17,226 research outputs found
Gut throughput rate and satiation of the invasive Lionfish (Pterois volitans) and its potential impact on an endemic, endangered Labrid fish Halichoeres socialis
The invasive Indo-Pacific Lionfish Pterois volitans has been recognized as a severe threat to indigenous fish species on Caribbean reefs. Previous studies have identified an extensive variety of Caribbean fishes in the stomachs of lionfish, but few have tried to quantify the impact these invaders could have on endemic or threatened species. The threatened Labrid fish Halichoeres socialis has been identified as the primary component of lionfish diet in Belizean lagoonal reef systems. This study aims to answer two questions: what is the average maximum number of prey-fish a lionfish can consume in one sitting, and at what rate can these lionfish pass a meal of three prey fish completely? To test lionfish satiation, the subjects were fed as many Pseudohemiculter dispar (a commercially available surrogate) as they could eat within a fifteen-minute window. During the digestion rate experiment, lionfish were fed three similarly sized P. dispar and allowed to digest in 3, 6, 9, 12, 15, 19, and 24 hour blocks. From observing prey throughput under near optimal laboratory conditions, the maximum potential impact of lionfish on native populations of Caribbean reef dwelling fishes can be estimated. Given the volume and mass of prey items consumed in this study between 593 and 4658 individual H. socialis could be consumed by a single lionfish in one year. Coupled with further investigation into H. socialis stock numbers, lionfish (P. volitans) could be considered a potentially immanent threat to fishes that exhibit body morphometrics like those of H. socialis at any stage of their life-history
Tracing the Dynamics of Disk Galaxies with Optical and IR Surface Photometry: Color Gradients in M99
We present optical and IR surface photometry of M99 (NGC 4254) at g, r_S i, J
and K'. We also present a K' image of M51 (NGC 5194) for comparison. Fourier
decomposition of the disk light reveals that the radial distribution of power
depends on wavelength, which in turn implies that the spiral structure traced
in the visual (i.e. young population I and dust) is different from the one
detected at 2 microns (i.e. old stellar disk). We observe radial modulation of
the power and a dependency of power with wavelength that are consistent with
modal theory of spiral structure.
A central motivation for our research is the fundamental idea of density wave
theory that the passage of a spiral density wave triggers star formation. We
have found a stellar population age gradient consistent with this scenario in a
reddening-free, red supergiant-sensitive, Q-like photometric parameter at 6 kpc
galactocentric distance across one of the arms of M99. We rule out that the
change in this parameter, Q(r_SJgi), across the arm is mainly due to dust. The
difference in Q(r_SJgi) going from the interarm regions to the arms also
indicates that arms cannot be due exclusively to crowding of stellar orbits.
We present the first measurement of Omega_p, the angular speed of the spiral
pattern, and of the location of the corotation radius, derived from the drift
velocity of the young stars away from their birth site. The measured Q(r_SJgi)
implies a star formation rate for M99 within the range of 10-20 M_odot/yr; a
disk stellar mass surface density of ~80 M_odot/pc^2; and a maximum
contribution of ~20 percent from red supergiants to the K' light in a small
region, and much smaller on average. We measure a K' arm--interarm contrast of
2-3, too high for M99 to be a truly isolated galaxy.Comment: 25 pages of uuencoded, compressed Postscript (text only). To appear
in 1 April 1996 issue of The Astrophysical Journal. Also available, together
with 2 uuencoded, compressed PostScript files with 10 figures each, at
http://astro.berkeley.edu/preprints.htm
Keck Observations of the Most Distant Galaxy: 8C1435+63 at z=4.25
We report on Keck observations and confirm the redshift of the most distant
galaxy known: 8C1435+63 at z=4.25. The spectrum shows a strong Ly line,
a Ly forest continuum break and a continuum break at
\AA. The Ly emission is spatially extended and
roughly aligned with the radio source. The galaxy shows a double structure in
the -band (1500\AA) which is aligned with the radio
axis; the two -band components spatially coincide with the nuclear and
southern radio components. Some fraction of the band emission could be due
to a nonthermal process such as inverse compton scattering. In the -band
(4200\AA), which may be dominated by starlight, the
galaxy has a very low surface brightness, diffuse morphology. The
morphology shows little relationship to the radio source structure, although
