447 research outputs found
HI and Star Formation Properties of Massive Galaxies: First Results from the GALEX Arecibo SDSS Survey
The GALEX Arecibo SDSS Survey (GASS) is an ambitious program designed to
investigate the cold gas properties of massive galaxies, a challenging
population for HI studies. Using the Arecibo radio telescope, GASS is gathering
high-quality HI-line spectra for an unbiased sample of ~1000 galaxies with
stellar masses greater than 10^10 Msun and redshifts 0.025 < z < 0.05,
uniformly selected from the SDSS spectroscopic and GALEX imaging surveys. The
galaxies are observed until detected or until a low gas mass fraction limit
(1.5-5%) is reached. We present initial results based on the first Data
Release, which consists of ~20% of the final GASS sample. We use this data set
to explore the main scaling relations of HI gas fraction with galaxy structure
and NUV-r colour, and show our best fit plane describing the relation between
gas fraction, stellar mass surface density and NUV-r colour. Interesting
outliers from this plane include gas-rich red sequence galaxies that may be in
the process of regrowing their disks, as well as blue, but gas-poor spirals.Comment: 4 pages, 2 figures. To appear in "Hunting for the Dark: The Hidden
Side of Galaxy Formation", Malta, 19-23 Oct. 2009, eds. V.P. Debattista &
C.C. Popescu, AIP Conf. Se
Quenching or Bursting: Star Formation Acceleration--A New Methodology for Tracing Galaxy Evolution
We introduce a new methodology for the direct extraction of galaxy physical
parameters from multi-wavelength photometry and spectroscopy. We use
semi-analytic models that describe galaxy evolution in the context of large
scale cosmological simulation to provide a catalog of galaxies, star formation
histories, and physical parameters. We then apply stellar population synthesis
models and a simple extinction model to calculate the observable broad-band
fluxes and spectral indices for these galaxies. We use a linear regression
analysis to relate physical parameters to observed colors and spectral indices.
The result is a set of coefficients that can be used to translate observed
colors and indices into stellar mass, star formation rate, and many other
parameters, including the instantaneous time derivative of the star formation
rate which we denote the {\it Star Formation Acceleration (SFA)}, We apply the
method to a test sample of galaxies with GALEX photometry and SDSS
spectroscopy, deriving relationships between stellar mass, specific star
formation rate, and star formation acceleration. We find evidence for a
mass-dependent SFA in the green valley, with low mass galaxies showing greater
quenching and higher mass galaxies greater bursting. We also find evidence for
an increase in average quenching in galaxies hosting AGN. A simple scenario in
which lower mass galaxies accrete and become satellite galaxies, having their
star forming gas tidally and/or ram-pressure stripped, while higher mass
galaxies receive this gas and react with new star formation can qualitatively
explain our results.Comment: 33 pages, 31 figures, ApJ accepte
The Narrow-band Ultraviolet Imaging Experiment for Wide-field Surveys (NUVIEWS)-I: Dust scattered continuum
We report on the first results of the Narrow-band Ultraviolet Imaging
Experiment for Wide-field Surveys (NUVIEWS), a sounding rocket experiment
designed to map the far-ultraviolet background in four narrow bands. This is
the first imaging measurement of the UV background to cover a substantial
fraction of the sky. The narrow band responses (145, 155, 161, and 174 nm, 7-10
nm wide) allow us to isolate background contributions from dust-scattered
continuum, H2 fluorescence, and CIV 155 nm emission. In our first flight, we
mapped one quarter of the sky with 5-10 arcminute imaging resolution. In this
paper, we model the dominant contribution of the background, dust-scattered
continuum. Our data base consists of a map of over 10,000 sq. degrees with 468
independent measurements in 6.25 by 6.25 sq. degree bins. Stars and
instrumental stellar halos are removed from the data. We present a map of the
continuum background obtained in the 174 nm telescope. We use a model that
follows Witt, Friedman, and Sasseen (1997: WFS) to account for the
inhomogeneous radiation field and multiple scattering effects in clouds. We
find that the dust in the diffuse interstellar medium displays a moderate
albedo (a=0.55+/-0.1) and highly forward scattering phase function parameter
(g=0.75+/-0.1) over a large fraction of the sky, similar to dust in star
forming regions. We also have discovered a significant variance from the model.Comment: 16 pages, 3 ps figures, submitted to Astrophysical Journal Letter
Enabling Technologies for Next Generation Ultraviolet Astrophysics, Planetary, and Heliophysics Missions
Our study sought to create a new paradigm in UV instrument design, detector technology, and
optics that will form the technological foundation for a new generation of ultraviolet missions.
This study brought together scientists and technologists representing the broad community of
astrophysicists, planetary and heliophysics physicists, and technologists working in the UV.
Next generation UV missions require major advances in UV instrument design, optics and
detector technology. UV offers one of the few remaining areas of the electromagnetic spectrum
where this is possible, by combining improvements in detector quantum efficiency (5-10x),
optical coatings and higher-performance wide-field spectrometers (5-10x), and increasing
multiplex advantage (100-1000x).
At the same time, budgets for future missions are tightly constrained. Attention has begun to turn
to small and moderate class missions to provide new observational capabilities on timescales that
maintain scientific vitality. Developments in UV technology offer a comparatively unique
opportunity to conceive of small (Explorer) and moderate (Probe, Discovery, New Millennium)
class missions that offer breakthrough science.
