751 research outputs found
Constraining the Thermal Dust Content of Lyman-Break Galaxies in an Overdense Field at z~5
We have carried out 870 micron observations in the J1040.7-1155 field, known
to host an overdensity of Lyman break galaxies at z=5.16 +/- 0.05. We do not
detect any individual source at the S(870)=3.0 mJy/beam (2 sigma) level. A
stack of nine spectroscopically confirmed z>5 galaxies also yields a
non-detection, constraining the submillimeter flux from a typical galaxy at
this redshift to S(870)<0.85 mJy, which corresponds to a mass limit
M(dust)<1.2x10^8 M_sun (2 sigma). This constrains the mass of thermal dust in
distant Lyman break galaxies to less than one tenth of their typical stellar
mass. We see no evidence for strong submillimeter galaxies associated with the
ultraviolet-selected galaxy overdensity, but cannot rule out the presence of
fainter, less massive sources.Comment: 5 pages, 2 figures. MNRAS in pres
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Life in the Atacama — Year 2: Geologic reconnaissance through long-range roving and implications on the search for life
The Life in the Atacama-2004 project, which included geological, morphological, and mineralogical mapping through combined satellite, field-based, and microscopic perspectives and long-range roving, led to the localization of potential habitats
Mechanical control of the directional stepping dynamics of the kinesin motor
Among the multiple steps constituting the kinesin's mechanochemical cycle,
one of the most interesting events is observed when kinesins move an 8-nm step
from one microtubule (MT)-binding site to another. The stepping motion that
occurs within a relatively short time scale (~100 microsec) is, however, beyond
the resolution of current experiments, therefore a basic understanding to the
real-time dynamics within the 8-nm step is still lacking. For instance, the
rate of power stroke (or conformational change), that leads to the
undocked-to-docked transition of neck-linker, is not known, and the existence
of a substep during the 8-nm step still remains a controversial issue in the
kinesin community. By using explicit structures of the kinesin dimer and the MT
consisting of 13 protofilaments (PFs), we study the stepping dynamics with
varying rates of power stroke (kp). We estimate that 1/kp <~ 20 microsec to
avoid a substep in an averaged time trace. For a slow power stroke with 1/kp>20
microsec, the averaged time trace shows a substep that implies the existence of
a transient intermediate, which is reminiscent of a recent single molecule
experiment at high resolution. We identify the intermediate as a conformation
in which the tethered head is trapped in the sideway binding site of the
neighboring PF. We also find a partial unfolding (cracking) of the binding
motifs occurring at the transition state ensemble along the pathways prior to
binding between the kinesin and MT.Comment: 26 pages, 10 figure
Limits on dust emission from z~5 LBGs and their local environments
We present 1.2mm MAMBO-2 observations of a field which is over-dense in Lyman
Break Galaxies (LBGs) at z~5. The field includes seven
spectroscopically-confirmed LBGs contained within a narrow (z=4.95+/-0.08)
redshift range and an eighth at z=5.2. We do not detect any individual source
to a limit of 1.6 mJy/beam (2*rms). When stacking the flux from the positions
of all eight galaxies, we obtain a limit to the average 1.2 mm flux of these
sources of 0.6mJy/beam. This limit is consistent with FIR imaging in other
fields which are over-dense in UV-bright galaxies at z~5. Independently and
combined, these limits constrain the FIR luminosity (8-1000 micron) to a
typical z~5 LBG of LFIR<~3x10^11 Lsun, implying a dust mass of Mdust<~10^8 Msun
(both assuming a grey body at 30K). This LFIR limit is an order of magnitude
fainter than the LFIR of lower redshift sub-mm sources (z~1-3). We see no
emission from any other sources within the field at the above level. While this
is not unexpected given millimetre source counts, the clustered LBGs trace
significantly over-dense large scale structure in the field at z = 4.95. The
lack of any such detection in either this or the previous work, implies that
massive, obscured star-forming galaxies may not always trace the same
structures as over-densities of LBGs, at least on the length scale probed here.
