1,824 research outputs found
Unravelling the Mysteries of the Leo Ring: An Absorption Line Study of an Unusual Gas Cloud
Since the 1980's discovery of the large (2x10^9 Msun) intergalactic cloud
known as the Leo Ring, this object has been the center of a lively debate about
its origin. Determining the origin of this object is still important as we
develop a deeper understanding of the accretion and feedback processes that
shape galaxy evolution. We present HST/COS observations of three sightlines
near the Ring, two of which penetrate the high column density neutral hydrogen
gas visible in 21 cm observations of the object. These observations provide the
first direct measurement of the metallicity of the gas in the Ring, an
important clue to its origins. Our best estimate of the metallicity of the ring
is ~10% Zsun, higher than expected for primordial gas but lower than expected
from an interaction. We discuss possible modifications to the interaction and
primordial gas scenarios that would be consistent with this metallicity
measurement.Comment: 11 pages, 7 figures, accepted Ap
A prescriptive approach to qualify and quantify customer value for value-based requirements engineering
Recently, customer-based product development is becoming a popular paradigm. Customer expectations and needs can be identified and transformed into requirements for product design with the help of various methods and tools. However, in many cases, these models fail to focus on the perceived value that is crucial when customers make the decision of purchasing a product. In this paper, a prescriptive approach to support value-based requirements engineering (RE) is proposed, describing the foundations, procedures and initial applications in the context of RE for commercial aircraft. An integrated set of techniques, such as means-ends analysis, part-whole analysis and multi-attribute utility theory is introduced in order to understand customer values in depth and width. Technically, this enables identifying the implicit value, structuring logically collected statements of customer expectations and performing value modelling and simulation. Additionally, it helps to put in place a system to measure customer satisfaction that is derived from the proposed approach. The approach offers significant potential to develop effective value creation strategies for the development of new product
Note and Comment
Suits Against Trustee; Bills and Notes--Nonnegotiable Notes--Liability of Indorser; Bonds--Joint Stock Association--Negotiability; Carriers--Free Transportation as a Penalty; Carriers--Waiver of Stipulations as to Suits; Constitutional Law--Due Process of Law--Indeterminate Sentence Law; Constitutional Law--Corporations--Foreign Corporations--Exclusion For Removal of Cause to Federal Courts; Constitutional Law--Powers of Constitutional Convention; Criminal Law--Capital Offense--Bail--When Granted; Criminal Law--Murder--Elements of Murder; Damages--Action by Husband for Loss of Wife\u27s Services; Damages--Failure to Deliver Telegram--Mental Suffering--Near Relative; Deeds--Joinder of Infant Husband; Divorce--Temporary Alimony and Counsel Fees--Appeal--Decisions Reviewable; Equity--Sworn Answers as Evidence--Proof to Overcome; Evidence--Opinion Evidence in Action for Libel; Evidence--The Best Evidence Rule; Fraudulent Conveyances--Delivery and Change of Possession of Growing Crops; Garnishment--Exemption--Proceeds of Insurance; Infants--Disaffirming Deed--Ejectment; Judgment--Enjoining Execution on Dormant Judgment; Master and Servant--Liability of Master to Servant for Injury Due to Defective Machinery-
The Properties of Two Low Redshift O VI Absorbers and Their Associated Galaxies Toward 3C 263
Ultraviolet observations of the QSO 3C 263 (zem = 0.652) with COS and FUSE
reveal O VI absorption systems at z = 0.06342 and 0.14072 . WIYN multi-object
spectrograph observations provide information about the galaxies associated
with the absorbers. The multi-phase system at z = 0.06342 traces cool
photoionized gas and warm collisionally ionized gas associated with a L ~
0.31L* compact spiral emission line galaxy with an impact parameter of 63 kpc.
