical
interaction between the outer ring and the spiral arm, 3) abnormal line ratios
from extreme local dust extinction. The current data do not enable us to
distinguish among those three possible interpretations. Our main conclusion is
that, even at the HST resolution, the shocked gas represents a small fraction
of the total ionized gas emission at less than 33% of the total. However, it
accounts for virtually all of the mechanical energy produced by the central
starburst in M83.
02/2011;
-
Loredana Spezzi,
Giacomo Beccari,
Guido De Marchi,
Erick T. Young,
Francesco Paresce,
Michael A. Dopita,
Morten Andersen,
Nino Panagia,
Bruce Balick,
Howard E. Bond, [......],
Jon A. Holtzman,
Randy A. Kimble,
Patrick J. McCarthy, Robert W. O'Connell,
Abhijit Saha,
Joseph I. Silk,
John T. Trauger,
Alistair R. Walker,
Bradley C. Whitmore,
Rogier A. Windhorst
[show abstract]
[hide abstract]
ABSTRACT: We use near-infrared data obtained with the Wide Field Camera 3 (WFC3) on the
Hubble Space Telescope to identify objects having the colors of brown dwarfs
(BDs) in the field of the massive galactic cluster NGC 3603. These are
identified through use of a combination of narrow and medium band filters
spanning the J and H bands, and which are particularly sensitive to the
presence of the 1.3-1.5{\mu}m H2O molecular band - unique to BDs. We provide a
calibration of the relationship between effective temperature and color for
both field stars and for BDs. This photometric method provides effective
temperatures for BDs to an accuracy of {\pm}350K relative to spectroscopic
techniques. This accuracy is shown to be not significantly affected by either
stellar surface gravity or uncertainties in the interstellar extinction. We
identify nine objects having effective temperature between 1700 and 2200 K,
typical of BDs, observed J-band magnitudes in the range 19.5-21.5, and that are
strongly clustered towards the luminous core of NGC 3603. However, if these are
located at the distance of the cluster, they are far too luminous to be normal
BDs. We argue that it is unlikely that these objects are either artifacts of
our dataset, normal field BDs/M-type giants or extra-galactic contaminants and,
therefore, might represent a new class of stars having the effective
temperatures of BDs but with luminosities of more massive stars. We explore the
interesting scenario in which these objects would be normal stars that have
recently tidally ingested a Hot Jupiter, the remnants of which are providing a
short-lived extended photosphere to the central star. In this case, we would
expect them to show the signature of fast rotation.
01/2011;
-
R. Mark Crockett,
Sugata Kaviraj,
Joseph I. Silk,
Bradley C. Whitmore, Robert W. O'Connell,
Max Mutchler,
Bruce Balick,
Howard E. Bond,
Daniela Calzetti,
C. Marcella Carollo, [......],
Randy A. Kimble,
Patrick J. McCarthy,
Francesco Paresce,
Abhijit Saha,
John T. Trauger,
Alistair R. Walker,
Rogier A. Windhorst,
Erick T. Young,
Hyunjin Jeong,
and Sukyoung K. Yi
[show abstract]
[hide abstract]
ABSTRACT: We present a spatially resolved near-UV/optical study, using the Wide Field Camera 3 (WFC3) on board the Hubble Space Telescope, of NGC 4150, a sub-L *, early-type galaxy (ETG) of around 6 × 109 M ☉, which has been observed as part of the WFC3 Early-Release Science Programme. Previous work indicates that this galaxy has a large reservoir of molecular hydrogen gas, exhibits a kinematically decoupled core (a likely indication of recent merging) and strong, central Hβ absorption (indicative of young stars). While relatively uninspiring in its optical image, the core of NGC 4150 shows ubiquitous near-UV emission and remarkable dusty substructure. Our analysis shows this galaxy to lie in the near-UV green valley, and its pixel-by-pixel photometry exhibits a narrow range of near-UV/optical colors that are similar to those of nearby E+A (post-starburst) galaxies and lie between those of M83 (an actively star-forming spiral) and the local quiescent ETG population. We parameterize the properties of the recent star formation (RSF; age, mass fraction, metallicity, and internal dust content) in the NGC 4150 pixels by comparing the observed near-UV/optical photometry to stellar models. The typical age of the RSF is around 0.9 Gyr, consistent with the similarity of the near-UV colors to post-starburst systems, while the morphological structure of the young component supports the proposed merger scenario. The typical RSF metallicity, representative of the metallicity of the gas fuelling star formation, is ~0.3-0.5 Z ☉. Assuming that this galaxy is a merger and that the gas is sourced mainly from the infalling companion, these metallicities plausibly indicate the gas-phase metallicity (GPM) of the accreted satellite. Comparison to the local mass-GPM relation suggests (crudely) that the mass of the accreted system is ~3 × 108 M ☉, making NGC 4150 a 1:20 minor merger. A summation of the pixel RSF mass fractions indicates that the RSF contributes ~2%-3% of the stellar mass. This work reaffirms our hypothesis that minor mergers play a significant role in the evolution of ETGs at late epochs.
