3,847 research outputs found
Probing the Birth of Super Star Clusters: Implications for Massive Star Formation
Super Star Clusters are one of the most extreme star forming environments in
the universe, and the most massive and dense of these may be proto globular
clusters. Like individual massive stars, the earliest stages of super star
cluster evolution are deeply obscured, and therefore our knowledge about their
birth environments is currently very incomplete. However, the study of natal
super star clusters has become somewhat of a cottage industry in recent years,
and the sample of such objects has been growing rapidly with high-quality
long-wavelength data now available from a number of observatories. The natal
super star clusters identified in thermal-infrared and radio observations
represent the youngest stage of massive star cluster evolution yet observed.
Their properties appear to be similar to those of ultracompact HII regions in
the Milky Way, but scaled up in total mass and luminosity. I will overview what
we think we know about these objects based on existing observations, discuss
their relationship to ultracompact HII regions, present new models of their
spectral energy distributions based on 3-D simulations, and outline some of the
most significant gaps in our current understanding.Comment: 10 pages, 6 figures, to appear in the proceedings of IAU Symp 227,
Massive Star Birth: A Crossroads of Astrophysics, (Cesaroni R., Churchwell
E., Felli M., Walmsley C. editors
Radio continuum observations of local star-forming galaxies using the Caltech Continuum Backend on the Green Bank Telescope
We observed radio continuum emission in 27 local (D < 70 Mpc) star-forming
galaxies with the Robert C. Byrd Green Bank Telescope between 26 GHz and 40 GHz
using the Caltech Continuum Backend. We obtained detections for 22 of these
galaxies at all four sub-bands and four more marginal detections by taking the
average flux across the entire bandwidth. This is the first detection (full or
marginal) at these frequencies for 22 of these galaxies. We fit spectral energy
distributions (SEDs) for all of the four-sub-band detections. For 14 of the
galaxies, SEDs were best fit by a combination of thermal free-free and
nonthermal synchrotron components. Eight galaxies with four-sub-band detections
had steep spectra that were only fit by a single nonthermal component. Using
these fits, we calculated supernova rates, total number of equivalent O stars,
and star formation rates within each ~23 arcsecond beam. For unresolved
galaxies, these physical properties characterize the galaxies' recent star
formation on a global scale. We confirm that the radio-far-infrared correlation
holds for the unresolved galaxies' total 33 GHz flux regardless of their
thermal fractions, though the scatter on this correlation is larger than that
at 1.4 GHz. In addition, we found that for the unresolved galaxies, there is an
inverse relationship between the ratio of 33 GHz flux to total far-infrared
flux and the steepness of the galaxy's spectral index between 1.4 GHz and 33
GHz. This relationship could be an indicator of the timescale of the observed
episode of star formation.Comment: 36 pages, 9 figures; accepted for publication in ApJ. First and
second author affiliation updated to reflect departmental name chang
Genomic and Transcriptomic Alterations Associated with STAT3 Activation in Head and Neck Cancer.
BackgroundHyperactivation of STAT3 via constitutive phosphorylation of tyrosine 705 (Y705) is common in most human cancers, including head and neck squamous carcinoma (HNSCC). STAT3 is rarely mutated in cancer and the (epi)genetic alterations that lead to STAT3 activation are incompletely understood. Here we used an unbiased approach to identify genomic and epigenomic changes associated with pSTAT3(Y705) expression using data generated by The Cancer Genome Atlas (TCGA).Methods and findingsMutation, mRNA expression, promoter methylation, and copy number alteration data were extracted from TCGA and examined in the context of pSTAT3(Y705) protein expression. mRNA expression levels of 1279 genes were found to be associated with pSTAT3(705) expression. Association of pSTAT3(Y705) expression with caspase-8 mRNA expression was validated by immunoblot analysis in HNSCC cells. Mutation, promoter hypermethylation, and copy number alteration of any gene were not significantly associated with increased pSTAT3(Y705) protein expression.ConclusionsThese cumulative results suggest that unbiased approaches may be useful in identifying the molecular underpinnings of oncogenic signaling, including STAT3 activation, in HNSCC. Larger datasets will likely be necessary to elucidate signaling consequences of infrequent alterations
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