6,862 research outputs found
Mapping Mass in the Local Universe
We only see a small fraction of the matter in the universe, but the rest
gives itself away by the impact of its gravity. Peculiar velocities have the
potential to be a powerful tool to trace this matter however previous peculiar
velocity surveys have struggled to meet their potential because of the large
errors on individual measurements, poor statistics and uneven sky coverage. The
2MASS Tully-Fisher (2MTF) survey will make use of existing high quality
rotations widths, new HI widths and 2MASS (2 Micron All-Sky Survey) photometry
to measure Tully-Fisher distances/peculiar velocities for all bright inclined
spirals in the 2MASS redshift survey (2MRS). This survey based on the 2MASS
galaxy catalog will provide a qualitatively better sample. It will provide
significant improvements in sky coverage especially near the plane of our
Galaxy which crosses the poorly understood "great attractor" region. I will
give a progress report on the 2MTF survey including a look at over 300 hours of
HI observations from the Green Bank Telescope (GBT) and a report on ongoing
southern hemisphere observations with the Parke s Radio Telescope. The new
spiral I-band field (SFI++) sample is currently the best available peculiar
velocity survey for use in the local universe. I will also report on some
preliminary results from this sample.Comment: To appear in ASP Conference Series as proceedings of NRAO 50th
Anniversary Symposium, "Frontiers of Astrophysics", June 18-21, 2007, A.
Bridle, J. Condon and G. Hunt eds. 10 pages including 4 figure
A Zoo of Galaxies
We live in a universe filled with galaxies with an amazing variety of sizes
and shapes. One of the biggest challenges for astronomers working in this field
is to understand how all these types relate to each other in the background of
an expanding universe. Modern astronomical surveys (like the Sloan Digital Sky
Survey) have revolutionised this field of astronomy, by providing vast numbers
of galaxies to study. The sheer size of the these databases made traditional
visual classification of the types galaxies impossible and in 2007 inspired the
Galaxy Zoo project (www.galaxyzoo.org); starting the largest ever scientific
collaboration by asking members of the public to help classify galaxies by type
and shape. Galaxy Zoo has since shown itself, in a series of now more than 30
scientific papers, to be a fantastic database for the study of galaxy
evolution. In this Invited Discourse I spoke a little about the historical
background of our understanding of what galaxies are, of galaxy classification,
about our modern view of galaxies in the era of large surveys. I finish with
showcasing some of the contributions galaxy classifications from the Galaxy Zoo
project are making to our understanding of galaxy evolution.
This publication has been made possible by the participation of more than
200,000 volunteers in the Galaxy Zoo project. Their contributions are
individually acknowledged at http://www.galaxyzoo.org/volunteers. KLM
acknowledges funding from the Peter and Patricia Gruber Foundation as the 2008
Peter and Patricia Gruber Foundation IAU Fellow, and from a 2010 Leverhulme
Trust Early Career Fellowship, as well as support from the Royal Astronomical
Society to attend the 28th GA of the IAU.Comment: 15 pages, 8 figures. Proceedings of Invited Discourse at the 27th IAU
General Assembly, in Beijing, China, August 2012. To appear in Highlights of
Astronomy, Volume 1
SFI++ II: A New I-band Tully-Fisher Catalog, Derivation of Peculiar Velocities and Dataset Properties
We present the SFI++ dataset, a homogeneously derived catalog of photometric
and rotational properties and the Tully-Fisher distances and peculiar
velocities derived from them. We make use of digital optical images, optical
long-slit spectra, and global HI line profiles to extract parameters of
relevance to disk scaling relations, incorporating several previously published
datasets as well as a new photometric sample of some 2000 objects. According to
the completeness of available redshift samples over the sky area, we exploit
both a modified percolation algorithm and the Voronoi-Delaunay method to assign
individual galaxies to groups as well as clusters, thereby reducing scatter
introduced by local orbital motions. We also provide corrections to the
peculiar velocities for both homogeneous and inhomogeneous Malmquist bias,
making use of the 2MASS Redshift Survey density field to approximate large
scale structure. We summarize the sample selection criteria, corrections made
to raw observational parameters, the grouping techniques, and our procedure for
deriving peculiar velocities. The final SFI++ peculiar velocity catalog of 4861
field and cluster galaxies is large enough to permit the study not just of the