The Astrophysical Journal 01/2011; 727(2):115. · 6.02 Impact Factor
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SDSS-III collaboration: Hiroaki Aihara,
Carlos Allende Prieto,
Deokkeun An,
Scott F. Anderson,
Éric Aubourg,
Eduardo Balbinot,
Timothy C. Beers,
Andreas A. Berlind,
Steven J. Bickerton,
Dmitry Bizyaev, [......],
David A. Wake,
Ji Wang,
Benjamin A. Weaver,
David H. Weinberg,
Martin White,
Simon D. M. White,
Brian Yanny,
Naoki Yasuda,
Christophe Yeche,
Idit Zehavi
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ABSTRACT: The Sloan Digital Sky Survey (SDSS) started a new phase in August 2008, with
new instrumentation and new surveys focused on Galactic structure and chemical
evolution, measurements of the baryon oscillation feature in the clustering of
galaxies and the quasar Ly alpha forest, and a radial velocity search for
planets around ~8000 stars. This paper describes the first data release of
SDSS-III (and the eighth counting from the beginning of the SDSS). The release
includes five-band imaging of roughly 5200 deg^2 in the Southern Galactic Cap,
bringing the total footprint of the SDSS imaging to 14,555 deg^2, or over a
third of the Celestial Sphere. All the imaging data have been reprocessed with
an improved sky-subtraction algorithm and a final, self-consistent photometric
recalibration and flat-field determination. This release also includes all data
from the second phase of the Sloan Extension for Galactic Understanding and
Evolution (SEGUE-2), consisting of spectroscopy of approximately 118,000 stars
at both high and low Galactic latitudes. All the more than half a million
stellar spectra obtained with the SDSS spectrograph have been reprocessed
through an improved stellar parameters pipeline, which has better determination
of metallicity for high metallicity stars.
01/2011;
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Daniel J. Eisenstein,
David H. Weinberg,
Eric Agol,
Hiroaki Aihara,
Carlos Allende Prieto,
Scott F. Anderson,
James A. Arns,
Eric Aubourg,
Stephen Bailey,
Eduardo Balbinot, [......],
John P. Wisniewski,
W. Michael Wood-Vasey,
Brian Yanny,
Naoki Yasuda,
Christophe Yeche,
Donald G. York,
Erick Young,
Gail Zasowski,
Idit Zehavi,
Bo Zhao
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ABSTRACT: Building on the legacy of the Sloan Digital Sky Survey (SDSS-I and II),
SDSS-III is a program of four spectroscopic surveys on three scientific themes:
dark energy and cosmological parameters, the history and structure of the Milky
Way, and the population of giant planets around other stars. In keeping with
SDSS tradition, SDSS-III will provide regular public releases of all its data,
beginning with SDSS DR8 (which occurred in Jan 2011). This paper presents an
overview of the four SDSS-III surveys. BOSS will measure redshifts of 1.5
million massive galaxies and Lya forest spectra of 150,000 quasars, using the
BAO feature of large scale structure to obtain percent-level determinations of
the distance scale and Hubble expansion rate at z<0.7 and at z~2.5. SEGUE-2,
which is now completed, measured medium-resolution (R=1800) optical spectra of
118,000 stars in a variety of target categories, probing chemical evolution,
stellar kinematics and substructure, and the mass profile of the dark matter
halo from the solar neighborhood to distances of 100 kpc. APOGEE will obtain
high-resolution (R~30,000), high signal-to-noise (S/N>100 per resolution
element), H-band (1.51-1.70 micron) spectra of 10^5 evolved, late-type stars,
measuring separate abundances for ~15 elements per star and creating the first
high-precision spectroscopic survey of all Galactic stellar populations (bulge,
bar, disks, halo) with a uniform set of stellar tracers and spectral
diagnostics. MARVELS will monitor radial velocities of more than 8000 FGK stars
