SBS0335-052 is a well studied Blue Compact Dwarf galaxy with one of the lowest metallicities of any known galaxy. It also contains 6 previously identified Super Star Clusters. We combine archival HST ...NICMOS images in the Pa alpha line and the 1.6 micron continuum of the eastern component, SBS0335-052E, with other space and ground based data to perform a multi-wavelength analysis of the super star clusters. We concentrate on the southern most clusters, designated S1 and S2, which appear to be the youngest clusters and are the strongest emitters of Pa alpha, radio, and x-ray flux. Our analysis leads to a possible model for S1 and perhaps S2 as a cluster of very young, massive stars with strong stellar winds. The wind density can be high enough to absorb the majority of ionizing photons within less than 1000 AU of the stars, creating very compact HII regions that emit optically thick radiation at radio wavelengths. These winds would then effectively quench the photoionizing flux very close to the stars. This can delay the onset of negative feedback by photoionization and photodissociation on star formation in the clusters. This is significant since SBS0335-052E resembles the conditions that were probably common for high redshift star formation in galaxies near the epoch of reionization.
The Advanced Technology Large-Aperture Space Telescope (ATLAST) is a set of mission concepts for the next generation of UVOIR space observatory with a primary aperture diameter in the 8-m to 16-m ...range that will allow us to perform some of the most challenging observations to answer some of our most compelling questions, including "Is there life elsewhere in the Galaxy?" We have identified two different telescope architectures, but with similar optical designs, that span the range in viable technologies. The architectures are a telescope with a monolithic primary mirror and two variations of a telescope with a large segmented primary mirror. This approach provides us with several pathways to realizing the mission, which will be narrowed to one as our technology development progresses. The concepts invoke heritage from HST and JWST design, but also take significant departures from these designs to minimize complexity, mass, or both. Our report provides details on the mission concepts, shows the extraordinary scientific progress they would enable, and describes the most important technology development items. These are the mirrors, the detectors, and the high-contrast imaging technologies, whether internal to the observatory, or using an external occulter. Experience with JWST has shown that determined competitors, motivated by the development contracts and flight opportunities of the new observatory, are capable of achieving huge advances in technical and operational performance while keeping construction costs on the same scale as prior great observatories.
In this article we investigate the morphology and stellar populations of
high-redshift galaxies through multi-waveband HST imaging and ground-based
spatially-resolved spectroscopy. We study the ...redshift evolution of galaxy
morphology in the Hubble Deep Field, using the deep IDT-NICMOS near-infrared
HST imaging coupled with spectroscopic and photometric redshifts. Using the
multi-waveband data to compare the appearance of galaxies at the same
rest-frame wavelengths reveals that "morphological k-corrections" (the change
in appearance when viewing high-z objects at shorter rest-frame wavelengths)
are only important in a minority of cases, and that galaxies were intrinsically
more peculiar at high redshift. One example of significant morphological
k-corrections is spiral galaxies, which often show more pronounced barred
structure in the near-infrared than in the optical. Therefore, the apparent
decline in the fraction of barred spirals at faint magnitudes in the optical
HDF may be due to band-shifting effects at the higher redshifts, rather than
intrinsic evolution. Using such features as the age-sensitive Balmer+4000Ang
break, the spatially- resolved colours of distant galaxies in
optical/near-infrared imaging can also be used to study their component stellar
populations. We supplement this with deep Keck/LRIS spectroscopy of two
extended sources: a chain galaxy at z=2.8 (HDF4-555.1, the "Hot Dog" - the
brightest U-drop Lyman-break galaxy in the HDF) and a pair of z=4.04
gravitationally lensed arcs behind the cluster Abell 2390. The absence of
measurable rotation across the z=2.8 chain galaxy implies that it is unikely to
be a disk viewed edge on. With the resolution enhancement from lensing, we
detect stellar populations of different ages in the z=4 arcs.
