2,082 research outputs found
Computing Matveev's complexity via crystallization theory: the boundary case
The notion of Gem-Matveev complexity has been introduced within
crystallization theory, as a combinatorial method to estimate Matveev's
complexity of closed 3-manifolds; it yielded upper bounds for interesting
classes of such manifolds. In this paper we extend the definition to the case
of non-empty boundary and prove that for each compact irreducible and
boundary-irreducible 3-manifold it coincides with the modified Heegaard
complexity introduced by Cattabriga, Mulazzani and Vesnin. Moreover, via
Gem-Matveev complexity, we obtain an estimation of Matveev's complexity for all
Seifert 3-manifolds with base and two exceptional fibers and,
therefore, for all torus knot complements.Comment: 27 pages, 14 figure
VIRIS: A Visual-Infrared Imaging System for the Lick Observatory 1-M Telescope
We describe a system in use at the Lick Observatory 1-m Nickel telescope for
near-simultaneous imaging at optical and near-infrared wavelengths. The
combined availability of a CCD and a NICMOS-3 camera makes the system
well-suited for photometric monitoring from 0.5-2.2 microns of a variety of
astrophysical objects. Our science program thus far has concentrated on
studying variability trends in young stellar objects.Comment: 11 pages LaTex, 3 Postscript figure, Pub. Astr. Soc. Pac. 1998, in
pres
A Tolman Surface Brightness Test for Universal Expansion, and the Evolution of Elliptical Galaxies in Distant Clusters
We use the intercept of the elliptical galaxy radius--surface brightness (SB)
relation at a fixed metric radius as the standard condition for the Tolman SB
test of the universal expansion. We use surface photometry in the optical and
near-IR of elliptical galaxies in Abell~2390 () and Abell~851
(), and compare them to the Coma cluster at . The
photometric data for each cluster are well-described by the Kormendy relation
, where in the optical and in the
near-IR. The scatter about this near-IR relation is only in
at the highest redshift, which is much smaller than at low redshifts,
suggesting a remarkable homogeneity of the cluster elliptical population at
. We use the intercept of these fixed-slope correlations at ~kpc (assuming ~km~s~Mpc, , and
, where the results are only weakly dependent on the cosmology) to
construct the Tolman SB test for these three clusters. The data are fully
consistent with universal expansion if we assume simple models of passive
evolution for elliptical galaxies, but are inconsistent with a non-expanding
geometry (the tired light cosmology) at the confidence level at
. These results suggest luminosity evolution in the restframe -band
of ~mag from to the present, and are consistent with
the ellipticals having formed at high redshift. The SB intercept in elliptical
galaxy correlations is thus a powerful tool for investigating models of their
evolution for significant lookback times.Comment: to appear in The Astrophysical Journal (Letters); 13 pages, including
3 Postscript figures and 1 table; uuencoded, compressed format; the paper is
also available in various formats from
http://astro.caltech.edu/~map/map.bibliography.refereed.htm
The Infrared Surface Brightness Fluctuation Distances to the Hydra and Coma Clusters
We present IR surface brightness fluctuation (SBF) distance measurements to
NGC 4889 in the Coma cluster and to NGC 3309 and NGC 3311 in the Hydra cluster.
