1,055 research outputs found
A Stellar Population Gradient in VII Zw 403 - Implications for the Formation of Blue Compact Dwarf Galaxies
We present evidence for the existence of an old stellar halo in the Blue
Compact Dwarf galaxy VII Zw 403. VII Zw 403 is the first Blue Compact Dwarf
galaxy for which a clear spatial segregation of the resolved stellar content
into a "core-halo" structure is detected. Multicolor HST/WFPC2 observations
indicate that active star formation occurs in the central region, but is
strikingly absent at large radii. Instead, a globular-cluster-like red giant
branch suggests the presence of an old (> 10 Gyr) and metal poor
(=-1.92) stellar population in the halo. While the vast majority of
Blue Compact Dwarf galaxies has been recognized to possess halos of red color
in ground-based surface photometry, our observations of VII Zw 403 establish
for the first time a direct correspondence between a red halo color and the
presence of old, red giant stars. If the halos of Blue Compact Dwarf galaxies
are all home to such ancient stellar populations, then the fossil record
conflicts with delayed-formation scenarios for dwarfs.Comment: Accepted for publication in the Ap
The stellar content of 10 dwarf irregular galaxies
We examine the stellar content of 10 dwarf irregular galaxies of which
broad-band CCD photometry was published in Hopp & Schulte-Ladbeck (1995). We
also present Halpha images for several of these galaxies. The galaxies in the
sample are located outside of the Local Group. Yet, they are still close enough
to be resolved into single stars from the ground but only the brightest stars
(or star clusters) are detected and there is severe crowding. The sample
galaxies were selected to be isolated from massive neighbors; about half of
them are (mostly peripheral) members of groups, the other half is located in
the field. We discuss the vicinity of the sample galaxies to other dwarf
galaxies.
In order to interpret single-star photometry and draw conclusions about the
stellar content or other distance-dependent quantities, it is crucial that
accurate distances to the galaxies be known. The distances to the sample
galaxies are not well known since all but one have not had a primary distance
indicator measured. We make an attempt to constrain the distances by
identifying the envelope of the brightest supergiants in B, B-R and R, B-R
color-magnitude diagrams, but the results are not very accurate (we estimate
the minimal error on the distance modulus is 1.36 mag). Nevertheless, the fact
that the sample galaxies are resolved with direct ground-based imaging
indicates that they are sufficiently nearby to represent good candidates for
observations with instruments that provide high spatial resolution, e.g.,
adaptive optics systems on large ground-based telescopes, or the Hubble Space
Telescope. ...Comment: 56 pages, 4 tables, 35 figures, The Astronomical Journal, accepte
Properties of Galaxies in and around Voids
Two surveys for intrinsically faint galaxies towards nearby voids have been
conducted at the MPI f\"ur Astronomie, Heidelberg. One selected targets from a
new diameter limited () catalog with morphological criteria while
the other used digitized objective prism Schmidt plates to select mainly HII
dwarf galaxies. For some 450 galaxies, redshifts and other optical data were
obtained. We studied the spatial distribution of the sample objects, their
luminosity function, and their intrinsic properties. Most of the galaxies
belong to already well known sheets and filaments. But we found about a dozen
highly isolated galaxies in each sample (nearest neighborhood distance ). These tend to populate additional structures and are not
distributed homogeneously throughout the voids. As our results on 'void
galaxies' still suffer from small sample statistics, I also tried to combine
similar existing surveys of nearby voids to get further hints on the larger
structure and on the luminosity function of the isolated galaxies. No
differences in the luminosity function of sheet and void galaxies could be
found. The optical and infrared properties of both samples are in the normal
range for samples dominated by late-type dwarfs. Follow-up HI studies show that
the isolated dwarfs in both samples have unusual high amount of neutral gas for
a given luminosity.Comment: 10 pages, 4 figures, latex, to appear in the proceedings of the
'Ringberg workshop on Large Scale Structure', hold Sep. 23-28, 199
More evidence for an intracluster planetary nebulae population in the Virgo cluster
We surveyed a 50 sq arcmin region in the Virgo cluster core to search for
intergalactic planetary nebulae, and found 11 candidates in the surveyed area.
