Engineering topics

Kurtz, Michael J.

Publications and source records attributed to Kurtz, Michael J..

17 records

DOE OSTI2021

Center for Astrophysics Optical Infrared Science Archive. I. FAST Spectrograph

We announce the public release of 141,531 moderate-dispersion optical spectra of 72,247 objects acquired over the past 25 yr with the FAST Spectrograph on the Fred L. Whipple Observatory 1.5 m Tillinghast telescope. We describe the data acquisition and processing so that scientists can understand the spectra. We highlight some of the largest FAst Spectrograph for the Tillinghast Telescope (FAST) survey programs, and make recommendations for use. The spectra have been placed in a Virtual Observatory–accessible archive and ready for download.

47 OTHER INSTRUMENTATION↗

DOE OSTI2016

SHELS: Complete Redshift surveys of two widely separated fields

The Smithsonian Hectospec Lensing Survey (SHELS) is a complete redshift survey covering two well-separated fields (F1 and F2) of the Deep Lens Survey (DLS). Both fields are more than 94% complete to a Galactic extinction corrected R {sub 0} = 20.2. Here, we describe the redshift survey of the F1 field centered at R.A.{sub 2000} = 00{sup h}53{sup m}25.ˢ3 and decl.{sub 2000} = 12°33′55″; like F2, the F1 field covers ∼4 deg{sup 2}. The redshift survey of the F1 field includes 9426 new galaxy redshifts measured with Hectospec on the MMT (published here). As a guide to future uses of the combined survey, we compare the mass metallicity relation and the distributions of D {sub n}4000 as a function of stellar mass and redshift for the two fields. The mass–metallicity relations differ by an insignificant 1.6σ. For galaxies in the stellar mass range 10{sup 10}–10{sup 11} M {sub ⊙}, the increase in the star-forming fraction with redshift is remarkably similar in the two fields. The seemingly surprising 31%–38% difference in the overall galaxy counts in F1 and F2 is probably consistent with the expected cosmic variance given the subtleties of the relative systematics in the two surveys. We also review the DLS cluster detections in the two fields: poorer photometric data for F1 precluded secure detection of the single massive cluster at z = 0.35 that we find in SHELS. Taken together, the two fields include 16,055 redshifts for galaxies with R{sub 0}⩽20.2 and 20,754 redshifts for galaxies with R ≤ 20.6. These dense surveys in two well-separated fields provide a basis for future investigations of galaxy properties and large-scale structure.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

SHELS: A complete galaxy redshift survey with R ≤ 20.6

The SHELS (Smithsonian Hectospec Lensing Survey) is a complete redshift survey covering two well-separated fields (F1 and F2) of the Deep Lens Survey to a limiting R = 20.6. Here we describe the redshift survey of the F2 field (R.A.{sub 2000} = 09{sup h}19{sup m}32.4 and decl.{sub 2000} = +30°00'00''). The survey includes 16,294 new redshifts measured with the Hectospec on the MMT. The resulting survey of the 4 deg{sup 2} F2 field is 95% complete to R = 20.6, currently the densest survey to this magnitude limit. The median survey redshift is z = 0.3; the survey provides a view of structure in the range 0.1 ≲ z ≲ 0.6. An animation displays the large-scale structure in the survey region. We provide a redshift, spectral index D {sub n}4000, and stellar mass for each galaxy in the survey. We also provide a metallicity for each galaxy in the range 0.2 <z < 0.38. To demonstrate potential applications of the survey, we examine the behavior of the index D {sub n}4000 as a function of galaxy luminosity, stellar mass, and redshift. The known evolutionary and stellar mass dependent properties of the galaxy population are cleanly evident in the data. We also show that the mass-metallicity relation previously determined from these data is robust to the analysis approach.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Comparison of galaxy clusters selected by weak-lensing, optical spectroscopy, and X-rays in the deep lens survey F2 field

We compare galaxy clusters selected in Chandra and XMM-Newton X-ray observations of the 4 deg{sup 2} Deep Lens Survey (DLS) F2 field to the cluster samples previously selected in the same field from a sensitive weak-lensing shear map derived from the DLS and from a detailed galaxy redshift survey—the Smithsonian Hectospec Lensing Survey (SHELS). Our Chandra and XMM-Newton observations cover 1.6 deg{sup 2} of the DLS F2 field, including all 12 weak-lensing peaks above a signal-to-noise ratio of 3.5, along with 16 of the 20 SHELS clusters with published velocity dispersions >500 km s{sup –1}. We detect 26 extended X-ray sources in this area and confirm 23 of them as galaxy clusters using the optical imaging. Approximately 75% of clusters detected in either X-ray or spectroscopic surveys are found in both; these follow the previously established scaling relations between velocity dispersion, L {sub X}, and T {sub X}. A lower percentage, 60%, of clusters are in common between X-ray and DLS samples. With the exception of a high false-positive rate in the DLS weak-lensing search (5 out of 12 DLS candidates appear to be false), differences between the three cluster detection methods can be attributed primarily to observational uncertainties and intrinsic scatter between different observables and cluster mass.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2014

