1,077 research outputs found
Spatially resolved spectroscopy of Coma cluster early-type galaxies - II:the minor axis dataset
We present minor axis, off set major axis and one diagonal long slit spectra for 10 E and S0 galaxies of the Coma cluster drawn from a magnitude-limited sample studied before. We derive rotation curves, velocity dispersion profiles and the H-3 and H-4 coefficients of the Hermite decomposition of the line of sight velocity distribution. Moreover, we derive the line index profiles of Mg, Fe and Hbeta line indices and assess their errors. The data will be used to construct dynamical models of the galaxies and study their stellar populations
Kinematic and stellar population properties of the counter-rotating components in the S0 galaxy NGC 1366
Context. Many disk galaxies host two extended stellar components that rotate in opposite directions. The analysis of the stellar populations of the counter-rotating components provides constraints on the environmental and internal processes that drive their formation. Aims. The S0 NGC 1366 in the Fornax cluster is known to host a stellar component that is kinematically decoupled from the main body of the galaxy. Here we successfully separated the two counter-rotating stellar components to independently measure the kinematics and properties of their stellar populations. Methods. We performed a spectroscopic decomposition of the spectrum obtained along the galaxy major axis and separated the relative contribution of the two counter-rotating stellar components and of the ionized-gas component. We measured the line-strength indices of the two counter-rotating stellar components and modeled each of them with single stellar population models that account for the \u3b1/Fe overabundance. Results. We found that the counter-rotating stellar component is younger, has nearly the same metallicity, and is less \u3b1/Fe enhanced than the corotating component. Unlike most of the counter-rotating galaxies, the ionized gas detected in NGC 1366 is neither associated with the counter-rotating stellar component nor with the main galaxy body. On the contrary, it has a disordered distribution and a disturbed kinematics with multiple velocity components observed along the minor axis of the galaxy. Conclusions. The different properties of the counter-rotating stellar components and the kinematic peculiarities of the ionized gas suggest that NGC 1366 is at an intermediate stage of the acquisition process, building the counter-rotating components with some gas clouds still falling onto the galaxy. \ua9 ESO 2017
Source finding, parametrization and classification for the extragalactic Effelsberg-Bonn HI Survey
Context. Source extraction for large-scale HI surveys currently involves
large amounts of manual labor. For data volumes expected from future HI surveys
with upcoming facilities, this approach is not feasible any longer.
Aims. We describe the implementation of a fully automated source finding,
parametrization, and classification pipeline for the Effelsberg-Bonn HI Survey
(EBHIS). With future radio astronomical facilities in mind, we want to explore
the feasibility of a completely automated approach to source extraction for
large-scale HI surveys.
Methods. Source finding is implemented using wavelet denoising methods, which
previous studies show to be a powerful tool, especially in the presence of data
defects. For parametrization, we automate baseline fitting, mask optimization,
and other tasks based on well-established algorithms, currently used
interactively. For the classification of candidates, we implement an artificial
neural network which is trained on a candidate set comprised of false positives
from real data and simulated sources. Using simulated data, we perform a
thorough analysis of the algorithms implemented.
Results. We compare the results from our simulations to the parametrization
accuracy of the HI Parkes All-Sky Survey (HIPASS) survey. Even though HIPASS is
more sensitive than EBHIS in its current state, the parametrization accuracy
and classification reliability match or surpass the manual approach used for
HIPASS data.Comment: 13 Pages, 13 Figures, 1 Table, accepted for publication in A&
Stronger Constraints on the Evolution of the Relation up to
We revisit the possibility of redshift evolution in the
relation with a sample of 22 Seyfert 1 galaxies with
black holes (BHs) in the mass range and redshift
range with spectra obtained from spatially resolved
Keck/Low-Resolution Imaging Spectrometer observations. Stellar velocity
dispersions were measured directly from the Mg Ib region, taking into
consideration the effect of Fe II contamination, active galactic nucleus (AGN)
dilution, and host-galaxy morphology on our measurements. BH masses are
estimated using the H line width, and the luminosity at 5100
\overset{\lower.5em\circ}{\mathrm{A}} is estimated from surface brightness
decomposition of the AGN from the host galaxy using high-resolution imaging
from the Hubble Space Telescope. Additionally, we investigate the use of the [O
III] emission line width as a surrogate for stellar velocity
dispersion, finding better correlation once corrected for Fe II contamination
and any possible blueshifted wing components. Our selection criteria allowed us
to probe lower-luminosity AGNs and lower-mass BHs in the non-local universe
than those measured in previous single-epoch studies. We find that any offset
in the relation up to is consistent with the
scatter of local BH masses, and address the sources of biases and uncertainties
that contribute to this scatter.Comment: Accepted 14 May 2019 for publication in ApJ. 42 pages, 12 figures, 4
tables. Corrected for typographical error
State Estimation with Model Reduction and Shape Variability. Application to biomedical problems
We develop a mathematical and numerical framework to solve state estimation
problems for applications that present variations in the shape of the spatial
domain. This situation arises typically in a biomedical context where inverse
problems are posed on certain organs or portions of the body which inevitably
involve morphological variations. If one wants to provide fast reconstruction
methods, the algorithms must take into account the geometric variability. We
develop and analyze a method which allows to take this variability into account
without needing any a priori knowledge on a parametrization of the geometrical
variations. For this, we rely on morphometric techniques involving
Multidimensional Scaling, and couple them with reconstruction algorithms that
make use of reduced model spaces pre-computed on a database of geometries. We
prove the potential of the method on a synthetic test problem inspired from the
reconstruction of blood flows and quantities of medical interest with Doppler
ultrasound imaging
The Stellar Mass Fundamental Plane: The virial relation and a very thin plane for slow-rotators
Early-type galaxies -- slow and fast rotating ellipticals (E-SRs and E-FRs)
and S0s/lenticulars -- define a Fundamental Plane (FP) in the space of
half-light radius , enclosed surface brightness and velocity
dispersion . Since and are distance-independent
measurements, the thickness of the FP is often expressed in terms of the
accuracy with which and can be used to estimate sizes .
