1,552 research outputs found
The Tully-Fisher relation of distant field galaxies
We examine the evolution of the Tully-Fisher relation (TFR) using a sample of
89 field spirals, with 0.1 < z < 1, for which we have measured confident
rotation velocities (Vrot). By plotting the residuals from the local TFR versus
redshift, or alternatively fitting the TFR to our data in several redshift
bins, we find evidence that luminous spiral galaxies are increasingly offset
from the local TFR with redshift, reaching a brightening of -1.0+-0.5 mag, for
a given Vrot, by approximately z = 1. Since selection effects would generally
increase the fraction of intrinsically-bright galaxies at higher redshifts, we
argue that the observed evolution is probably an upper limit.
Previous studies have used an observed correlation between the TFR residuals
and Vrot to argue that low mass galaxies have evolved significantly more than
those with higher mass. However, we demonstrate that such a correlation may
exist purely due to an intrinsic coupling between the Vrot scatter and TFR
residuals, acting in combination with the TFR scatter and restrictions on the
magnitude range of the data, and therefore it does not necessarily indicate a
physical difference in the evolution of galaxies with different Vrot.
Finally, if we interpret the luminosity evolution derived from the TFR as due
to the evolution of the star formation rate (SFR) in these luminous spiral
galaxies, we find that SFR(z) is proportional to (1+z)^(1.7+-1.1), slower than
commonly derived for the overall field galaxy population. This suggests that
the rapid evolution in the SFR density of the universe observed since
approximately z = 1 is not driven by the evolution of the SFR in individual
bright spiral galaxies. (Abridged.)Comment: 14 pages, 10 figures, accepted by MNRA
Journal Staff
Electrical properties and strain gauge factor of Cr/SiOx cermet films with compositions 50/50 and 70/30 wt% were investigated in order to evaluate their use in strain gauge devices. The films were deposited by flash evaporation. The microstructures and resulting phases were characterized by electron diffraction and electron microscopy. The influence of the thickness and deposition rate on the sheet resistance, the temperature coefficient of resistance and the gauge factor were investigated. The results are consistent with a mixed conduction mechanism with metallic and a thermally activated tunneling components, between interconnected and discrete conductive phases, respectively.Se investigaron las propiedades eléctricas y el factor extensométrico de películas del cermet- Cr/SiOx en composiciones 50/50 y 70/30 % en peso, para evaluar su uso en dispositivos "strain gauge". Las películas fueron depositadas por evaporación "flash". Las estructuras y fases resultantes fueron caracterizadas por microscopía y difracción de electrones. Se estudió la influencia del espesor y la velocidad del depósito sobre la resistencia laminar, el coeficiente térmico de resistencia y el factor extensométrico. Los resultados son consistentes con un mecanismo de conducción mixto, con una componente metálica y otra por efecto túnel térmicamente activado, entre fases conductoras interconectadas y discretas, respectivamente
Morphology-dependent trends of galaxy age with environment in Abell 901/902 seen with COMBO-17
We investigate correlations between galaxy age and environment in the Abell
901/2 supercluster for separate morphologies. Using COMBO-17 data, we define a
sample of 530 galaxies, complete at on an area of (Mpc/). We explore several age indicators including an
extinction-corrected residual from the colour-magnitude relation (CMR). As a
result, we find a clear trend of age with density for galaxies of all
morphologies that include a spheroidal component, in the sense that galaxies in
denser environments are older. This trend is not seen among Scd/Irr galaxies
since they all have young ages. However, the trend among the other types is
stronger for fainter galaxies. While we also see an expected age-morphology
relation, we find no evidence for a morphology-density relation at fixed age.Comment: Accepted for publication in MNRAS (Letters
LGBT Employee Groups: Goals and Organizational Structures
The problem and the solution. Lesbian, gay, bisexual, and transgender (LGBT) employees oftentimes face isolation, difficult workplace climates, and inequitable benefits and policies. LGBT employee groups offer a space for social support and provide an organized platform from which employees can advocate for changes within their workplaces.We provide a social and historical background on LGBT employee groups and provide a framework/continuum for understanding different approaches to operating these groups.These groups vary in their organizational structures and in their goals. Groups can adopt emergent organizational styles or take more orderly and structured approaches to organizing. Goals for these groups include bringing broader social change and improving organizational effectiveness. These groups provide human resource development that benefits individuals, organizations, communities, and societies
What has an Impact on Grades? Instructor-Made Videos, Communication, and Timing in An Online Statistics Course
