106 research outputs found
Testing the Peculiar Velocity Field predicted from Redshift Surveys
The reconstruction of the peculiar velocity field from the 1.936~Jy iras
selected sample of galaxies is compared to a similar reconstruction from an
optically selected sample. A general method for combining different samples to
reconstruct a self-consistent density and peculiar velocity field is presented.
The method is applied to determine how sensitive the derived peculiar velocity
field is to the characteristics of the sample used. The possibility that the
iras galaxies do not trace the general galaxy population is explored adopting a
simple model of linear biasing between the iras and optical samples. We find
that the velocity fields derived from the two samples are consistent, within
the estimated shot noise error, for the case of no relative bias. This result
suggests that the predicted peculiar velocity field based on iras samples is
not sensitive to the sampling properties of iras galaxies. Combined with
previous suggestion of a relative biasing of iras galaxies on small scales
(about 5 h^-1Mpc), this result suggests scale dependent biasing.Comment: tar-compressed and uudecoded postscript files, 12 pages+8 figure
Cluster vs. Field Elliptical Galaxies and Clues on their Formation
Using new observations for a sample of 931 early-type galaxies we investigate
whether the \mg2--\so relation shows any dependence on the local environment.
The galaxies have been assigned to three different environments depending on
the local overdensity: clusters, groups, and field, having used our
completeredshift database to guide the assignment of galaxies. It is found that
cluster, group and field early-type galaxies follow almost identical \mg2--\so\
relations, with the largest \mg2 zero-point difference (clusters minus field)
being only mag. No correlation of the residuals is found with
the morphological type or the bulge to disk ratio. Using stellar population
models in a differential fashion, this small zero-point difference implies a
luminosity-weighted age difference of only Gyr between the
corresponding stellar populations, with field galaxies being younger. The
mass-weighted age difference could be significantly smaller, if minor events of
late star formation took place preferentially in field galaxies. We combine
these results with the existing evidence for the bulk of stars in cluster
early-type galaxies having formed at very high redshift, and conclude that the
bulk of stars in galactic spheroids had to form at high redshifts (z\gsim 3),
no matter whether such spheroids now reside in low or high density regions. The
cosmological implications of these findings are briefly discussed.Comment: 16 pages, 2 figures, accepted for publication in the ApJ.
Line strengths of early-type galaxies
In this paper we present measurements of velocity dispersions and Lick
indices for 509 galaxies in the local Universe, based on high signal-to-noise,
long slit spectra obtained with the 1.52 m ESO telescope at La Silla. The
conversion of our measurements into the Lick/IDS system was carried out
following the general prescription of Worthey and Ottaviani 1997. Comparisons
of our measurements with those of other authors show, in general, good
agreement. We also examine the dependence between these indices (e.g., Hbeta,
Mg_2, Fe5270 and NaD) and the central velocity dispersion (sigma), and we find
that they are consistent with those previously reported in the literature.
Benefiting from the relatively large size of the sample, we are able to
investigate the dependence of these relations on morphology and environment,
here represented by the local galaxy density. We find that for metallic lines
these relations show no significant dependence on environment or morphology,
except in the case of NaD, which shows distinct behavior for E and S0. On the
other hand, the Hbeta-logsigma shows a significant difference as a function of
the local density of galaxies, which we interpret as being caused by the
truncation of star formation in high density environments. Comparing our
results with those obtained by other authors we find a few discrepancies,
adding to the ongoing debate about the nature of these relations. Finally, we
report that the scatter of the Mg indices versus sigma relations correlate with
Hbeta, suggesting that age may contribute to the scatter. Furthermore, this
scatter shows no significant dependence on morphology or environment. Our
results are consistent with the current downsizing model, where low mass
galaxies have an extended star formation history (abridged).Comment: 88 pages, 24 figures, to be published in AJ, for further information
see http://staff.on.br/ogand
Do observed metallicity gradients of early-type galaxies support a hybrid formation scenario?
We measure radial gradients of the Mg2 index in 15 E-E/S0 and 14 S0 galaxies.
Our homogeneous data set covers a large range of internal stellar velocity
dispersions (2.0<logsigma<2.5) and Mg2 gradients (dMg2/dlogr/re* up to
-0.14mag/dex). We find for the first time, a noticeable lower boundary in the
relation between Mg2 gradient and sigma along the full range of sigma, which
may be populated by galaxies predominantly formed by monolithic collapse. At
high sigma, galaxies showing flatter gradients could represent objects which
suffered either important merging episodes or later gas accretion. These
processes contribute to the flattening of the metallicity gradients and their
increasing importance could define the distribution of the objects above the
boundary expected by the ``classical'' monolithic process. This result is in
marked contrast with previous works which found a correlation between
dMg2/dlogr/re* and sigma confined to the low mass galaxies, suggesting that
only galaxies below some limiting sigma were formed by collapse whereas the
massive ones by mergers. We show observational evidence that a hybrid scenario
could arise also among massive galaxies. Finally, we estimated d[Z/H] from Mg2
and Hbeta measurements and single stellar population models. The conclusions
remain the same, indicating that the results cannot be ascribed to age effects
on Mg2.Comment: 11 pages, 2 figures, to appear in ApJLetter
Fundamental research questions in subterranean biology
Five decades ago, a landmark paper inSciencetitledThe Cave Environmentheralded caves as ideal natural experimental laboratories in which to develop and address general questions in geology, ecology, biogeography, and evolutionary biology. Although the 'caves as laboratory' paradigm has since been advocated by subterranean biologists, there are few examples of studies that successfully translated their results into general principles. The contemporary era of big data, modelling tools, and revolutionary advances in genetics and (meta)genomics provides an opportunity to revisit unresolved questions and challenges, as well as examine promising new avenues of research in subterranean biology. Accordingly, we have developed a roadmap to guide future research endeavours in subterranean biology by adapting a well-established methodology of 'horizon scanning' to identify the highest priority research questions across six subject areas. Based on the expert opinion of 30 scientists from around the globe with complementary expertise and of different academic ages, we assembled an initial list of 258 fundamental questions concentrating on macroecology and microbial ecology, adaptation, evolution, and conservation. Subsequently, through online surveys, 130 subterranean biologists with various backgrounds assisted us in reducing our list to 50 top-priority questions. These research questions are broad in scope and ready to be addressed in the next decade. We believe this exercise will stimulate research towards a deeper understanding of subterranean biology and foster hypothesis-driven studies likely to resonate broadly from the traditional boundaries of this field.Peer reviewe
Impure Public Goods and Technological Interdependencies
Impure public goods represent an important group of goods. Almost every public good exerts not only effects which are public to all but also effects which are private to the producer of this good. What is often omitted in the analysis of impure public goods is the fact that – regularly – these private effects can also be generated independently of the public good. In our analysis we focus on the effects alternative technologies – independently generating the private effects of the public good – may have on the provision of impure public goods. After the investigation in an analytical impure public good model, we numerically simulate the effects of alternative technologies in a parameterized model for climate policy in Germany
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