73 research outputs found
Determination of Galaxy Spin Vectors in the Pisces-Perseus Supercluster with the Arecibo Telescope
We use HI observations made with the upgraded Arecibo 305M Telescope in
August 1998 to obtain accurate spin vector determinations for 54 nearly edge-on
galaxies in the Minnesota Automated Plate Scanner Pisces-Perseus Survey
(MAPS-PP). We introduce a simple observational technique of determining the
sense of rotation for galaxies, even when their HI disks are not fully
resolved. We examined the spin vector distribution of these 54 galaxies for
evidence of preferential galaxy alignments. We use the Kuiper statistic, a
variant of the Kolmogorov--Smirnov statistic, to determine the significance of
any anisotropies in the distribution of galaxy spin vectors. The possibility of
``spin vector domains'' is also investigated. We find no significant evidence
of preferential galaxy alignments in this sample. However, we show tha t the
small sample size places weak limits on the level of galaxy alignments.Comment: 22 pages, 7 figures, Accepted for Publication in Astronomical Journa
Mapping the Asymmetric Thick Disk: The Hercules Thick Disk Cloud
The stellar asymmetry of faint thick disk/inner halo stars in the first
quadrant first reported by Larsen & Humphreys (1996) and investigated further
by Parker et al. (2003, 2004) has been recently confirmed by SDSS (Juric et al.
2008). Their interpretation of the excess in the star counts as a ringlike
structure, however, is not supported by critical complimentary data in the
fourth quadrant not covered by SDSS. We present stellar density maps from the
Minnesota Automated Plate Scanner (MAPS) Catalog of the POSS I showing that the
overdensity does not extend into the fourth quadrant. The overdensity is most
probably not a ring. It could be due to interaction with the disk bar, evidence
for a triaxial thick disk, or a merger remnant/stream. We call this feature the
Hercules Thick Disk Cloud.Comment: 11 pages, 5 figures, to be published in Astrophysical Journal Letter
How Long Do Endoprosthetic Reconstructions for Proximal Femoral Tumors Last?
As the life expectancy of patients with musculoskeletal tumors improves, long-term studies of endoprosthetic reconstructions are necessary to establish realistic expectations for the implants and compare them to other reconstruction approaches.
(1) What is the long-term survival of cemented bipolar proximal femoral replacements? (2) How does prosthesis survival compare to patient survival among patients with Stage I, II, and III disease? (3) Do modular implants outperform custom-built prostheses? (4) Do some proximal femoral replacements require conversion to THA?
We retrospectively reviewed all 86 proximal femoral replacements used for tumor reconstruction from 1982 to 2008. Primary diagnoses were 43 high-grade tumors (IIA/IIB), 20 low-grade tumors (IA/IB or benign), and 23 with metastatic disease. We reviewed prosthesis survival, patient survival, complication rates, functional outcomes, and rates of conversion to THA.
Five of 86 patients (5.8%) required revision of the femoral component. Five-, 10-and 20-year implant survivorships were 93%, 84%, and 56%, respectively. All patients with low-grade disease survived; the 5-year survival rate for patients with metastatic disease was 16%; the 5-, 10-, and 20-year survival for IIA/IIB patients was 54%, 50%, and 44%, respectively. Five of 86 patients (5.8%) underwent conversion to THA for groin pain.
Cemented bipolar proximal femoral replacements after tumor resection proved a durable reconstruction technique. The implants outlived patients with metastatic disease and high-grade localized disease while patients with low-grade disease outlived their implants. The survival of modular prostheses was comparable to that of older, one-piece custom designs.
