3,831 research outputs found
Biotechnological production of vanillin from natural feedstocks and development of new procedures for the recovery of the product
This PhD research project was focused on innovative biotechnological production and recovery of vanillin and vanillin precursors. Experiments carried out using whole cells or crude enzyme preaparations demonstrated that: selective recovery of the product, using macroporous resins, enhances the biological conversion of ferulic acid to vanillin using resting cells of Escherichia coli FR13 strain; (b) thermal pre-treatment at 55°C of crude PVA acylase from Streptomyces mobaraensis DSM40847 improves the conversion of capsaicin to vanillylamin
Clumpy streams in a smooth dark halo: the case of Palomar 5
By means of direct N-body simulations and simplified numerical models, we
study the formation and characteristics of the tidal tails around Palomar 5,
along its orbit in the Milky Way potential. Unlike previous findings, we are
able to reproduce the substructures observed in the stellar streams of this
cluster, without including any lumpiness in the dark matter halo. We show that
overdensities similar to those observed in Palomar 5 can be reproduced by the
epicyclic motion of stars along its tails, i.e. a simple local accumulation of
orbits of stars that escaped from the cluster with very similar positions and
velocities. This process is able to form stellar clumps at distances of several
kiloparsecs from the cluster, so it is not a phenomenon confined to the inner
part of Palomar 5's tails, as previously suggested. Our models can reproduce
the density contrast between the clumps and the surrounding tails found in the
observed streams, without including any lumpiness in the dark halo, suggesting
new upper limits on its granularity.Comment: 6 pages, 7 figures. A&A Letters, accepted. Top panel of Fig. A1
replaced, minor typos corrected. High resolution version available at
http://mygepi.obspm.fr/~paola/Pal5
Looking for a needle in a haystack : how to measure the length of a stellar bar?
One of the challenges related to stellar bars is to determine accurately the
length of the bar in a disc galaxy. In past literature, a wide variety of
methods has been employed to measure the extent of a bar. However, a systematic
study on determining the robustness and accuracy of different bar length
estimators is still beyond our grasp. Here, we investigate the accuracy and the
correlation (if any) between different bar length measurement methods while
using an -body model of a barred galaxy where the bar evolves
self-consistently in presence of a live dark matter halo. We investigate the
temporal evolution of the bar length, using different estimators (involving
isophotal analysis of de-projected surface brightness distribution and Fourier
decomposition of surface density), and study their robustness and accuracy.
Further attempts have been made towards determining correlation between any two
of these bar length estimators used here. In presence of spirals, the bar
length estimators which only consider the amplitudes of different Fourier
moments (and do not take into account the phase-angle of Fourier moment),
systematically overestimate the length of the bar. The strength dark-gaps
(produced by bars) correlates strongly with the bar length in early rapid
growth phase, and is only weakly anti-correlated during subsequent quiescent
phase of bar evolution. However, the location of dark-gaps correlates only
weakly with the bar length, hence can not be used as a robust proxy for
determining the bar length. In addition, the bar length estimators, obtained
using isophotal analysis of de-projected surface brightness distribution,
systematically overestimate the bar length. The implications of bar length
over(under)estimation in the context of determining fast/slow bars are further
discussed.Comment: 12 pages, 10 figures (including appendix), comments are welcome
The Milky Way as a High Redshift Galaxy: The Importance of Thick Disk Formation in Galaxies
We compare the star-formation history and dynamics of the Milky Way (MW) with
the properties of distant disk galaxies. During the first ~4 Gyr of its
evolution, the MW formed stars with a high star-formation intensity (SFI),
Sigma_SFR~0.6 Msun/yr/kpc2 and as a result, generated outflows and high
turbulence in its interstellar medium. This intense phase of star formation
corresponds to the formation of the thick disk. The formation of the thick disk
is a crucial phase which enables the MW to have formed approximately half of
its total stellar mass by z~1 which is similar to "MW progenitor galaxies"
selected by abundance matching. This agreement suggests that the formation of
the thick disk may be a generic evolutionary phase in disk galaxies. Using a
simple energy injection-kinetic energy relationship between the 1-D velocity
dispersion and SFI, we can reproduce the average perpendicular dispersion in
stellar velocities of the MW with age. This relationship, its inferred
evolution, and required efficiency are consistent with observations of galaxies
from z~0-3. The high turbulence generated by intense star formation naturally
resulted in a thick disk, a chemically well-mixed ISM, and is the mechanism
that links the evolution of MW to the observed characteristics of distant disk
galaxies.Comment: 5 pages, 4 figures; accepted to ApJ Letter
A Vertical Resonance Heating Model for X- or Peanut-Shaped Galactic Bulges
We explore a second order Hamiltonian vertical resonance model for X-shaped
or peanut-shaped galactic bulges. The X-shape is caused by the 2:1 vertical
Lindblad resonance with the bar, with two vertical oscillation periods per
