266 research outputs found
Metallicity dependent calibrations of flux based SFR tracers
No full textWe present new calibrations of the widely used , , and UV luminosity vs. star
formation rate (SFR) relations. Using our evolutionary synthesis code GALEV we
compute the different calibrations for 5 metallicities, from 1/50 solar up to 2.5 solar. We find significant changes in the calibrations for lower
metallicities compared to the standard calibrations using solar input physics.
The Impact of Starbursts and Post-Starbursts on the Photometric Evolution of High Redshift Galaxies
No full textWe present evolutionary synthesis models for galaxies of spectral types Sa
through Sd with starbursts of various strengths triggered at various redshifts
and study their photometric evolution before, during, and after their bursts in
a cosmological context. We find that bursts at high redshift, even very strong
ones, only cause a small blueing of their intrinsically blue young parent
galaxies. At lower redshift, even small bursts cause a significant blueing of
their intrinsically redder galaxies. While the burst phase is generally short,
typically a few hundred Myr in normal-mass galaxies, the postburst stage with
its red colors and, in particular the very red ones for early bursts at high
redshift, is much longer, of the order of several Gyr. Even without any dust,
which in the postburst stage is not expected to play an important role anyway,
models easily reach the colors of EROs in the redshift range z=2 through z=0.5
after starbursts at redshifts between 2 and 4. We therefore propose a third
alternative for the ERO galaxies beyond the two established ones of passive
galaxies vs. dusty starbursts: the dust-free post-(strong-)starbursts. A very
first comparison of our models to HDF data with photometric redshifts shows
that almost all of the outliers that could not be described with our chemically
consistent models for undisturbed normal galaxy types E through Sd can now be
explained very well. Galaxies in the redshift range from z=2.5 to z=0.5 that
are redder, and in some cases much redder, than our reddest undisturbed model
for a high-metallicity classical elliptical are well described by
post-starburst models after starbursts at redshifts between 2 and 4. Galaxies
bluer than our bluest low metallicity Sd model, most of which have redshifts
lower than 1, are well explained by ongoing starbursts.Comment: 12 pages, accepted by Astron. & Astrophysics Nov. 17, 200
Evolutionary synthesis models for the formation of S0 galaxies in clusters
No full textRich galaxy clusters in the local Universe show a large population of S0 galaxies
(~40% of all luminous galaxies). With increasing redshift the fraction of this S0
galaxy population is observed to strongly decrease (e.g. by a factor ~ to
) in favor of the spiral galaxy fraction while the number of bright ellipticals
does not seem to change. The infalling field galaxy population that successively builds
up the cluster also is spiral rich and S0 poor. It has hence been suspected that galaxy
transformation processes, either due to galaxy – galaxy or to galaxy – ICM
interactions, are responsible for this change. Complementing dynamical and morphological
studies, we use evolutionary synthesis models describing various possible effects of
those interactions on the star formation rates of the infalling spirals. We study the
effects of starbursts of various strengths as well as of the truncation of star formation
on the color and luminosity evolution of model galaxies of various spectral types.
Comparison with observed properties of the local S0 galaxy population is used to
constrain possible S0 formation mechanisms. We find that star formation truncation
in spiral galaxies earlier than Sd-type, if occurring not too long ago, as well as
starbursts more than 3 Gyr ago and followed by complete star formation extinction in
spirals – again earlier than Sd– may well account for the observed average S0
luminosities and colors. Late-type galaxies (Sd), even after a strong burst, remain
either too blue or too faint. Our results are in agreement with studies of spectral
features of cluster S0s but allow for stronger constraints
Determination of enantiomerization barriers of hypericin and pseudohypericin by dynamic high-performance liquid chromatography on immobilized polysaccharide-type chiral stationary phases and off-column racemization experiments
No full textDirect enantiomer separation of hypericin, pseudohypericin, and protohypericin
was accomplished by high-performance liquid chromatography (HPLC) using
immobilized polysaccharide-type chiral stationary phases (CSPs). Enantioselectivities
up to 1.30 were obtained in the polar-organic elution mode whereby for hypericin and
pseudohypericin Chiralpak IC [chiral selector being cellulose tris(3,5-dichlorophenylcarbamate)]
and for protohypericin Chiralpak IA (chiral selector being the 3,5-dimethylphenylcarbamate
of amylose) gave favorable results. Enantiomers were distinguished by
on-line electronic circular dichroism detection. Optimized enantioselective chromatographic
conditions were the basis for determining stereodynamic parameters of the
enantiomer interconversion process of hypericin and pseudohypericin. Rate constants
