269 research outputs found
Unveiling Palomar 2: The Most Obscure Globular Cluster in the Outer Halo
We present the first color-magnitude study for Palomar 2, a distant and
heavily obscured globular cluster near the Galactic anticenter. Our (V,V-I)
color-magnitude diagram (CMD), obtained with the UH8K camera at the CFHT,
reaches V(lim) = 24 and clearly shows the principal sequences of the cluster,
though with substantial overall foreground absorption and differential
reddening. The CMD morphology shows a well populated red horizontal branch with
a sparser extension to the blue, similar to clusters such as NGC 1261, 1851, or
6229 with metallicities near [Fe/H] = -1.3, placing it about 34 kpc
from the Galactic center. We use starcounts of the bright stars to measure the
core radius, half-mass radius, and central concentration of the cluster. Its
integrated luminosity is M_V = -7.9, making it clearly brighter and more
massive than most other clusters in the outer halo.Comment: 25 pages, aastex, with 8 postscript figures; accepted for publication
in AJ, September 1997. Also available by e-mail from
[email protected]. Please consult Harris directly for (big)
postscript files of Figures 1a,b (the images of the cluster
The Physical Conditions and Dynamics of the Interstellar Medium in the Nucleus of M83: Observations of CO and CI
This paper presents CI, CO J=4-3, and CO J=3-2 maps of the barred spiral
galaxy M83 taken at the James Clerk Maxwell Telescope. Observations indicate a
double peaked structure which is consistent with gas inflow along the bar
collecting at the inner Lindblad resonance. This structure suggests that
nuclear starbursts can occur even in galaxies where this inflow/collection
occurs, in contrast to previous studies of barred spiral galaxies. However, the
observations also suggest that the double peaked emission may be the result of
a rotating molecular ring oriented nearly perpendicular to the main disk of the
galaxy. The CO J=4-3 data indicate the presence of warm gas in the nucleus that
is not apparent in the lower-J CO observations, which suggests that CO J=1-0
emission may not be a reliable tracer of molecular gas in starburst galaxies.
The twelve CI/CO J=4-3 line ratios in the inner 24'' x 24'' are uniform at the
2 sigma level, which indicates that the CO J=4-3 emission is originating in the
same hot photon-dominated regions as the CI emission. The CO J=4-3/J=3-2 line
ratios vary significantly within the nucleus with the higher line ratios
occurring away from peaks of emission along an arc of active star forming
regions. These high line ratios (>1) likely indicate optically thin gas created
by the high temperatures caused by star forming regions in the nucleus of this
starburst galaxy.Comment: 15 pages with 10 figures. To appear in the August 10 1998 issue of
The Astrophysical Journa
Identity Foreclosure, Athletic Identity, and College Sport Participation
A study was conducted with 502 college students (246 non-athletes, 90 intramural athletes, and 166 intercollegiate athletes) to investigate the relationship between self-identity variables (i.e., identity foreclosure and athletic identity) and college sport participation. The researchers used two scales, the foreclosure subscale of the Objective Measure of Ego Identity Status (OM-EIS, Adams et al., 1979) and the Athletic Identity Measurement Scale (AIMS, Brewer et al., 1993). Results indicated that identity foreclosure and athletic identity increase with level of sport participation. Identity foreclosure was significantly lower for upperclass students than for underclass students among non-athletes, but not among intramural and intercollegiate student-athletes. No gender differences were found. These findings suggested that intercollegiate student-athletes may commit to the role of "athlete" without exploring alternative identities. Implications of the results for the academic and career development of student-athletes were discussed. "The results of this study imply that college student-athletes may identify strongly with the athlete role to the extent that they fail to explore alternative identities." - p.
