2,444 research outputs found
The Las Campanas Infra-red Survey. V. Keck Spectroscopy of a large sample of Extremely Red Objects
(Abridged) We present deep Keck spectroscopy, using the DEIMOS and LRIS
spectrographs, of a large and representative sample of 67 ``Extremely Red
Objects'' (EROs) to H=20.5, with I-H>3.0, in three of the Las Campanas Infrared
Survey fields. Spectroscopic redshifts are determined for 44 sources, of which
only two are contaminating low mass stars. When allowance is made for
incompleteness, the spectroscopic redshift distribution closely matches that
predicted earlier on the basis of photometric data. Our spectra are of
sufficient quality that we can address the important question of the nature and
homogeneity of the z>0.8 ERO population. A dominant old stellar population is
inferred for 75% of our spectroscopic sample; a higher fraction than that seen
in smaller, less-complete samples with broader photometric selection criteria
(e.g. R-K). However, only 28% have spectra with no evidence of recent star
formation activity, such as would be expected for a strictly passively-evolving
population. More than ~30% of our absorption line spectra are of the `E+A' type
with prominent Balmer absorption consistent, on average, with mass growth of
5-15% in the past Gyr. We use our spectroscopic redshifts to improve earlier
estimates of the spatial clustering of this population as well as to understand
the significant field-to-field variation. Our spectroscopy enables us to
pinpoint a filamentary structure at z=1.22 in the Chandra Deep Field South.
Overall, our study suggests that the bulk of the ERO population is an
established population of clustered massive galaxies undergoing intermittent
activity consistent with continued growth over the redshift interval 0.8<z<1.6.Comment: 27 pages, including 14 figures and appendix of spectra (at low
resolution). Full resolution paper can be found at
http://www.ast.cam.ac.uk/~md . To appear in MNRA
The role of quenching time in the evolution of the mass-size relation of passive galaxies from the WISP survey
We analyze how passive galaxies at z 1.5 populate the mass-size plane
as a function of their stellar age, to understand if the observed size growth
with time can be explained with the appearance of larger quenched galaxies at
lower redshift. We use a sample of 32 passive galaxies extracted from the Wide
Field Camera 3 Infrared Spectroscopic Parallel (WISP) survey with spectroscopic
redshift 1.3 z 2.05, specific star-formation rates lower
than 0.01 Gyr, and stellar masses above 4.5 10
M. All galaxies have spectrally determined stellar ages from fitting of
their rest-frame optical spectra and photometry with stellar population models.
When dividing our sample into young (age 2.1 Gyr) and old (age 2.1
Gyr) galaxies we do not find a significant trend in the distributions of the
difference between the observed radius and the one predicted by the mass-size
relation. This result indicates that the relation between the galaxy age and
its distance from the mass-size relation, if it exists, is rather shallow, with
a slope alpha -0.6. At face value, this finding suggests that
multiple dry and/or wet minor mergers, rather than the appearance of newly
quenched galaxies, are mainly responsible for the observed time evolution of
the mass-size relation in passive galaxies.Comment: Accepted for publication in ApJ Letters; 6 pages, 3 figures, 1 tabl
Construction and measurements of a vacuum-swing-adsorption radon-mitigation system
Long-lived alpha and beta emitters in the Rn decay chain on (and
near) detector surfaces may be the limiting background in many experiments
attempting to detect dark matter or neutrinoless double-beta decay, and in
screening detectors. In order to reduce backgrounds from radon-daughter
plate-out onto the wires of the BetaCage during its assembly, an
ultra-low-radon cleanroom is being commissioned at Syracuse University using a
vacuum-swing-adsorption radon-mitigation system. The radon filter shows
~20 reduction at its output, from 7.470.56 to 0.370.12
Bq/m, and the cleanroom radon activity meets project requirements, with a
lowest achieved value consistent with that of the filter, and levels
consistently < 2 Bq/m.Comment: 5 pages, 3 figures, Proceedings of Low Radioactivity Techniques (LRT)
2013, Gran Sasso, Italy, April 10-12, 201
Potential energy and dipole moment surfaces of H3- molecule
A new potential energy surface for the electronic ground state of the
simplest triatomic anion H3- is determined for a large number of geometries.
