3,402 research outputs found
Stellar Motion around Spiral Arms: Gaia Mock Data
We compare the stellar motion around a spiral arm created in two different
scenarios, transient/co-rotating spiral arms and density-wave-like spiral arms.
We generate Gaia mock data from snapshots of the simulations following these
two scenarios using our stellar population code, SNAPDRAGONS, which takes into
account dust extinction and the expected Gaia errors. We compare the observed
rotation velocity around a spiral arm similar in position to the Perseus arm,
and find that there is a clear difference in the velocity features around the
spiral arm between the co-rotating spiral arm and the density-wave-like spiral
arm. Our result demonstrates that the volume and accuracy of the Gaia data are
sufficient to clearly distinguish these two scenarios of the spiral arms.Comment: 5 pages, 1 figure, to appear in the proceedings of "The Milky Way
Unravelled by Gaia: GREAT Science from the Gaia Data Releases", Barcelona,
1-5 December 2014, eds. N. Walton, F. Figueras, C. Soubira
Faraday rotation maps of disk galaxies
Faraday rotation is one of the most widely used observables to infer the
strength and configuration of the magnetic field in the ionised gas of the
Milky Way and nearby spiral galaxies. Here we compute synthetic Faraday
rotation maps at for a set of disk galaxies from the Auriga
high-resolution cosmological simulations, for different observer positions
within and outside the galaxy. We find that the strength of the Faraday
rotation of our simulated galaxies for a hypothetic observer at the solar
circle is broadly consistent with the Faraday rotation seen for the Milky Way.
The same holds for an observer outside the galaxy and the observed signal of
the nearby spiral galaxy M51. However, we also find that the structure and
angular power spectra of the synthetic all-sky Faraday rotation maps vary
strongly with azimuthal position along the solar circle. We argue that this
variation is a result of the structure of the magnetic field of the galaxy that
is dominated by an azimuthal magnetic field ordered scales of several kpc, but
has radial and vertical magnetic field components that are only ordered on
scales of 1-2 kpc. Because the magnetic field strength decreases exponentially
with height above the disk, the Faraday rotation for an observer at the solar
circle is dominated by the local environment. This represents a severe obstacle
for attempts to reconstruct the global magnetic field of the Milky Way from
Faraday rotation maps alone without including additional observables.Comment: 10 pages, 10 figures, accepted by MNRA
Can we really pick and choose? Benchmarking various selections of Gaia Enceladus/Sausage stars in observations with simulations
Large spectroscopic surveys plus Gaia astrometry have shown us that the inner stellar halo of the Galaxy is dominated by the debris of Gaia Enceladus/Sausage (GES). With the richness of data at hand, there are a myriad of ways these accreted stars have been selected. We investigate these GES selections and their effects on the inferred progenitor properties using data constructed from APOGEE and Gaia. We explore selections made in eccentricity, energy-angular momentum (E-Lz), radial action-angular momentum (Jr-Lz), action diamond, and [Mg/Mn]-[Al/Fe] in the observations, selecting between 144 and 1279 GES stars with varying contamination from in-situ and other accreted stars. We also use the Auriga cosmological hydrodynamic simulations to benchmark the different GES dynamical selections. Applying the same observational GES cuts to nine Auriga galaxies with a GES, we find that the Jr-Lz method is best for sample purity and the eccentricity method for completeness. Given the average metallicity of GES (â1.28 < [Fe/H] < â1.18), we use the z = 0 massâmetallicity relationship to find an average of âŒ4 Ă 108âMâ. We adopt a similar procedure and derive for the GES-like systems in Auriga and find that the eccentricity method overestimates the true by âŒ2.6 Ă while E-Lz underestimates by âŒ0.7 Ă. Lastly, we estimate the total mass of GES to be using the relationship between the metallicity gradient and the GES-to-in-situ energy ratio. In the end, we cannot just âpick and chooseâ how we select GES stars, and instead should be motivated by the science question
Can we really pick and choose? Benchmarking various selections of Gaia Enceladus/Sausage stars in observations with simulations
Large spectroscopic surveys plus Gaia astrometry have shown us that the inner
stellar halo of the Galaxy is dominated by the debris of Gaia Enceladus/Sausage
(GES). With the richness of data at hand, there are a myriad of ways these
accreted stars have been selected. We investigate these GES selections and
their effects on the inferred progenitor properties using data constructed from
APOGEE and Gaia. We explore selections made in eccentricity, energy-angular
momentum (E-Lz), radial action-angular momentum (Jr-Lz), action diamond, and
[Mg/Mn]-[Al/Fe] in the observations, selecting between 144 and 1,279 GES stars
with varying contamination from in-situ and other accreted stars. We also use
the Auriga cosmological hydrodynamic simulations to benchmark the different GES
dynamical selections. Applying the same observational GES cuts to nine Auriga
galaxies with a GES, we find that the Jr-Lz method is best for sample purity
and the eccentricity method for completeness. Given the average metallicity of
GES (-1.28 < [Fe/H] < -1.18), we use the mass-metallicity relationship to
find an average of . We
adopt a similar procedure and derive for the GES-like systems
in Auriga and find that the eccentricity method overestimates the true by while E-Lz underestimates by .
