7,196 research outputs found
Extending the redshift distribution of submm galaxies: Identification of a z~4 submm galaxy
We present the identification of a bright submillimeter galaxy (SMG) in the
field of Abell 2218. The galaxy has a spectroscopic redshift of ~4, and is
currently the highest redshift SMG known. It is detected at all wavelengths
from optical to submm, including the Spitzer IRAC bands. We discuss the
properties of this galaxy, which is undergoing intense star formation at a
rate~600 Msun/yr. We also compare the properties to those of radio-preselected
submm-bright galaxies. The z~4 result extends the redshift distribution of
SMGs.Comment: 4 pages, 4 figures, uses asp2004.sty. To appear in the proceedings of
the conference "Infrared Diagnostics of Galaxy Evolution", Pasadena, CA,
14-16 November 2005, ed. R. Char
A Submillimeter Selected Quasar in the Field of Abell 478
We report the discovery of a z=2.83 quasar in the field of the cooling flow
galaxy cluster Abell 478. This quasar was first detected in a submm survey of
star forming galaxies at high redshifts, as the brightest source. We discuss
the optical spectrum and far-IR spectral energy distribution (SED) of this
object.Comment: 4 pages, 3 figures, in "Deep Millimeter Surveys: Implications for
Galaxy Formation and Evolution", ed. J. Lowenthal and D. Hughes, World
Scientific Publisher
Gravitationally lensed radio emission associated with SMM J16359+6612, a multiply imaged submillimeter galaxy behind A2218
We report the detection of discrete, lensed radio emission from the multiply
imaged, z=2.516 submillimetre selected galaxy, SMM J16359+6612. All three
images are detected in deep WSRT 1.4 GHz and VLA 8.2 GHz observations, and the
radio positions are coincident with previous sub-mm SCUBA observations of this
system. This is the widest separation lens system to be detected in the radio
so far, and the first time that multiply imaged lensed radio emission has been
detected from a star forming galaxy -- all previous multiply-lensed radio
systems being associated with radio-loud AGN. Taking into account the total
magnification of ~45, the WSRT 1.4 GHz observations suggest a star formation
rate of 500 Solar mass/yr. The source has a steep radio spectrum (alpha -0.7)
and an intrinsic flux density of just 3 microJy at 8.2 GHz. Three other SCUBA
sources in the field are also detected by the WSRT, including SMMJ16359+66118,
a singly imaged (and magnified) arclet at z=1.034. Higher resolution radio
observations of SMMJ16359+6612 (and other highly magnified star forming
galaxies) provide a unique opportunity to study the general properties and
radio morphology of intrinsically faint, distant and obscured star forming
galaxies. They can also help to constrain the technical specification of next
generation radio telescopes, such as the Square Kilometre Array.Comment: 5 pages, 2 figures, to appear in A&A letter
The cosine law at the atomic scale: Toward realistic simulations of Knudsen diffusion
We propose to revisit the diffusion of atoms in the Knudsen regime in terms
of a complex dynamical reflection process. By means of molecular dynamics
simulation we emphasize the asymptotic nature of the cosine law of reflection
at the atomic scale, and carefully analyze the resulting strong correlations in
the reflection events. A dynamical interpretation of the accomodation
coefficient associated to the slip at the wall interface is also proposed.
Finally, we show that the first two moments of the stochastic process of
reflection non uniformly depend on the incident angle
Design and Use of a Large-Scale Liquid Helium Conversion System
A large-scale liquid helium (LHe) to high-pressure (HP) gas conversion system has been implemented at the John F. Kennedy Space Center (KSC). Helium is used by the Space Shuttle, Titan, Atlas, and Delta programs for prelaunch processing, during launch count-down, and for postlaunch securing. The first phase of modifications to the Compressor Converter Facility (CCF), operational in April 1998, allowed the facility to accept bulk liquid helium from tanker containers and to off-load the helium at super-critical pressures. The second phase of modifications, planned to be operational by January 2001, will implement a 227-cubic-meter (m(sup 3)) on-site liquid helium storage system. This paper describes the design and operation of the current system and discusses the design and implementation for the second phase system
Physical properties and morphology of a newly identified compact z=4.04 lensed submillimeter galaxy in Abell 2218
We present the identification of a bright submm source, SMMJ163555.5+661300,
detected in the lensing cluster Abell2218, for which we have accurately
determined the position using observations from the Submillimeter Array (SMA).