Our study began with the science,
reviewing the breakthrough science
questions that compel the development of
new observational capabilities in the next
10-20 years. We invented a framework for
highlighting the objectives of UV
measurement capabilities: following the
history of baryons from the intergalactic
medium to stars and planets. In
astrophysics, next generation space UV missions will detect and map faint emission and
tomographically map absorption from intergalactic medium baryons that delineate the structure
of the Universe, map the circum-galactic medium that is the reservoir of galaxy-building gas,
map the warm-hot ISM of our Galaxy, explore star-formation within the Local group and beyond,
trace gas in proto-planetary disks and extended atmospheres of exoplanets, and record the
transient UV universe. Solar system planetary atmospheric physics and chemistry, aurorae,
surface composition and magnetospheric environments and interactions will be revealed using
UV spectroscopy. UV spectroscopy may even detect life on an exoplanet.
Our study concluded that with UV technology developments within reach over the next 5-
10 years, we can conceive moderate-class missions that will answer many of the compelling
science questions driving the field.
We reviewed the science measurement requirements for these pioneering new areas and
corresponding technology requirements. We reviewed and evaluated the emerging technologies,
and developed a figure of merit based on potential science impact, state of readiness, required
investment, and potential for highly leveraged progress in a 5-10 year horizon. From this we
were able to develop a strategy for technology development. Some of this technology
development will be subject to funding calls from federal agencies. A subset form a portfolio of
highly promising technologies that are ideal for funding from a KISS Development Program.
One of our study’s principal conclusions was that UV detector performance drives every aspect
of the scientific capability of future missions, and that two highly flexible detector technologies
were at the tipping point for major breakthroughs. These are Gen-2 borosilicate Atomic Layer
Deposition (ALD) coated microchannel plate detectors with GaN photocathodes, and ALDantireflection
(AR) coated, delta-doped photon-counting CCD detectors. Both offer the potential
for QE>50% combined with large formats and pixel counts, low background, and sky-limited
photon-counting performance over the 100-300 nm band. Ramped AR coatings for
spectroscopic detectors could achieve QE’s as high as 80%!
A second conclusion was that UV coatings are on the threshold of a major breakthrough. UV
coatings permeate every aspect of telescope and instrument design. Efficient, robust, ultra-thin
and highly uniform reflective coatings applied with Atomic Layer Deposition (ALD) offer the
possibility of high-performance, wide-field, highly-multiplexed UV spectrometers and a broadband
reach covering the scientifically critical 100-120 nm range (home of 50% of all atomic and
molecular resonance lines). Our study concluded that UV coating advances made possible by
ALD is the principle technology advance that will enable a joint UV-optical general
astrophysics and exoEarth imaging flagship mission.
A third conclusion was that the revolution in micro- and nano-fabrication technology offers a
cornucopia of new possibilities for revolutionary UV technology developments in the near future.
An immediate example is the application of new microlithography techniques to patterning UV
diffraction gratings that are highly efficient and designed to enable wide-field, high-resolution
spectroscopy. These techniques could support the development of new detectors that could
discriminate optical and UV photons and potentially energy-resolving detection.
Relatively modest investments in technology development over the next 5-10 years could
provide advances in detectors, coatings, diffractive elements, and filters that would result
in an effective increase in science capability of 100-1000!
The study brought together a diverse community, led to many new ideas and collaborations, and
brought cohesion and common purpose to UV practitioners. This will have a lasting and positive
impact on the future of our field
WSRT Ultra-Deep Neutral Hydrogen Imaging of Galaxy Clusters at z=0.2, a Pilot Survey of Abell 963 and Abell 2192
A pilot study with the powerful new backend of the Westerbork Synthesis Radio
Telescope (WSRT) of two galaxy clusters at z=0.2 has revealed neutral hydrogen
emission from 42 galaxies. The WSRT probes a total combined volume of 3.4x10^4
Mpc^3 at resolutions of 54x86 kpc^2 and 19.7 km/s, surveying both clusters and
the large scale structure in which they are embedded. In Abell 963, a
dynamically relaxed, lensing Butcher-Oemler cluster with a high blue fraction,
most of the gas-rich galaxies are located between 1 and 3 Mpc in projection,
northeast from the cluster core. Their velocities are slightly redshifted with
respect to the cluster, and this is likely a background group. None of the blue
galaxies in the core of Abell 963 are detected in HI, although they have
similar colors and luminosities as the HI detected galaxies in the cluster
outskirts and field. Abell 2192 is less massive and more diffuse. Here, the
gas-rich galaxies are more uniformly distributed. The detected HI masses range
from 5x10^9 to 4x10^10 Msun. Some galaxies are spatially resolved, providing
rudimentary rotation curves useful for detailed kinematic studies of galaxies
in various environments. This is a pilot for ultra-deep integrations down to HI
masses of 8x10^8 Msun, providing a complete survey of the gas content of
galaxies at z=0.2, probing environments ranging from cluster cores to voids.Comment: 5 pages, 6 figures + 1 Plate, accepted for publication in the
Astrophysical Journal Letter
FIREBALL: Detector, data acquisition and reduction
The Faint Intergalactic Redshifted Emission Balloon (FIREBALL) had its first scientific flight in June 2009. The instrument combines microchannel plate detector technology with fiber-fed integral field spectroscopy on an unstable stratospheric balloon gondola platform. This unique combination poses a series of calibration and data reduction challenges that must be addressed and resolved to allow for accurate data analysis. We discuss our approach and some of the methods we are employing to accomplish this task
UV photon-counting CCD detectors that enable the next generation of UV spectroscopy missions: AR coatings that can achieve 80-90% QE
We describe recent progress in the development of anti-reflection coatings for use at UV wavelengths on CCDs and other Si-based detectors. We have previously demonstrated a set of coatings which are able to achieve greater than 50% QE in 4 bands from 130nm to greater than 300nm. We now present new refinements of these AR-coatings which will improve performance in a narrower bandpass by 50% over previous work. Successful test films have been made to optimize transmission at 190nm, reaching 80% potential transmission
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