Reducing systematic error in weak lensing cluster surveys

Weak lensing provides an important route toward collecting samples of clusters of galaxies selected by mass. Subtle systematic errors in image reduction can compromise the power of this technique. We use the B-mode signal to quantify this systematic error and to test methods for reducing this error. We show that two procedures are efficient in suppressing systematic error in the B-mode: (1) refinement of the mosaic CCD warping procedure to conform to absolute celestial coordinates and (2) truncation of the smoothing procedure on a scale of 10'. Application of these procedures reduces the systematic error to 20% of its original amplitude. We provide an analytic expression for the distribution of the highest peaks in noise maps that can be used to estimate the fraction of false peaks in the weak-lensing κ-signal-to-noise ratio (S/N) maps as a function of the detection threshold. Based on this analysis, we select a threshold S/N = 4.56 for identifying an uncontaminated set of weak-lensing peaks in two test fields covering a total area of ∼3 deg{sup 2}. Taken together these fields contain seven peaks above the threshold. Among these, six are probable systems of galaxies and one is a superposition. We confirm the reliability of these peaks with dense redshift surveys, X-ray, and imaging observations. The systematic error reduction procedures we apply are general and can be applied to future large-area weak-lensing surveys. Our high-peak analysis suggests that with an S/N threshold of 4.5, there should be only 2.7 spurious weak-lensing peaks even in an area of 1000 deg{sup 2}, where we expect ∼2000 peaks based on our Subaru fields.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS2005

New Features in the ADS Abstract Service

The NASA-ADS Abstract Service provides a sophisticated search capability for the literature in Astronomy, Planetary Sciences, Physics/Geophysics, and Space Instrumentation. The ADS is funded by NASA and access to the ADS services is free to anybody world-wide without restrictions. It allows the user to search the literature by author, title, and abstract text.

Eichhorn, Guenther↗

NASA NTRS1995

Automated spectral classification and the GAIA project

Two dimensional spectral types for each of the stars observed in the global astrometric interferometer for astrophysics (GAIA) mission would provide additional information for the galactic structure and stellar evolution studies, as well as helping in the identification of unusual objects and populations. The classification of the large quantity generated spectra requires that automated techniques are implemented. Approaches for the automatic classification are reviewed, and a metric-distance method is discussed. In tests, the metric-distance method produced spectral types with mean errors comparable to those of human classifiers working at similar resolution. Data and equipment requirements for an automated classification survey, are discussed. A program of auxiliary observations is proposed to yield spectral types and radial velocities for the GAIA-observed stars.

Lasala, Jerry↗

NASA NTRS1995

The widest practicable dissemination: The NASA technical report server

The National Aeronautics and Space Act of 1958 established NASA and charged it to 'provide for the widest practicable and appropriate dissemination of information concerning...its activities and the results thereof.' The search for innovative methods to distribute NASA's information lead a grass-roots team to create the NASA Technical Report Server (NTRS), which uses the World Wide Web and other popular Internet-based information systems as search engines. The NTRS is an inter-center effort which provides uniform access to various distributed publication servers residing on the Internet. Users have immediate desktop access to technical publications from NASA centers and institutes. The NTRS is comprised of several units, some constructed especially for inclusion in NTRS, and others that are existing NASA publication services that NTRS reuses. This paper presents the NTRS architecture, usage metrics, and the lessons learned while implementing and maintaining the services over the initial six-month period. The NTRS is largely constructed with freely available software running on existing hardware. NTRS builds upon existing hardware and software, and the resulting additional exposure for the body of literature contained will allow NASA to ensure that its institutional knowledge base will continue to receive the widest practicable and appropriate dissemination.

Nelson, Michael L.↗

NASA NTRS1995

The Widest Practicable Dissemination: The NASA Technical Report Server

The National Aeronautics and Space Act of 1958 established NASA and charged it to "provide for the widest practicable and appropriate dissemination of information concerning [...] its activities and the results thereof." The search for innovative methods to distribute NASA s information lead a grass-roots team to create the NASA Technical Report Server (NTRS), which uses the World Wide Web and other popular Internet-based information systems as search engines. The NTRS is an inter-center effort which provides uniform access to various distributed publication servers residing on the Internet. Users have immediate desktop access to technical publications from NASA centers and institutes. The NTRS is comprised of several units, some constructed especially for inclusion in NTRS, and others that are existing NASA publication services that NTRS reuses. This paper presents the NTRS architecture, usage metrics, and the lessons learned while implementing and maintaining the services over the initial 6-month period. The NTRS is largely constructed with freely available software running on existing hardware. NTRS builds upon existing hardware and software, and the resulting additional exposure for the body of literature contained will allow NASA to ensure that its institutional knowledge base will continue to receive the widest practicable and appropriate dissemination.

