1,299 research outputs found
HI Imaging of LGS 3 and an Apparently Interacting High-Velocity Cloud
We present a 93' by 93' map of the area near the Local Group dwarf galaxy LGS
3, centered on an HI cloud 30' away from the galaxy. Previous authors
associated this cloud with LGS 3 but relied on observations made with a 36'
beam. Our high-resolution (3.4'), wide-field Arecibo observations of the region
reveal that the HI cloud is distinct from the galaxy and suggest an interaction
between the two. We point out faint emission features in the map that may be
gas that has been tidally removed from the HI cloud by LGS 3. We also derive
the rotation curve of the cloud and find that it is in solid-body rotation out
to a radius of 10', beyond which the rotation velocity begins to decline.
Assuming a spherical geometry for the cloud, the implied mass is 2.8 x 10^7
(d/Mpc) M_{Sun}, where d is the distance in Mpc. The observed HI mass is 5.5 x
10^6 (d/Mpc)^2 M_{Sun}, implying that the cloud is dark-matter dominated unless
its distance is at least 1.9 Mpc. We propose that the cloud is a high-velocity
cloud that is undergoing a tidal interaction with LGS 3 and therefore is
located roughly 700 kpc away from the Milky Way. The cloud then contains a
total mass of ~2.0 x 10^7 M_{Sun}, 82% of which consists of dark matter.Comment: 5 pages, 2 color figures. Accepted for publication in ApJ Letter
OH yields from the CH3CO+O-2 reaction using an internal standard
Laser flash photolysis of CH3C(O)OH at 248 nm was used to create equal zero time yields of CH3CO and OH. The absolute OH yield from the CH3CO + O2 (+M) reaction was determined by following the OH temporal profile using the zero time
OH concentration as an internal standard. The OH yield from CH3CO + O2 (+M) was observed to decrease with increasing pressure with an extrapolated zero pressure yield
close to unity (1.1 ± 0.2, quoted uncertainties correspond to 95% confidence limits). The results are in quantitative agreement with those obtained from 248 nm acetone
photolysis in the presence of O2
Tightly Correlated HI and FUV Emission in the Outskirts of M83
We compare sensitive HI data from The HI Nearby Galaxy Survey (THINGS) and
deep far UV (FUV) data from GALEX in the outer disk of M83. The FUV and HI maps
show a stunning spatial correlation out to almost 4 optical radii (r25),
roughly the extent of our maps. This underscores that HI traces the gas
reservoir for outer disk star formation and it implies that massive (at least
low level) star formation proceeds almost everywhere HI is observed. Whereas
the average FUV intensity decreases steadily with increasing radius before
leveling off at ~1.7 r25, the decline in HI surface density is more subtle. Low
HI columns (<2 M_solar/pc^2) contribute most of the mass in the outer disk,
which is not the case within r25. The time for star formation to consume the
available HI, inferred from the ratio of HI to FUV intensity, rises with
increasing radius before leveling off at ~100 Gyr, i.e., many Hubble times,
near ~1.7 r25. Assuming the relatively short H2 depletion times observed in the
inner parts of galaxies hold in outer disks, the conversion of HI into bound,
molecular clouds seems to limit star formation in outer galaxy disks. The long
consumption times suggest that most of the extended HI observed in M83 will not
be consumed by in situ star formation. However, even these low star formation
rates are enough to expect moderate chemical enrichment in a closed outer disk.Comment: Accepted for Publication in ApJ
Exploring a School-University Model for Professional Development with Classroom Staff: Teaching Trauma-Informed Approaches
Schools serving communities with high rates of poverty face the profound challenge of meeting the needs of students who are often exposed to significant family and environmental stressors and trauma. Classroom staff are vital members of schoolcommunities who often work closely with students with the highest needs, but they are typically not provided with professionaldevelopment opportunities to develop skills for social-emotional learning intervention. This study, conducted in three parts, describes (1) a needs assessment with classroom staff to determine their learning needs, (2) the development and implementation of a series ofprofessional development workshops that incorporated findings from the needs assessment, and (3) post-workshop surveys and focus groups to assess the impact of the workshops and identify ongoing professional development needs. Findings include themes of continuing concern regarding learning, school climate, and the need to address stress and trauma in students\u27 lives. Additionally, findings point to the workplace environment as creating barriers for classroom staff to implement new strategies and make use of the knowledge and skills gained in the workshops. Implications for building or enhancing a trauma-informed school community are discussed
The infant-feeding practices of mothers enrolled in the prevention of mother-to-child transmission of HIV programme at a primary health care clinic in the Mpumalanga province, South Africa
