20 research outputs found
Structure, mass and distance of the Virgo cluster from a Tolman-Bondi model
We have applied a relativistic Tolman-Bondi model of the Virgo cluster to a
sample of 183 galaxies with measured distances within a radius of 8 degrees
from M87. We find that the sample is significantly contaminated by background
galaxies which lead to too large a cluster mean distance if not excluded. The
Tolman-Bondi model predictions, together with the HI deficiency of spiral
galaxies, allows one to identify these background galaxies. One such galaxy is
clearly identified among the 6 calibrating galaxies with Cepheid distances. As
the Tolman-Bondi model predicts the expected distance ratio to the Virgo
distance, this galaxy can still be used to estimate the Virgo distance, and the
average value over the 6 galaxies is 15.4 +- 0.5 Mpc.
Well-known background groups of galaxies are clearly recovered, together with
filaments of galaxies which link these groups to the main cluster, and are
falling into it. No foreground galaxy is clearly detected in our sample.
Applying the B-band Tully-Fisher method to a sample of 51 true members of the
Virgo cluster according to our classification gives a cluster distance of 18.0
+- 1.2 Mpc, larger than the mean Cepheid distance.
Finally, the same model is used to estimate the Virgo cluster mass, which is
M = 1.2 10^{15} Msun within 8 degrees from the cluster center (2.2 Mpc radius),
and amounts to 1.7 virial mass.Comment: 12 pages, 7 figures. Astronomy and Astrophysics, in press (accepted
May 31, 2001
Are the HI deficient galaxies on the outskirts of Virgo recent arrivals?
The presence on the Virgo cluster outskirts of spiral galaxies with gas
deficiencies as strong as those of the inner galaxies stripped by the
intracluster medium has led us to explore the possibility that some of these
peripheral objects are not newcomers. A dynamical model for the collapse and
rebound of spherical shells under the point mass and radial flow approximations
has been developed to account for the amplitude of the motions in the Virgo I
cluster (VIC) region. According to our analysis, it is not unfeasible that
galaxies far from the cluster, including those in a gas-deficient group well to
its background, went through its core a few Gyr ago. The implications would be:
(1) that the majority of the HI-deficient spirals in the VIC region might have
been deprived of their neutral hydrogen by interactions with the hot
intracluster medium; and (2) that objects spending a long time outside the
cluster cores might keep the gas deficient status without altering their
morphology.Comment: Accepted for publication in ApJ. 4 pages, 3 figures. Uses emulateapj
HI 2334+26: An Extended HI Cloud near Abell 2634
We report the serendipitous discovery of a large HI cloud with an associated
HI mass of M and a heliocentric velocity
8800 \kms, located near the periphery of the cluster of galaxies Abell 2634.
Its velocity field appears to be very quiescent, as no gradients in the peak
velocity are seen over its extent of 143 by 103 kpc. The
distribution of gas is poorly resolved spatially, and it is thus difficult at
this time to ascertain the nature of the cloud. At least two relatively small,
actively star--forming galaxies appear to be embedded in the HI gas, which may
(a) be an extended gaseous envelope surrounding one or both galaxies, (b) have
been spread over a large region by a severe episode of tidal disruption or (c)
have been affected by the ram pressure resulting from its motion through the
intracluster gas of A2634.Comment: 12 pages plus 2 tables (AAS LaTeX macro v3.0), 4 figures not
included. To appear in the A
On the Origin of the Inner Structure of Halos
We calculate by means of the Press-Schechter formalism the density profile
developed by dark-matter halos during accretion, i.e., the continuous
aggregation of small clumps. We find that the shape of the predicted profile is
similar to that shown by halos in high-resolution cosmological simulations.
