240 research outputs found
Disk galaxies with broken luminosity profiles from cosmological simulations
We present SPH cosmological simulations of the formation of three disk
galaxies with a detailed treatment of chemical evolution and cooling. The
resulting galaxies have properties compatible with observations: relatively
high disk-to-total ratios, thin stellar disks and good agreement with the
Tully-Fisher and the luminosity-size relations. They present a break in the
luminosity profile at 3.0 +- 0.5 disk scale lengths, while showing an
exponential mass profile without any apparent breaks, in line with recent
observational results. Since the stellar mass profile is exponential, only
differences in the stellar populations can be the cause of the luminosity
break. Although we find a cutoff for the star formation rate imposed by a
density threshold in our star formation model, it does not coincide with the
luminosity break and is located at 4.3 +- 0.4 disk scale lengths, with star
formation going on between both radii. The color profiles and the age profiles
are "U-shaped", with the minimum for both profiles located approximately at the
break radius. The SFR to stellar mass ratio increases until the break,
explaining the coincidence of the break with the minimum of the age profile.
Beyond the break we find a steep decline in the gas density and, consequently,
a decline in the SFR and redder colors. We show that most stars (64-78%) in the
outer disk originate in the inner disk and afterwards migrate there. Such
stellar migrations are likely the main origin of the U-shaped age profile and,
therefore, of the luminosity break.Comment: 8 pages, 4 figures. Accepted by ApJ
Wavelength calibration of the JWST-MIRI medium resolution spectrometer
We present the wavelength and spectral resolution characterisation of the
Integral Field Unit (IFU) Medium Resolution Spectrometer for the Mid-InfraRed
Instrument (MIRI), to fly onboard the James Webb Space Telescope in 2014. We
use data collected using the Verification Model of the instrument and develop
an empirical method to calibrate properties such as wavelength range and
resolving power in a portion of the spectrometer's full spectral range (5-28
microns). We test our results against optical models to verify the system
requirements and combine them with a study of the fringing pattern in the
instrument's detector to provide a more accurate calibration. We show that
MIRI's IFU spectrometer will be able to produce spectra with a resolving power
above R=2800 in the wavelength range 6.46-7.70 microns, and that the unresolved
spectral lines are well fitted by a Gaussian profile.Comment: 12 pages, submitted to SPIE Proceedings vol. 7731, Space Telescopes
and Instrumentation 2010: Optical, Infrared, and Millimeter Wav
Cosmic Evolution of Stellar Disk Truncations: From z~1 to the Local Universe
We have conducted the largest systematic search so far for stellar disk
truncations in disk-like galaxies at intermediate redshift (z<1.1), using the
Great Observatories Origins Deep Survey South (GOODS-S) data from the Hubble
Space Telescope - ACS. Focusing on Type II galaxies (i.e. downbending profiles)
we explore whether the position of the break in the rest-frame B-band radial
surface brightness profile (a direct estimator of the extent of the disk where
most of the massive star formation is taking place), evolves with time. The
number of galaxies under analysis (238 of a total of 505) is an order of
magnitude larger than in previous studies. For the first time, we probe the
evolution of the break radius for a given stellar mass (a parameter well suited
to address evolutionary studies). Our results suggest that, for a given stellar
mass, the radial position of the break has increased with cosmic time by a
factor 1.3+/-0.1 between z~1 and z~0. This is in agreement with a moderate
inside-out growth of the disk galaxies in the last ~8 Gyr. In the same period
of time, the surface brightness level in the rest-frame B-band at which the
break takes place has increased by 3.3+/-0.2 mag/arcsec^2 (a decrease in
brightness by a factor of 20.9+/-4.2). We have explored the distribution of the
