42 research outputs found
Classic Article: The influence of deposit-feeding organisms on sediment stability and community trophic structure
Deposit-feeding and suspension-feeding benthos in Buzzards Bay, Massachusetts, show marked spatial separation; suspension feeders are largely confined to sandy or firm mud bottoms while deposit feeders attain high densities on soft muddy substrata. Food source and bottom stability have been investigated as potential factors effecting this trophic-group separation. Between October 4, 1967 and August 22, 1969, observations were made at 11 stations in Buzzards Bay, Massachusetts, along two widely separated transects over bottoms ranging in texture from silt to fine and medium sand. Water depths at these stations ranged from 3 m to 20 m. Scuba divers made many of the field observations and collected most of the samples. This study included sampling of benthic macrofauna, taking bottom photographs, analyzing sedimentary structures, texture, organic content and water content of the sediments, and measuring both water currents and suspended sediment above the bottom. Laboratory experiments were also carried out to determine differential resuspension between burrowed and unburrowed muds. Intensive reworking of the upper few centimeters of a mud bottom by deposit feeders produces a fluid fecal-rich surface that is easily resuspended by low-velocity tidal currents. We suggest that the physical instability of this fecal surface tends to: (i) clog the filtering structures of suspension-feeding organisms, (ii) bury newly settled larvae or discourage the settling of suspension-feeding larvae, and (iii) prevent sessile epifauna from attaching to an unstable mud bottom. Thus suspension feeders are unable to successfully populate all areas of the bottom where a suspended food source is available, especially in areas where mud bottoms are intensively reworked by deposit feeders. Modification of the benthic environment by deposit feeders, resulting in the exclusion of many suspension feeders and sessile epifauna, is an example of trophic group amensalism. This biotic relationship appears to be important in shaping trophic-group distributions in embayments and basins on continental shelves
Growth and predation activity at deep-sea hydrothermal vents along the Galápagos Rift
Growth rates of unclassified mussels collected from hydrothermal vents on the Pacific Ocean (2500 m) are among the highest recorded for deep-sea species. Mature mussels have mean growth rates of about 1 cm yr-1 which are comparable to growth rates of shallow water mussels...
Hubble Space Telescope Imaging of Lyman Alpha Emission at z=4.4
We present the highest redshift detections of resolved Lyman alpha emission,
using Hubble Space Telescope/ACS F658N narrowband-imaging data taken in
parallel with the Wide Field Camera 3 Early Release Science program in the
GOODS CDF-S. We detect Lyman alpha emission from three spectroscopically
confirmed z = 4.4 Lyman alpha emitting galaxies (LAEs), more than doubling the
sample of LAEs with resolved Lyman alpha emission. Comparing the light
distribution between the rest-frame ultraviolet continuum and narrowband
images, we investigate the escape of Lyman alpha photons at high redshift.
While our data do not support a positional offset between the Lyman alpha and
rest-frame ultraviolet (UV) continuum emission, the half-light radii in two out
of the three galaxies are significantly larger in Lyman alpha than in the
rest-frame UV continuum. This result is confirmed when comparing object sizes
in a stack of all objects in both bands. Additionally, the narrowband flux
detected with HST is significantly less than observed in similar filters from
the ground. These results together imply that the Lyman alpha emission is not
strictly confined to its indigenous star-forming regions. Rather, the Lyman
alpha emission is more extended, with the missing HST flux likely existing in a
diffuse outer halo. This suggests that the radiative transfer of Lyman alpha
photons in high-redshift LAEs is complicated, with the interstellar-medium
geometry and/or outflows playing a significant role in galaxies at these
redshifts.Comment: Submitted to the Astrophysical Journal. 11 pages, 10 figure
Hubble Space Telescope WFC3 Early Release Science: Emission-Line Galaxies from Infrared Grism Observations
We present grism spectra of emission-line galaxies (ELGs) from 0.6-1.6
microns from the Wide Field Camera 3 on the Hubble Space Telescope. These new
infrared grism data augment previous optical Advanced Camera for Surveys G800L
0.6-0.95 micron grism data in GOODS-South from the PEARS program, extending the
wavelength covereage well past the G800L red cutoff. The ERS grism field was
observed at a depth of 2 orbits per grism, yielding spectra of hundreds of
faint objects, a subset of which are presented here. ELGs are studied via the
Ha, [OIII], and [OII] emission lines detected in the redshift ranges 0.2<z<1.4,
1.2<z<2.2 and 2.0<z<3.3 respectively in the G102 (0.8-1.1 microns; R~210) and
G141 (1.1-1.6 microns; R~130) grisms. The higher spectral resolution afforded
by the WFC3 grisms also reveals emission lines not detectable with the G800L
grism (e.g., [SII] and [SIII] lines). From these relatively shallow
observations, line luminosities, star-formation rates, and grism spectroscopic
redshifts are determined for a total of 48 ELGs to m(AB)~25 mag. Seventeen
GOODS-South galaxies that previously only had photometric redshifts now have
new grism-spectroscopic redshifts, in some cases with large corrections to the
photometric redshifts (Delta(z)~0.3-0.5). Additionally, one galaxy had no
previously-measured redshift but now has a secure grism-spectroscopic redshift,
for a total of 18 new GOODS-South spectroscopic redshifts. The faintest source
in our sample has a magnitude m(AB)=26.9 mag. The ERS grism data also reflect
the expected trend of lower specific star formation rates for the highest mass
galaxies in the sample as a function of redshift, consistent with downsizing
and discovered previously from large surveys. These results demonstrate the
remarkable efficiency and capability of the WFC3 NIR grisms for measuring
galaxy properties to faint magnitudes and redshifts to z>2.Comment: Accepted for publication in AJ. Updated to include referee comments.
