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Made-to-measure dynamical particle models of elliptical galaxies
Get PDFNMAGIC modelling:
Syer and Tremaine (1996) proposed a made-to-measure (M2M) algorithmto construct N-particle
systems from observational data and used it to generate a triaxial model from density observables.
The first practical application was made by Bissantz et al. (2004), who constructed a
dynamical model of the projected face-on density distribution of the Milky Way. So far, only
density constraints have been considered and all models have been evolved in predetermined
potentials.
In chapter 2, a χ2-made-to-measure (χ2M2M) algorithm was developed, extending earlier
ideas by Syer and Tremaine. An important component of the new method is the use of the
standard χ2 merit function at the heart of the algorithm, which allows to assess the quality of a
model fit directly. In addition, kinematic observables including higher order moments have been
incorporated. Hence, kinematic and density (or surface density) constraints can be used to tailor
particle models. The new χ2M2M method was implemented in a fast, parallel code, NMAGIC.
This code also incorporates an optional but fast potential solver, allowing it to recompute the
potential during a model fit and, in addition, to test the stability of the final particle model.
The NMAGIC implementation of the χ2M2M algorithm is highly efficient, with a sequential
fraction of only ∼ 1%.
The geometric flexibility and performance of NMAGIC was illustrated with a number of
tests using spherical, oblate and triaxial target models. In the spherical experiments, the correct
isotropic target model was recovered, independently of the adopted initial conditions. The initial
model with density closer to the density of the final model had smaller final deviations from the
target observables, and a narrower distribution of weights.
The oblate tests showed that a large phase-space gradient can be recovered if present, and
illustrated the advantage of integral field data over slit data for constraining the model.
The triaxial experiments demonstrated that it is possible to start from a spherical model and
converge to a triaxial target, and illustrated NMAGIC’s ability in constructing models for triaxial
elliptical galaxies with which nature confronts us. A second triaxial experiment, in which a
slowly rotating model was used as a target for a non-rotating model, revealed that the residuals
in the first order kinematic moment are correlated. This gives a signature of tumbling which,
at least for this triaxial system, allows to distinguish between internal stellar streaming and
pattern rotation within Re, provided a full velocity field is available. However, a more complete
study of this problem is needed to firm up this result. This experiment also demonstrates the
usefulness of the χ2M2M algorithm for modelling mock (rather than real) galaxies in order to
learn about their dynamics. Such an experiment would not have been practical with standard
N-body simulations.
In chapter 3, I extended NMAGIC to account for seeing effects and proposed and implemented
an efficient method to estimate the mass-to-light ratio �. Tests of this scheme using
isotropic rotator input models have shown that the method recovers � within a few percent both
for self-consistent and dark matter dominated target galaxies. In addition, a likelihood scheme
was implemented, by which discrete velocity measurements can be taken into account without
binning them beforehand.
The modelling of NGC 4697 and NGC 3379, presented in chapters 3 and 4, respectively,
showed that the χ2M2M/NMAGIC particle method is a very promising modelling technique. In
fact, it has already gone further than the Schwarzschild method in that the gravitational potential
of the stars has been allowed to vary in the modelling, the mass-to-light ratio has been adapted
on the fly and the stability of the models has been checked.
Compared to the Schwarzschild method, the main advantages of the χ2M2M algorithm
as implemented in NMAGIC are that no symmetry restrictions have to be made and that no
complicated procedure for orbit sampling is needed. Another advantage is that the gravitational
potential can be evolved self-consistently, which further allows to test the stability of a model
after the correction phase. Every χ2M2M model corresponds to a computation of an orbit
library in the Schwarzschild method. In problems where the same orbit library can be reused,
Schwarzschild’s method is more efficient.
The present implementation of NMAGIC is optimized for modeling nearly spherical systems.
This is mainly due to the potential solver and the density observables (Alm), both based
on a spherical harmonics decomposition of the density distribution.
In the next two sections below, I will discuss the astronomical results from the dynamical
modelling of NGC 4697 and NGC 3379.
Astronomical results:
NGC 4697:
Chapter 3 presented a dynamical study of the E4 galaxy NGC 4697 using surface brightness
measurements and a combined kinematic data set, which runs from the center of the galaxy to
about 4.5 effective radii. The kinematic data set consists of long slit spectroscopic data and
discrete PNe velocity measurements.
Even though NMAGIC does not require any symmetry assumptions for the modelling, I have
forced the method to generate axisymmetric particle models for NGC 4697. Both self-consistent
models without dark matter, and models following a sequence of circular speed curves with
increasing dark halo contributions have been investigated. The PN data have been used both
binned on two different spatial grids, as well as with the new likelihood scheme, to make sure
that the results are not biased by the way the PNe data are incorporated.
