2,448 research outputs found
Ares I-X Flight Data Evaluation: Executive Overview
NASA's Constellation Program (CxP) successfully launched the Ares I-X flight test vehicle on October 28, 2009. The Ares I-X flight was a developmental flight test to demonstrate that this very large, long, and slender vehicle could be controlled successfully. The flight offered a unique opportunity for early engineering data to influence the design and development of the Ares I crew launch vehicle. As the primary customer for flight data from the Ares I-X mission, the Ares Projects Office (APO) established a set of 33 flight evaluation tasks to correlate flight results with prospective design assumptions and models. The flight evaluation tasks used Ares I-X data to partially validate tools and methodologies in technical disciplines that will ultimately influence the design and development of Ares I and future launch vehicles. Included within these tasks were direct comparisons of flight data with preflight predictions and post-flight assessments utilizing models and processes being applied to design and develop Ares I. The benefits of early development flight testing were made evident by results from these flight evaluation tasks. This overview provides summary information from assessment of the Ares I-X flight test data and represents a small subset of the detailed technical results. The Ares Projects Office published a 1,600-plus-page detailed technical report that documents the full set of results. This detailed report is subject to the International Traffic in Arms Regulations (ITAR) and is available in the Ares Projects Office archives files
The SAMI galaxy survey: Can we trust aperture corrections to predict star formation?
In the low-redshift Universe (z < 0.3), our view of galaxy evolution is primarily based on fibre optic spectroscopy surveys. Elaborate methods have been developed to address aperture effects when fixed aperture sizes only probe the inner regions for galaxies of ever decreasing redshift or increasing physical size. These aperture corrections rely on assumptions about the physical properties of galaxies. The adequacy of these aperture corrections can be tested with integral-field spectroscopic data. We use integral-field spectra drawn from 1212 galaxies observed as part of the SAMI Galaxy Survey to investigate the validity of two aperture correction methods that attempt to estimate a galaxy's total instantaneous star formation rate. We show that biases arise when assuming that instantaneous star formation is traced by broad-band imaging, and when the aperture correction is built only from spectra of the nuclear region of galaxies. These biases may be significant depending on the selection criteria of a survey sample. Understanding the sensitivities of these aperture corrections is essential for correct handling of systematic errors in galaxy evolution studies
L Dwarfs Found in Sloan Digital Sky Survey Commissioning Data II. Hobby-Eberly Telescope Observations
Low dispersion optical spectra have been obtained with the Hobby-Eberly
Telescope of 22 very red objects found in early imaging data from the Sloan
Digital Sky Survey. The objects are assigned spectral types on the 2MASS system
(Kirkpatrick et al. 1999) and are found to range from late M to late L. The
red- and near-infrared colors from SDSS and 2MASS correlate closely with each
other, and most of the colors are closely related to spectral type in this
range; the exception is the (i^* - z^*) color, which appears to be independent
of spectral type between about M7 and L4. The spectra suggest that this
independence is due to the disappearance of the TiO and VO absorption in the
i-band for later spectral types; to the presence of strong Na I and K I
absorption in the i-band; and to the gradual disappearance of the 8400 Angstrom
absorption of TiO and FeH in the z-band.Comment: 20 pages, 7 figures, accepted by AJ, a version with higher resolution
figures can be found at ftp://ftp.astro.psu.edu/pub/dps/hetld.p
The SAMI Galaxy Survey: : extraplanar gas, galactic winds, and their association with star formation history
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society. ©: 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society, the version of record is available on line at doi: 10.1093/mnras/stw017We investigate a sample of 40 local, main-sequence, edge-on disc galaxies using integral field spectroscopy with the Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey to understand the link between properties of the extraplanar gas and their host galaxies. The kinematics properties of the extraplanar gas, including velocity asymmetries and increased dispersion, are used to differentiate galaxies hosting large-scale galactic winds from those dominated by the extended diffuse ionized gas. We find rather that a spectrum of diffuse gas-dominated to wind dominated galaxies exist. The wind-dominated galaxies span a wide range of star formation rates () across the whole stellar mass range of the sample (). The wind galaxies also span a wide range in SFR surface densities () that is much lower than the canonical threshold of . The wind galaxies on average have higher SFR surface densities and higher values than those without strong wind signatures. The enhanced indicates that bursts of star formation in the recent past are necessary for driving large-scale galactic winds. We demonstrate with Sloan Digital Sky Survey data that galaxies with high SFR surface density have experienced bursts of star formation in the recent past. Our results imply that the galactic winds revealed in our study are indeed driven by bursts of star formation, and thus probing star formation in the time domain is crucial for finding and understanding galactic winds.Peer reviewe
Plasma Dynamics
Contains research objectives and summary of research on twenty-one projects split into three sections, with four sub-sections in the second section and reports on twelve research projects.National Science Foundation (Grant ENG75-06242)U.S. Energy Research and Development Administration (Contract E(11-1)-2766)U.S. Energy Research and Development Agency (Contract E(11-1)-3070)U.S. Energy Research and Development Administration (Contract E(11-1)-3070)Research Laboratory of Electronics, M.I.T. Industrial Fellowshi
Active Galactic Nuclei in the Sloan Digital Sky Survey: II. Emission-Line Luminosity Function