Nelson, Michael L.↗

NASA NTRS1995

The NASA Technical Report Server

The National Aeronautics and Space Act of 1958 established NASA and charged it to "provide for the widest practicable and appropriate dissemination of information concerning its activities and the results thereof." The search for innovative methods to distribute NASA's information lead a grass-roots team to create the NASA Technical Report Server (NTRS), which uses the World Wide Web and other popular Internet-based information systems as search engines. The NTRS is an inter-center effort which provides uniform access to various distributed publication servers residing on the Internet. Users have immediate desktop access to technical publications from NASA centers and institutes. The NTRS is comprised of several units, some constructed especially for inclusion in NTRS, and others that are existing NASA publication services that NTRS reuses. This paper presents the NTRS architecture, usage metrics, and the lessons learned while implementing and maintaining the service. The NTRS is largely constructed with freely available software running on existing hardware. NTRS builds upon existing hardware and software, and the resulting additional exposure for the body of literature contained ensures that NASA's institutional knowledge base will continue to receive the widest practicable and appropriate dissemination.

Nelson, Michael L.↗

NASA NTRS1992

The velocity-distance relation for galaxies on a bubble

The characteristic diameter of the most prominent void in the redshift survey of de Lapparent et al. (1986) is measured. Distances and peculiar velocities to individual galaxies are derived, and it is shown that the void is approximately a 'Hubble Bubble' in which the near and far edges are separating with the general expansion of the universe. At the 3 sigma level, infall toward the Coma cluster is detected for a portion of the bubble wall. Limits on the net outflow from the void and infall into Coma are used to estimate Omega.

Bothun, Gregory D.↗

NASA NTRS1992

Visualizing the universe, part 2

It is now possible to create animated views of the universe that are realistic, physically relevant, and breathtaking. To demonstrate the point, we describe our efforts to navigate the CfA redshift survey. For our project, we selected several CCD images of spiral and elliptical galaxies, and placed them at their observed positions in redshift space. We demonstrate how, by choreographing aesthetically pleasing trajectories, we are able to develop our own and the viewer's intuition about the large-scale structures found in the CfA redshift survey. We show for instance that three-dimensional motion enhances significantly our perception of voids and sheets in the distribution of galaxies. Such sophistication happily has become possible with the 'coming of age' of observational cosmology, as data have grown to drive the field.

Falco, Emilio E.↗

NASA NTRS1990

Redshifts for fainter galaxies in the first CfA survey slice. II

Redshifts were measured for 96 galaxies in right ascension alpha between 8h and 17h declination delta between 30 and 31 deg, and with m(Zwicky) in the range 15.6-15.7. These correspond to 94 of the 96 entries in the Zwicky-Nilson merged catalog. The declination range delta between 29 deg and 31 deg is now complete to m(Zwicky) = 15.7. The structures in the first 6-deg-wide slice of the Center for Astrophysics redshift survey slice (delta between 26.5 and 32.5 deg are clearly defined in the 2-deg-wide slightly deeper sample; the fainter galaxies trace the structures defined by the brighter ones.

Wegner, Gary↗

NASA NTRS1989

A combined optical/X-ray study of the Galaxy cluster Abell 2256

The dynamics of Abell 2256 is investigated by combining X-ray observations of the intracluster gas with optical observations of the galaxy distribution and kinematics. Magnitudes and positions are presented for 172 galaxies and new redshifts for 75. Abell 2256 is similar to the Coma Cluster in its X-ray luminosity, mass, and galaxy density. Both the X-ray surface brightness and the galaxy surface density distributions exhibit an elliptical morphology. The radial galaxy distribution is steeper than the density profile of the X-ray-emitting gas, yet the galaxy velocity dispersion is higher than the equivalent value for the gas. Under the simplest assumptions that the galaxy velocity distribution is isotropic and the gas is isothermal, the galaxies and gas cannot be in hydrostatic equilibrium in a common gravitational potential. Models consistent with available data have mass-to-light ratios which increase with radius and galaxy orbits that are anisotropic with a radial bias.

Fabricant, Daniel G.↗

NASA NTRS1989

Classification and knowledge

Automated procedures to classify objects are discussed. The classification problem is reviewed, and the relation of epistemology and classification is considered. The classification of stellar spectra and of resolved images of galaxies is addressed.

Kurtz, Michael J.↗

NASA NTRS1988

The kinematics and dynamics of the rich cluster of galaxies Abell 539

A sample of 289 redshifts within 10 deg of the center of the cluster A539 have been obtained in order to investigate the cluster kinematics and dynamics. Within 1 Mpc of the center, the physical parameters of A539 are found to be typical of those of rich clusters. It is shown that early-type galaxies are more concentrated toward the cluster center and that the velocity distributions of early-type and late-type galaxies differ marginally.

Ostriker, Eve C.↗

NASA NTRS1988

The search for structure - Object classification in large data sets

Research concerning object classifications schemes are reviewed, focusing on large data sets. Classification techniques are discussed, including syntactic, decision theoretic methods, fuzzy techniques, and stochastic and fuzzy grammars. Consideration is given to the automation of MK classification (Morgan and Keenan, 1973) and other problems associated with the classification of spectra. In addition, the classification of galaxies is examined, including the problems of systematic errors, blended objects, galaxy types, and galaxy clusters.

Kurtz, Michael J.↗