Level IV, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence
Mapping the Asymmetric Thick Disk I. A Search for Triaxiality
A significant asymmetry in the distribution of faint blue stars in the inner
Galaxy, Quadrant 1 (l = 20 to 45 degrees) compared to Quadrant 4 was first
reported by Larsen & Humphreys (1996). Parker et al (2003, 2004) greatly
expanded the survey to determine its spatial extent and shape and the
kinematics of the affected stars. This excess in the star counts was
subsequently confirmed by Juric et al. (2008) using SDSS data. Possible
explanations for the asymmetry include a merger remnant, a triaxial Thick Disk,
and a possible interaction with the bar in the Disk. In this paper we describe
our program of wide field photometry to map the asymmetry to fainter magnitudes
and therefore larger distances. To search for the signature of triaxiality, we
extended our survey to higher Galactic longitudes. We find no evidence for an
excess of faint blue stars at l > 55 degrees including the faintest magnitude
interval. The asymmetry and star count excess in Quadrant 1 is thus not due to
a triaxial Thick Disk.Comment: 36 pages, 8 figures. Accepted by Astronomical Journa
Mapping the Asymmetric Thick Disk: II Distance, Size and Mass of the Hercules Thick Disk Cloud
The Hercules Thick Disk Cloud (Larsen et al. 2008) was initially discovered
as an excess in the number of faint blue stars between quadrants 1 and 4 of the
Galaxy. The origin of the Cloud could be an interaction with the disk bar, a
triaxial thick disk or a merger remnant or stream. To better map the spatial
extent of the Cloud along the line of sight, we have obtained multi-color UBVR
photometry for 1.2 million stars in 63 fields approximately 1 square degree
each. Our analysis of the fields beyond the apparent boundaries of the excess
have already ruled out a triaxial thick disk as a likely explanation (Larsen,
Humphreys and Cabanela 2010) In this paper we present our results for the star
counts over all of our fields, determine the spatial extent of the over density
across and along the line of sight, and estimate the size and mass of the
Cloud. Using photometric parallaxes, the stars responsible for the excess are
between 1 and 6 kiloparsecs from the Sun, 0.5 -- 4 kpc above the Galactic
plane, and extends approximately 3-4 kiloparsecs across our line of sight. It
is thus a major substructure in the Galaxy. The distribution of the excess
along our sight lines corresponds with the density contours of the bar in the
Disk, and its most distant stars are directly over the bar. We also see through
the Cloud to its far side. Over the entire 500 square degrees of sky containing
the Cloud, we estimate more than 5.6 million stars and 1.9 million solar masses
of material. If the over density is associated with the bar, it would exceed
1.4 billion stars and more than than 50 million solar masses. Finally, we argue
that the Hercules-Aquila Cloud (Belokurov et al. 2007) is actually the Hercules
Thick Disk Cloud.Comment: 52 pages, 13 figure
Galaxies on the Blue Edge
We have successfully constructed a catalog of HI-rich galaxies selected from
the Minnesota Automated Plate Scanner Catalog of the Palomar Observatory Sky
Survey (POSS I) based solely on optical criteria. We identify HI-rich
candidates by selecting the bluest galaxies at a given apparent magnitude,
those galaxies on the "blue edge" of POSS I color-magnitude parameter space.
Subsequent 21-cm observations on the upgraded Arecibo 305m dish detected over
50% of the observed candidates. The detected galaxies are HI-rich with HI
masses comparable to "normal" high surface brightness disk galaxies and they
have gas mass-to-light ratios ranging from 0.1 to 4.8 (in solar units).
Comparison of our candidate galaxies with known low surface brightness galaxies
(hereafter LSBs) shows that they exhibit similar optical and HI properties to
that population. We also show that previously identified LSBs, including
several LSBs with red B-V colors, preferentially occupy the "blue edge" of POSS
I color-magnitude parameter space. Their presence on the "blue edge" appears to
be a selection effect due to differing plate limits in the two POSS I
bandpasses. This suggests the POSS I is a good filter for separating galaxies
on the higher surface brightness end of the LSB population from the general
population of galaxies in the night sky.Comment: 56 pages, 19 figures, to be published in the Astronomical Journal
(July 1, 2002
The FIRST Bright Quasar Survey. II. 60 Nights and 1200 Spectra Later
We have used the VLA FIRST survey and the APM catalog of the POSS-I plates as
the basis for constructing a new radio-selected sample of optically bright
quasars. This is the first radio-selected sample that is competitive in size
with current optically selected quasar surveys. Using only two basic criteria,
radio-optical positional coincidence and optical morphology, quasars and BL
Lacs can be identified with 60% selection efficiency; the efficiency increases
to 70% for objects fainter than magnitude 17. We show that a more sophisticated
selection scheme can predict with better than 85% reliability which candidates
will turn out to be quasars.