Its accuracy is improved at short and large distances compared to previous
studies. The permanent dipole moment surface of the state is also computed for
the first time. Nine vibrational levels of H3- and fourteen levels of D3- are
obtained, bound by at most ~70 cm^{-1} and ~ 126 cm^{-1} respectively. These
results should guide the spectroscopic search of the H3- ion in cold gases
(below 100K) of molecular hydrogen in the presence of H3- ions
The BetaCage, an ultra-sensitive screener for surface contamination
Material screening for identifying low-energy electron emitters and
alpha-decaying isotopes is now a prerequisite for rare-event searches (e.g.,
dark-matter direct detection and neutrinoless double-beta decay) for which
surface radiocontamination has become an increasingly important background. The
BetaCage, a gaseous neon time-projection chamber, is a proposed ultra-sensitive
(and nondestructive) screener for alpha- and beta-emitting surface contaminants
to which existing screening facilities are insufficiently sensitive.
Sensitivity goals are 0.1 betas per keV-m-day and 0.1 alphas per m-day,
with the former limited by Compton scattering of photons in the screening
samples and (thanks to tracking) the latter expected to be signal-limited;
radioassays and simulations indicate backgrounds from detector materials and
radon daughters should be subdominant. We report on details of the background
simulations and detector design that provide the discrimination, shielding, and
radiopurity necessary to reach our sensitivity goals for a chamber with a
9595 cm sample area positioned below a 40 cm drift region and
monitored by crisscrossed anode and cathode planes consisting of 151 wires
each.Comment: 5 pages, 3 figures, Proceedings of Low Radioactivity Techniques (LRT)
2013, Gran Sasso, Italy, April 10-12, 201
A New Measurement of the Stellar Mass Density at z~5: Implications for the Sources of Cosmic Reionization
We present a new measurement of the integrated stellar mass per comoving
volume at redshift 5 determined via spectral energy fitting drawn from a sample
of 214 photometrically-selected galaxies with z'<26.5 in the southern GOODS
field. Following procedures introduced by Eyles et al. (2005), we estimate
stellar masses for various sub-samples for which reliable and unconfused
Spitzer IRAC detections are available. A spectroscopic sample of 14 of the most
luminous sources with =4.92 provides a firm lower limit to the stellar mass
density of 1e6 Msun/Mpc^3. Several galaxies in this sub-sample have masses of
order 10^11 Msun implying significant earlier activity occurred in massive
systems. We then consider a larger sample whose photometric redshifts in the
publicly-available GOODS-MUSIC catalog lie in the range 4.4 <z 5.6. Before
adopting the GOODS-MUSIC photometric redshifts, we check the accuracy of their
photometry and explore the possibility of contamination by low-z galaxies and
low-mass stars. After excising probable stellar contaminants and using the z'-J
color to exclude any remaining foreground red galaxies, we conclude that 196
sources are likely to be at z~5. The implied mass density from the unconfused
IRAC fraction of this sample, scaled to the total available, is 6e6 Msun/Mpc^3.
We discuss the uncertainties as well as the likelihood that we have
underestimated the true mass density. Including fainter and quiescent sources
the total integrated density could be as high as 1e7 Msun/Mpc^3. Using the
currently available (but highly uncertain) rate of decline in the star
formationhistory over 5 <z< 10, a better fit is obtained for the assembled mass
at z~5 if we admit significant dust extinction at early times or extend the
luminosity function to very faint limits. [abridged]Comment: Accepted for Publication in ApJ, 39 page
Evaluating Banking Websites Privacy Statements – A New Zealand Perspective on Ensuring Business Confidence
Because banks deal with highly personal detailed and sensitive information, they need to establish and maintain the confidence of their customers more assiduously than most other businesses. The rise of internet banking and the advantages to be gained from the garnering of personal data from websites places banks in a position to exploit customer data in a way that might infringe ethical considerations. This investigation analyses the website privacy statements of New Zealand banks in terms of the provisions of the New Zealand Privacy Act. The intention was to find an objective basis for the assessment of business integrity, to explore how confidence in electronic commerce can be assured. The investigation finds that the use of privacy legislation principles as a means of evaluating website privacy statements is revealing and convincing. It is considered that customer confidence will increasingly impact on Internet businesses, and business integrity as demonstrated by comprehensive and relevant privacy statements will go a long way to provide those assurances
- …