Updated sample using improved reduction contains 23 new galaxies (Table 1;
Figures 2 & 3
Hubble Space Telescope STIS Observations of GRB 000301C: CCD Imaging and Near-Ultraviolet MAMA Spectroscopy
We present Space Telescope Imaging Spectrograph observations of the optical transient (OT) counterpart of the γ-ray burster GRB 000301C obtained 5 days after the burst, on 2000 March 6. CCD clear-aperture imaging reveals a R ≃ 21.50 ± 0.15 source with no apparent host galaxy. An 8000 s, 1150 Å 18 on the line of sight to the OT. This measured redshift is conservatively a lower limit to the GRB redshift. However, as all other GRBs that have deep Hubble Space Telescope images appear to lie on the stellar field of a host galaxy, and as the large H I column density measured here and in later ground-based observations is unlikely on a random line of sight, we believe we are probably seeing absorption from H I in the host galaxy. In any case, this represents the largest direct redshift determination of a γ-ray burster to date. Our data are compatible with an OT spectrum represented by a power law with an intrinsic index α = 1.2 (f_ν ∝ ν^(-α)) and no extinction in the host galaxy, or with α = 0.5 and extinction by SMC-like dust in the OT rest frame with A_V = 0.15. The large N_(H I) and the lack of a detected host are similar to the situation for damped Lyα absorbers at z > 2
The Hubble Space Telescope Wide Field Camera 3 Early Release Science data: Panchromatic Faint Object Counts for 0.2-2 microns wavelength
We describe the Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) Early
Release Science (ERS) observations in the Great Observatories Origins Deep
Survey (GOODS) South field. The new WFC3 ERS data provide calibrated, drizzled
mosaics in the UV filters F225W, F275W, and F336W, as well as in the near-IR
filters F098M (Ys), F125W (J), and F160W (H) with 1-2 HST orbits per filter.
Together with the existing HST Advanced Camera for Surveys (ACS) GOODS-South
mosaics in the BViz filters, these panchromatic 10-band ERS data cover 40-50
square arcmin at 0.2-1.7 {\mu}m in wavelength at 0.07-0.15" FWHM resolution and
0.090" Multidrizzled pixels to depths of AB\simeq 26.0-27.0 mag (5-{\sigma})
for point sources, and AB\simeq 25.5-26.5 mag for compact galaxies.