scale lengths of the disks in the region inside the break, and how this
parameter relates to the break radius. We also present results of the
statistical analysis of profiles of artificial galaxies, to assess the
reliability of our results.Comment: 22 pages, 14 figures, accepted for publication in ApJ. Figures 1, 3
and 6 have somehow downgraded resolution to match uploading requirement
The kinematics of water masers in the stellar molecular outflow source IRAS 19134+2131
Using the Very Large Array (VLA) and the Very Long Baseline Array (VLBA), we have observed water maser emission in the proto-planetary nebula candidate IRAS 19134+2131, in which the water maser spectrum has two groups of emission features separated in radial velocity by âŒ100 km s^â1. The blue-shifted and red-shifted clusters of maser features are clearly separated spatially by âŒ150 mas, indicative of a fast collimated flow. However, not all of the maser features are aligned along the axis of the flow, as is seen in the similar high-velocity water maser source, W43A. Comparing the VLA and VLBA maps of the water maser source, we find 4 maser features that were active for 2 years. Using only VLBA data, we identified proper motions for 8 maser features. The full 3D outflow velocity is estimated to be âŒ130 km s^â1, indicating that the dynamical age of the flow is only âŒ50 yr. On the basis of the relative positions with respect to the nearby extragalactic reference source, J1925+2106, we also obtain a secular motion of IRAS 19134+2131 of ÎŒl = â4.6 ± 0.7 mas yr^â1 along the Galactic plane toward the Galactic centre. This indicates a âfar distanceâ (â„16 kpc) for IRAS 19134+2131 if the Galactic rotation curve remains flat at 220 km s^â1.Hachisuka, Kazuya, [email protected]
Hybrid fibroin/polyurethane small-diameter vascular grafts: from fabrication to in vivo preliminary assessment
To address the need of alternatives to autologous vessels for small-calibre vascular applications (e.g. cardiac surgery), a bio-hybrid semi-degradable material composed of silk fibroin (SF) and polyurethane (Silkothane (R)) was herein used to fabricate very small-calibre grafts (o(in) = 1.5 mm) via electrospinning. Bio-hybrid grafts were in vitro characterized in terms of morphology and mechanical behaviour, and compared to similar grafts of pure SF. Similarly, two native vessels from a rodent model (abdominal aorta and vena cava) were harvested and characterized. Preliminary implants were performed on Lewis rats to confirm the suitability of Silkothane (R) grafts for small-calibre applications, specifically as aortic insertion and femoral shunt. The manufacturing process generated pliable grafts consisting of a randomized fibrous mesh and exhibiting similar geometrical features to rat aortas. Both Silkothane (R) and pure SF grafts showed radial compliances in the range from 1.37 +/- 0.86 to 1.88 +/- 1.01% 10(-2) mmHg(-1), lower than that of native vessels. The Silkothane (R) small-calibre devices were also implanted in rats demonstrating to be adequate for vascular applications; all the treated rats survived the surgery for three months after implantation, and 16 rats out of 17 (94%) still showed blood flow inside the graft at sacrifice. The obtained results lay the basis for a deeper investigation of the interaction between the Silkothane (R) graft and the implant site, which may deal with further analysis on the potentialities in terms of degradability and tissue formation, on longer time-points
The environmental dependence of the structure of outer galactic discs in STAGES spiral galaxies
We present an analysis of V-band radial surface brightness profiles for
spiral galaxies from the field and cluster environments using Hubble Space
Telescope/Advanced Camera for Surveys imaging and data from the Space Telescope
A901/2 Galaxy Evolution Survey (STAGES). We use a large sample of ~330 face-on
to intermediately inclined spiral galaxies and assess the effect of the galaxy
environment on the azimuthally averaged radial surface brightness mu profiles
for each galaxy in the outer stellar disc (24 < mu < 26.5 mag per sq arcsec).