the major axis of the emission is elongated roughly in the direction of the
radio source axis. The galaxian continuum is very red () and if the
continuum is due to starlight, implies a formation redshift of . We
speculate that this galaxy may be the progenitor of a present day cD galaxy.Comment: 4 pages + 4 figures; uuencoded tar compressed PostScript files;
figures and tables included. To appear in 1 Jan 1995 issue of The
Astrophysical Journal, Letters. Please direct requests/questions/comments to
[email protected]
Discovery of extreme asymmetry in the debris disk surrounding HD 15115
We report the first scattered light detection of a dusty debris disk
surrounding the F2V star HD 15115 using the Hubble Space Telescope in the
optical, and Keck adaptive optics in the near-infrared. The most remarkable
property of the HD 15115 disk relative to other debris disks is its extreme
length asymmetry. The east side of the disk is detected to ~315 AU radius,
whereas the west side of the disk has radius >550 AU. We find a blue optical to
near-infrared scattered light color relative to the star that indicates grain
scattering properties similar to the AU Mic debris disk. The existence of a
large debris disk surrounding HD 15115 adds further evidence for membership in
the Beta Pic moving group, which was previously argued based on kinematics
alone. Here we hypothesize that the extreme disk asymmetry is due to dynamical
perturbations from HIP 12545, an M star 0.5 degrees (0.38 pc) east of HD 15115
that shares a common proper motion vector, heliocentric distance, galactic
space velocity, and age.Comment: 4 pages, 3 figures, ApJ Letters, accepte
Theoretical Predictions for Surface Brightness Fluctuations and Implications for Stellar Populations of Elliptical Galaxies
(Abridged) We present new theoretical predictions for surface brightness
fluctuations (SBFs) using models optimized for this purpose. Our predictions
agree well with SBF data for globular clusters and elliptical galaxies. We
provide refined theoretical calibrations and k-corrections needed to use SBFs
as standard candles. We suggest that SBF distance measurements can be improved
by using a filter around 1 micron and calibrating I-band SBFs with the
integrated V-K galaxy color. We also show that current SBF data provide useful
constraints on population synthesis models, and we suggest SBF-based tests for
future models. The data favor specific choices of evolutionary tracks and
spectra in the models among the several choices allowed by comparisons based on
only integrated light. In addition, the tightness of the empirical I-band SBF
calibration suggests that model uncertainties in post-main sequence lifetimes
are less than +/-50% and that the IMF in ellipticals is not much steeper than
that in the solar neighborhood. Finally, we analyze the potential of SBFs for
probing unresolved stellar populations. We find that optical/near-IR SBFs are
much more sensitive to metallicity than to age. Therefore, SBF magnitudes and
colors are a valuable tool to break the age/metallicity degeneracy. Our initial
results suggest that the most luminous stellar populations of bright cluster
galaxies have roughly solar metallicities and about a factor of three spread in
age.Comment: Astrophysical Journal, in press (uses Apr 20, 2000 version of
emulateapj5.sty). Reposted version has a minor cosmetic change to Table
Environmental Impact on the Southeast Limb of the Cygnus Loop
We analyze observations from the Chandra X-ray Observatory of the southeast
knot of the Cygnus Loop supernova remnant. In this region, the blast wave
propagates through an inhomogeneous environment. Extrinsic differences and
subsequent multiple projections along the line of sight rather than intrinsic
shock variations, such as fluid instabilities, account for the apparent
complexity of the images. Interactions between the supernova blast wave and
density enhancements of a large interstellar cloud can produce the
morphological and spectral characteristics. Most of the X-ray flux arises in
such interactions, not in the diffuse interior of the supernova remnant.
Additional observations at optical and radio wavelengths support this account
of the existing interstellar medium and its role in shaping the Cygnus Loop,
and they demonstrate that the southeast knot is not a small cloud that the
blast wave has engulfed. These data are consistent with rapid equilibration of
electron and ion temperatures behind the shock front, and the current blast
wave velocity v_{bw} approx 330 km/s. Most of this area does not show strong
evidence for non-equilibrium ionization conditions, which may be a consequence
of the high densities of the bright emission regions.Comment: To appear in ApJ, April 1, 200
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