55 research outputs found
GalPak3D: A Bayesian parametric tool for extracting morpho-kinematics of galaxies from 3D data
We present a method to constrain galaxy parameters directly from
three-dimensional data cubes. The algorithm compares directly the data with a
parametric model mapped in coordinates. It uses the spectral
lines-spread function (LSF) and the spatial point-spread function (PSF) to
generate a three-dimensional kernel whose characteristics are instrument
specific or user generated. The algorithm returns the intrinsic modeled
properties along with both an `intrinsic' model data cube and the modeled
galaxy convolved with the 3D-kernel. The algorithm uses a Markov Chain Monte
Carlo (MCMC) approach with a nontraditional proposal distribution in order to
efficiently probe the parameter space. We demonstrate the robustness of the
algorithm using 1728 mock galaxies and galaxies generated from hydrodynamical
simulations in various seeing conditions from 0.6" to 1.2". We find that the
algorithm can recover the morphological parameters (inclination, position
angle) to within 10% and the kinematic parameters (maximum rotation velocity)
to within 20%, irrespectively of the PSF in seeing (up to 1.2") provided that
the maximum signal-to-noise ratio (SNR) is greater than pixel
and that the ratio of the galaxy half-light radius to seeing radius is greater
than about 1.5. One can use such an algorithm to constrain simultaneously the
kinematics and morphological parameters of (nonmerging) galaxies observed in
nonoptimal seeing conditions. The algorithm can also be used on adaptive-optics
(AO) data or on high-quality, high-SNR data to look for nonaxisymmetric
structures in the residuals.Comment: 16 pages, 10 figures, accepted to publication in AJ, revised version
after proofs corrections. Algorithm available at http://galpak.irap.omp.e
A fast, efficient and sequence-independent method for flexible multiple segmental isotope labeling of RNA using ribozyme and RNase H cleavage
Structural information on RNA, emerging more and more as a major regulator in gene expression, dramatically lags behind compared with information on proteins. Although NMR spectroscopy has proven to be an excellent tool to solve RNA structures, it is hampered by the severe spectral resonances overlap found in RNA, limiting its use for large RNA molecules. Segmental isotope labeling of RNA or ligation of a chemically synthesized RNA containing modified nucleotides with an unmodified RNA fragment have proven to have high potential in overcoming current limitations in obtaining structural information on RNA. However, low yields, cumbersome preparations and sequence requirements have limited its broader application in structural biology. Here we present a fast and efficient approach to generate multiple segmentally labeled RNAs with virtually no sequence requirements with very high yields (up to 10-fold higher than previously reported). We expect this approach to open new avenues in structural biology of RN
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Engineering the semiconductor/oxide interaction for stacking twin suppression in single crystalline epitaxial silicon(111)/insulator/Si(111) heterostructures
The integration of alternative semiconductor layers on the Si material platform via oxide heterostructures is of interest to increase the performance and/or functionality of future Si-based integrated circuits. The single crystalline quality of epitaxial (epi) semiconductor-insulator-Si heterostructures is however limited by too high defect densities, mainly due to a lack of knowledge about the fundamental physics of the heteroepitaxy mechanisms at work. To shed light on the physics of stacking twin formation as one of the major defect mechanisms in (111)-oriented fcc-related heterostructures on Si(111), we report a detailed experimental and theoretical study on the structure and defect properties of epi-Si(111)/Y2O 3/Pr2O3/Si(111) heterostructures. Synchrotron radiation-grazing incidence x-ray diffraction (SR-GIXRD) proves that the engineered Y2O3/Pr2O3 buffer dielectric heterostructure on Si(111) allows control of the stacking sequence of the overgrowing single crystalline epi-Si(111) layers. The epitaxy relationship of the epi-Si(111)/insulator/Si(111) heterostructure is characterized by a type A/B/A stacking configuration. Theoretical ab initio calculations show that this stacking sequence control of the heterostructure is mainly achieved by electrostatic interaction effects across the ionic oxide/covalent Si interface (IF). Transmission electron microscopy (TEM) studies detect only a small population of misaligned type B epi-Si(111) stacking twins whose location is limited to the oxide/epiSi IF region. Engineering the oxide/semiconductor IF physics by using tailored oxide systems opens thus a promising approach to grow heterostructures with well-controlled properties. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft
Possible Signatures of a Cold-Flow Disk from MUSE using a z=1 galaxy--quasar pair towards SDSSJ1422-0001
We use a background quasar to detect the presence of circum-galactic gas
around a low-mass star forming galaxy. Data from the new Multi Unit
Spectroscopic Explorer (MUSE) on the VLT show that the host galaxy has a
dust-corrected star-formation rate (SFR) of 4.70.2 Msun/yr, with no
companion down to 0.22 Msun/yr (5 ) within 240 kpc (30"). Using a
high-resolution spectrum (UVES) of the background quasar, which is fortuitously
aligned with the galaxy major axis (with an azimuth angle of only
), we find, in the gas kinematics traced by low-ionization lines,
distinct signatures consistent with those expected for a "cold flow disk"
extending at least 12 kpc (). We estimate the mass accretion
rate to be at least two to three times larger than the SFR,
using the geometric constraints from the IFU data and the HI column density of
obtained from a {\it HST}/COS NUV spectrum. From
a detailed analysis of the low-ionization lines (e.g. ZnII, CrII, TiII, MnII,
SiII), the accreting material appears to be enriched to about 0.4
(albeit with large uncertainties: ), which is
comparable to the galaxy metallicity (), implying a
large recycling fraction from past outflows. Blue-shifted MgII and FeII
absorptions in the galaxy spectrum from the MUSE data reveal the presence of an
outflow. The MgII and FeII doublet ratios indicate emission infilling due to
scattering processes, but the MUSE data do not show any signs of fluorescent
FeII* emission.Comment: 17 pages, 11 figures, in press (ApJ), minor edits after the proofs.
Data available at http://muse-vlt.eu/science/j1422
New criteria for the selection of galaxy close pairs from cosmological simulations: evolution of the major and minor merger fraction in MUSE deep fields
International audienceIt is still a challenge to assess the merger fraction of galaxies at different cosmic epochs in order to probe the evolution of their mass assembly. Using the Illustris cosmological simulation project, we investigate the relation between the separation of galaxies in a pair, both in velocity and projected spatial separation space, and the probability that these interacting galaxies will merge in the future. From this analysis, we propose a new set of criteria to select close pairs of galaxies along with a new corrective term to be applied to the computation of the galaxy merger fraction. We then probe the evolution of the major and minor merger fraction using the latest MUSE deep observations over the Hubble Ultra Deep Field, Hubble Deep Field South, COSMOS-Gr30 and Abell 2744 regions. From a parent sample of 2483 galaxies with spectroscopic redshifts, we identify 366 close pairs spread over a large range of redshifts (0.2 < z < 6) and stellar masses (10 7 â 10 11 M). Using the stellar mass ratio between the secondary and primary galaxy as a proxy to split the sample into major, minor and very minor mergers, we found a total of 183 major, 142 minor and 47 very minor close pairs corresponding to a mass ratio range of 1:1-1:6, 1:6-1:100 and lower than 1:100, respectively. Due to completeness issues, we do not consider the very minor pairs in the analysis. Overall, the major merger fraction increases up to z â 2 â 3 reaching 25% for pairs with the most massive galaxy with a stellar mass M â„ 10 9.5 M. Beyond this redshift, the fraction decreases down to ⌠5% at z â 6. The major merger fraction for lower mass primary galaxies M †10 9.5 M , seems to follow a more constant evolutionary trend with redshift. Thanks to the addition of new MUSE fields and new selection criteria, the increased statistics of the pair samples allow to narrow significantly the error bars compared to our previous analysis (Ventou et al. 2017). The evolution of the minor merger fraction is roughly constant with cosmic time, with a fraction of 20% at z < 3 and a slow decrease between 3 †z †6 to 8 â 13%
MusE GAs FLOw and Wind (MEGAFLOW) IX. The impact of gas flows on the relations between the mass, star formation rate and metallicity of galaxies
We study the link between gas flow events and key galaxy scaling relations:
the relations between star formation rate (SFR) and stellar mass (the main
sequence, MS), gas metallicity and stellar mass (the mass-metallicity relation,
MZR) and gas metallicity, stellar mass and SFR (the fundamental metallicity
relation, FMR). Using all star-forming galaxies (SFGs) in the 22 MUSE fields of
the MusE GAs FLOw and Wind (MEGAFLOW) survey, we derive the MS, MZR and FMR
scaling relations for 385 SFGs with at
redshifts 0.35 < z < 0.85. Using the MUSE data and complementary X-Shooter
spectra at 0.85 < z < 1.4, we determine the locations of 21 SFGs associated
with inflowing or outflowing circumgalactic gas (i.e. with strong MgII
absorption in background quasar spectra) relative to these scaling relations.