This paper presents the second installment of the FIRST Bright Quasar Survey
with a catalog of 636 quasars distributed over 2682 square degrees. The quasar
sample is characterized and all spectra are displayed. The FBQS detects both
radio-loud and radio-quiet quasars out to a redshift z>3. We find a large
population of objects of intermediate radio-loudness; there is no evidence in
our sample for a bimodal distribution of radio characteristics. The sample
includes ~29 broad absorption line quasars, both high and low ionization, and a
number of new objects with remarkable optical spectra.Comment: 41 pages plus 39 gifs which contain all quasar spectra. Accepted for
publication in the Astrophysical Journal Supplement Serie
Optically bright Active Galactic Nuclei in the ROSAT-Faint Source Catalogue
To build a large, optically bright, X-ray selected AGN sample we have
correlated the ROSAT-FSC catalogue of X-ray sources with the USNO catalogue
limited to objects brighter than O=16.5 and then with the APS database. Each of
the 3,212 coincidences was classified using the slitless Hamburg spectra. 493
objects were found to be extended and 2,719 starlike. Using both the extended
objects and the galaxies known from published catalogues we built up a sample
of 185 galaxies with O_APS < 17.0 mag, which are high-probability counterparts
of RASS-FSC X-ray sources. 130 galaxies have a redshift from the literature and
for another 34 we obtained new spectra. The fraction of Seyfert galaxies in
this sample is 20 %. To select a corresponding sample of 144 high-probability
counterparts among the starlike sources we searched for very blue objects in an
APS-based color-magnitude diagram. Forty-one were already known AGN and for
another 91 objects we obtained new spectra, yielding 42 new AGN, increasing
their number in the sample to 83. This confirms that surveys of bright QSOs are
still significantly incomplete. On the other hand we find that, at a flux limit
of 0.02 count /-1 and at this magnitude, only 40 % of all QSOs are detected by
ROSAT.Comment: 17 pages, 16 figures, accepted by A&
Radio-optical scrutiny of compact AGN: Correlations between properties of pc-scale jets and optical nuclear emission
We study the correlations between the Very Long Baseline Array radio emission
at 15 GHz, extended emission at 151 MHz, and optical nuclear emission at 5100
AA for a complete sample of 135 compact jets. We use the partial Kendall's tau
correlation analysis to check the link between radio properties of parsec-scale
jets and optical luminosities of host AGN. We find a significant positive
correlation for 99 quasars between optical nuclear luminosities and total radio
(VLBA) luminosities of unresolved cores at 15 GHz originated at milliarcseconds
scales. For 18 BL Lacs, the optical continuum emission correlates with the
radio emission of the jet at 15 GHz. We suggest that the radio and optical
emission are beamed and originate in the innermost part of the
sub--parsec-scale jet in quasars. Analysis of the relation between the apparent
speed of the jet and the optical nuclear luminosity at 5100 AA supports the
relativistic beaming model for the optical emission generated in the jet, and
allows the peak values of the intrinsic optical luminosity of the jet and its
Lorentz factor to be estimated for the populations of quasars, BL Lacs, and
radio galaxies. The radio-loudness of quasars is found to increase at high
redshifts, which can be a result of lower efficiency of the accretion in AGN
having higher radio luminosities. A strong positive correlation is found
between the intrinsic kinetic power of the jet and the apparent luminosities of
the total and the unresolved core emission of the jet at 15 GHz. This
correlation is interpreted in terms of intrinsically more luminous parsec-scale
jet producing more luminous extended structure which is detectable at low radio
frequencies, 151 MHz. A possibility that the low frequency radio emission is
relativistically beamed in superluminal AGN and therefore correlates with radio
luminosity of the jet at 15 GHz can not be ruled out (abridged).Comment: 16 pages, 10 figuers; minor comments are added; accepted to A&
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