We explicitly corrected for the contributions to the fluctuations from globular
clusters, background galaxies, and residual background variance. We measured a
distance of 85 +/- 10 Mpc to NGC 4889 and a distance of 46 +/- 5 Mpc to the
Hydra cluster. Adopting recession velocities of 7186 +/- 428 km/s for Coma and
4054 +/- 296 km/s for Hydra gives a mean Hubble constant of H_0 = 87 +/- 11
km/s/Mpc. Corrections for residual variances were a significant fraction of the
SBF signal measured, and, if underestimated, would bias our measurement towards
smaller distances and larger values of H_0. Both NICMOS on the Hubble Space
Telescope and large-aperture ground-based telescopes with new IR detectors will
make accurate SBF distance measurements possible to 100 Mpc and beyond.Comment: 24 pages, 4 PostScript figures, 2 JPEG images; accepted for
publication in Ap
PG 1700+518 Revisited: Adaptive Optics Imaging and a Revised Starburst Age for the Companion
We present the results of adaptive-optics imaging of the z=0.2923 QSO PG
1700+518 in the J and H bands. The extension to the north of the QSO is clearly
seen to be a discrete companion with a well-defined tidal tail, rather than a
feature associated with the host galaxy of PG 1700+518 itself. On the other
hand, an extension to the southwest of the QSO (seen best in deeper, but
lower-resolution, optical images) does likely comprise tidal material from the
host galaxy. The SED derived from images in J, H, and two non-standard optical
bands indicates the presence of dust intermixed with the stellar component. We
use our previously reported Keck spectrum of the companion, the SED found from
the imaging data, and updated spectral-synthesis models to constrain the
stellar populations in the companion and to redetermine the age of the
starburst. While our best-fit age of 0.085 Gyr is nearly the same as our
earlier determination, the fit of the new models is considerably better. This
age is found to be remarkably robust with respect to different assumptions
about the nature of the older stellar component and the effects of dust.Comment: 11 pages; includes two eps figures. Latex (AASTEX). Two additional
figures in gif format. Postscript version including all figs. (424 kb) can be
obtained from http://www.ifa.hawaii.edu/~canaguby/preprints.html To appear in
ApJ. Letter
Near-Infrared Adaptive Optics Imaging of the Central Regions of Nearby Sc Galaxies: I. M33
Near-infrared images obtained with the Canada-France-Hawaii Telescope (CFHT)
Adaptive Optics Bonnette (AOB) are used to investigate the stellar content
within 18 arcsec of the center of the Local Group spiral galaxy M33. AGB stars
with near-infrared spectral-energy distributions similar to those of giants in
the solar neighborhood and Baade's Window are detected over most of the field.
The bolometric luminosity function (LF) of these stars has a discontinuity near
M_{bol} = -5.25, and comparisons with evolutionary tracks suggest that most of
the AGB stars formed in a burst of star formation 1 - 3 Gyr in the past. The
images are also used to investigate the integrated near-infrared photometric
properties of the nucleus and the central light concentration. The nucleus is
bluer than the central light concentration, in agreement with previous studies
at visible wavelengths. The CO index of the central light concentration 0.5
arcsec from the galaxy center is 0.05, which corresponds to [Fe/H] = -1.2 for
simple stellar systems. Hence, the central light concentration could not have
formed from the chemically-enriched material that dominates the present-day
inner disk of M33.Comment: 23 pages of text + 11 figures; to appear in A
B3 0003+387: AGN Marked Large-Scale Structure at z=1.47?
We present evidence for a significant overdensity of red galaxies, as much as
a factor of 14 over comparable field samples, in the field of the z=1.47 radio
galaxy B3 0003+387. The colors and luminosities of the brightest red galaxies
are consistent with their being at z>0.8. The radio galaxy and one of the red
galaxies are separated by 5" and show some evidence of a possible interaction.
However, the red galaxies do not show any strong clustering around the radio
galaxy nor around any of the brighter red galaxies. The data suggest that we
are looking at a wall or sheet of galaxies, possibly associated with the radio
galaxy at z=1.47. Spectroscopic redshifts of these red galaxies will be
necessary to confirm this large-scale structure.Comment: 19 pages, 7 figures, LaTeX2e/AASTeX v5.0.2. The full photometric
catalog is included as a separate deluxetable file. To appear in the
Astronomical Journal (~Nov 00
Colors and K-Band Counts of Extremely Faint Field Galaxies
We combine deep K-band (Keck) with V- and I-band (NTT) observations of two
high-Galactic latitude fields, surveying a total of ~2 sq. arcmin. The K-band
galaxy counts continue to rise above K=22, reaching surface densities of few x
10^5 per sq. degree. The slope for the counts is (d log(N) per mag per sq.
degree) = 0.23 +/- 0.02 between K=18-23, consistent with other deep K surveys.
The numbers of galaxies in each mag bin is about two times greater than the
galaxy counts of Djorgovski et al. (1995).