This study investigates student success in an online introductory statistics class. We examine the impact of several variables: amount of time that a student watches instructor-made videos (IMV), the nature of communication between the student and the instructor, and the amount of time spent on completing the online assignments and exams on student grades in an introductory level online statistics course. Findings suggest that IMVs of short dur ation, the subject- related communication between the student and the instructor, and homework completion time have significant association with student performance. Though the average time spent on online exams does not show a statistical association with student grades, the results indicate that the students who complete the exam between two-to-four hours perform better than the students who spend less than two hours or more than four hours to complete the exam
Flows and uses of diaspora remittances by receiving households in Guyana
Este artigo é baseado em um caso de método misto mais amplo sobre as potencialidades e os desafios da migração e remessas para a economia da Guiana. Dados para o estudo foram coletados por meio de questionários, entrevistas, discussões em grupo, arquivos, e observações (direta e participante). Este artigo centra-se especificamente sobre os fluxos e uso das remessas monetárias e não monetárias pelas famílias guianenses que as recebem. O estudo também confirma uma dependência significativa de remessas por parte das famílias para satisfazer as suas necessidades básicas, o que confirma ainda mais a vulnerabilidade da economia da Guiana para responder a choques da economia dos países dos quais as remessas são remetidas. Apesar destes fluxos e da dependência evidente das remessa por parte das famílias que as recebem, uma política, que vise maximizar os benefícios para as famílias e a economia, ainda está para ser elaborada e implantada. Além de fazer sugestões esse respeito, indica-se futuros estudos, com a finalidade de fortalecer as políticas e a literatura existente sobre o fluxo, o uso e o impacto das remessas nas famílias guianenses
LGBTQ Employee Groups: Who Are Th ey Good For? How Are They Organized?
LGBTQ employees seek workplace change through formal and informal groups. Some groups emphasize broader social change and others focus on organizational performance. We provide the social and historical background of these groups and provide a framework for understanding their goals and aims
Star formation rates and chemical abundances of emission line galaxies in intermediate-redshift clusters
We examine the evolutionary status of luminous, star-forming galaxies in
intermediate-redshift clusters by considering their star formation rates and
the chemical and ionsiation properties of their interstellar emitting gas. Our
sample consists of 17 massive, star-forming, mostly disk galaxies with
M_{B}<-20, in clusters with redshifts in the range 0.31< z <0.59, with a median
of =0.42. We compare these galaxies with the identically selected and
analysed intermediate-redshift field sample of Mouhcine et al. (2006), and with
local galaxies from the Nearby Field Galaxy Survey of Jansen et al. (2000).
From our optical spectra we measure the equivalent widths of OII, Hbeta and
OIII emission lines to determine diagnostic line ratios, oxygen abundances, and
extinction-corrected star formation rates. The star-forming galaxies in
intermediate-redshift clusters display emission line equivalent widths which
are, on average, significantly smaller than measured for field galaxies at
comparable redshifts. However, a contrasting fraction of our cluster galaxies
have equivalent widths similar to the highest observed in the field. This
tentatively suggests a bimodality in the star-formation rates per unit
luminosity for galaxies in distant clusters. We find no evidence for further
bimodalities, or differences between our cluster and field samples, when
examining additional diagnostics and the oxygen abundances of our galaxies.
This maybe because no such differences exist, perhaps because the cluster
galaxies which still display signs of star-formation have recently arrived from
the field. In order to examine this topic with more certainty, and to further
investigate the way in which any disparity varies as a function of cluster
properties, larger spectroscopic samples are needed.Comment: 10 pages, 6 figures, MNRAS in pres
Clustering of red Galaxies near the Radio-loud Quasar 1335.8+2834 at z=1.1
We have obtained new deep optical and near-infrared images of the field of
the radio-loud quasar 1335.8+2834 at where an excess in the surface
number density of galaxies was reported by Hutchings et al. [AJ, 106, 1324]
from optical data. We found a significant clustering of objects with very red
optical-near infrared colors, and near the quasar. The colors and magnitudes of the reddest objects
are consistent with those of old (12 Gyr old at z=0) passively-evolving
elliptical galaxies seen at , clearly defining a `red envelope' like
that found in galaxy clusters at similar or lower redshifts. This evidence
strongly suggests that the quasar resides in a moderately-rich cluster of
galaxies (richness-class ). There is also a relatively large fraction
of objects with moderately red colors () which have a
distribution on the sky similar to that of the reddest objects. They may be
interpreted as cluster galaxies with some recent or on-going star formation.Comment: 14 pages text, 5 PostScript figures, 1 GIF figure, and 1 combined PS
file. Accepted for ApJ, Letter
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