1,727 research outputs found
Companions of Qsos at Redshift 1.1
We discuss broad- and narrow-band imaging of 7 arcmin fields of 14 QSOs with
redshift ~1.1. The narrow-band filters were chosen to detect redshifted [O II]
3727A, and the broad bands are R and I, which correspond to rest wavelengths
{}~3300A and ~3800A. In 100 arcsec subfields surrounding the QSOs, we detect an
excess of typically 15 detected objects over the background of 25. Several of
the QSO subfields also contain an excess of blue (R-I < 1.0) galaxies compared
with the other subfields. Finally, several of the QSO subfields contain an
excess of galaxies with significant narrow-band flux compared with the other
subfields, and many of these are also blue. Most of the QSOs are radio-quiet in
a region of sky overpopulated with z=1.1 QSOs, and 3 others are radio-loud from
other parts of the sky. We suggest that most of these z=1.1 QSOs are in compact
groups of starbursting galaxies. In our data, there is no significant
difference between radio-loud and radio-quiet QSOs. We discuss cosmic
evolutionary implications.Comment: 9 pages Plain Tex, 8 figures upon request, SISSA-DAO-94-00
The Stellar Content Near the Galactic Center
High angular resolution J, H, K, and L' images are used to investigate the
stellar content within 6 arcsec of SgrA*. The data, which are complete to K ~
16, are the deepest multicolor observations of the region published to date.Comment: 34 pages, including 12 figure
Algorithms for the workflow satisfiability problem engineered for counting constraints
The workflow satisfiability problem (WSP) asks whether there exists an
assignment of authorized users to the steps in a workflow specification that
satisfies the constraints in the specification. The problem is NP-hard in
general, but several subclasses of the problem are known to be fixed-parameter
tractable (FPT) when parameterized by the number of steps in the specification.
In this paper, we consider the WSP with user-independent counting constraints,
a large class of constraints for which the WSP is known to be FPT. We describe
an efficient implementation of an FPT algorithm for solving this subclass of
the WSP and an experimental evaluation of this algorithm. The algorithm
iteratively generates all equivalence classes of possible partial solutions
until, whenever possible, it finds a complete solution to the problem. We also
provide a reduction from a WSP instance to a pseudo-Boolean SAT instance. We
apply this reduction to the instances used in our experiments and solve the
resulting PB SAT problems using SAT4J, a PB SAT solver. We compare the
performance of our algorithm with that of SAT4J and discuss which of the two
approaches would be more effective in practice
The Gravitational Lens CFRS03.1077
An exquisite gravitational arc with a radius of 2.1" has been discovered
around the z = 0.938 field elliptical galaxy CFRS03.1077 during HST
observations of Canada-France Redshift Survey (CFRS) fields. Spectroscopic
observations of the arc show that the redshift of the resolved lensed galaxy is
z = 2.941. This gravitational lens-source system is well-fitted using the
position angle and ellipticity derived from the visible matter distribution and
an isothermal mass profile with a mass corresponding to sigma =387+-5 km/s.
Surprisingly, given the evidence for passive evolution of elliptical galaxies,
this is in good agreement with an estimate based on the fundamental plane for z
= 0 ellipticals. This, perhaps, indicates that this galaxy has not shared in
the significant evolution observed for average elliptical galaxies at z ~ 1. A
second elliptical galaxy with similar luminosity from the CFRS survey, CFRS
14.1311 at z=0.807, is also a lens but in this case the lens model gives a much
smaller mass-to-light ratio, i.e., it appears to confirm the expected
evolution. This suggests that this pair of field elliptical galaxies may have
very different evolutionary histories, a significant result if confirmed.
Clearly, CFRS03.1077 demonstrates that these "Einstein rings" are powerful
probes of high redshift galaxies.Comment: 11 pages, 5 figures, accepted by Ap.
THE CANADA-FRANCE REDSHIFT SURVEY IX: HST Imaging of High-Redshift Field Galaxies
HST B and I images are presented of 32 CFRS galaxies with secure redshifts in
the range 0.5 < z < 1.2. These galaxies exhibit the same range of morphological
types as seen locally, i.e., ellipticals, spirals and irregulars. The galaxies
look far less regular in the images (rest-frame ultraviolet) than at longer
wavelengths, underlining the fact that optical images of galaxies at still
higher redshift should be interpreted with caution. Quantitative analyses of
the galaxies yield disk sizes, bulge fractions, and colors for each component.
At these redshifts, galaxy disks show clear evidence for surface brightness
evolution. The mean rest-frame central surface brightness of the disks of
normal late-type galaxies is mu_{AB}(B)=20.2 \pm 0.25 mag arcsec^{-2}, about
1.2 mag brighter than the Freeman (1970) value. Some degree of peculiarity is
measurable in 10 (30%) of the galaxies and 4 (13%) show clear signs of
interaction/mergers. There are 9 galaxies (30%) dominated by blue compact
components. These components, which appear to be related to star formation,
occur most often in peculiar/asymmetric galaxies (some of which appear to be
interacting), but a few are in otherwise normal galaxies. Thus, of the galaxies
bluer than present-day Sb, one-third are "blue nucleated galaxies", and half
are late-type galaxies with disks which are significantly brighter than normal
galaxies at z=0. Taken together, these two effects must be responsible for much
of the observed evolution of the luminosity function of blue galaxies.Comment: uuencoded compressed postscript, 8 pages, 1 table + 5 figures in a
separate part. Also available at http://www.astro.utoronto.ca/~lilly/CFRS/ .
Accepted for publication in ApJ Letter
QSO hosts and environments at z=0.9 to 4.2: JHK images with adaptive optics
We have observed nine QSOs with redshifts 0.85 to 4.16 at near-IR wavelengths
with the adaptive optics bonnette of the Canada-France-Hawaii telescope.
Exposure times ranged from 1500 to 24000s (mostly near 7000s) in J, H, or K
bands, with pixels 0.035 arcsec on the sky. The FWHM of the co-added images at
the location of the quasars are typically 0.16 arcsec. Including another QSO
published previously, we find associated QSO structure in at least eight of ten
objects, including the QSO at z = 4.16. The structures seen in all cases
include long faint features which appear to be tidal tails. In four cases we
have also resolved the QSO host galaxy, but find them to be smooth and
symmetrical: future PSF removal may expand this result. Including one object
previously reported, of the nine objects with more extended structure, five are
radio-loud, and all but one of these appear to be in a dense small group of
compact galaxy companions. The radio-quiet objects do not occupy the same dense
environments, as seen in the NIR. In this small sample we do not find any
apparent trends of these properties with redshift, over the range 0.8 < z <
2.4. The colors of the host galaxies and companions are consistent with young
stellar populations at the QSO redshift. Our observations suggest that adaptive
optic observations in the visible region will exhibit luminous signatures of
the substantial star-formation activity that must be occurring.Comment: 22 pages including 10 tables, plus 11 figures. To appear in A
Remarks on the Basic Plan of the Terminal Abdominal Structures of the Males of Winged Insects
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