4,931 research outputs found
SFI++ II: A New I-band Tully-Fisher Catalog, Derivation of Peculiar Velocities and Dataset Properties
We present the SFI++ dataset, a homogeneously derived catalog of photometric
and rotational properties and the Tully-Fisher distances and peculiar
velocities derived from them. We make use of digital optical images, optical
long-slit spectra, and global HI line profiles to extract parameters of
relevance to disk scaling relations, incorporating several previously published
datasets as well as a new photometric sample of some 2000 objects. According to
the completeness of available redshift samples over the sky area, we exploit
both a modified percolation algorithm and the Voronoi-Delaunay method to assign
individual galaxies to groups as well as clusters, thereby reducing scatter
introduced by local orbital motions. We also provide corrections to the
peculiar velocities for both homogeneous and inhomogeneous Malmquist bias,
making use of the 2MASS Redshift Survey density field to approximate large
scale structure. We summarize the sample selection criteria, corrections made
to raw observational parameters, the grouping techniques, and our procedure for
deriving peculiar velocities. The final SFI++ peculiar velocity catalog of 4861
field and cluster galaxies is large enough to permit the study not just of the
global statistics of large scale flows but also of the {\it details} of the
local velocity field.Comment: 14 pages, 6 figures, 4 external online tables, accepted for
publication in ApJ
SpecPro: An Interactive IDL Program for Viewing and Analyzing Astronomical Spectra
We present an interactive IDL program for viewing and analyzing astronomical
spectra in the context of modern imaging surveys. SpecPro's interactive design
lets the user simultaneously view spectroscopic, photometric, and imaging data,
allowing for rapid object classification and redshift determination. The
spectroscopic redshift can be determined with automated cross-correlation
against a variety of spectral templates or by overlaying common emission and
absorption features on the 1-D and 2-D spectra. Stamp images as well as the
spectral energy distribution (SED) of a source can be displayed with the
interface, with the positions of prominent photometric features indicated on
the SED plot. Results can be saved to file from within the interface. In this
paper we discuss key program features and provide an overview of the required
data formats.Comment: Accepted for publication in the Publications of the Astronomical
Society of the Pacific (PASP) journal. Website: specpro.caltech.ed
SFI++ I: A New I-band Tully-Fisher Template, the Cluster Peculiar Velocity Dispersion and H0
The SFI++ consists of ~5000 spiral galaxies which have measurements suitable
for the application of the I-band Tully-Fisher (TF) relation. This sample
builds on the SCI and SFI samples published in the 1990s but includes
significant amounts of new data as well as improved methods for parameter
determination. We derive a new I-band TF relation from a subset of this sample
which consists of 807 galaxies in the fields of 31 nearby clusters and groups.
This sample constitutes the largest ever available for the calibration of the
TF template and extends the range of line-widths over which the template is
reliably measured. Careful accounting is made of observational and sample
biases such as incompleteness, finite cluster size, galaxy morphology and
environment. We find evidence for a type-dependent TF slope which is shallower
for early type than for late type spirals. The line-of-sight cluster peculiar
velocity dispersion is measured for the sample of 31 clusters. This value is
directly related to the spectrum of initial density fluctuations and thus
provides an independent verification of the best fit WMAP cosmology and an
estimate of Omega^0.6 sigma_8 = 0.52+/-0.06. We also provide an independent
measure of the TF zeropoint using 17 galaxies in the SFI++ sample for which
Cepheid distances are available. In combination with the ``basket of clusters''
template relation these calibrator galaxies provide a measure of H0 = 74+/-2
(random) +/-6 (systematic) km/s/Mpc.Comment: Accepted by ApJ (scheduled for 20 Dec 2006, issue 653). 21 pages (2
column emulateapj) including 12 figures. Version 2 corrects typos and other
small errors noticed in proof
Dissecting Photometric Redshift for Active Galactic Nucleus Using XMM- and Chandra-COSMOS Samples
In this paper, we release accurate photometric redshifts for 1692 counterparts to Chandra sources in the central square degree of the Cosmic Evolution Survey (COSMOS) field. The availability of a large training set of spectroscopic redshifts that extends to faint magnitudes enabled photometric redshifts comparable to the highest quality results presently available for normal galaxies. We demonstrate that morphologically extended, faint X-ray sources without optical variability are more accurately described by a library of normal galaxies (corrected for emission lines) than by active galactic nucleus (AGN) dominated templates, even if these sources have AGN-like X-ray luminosities. Preselecting the library on the bases of the source properties allowed us to reach an accuracy σ_(Δz/(1+z(spec))~0.015 with a fraction of outliers of 5.8% for the entire Chandra-COSMOS sample. In addition, we release revised photometric redshifts for the 1735 optical counterparts of the XMM-detected sources over the entire 2 deg^2 of COSMOS. For 248 sources, our updated photometric redshift differs from the previous release by Δz > 0.2. These changes are predominantly due to the inclusion of newly available deep H-band photometry (H_(AB) = 24 mag). We illustrate once again the importance of a spectroscopic training sample and how an assumption about the nature of a source together, with the number and the depth of the available bands, influences the accuracy of the photometric redshifts determined for AGN. These considerations should be kept in mind when defining the observational strategies of upcoming large surveys targeting AGNs, such as eROSITA at X-ray energies and the Australian Square Kilometre Array Pathfinder Evolutionary Map of the Universe in the radio band