Lastly, we estimate the total mass of GES to be using the relationship between the metallicity gradient and
the GES-to-in-situ energy ratio. In the end, we cannot just `pick and choose'
how we select GES stars, and instead should be motivated by the science
question.Comment: 20 pages, 14 figures, submitted to MNRA
Economics of education research: a review and future prospects
In this paper we offer an appraisal of the economics of education research area, charting its history as a field and discussing the ways in which economists have contributed both to education research and to education policy-making. In particular, we highlight the theoretical and methodological contributions that economists have made to the field of education during the last 50 years. Despite the success of the economics of education as a field of inquiry, we argue that some of the contributions made by economists could be limited if the economics of education is seen as quite distinct from the other disciplines working in the field of education. In these areas of common interest, economists need to work side by side with the other major disciplines in the field of education if their contribution to the field is to be maximised, particularly in terms of applying improved methodology. We conclude that the study of education acquisition and its economic and social impact in the economics of education research area is very likely to remain a fertile research ground. Acknowledgement
Healthcare choice: Discourses, perceptions, experiences and practices
Policy discourse shaped by neoliberal ideology, with its emphasis on marketisation and competition, has highlighted the importance of choice in the context of healthcare and health systems globally. Yet, evidence about how so-called consumers perceive and experience healthcare choice is in short supply and limited to specific healthcare systems, primarily in the Global North. This special issue aims to explore how choice is perceived and utilised in the context of different systems of healthcare throughout the world, where choice, at least in policy and organisational terms, has been embedded for some time. The articles are divided into those emphasising: embodiment and the meaning of choice; social processes associated with choice; the uncertainties, risks and trust involved in making choices; and issues of access and inequality associated with enacting choice. These sociological studies reveal complexities not always captured in policy discourse and suggest that the commodification of healthcare is particularly problematic
Rethinking place and the social work office in the delivery of children's social work services
Limited attention has been given to the concept of place in social work research and practice. This paper draws on the national evaluation of social work practices (SWPs) in England undertaken between 2009 and 2012. SWPs were pilot organisations providing independent social work services for children in out-of-home care in five sites. One factor distinguishing some of these pilots was their attention to place. The evaluation employed a mixed methods approach and we use data from interviews with 121 children and young people in out-of-home care, 19 birth parents and 31 interviews with SWP staff which explored their views and experiences of the SWP offices. Children and young people
were alert to the stigma which could attach to social work premises and appreciated offices which were planned and furnished to appear less institutional and more ânormalâ. Daily interactions with staff which conveyed a sense of recognition and value to service users also contributed to a view of some SWP offices as accessible and welcoming places. Both children and parents appreciated offices that provided fun activities that positioned them as active rather than passive. Staff valued opportunities for influencing planning decisions about offices and place
was seen to confer a value on them as well as on service users. However, not all the SWPs were able to achieve these aspects of place, and engaging children and families in place was less likely when the service user population was widely dispersed. Recognising the importance of place and how place is constructed through relationships between people as well as through the physical environment appeared to be key to creating offices that combated the stigma attached to out-of-home care.
Those leading and managing childrenâs services should explore ways of involving local communities in planning social work offices and turn attention to making these offices accessible, welcoming, places
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