The optical and near infrared magnitudes of all objects detected in the V+I+K
image are discussed in the context of grids of isochrone synthesis galaxy
evolutionary models (Bruzual & Charlot 1993, 1995). The colors of most of the
observed galaxies are consistent with a population drawn from a broad redshift
distribution. A few galaxies at K=19-20 are red in both colors (V-I>3; I-K>2),
consistent with being early-type galaxies having undergone a burst of star
formation at z>5 and viewed at z~1. At K>20, we find ~8 ``red outlier''
galaxies with I-K>4 and V-I<2.5, whose colors are difficult to mimic by a
single evolving or non-evolving stellar population at any redshift. They are
likely either low-metallicity, dusty dwarf galaxies, or old galaxies at high
redshift (z>1.2). Their surface density is several per square arcminute, which
is so high that they are probably common objects of low luminosity .Comment: 28 pages, 9 Figures (2 Plates), uses aaspp4.sty. The complete paper
(including large figures and the plates) are available via anonymous ftp at
ftp://coma.berkeley.edu/pub/lmoustakas/ . To appear in the Astrophysical
Journal, Feb 1 1997, vol. 47
Low-Mass Star Formation and the Initial Mass Function in the Rho Ophiuchi Cloud Core
We have obtained moderate-resolution (R=800-1200) K-band spectra for ~100
stars within and surrounding the cloud core of rho Oph. We have measured
spectral types and continuum veilings and have combined this information with
results from new deep imaging. The IMF peaks at about 0.4 M_sun and slowly
declines to the hydrogen burning limit with a slope of ~-0.5 in logarithmic
units (Salpeter is +1.35). Our lower limits on the numbers of substellar
objects demonstrate that the IMF probably does not fall more steeply below the
hydrogen burning limit, at least down to ~0.02 M_sun. We then make the first
comparison of mass functions of stars and pre-stellar clumps (Motte, Andre, &
Neri) measured in the same region. The similar behavior of the two mass
functions in rho Oph supports the suggestion of Motte et al. and Testi &
Sargent that the stellar mass function in young clusters is a direct product of
the process of cloud fragmentation. After considering the effect of extinction
on the SED classifications of the sample, we find that ~17% of the rho Oph
stars are Class I, implying ~0.1 Myr for the lifetime of this stage. In spectra
separated by two years, we observe simultaneous variability in the Br gamma
emission and K-band continuum veiling for two stars, where the hydrogen
emission is brighter in the more heavily veiled data. This behavior indicates
that the disk may contribute significantly to continuous K-band emission, in
contrast to the proposal that the infalling envelope always dominates. Our
detection of strong 2 micron veiling (r_K=1-4) in several Class II and III
stars, which should have disks but little envelope material, further supports
this proposition.Comment: 35 pages, 14 figures, accepted to Ap
Low Mass Stars and Substellar Objects in the NGC 1333 Molecular Cloud
We present the results of near-infrared imaging and low-resolution near-
infrared spectroscopy of low mass objects in the NGC 1333 molecular cloud. A
JHK survey of an 11.4' x 11.7' area of the northern cluster was conducted to a
sensitivity of K < 16 mag. Using near-infrared magnitudes and colors from this
and previously published surveys, twenty-five brown dwarf candidates were
selected toward the high extinction cloud core. Spectra in the K band were
obtained and comparisons of the depths of water vapor absorption bands in our
candidate objects with a grid of dwarf,subgiant, and giant standards were made
to derive spectral types. These data were then used to derive effective
temperatures and stellar luminosities which, when combined with theoretical
tracks and isochrones for pre-main sequence objects, resulted in estimates for
their masses and ages. The models suggest a median age for the sample of < 1
Myr with substellar masses for at least 9 of the candidates including the x-ray
flare source ASR 24. Surface gravities have been estimated for the brown dwarf
candidates and, for a given spectral type,found to resemble more closely dwarfs
than giants. Using the near-infrared imaging data and age estimates from the
spectroscopic sample, an extinction-limited sample in the northern cluster was
defined. Consistent with recent studies of other young clusters, this sample
exhibits an accretion disk frequency of 0.75 +-0.20 and a mass spectrum slope
across the hydrogen-burning limit of alpha < 1.6 where dN/dM ~ M^-(alpha).Comment: 22 postscript pages, 12 postscript figures, and 3 postscript tables.
Accepted for publication in the Astronomical Journal (February, 2004
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