Compared to a control sample of galaxies without gas flows (i.e., without MgII
absorption within 70 kpc of the quasar), SFGs with inflow events (i.e., MgII
absorption along the major axis) are preferentially located above the MS, while
SFGs with ouflow events (i.e., MgII absorption along the minor axis) are
preferentially more metal rich. Our observations support the scenario in which
gas accretion increases the SFR while diluting the metal content and where
circumgalactic outflows are found in more metal-rich galaxies.Comment: 13 pages, 8 figure
PDRs4All VI: Probing the Photochemical Evolution of PAHs in the Orion Bar Using Machine Learning Techniques
[Abridged] JWST observations of the Orion Bar have shown the incredible
richness of PAH bands and their variation on small scales. We aim to probe the
photochemical evolution of PAHs across the key zones of the photodissociation
region (PDR) that is the Orion Bar using unsupervised machine learning. We use
NIRSpec and MIRI IFU data from the JWST ERS Program PDRs4All. We lever
bisecting k-means clustering to generate detailed spatial maps of the spectral
variability in several wavelength regions. We discuss the variations in the
cluster profiles and connect them to the local physical conditions. We
interpret these variations with respect to the key zones: the HII region, the
atomic PDR zone, and the three dissociation fronts. The PAH emission exhibits
spectral variation that depends strongly on spatial position in the PDR. We
find the 8.6um band to behave differently than all other bands which vary
systematically with one another. We find uniform variation in the 3.4-3.6um
bands and 3.4/3.3 intensity ratio. We attribute the carrier of the 3.4-3.6um
bands to a single side group attached to very similarly sized PAHs. Cluster
profiles reveal a transition between characteristic profiles classes of the
11.2um feature from the atomic to the molecular PDR zone. We find the carriers
of each of the profile classes to be independent, and reason the latter to be
PAH clusters existing solely deep in the molecular PDR. Clustering also reveals
a connection between the 11.2 and 6.2um bands; and that clusters generated from
variation in the 10.9-11.63um region can be used to recover those in the
5.95-6.6um region. Clustering is a powerful tool for characterizing PAH
variability on both spatial and spectral scales. For individual bands as well
as global spectral behaviours, we find UV-processing to be the most important
driver of the evolution of PAHs and their spectral signatures in the Orion Bar.Comment: 28 pages, 20 figures, submitted to A&
MusE gas flow and wind (MEGAFLOW) VIII: discovery of a MgII emission halo probed by a quasar sightline
Galaxie
Gas Accretion in Star-Forming Galaxies
Cold-mode gas accretion onto galaxies is a direct prediction of LCDM
simulations and provides galaxies with fuel that allows them to continue to
form stars over the lifetime of the Universe. Given its dramatic influence on a
galaxy's gas reservoir, gas accretion has to be largely responsible for how
galaxies form and evolve. Therefore, given the importance of gas accretion, it
is necessary to observe and quantify how these gas flows affect galaxy
evolution. However, observational data have yet to conclusively show that gas
accretion ubiquitously occurs at any epoch. Directly detecting gas accretion is
a challenging endeavor and we now have obtained a significant amount of
observational evidence to support it. This chapter reviews the current
observational evidence of gas accretion onto star-forming galaxies.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by
Springer. This chapter includes 22 pages with 7 Figure
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