Furthermore, the mass-concentration relation is correctly reproduced at any
redshift in all the hierarchical cosmologies analyzed, except for very large
halo masses. The role of major mergers, which can cause the rearrangement of
the halo structure through violent relaxation, is also investigated. We show
that, as a result of the boundary conditions imposed by the matter continuously
infalling into the halo during the violent relaxation process, the shape of the
density profile emerging from major mergers is essentially identical to the
shape the halo would have developed through pure accretion. This result
explains why, according to high-resolution cosmological simulations, relaxed
halos of a given mass have the same density profile regardless of whether they
have had a recent merger or not, and why both spherical infall and hierarchical
assembly lead to very similar density profiles. Finally, we demonstrate that
the density profile of relaxed halos is not affected either by the capture of
clumps of intermediate mass.Comment: 14 pages, 8 figures, accepted for publication in ApJ. Minor changes,
matches the published version. To appear in the ApJ August 10, 2003 issu
New GOLD classification: longitudinal data on group assignment
Rationale: Little is known about the longitudinal changes associated with using the 2013 update of the
multidimensional GOLD strategy for chronic obstructive pulmonary disease (COPD).
Objective: To determine the COPD patient distribution of the new GOLD proposal and evaluate how this
classification changes over one year compared with the previous GOLD staging based on spirometry only.
Methods: We analyzed data from the CHAIN study, a multicenter observational Spanish cohort of COPD patients
who are monitored annually. Categories were defined according to the proposed GOLD: FEV1%, mMRC dyspnea,
COPD Assessment Test (CAT), Clinical COPD Questionnaire (CCQ), and exacerbations-hospitalizations. One-year
follow-up information was available for all variables except CCQ data.
Results: At baseline, 828 stable COPD patients were evaluated. On the basis of mMRC dyspnea versus CAT, the
patients were distributed as follows: 38.2% vs. 27.2% in group A, 17.6% vs. 28.3% in group B, 15.8% vs. 12.9% in
group C, and 28.4% vs. 31.6% in group D. Information was available for 526 patients at one year: 64.2% of patients
remained in the same group but groups C and D show different degrees of variability. The annual progression by
group was mainly associated with one-year changes in CAT scores (RR, 1.138; 95%CI: 1.074-1.206) and BODE index
values (RR, 2.012; 95%CI: 1.487-2.722).
Conclusions: In the new GOLD grading classification, the type of tool used to determine the level of symptoms
can substantially alter the group assignment. A change in category after one year was associated with longitudinal
changes in the CAT and BODE index
Predictors of Hospitalized Exacerbations and Mortality in Chronic Obstructive Pulmonary Disease
Background and Aim Exacerbations of chronic obstructive pulmonary disease (COPD) carry significant consequences for patients and are responsible for considerable health-care costs?particularly if hospitalization is required. Despite the importance of hospitalized exacerbations, relatively little is known about their determinants. This study aimed to analyze predictors of hospitalized exacerbations and mortality in COPD patients. Methods This was a retrospective population-based cohort study.We selected 900 patients with confirmed COPD aged 35 years by simple random sampling among all COPD patients in Cantabria (northern Spain) on December 31, 2011. We defined moderate exacerbations as events that led a care provider to prescribe antibiotics or corticosteroids and severe exacerbations as exacerbations requiring hospital admission.We observed exacerbation frequency over the previous year (2011) and following year (2012). We categorized patients according to COPD severity based on forced expiratory volume in 1 second (Global Initiative for Chronic Obstructive Lung Disease [GOLD] grades 1?4). We estimated the odds ratios (ORs) by logistic regression, adjusting for age, sex, smoking status, COPD severity, and frequent exacerbator phenotype the previous year. Results Of the patients, 16.4%had 1 severe exacerbations, varying from 9.3%in mild GOLD grade 1 to 44%in very severe COPD patients. A history of at least two prior severe exacerbations was positively associated with new severe exacerbations (adjusted OR, 6.73; 95%confidence interval [CI], 3.53?12.83) and mortality (adjusted OR, 7.63; 95%CI, 3.41?17.05). Older age and several comorbidities, such as heart failure and diabetes, were similarly associated. Conclusions Hospitalized exacerbations occurred with all grades of airflow limitation. A history of severe exacerbations was associated with new hospitalized exacerbations and mortality
New GOLD classification: longitudinal data on group assignment
In the new GOLD grading classification, the type of tool used to determine the level of symptoms can substantially alter the group assignment. A change in category after one year was associated with longitudinal changes in the CAT and BODE index