58 research outputs found
Flattening of Galaxies of Different Morphological Types in Subclusters of Coma
The dependence of flattening of galaxies on the density of galaxies in
subclusters selected around galaxies NGC4889, NGC4874 and NGC4839 in the Coma
cluster has been studied. The mean values of observed ratios of galaxy
diameters and histograms of their distributions indicate that in the central,
dense regions of subclusters E and S0 type galaxies are close to spheroidals.
Spiral galaxies in subcllusters are found with a hydrogen deficit that about 5
times exceeds the hydrogen deficit in spirals within the halo of the Coma
cluster. Most of spirals with a hydrogen deficit in the subcluster around NGC
4874 according to their 3-D coordinates are located closer to the south-east
edge of this subcluster near an extended gas filament in the x-ray region. This
may indicate over the move of this subcluster toward the central condensation
of faint galaxies in the Coma cluster for a possible merge with it.Comment: This material is a slightly corrected version of an article published
in the "Astrophysics", Vol. 50, No. 3, 2007
Equilibrium configuration of a bounded inextensible membrane subject to solar radiation pressure
The equilibrium shape of a thin inextensible membrane subject to solar radiation pressure under given boundary constraints is studied. The membrane is assumed to be insusceptible to elastic deformation and to have negligible bending resistance, and its steady-state shape is therefore described by a developable surface (i.e., a surface of zero Gaussian curvature), resulting from an equilibrium between radiation pressure and membrane tension forces. A quantitative understanding of the mechanics of such membranes is essential in characterizing the dynamics of solar sail spacecraft that use sail wing tip displacement as an attitude control mode. The analysis in this paper develops a theoretical foundation for the billowed wing shape. Under reasonable simplifying assumptions, the key result is that solar radiation pressure and a given wing tip displacement yield a billowed solar sail wing with the shape of a generalized cylinder (i.e., a developable ruled surface, whose rulings are all parallel, rather than a general developable with variable ruling directions). The base curve geometry for the solar sail is also determined as the solution to a boundary value problem. The results presented herein allow the shape of the billowed membrane to be computed to any desired precision, for any given tip displacement
Environmental dependence of the galaxy stellar mass function in the Dark Energy Survey Science Verification data
Measurements of the galaxy stellar mass function are crucial to understand the formation of galaxies in the Universe. In a hierarchical clustering paradigm, it is plausible that there is a connection between the properties of galaxies and their environments. Evidence for environmental trends has been established in the local Universe. The Dark Energy Survey (DES) provides large photometric data sets that enable further investigation of the assembly of mass. In this study, we use ˜3.2 million galaxies from the (South Pole Telescope) SPT-East field in the DES science verification (SV) data set. From grizY photometry, we derive galaxy stellar masses and absolute magnitudes, and determine the errors on these properties using Monte Carlo simulations using the full photometric redshift probability distributions. We compute galaxy environments using a fixed conical aperture for a range of scales. We construct galaxy environment probability distribution functions and investigate the dependence of the environment errors on the aperture parameters. We compute the environment components of the galaxy stellar mass function for the redshift range 0.15 < z < 1.05. For z < 0.75, we find that the fraction of massive galaxies is larger in high-density environment than in low-density environments. We show that the low-density and high-density components converge with increasing redshift up to z ˜ 1.0 where the shapes of the mass function components are indistinguishable. Our study shows how high-density structures build up around massive galaxies through cosmic time
Dwarf Elliptical Galaxies
Dwarf elliptical (dE) galaxies, with blue absolute magnitudes typically
fainter than , are the most numerous type of galaxy in the nearby
universe. Tremendous advances have been made over the past several years in
delineating the properties of both Local Group satellite dE's and the large dE
populations of nearby clusters. We review some of these advances, with
particular attention to how well currently available data can constrain 1)
models for the formation of dE's, 2) the physical and evolutionary connections
between different types of galaxies (nucleated and nonnucleated dE's, compact
E's, irregulars, and blue compact dwarfs) that overlap in the same portion of
the mass-spectrum of galaxies, 3) the contribution of dE's to the galaxy
luminosity functions in clusters and the field, 4) the star-forming histories
of dE's and their possible contribution to faint galaxy counts, and 5) the
clustering properties of dE's. In addressing these issues, we highlight the
extent to which selection effects temper these constraints, and outline areas
where new data would be particularly valuable.Comment: 63p, uuencoded compressed postscript, 2/8 figs included, A&A Review
in press, request paper copies from [email protected], STScI 86
Modified Rodrigues Parameters: An Efficient Representation of Orientation in 3D Vision and Graphics
Galaxy bulges and their massive black holes: a review
With references to both key and oft-forgotten pioneering works, this article
starts by presenting a review into how we came to believe in the existence of
massive black holes at the centres of galaxies. It then presents the historical
development of the near-linear (black hole)-(host spheroid) mass relation,
before explaining why this has recently been dramatically revised. Past
disagreement over the slope of the (black hole)-(velocity dispersion) relation
is also explained, and the discovery of sub-structure within the (black
hole)-(velocity dispersion) diagram is discussed. As the search for the
fundamental connection between massive black holes and their host galaxies
continues, the competing array of additional black hole mass scaling relations
for samples of predominantly inactive galaxies are presented.Comment: Invited (15 Feb. 2014) review article (submitted 16 Nov. 2014). 590
references, 9 figures, 25 pages in emulateApJ format. To appear in "Galactic
Bulges", E. Laurikainen, R.F. Peletier, and D.A. Gadotti (eds.), Springer
Publishin
Thermo‐time domain reflectometry to evaluate unsaturated soils contaminated with nonaqueous phase liquids
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