2,725 research outputs found
Velocity Dispersion of 335 Galaxy Clusters Selected from the Sloan Digital Sky Survey: Statistical Evidence for Dynamical Interaction, and Against Ram-Pressure Stripping
There has been plenty of observational evidence of cluster galaxy evolution.
However, it has been difficult to identify the origin of the cluster galaxy
evolution. Here we show that gravitational interaction/friction between
galaxies is the statistically dominant physical mechanism responsible for the
cluster galaxy evolution, and that the well-favored ram-pressure stripping by
the cluster gas is not statistically driving the cluster galaxy evolution.
We have constructed the largest composite cluster with 14548 member galaxies
out of 335 clusters with ~>300 km/s carefully selected from the SDSS. By
measuring velocity dispersions of various subsamples of galaxies in this
composite cluster, we found that bright cluster galaxies (Mz<-23) have
significantly smaller velocity dispersion than faint galaxies (Mz>-23). We
interpret this as direct evidence of the dynamical interaction/friction between
cluster galaxies, where massive galaxies lose their velocity through the energy
equipartition during the dynamical interaction/friction with less massive
galaxies. We also found that star-forming late-type galaxies have a larger
velocity dispersion than passive late-type galaxies. This is inconsistent with
the ram-pressure stripping model; since the ram-pressure is proportional to
sigma v^2 (i.e., stronger for galaxies with high velocity), the ram-pressure
stripping cannot explain the observed trends of passive (evolved) galaxies
having low velocity rather than high velocity. On the other hand, the result is
again consistent with the dynamical galaxy-galaxy interaction/friction, where
more evolved (passive) galaxies lose their velocity through dynamical
interaction/friction.Comment: MNRAS in pres
「ストリートファイター」は武道か? : ヴァーチャル・ニンジャ理論、イデオロギー、ファイティングゲーム・プレーヤーの意図的な自己変容
This experimental article explores the question of whether it is possible to examine the experience of playing fighting games (video games) as a form of self-cultivation or practice and, in so doing, whether it becomes possible to shift the debate about the potential impact of violent video games on the people who play them (and on society around them). The article draws on five years of surveys and interviews with gamers from around the world, but seeks to interpret this data through a critical and creative reading of the games themselves as well as a reading of the so-called bushidō tradition (of texts about the intersection between Zen and the martial arts). The article concludes that fighting games might be experienced as forms of martial arts in themselves, complete with potentials for self-transformation, but that this form of engagement requires appropriate intentionality from players, which provokes a space for a manifesto to guide players’ intentions
From the Dragon to the Beast: The Martial Monk and Virtual Ninja as Actual Martial Artists
Navigating between society’s moral panics about the influence of violent videogames and philosophical texts about selfcultivation in the martial arts, this extract from the monograph, The Virtual Ninja Manifesto: Fighting Games, Martial Arts, and Gamic Orientalism, asks whether the figure of the ‘virtual ninja’ can emerge as an aspirational figure in the twenty-first century, modeled on the 'event' of Bruce Lee. The work seeks to illustrate the argument that the kind of training required to master videogames approximates the kind of training described in Zen literature on the martial arts. It suggests that the shift from the actual dōjō to a digital dōjō represents only a change in the technological means of practice. It explores the possibility that, after Bruce Lee and Daigo Umehara, martial arts games can promote spiritual development
Near-infrared spectroscopy of EX Lupi in outburst
EX Lup is the prototype of the EXor class of young eruptive stars: objects
showing repetitive brightenings due to increased accretion from the
circumstellar disk to the star. In this paper, we report on medium-resolution
near-infrared spectroscopy of EX\,Lup taken during its extreme outburst in
2008, as well as numerical modeling with the aim of determining the physical
conditions around the star. We detect emission lines from atomic hydrogen,
helium, and metals, as well as first overtone bandhead emission from carbon
monoxide. Our results indicate that the emission lines are originating from gas
located in a dust-free region within ~ 0.2 AU of the star. The profile of the
CO bandhead indicates that the CO gas has a temperature of 2500 K, and is
located in the inner edge of the disk or in the outer parts of funnel flows.
The atomic metals are probably co-located with the CO. Some metallic lines are
fluorescently excited, suggesting direct exposure to ultraviolet photons. The
Brackett series indicates emission from hot (10000 K) and optically thin gas.