Luminous Infrared Galaxies with the Submillimeter Array: I. Survey Overview and the Central Gas to Dust Ratio
We present new data obtained with the Submillimeter Array for a sample of
fourteen nearby luminous and ultraluminous infrared galaxies. The galaxies were
selected to have luminosity distances D < 200 Mpc and far-infrared luminosities
log(L_FIR) > 11.4. The galaxies were observed with spatial resolutions of order
1 kpc in the CO J=3-2, CO J=2-1, 13CO J=2-1, and HCO+ J=4-3 lines as well as
the continuum at 880 microns and 1.3 mm. We have combined our CO and continuum
data to measure an average gas-to-dust mass ratio of 120 +/- 28 (rms deviation
109) in the central regions of these galaxies, very similar to the value of 150
determined for the Milky Way. This similarity is interesting given the more
intense heating from the starburst and possibly accretion activity in the
luminous infrared galaxies compared to the Milky Way. We find that the peak H_2
surface density correlates with the far-infrared luminosity, which suggests
that galaxies with higher gas surface densities inside the central kiloparsec
have a higher star formation rate. The lack of a significant correlation
between total H_2 mass and far-infrared luminosity in our sample suggests that
the increased star formation rate is due to the increased availability of
molecular gas as fuel for star formation in the central regions. In contrast to
previous analyses by other authors, we do not find a significant correlation
between central gas surface density and the star formation efficiency, as trace
by the ratio of far-infrared luminosity to nuclear gas mass. Our data show that
it is the star formation rate, not the star formation efficiency, that
increases with increasing central gas surface density in these galaxies.Comment: 66 pages, 39 figures, aastex preprint format; to be published in ApJ
Supplements. Version of paper with full resolution figures available at
http://www.physics.mcmaster.ca/~wilson/www_xfer/ULIRGS_publi
SMA Imaging of CO(3-2) Line and 860 micron Continuum of Arp 220 : Tracing the Spatial Distribution of Luminosity
We used the Submillimeter Array (SMA) to image 860 micron continuum and
CO(3-2) line emission in the ultraluminous merging galaxy Arp 220, achieving a
resolution of 0.23" (80 pc) for the continuum and 0.33" (120 pc) for the line.
The CO emission peaks around the two merger nuclei with a velocity signature of
gas rotation around each nucleus, and is also detected in a kpc-size disk
encompassing the binary nucleus. The dust continuum, in contrast, is mostly
from the two nuclei. The beam-averaged brightness temperature of both line and
continuum emission exceeds 50 K at and around the nuclei, revealing the
presence of warm molecular gas and dust. The dust emission morphologically
agrees with the distribution of radio supernova features in the east nucleus,
as expected when a starburst heats the nucleus. In the brighter west nucleus,
however, the submillimeter dust emission is more compact than the supernova
distribution. The 860 micron core, after deconvolution, has a size of 50-80 pc,
consistent with recent 1.3 mm observations, and a peak brightness temperature
of (0.9-1.6)x10^2 K. Its bolometric luminosity is at least 2x10^{11} Lsun and
could be ~10^{12} Lsun depending on source structure and 860 micron opacity,
which we estimate to be of the order of tau_{860} ~ 1 (i.e., N_{H_2} ~ 10^{25}
cm^{-2}). The starbursting west nuclear disk must have in its center a dust
enshrouded AGN or a very young starburst equivalent to hundreds of super star
clusters. Further spatial mapping of bolometric luminosity through
submillimeter imaging is a promising way to identify the heavily obscured
heating sources in Arp 220 and other luminous infrared galaxies.Comment: ApJ. in press. 26 pages, 10 figure
PSP toxin levels and plankton community composition and abundance in size-fractionated vertical profiles during spring/summer blooms of the toxic dinoflagellate Alexandrium fundyense in the Gulf of Maine and on Georges Bank, 2007, 2008, and 2010 : 1. Toxin levels
This paper is not subject to U.S. copyright. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 103 (2014): 329–349, doi:10.1016/j.dsr2.2013.04.013.As part of the NOAA ECOHAB funded Gulf of Maine Toxicity (GOMTOX)1 project, we determined Alexandrium fundyense abundance, paralytic shellfish poisoning (PSP) toxin composition, and concentration in quantitatively-sampled size-fractionated (20–64, 64–100, 100–200, 200–500, and >500 μm) particulate water samples, and the community composition of potential grazers of A. fundyense in these size fractions, at multiple depths (typically 1, 10, 20 m, and near-bottom) during 10 large-scale sampling cruises during the A. fundyense bloom season (May–August) in the coastal Gulf of Maine and on Georges Bank in 2007, 2008, and 2010. Our findings were as follows: (1) when all sampling stations and all depths were summed by year, the majority (94%±4%) of total PSP toxicity was contained in the 20–64 μm size fraction; (2) when further analyzed by depth, the 20–64 μm size fraction was the primary source of toxin for 97% of the stations and depths samples over three years; (3) overall PSP toxin profiles were fairly consistent during the three seasons of sampling with gonyautoxins (1, 2, 3, and 4) dominating (90.7%±5.5%), followed by the carbamate toxins saxitoxin (STX) and neosaxitoxin (NEO) (7.7%±4.5%), followed by n-sulfocarbamoyl toxins (C1 and 2, GTX5) (1.3%±0.6%), followed by all decarbamoyl toxins (dcSTX, dcNEO, dcGTX2&3) (<1%), although differences were noted between PSP toxin compositions for nearshore coastal Gulf of Maine sampling stations compared to offshore Georges Bank sampling stations for 2 out of 3 years; (4) surface cell counts of A. fundyense were a fairly reliable predictor of the presence of toxins throughout the water column; and (5) nearshore surface cell counts of A. fundyense in the coastal Gulf of Maine were not a reliable predictor of A. fundyense populations offshore on Georges Bank for 2 out of the 3 years sampled.Vangie Shue was supported through the FDA and also through the Thomas Jefferson High School for Science and Technology Mentorship Program. Research support was provided by National Oceanic and Atmospheric Administration Grant NA06NOS4780245 for the Gulf of Maine Toxicity (GOMTOX) program. BAK, DJM, and DMA were partially supported by the Woods Hole Center for Oceans and Human Health through National Science Foundation Grants OCE-0430724 and OCE-0911031 and National Institute of Environmental Health Sciences Grant 1P50-ES01274201
Panchromatic Observations of SN 2011dh Point to a Compact Progenitor Star
We report the discovery and detailed monitoring of X-ray emission associated
with the Type IIb SN 2011dh using data from the Swift and Chandra satellites,
placing it among the best studied X-ray supernovae to date. We further present
millimeter and radio data obtained with the SMA, CARMA, and EVLA during the
first three weeks after explosion. Combining these observations with early
optical photometry, we show that the panchromatic dataset is well-described by
non-thermal synchrotron emission (radio/mm) with inverse Compton scattering
(X-ray) of a thermal population of optical photons. In this scenario, the shock
partition fractions deviate from equipartition by a factor, (e_e/e_B) ~ 30. We
derive the properties of the shockwave and the circumstellar environment and
find a shock velocity, v~0.1c, and a progenitor mass loss rate of ~6e-5
M_sun/yr. These properties are consistent with the sub-class of Type IIb SNe
characterized by compact progenitors (Type cIIb) and dissimilar from those with
extended progenitors (Type eIIb). Furthermore, we consider the early optical
emission in the context of a cooling envelope model to estimate a progenitor
radius of ~1e+11 cm, in line with the expectations for a Type cIIb SN.
Together, these diagnostics are difficult to reconcile with the extended radius
of the putative yellow supergiant progenitor star identified in archival HST
observations, unless the stellar density profile is unusual. Finally, we
searched for the high energy shock breakout pulse using X-ray and gamma-ray
observations obtained during the purported explosion date range. Based on the
compact radius of the progenitor, we estimate that the breakout pulse was
detectable with current instruments but likely missed due to their limited
temporal/spatial coverage. [Abridged]Comment: (27 pages, 5 figures, 2 tables, final version to appear in ApJ
High-Resolution Submillimeter Imaging of the Ly-alpha Blob1 in SSA 22
We present ~2" resolution submillimeter observations of the submillimeter
luminous giant Ly-alpha blob (LAB1) in the SSA 22 protocluster at redshift
z=3.1 with the Submillimeter Array (SMA). Although the expected submillimeter
flux density is 16 mJy at 880 micron, no emission is detected with the 2".4 x
1".9 (18 x 14 kpc) beam at the 3 sigma level of 4.2 mJy beam^{-1} in the SMA
field of view of 35". This is in contrast to the previous lower angular
resolution (15") observations where a bright (17 mJy) unresolved submillimeter
source was detected at 850 micron toward the LAB1 using the Submillimeter
Common-User Bolometer Array on the James Clerk Maxwell Telescope. The SMA
non-detection suggests that the spatial extent of the submillimeter emission of
LAB1 should be larger than 4" (>30 kpc). The most likely interpretation of the
spatially extended submillimeter emission is that starbursts occur throughout
the large area in LAB1. Some part of the submillimeter emission may come from
spatially extended dust expelled from starburst regions by galactic superwind.
The spatial extent of the submillimeter emission of LAB1 is similar to those of
high redshift radio galaxies rather than submillimeter galaxies.Comment: 7 pages, 5 figures, accepted for publication in Ap
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