The measured fluxes of these unresolved sources are consistent with these
objects being planetary nebulae from an intracluster population of stars. We
compute the cumulative luminosity function of these 11 planetary nebula
candidates. If we assume that they belong to the Virgo cluster, their
cumulative luminosity function is in good agreement with planetary nebula
luminosity function simulations. This comparison allows us to estimate the
surface mass density of the intracluster stellar population at the surveyed
field in the cluster core.Comment: ApJ Letters, in press. A .ps file is also available at:
http://www.usm.uni-muenchen.de:8001/people/mendez/preprints/preprints.htm
The interaction of lean and building information modeling in construction
Lean construction and Building Information Modeling are quite different initiatives, but both are having profound impacts on the construction industry. A rigorous analysis of the myriad specific interactions between them indicates that a synergy exists which, if properly understood in theoretical terms, can be exploited to improve construction processes beyond the degree to which it might be improved by application of either of these paradigms independently. Using a matrix that juxtaposes BIM functionalities with prescriptive lean construction principles, fifty-six interactions have been identified, all but four of which represent constructive interaction. Although evidence for the majority of these has been found, the matrix is not considered complete, but rather a framework for research to
explore the degree of validity of the interactions. Construction executives, managers, designers and developers of IT systems for construction can also benefit from the framework as an aid to recognizing the potential synergies when planning their lean and BIM adoption strategies
The FORS Deep Field: Field selection, photometric observations and photometric catalog
The FORS Deep Field project is a multi-colour, multi-object spectroscopic
investigation of an approx. 7 times 7 region near the south galactic pole based
mostly on observations carried out with the FORS instruments attached to the
VLT telescopes. It includes the QSO Q 0103-260 (z = 3.36). The goal of this
study is to improve our understanding of the formation and evolution of
galaxies in the young Universe. In this paper the field selection, the
photometric observations, and the data reduction are described. The source
detection and photometry of objects in the FORS Deep Field is discussed in
detail. A combined B and I selected UBgRIJKs photometric catalog of 8753
objects in the FDF is presented and its properties are briefly discussed. The
formal 50% completeness limits for point sources, derived from the co-added
images, are 25.64, 27.69, 26.86, 26.68, 26.37, 23.60 and 21.57 in U, B, g, R,
I, J and Ks (Vega-system), respectively. A comparison of the number counts in
the FORS Deep Field to those derived in other deep field surveys shows very
good agreement.Comment: 15 pages, 11 figures (included), accepted for publication in A&
Kinematics of the Hercules Supercluster
The Hercules Supercluster consists of the Abell clusters 2147, 2151, and
2152. Previous studies of the kinematics have been confounded by the difficulty
of correctly assigning galaxies to the individual clusters, which are not
well-separated. Our study has a total of 468 available velocities for galaxies
in the region, 175 of them new. 414 galaxies are in the supercluster, about
three times the number used in the previous supercluster study. We verify the
existence of the three individual clusters and compute their individual
dynamical parameters. We investigate several techniques for assigning galaxy
membership to clusters in this crowded field. We use the KMM mixture-modeling
algorithm to separate the galaxies into clusters; we find that A2152 has a
higher mean velocity than previous studies have reported. A2147 and A2152 also
have lower velocity dispersions: 821(+68)(-55) and 715(+81)(-61) km/s. The
assignment of galaxies to either A2152 or A2147 requires velocity and position
information. We study the kinematics of the supercluster using the two-body
formalism of Beers, Geller, and Huchra (1982) and conclude that A2147 and A2151
are probably bound to each other, and that the supercluster as a whole may also
be bound. The mass of the supercluster, if bound, is (7.6\pm2.0)\times 10^{15}
h^{-1} M_{\sun}; with the supercluster luminosity, (1.4\pm0.2) \times 10^{13}
h^{-2} L_{\sun}, this yields Omega = 0.34\pm0.1$.Comment: 61 pages, 14 figures, accepted to A
Transgenic Expression of the Anti-parasitic Factor TEP1 in the Malaria Mosquito Anopheles gambiae
Mosquitoes genetically engineered to be resistant to Plasmodium parasites represent a promising novel approach in the fight against malaria. The insect immune system itself is a source of anti-parasitic genes potentially exploitable for transgenic designs. The Anopheles gambiae thioester containing protein 1 (TEP1) is a potent anti-parasitic protein. TEP1 is secreted and circulates in the mosquito hemolymph, where its activated cleaved form binds and eliminates malaria parasites. Here we investigated whether TEP1 can be used to create malaria resistant mosquitoes. Using a GFP reporter transgene, we determined that the fat body is the main site of TEP1 expression. We generated transgenic mosquitoes that express TEP1r, a potent refractory allele of TEP1, in the fat body and examined the activity of the transgenic protein in wild-type or TEP1 mutant genetic backgrounds. Transgenic TEP1r rescued loss-of-function mutations, but did not increase parasite resistance in the presence of a wild-type susceptible allele. Consistent with previous reports, TEP1 protein expressed from the transgene in the fat body was taken up by hemocytes upon a challenge with injected bacteria. Furthermore, although maturation of transgenic TEP1 into the cleaved form was impaired in one of the TEP1 mutant lines, it was still sufficient to reduce parasite numbers and induce parasite melanization. We also report here the first use of Transcription Activator Like Effectors (TALEs) in Anopheles gambiae to stimulate expression of endogenous TEP1. We found that artificial elevation of TEP1 expression remains moderate in vivo and that enhancement of endogenous TEP1 expression did not result in increased resistance to Plasmodium. Taken together, our results reveal the difficulty of artificially influencing TEP1-mediated Plasmodium resistance, and contribute to further our understanding of the molecular mechanisms underlying mosquito resistance to Plasmodium parasites
- âŠ