Purpose: To determine whether mothers attending a primary health care (PHC) clinic in the Mpumalanga province, South Africa for post-deliveryprevention of mother-to-child transmission (PMTCT) of the Human Immunodeficiency Virus (HIV) follow-up care were adhering to the recommendationof exclusive infant-feeding practices, and to identify possible areas for improvement of the PMTCT of HIV services at the clinic.Setting: A municipal PHC clinic in White River, a semi-urban town in Mpumalanga, South Africa.Design: A cross-sectional descriptive study using a structured infant-feeding questionnaire.Subjects: All mothers attending the clinic for post-delivery PMTCT of HIV follow-up care during a four-month period from 1 November 2007 to29 February 2008.Results: A total of 33 mothers with infants attended the clinic during the period. All 33 mothers took part in the questionnaire study. Thirtyquestionnaires were subsequently found suitable for analysis. The mothers were predominantly rural, with low levels of education and no formalemployment. Their ages ranged from 22 to 42 years, with a mean of 30.7 years. Fifteen (50%) of the 30 mothers practised exclusive replacementfeeding (ERF), 8 (27%) practised exclusive breast-feeding (EBF), and 7 (23%) practised mixed feeding.Conclusion: More than three-quarters of the mothers practised the recommended exclusive infant-feeding methods for PMTCT of HIV, with ERF asthe most popular choice. However, the infant-feeding practices could not be generalised as the attendance of mothers for post-delivery follow-upcare at the clinic was very poor during the study period. This poor attendance was attributed to frequent non-availability of free formula milk for theprogramme. Better quality counselling is needed to further increase the adherence to exclusive infant-feeding practices, and to improve the uptakeof post-delivery follow-up care
The Distances of SNR W41 and overlapping HII regions
New HI images from the VLA Galactic Plane Survey show prominent absorption
features associated with the supernovae remnant G23.3-0.3 (SNR W41). We
highlight the HI absorption spectra and the CO emission spectra of eight
small regions on the face of W41, including four HII regions, three non-thermal
emission regions and one unclassified region. The maximum velocity of
absorption for W41 is 782 km/s and the CO cloud at radial velocity
955 km/s is behind W41. Because an extended TeV source, a diffuse X-ray
enhancement and a large molecular cloud at radial velocity 775 km/s are
also projected at the center of W41, these yield the kinematic distance of 3.9
to 4.5 kpc for W41. For HII regions, our analyses reveal that both G23.42-0.21
and G23.07+0.25 are at the far kinematic distances (9.9 kpc and
10.6 kpc respectively) of their recombination-line velocities (1030.5 km/s
and 89.62.1 km/s respectively), G23.07-0.37 is at the near kinematic
distance (4.40.3 kpc) of its recombination-line velocity (82.72.0
km/s), and G23.27-0.27 is probably at the near kinematic distance (4.10.3
kpc) of its recombination-line velocity (76.10.6 km/s).Comment: 11 pages, 3 figs., 2 tables, accepted by A
A Magellanic Origin for the Warp of the Galaxy
We show that a Magellanic Cloud origin for the warp of the Milky Way can
explain most quantitative features of the outer HI layer recently identified by
Levine, Blitz & Heiles (2005). We construct a model similar to that of Weinberg
(1998) that produces distortions in the dark matter halo, and we calculate the
combined effect of these dark-halo distortions and the direct tidal forcing by
the Magellanic Clouds on the disk warp in the linear regime. The interaction of
the dark matter halo with the disk and resonances between the orbit of the
Clouds and the disk account for the large amplitudes observed for the vertical
m=0,1,2 harmonics. The observations lead to six constraints on warp forcing
mechanisms and our model reasonably approximates all six. The disk is shown to
be very dynamic, constantly changing its shape as the Clouds proceed along
their orbit. We discuss the challenges to MOND placed by the observations.Comment: 4 pages, 3 figures, submitted to ApJ Letters. Additional graphics, 3d
visualizations and movies available at
http://www.astro.umass.edu/~weinberg/lm
Is There a Fundamental Line for Disk Galaxies?
We show that there are strong local correlations between metallicity, surface
brightness, and dynamical mass-to-light ratio within M33, analogous to the
fundamental line of dwarf galaxies identified by Prada & Burkert (2002). Using
near-infrared imaging from 2MASS, the published rotation curve of M33, and
literature measurements of the metallicities of HII regions and supergiant
stars, we demonstrate that these correlations hold for points at radial
distances between 140 pc and 6.2 kpc from the center of the galaxy. At a given
metallicity or surface brightness, M33 has a mass-to-light ratio approximately
four times as large as the Local Group dwarf galaxies; other than this constant
offset, we see broad agreement between the M33 and dwarf galaxy data. We use
analytical arguments to show that at least two of the three fundamental line
correlations are basic properties of disk galaxies that can be derived from
very general assumptions. We investigate the effect of supernova feedback on
the fundamental line with numerical models and conclude that while feedback
clearly controls the scatter in the fundamental line, it is not needed to
create the fundamental line itself, in agreement with our analytical
calculations. We also compare the M33 data with measurements of a simulated
disk galaxy, finding that the simulation reproduces the trends in the data
correctly and matches the fundamental line, although the metallicity of the
simulated galaxy is too high, and the surface brightness is lower than that of
M33.Comment: 14 pages, 14 figures (5 in color). Accepted for publication in Ap
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