The main result is that models both with and without dark matter are consistent with all
the data. These models fit all kinematic data with χ2/N < 1, both in potentials with only
luminous matter and in potentials including sufficiently massive halos to generate nearly flat
circular rotation curves. The massive dark halo models tend to fit the data slightly better in
the sense of lower χ2/N, for both the slit kinematics and the PN data, but these variations are
small and not yet statistically significant. To exclude models without dark matter would require
PN velocities at even larger radii than currently available, out to an estimated ≃ 6Re from the
center.
These models differ from earlier studies performed byM´endez et al. (2001) in the sense that
we generate axisymmetric models instead of spherical ones and that our models are flexible with
regard to anisotropy. The best-fitting models are slightly radially anisotropic, with β ≃ 0.3 at the
center, increasing to β ≃ 0.5 at∼
> 2Re. This is consistent with the value given by Dekel et al.
(2005) obtained from merger simulations carried out within the �CDM cosmology framework.
NGC 3379:
In chapter 4, the dynamical modelling of the intermediate luminosity E1 galaxy NGC 3379 was
presented. The models were constructed using photometric and kinematic observations for this
galaxy. Again, a combined kinematic data set was used, consisting of long slit spectroscopic
data with SAURON integral field absorption line kinematics and PN velocity measurements
with the PN.S instrument from Douglas et al. (2007). The combined data set runs from the
center of NGC 3379 to about 7 effective radii. This is the first time that integral field SAURON
kinematic data of a real galaxy has been incorporated in NMAGIC.
Both self-consistent models without dark matter, and models following a sequence of circular
speed curves with increasing dark halo contributions have been investigated.
Several dynamical models, with and without DM, produce a viable fit to all the data. For
assumed spherical symmetry the data is consistent with near-isotropic models dominated by
stellar mass and with radially anisotropic models in moderately massive halos with DMfractions
≃ 60 percentage at 7 Re. In addition, a series of of oblate models have been constructed which
essentially confirm the spherical results.
The main conclusion is that the steeply declining PNe velocity dispersion profile is consistent
with a variety of DM halos. It is difficult to constrain the potential in this galaxy with the
present data. This is mainly due to the well known mass anisotropy degeneracy, which masks
the DM distribution by preferentially populating radial orbits. Hence the possibility remains
that NGC 3379 has the kind of dark matter halo that is consistent with the current �CDM
paradigm
The X-ray-faint early-type galaxy NGC 4697
No full textWe analyze archival ROSAT HRI, ROSAT PSPC, and ASCA data of the X-ray-faint early-type galaxy NGC 4697. The joint ROSAT PSPC + ASCA spectrum is fitted by a two-component thermal model, a MEKAL model with kT(MEKAL) = 0.26(-0.03)(+0.04) keV with low metallicity and a bremsstrahlung model with kT(BREM) = 5.2(-1.6)(+3.0) keV. A similar model was found to fit the spectra of another faint early-type galaxy (NGC 4382) and the bulge of M31. We interpret this soft emission as a combination of emission from a soft component of low-mass X-ray binaries (LMXBs) and from a low-temperature interstellar medium, although the relative contributions of the two components could not be determined. Twelve point sources were identified within 4 ' of NGC 4697, of which 11 are most likely LMXBs associated with the galaxy. The soft X-ray colors of four of the LMXBs in NGC 4697 support the claim that LMXBs possess a soft spectral component. Finally, we present a simulation of what we believe the Chandra data of NGC 4697 will look like
Linked collectors and determiners for: Systematics of the Mecocephala group (Hemiptera: Heteroptera: Pentatomidae) based on a phylogenetic perspective: Inclusion of Hypanthracos, description of three new genera, and redescription of Ogmocoris.