The cool photoionized gas in the absorber is well modeled with log U ~ -2.6,
log N(H) ~17.8, log n(H) ~ -3.3 and [Si/H] = -0.14\pm0.23. The collisionally
ionized gas containing C IV and O VI probably arises in cooling shock heated
transition temperature gas with log T ~ 5.5. The absorber is likely tracing
circumgalactic gas enriched by gas ejected from the spiral emission line
galaxy. The simple system at z = 0.14072 only contains O VI and broad and
narrow H I. The O VI with b = 33.4\pm11.9 km s-1 is likely associated with the
broad H I {\lambda}1215 absorption with b = 86.7\pm15.4 km s-1. The difference
in Doppler parameters implies the detection of a very large column of warm gas
with log T = 5.61(+0.16, -0.25), log N(H) = 19.54(+0.26, -0.44) and [O/H] =
-1.48 (+0.46, -0.26). This absorber is possibly associated with a 1.6L*
absorption line galaxy with an impact parameter of 617 kpc although an origin
in warm filament gas or in the halo of a fainter galaxy is more likely.Comment: Accepted by the Astrophysical Journal. 24 pages and 9 figure
Very Isolated Early-Type Galaxies
We use the Karachentseva (1973) ``Catalogue of Very Isolated Galaxies'' to
investigate a candidate list of >100 very isolated early-type galaxies.
Broad-band imaging and low resolution spectroscopy are available for a large
fraction of these candidates and result in a sample of 102 very isolated
early-type galaxies, including 65 ellipticals and 37 S0 galaxies. Many of these
systems are quite luminous and the resulting optical luminosity functions of
the Es and early-types (E+S0s) show no statistical differences when compared to
luminosity functions dominated by group and cluster galaxies. However, whereas
S0s outnumber Es 4:1 in the CfA survey, isolated Es outnumber S0s by nearly
2:1. We conclude that very isolated elliptical galaxies show no evidence for a
different formation and/or evolution process compared to Es formed in groups or
clusters, but that most S0s are formed by a mechanism (e.g., gas stripping)
that occurs only in groups and rich clusters. Our luminosity function results
for ellipticals are consistent with very isolated ellipticals being formed by
merger events, in which no companions remain.
CHANDRA observations were proposed to test specifically the merger hypothesis
for isolated ellipticals. However, this program has resulted in the observation
of only one isolated early-type galaxy, the S0 KIG 284, which was not detected
at a limit well below that expected for a remnant group of galaxies. Therefore,
the hypothesis remains untested that very isolated elliptical galaxies are the
remains of a compact group of galaxies which completely merged.Comment: 19 pages, 3 figures; AJ in pres
A z=0.9 supercluster of X-ray luminous, optically-selected, massive galaxy clusters
We report the discovery of a compact supercluster structure at z=0.9. The
structure comprises three optically-selected clusters, all of which are
detected in X-rays and spectroscopically confirmed to lie at the same redshift.
The Chandra X-ray temperatures imply individual masses of ~5x10^14 Msun. The
X-ray masses are consistent with those inferred from optical--X-ray scaling
relations established at lower redshift. A strongly-lensed z~4 Lyman break
galaxy behind one of the clusters allows a strong-lensing mass to be estimated
for this cluster, which is in good agreement with the X-ray measurement.
Optical spectroscopy of this cluster gives a dynamical mass in good agreement
with the other independent mass estimates. The three components of the
RCS2319+00 supercluster are separated from their nearest neighbor by a mere <3
Mpc in the plane of the sky and likely <10 Mpc along the line-of-sight, and we
interpret this structure as the high-redshift antecedent of massive (~10^15
Msun) z~0.5 clusters such as MS0451.5-0305.Comment: ApJ Letters accepted. 5 pages in emulateapj, 3 figure
The Cosmic Background Imager
Design and performance details are given for the Cosmic Background Imager
(CBI), an interferometer array that is measuring the power spectrum of
fluctuations in the cosmic microwave background radiation (CMBR) for multipoles
in the range 400 < l < 3500. The CBI is located at an altitude of 5000 m in the
Atacama Desert in northern Chile. It is a planar synthesis array with 13 0.9-m
diameter antennas on a 6-m diameter tracking platform. Each antenna has a
cooled, low-noise receiver operating in the 26-36 GHz band. Signals are
cross-correlated in an analog filterbank correlator with ten 1 GHz bands. This
allows spectral index measurements which can be used to distinguish CMBR
signals from diffuse galactic foregrounds. A 1.2 kHz 180-deg phase switching
scheme is used to reject cross-talk and low-frequency pick-up in the signal
processing system. The CBI has a 3-axis mount which allows the tracking
platform to be rotated about the optical axis, providing improved (u,v)
coverage and a powerful discriminant against false signals generated in the
receiving electronics. Rotating the tracking platform also permits polarization
measurements when some of the antennas are configured for the orthogonal
polarization.Comment: 14 pages. Accepted for publication in PASP. See also
http://www.astro.caltech.edu/~tjp/CBI
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