600 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
Women of the Future in the Royal Astronomical Society
In this article we wonder what the next 100 years will bring for women in
astronomy in the UK. After this year of looking back and celebrating 100 years
of women in the Royal Astronomical Society (RAS), we now ask: what might the
future hold? Extrapolating current trends, when might we expect equality in the
genders of RAS members, speakers at meetings, award winners and more?
Ultimately, when might we stop needing to talk about women in astronomy at all
- when it will be as irrelevant to the conversation about astronomy as being a
male astronomer is?Comment: 5 pages, invited article in Astronom & Geophysics, 57 (2016
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
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 &
Morphology in the Era of Large Surveys
The study of galaxies has changed dramatically over the past few decades with
the advent of large-scale astronomical surveys. These large collaborative
efforts have made available high-quality imaging and spectroscopy of hundreds
of thousands of systems, providing a body of observations which has
significantly enhanced our understanding not only of cosmology and large-scale
structure in the universe but also of the astrophysics of galaxy formation and
evolution. Throughout these changes, one thing that has remained constant is
the role of galaxy morphology as a clue to understanding galaxies. But
obtaining morphologies for large numbers of galaxies is challenging; this
topic, "Morphology in the era of large surveys", was the subject of a recent
discussion meeting at the Royal Astronomical Society, and this "Astronomy and
Geophysics" article is a report on that meeting.Comment: Meeting Report article published in the October 2013 issue of the
Royal Astronomical Society journal Astronomy and Geophysics. 4 page pdf with
colour image
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
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