46 research outputs found
Low surface brightness galaxies and tidally triggered star formation
Counts of companions to low surface brightness (LSB) galaxies are presented and these are compared to counts of companions to normal galaxies obtained with the same techniques and criteria. Our results are consistent with LSB's having no clustered companions and support the hypothesis that LSB galaxies have low star-formation rates because they lack external tidal triggering
The clustering of galaxies and groups
We show that there are typically 8 satellites in the magnitude range -16 ≥M(_BT)≥ -18 within a projected distance of 1h(^-1)Mpc of a bright galaxy, their surface density being described by a power law of slope ~ 0.8. If the clustering of the bright galaxies is accounted for this corresponds to 4 satellites and a steeper slope. The satellite distributions around late and early type galaxies are significantly different. The bright-faint cross-correlation function has a lower amplitude than the bright autocorrelation function. However, we also find that faint satellites are more strongly clustered around bright galaxies than brighter satellites are, contradicting theoretical expectations. We look at the dynamics of satellites around Milky Way-like galaxies. The observations are consistent with galaxies having isothermal dark halos, containing ~ 10(^12)Mo out to at least 150h(^-1)kpc. The circular velocity of the halo is equal to the circular velocity of the inner parts of the bright galaxy. We place a 95% lower limit on the density of the Universe, Ω > 0.024 by assuming that all the mass in the Universe is within 150h-'kpc of bright galaxies. We confirm the Holmberg effect: an excess of satellites close to the minor axis of the bright galaxy. We show that Low Surface Brightness (LSB) galaxies have fewer close companions than High Surface Brightness galaxies. Since LSB galaxies have a low star formation rate, this is consistent with theories in which star formation is tidally triggered. We develop a method for estimating the clustering of objects of particular masses, based on the statistics of a gaussian field. This allows the clustering to be estimated in the mildly non-linear regime, giving results which are in good agreement with the results of numerical simulations. Our results lead us to suggest that objects of above and below the average mass exist in separate regions of the Universe. We demonstrate the potentia
Probing Dark Matter Substructure in Lens Galaxies
We investigate the effects of numerous dark matter subhalos in a galaxy-sized
halo on the events of strong lensing, to assess their presence as expected from
the cold dark matter scenario. Lens galaxies are represented by a smooth
ellipsoid in an external shear field and additional cold dark matter subhalos
taken from Monte Carlo realizations which accord with recent N-body results. We
also consider other possible perturbers, globular clusters and luminous dwarf
satellites, for comparison. We then apply the models to the particular lens
systems with four images, B1422+231 and PG1115+080, for which smooth lens
models are unable to reproduce both the positions of the images and their radio
flux ratios or dust-free optical flux ratios simultaneously. We show that the
perturbations by both globular clusters and dwarf satellites are too small to
change the flux ratios, whereas cold dark matter subhalos are most likely
perturbers to reproduce the observed flux ratios in a statistically significant
manner. This result suggests us the presence of numerous subhalos in lens
galaxies, which is consistent with the results of cosmological N-body
simulations.Comment: 19 pages, including 5 figures, ApJ in pres
A randomised crossover trial comparing Thai and Swedish massage for fatigue and depleted energy
SUMMARY\ud
Background\ud
The aim of this study was to compare the efficacy and social constructions of Thai\ud
massage (TM) and Swedish massage (SM) for patients experiencing fatigue or\ud
depleted energy.\ud
Method\ud
Twenty participants were randomised to receive three once-weekly TM treatments\ud
and three once-weekly SM treatments, with crossover after three massages.\ud
Symptom checklists were administered at three time points and included\ud
Activation-Deactivation Adjective Check List and VAS Scale. Qualitative data\ud
were collected through semi-structured interviews and participants’ diary entries.\ud
Results\ud
Both massage types enhanced physical, emotional and mental wellbeing through\ud
improved sleep, relaxation, relief of stress and relief of muscular tension. TM\ud
alone showed specific energising and psychological stimulation results, along with\ud
carry-over effect and longer lasting benefits. Ninety-five percent of participants\ud
found relief from their initial reason presenting symptoms\ud
Conclusion\ud
TM or SM can relieve symptoms of fatigue or low energy by releasing stress,\ud
promoting relaxation, relieving muscular aches and pains and improving energy.\ud
SM results in a larger effect in relaxation and improved sleep whereas TM results\ud
in a larger effect in energising, rejuvenating and mentally stimulating effects.\ud
Keywords: Complementary Therapies; Therapy, Soft Tissue; Massage; Cross-\ud
Over Studie
The mental health safety improvement programme: a national quality improvement collaborative to reduce restrictive practice in England