global statistics of large scale flows but also of the {\it details} of the
local velocity field.Comment: 14 pages, 6 figures, 4 external online tables, accepted for
publication in ApJ
The Impact of Distance Uncertainties on Local Luminosity and Mass Functions
In order to investigate discrepancies between recent published estimates of
the the HI mass function (HIMF), we explore the impact of distance
uncertainties on the derivation of the faint end slope of mass and luminosity
functions of galaxies in the local volume by deriving HIMFs from mock HI
surveys. We consider various survey geometries and depths and compare the HIMFs
measured when using ``real'' distances, distances derived by assuming pure
Hubble flow and distances assigned from parametric models of the local velocity
field. The effect is variable and dependent on the exact survey geometry, but
can easily lead to incorrect estimates of the HIMF, particularly at the low
mass end. We show that at least part of the discrepancies among recent
derivations of the HIMF can be accounted for by the use of different methods to
assign distances. We conclude that a better understanding of the local velocity
field will be necessary for accurate determinations of the local galaxy
luminosity and mass functions.Comment: 4 pages, accepted to ApJ
Global MHD Simulations of Neptune's Magnetosphere
A global magnetohydrodynamic (MHD) simulation has been performed in order to investigate the outer boundaries of Neptune's magnetosphere at the time of Voyager 2's flyby in 1989 and to better understand the dynamics of magnetospheres formed by highly inclined planetary dipoles. Using the MHD code Gorgon, we have implemented a precessing dipole to mimic Neptune's tilted magnetic field and rotation axes. By using the solar wind parameters measured by Voyager 2, the simulation is verified by finding good agreement with Voyager 2 magnetometer observations. Overall, there is a large-scale reconfiguration of magnetic topology and plasma distribution. During the “pole-on” magnetospheric configuration, there only exists one tail current sheet, contained between a rarefied lobe region which extends outward from the dayside cusp, and a lobe region attached to the nightside cusp. It is found that the tail current always closes to the magnetopause current system, rather than closing in on itself, as suggested by other models. The bow shock position and shape is found to be dependent on Neptune's daily rotation, with maximum standoff being during the pole-on case. Reconnection is found on the magnetopause but is highly modulated by the interplanetary magnetic field (IMF) and time of day, turning “off” and “on” when the magnetic shear between the IMF and planetary fields is large enough. The simulation shows that the most likely location for reconnection to occur during Voyager 2's flyby was far from the spacecraft trajectory, which may explain the relative lack of associated signatures in the observations
The Elliptical Galaxy formerly known as the Local Group: Merging the Globular Cluster Systems
Prompted by a new catalogue of M31 globular clusters, we have collected
together individual metallicity values for globular clusters in the Local
Group. Although we briefly describe the globular cluster systems of the
individual Local Group galaxies, the main thrust of our paper is to examine the
collective properties. In this way we are simulating the dissipationless merger
of the Local Group, into presumably an elliptical galaxy. Such a merger is
dominated by the Milky Way and M31, which appear to be fairly typical examples
of globular cluster systems of spiral galaxies.
The Local Group `Elliptical' has about 700 +/- 125 globular clusters, with a
luminosity function resembling the `universal' one. The metallicity
distribution has peaks at [Fe/H] ~ -1.55 and -0.64 with a metal-poor to
metal-rich ratio of 2.5:1. The specific frequency of the Local Group Elliptical
is initially about 1 but rises to about 3, when the young stellar populations
fade and the galaxy resembles an old elliptical. The metallicity distribution
and stellar population corrected specific frequency are similar to that of some
known early type galaxies. Based on our results, we briefly speculate on the
origin of globular cluster systems in galaxies.Comment: 22 pages, Latex, 4 figures, 5 tables, submitted to A &
SFI++ I: A New I-band Tully-Fisher Template, the Cluster Peculiar Velocity Dispersion and H0
The SFI++ consists of ~5000 spiral galaxies which have measurements suitable
for the application of the I-band Tully-Fisher (TF) relation. This sample
builds on the SCI and SFI samples published in the 1990s but includes
significant amounts of new data as well as improved methods for parameter
determination. We derive a new I-band TF relation from a subset of this sample
which consists of 807 galaxies in the fields of 31 nearby clusters and groups.
