5,540 research outputs found
The Mass of the Centaurus A Group of Galaxies
The mass M, and the radius R_h, of the Centaurus A group are estimated from
the positions and radial velocities of 30 probable cluster members. For an
assumed distance of 3.9 Mpc it is found that R_h \sim 640 kpc. The velocity
dispersion in the Cen A group is 114 \pm 21 km/s. From this value, and R_h =
640 kpc, the virial theorem yields a total mass of 1.4 \times 10^{13} M_{\sun}
for the Cen A group. The projected mass method gives a mass of 1.8 \times
10^{13} M_{\sun}. These values suggest that the Cen A group is about seven
times as massive as the Local Group. The Cen A mass-to-light ratio is found to
be M/L_B = 155-200 in solar units. The cluster has a zero-velocity radius R_0 =
2.3 Mpc.Comment: 8 pages, 1 figure, in LaTeX format; to appear in the Astronomical
Journal in January 200
Are the Luminosities of RR Lyrae Stars Affected by Second Parameter Effects?
There is a serious discrepancy between the distance to the LMC derived from
the Cepheid Period-Luminosity relation and that obtained by using the Galactic
calibration for the luminosity of RR Lyrae stars. It is suggested that this
problem might be due to the fact that second parameter effects make it
inappropriate to apply Galactic calibrations to RR Lyrae variables in the
Magellanic Clouds, i.e. Mv(RR) could depend on both [Fe/H] and on one or more
second parameters.Comment: 10 pages as uuencoded compressed Postscript. Also available at
http://www.dao.nrc.ca/DAO/SCIENCE/science.htm
Geometricity for derived categories of algebraic stacks
We prove that the dg category of perfect complexes on a smooth, proper
Deligne-Mumford stack over a field of characteristic zero is geometric in the
sense of Orlov, and in particular smooth and proper. On the level of
triangulated categories, this means that the derived category of perfect
complexes embeds as an admissible subcategory into the bounded derived category
of coherent sheaves on a smooth, projective variety. The same holds for a
smooth, projective, tame Artin stack over an arbitrary field.Comment: 31 page
Killing spinor space-times and constant-eigenvalue Killing tensors
A class of Petrov type D Killing spinor space-times is presented, having the
peculiar property that their conformal representants can only admit Killing
tensors with constant eigenvalues.Comment: 11 pages, submitted to CQ
The Luminosity Distribution of Local Group Galaxies
From a rediscussion of Local Group membership, and of distances to individual
galaxies, we obtain values for 35 probable and possible Local Group
members. The luminosity function of these objects is well fitted by a Schechter
function with faint end slope . The probability that the
luminosity distribution of the Local Group is a single Schechter function with
steeper than -1.3 is less than 1 per cent. However, more complicated
luminosity functions, such as multi-component Schechter functions with steep
faint-end slopes, cannot be ruled out. There is some evidence that the
luminosity distribution of dwarf spheroidal galaxies in the Local Group is
steeper than that of dwarf irregular galaxies.Comment: 13 pages, 2 figures, accepted for publication in The Astronomical
Journal. Figure 2 replaced, conclusion based on this figure change
Some Global Characteristics of the Galactic Globular Cluster System
The relations between the luminosities , the metallicities ,
the Galactocentric radii , and the central concentration indices of
Galactic globular clusters are discussed. It is found that the most luminous
clusters rarely have collapsed cores. The reason for this might be that the
core collapse time scales for such populous clusters are greater than the age
of the Galaxy. Among those clusters, for which the structure has not been
modified by core collapse, there is a correlation between central concentration
and integrated luminosity, in the sense that the most luminous clusters have
the strongest central concentration. The outermost region of the Galaxy with
kpc was apparently not able to form metal-rich globular
clusters, whereas such clusters (of which Ter 7 is the prototype) were able to
form in some nearby dwarf spheroidal galaxies. It is not yet clear how the
popular hypothesis that globular clusters were initially formed with a single
power law mass spectrum can be reconciled with the observation that both (1)
Galactic globular clusters with kpc, and (2) the globulars associated
with the Sagittarius dwarf, appear to have bi-modal luminosity functions.Comment: 15 pages, 1 figur
Caltech Faint Galaxy Redshift Survey XV: Classification of Galaxies with 0.2 < z < 1.1 in the Hubble Deep Field (North) and its Flanking Fields
To circumvent the spatial effects of resolution on galaxy classification, the
images of 233 objects of known redshift in the Hubble Deep Field (HDF) and its
Flanking Fields (FF) that have redshifts in the range 0.20 < z < 1.10 were
degraded to the resolution that they would have had if they were all located at
a redshift z= 1.00. As in paper XIV of the present series, the effects of
shifts in rest wavelength were mitigated by using R-band images for the
classification of galaxies with 0.2 < z < 0.6 and I-band images for objects
with redshifts 0.6 < z < 1.1. A special effort was made to search for bars in
distant galaxies. The present data strongly confirm the previous conclusion
that the Hubble tuning fork diagram only provides a satisfactory framework for
the classification of galaxies with z ~< 0.3. More distant disk galaxies are
often difficult to shoehorn into the Hubble classification scheme. The paucity
of barred spirals and of grand-design spirals at large redshifts is confirmed.
