684 research outputs found
Mapping the distribution of luminous and dark matter in strong lensing galaxies
We present the distribution of luminous and dark matter in a set of strong
lensing (early-type) galaxies. By combining two independent techniques -
stellar population synthesis and gravitational lensing - we can compare the
baryonic and dark matter content in these galaxies within the regions that can
be probed using the images of the lensed background source. Two samples were
studied, extracted from the CASTLES and SLACS surveys. The former probes a
wider range of redshifts and allows us to explore the mass distribution out to
~5Re. The high resolution optical images of the latter (using HST/ACS) are used
to show a pixellated map of the ratio between total and baryonic matter. We
find dark matter to be absent in the cores of these galaxies, with an
increasing contribution at projected radii R>Re. The slopes are roughly
compatible with an isothermal slope (better interpreted as an adiabatically
contracted NFW profile), but a large scatter in the slope exists among
galaxies. There is a trend suggesting most massive galaxies have a higher
content of dark matter in the regions probed by this analysis.Comment: 10 pages, 6 figures. To appear in "Dark Galaxies and Lost Baryons",
IAU244 conference proceeding
Mapping the Distribution of Luminous and Dark Matter in Strong Lensing Galaxies
We present the distribution of luminous and dark matter in a set of strong lensing (early-type) galaxies. By combining two independent techniques - stellar population synthesis and gravitational lensing - we can compare the baryonic and dark matter content in these galaxies within the regions that can be probed using the images of the lensed background source. Two samples were studied, extracted from the CASTLES and SLACS surveys. The former probes a wider range of redshifts and allows us to explore the mass distribution out to ~ 5Re. The high resolution optical images of the latter (using HST/ACS) are used to show a pixellated map of the ratio between total and baryonic matter. We find dark matter to be absent in the cores of these galaxies, with an increasing contribution at projected radii R Re. The slopes are roughly compatible with an isothermal slope (better interpreted as an adiabatically contracted NFW profile), but a large scatter in the slope exists among galaxies. There is a trend suggesting most massive galaxies have a higher content of dark matter in the regions probed by this analysi
Predicting spectral features in galaxy spectra from broad-band photometry
We explore the prospects of predicting emission line features present in
galaxy spectra given broad-band photometry alone. There is a general consent
that colours, and spectral features, most notably the 4000 A break, can predict
many properties of galaxies, including star formation rates and hence they
could infer some of the line properties. We argue that these techniques have
great prospects in helping us understand line emission in extragalactic objects
and might speed up future galaxy redshift surveys if they are to target
emission line objects only. We use two independent methods, Artifical Neural
Neworks (based on the ANNz code) and Locally Weighted Regression (LWR), to
retrieve correlations present in the colour N-dimensional space and to predict
the equivalent widths present in the corresponding spectra. We also investigate
how well it is possible to separate galaxies with and without lines from broad
band photometry only. We find, unsurprisingly, that recombination lines can be
well predicted by galaxy colours. However, among collisional lines some can and
some cannot be predicted well from galaxy colours alone, without any further
redshift information. We also use our techniques to estimate how much
information contained in spectral diagnostic diagrams can be recovered from
broad-band photometry alone. We find that it is possible to classify AGN and
star formation objects relatively well using colours only. We suggest that this
technique could be used to considerably improve redshift surveys such as the
upcoming FMOS survey and the planned WFMOS survey.Comment: 10 pages 7 figures summitted to MNRA
Stellar and total mass in early-type lensing galaxies
For 18 well-observed gravitationally lensed QSOs, we compare new
non-parametric mass profiles for the lensing galaxies with stellar-population
models derived from published HST photometry. The large volume of parameter
space searched -- with respect to the possible star formation histories --
allows us to infer robust estimates and uncertainties for the stellar masses.
The most interesting results are: (1) the transition from little or no dark
matter in the inner regions (<r_e) to dark matter dominating on the ~5r_e scale
(~20 kpc) is clearly seen in massive ellipticals; (2) Such a trend is not seen
in lower-mass galaxies, so that the stellar content dominates the mass budget
out to ~5r_e; (3) the radial gradient in the dark-matter fraction for these
intermediate redshift galaxies agrees with published data on nearby galaxies.