No full textNatural history specimen data linked to collectors and determiners held within, "Systematics of the Mecocephala group (Hemiptera: Heteroptera: Pentatomidae) based on a phylogenetic perspective: Inclusion of Hypanthracos, description of three new genera, and redescription of Ogmocoris". Claims or attributions were made on Bionomia by volunteer Scribes, <a href="http://bionomia.net/dataset/30c89eb0-738f-4697-8f3b-1e7eadf169ee">https://bionomia.net/dataset/30c89eb0-738f-4697-8f3b-1e7eadf169ee</a> using specimen data from the dataset aggregated by the Global Biodiversity Information Facility, <a href="https://gbif.org/dataset/30c89eb0-738f-4697-8f3b-1e7eadf169ee">https://gbif.org/dataset/30c89eb0-738f-4697-8f3b-1e7eadf169ee</a>. Formatted as a Frictionless Data package
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NGC 4261 and NGC 4697: Rejuvenated Elliptical Galaxies
No full textChandra images present evidence of a nonuniform spatial distribution of discrete X-ray sources in the elliptical galaxy NGC 4261. This nonuniform distribution is inconsistent with the optical morphology of NGC 4261 at greater than a 99.9% confidence level. Similar evidence is seen in one more elliptical galaxy (NGC 4697; 98% confidence level) out of five cases we investigated. NGC 4261 and NGC 4697 have old stellar populations (9-15 Gyr) and fine-structure parameters of 1 and 0, respectively, suggesting that no recent merging activity occurred. On the basis of simulations of galaxy interactions, we propose that the X-ray sources responsible for the nonuniform distribution are associated with young stellar populations, related to the rejuvenating fallback of material in tidal tails onto a relaxed merger remnant or to shock-induced star formation along the tidal tails.Accepted Manuscrip
Pärnu muuseum. Amandus Adamson. Lapse pea (kunstniku vanem tütar). (nr. 4697)
No full textKlaasnegatiiv 9x12 vertikaalneTekst negatiivi ümbrikul: Pärnu muuseum. Adamson:Lapse pea /kunstniku vanem tütar,a1917/ nr 4697. Foto Tuulse, 1943. Tempel: Instituu
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Chandra X-ray observations of the X-ray faint elliptical galaxy NGC 4697
No full textA Chandra ACIS S3 observation of the X-ray faint elliptical galaxy NGC 4697 resolves much of the X-ray emission (61% of the counts from within one effective radius) into 90 point sources, of which similar to 80 are low-mass X-ray binaries (LMXBs) associated with this galaxy. The dominance of LMXBs indicates that X-ray faint early-type galaxies have lost much of their interstellar gas. On the other hand, a modest portion of the X-ray emission from NGC 4697 is due to hot gas. Of the unresolved emission, it is likely that about half is from fainter unresolved LMXBs, while the other half (similar to 23% of the total count rate) is from interstellar gas. The X-ray-emitting gas in NGC 4697 has a rather low temperature (kT = 0.29 keV). The emission from the gas is very extended, with a much flatter surface brightness profile than the optical light, and has an irregular, L-shaped morphology. The physical state of the hot gas is uncertain; the X-ray luminosity and extended surface brightness are inconsistent with a global supersonic wind, a partial wind, or a global cooling inflow. The gas may be undergoing subsonic inflation, rotationally induced outflow, or ram pressure stripping. X-ray spectra of the resolved sources and diffuse emission show that the soft X-ray spectral component, found in this and other X-ray faint ellipticals with ROSAT, is due to interstellar gas. The cumulative LMXB spectrum is well fitted by thermal bremsstrahlung at kT = 8.1 keV, without a significant soft component. NGC 4697 has a central X-ray source with a luminosity of L(X) = 8 x 10(38) ergs s(-1), which may be due to an active galactic nucleus and/or one or more LMXBs. At most, the massive black hole (BH) at the center of this galaxy is radiating at a very small fraction (less than or equal to4 x 10(-8)) of its Eddington luminosity. Three of the resolved sources in NGC 4697 are supersoft sources. In the outer regions of NGC 4697, seven of the LMXBs (about 20%) are coincident with candidate globular clusters, which indicates that globulars have a high probability of containing X-ray binaries compared to the normal stellar population. We suggest that all of the LMXBs may have been formed in globulars. The X-ray to optical luminosity ratio for the LMXBs in NGC 4697 is L(X)(LMXB, 0.3-10 keV)/L(B) = 8.1 X 10(29) ergs s(-1) L(B.)(-1), which is about 35% higher than the value for the bulge of M31. Other comparisons suggest that there are significant variations (factor of greater than or similar to2) in the LMXB X-ray-to-optical ratios of early-type galaxies and spiral bulges. The X-ray luminosity function of NGC 4697 is also flatter than that found for the bulge of M31. The X-ray luminosities (0.3-10 keV) of the resolved LMXBs range from similar to5 x 10(37) to similar to2.5 X 10(39) ergs s(-1). The luminosity function of the LMXBs has a "knee" at 3.2 X 10(38) ergs s(-1), which is approximately the Eddington luminosity of a 1.4 M. neutron star (NS). This knee appears to be a characteristic feature of the LMXB population of early-type galaxies, and we argue that it separates BH and NS binaries. This characteristic luminosity could be used as a distance estimator. If they are Eddington limited, the brightest LMXBs contain fairly massive accreting BHs. The presence of this large population of NS and massive BH stellar remnants in this elliptical galaxy shows that it (or its progenitors) once contained a large population of massive main-sequence stars
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