275 research outputs found
Rapid Star Formation in the Presence of Active Galactic Nuclei
Recent observations reveal galaxies in the early Universe (2<z<6.4) with
large reservoirs of molecular gas and extreme star formation rates. For a very
large range of sources, a tight relationship exists between star formation rate
and the luminosity of the HCN J=1-0 spectral line, but sources at redshifts of
z~2 and beyond do not follow this trend. The deficit in HCN is conventionally
explained by an excess of infrared (IR) radiation due to active galactic nuclei
(AGN). We show in this letter not only that the presence of AGN cannot account
for the excess of IR over molecular luminosity, but also that the observed
abundance of HCN is in fact consistent with a population of stars forming from
near-primordial gas.Comment: 4 pages, 1 figure. Accepted by the Astrophysical Journal Letter
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
The Ultraviolet Attenuation Law in Backlit Spiral Galaxies
(Abridged) The effective extinction law (attenuation behavior) in galaxies in
the emitted ultraviolet is well known only for actively star-forming objects
and combines effects of the grain properties, fine structure in the dust
distribution, and relative distributions of stars and dust. We use GALEX, XMM
Optical Monitor, and HST data to explore the UV attenuation in the outer parts
of spiral disks which are backlit by other UV-bright galaxies, starting with
candidates provided by Galaxy Zoo participants. Our analysis incorporates
galaxy symmetry, using non-overlapping regions of each galaxy to derive error
estimates on the attenuation measurements. The entire sample has an attenuation
law close to the Calzetti et al. (1994) form; the UV slope for the overall
sample is substantially shallower than found by Wild et al. (2011), a
reasonable match to the more distant galaxies in our sample but not to the
weighted combination including NGC 2207. The nearby, bright spiral NGC 2207
alone gives accuracy almost equal to the rest of our sample, and its outer arms
have a very low level of foreground starlight. This "grey" law can be produced
from the distribution of dust alone, without a necessary contribution from
differential escape of stars from dense clouds. The extrapolation needed to
compare attenution between backlit galaxies at moderate redshifts, and local
systems from SDSS data, is mild enough to allow use of galaxy overlaps to trace
the cosmic history of dust. For NGC 2207, the covering factor of clouds with
small optical attenuation becomes a dominant factor farther into the
ultraviolet, which opens the possibility that widespread diffuse dust dominates
over dust in star-forming regions deep into the ultraviolet. Comparison with
published radiative-transfer models indicates that the role of dust clumping
dominates over differences in grain populations, at this spatial resolution.Comment: In press, Astronomical Journa
Characterising Volunteers' Task Execution Patterns Across Projects on Multi-Project Citizen Science Platforms
Citizen science projects engage people in activities that are part of a
scientific research effort. On multi-project citizen science platforms,
scientists can create projects consisting of tasks. Volunteers, in turn,
participate in executing the project's tasks. Such type of platforms seeks to
connect volunteers and scientists' projects, adding value to both. However,
little is known about volunteer's cross-project engagement patterns and the
benefits of such patterns for scientists and volunteers. This work proposes a
Goal, Question, and Metric (GQM) approach to analyse volunteers' cross-project
task execution patterns and employs the Semiotic Inspection Method (SIM) to
analyse the communicability of the platform's cross-project features. In doing
so, it investigates what are the features of platforms to foster volunteers'
cross-project engagement, to what extent multi-project platforms facilitate the
attraction of volunteers to perform tasks in new projects, and to what extent
multi-project participation increases engagement on the platforms. Results from
analyses on real platforms show that volunteers tend to explore multiple
projects, but they perform tasks regularly in just a few of them; few projects
attract much attention from volunteers; volunteers recruited from other
projects on the platform tend to get more engaged than those recruited outside
the platform. System inspection shows that platforms still lack personalised
and explainable recommendations of projects and tasks. The findings are
translated into useful claims about how to design and manage multi-project
platforms.Comment: XVIII Brazilian Symposium on Human Factors in Computing Systems
(IHC'19), October 21-25, 2019, Vit\'oria, ES, Brazi
Galaxy Zoo: Morphological Classification and Citizen Science
We provide a brief overview of the Galaxy Zoo and Zooniverse projects,
including a short discussion of the history of, and motivation for, these
projects as well as reviewing the science these innovative internet-based
citizen science projects have produced so far. We briefly describe the method
of applying en-masse human pattern recognition capabilities to complex data in
data-intensive research. We also provide a discussion of the lessons learned
from developing and running these community--based projects including thoughts
on future applications of this methodology. This review is intended to give the
reader a quick and simple introduction to the Zooniverse.Comment: 11 pages, 1 figure; to be published in Advances in Machine Learning
and Data Mining for Astronom
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