delivered by computational simulation of dynamic HPLC elution profiles (stochastic
model, consideration of peak tailing) were used to calculate averaged enantiomerization
barriers (DG]
enant) of 97.6–99.6 kJ/mol for both compounds (investigated temperature
range 25–458C). Complementary variable temperature off-column (i.e., in solution) racemization
experiments delivered DG]
enant 5 97.1–98.0 kJ/mol (27–458C) for hypericin and
DG]
enant 5 98.9–101.4 kJ/mol (25–558C) for pseudohypericin. An activation enthalpy of
DH# 5 86.0 kJ/mol and an activation entropy of DS# 5 237.7 J/(K mol) were calculated
from hypericin racemization kinetics in solution, whereas for pseudohypericin these
figures amounted to 74.1 kJ/mol and 282.6 J/(K mol), respectively. Although the natural
phenanthroperylene quinone pigments hypericin and pseudohypericin as well as
their biological precursor protohypericin are chiral and can be separated by enantioselective
HPLC low enantiomerization barriers seem to prevent the occurrence of an
excess of one enantiomer under typical physiological conditions—at least as long as
stereoselective intermolecular interactions with other chiral entities are absen
Chemically Consistent Evolutionary Synthesis
No full textTo account for the range of stellar metallicities in local galaxies and for the increasing importance of low metallicities at higher redshift we present chemically consistent models for the spectral and chemical evolution of galaxies over cosmological timescales. We discuss advantages, limitations and future prospects of our approach
Chemically consistent evolution of galaxies II. Spectrophotometric evolution from zero to high redshift
No full textThe composite stellar populations of galaxies comprise stars of a
wide range of metallicities. Subsolar metallicities become increasingly
important, both in the local universe when going from early towards later galaxy
types as well as for dwarf galaxies and for all types of galaxies towards higher
redshifts.
We present a new generation of chemically consistent evolutionary synthesis models
for galaxies of various spectral types from E through Sd. The models follow the
chemical enrichment of the ISM and take into account the increasing initial
metallicity of successive stellar generations using recently published metallicity
dependent stellar evolutionary isochrones, spectra and yields.
Our first set of closed-box 1-zone models does not include any spatial resolution or
dynamics. For a Salpeter initial mass function (IMF) the star formation rate
(SFR) and its time evolution are shown to successfully parameterise spectral
galaxy types E, ..., Sd. We show how the stellar metallicity distribution in various
galaxy types build up with time to yield after ~12 Gyr agreement with stellar
metallicity distributions observed in our and other local galaxies.
The models give integrated galaxy spectra over a wide wavelength
range (90.9 Å–160 μm), which for ages of ~12 Gyr are in good
agreement not only with observed broad band colours but also with template
spectra for the respective galaxy types.
Using filter functions for Johnson-Cousins , IC, as well as
for HST broad band filters in the optical and Bessel & Brett's NIR J, H, K filter
system, we calculate the luminosity and colour evolution of model galaxies over a
Hubble time.
Including a standard cosmological model () and the
attenuation by intergalactic hydrogen we present evolutionary and cosmological
corrections as well as apparent luminosities in various filters over the redshift
range from to the present for our galaxy types and compare to earlier
models using single (=solar) metallicity input physics only. We also resent a first
comparison of our cc models to HDF data. A more detailed comparison with Hubble
Deep Field (HDF) and other deep field data and an analysis and interpretation of high
redshift galaxies in terms of ages, metallicities, star formation histories and,
galaxy types will be the subject of a forthcoming paper
Bicker, J. C. (Death, 1876-12-09)
No full textAddress: 111 McMicken Ave.Age at death: 63 yrsPg 213/1876/136/M W M/Germany/Dr. M. Kellar/J. Schreiber/Walnut HillsOriginal record filed in drawer labeled 'BETZER-BIERE'
The use of indigenous knowledge in development: problems and challenges
No full textThe use of indigenous knowledge has been seen by many as an alternative way of promoting development in poor rural communities in many parts of the world. By reviewing much of the recent work on indigenous knowledge, the paper suggests that a number of problems and tensions has resulted in indigenous knowledge not being as useful as hoped for or supposed. These include problems emanating from a focus on the (arte)factual; binary tensions between western science and indigenous knowledge systems; the problem of differentiation and power relations; the romanticization of indigenous knowledge; and the all too frequent decontextualization of indigenous knowledge
Bicker, Mary J. (Death, 1880-01-04)
No full textAddress: 106 Clay St.Age at death: 1 yrPg 1/1880/37/F W S/City/Dr. P. M. Bigney/Osseforth/St. John'sOriginal record filed in drawer labeled 'BETZER-BIERE'
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