Simultaneous calculation of the helical pitch and the twist elastic constant in chiral liquid crystals from intermolecular torques
We present a molecular simulation method that yields simultaneously the equilibrium pitch wave number q and the twist elastic constant K2 of a chiral nematic liquid crystal by sampling the torque density. A simulation of an untwisted system in periodic boundary conditions gives the product K2q; a further simulation with a uniform twist applied provides enough information to separately determine the two factors. We test our new method for a model potential, comparing the results with K2q from a thermodynamic integration route, and with K2 from an order fluctuation analysis. We also present a thermodynamic perturbation theory analysis valid in the limit of weak chirality
2MTF I. The Tully-Fisher Relation in the 2MASS J, H and K Bands
The 2 Micron All-Sky Survey (2MASS) Tully-Fisher Survey (2MTF) aims to
measure Tully-Fisher (TF) distances to all bright inclined spirals in the 2MASS
Redshift Survey (2MRS). Essential to this project is a universal calibration of
the TF relation in the 2MASS J (1.2 um), H (1.6 um) and K (2.2 um) bands. We
present the first bias corrected or universal TF template in these bands. We
find that the slope of the TF relation becomes steeper as the wavelength
increases being close to L \propto v^4 in K-band and L \propto v^3.6 in J and
H-bands. We also investigate the dependence on galaxy morphology showing that
in all three bands the relation is steeper for later type spirals which also
have a dimmer TF zeropoint than earlier type spirals. We correct the final
relation to that for Sc galaxies. Finally we study the scatter from the TF
relation fitting for a width dependent intrinsic scatter which is not found to
vary significantly with wavelength.Comment: 13 pages, 5 figures. AJ, accepted (scheduled for June 2008). v2 is as
accepted by AJ and includes only minor textual changes from v1. v3 includes a
3 page erratum published as Masters et al. 2014. A coding error was
discovered and corrected, resulting in small changes in the slope and offsets
offsets of the TF relation. All qualitative results still hold. We apologise
for the inconvenienc
The effect of surgical approach on the histology of the femoral head following resurfacing of the hip : analysis of retrieval specimens
Objectives: We aimed to determine the effect of surgical approach on the histology of the femoral head following resurfacing of the hip.
Methods: We performed a histological assessment of the bone under the femoral component taken from retrieval specimens of patients having revision surgery following resurfacing of the hip. We compared the number of empty lacunae in specimens from patients who had originally had a posterior surgical approach with the number in patients having alternative surgical approaches.
Results: We found a statistically significant increase in the percentage of empty lacunae in retrieval specimens from patients who had the posterior approach compared with other surgical approaches (p < 0.001).
Conclusions: This indicates that the vascular compromise that occurs during the posterior surgical approach does have long-term effects on the bone of the femoral head, even if it does not cause overt avascular necrosis
Groups of Galaxies in the Two Micron All-Sky Redshift Survey
We present the results of applying a percolation algorithm to the initial
release of the Two Micron All-Sky Survey Extended Source Catalog, using
subsequently measured redshifts for almost all of the galaxies with K < 11.25
mag. This group catalog is based on the first near-IR all-sky flux-limited
survey that is complete to |b| = 5 deg. We explore the dependence of the
clustering on the length and velocity scales involved. The paper describes a
group catalog, complete to a limiting redshift of 10,000 km/s, created by
maximizing the number of groups containing 3 or more members. A second catalog
is also presented, created by requiring a minimum density contrast of 80 to
identify groups. We identify known nearby clusters in the catalogs and contrast
the groups identified in the two catalogs. We examine and compare the
properties of the determined groups and verify that the results are consistent
with the UZC-SSRS2 and northern CfA redshift survey group catalogs. The all-sky
nature of the catalog will allow the development of a flow-field model based on
the density field inferred from the estimated cluster masses.Comment: Accepted for publication in ApJ (29 pages including 13 figures). A
version with high-resolution figures is available at
http://www.cfa.harvard.edu/~acrook/preprints
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