In this paper, we describe: a) the scientific rationale, and the data taking
plus reduction procedures of the panchromatic 10-band ERS mosaics; b) the
procedure of generating object catalogs across the 10 different ERS filters,
and the specific star-galaxy separation techniques used; and c) the reliability
and completeness of the object catalogs from the WFC3 ERS mosaics. The
excellent 0.07-0.15" FWHM resolution of HST/WFC3 and ACS makes star- galaxy
separation straightforward over a factor of 10 in wavelength to AB\simeq 25-26
mag from the UV to the near-IR, respectively.Comment: 51 pages, 71 figures Accepted to ApJS 2011.01.2
HST/STIS observations of GRB000301C: CCD imaging and NUV MAMA spectroscopy
We present HST/STIS observations of the optical counterpart (OT) of the
gamma-ray burster GRB 000301C obtained on 2000 March 6, five days after the
burst. CCD clear aperture imaging reveals a R ~ 21.50+/-0.15 source with no
apparent host galaxy. An 8000 s, 1150 < lambda/A < 3300 NUV-MAMA prism spectrum
shows a relatively flat continuum (in f_lambda) between 2800 and 3300 A, with a
mean flux 8.7 (+0.8,-1.6)+/- 2.6 10^(-18) ergs/s/cm^2/A, and a sharp break
centered at 2797+/-25 A. We interpret it as HI Lyman break at z = 2.067+/-0.025
indicating the presence of a cloud with a HI column density log(HI) > 18 on the
line-of-sight to the OT. This value is conservatively a lower limit to the GRB
redshift. However, the facts that large N(HI) system are usually considered as
progenitors of present day galaxies and that other OTs are found associated
with star forming galaxies strongly suggest that it is the GRB redshift. In any
case, this represents the largest direct redshift determination of a gamma-ray
burster to date. Our data are compatible with an OT spectrum represented by a
power-law with an intrinsic index \alpha = 1.2((f_nu \propto nu^-alpha) and no
extinction in the host galaxy or with alpha = 0.5 and extinction by a SMC-like
dust in the OT rest-frame with A_V = 0.15. The large N(HI) and the lack of
detected host is similar to the situation for damped Ly-alpha absorbers at z >
2.Comment: Replaced by final version. 10 p., 2 fig. Scheduled to appear in ApJ
555 n2 Jul 10, 2001. Minor changes, both redshift and mean near UV flux are
revised with slightly larger values, due to a wrong offset sign in the
wavelength calibratio
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
Hubble Space Telescope STIS Observations of GRB 000301C: CCD Imaging and Near-Ultraviolet MAMA Spectroscopy
We present Space Telescope Imaging Spectrograph observations of the optical transient (OT) counterpart of the γ-ray burster GRB 000301C obtained 5 days after the burst, on 2000 March 6. CCD clear-aperture imaging reveals a R ≃ 21.50 ± 0.15 source with no apparent host galaxy. An 8000 s, 1150 Å 18 on the line of sight to the OT. This measured redshift is conservatively a lower limit to the GRB redshift. However, as all other GRBs that have deep Hubble Space Telescope images appear to lie on the stellar field of a host galaxy, and as the large H I column density measured here and in later ground-based observations is unlikely on a random line of sight, we believe we are probably seeing absorption from H I in the host galaxy. In any case, this represents the largest direct redshift determination of a γ-ray burster to date. Our data are compatible with an OT spectrum represented by a power law with an intrinsic index α = 1.2 (f_ν ∝ ν^(-α)) and no extinction in the host galaxy, or with α = 0.5 and extinction by SMC-like dust in the OT rest frame with A_V = 0.15. The large N_(H I) and the lack of a detected host are similar to the situation for damped Lyα absorbers at z > 2
Observations of Ly Emitters at High Redshift
In this series of lectures, I review our observational understanding of
high- Ly emitters (LAEs) and relevant scientific topics. Since the
discovery of LAEs in the late 1990s, more than ten (one) thousand(s) of LAEs
have been identified photometrically (spectroscopically) at to . These large samples of LAEs are useful to address two major astrophysical
issues, galaxy formation and cosmic reionization. Statistical studies have
revealed the general picture of LAEs' physical properties: young stellar
populations, remarkable luminosity function evolutions, compact morphologies,
highly ionized inter-stellar media (ISM) with low metal/dust contents, low
masses of dark-matter halos. Typical LAEs represent low-mass high- galaxies,
high- analogs of dwarf galaxies, some of which are thought to be candidates
of population III galaxies. These observational studies have also pinpointed
rare bright Ly sources extended over kpc, dubbed
Ly blobs, whose physical origins are under debate. LAEs are used as
probes of cosmic reionization history through the Ly damping wing
absorption given by the neutral hydrogen of the inter-galactic medium (IGM),
which complement the cosmic microwave background radiation and 21cm
observations. The low-mass and highly-ionized population of LAEs can be major
sources of cosmic reionization. The budget of ionizing photons for cosmic
reionization has been constrained, although there remain large observational
uncertainties in the parameters. Beyond galaxy formation and cosmic
reionization, several new usages of LAEs for science frontiers have been
suggested such as the distribution of {\sc Hi} gas in the circum-galactic
medium and filaments of large-scale structures. On-going programs and future
telescope projects, such as JWST, ELTs, and SKA, will push the horizons of the
science frontiers.Comment: Lecture notes for `Lyman-alpha as an Astrophysical and Cosmological
Tool', Saas-Fee Advanced Course 46. Verhamme, A., North, P., Cantalupo, S., &
Atek, H. (eds.) --- 147 pages, 103 figures. Abstract abridged. Link to the
lecture program including the video recording and ppt files :
https://obswww.unige.ch/Courses/saas-fee-2016/program.cg