We briefly discuss the implications of these results for future observations
with ALMA.Comment: 10 pages, 6 figures, MNRAS Accepte
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Spectroscopic results from the Life in the Atacama (LITA) project 2004 field season
Analysis of spectroscopy datasets from rover field tests in the Atacama Desert (Chile), focusing on the composition of the surface and identification of potential habitats for life
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Searching for life with rovers: exploration methods and science results from the 2004 field campaign of the “Life in the Atacama” project and applications to future Mars Missions
LITA develops and field tests a long-range automated rover and a science payload to search for microbial life in the Atacama. The Atacama's evolution provides a unique training ground for designing and testing exploration strategies and life detection methods for the search for life on Mars
Site investigation for the effects of vegetation on ground stability
The procedure for geotechnical site investigation is well established but little attention is currently given to investigating the potential of vegetation to assist with ground stability. This paper describes how routine investigation procedures may be adapted to consider the effects of the vegetation. It is recommended that the major part of the vegetation investigation is carried out, at relatively low cost, during the preliminary (desk) study phase of the investigation when there is maximum flexibility to take account of findings in the proposed design and construction. The techniques available for investigation of the effects of vegetation are reviewed and references provided for further consideration. As for general geotechnical investigation work, it is important that a balance of effort is maintained in the vegetation investigation between (a) site characterisation (defining and identifying the existing and proposed vegetation to suit the site and ground conditions), (b) testing (in-situ and laboratory testing of the vegetation and root systems to provide design parameters) and (c) modelling (to analyse the vegetation effects)
AzTEC Millimetre Survey of the COSMOS Field - II. Source Count Overdensity and Correlations with Large-Scale Structure
We report an over-density of bright sub-millimetre galaxies (SMGs) in the
0.15 sq. deg. AzTEC/COSMOS survey and a spatial correlation between the SMGs
and the optical-IR galaxy density at z <~ 1.1. This portion of the COSMOS field
shows a ~ 3-sigma over-density of robust SMG detections when compared to a
background, or "blankfield", population model that is consistent with SMG
surveys of fields with no extragalactic bias. The SMG over-density is most
significant in the number of very bright detections (14 sources with measured
fluxes S(1.1mm) > 6 mJy), which is entirely incompatible with sample variance
within our adopted blank-field number densities and infers an over-density
significance of >> 4. We find that the over-density and spatial correlation to
optical-IR galaxy density are most consistent with lensing of a background SMG
population by foreground mass structures along the line of sight, rather than
physical association of the SMGs with the z <~ 1.1 galaxies/clusters. The SMG
positions are only weakly correlated with weak-lensing maps, suggesting that
the dominant sources of correlation are individual galaxies and the more
tenuous structures in the region and not the massive and compact clusters.
These results highlight the important roles cosmic variance and large-scale
structure can play in the study of SMGs.Comment: 12 pages, 11 figures, 2 tables, accepted for publication in MNRA
Selection of ULIRGs in Infrared and Submm Surveys
We examine the selection characteristics of infrared and sub-mm surveys with
IRAS, Spitzer, BLAST, Herschel and SCUBA and identify the range of dust
temperatures these surveys are sensitive to, for galaxies in the ULIRG
luminosity range (12<log(LIR)<13), between z=0 and z=4. We find that the extent
of the redshift range over which surveys are unbiased is a function of the
wavelength of selection, flux density limit and ULIRG luminosity. Short
wavelength (<200{\mu}m) surveys with IRAS, Spitzer/MIPS and Herschel/PACS are
sensitive to all SED types in a large temperature interval (17-87K), over a
substantial fraction of their accessible redshift range. On the other hand,
long wavelength (>200{\mu}m) surveys with BLAST, Herschel/ SPIRE and SCUBA are
significantly more sensitive to cold ULIRGs, disfavouring warmer SEDs even at
low redshifts. We evaluate observations in the context of survey selection
effects, finding that the lack of cold ULIRGs in the local (z<0.1) Universe is
not a consequence of selection and that the range of ULIRG temperatures seen
locally is only a subset of a much larger range which exists at high redshift.
We demonstrate that the local luminosity-temperature (L-T) relation, which
indicates that more luminous sources are also hotter, is not applicable in the
distant Universe when extrapolated to the ULIRG regime, because the scatter in
observed temperatures is too large. Finally, we show that the difference
between the ULIRG temperature distributions locally and at high redshift is not
the result of galaxies becoming colder due to an L-T relation which evolves as
a function of redshift. Instead, they are consistent with a picture where the
evolution of the infrared luminosity function is temperature dependent, i.e.
cold galaxies evolve at a faster rate than their warm counterparts.Comment: 11 pages, 6 figures, accepted for publication in MNRA
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