The identified optical counterpart has a spectroscopic redshift of
z=4.044+-0.001 if we attribute the single emission line detected at
lambda=6140AA to Lyman-alpha. This redshift identification is in good agreement
with the optical/near-infrared photometric redshift as well as the submm flux
ratio S_450/S_850~1.6, the radio-submm flux ratio S_1.4/S_850 < 0.004, and the
24um to 850um flux ratio S_24/S_850 < 0.005. Correcting for the gravitational
lensing amplification of ~5.5, we find that the source has a far-infrared
luminosity of 1.3x10^12 Lsun, which implies a star formation rate of 230
Msun/yr. This makes it the lowest-luminosity SMG known at z>4 to date. Previous
CO(4-3) emission line obserations yielded a non-detection, for which we derived
an upper limit of the CO line luminosity of L'_CO = 0.3x10^10 K km/s/pc^2,
which is not inconsistent with the L'_CO - L_FIR relation for starburst
galaxies. The best fit model to the optical and near-infrared photometry give a
stellar population with an age of 1.4 Gyr and a stellar mass of 1.6x10^10 Msun.
The optical morphology is compact and in the source plane the galaxy has an
extent of ~6kpc x 3kpc with individual star forming knots of <500 pc in size.
J163556 is not resolved in the SMA data and we place a strict upper limit on
the size of the starburst region of 8kpc x 3kpc, which implies a lower limit on
the star formation rate surface density of 12 Msun/yr/kpc^2. The redshift of
J163556 extends the redshift distribution of faint, lensed SMGs, and we find no
evidence that these have a different redshift distribution than bright SMGs.Comment: Accepted for publication in ApJ. 11 pages, 7 figure
New CO detections of lensed submillimeter galaxies in A2218: Probing molecular gas in the LIRG regime at high redshift
Context: Submillimeter galaxies (SMGs) are distant, dusty galaxies undergoing
star formation at prodigious rates. Recently there has been major progress in
understanding the nature of the bright SMGs (i.e. S(850um)>5mJy). The samples
for the fainter SMGs are small and are currently in a phase of being built up
through identification studies. Aims: We study the molecular gas content in two
SMGs, SMMJ163555 and SMMJ163541, at z=1.034 and z=3.187 with unlensed submm
fluxes of 0.4mJy and 6.0mJy. Both SMGs are gravitationally lensed by the
foreground cluster A2218. Methods: IRAM Plateau de Bure Interferometry
observations at 3mm were obtained for the lines CO(2-1) for SMMJ163555 and
CO(3-2) for SMMJ163541. Additionally we obtained CO(4-3) for the candidate
z=4.048 SMMJ163556 with an unlensed submm flux of 2.7mJy. Results: CO(2-1) was
detected for SMMJ163555 at z=1.0313 with an integrated line intensity of
1.2+-0.2Jy km/s and a line width of 410+-120 km/s. From this a gas mass of
1.6x10^9 Msun is derived and a star formation efficiency of 440Lsun/Msun is
estimated. CO(3-2) was detected for SMMJ163541 at z=3.1824, possibly with a
second component at z=3.1883, with an integrated line intensity of 1.0+-0.1 Jy
km/s and a line width of 280+-50 km/s. From this a gas mass of 2.2x10^10 Msun
is derived and a star formation efficiency of 1000 Lsun/Msun is estimated. For
SMMJ163556 the CO(4-3) is undetected within the redshift range 4.035-4.082 down
to a sensitivity of 0.15 Jy km/s. Conclusions: Our CO line observations confirm
the optical redshifts for SMMJ163555 and SMMJ163541. The CO line luminosity
L'_CO for both galaxies is consistent with the L_FIR-L'_CO relation. SMMJ163555
has the lowest FIR luminosity of all SMGs with a known redshift and is one of
the few high redshift LIRGs whose properties can be estimated prior to ALMA.Comment: 7 pages, 4 figures. A&A in pres
Economic, Neurobiological and Behavioral Perspectives on Building America's Future Workforce
A growing proportion of the U.S. workforce will have been raised in disadvantaged environments that are associated with relatively high proportions of individuals with diminished cognitive and social skills. A cross-disciplinary examination of research in economics, developmental psychology, and neurobiology reveals a striking convergence on a set of common principles that account for the potent effects of early environment on the capacity for human skill development. Central to these principles are the findings that early experiences have a uniquely powerful influence on the development of cognitive and social skills, as well as on brain architecture and neurochemistry; that both skill development and brain maturation are hierarchical processes in which higher level functions depend on, and build on, lower level functions; and that the capacity for change in the foundations of human skill development and neural circuitry is highest earlier in life and decreases over time. These findings lead to the conclusion that the most efficient strategy for strengthening the future workforce, both economically and neurobiologically, and for improving its quality of life is to invest in the environments of disadvantaged children during the early childhood years.
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