We show that: 1) The thickness of the FP depends strongly on morphology. If the
sample only includes E-SRs, then the observed scatter in is ,
of which only is intrinsic. Removing galaxies with
further reduces the observed scatter to ( intrinsic). The observed scatter increases to the usually
quoted in the literature if E-FRs and S0s are added. If the FP is defined using
the eigenvectors of the covariance matrix of the observables, then the E-SRs
again define an exceptionally thin FP, with intrinsic scatter of only
orthogonal to the plane. 2) The structure within the FP is most easily
understood as arising from the fact that and are nearly
independent, whereas the and correlations are nearly
equal and opposite. 3) If the coefficients of the FP differ from those
associated with the virial theorem the plane is said to be `tilted'. If we
multiply by the global stellar mass-to-light ratio and we account
for non-homology across the population by using S\'ersic photometry, then the
resulting stellar mass FP is less tilted. Accounting self-consistently for
gradients will change the tilt. The tilt we currently see suggests that
the efficiency of turning baryons into stars increases and/or the dark matter
fraction decreases as stellar surface brightness increases.Comment: 13 pages, 9 figures, 3 tables, accepted for publication in MNRA
Graph Spectral Image Processing
Recent advent of graph signal processing (GSP) has spurred intensive studies
of signals that live naturally on irregular data kernels described by graphs
(e.g., social networks, wireless sensor networks). Though a digital image
contains pixels that reside on a regularly sampled 2D grid, if one can design
an appropriate underlying graph connecting pixels with weights that reflect the
image structure, then one can interpret the image (or image patch) as a signal
on a graph, and apply GSP tools for processing and analysis of the signal in
graph spectral domain. In this article, we overview recent graph spectral
techniques in GSP specifically for image / video processing. The topics covered
include image compression, image restoration, image filtering and image
segmentation
The SAMI Galaxy Survey: revisiting galaxy classification through high-order stellar kinematics
Recent cosmological hydrodynamical simulations suggest that integral field spectroscopy can connect the high-order stellar kinematic moments h3 (~skewness) and h4 (~kurtosis) in galaxies to their cosmological assembly history. Here, we assess these results by measuring the stellar kinematics on a sample of 315 galaxies, without a morphological selection, using two-dimensional integral field data from the SAMI Galaxy Survey. Proxies for the spin parameter () and ellipticity () are used to separate fast and slow rotators; there exists a good correspondence to regular and non-regular rotators, respectively, as also seen in earlier studies. We confirm that regular rotators show a strong h3 versus anti-correlation, whereas quasi-regular and non-regular rotators show a more vertical relation in h3 and . Motivated by recent cosmological simulations, we develop an alternative approach to kinematically classify galaxies from their individual h3 versus signatures. Within the SAMI Galaxy Survey, we identify five classes of high-order stellar kinematic signatures using Gaussian mixture models. Class 1 corresponds to slow rotators, whereas Classes 2–5 correspond to fast rotators. We find that galaxies with similar {\lambda }_{{R}_{{\rm{e}}}}\mbox{--}{\epsilon }_{{\rm{e}}} values can show distinctly different {h}_{3}\mbox{--}V/\sigma signatures. Class 5 objects are previously unidentified fast rotators that show a weak h3 versus anti-correlation. From simulations, these objects are predicted to be disk-less galaxies formed by gas-poor mergers. From morphological examination, however, there is evidence for large stellar disks. Instead, Class 5 objects are more likely disturbed galaxies, have counter-rotating bulges, or bars in edge-on galaxies. Finally, we interpret the strong anti-correlation in h3 versus as evidence for disks in most fast rotators, suggesting a dearth of gas-poor mergers among fast rotators
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