In 2018, 38 mental health inpatient wards belonging to NHS trusts across England took part in the national reducing restrictive practice collaborative project, which aimed to reduce the use of rapid tranquillisation, restraint and seclusion of patients by 33%. Teams were supported to use quality improvement tools by skilled coaches as part of a national collaborative learning system. At the end of the programme, the overall use of restrictive practice had reduced by 15%. Of the teams that achieved improvements, the average reduction in restrictive practice was 61%. Across the collaborative there were improvements in the mean monthly use of restraints and rapid tranquillisation, and in the total use of all three measures of restrictive practice combined. Support from quality improvement coaches allowed ideas to be tested across the collaborative, enabling the creation of a theory of change for reducing restrictive practice based on areas with a high degree of belief to inform future improvement work in this area
The Dwarf Galaxy Population of the Dorado group down to Mv=-11
We present V and I CCD photometry of suspected low-surface brightness dwarf
galaxies detected in a survey covering ~2.4 deg^2 around the central region of
the Dorado group of galaxies. The low-surface brightness galaxies were chosen
based on their sizes and magnitudes at the limiting isophote of 26.0V\mu. The
selected galaxies have magnitudes brighter than V=20 (Mv=-11 for an assumed
distance to the group of 17.2 Mpc), with central surface brightnesses \mu0>22.5
V mag/arcsec^2, scale lengths h>2'', and diameters > 14'' at the limiting
isophote. Using these criteria, we identified 69 dwarf galaxy candidates. Four
of them are large very low-surface brightness galaxies that were detected on a
smoothed image, after masking high surface brightness objects. Monte Carlo
simulations performed to estimate completeness, photometric uncertainties and
to evaluate our ability to detect extended low-surface brightness galaxies show
that the completeness fraction is, on average, > 80% for dwarf galaxies with
and 22.5<\mu0<25.5 V mag/arcsec^2, for the range of sizes
considered by us (D>14''). The V-I colors of the dwarf candidates vary from
-0.3 to 2.3 with a peak on V-I=0.98, suggesting a range of different stellar
populations in these galaxies. The projected surface density of the dwarf
galaxies shows a concentration towards the group center similar in extent to
that found around five X-ray groups and the elliptical galaxy NGC1132 studied
by Mulchaey and Zabludoff (1999), suggesting that the dwarf galaxies in Dorado
are probably physically associated with the overall potential well of the
group.Comment: 32 pages, 16 postscript figures and 3 figures in GIF format, aastex
v5.0. To appear in The Astronomical Journal, January 200
The Properties of Poor Groups of Galaxies: III. The Galaxy Luminosity Function
We obtain R-band photometry for galaxies in six nearby poor groups for which
we have spectroscopic data, including 328 new galaxy velocities. For the five
groups with luminous X-ray halos, the composite group galaxy luminosity
function (GLF) is fit adequately by a Schechter function with Mstar = -21.6 +/-
0.4 + 5log h and alpha = -1.3 +/- 0.1. We also find that (1) the ratio of
dwarfs to giants is significantly larger for the five groups with luminous
X-ray halos than for the one marginally X-ray detected group, (2) the composite
GLF for the luminous X-ray groups is consistent in shape with that for rich
clusters, (3) the composite group GLF rises more steeply at the faint end than
that of the field, (4) the shape difference between the field and composite
group GLF's results mostly from the population of non-emission line galaxies,
whose dwarf-to-giant ratio is larger in the denser group environment than in
the field, and (5) the non-emission line dwarfs are more concentrated about the
group center than the non-emission line giants. This last result indicates that
the dwarfs and giants occupy different orbits (i.e., have not mixed completely)
and suggests that the populations formed at a different times. Our results show
that the shape of the GLF varies with environment and that this variation is
due primarily to an increase in the dwarf-to-giant ratio of quiescent galaxies
in higher density regions, at least up to the densities characteristic of X-ray
luminous poor groups. This behavior suggests that, in some environments, dwarfs
are more biased than giants with respect to dark matter. This trend conflicts
with the prediction of standard biased galaxy formation models. (Abridged)Comment: 36 pages, AASLaTeX with 8 figures. Table 1 also available at
http://atropos.as.arizona.edu/aiz/papers/all_grp_lf_ascii.dat.final . To
appear in Ap
The Luminosity Function of Galaxies in Compact Groups
From R-band images of 39 Hickson compact groups (HCGs), we use galaxy counts
to determine a luminosity function extending to M_R=-14.0, approximately two
magnitudes deeper than previous compact group luminosity functions. We find
that a single Schechter function is a poor fit to the data, so we fit a
composite function consisting of separate Schechter functions for the bright
and faint galaxies. The bright end is best fit with M^*=-21.6 and alpha=-0.52
and the faint end with M^*=-16.1 and alpha=-1.17. The decreasing bright end
slope implies a deficit of intermediate luminosity galaxies in our sample of
HCGs and the faint end slope is slightly steeper than that reported for earlier
HCG luminosity functions. Furthermore, luminosity functions of subsets of our
sample reveal more substantial dwarf populations for groups with x-ray halos,
groups with tidal dwarf candidates, and groups with a dominant elliptical or
lenticular galaxy. Collectively, these results support the hypothesis that
within compact groups, the initial dwarf galaxy population is replenished by
"subsequent generations" formed in the tidal debris of giant galaxy
interactions.Comment: 26 pages, to be published in The Astrophysical Journal, 8 greyscale
plates (figures 1 and 2) can be retrieved at
http://www.astro.psu.edu/users/sdh/pubs.htm