orbital period in the bar frame. We examine N-body simulations and find that
due to the bar slowing down and disk thickening during bar buckling, the
resonance and associated peanut-shape moves outward. The peanut-shape is
consistent with the location of the vertical resonance, independent of whether
the bar buckled or not. We estimate the resonance width from the potential m=4
Fourier component and find that the resonance is narrow, affecting orbits over
a narrow range in the angular momentum distribution, dL/L ~ 0.05. As the
resonance moves outward, stars originally in the mid plane are forced out of
the mid plane into orbits just within the resonance separatrix. The height of
the separatrix orbits, estimated from the Hamiltonian model, is approximately
consistent with the peanut-shape height. The X-shape is comprised of stars in
the vicinity of the resonance separatrix. The velocity distributions from the
simulations illustrate that low inclination orbits are depleted within
resonance. Within resonance, the vertical velocity distribution is broad,
consistent with resonant heating caused by the passage of the resonance through
the disk. In the Milky Way bulge we relate the azimuthally averaged mid-plane
mass density near the vertical resonance to the rotation curve and bar pattern
speed. At an estimated vertical resonance galactocentric radius of ~1.3 kpc, we
confirm a mid-plane density of ~5x10^8 Msol/kpc^3, consistent with recently
estimated mass distributions. We find that the rotation curve, bar pattern
speed, 2:1 vertical resonance location, X-shape tips, and mid-plane mass
density, are all self-consistent in the Milky Way galaxy bulge.Comment: accepted for publication in MNRA
The slowing down of galaxy disks in dissipationless minor mergers
We have investigated the impact of dissipationless minor galaxy mergers on
the angular momentum of the remnant. Our simulations cover a range of initial
orbital characteristics and the system consists of a massive galaxy with a
bulge and disk merging with a much less massive (one-tenth or one-twentieth)
gasless companion which has a variety of morphologies (disk- or
elliptical-like) and central baryonic mass concentrations. During the process
of merging, the orbital angular momentum is redistributed into the internal
angular momentum of the final system; the internal angular momentum of the
primary galaxy can increase or decrease depending on the relative orientation
of the orbital spin vectors (direct or retrograde), while the initially
non-rotating dark matter halo always gains angular momentum. The specific
angular momentum of the stellar component always decreases independent of the
orbital parameters or morphology of the satellite, the decrease in the rotation
velocity of the primary galaxy is accompanied by a change in the anisotropy of
the orbits, and the ratio of rotation speed to velocity dispersion of the
merger remnant is lower than the initial value, not only due to an increase in
the dispersion but also to the slowing -down of the disk rotation. We briefly
discuss several astrophysical implications of these results, suggesting that
minor mergers do not cause a "random walk" process of the angular momentum of
the stellar disk component of galaxies, but rather a steady decrease. Minor
mergers may play a role in producing the large scatter observed in the
Tully-Fisher relation for S0 galaxies, as well as in the increase of the
velocity dispersion and the decrease in at large radii as observed
in S0 galaxies.Comment: 10 pages, 10 figures, accepted for publication in A&
NGC 6340: an old S0 galaxy with a young polar disc. Clues from morphology, internal kinematics and stellar populations
Lenticular galaxies are believed to form by a combination of environmental
effects and secular evolution. We study the nearby disc-dominated S0 galaxy NGC
6340 photometrically and spectroscopically to understand the mechanisms of S0
formation and evolution in groups. We use SDSS images to build colour maps and
light profile of NGC 6340 which we decompose using a three-component model
including Sersic and two exponential profiles. We also use Spitzer images to
study the morphology of regions containing warm ISM and dust. Then, we
re-process and re-analyse deep long-slit spectroscopic data for NGC 6340 and
recover its stellar and gas kinematics, distribution of age and metallicity
with the NBursts full spectral fitting. We obtain the profiles of internal
kinematics, age, and metallicity out to >2 half-light radii. The three
structural components of NGC 6340 are found to have distinct kinematical and
stellar population properties. We see a kinematical misalignment between inner
and outer regions of the galaxy. We confirm the old metal-rich centre and a
wrapped inner gaseous polar disc (r~1 kpc) having weak ongoing star formation,
counter-rotating in projection with respect to the stars. The central compact
pseudo-bulge of NGC 6340 looks very similar to compact elliptical galaxies. In
accordance with the results of numerical simulations, we conclude that
properties of NGC 6340 can be explained as the result of a major merger of
early-type and spiral galaxies which occurred about 12 Gyr ago. The
intermediate exponential structure might be a triaxial pseudo-bulge formed by a
past bar structure. The inner compact bulge could be the result of a nuclear
starburst triggered by the merger. The inner polar disc appeared recently,
1/3-1/2 Gyr ago as a result of another minor merger or cold gas accretion.Comment: 12 pages, 8 figures, accepted to A&
Bars and boxy/peanut bulges in thin and thick discs. II. Can bars form in hot thick discs?