with the sensitivity and cadence (10-40 m/s, ~24 visits per star) needed to
detect giant planets with periods up to two years, providing an unprecedented
data set for understanding the formation and dynamical evolution of giant
planet systems. (Abridged)
01/2011;
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Steven L. Finkelstein,
Seth H. Cohen,
Rogier A. Windhorst,
Russell E. Ryan,
Nimish P. Hathi,
Keely D. Finkelstein,
Jay Anderson,
Norman A. Grogin,
Anton M. Koekemoer,
Sangeeta Malhotra, [......],
Jon A. Holtzman,
Randy A. Kimble,
Gerard Luppino,
Francesco Paresce,
Abhijit Saha,
Joseph I. Silk,
John T. Trauger,
Alistair R. Walker,
Bradley C. Whitmore,
Erick T. Young
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ABSTRACT: We present the highest redshift detections of resolved Lyman alpha emission, using Hubble Space Telescope/ACS F658N narrowband-imaging data taken in parallel with the Wide Field Camera 3 Early Release Science program in the GOODS CDF-S. We detect Lyman alpha emission from three spectroscopically confirmed z = 4.4 Lyman alpha emitting galaxies (LAEs), more than doubling the sample of LAEs with resolved Lyman alpha emission. Comparing the light distribution between the rest-frame ultraviolet continuum and narrowband images, we investigate the escape of Lyman alpha photons at high redshift. While our data do not support a positional offset between the Lyman alpha and rest-frame ultraviolet (UV) continuum emission, the half-light radii in two out of the three galaxies are significantly larger in Lyman alpha than in the rest-frame UV continuum. This result is confirmed when comparing object sizes in a stack of all objects in both bands. Additionally, the narrowband flux detected with HST is significantly less than observed in similar filters from the ground. These results together imply that the Lyman alpha emission is not strictly confined to its indigenous star-forming regions. Rather, the Lyman alpha emission is more extended, with the missing HST flux likely existing in a diffuse outer halo. This suggests that the radiative transfer of Lyman alpha photons in high-redshift LAEs is complicated, with the interstellar-medium geometry and/or outflows playing a significant role in galaxies at these redshifts. Comment: Submitted to the Astrophysical Journal. 11 pages, 10 figures
08/2010;
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Giacomo Beccari,
Loredana Spezzi,
Guido De Marchi,
Francesco Paresce,
Erick Young,
Morten Andersen,
Nino Panagia,
Bruce Balick,
Howard Bond,
Daniela Calzetti, [......],
Jon A. Holtzman,
Randy A. Kimble,
Patrick J. McCarthy, Robert W. O'Connell,
Abhijit Saha,
Joseph I. Silk,
John T. Trauger,
Alistair R. Walker,
Bradley C. Whitmore,
Rogier A. Windhorst
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ABSTRACT: Early release science observations of the cluster NGC3603 with the WFC3 on the refurbished HST allow us to study its recent star formation history. Our analysis focuses on stars with Halpha excess emission, a robust indicator of their pre-main sequence (PMS) accreting status. The comparison with theoretical PMS isochrones shows that 2/3 of the objects with Halpha excess emission have ages from 1 to 10 Myr, with a median value of 3 Myr, while a surprising 1/3 of them are older than 10 Myr. The study of the spatial distribution of these PMS stars allows us to confirm their cluster membership and to statistically separate them from field stars. This result establishes unambiguously for the first time that star formation in and around the cluster has been ongoing for at least 10-20 Myr, at an apparently increasing rate. Comment: 10 pages, 8 figures, accepted for publication in The Astrophysical Journal
The Astrophysical Journal 07/2010; · 6.02 Impact Factor