The hydrogen lines display a strong spectro-astrometric signal, suggesting that
the hydrogen emission is probably not coming from an equatorial boundary layer;
a funnel flow or disk wind origin is more likely. This picture is broadly
consistent with the standard magnetospheric accretion model usually assumed for
normally accreting T Tauri stars. Our results also set constraints on the
eruption mechanism, supporting a model where material piles up around the
corotation radius and episodically falls onto the star.Comment: 12 pages, 8 figures, 1 table, accepted for publication in Ap
Seyfert's Sextet: where is the gas?
Seyfert's Sextet (a.k.a HCG 79) is one of the most compact and isolated
galaxy groups in the local Universe. It shows a prominent diffuse light
component that accounts for ~50% of the total observed light. This likely
indicates that the group is in an advanced evolutionary phase, which would
predict a significant hot gaseous component. Previous X-ray observations had
suggested a low luminosity for this system, but with large uncertainties and
poor resolution. We present the results from a deep (70 ks), high resolution
Chandra observation of Seyfert's Sextet, requested with the aim of separating
the X-ray emission associated with the individual galaxies from that of a more
extended inter-galactic component. We discuss the spatial and spectral
characteristics of this group we derive with those of a few similar systems
also studied in the X-ray band. The high resolution X-ray image indicates that
the majority of the detected emission does not arise in the compact group but
is concentrated towards the NW and corresponds to what appears to be a
background galaxy cluster. The emission from the group alone has a total
luminosity of ~1x10^40 erg/s in the (0.5-5) keV band. Most of the luminosity
can be attributed to the individual sources in the galaxies, and only ~2x10^39
erg/s is due to a gaseous component. However, we find that this component is
also mostly associated with the individual galaxies of the Sextet, leaving
little or no residual in a truly IGM component. The extremely low luminosity of
the diffuse emission in Seyfert's Sextet might be related to its small total
mass.Comment: 8 pages, 7 figures. Accepted on A&
Optical spectroscopy of EX Lupi during quiescence and outburst: Infall, wind, and dynamics in the accretion flow
We explore the accretion mechanisms in EX Lupi, prototype of EXor variables,
during its quiescence and outburst phases. We analyse high-resolution optical
spectra taken before, during, and after its 2008 outburst. In quiescence and
outburst, the star presents many permitted emission lines, including typical
CTTS lines and numerous neutral and ionized metallic lines. During the
outburst, the number of emission lines increases to over a thousand, with
narrow plus broad component structure (NC+BC). The BC profile is highly
variable on short timescales (24-72h). An active chromosphere can explain the
metallic lines in quiescence and the outburst NC. The dynamics of the BC line
profiles suggest an origin in a hot, dense, non-axisymmetric, and non-uniform
accretion column that suffers velocity variations along the line-of-sight on
timescales of days. Assuming Keplerian rotation, the emitting region would be
located at ~0.1-0.2 AU, consistent with the inner disk rim, but the velocity
profiles of the lines reveal a combination of rotation and infall. Line ratios
of ions and neutrals can be reproduced with a temperature of T~6500 K for
electron densities of a few times 10cm in the line-emitting
region. The data confirm that the 2008 outburst was an episode of increased
accretion, albeit much stronger than previous EX Lupi and typical EXors
outbursts. The line profiles are consistent with the infall/rotation of a
non-axisymmetric structure that could be produced by clumpy accretion during
the outburst phase. A strong inner disk wind appears in the epochs of higher
accretion. The rapid recovery of the system after the outburst and the
similarity between the pre-outburst and post-outburst states suggest that the
accretion channels are similar during the whole period, and only the accretion
rate varies, providing a superb environment for studying the accretion
processes.Comment: 15 pages plus 26 pages online material, accepted by A&
The origin of redshift asymmetries: How LambdaCDM explains anomalous redshift
Several authors have found a statistically significant excess of galaxies
with higher redshifts relative to the group centre, so-called discordant
redshifts, in particular in groups where the brightest galaxy, identified in
apparent magnitudes, is a spiral. Our aim is to explain the observed redshift
excess. We use a semi-analytical galaxy catalogue constructed from the
Millennium Simulation to study redshift asymmetries in spiral-dominated groups
in the Lambda cold dark matter (LambdaCDM) cosmology. We show that discordant
redshifts in small galaxy groups arise when these groups are gravitationally
unbound and the dominant galaxy of the group is misidentified. The redshift
excess is especially significant when the apparently brightest galaxy can be
identified as a spiral, in full agreement with observations. On the other hand,
the groups that are gravitationally bound do not show a significant redshift
asymmetry. When the dominant members of groups in mock catalogues are
identified by using the absolute B-band magnitudes, our results show a small
blueshift excess. This result is due to the magnitude limited observations that
miss the faint background galaxies in groups. When the group centre is not
correctly identified it may cause the major part of the observed redshift
excess. If the group is also gravitationally unbound, the level of the redshift
excess becomes as high as in observations. There is no need to introduce any
"anomalous" redshift mechanism to explain the observed redshift excess.