This result can help reconcile the discrepancies found in recent estimates of
dark matter in elliptical galaxies using different techniques (e.g. Planetary
nebulae versus X-ray). The observed trend suggests the stellar component in
massive galaxies extends further out in terms of the dark matter scale radius.Comment: 4 pages, 4 figures, uses emulateapj. Accepted for publication in The
Astrophysical Journal Letter
Sequence, structure, and binding site analysis of kirkiin in comparison with ricin and other type 2 rips
Kirkiin is a new type 2 ribosome-inactivating protein (RIP) purified from the caudex of Adenia kirkii with a cytotoxicity compared to that of stenodactylin. The high toxicity of RIPs from Adenia genus plants makes them interesting tools for biotechnology and therapeutic applications, particularly in cancer therapy. The complete amino acid sequence and 3D structure prediction of kirkiin are here reported. Gene sequence analysis revealed that kirkiin is encoded by a 1572 bp open reading frame, corresponding to 524 amino acid residues, without introns. The amino acid sequence analysis showed a high degree of identity with other Adenia RIPs. The 3D structure of kirkiin preserves the overall folding of type 2 RIPs. The key amino acids of the active site, described for ricin and other RIPs, are also conserved in the kirkiin A chain. Sugar affinity studies and docking experiments revealed that both the 1α and 2γ sites of the kirkiin B chain exhibit binding activity toward lactose and D-galactose, being lower than ricin. The replacement of His246 in the kirkiin 2γ site instead of Tyr248 in ricin causes a different structure arrangement that could explain the lower sugar affinity of kirkiin with respect to ricin
Functional expression of a penicillin acylase from the extreme thermophile Thermus thermophilus HB27 in Escherichia coli
Background: Penicillin acylases (PACs) are enzymes of industrial relevance in the manufacture of beta-lactam antibiotics. Development of a PAC with a longer half-life under the reaction conditions used is essential for the improvement of the operational stability of the process. A gene encoding a homologue to Escherichia coli PAC was found in the genome of the thermophilic bacterium Thermus thermophilus (Tth) HB27. Because of the nature of this PAC and its complex maturation that is crucial to reach its functional heterodimeric final conformation, the overexpression of this enzyme in a heterologous mesophilic host was a challenge. Here we describe the purification and characterization of the PAC protein from Tth HB27 overexpressed in Escherichia coli. Results: Fusions to a superfolder green fluorescent protein and differential membrane solubilization assays indicated that the enzyme remains attached through its amino-terminal end to the outer side of the cytoplasmic membrane of Tth cells. In order to overexpress this PAC in E. coli cells, a variant of the protein devoid of its membrane anchoring segment was constructed. The effect of the co-expression of chaperones and calcium supplementation of the culture medium was investigated. The total production of PAC was enhanced by the presence of DnaK/J and GrpE and even more by trigger factor and GroEL/ES. In addition, 10 mM calcium markedly improved both PAC specific and volumetric activities. Recombinant PAC was affinity-purified and proper maturation of the protein was confirmed by SDS-PAGE and MALDI-TOF analysis of the subunits. The recombinant protein was tested for activity towards several penicillins, cephalosporins and homoserine lactones. Hydrophobic acyl-chain penicillins were preferred over the rest of the substrates. Penicillin K (octanoyl penicillin) was the best substrate, with the highest specificity constant value (16.12 mM-1.seg-1). The optimum pH was aprox. 4 and the optimum temperature was 75 [DEGREE SIGN]C. The half-life of the enzyme at this temperature was 9.2 h. Conclusions: This is the first report concerning the heterologous expression of a pac gene from a thermophilic microorganism in the mesophilic host E. coli. The recombinant protein was identified as a penicillin K-deacylating thermozymeL.T., A.H. and J.B. acknowledge funding from the Spanish Ministry of Science (grants CIT 010000-2009-29, RyC2006-02441) and an institutional grant from Fundación Ramón Areces to CBMS
Luminous Red Galaxies in Simulations: Cosmic Chronometers?
There have been a number of attempts to measure the expansion rate of the
universe at high redshift using Luminous Red Galaxies (LRGs) as "chronometers".
The method generally assumes that stars in LRGs are all formed at the same
time. In this paper, we quantify the uncertainties on the measurement of H(z)
which arise when one considers more realistic, extended star formation
histories. In selecting galaxies from the Millennium Simulation for this study,
we show that using rest-frame criteria significantly improves the homogeneity
of the sample and that H(z) can be recovered to within 3% at z~0.42 even when
extended star formation histories are considered. We demonstrate explicitly
that using Single Stellar Populations to age-date galaxies from the
semi-analytical simulations provides insufficient accuracy for this experiment
but accurate ages are obtainable if the complex star formation histories
extracted from the simulation are used. We note, however, that problems with
SSP-fitting might be overestimated since the semi-analytical models tend to
over predict the late-time star-formation in LRGs. Finally, we optimize an
observational program to carry out this experiment.Comment: 11 pages, 10 figures. Accepted to MNRAS
The Fundamental Surface of Quad Lenses
In a quadruply imaged lens system the angular distribution of images around
the lens center is completely described by three relative angles. We show
empirically that in the 3D space of these angles, spanning 180 x 180 x 90
degrees, quads from simple two-fold symmetric lenses of arbitrary radial
density profile and arbitrary radially dependent ellipticity or external shear
define a nearly invariant 2D surface. We give a fitting formula for the surface
using SIS+elliptical lensing potential. Various circularly symmetric mass
distributions with shear up to 0.4 deviate from it by typically, rms~0.1 deg,
while elliptical mass distributions with ellipticity of up 0.4 deviate from it
by rms~1.5 deg. The existence of a near invariant surface gives a new insight
into the lensing theory and provides a framework for studying quads. It also
allows one to gain information about the lens mass distribution from the image
positions alone, without any recourse to mass modeling. As an illustration, we
show that about 3/4 of observed galaxy-lens quads do not belong to this surface
within observational error, and so require additional external shear or
substructure to be modeled adequately.Comment: 24 pages, 9 figures, accepted to MNRA
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