This sample constitutes the largest ever available for the calibration of the
TF template and extends the range of line-widths over which the template is
reliably measured. Careful accounting is made of observational and sample
biases such as incompleteness, finite cluster size, galaxy morphology and
environment. We find evidence for a type-dependent TF slope which is shallower
for early type than for late type spirals. The line-of-sight cluster peculiar
velocity dispersion is measured for the sample of 31 clusters. This value is
directly related to the spectrum of initial density fluctuations and thus
provides an independent verification of the best fit WMAP cosmology and an
estimate of Omega^0.6 sigma_8 = 0.52+/-0.06. We also provide an independent
measure of the TF zeropoint using 17 galaxies in the SFI++ sample for which
Cepheid distances are available. In combination with the ``basket of clusters''
template relation these calibrator galaxies provide a measure of H0 = 74+/-2
(random) +/-6 (systematic) km/s/Mpc.Comment: Accepted by ApJ (scheduled for 20 Dec 2006, issue 653). 21 pages (2
column emulateapj) including 12 figures. Version 2 corrects typos and other
small errors noticed in proof
Art Therapy and Art History Theories, an Inquiry
This research uses critical theory inquiry with interviews and arts-based research to explore biases about art making in clinical art therapy practice. The literature review establishes an historical link between theoretical tenets in fields of art therapy and art history. Participants are chosen from experts in the fields of art therapy and art history. Interviews explore what art making means to each participant, utilizing both verbal and arts-based processing. The data is condensed through coding and arts-based reflection, and seven emergent themes are identified. The themes are checked with the participants for accuracy. The findings of the paper integrate the insight from the literature review with the expressed views of the participants to illuminate meaning-making processes of art. The paper concludes with identification of an “art historical lens” for practicing art therapy and discussion of treatment considerations, limitations of the study, and suggestions for further research
Encounters beyond the interface: Data structures, material feminisms, and composition
This dissertation argues that data literacy should be taught in college writing classes along with other new media literacies. Drawing from several areas of study, this dissertation establishes a definition of data literacy, introduces a feminist methodological approach to Big Data and data studies, and makes a case for teaching data literacy in first year composition and professional writing courses as a foundational writing-related literacy. Information written into and read from databases supports research activities in any number of fields from STEM to the humanities; while different disciplines approach databases and data structures from diverse perspectives, all students need foundational data literacies.
Nearly all digital environments are facilitated in some way by databases. They drive a range of web applications in ways that most users do not realize. On the surface, only GUIs are visible, and sets of data could be presented in any number of ways through them in the form of visuals, texts, and sound. It is important that students learn how data structures influence what comes across in the interface. By having students rhetorically analyze databases and then create them, composition teachers can help to demystify these ubiquitous yet invisible technocultural objects. Becoming aware of data structures gives students insight into how digital compositions emerge, empowering them to be more than “users” or “subjects” that use technological “objects.” Ideally, they would gain insight into how both “sides” of this encounter arise in dependence on many contributing factors, such as the standards, classifications, and categories perpetuated by techno-cultural infrastructures.
Developing a socio-ontological methodology that combines scholarship in both feminist new materialisms and feminist rhetorical methodologies, this dissertation discusses the importance of researcher positionality. The socio-ontological methodology developed here expands on social constructivist theories to view all participants in a situation, including non-human ones, as mutually existing in dependence upon each other. Within this framework, contemplative mapping helps to articulate how the researcher does not exist outside of the research situation and assists in helping to make the situation uncanny, so that we can question assumptions and think through processes.
Providing a foundational understanding of why data structures have become important to our professional and personal lives, this dissertation explains the public fascination with Big Data and exposes the ways that individuals can be affected by data collection practices, examining how the data structures that enable what comes across in user interfaces can be understood and taught in the context of writing studies
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