Further, as the Friends-of-Friends percolation algorithm picks out the
expanding parts of groups, in addition to the gravitationally bound group
cores, group catalogues constructed in this way cannot be used as if the groups
are purely bound systems.Comment: Accepted for publication in A&
Near-Infrared and Optical Luminosity Functions from the 6dF Galaxy Survey
Luminosity functions and their integrated luminosity densities are presented
for the 6dF Galaxy Survey (6dFGS). This ongoing survey ultimately aims to
measure around 150,000 redshifts and 15,000 peculiar velocities over almost the
entire southern sky at |b|>10 deg. The main target samples are taken from the
2MASS Extended Source Catalog and the SuperCOSMOS Sky Survey catalogue, and
comprise 138,226 galaxies complete to (K, H, J, rF, bJ) = (12.75, 13.00, 13.75,
15.60, 16.75). These samples are comparable in size to the optically-selected
Sloan Digital Sky Survey and 2dF Galaxy Redshift Survey samples, and improve on
recent near-infrared-selected redshift surveys by more than an order of
magnitude in both number and sky coverage. The partial samples used in this
paper contain a little over half of the total sample in each band and are ~90
percent complete.
Luminosity distributions are derived using the 1/Vmax, STY and SWML
estimators, and probe 1 to 2 absolute magnitudes fainter in the near-infrared
than previous surveys. The effects of magnitude errors, redshift incompleteness
and peculiar velocities have been taken into account and corrected throughout.
Generally, the 6dFGS luminosity functions are in excellent agreement with those
of similarly-sized surveys. Our data are of sufficient quality to demonstrate
that a Schechter function is not an ideal fit to the true luminosity
distribution, due to its inability to simultaneously match the faint end slope
and rapid bright end decline. Integrated luminosity densities from the 6dFGS
are consistent with an old stellar population and moderately declining star
formation rate.Comment: 20 pages, 15 figures. MNRAS published. Replaces earlier version
carrying a typo in Table 6. High resolution versions of the figures can be
obtained from http://www.aao.gov.au/local/www/6df/Publication
The Galaxy Population of Low-Redshift Abell Clusters
We present a study of the luminosity and color properties of galaxies
selected from a sample of 57 low-redshift Abell clusters. We utilize the
non-parametric dwarf-to-giant ratio (DGR) and the blue galaxy fraction (fb) to
investigate the clustercentric radial-dependent changes in the cluster galaxy
population. Composite cluster samples are combined by scaling the counting
radius by r200 to minimize radius selection bias. The separation of galaxies
into a red and blue population was achieved by selecting galaxies relative to
the cluster color-magnitude relation. The DGR of the red and blue galaxies is
found to be independent of cluster richness (Bgc), although the DGR is larger
for the blue population at all measured radii. A decrease in the DGR for the
red and red+blue galaxies is detected in the cluster core region, while the
blue galaxy DGR is nearly independent of radius. The fb is found not to
correlate with Bgc; however, a steady decline toward the inner-cluster region
is observed for the giant galaxies. The dwarf galaxy fb is approximately
constant with clustercentric radius except for the inner cluster core region
where fb decreases. The clustercentric radial dependence of the DGR and the
galaxy blue fraction, indicates that it is unlikely that a simple scenario
based on either pure disruption or pure fading/reddening can describe the
evolution of infalling dwarf galaxies; both outcomes are produced by the
cluster environment.Comment: 28 pages, 6 figures, accepted for publication in Ap
- …