The Milky Way as well as a majority of external galaxies possess a thick
disc. However, the dynamical role of the (geometrically) thick disc on the bar
formation and evolution is not fully understood. Here, we investigate the
effect of thick discs in bar formation and evolution by means of a suite of
N-body models of (kinematically cold) thin-(kinematically hot) thick discs. We
systematically vary the mass fraction of the thick disc, the thin-to-thick disc
scale length ratio as well as thick disc's scale height to examine the bar
formation under diverse dynamical scenarios. Bars form almost always in our
models, even in presence of a massive thick disc. The part of the bar
constituted by the thick disc closely follows the overall growth and temporal
evolution of the part of the bar constituted by the thin disc, only the part of
the bar in the thick disc is weaker than the part of the bar in the thin disc.
The formation of stronger bars is associated with a simultaneous larger loss of
angular momentum and a larger radial heating. In addition, we demonstrate a
preferential loss of angular momentum and a preferential radial heating of disc
stars, along the azimuthal direction within the extent of the bar, in both thin
and thick disc stars. For purely thick disc models (without any thin disc), the
bar formation critically depends on the disc scale length and scale height. A
larger scale length and/or a larger vertical scale height delays the bar
formation time and/or suppresses the bar formation almost completely in
thick-disc-only models. We find that the Ostriker-Peeble criterion predicts the
bar instability scenarios in our models better than the
Efstathiou-Lake-Negroponte criterion.Comment: 20 pages, 14 figures, 1 table (including appendix), accepted for
publication in A&
Astrocomp: a web service for the use of high performance computers in Astrophysics
Astrocomp is a joint project, developed by the INAF-Astrophysical Observatory
of Catania, University of Roma La Sapienza and Enea. The project has the goal
of providing the scientific community of a web-based user-friendly interface
which allows running parallel codes on a set of high-performance computing
(HPC) resources, without any need for specific knowledge about parallel
programming and Operating Systems commands. Astrocomp provides, also, computing
time on a set of parallel computing systems, available to the authorized user.
At present, the portal makes a few codes available, among which: FLY, a
cosmological code for studying three-dimensional collisionless self-gravitating
systems with periodic boundary conditions; ATD, a parallel tree-code for the
simulation of the dynamics of boundary-free collisional and collisionless
self-gravitating systems and MARA, a code for stellar light curves analysis.
Other codes are going to be added to the portal.Comment: LaTeX with elsart.cls and harvard.sty (included). 7 pages. To be
submitted to a specific journa
Gas inflows, star formation and metallicity evolution in galaxy pairs
It has been known since many decades that galaxy interactions can induce star
formation (hereafter SF) enhancements and that one of the driving mechanisms of
this enhancement is related to gas inflows into the central galaxy regions,
induced by asymmetries in the stellar component, like bars. In the last years
many evidences have been accumulating, showing that interacting pairs have
central gas-phase metallicities lower than those of field galaxies, by {\sim}
0.2-0.3 dex on average. These diluted ISM metallicities have been explained as
the result of inflows of metal-poor gas from the outer disk to the galaxy
central regions. A number of questions arises: What's the timing and the
duration of this dilution? How and when does the SF induced by the gas inflow
enrich the circumnuclear gas with re-processed material? Is there any
correlation between the timing and strength of the dilution and the timing and
intensity of the SF? By means of Tree-SPH simulations of galaxy major
interactions, we have studied the effect that gas inflows have on the ISM
dilution, and the effect that the induced SF has, subsequently, in re-enriching
the nuclear gas. In this contribution, we present the main results of this
study.Comment: Proceedings of the IAU Symposium 277 "Tracing the Ancestry of
Galaxies", 4 pages, 2 figure
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