It is concluded that the morphology of disk galaxies observed at look-back
times smaller than 3--4 Gyr differs systematically from that of more distant
galaxies viewed at look-back times of 4--8 Gyr. The disks of late-type spirals
at z >0.5 are seen to be more chaotic than those of their nearer counterparts.
Furthermore the spiral structure in distant early-type spirals appears to be
less well-developed than it is in nearby early-galaxies.Comment: Accepted for publication in the A
Rotating solenoidal perfect fluids of Petrov type D
We prove that aligned Petrov type D perfect fluids for which the vorticity
vector is not orthogonal to the plane of repeated principal null directions and
for which the magnetic part of the Weyl tensor with respect to the fluid
velocity has vanishing divergence, are necessarily purely electric or locally
rotationally symmetric. The LRS metrics are presented explicitly.Comment: 6 pages, no figure
Are prosocials unique in their egalitarianism? The pursuit of equality in outcomes among individualists.
The present research aims to elucidate to what extent the motive to ensure equality in outcomes is general and to what extent it interacts with other important motives such as maximizing own or collective gains. Because individuals may have different considerations and motivations in decision-making situations, it is likely that people with a different social value orientation will respond differently to an unequal distribution of outcomes. Contrary to our expectations, not only prosocials care about equality in outcomes. In study 1, we found that individualists choose to forego personal gains, despite obvious selfish reasons to cooperate, when outcomes were distributed unequally. In a second experiment we replicate this finding and show that individualists, just as do prosocials, demand equality in outcomes in interdependent situations. Our studies suggest that typifying individualists as solely being concerned about enhancing personal outcomes is too limited.Cooperation; Decision making; Demand; Distribution; Equality; Personal; Research; Social Value Orientation; Social values; Studies; Tit-For-Tat; Value;
The Nearest Group of Galaxies
The small Antlia-Sextans clustering of galaxies is located at a distance of
only 1.36 Mpc from the Sun, and 1.72 Mpc from the adopted barycenter of the
Local Group. The latter value is significantly greater than the radius of the
zero- velocity surface of the Local Group which, for an assumed age of 14 Gyr,
has Ro = 1.18 " 0.15 Mpc. This, together with the observation that the members
of the Ant-Sex group have a mean redshift of +114 " 12 km s-1 relative to the
centroid of the Local Group, suggests that the Antlia-Sextans group is not
bound to our Local Group, and that it is expanding with the Hubble flow. If
this conclusion is correct, then Antlia-Sextans may be the nearest external
clustering of galaxies. The total galaxian population of the Ant-Sex group is ~
1/5 that of the Local Group. However, the integrated luminosity of Ant-Sex is
two orders of magnitude lower than that of the Local Group.
Subject headings: Galaxies - clusters: individual (Antlia-Sextans)Comment: Has been accepted for publication in the Astrophysical Journal
Letter
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