The emission line luminosity function of active galactic nuclei (AGN) is
measured from about 3000 AGN included in the main galaxy sample of the Sloan
Digital Sky Survey within a redshift range of . The \Ha and
[OIII] luminosity functions for Seyferts cover luminosity range
of in H and the shapes are well fit by broken power
laws, without a turnover at fainter nuclear luminosities. Assuming a universal
conversion from emission line strength to continuum luminosity, the inferred B
band magnitude luminosity function is comparable both to the AGN luminosity
function of previous studies and to the low redshift quasar luminosity function
derived from the 2dF redshift survey. The inferred AGN number density is
approximately 1/5 of all galaxies and about of the total
light of galaxies in the -band comes from the nuclear activity. The numbers
of Seyfert 1s and Seyfert 2s are comparable at low luminosity, while at high
luminosity, Seyfert 1s outnumber Seyfert 2s by a factor of 2-4. In making the
luminosity function measurements, we assumed that the nuclear luminosity is
independent of the host galaxy luminosity, an assumption we test {\it a
posteriori}, and show to be consistent with the data. Given the relationship
between black hole mass and host galaxy bulge luminosity, the lack of
correlation between nuclear and host luminosity suggests that the main variable
that determines the AGN luminosity is the Eddington ratio, not the black hole
mass. This appears to be different from luminous quasars, which are most likely
to be shining near the Eddington limit.Comment: AASTeX v5.02 preprint; 35 pages, including 2 table and 12 figures. To
appear in the April 2005 issue of AJ. See astro-ph/0501059 for Paper
The SAMI Galaxy Survey: Cubism and covariance, putting round pegs into square holes
We present a methodology for the regularization and combination of sparse sampled and irregularly gridded observations from fibre-optic multiobject integral field spectroscopy. The approach minimizes interpolation and retains image resolution on combining subpixel dithered data. We discuss the methodology in the context of the Sydney-AAO multiobject integral field spectrograph (SAMI) Galaxy Survey underway at the Anglo-Australian Telescope. The SAMI instrument uses 13 fibre bundles to perform high-multiplex integral field spectroscopy across a 1° diameter field of view. The SAMI Galaxy Survey is targeting ~3000 galaxies drawn from the full range of galaxy environments. We demonstrate the subcritical sampling of the seeing and incomplete fill factor for the integral field bundles results in only a 10 per cent degradation in the final image resolution recovered. We also implement a new methodology for tracking covariance between elements of the resulting data cubes which retains 90 per cent of the covariance information while incurring only a modest increase in the survey data volume
The SAMI Galaxy Survey: revisiting galaxy classification through high-order stellar kinematics
Recent cosmological hydrodynamical simulations suggest that integral field spectroscopy can connect the high-order stellar kinematic moments h3 (~skewness) and h4 (~kurtosis) in galaxies to their cosmological assembly history. Here, we assess these results by measuring the stellar kinematics on a sample of 315 galaxies, without a morphological selection, using two-dimensional integral field data from the SAMI Galaxy Survey. Proxies for the spin parameter () and ellipticity () are used to separate fast and slow rotators; there exists a good correspondence to regular and non-regular rotators, respectively, as also seen in earlier studies. We confirm that regular rotators show a strong h3 versus anti-correlation, whereas quasi-regular and non-regular rotators show a more vertical relation in h3 and . Motivated by recent cosmological simulations, we develop an alternative approach to kinematically classify galaxies from their individual h3 versus signatures. Within the SAMI Galaxy Survey, we identify five classes of high-order stellar kinematic signatures using Gaussian mixture models. Class 1 corresponds to slow rotators, whereas Classes 2–5 correspond to fast rotators. We find that galaxies with similar {\lambda }_{{R}_{{\rm{e}}}}\mbox{--}{\epsilon }_{{\rm{e}}} values can show distinctly different {h}_{3}\mbox{--}V/\sigma signatures. Class 5 objects are previously unidentified fast rotators that show a weak h3 versus anti-correlation. From simulations, these objects are predicted to be disk-less galaxies formed by gas-poor mergers. From morphological examination, however, there is evidence for large stellar disks. Instead, Class 5 objects are more likely disturbed galaxies, have counter-rotating bulges, or bars in edge-on galaxies. Finally, we interpret the strong anti-correlation in h3 versus as evidence for disks in most fast rotators, suggesting a dearth of gas-poor mergers among fast rotators
The SDSS Quasar Survey: Quasar Luminosity Function from Data Release Three
We determine the number counts and z=0-5 luminosity function for a
well-defined, homogeneous sample of quasars from the Sloan Digital Sky Survey
(SDSS). We conservatively define the most uniform statistical sample possible,
consisting of 15,343 quasars within an effective area of 1622 deg^2 that was
derived from a parent sample of 46,420 spectroscopically confirmed broad-line
quasars in the 5282 deg^2 of imaging data from SDSS Data Release Three. The
sample extends from i=15 to i=19.1 at z3. The number
counts and luminosity function agree well with the results of the 2dF QSO
Survey, but the SDSS data probe to much higher redshifts than does the 2dF
sample. The number density of luminous quasars peaks between redshifts 2 and 3,
although uncertainties in the selection function in this range do not allow us
to determine the peak redshift more precisely. Our best fit model has a flatter
bright end slope at high redshift than at low redshift. For z<2.4 the data are
best fit by a redshift-independent slope of beta = -3.1 (Phi(L) propto L^beta).
Above z=2.4 the slope flattens with redshift to beta=-2.37 at z=5. This slope
change, which is significant at a >5-sigma level, must be accounted for in
models of the evolution of accretion onto supermassive black holes.Comment: 57 pages, 21 figures (9 color); minor changes to reflect the version
accepted by AJ; higher resolution version available at
ftp://ftp.astro.princeton.edu/gtr/dr3qlf/Feb1306
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