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Rogier A. Windhorst,
Seth H. Cohen,
Nimish P. Hathi,
Patrick J. McCarthy,
Ryan, Jr., Russell E,
Haojing Yan,
Ivan K. Baldry,
Simon P. Driver,
Jay A. Frogel,
David T. Hill, [......],
Randy A. Kimble,
John W. MacKenty,
Max Mutchler,
Francesco Paresce,
Abihit Saha,
Joseph I. Silk,
John Trauger,
Alistair R. Walker,
Bradley C. Whitmore,
Erick Young
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ABSTRACT: We describe the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) Early
Release Science (ERS) observations in the Great Observatories Origins Deep
Survey (GOODS) South field. The new WFC3 ERS data provide calibrated, drizzled
mosaics in the UV filters F225W, F275W, and F336W, as well as in the near-IR
filters F098M (Ys), F125W (J), and F160W (H) with 1-2 HST orbits per filter.
Together with the existing HST Advanced Camera for Surveys (ACS) GOODS-South
mosaics in the BViz filters, these panchromatic 10-band ERS data cover 40-50
square arcmin at 0.2-1.7 {\mu}m in wavelength at 0.07-0.15" FWHM resolution and
0.090" Multidrizzled pixels to depths of AB\simeq 26.0-27.0 mag (5-{\sigma})
for point sources, and AB\simeq 25.5-26.5 mag for compact galaxies.
In this paper, we describe: a) the scientific rationale, and the data taking
plus reduction procedures of the panchromatic 10-band ERS mosaics; b) the
procedure of generating object catalogs across the 10 different ERS filters,
and the specific star-galaxy separation techniques used; and c) the reliability
and completeness of the object catalogs from the WFC3 ERS mosaics. The
excellent 0.07-0.15" FWHM resolution of HST/WFC3 and ACS makes star- galaxy
separation straightforward over a factor of 10 in wavelength to AB\simeq 25-26
mag from the UV to the near-IR, respectively.
05/2010;
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ABSTRACT: We present the results of a Hubble Space Telescope (HST) study of dwarf galaxies in the outer regions of the nearby rich Perseus Cluster, down to M_V = -12, and compare these with the dwarf population in the cluster core from our previous HST imaging. In this paper we examine how properties such as the colour magnitude relation, structure and morphology are affected by environment for the lowest mass galaxies. Dwarf galaxies are excellent tracers of the effects of environment due to their low masses, allowing us to derive their environmentally based evolution, which is more subtle in more massive galaxies. We identify 11 dwarf elliptical (dE) and dwarf spheroidal (dSph) galaxies in the outer regions of Perseus, all of which are previously unstudied. We measure the (V-I)_0 colours of our newly discovered dEs, and find that these dwarfs lie on the same red sequence as those in the cluster core. The morphologies of these dwarfs are examined by quantifying their light distributions using CAS parameters, and we find that dEs in the cluster outskirts are on average more disturbed than those in the core, with =0.13\pm0.09 and =0.18\pm0.08, compared to =0.02\pm0.04, =0.01\pm0.07 for those in the core. Based on these results, we infer that these objects are ``transition dwarfs'', likely in the process of transforming from late-type to early type galaxies as they infall into the cluster, with their colours transforming before their structures. When we compare the number counts for both the core and outer regions of the cluster, we find that below M_V = -12, the counts in the outer regions of the cluster exceed those in the core. This is evidence that in the very dense region of the cluster, dwarfs are unable to survive unless they are sufficiently massive to prevent their disruption by the cluster potential and interactions with other galaxies. Comment: 14 pages, 11 figures. MNRAS accepted
01/2010;