We measured infrared surface brightness fluctuation (SBF) distances to an
isotropically-distributed sample of 16 distant galaxies with redshifts reaching
10,000 km/s using the near-IR camera and ...multi-object spectrometer (NICMOS) on
the Hubble Space Telescope (HST). The excellent spatial resolution, very low
background, and brightness of the IR fluctuations yielded the most distant SBF
measurements to date. Twelve nearby galaxies were also observed and used to
calibrate the F160W (1.6 micron) SBF distance scale. Of these, three have
Cepheid variable star distances measured with HST and eleven have optical
I-band SBF distance measurements. A distance modulus of 18.5 mag to the Large
Magellanic Cloud was adopted for this calibration. We present the F160W SBF
Hubble diagram and find a Hubble constant Ho=76 +/- 1.3 (1-sigma statistical)
+/- 6 (systematic) km/s/Mpc. This result is insensitive to the velocity model
used to correct for local bulk motions. Restricting the fit to the six most
distant galaxies yields the smallest value of Ho=72 +/- 2.3 km/s/Mpc consistent
with the data. This 6% decrease in the Hubble constant is consistent with the
hypothesis that the Local Group inhabits an under-dense region of the universe,
but is also consistent with the best-fit value of Ho=76 km/s/Mpc at the
1.5-sigma level.
In this article we investigate the morphology and stellar populations of high-redshift galaxies through multi-waveband HST imaging and ground-based spatially-resolved spectroscopy. We study the ...redshift evolution of galaxy morphology in the Hubble Deep Field, using the deep IDT-NICMOS near-infrared HST imaging coupled with spectroscopic and photometric redshifts. Using the multi-waveband data to compare the appearance of galaxies at the same rest-frame wavelengths reveals that "morphological k-corrections" (the change in appearance when viewing high-z objects at shorter rest-frame wavelengths) are only important in a minority of cases, and that galaxies were intrinsically more peculiar at high redshift. One example of significant morphological k-corrections is spiral galaxies, which often show more pronounced barred structure in the near-infrared than in the optical. Therefore, the apparent decline in the fraction of barred spirals at faint magnitudes in the optical HDF may be due to band-shifting effects at the higher redshifts, rather than intrinsic evolution. Using such features as the age-sensitive Balmer+4000Ang break, the spatially- resolved colours of distant galaxies in optical/near-infrared imaging can also be used to study their component stellar populations. We supplement this with deep Keck/LRIS spectroscopy of two extended sources: a chain galaxy at z=2.8 (HDF4-555.1, the "Hot Dog" - the brightest U-drop Lyman-break galaxy in the HDF) and a pair of z=4.04 gravitationally lensed arcs behind the cluster Abell 2390. The absence of measurable rotation across the z=2.8 chain galaxy implies that it is unikely to be a disk viewed edge on. With the resolution enhancement from lensing, we detect stellar populations of different ages in the z=4 arcs.
"Weathering the Storm: Sverre Petterssen, the D-Day Forecast, and the Rise of Modern Meteorology" by Sverre Petterssen and edited by James Rodger Fleming is reviewed.
We measured infrared surface brightness fluctuation (SBF) distances to an isotropically-distributed sample of 16 distant galaxies with redshifts reaching 10,000 km/s using the near-IR camera and ...multi-object spectrometer (NICMOS) on the Hubble Space Telescope (HST). The excellent spatial resolution, very low background, and brightness of the IR fluctuations yielded the most distant SBF measurements to date. Twelve nearby galaxies were also observed and used to calibrate the F160W (1.6 micron) SBF distance scale. Of these, three have Cepheid variable star distances measured with HST and eleven have optical I-band SBF distance measurements. A distance modulus of 18.5 mag to the Large Magellanic Cloud was adopted for this calibration. We present the F160W SBF Hubble diagram and find a Hubble constant Ho=76 +/- 1.3 (1-sigma statistical) +/- 6 (systematic) km/s/Mpc. This result is insensitive to the velocity model used to correct for local bulk motions. Restricting the fit to the six most distant galaxies yields the smallest value of Ho=72 +/- 2.3 km/s/Mpc consistent with the data. This 6% decrease in the Hubble constant is consistent with the hypothesis that the Local Group inhabits an under-dense region of the universe, but is also consistent with the best-fit value of Ho=76 km/s/Mpc at the 1.5-sigma level.
From 1964 to 1973, 50 patients who initially underwent ileostomy for inflammatory bowel disease at the Lahey Clinic required 84 revisions. The commonest reason for revision was stenosis. Fistula, ...prolapse, and retraction followed in order of frequency. Patients with Crohn's disease seemed to have a higher incidence of revision, but this was not statistically significant. Other reasons for revision were analyzed, and recommendations for treatment were discussed. Retrospective study revealed that 50% of ileostomy revisions were performed for probably preventable complications.