For galaxies with a purely exponential outer disc (~50 per cent), we determine
the significance of an environmental dependence on the outer disc scalelength
h_out. For galaxies with a broken exponential in their outer disc, either
down-bending (truncation, ~10 per cent) or up-bending (anti-truncation, ~40 per
cent), we measure the strength T (outer-to-inner scalelength ratio,
log_10(h_out/h_in) of the mu breaks and determine the significance of an
environmental dependence on break strength T. Surprisingly, we find no evidence
to suggest any such environmental dependence on either outer disc scalelength
h_out or break strength T, implying that the galaxy environment is not
affecting the stellar distribution in the outer stellar disc. We also find that
for galaxies with small effective radii (r_e < 3 kpc) there is a lack of outer
disc truncations in both the field and cluster environments. Our results
suggest that the stellar distribution in the outer disc of spiral galaxies is
not significantly affected by the galaxy environment.Comment: Accepted to MNRAS. Appendix A available at
http://www.nottingham.ac.uk/~ppxdtm/STAGES_profiles_appendix.pd
On the stability of standing waves of Klein-Gordon equations in a semiclassical regime
We investigate the orbital stability and instability of standing waves for
two classes of Klein-Gordon equations in the semi-classical regime.Comment: 9 page
The MIRI Medium Resolution Spectrometer calibration pipeline
The Mid-Infrared Instrument (MIRI) Medium Resolution Spectrometer (MRS) is
the only mid-IR Integral Field Spectrometer on board James Webb Space
Telescope. The complexity of the MRS requires a very specialized pipeline, with
some specific steps not present in other pipelines of JWST instruments, such as
fringe corrections and wavelength offsets, with different algorithms for point
source or extended source data. The MRS pipeline has also two different
variants: the baseline pipeline, optimized for most foreseen science cases, and
the optimal pipeline, where extra steps will be needed for specific science
cases. This paper provides a comprehensive description of the MRS Calibration
Pipeline from uncalibrated slope images to final scientific products, with
brief descriptions of its algorithms, input and output data, and the accessory
data and calibration data products necessary to run the pipeline.Comment: 10 pages, 8 figure
Interpreting the Evolution of the Size - Luminosity Relation for Disk Galaxies from Redshift 1 to the Present
A sample of very high resolution cosmological disk galaxy simulations is used
to investigate the evolution of galaxy disk sizes back to redshift 1 within the
Lambda CDM cosmology. Artificial images in the rest frame B band are generated,
allowing for a measurement of disk scale lengths using surface brightness
profiles as observations would, and avoiding any assumption that light must
follow mass as previous models have assumed. We demonstrate that these
simulated disks are an excellent match to the observed magnitude - size
relation for both local disks, and for disks at z=1 in the magnitude/mass range
of overlap. We disentangle the evolution seen in the population as a whole from
the evolution of individual disk galaxies. In agreement with observations, our
simulated disks undergo roughly 1.5 magnitudes/arcsec^2 of surface brightness
dimming since z=1. We find evidence that evolution in the magnitude - size
plane varies by mass, such that galaxies with M* > 10^9 M_sun undergo more
evolution in size than luminosity, while dwarf galaxies tend to evolve
potentially more in luminosity. The disks grow in such a way as to stay on
roughly the same stellar mass - size relation with time. Finally, due to an
evolving stellar mass - SFR relation, a galaxy at a given stellar mass (or
size) at z=1 will reside in a more massive halo and have a higher SFR, and thus
a higher luminosity, than a counterpart of the same stellar mass at z=0.Comment: Version resubmitted to ApJ, after referee's comment
Safety of partially defatted house cricket (Acheta domesticus) powder as a novel food pursuant to Regulation (EU) 2015/2283
Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver an opinion on defatted house cricket (Acheta domesticus) powder as a novel food (NF) pursuant to Regulation (EU) 2015/2283. The NF is proposed as dry powder. The main components of the NF are protein, fat and fibre (chitin). The Panel notes that the concentration of contaminants in the NF depends on the occurrence levels of these substances in the insect feed. The Panel further notes that there are no safety concerns regarding the stability of the NF if the NF complies with the proposed specification limits during its entire shelf life. The NF has a high protein content, although the true protein levels are overestimated when using the nitrogen-to-protein conversion factor of 6.25 due to the presence of non-protein nitrogen from chitin. The applicant proposed to use the NF as food ingredient in a number of food products. The target population proposed by the applicant is the general population. The Panel notes that, considering the composition of the NF and the proposed conditions of use, the consumption of the NF is not nutritionally disadvantageous. The Panel notes that no genotoxicity and no subchronic toxicity studies with the NF were provided by the applicant. Considering that no safety concerns arise from the history of use of the source of the NF (A. domesticus), and the limited difference between the whole insect and the partially defatted NF, the Panel identified no other safety concerns than allergenicity. The Panel considers that the consumption of the NF might trigger primary sensitisation to A. domesticus proteins and may cause allergic reactions in subjects allergic to crustaceans, mites and molluscs. Additionally, allergens from the feed may end up in the NF. That aside, the Panel concludes that the NF is safe under the proposed uses and use levels
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