29 research outputs found
Mid-Infrared Evidence for Accelerated Evolution in Compact Group Galaxies
We find evidence for accelerated evolution in compact group galaxies from the
distribution in mid-infrared colorspace of 42 galaxies from 12 Hickson Compact
Groups (HCGs) compared to the the distributions of several other samples
including the LVL+SINGS galaxies, interacting galaxies, and galaxies from the
Coma Cluster. We find that the HCG galaxies are not uniformly distributed in
colorspace, as well as quantitative evidence for a gap. Galaxies in the infall
region of the Coma cluster also exhibit a non-uniform distribution and a less
well defined gap, which may reflect a similarity with the compact group
environment. Neither the Coma Center or interacting samples show evidence of a
gap, leading us to speculate that the gap is unique to the environment of high
galaxy density where gas has not been fully processed or stripped.Comment: To appear in the Proceedings of the Galaxy Wars: Stellar Populations
and Star Formation in Interacting Galaxies Conferenc
Compact Groups in the UZC galaxy sample: II. Connections between morphology, luminosity and large-scale density
The nature of Compact Groups (CGs) is investigated by comparing the
luminosities and morphologies of CG galaxies, CG Neighbours and Isolated
galaxies. CGs turn out to include more early type galaxies than Isolated
galaxies and fewer low-luminosity galaxies. The 33 CGs with a dominant E/S0 and
the 30 CGs with a dominant spiral have similar LF parameters. Spiral dominated
CGs have fewer galaxies at high and low luminosity in comparison with their
Neighbours, while E-S0 dominated CGs seem to lack only faint galaxies when
compared to their Neighbours. Ellipticals which are the dominant galaxy of a CG
are also brighter than all their Neighbours, while this holds true for only
half of the dominant spirals and S0s. Relations linking the number of
Neighbours of dominant E-S0s to the luminosity of E-S0s and to the difference
between the first and the second ranked CG members do suggest a link between
the formation of bright early-type galaxies and the presence of a group-like
potential. No similar relations are found for dominant spirals. These tentative
results are compatible with the assumption that CG dominant Ellipticals are
anomalous galaxies whose formation might have been a secondary outcome during
the process of groups formation.Comment: 12 pages, 9 figures, A&A, accepte
Ages and Metallicities of Hickson Compact Group Galaxies
Hickson Compact Groups (HCGs) constitute an interesting extreme in the range
of environments in which galaxies are located, as the space density of galaxies
in these small groups are otherwise only found in the centres of much larger
clusters. The work presented here uses Lick indices to make a comparison of
ages and chemical compositions of galaxies in HCGs with those in other
environments (clusters, loose groups and the field). The metallicity and
relative abundance of `-elements' show strong correlations with galaxy
age and central velocity dispersion, with similar trends found in all
environments. However, we show that the previously reported correlation between
-element abundance ratios and velocity dispersion disappears when a
full account is taken of the the abundance ratio pattern in the calibration
stars. This correlation is thus found to be an artifact of incomplete
calibration to the Lick system.
Variations are seen in the ranges and average values of age, metallicity and
-element abundance ratios for galaxies in different environments. Age
distributions support the hierarchical formation prediction that field galaxies
are on average younger than their cluster counterparts. However, the ages of
HCG galaxies are shown to be more similar to those of cluster galaxies than
those in the field, contrary to the expectations of current hierarchical
models. A trend for lower velocity dispersion galaxies to be younger was also
seen. This is again inconsistent with hierarchical collapse models, but is
qualitatively consistent with the latest N-body-SPH models based on monolithic
collapse in which star formation continues for many Gyr in low mass halos.Comment: 18 pages. Submitted for publication in MNRA
Characterising galaxy groups: spectroscopic observations of the Shakhbazyan sample
Groups of galaxies are the most common cosmic structures. However, due to the
poor statistics, projection effects and the lack of accurate distances, our
understanding of their dynamical and evolutionary status is still limited. This
is particularly true for the so called Shakhbazyan groups (SHK) which are still
largely unexplored due to the lack of systematic spectroscopic studies of both
their member galaxies and the surrounding environment. In our previous paper,
we investigated the statistical properties of a large sample of SHK groups
using Sloan Digital Sky Survey data and photometric redshifts. Here we present
the follow-up of 5 SHK groups (SHK 10, 71, 75, 80, 259) observed within our
spectroscopic campaign with the Telescopio Nazionale Galileo, aimed at
confirming their physical reality and strengthening our photometric results.
For each of the selected groups we were able to identify between 6 and 13
spectroscopic members, thus confirming the robustness of the photometric
redshift approach in identifying real galaxy over-densities. Consistently with
the finding of our previous paper, the structures studied here have properties
spanning from those of compact and isolated groups to those of loose groups.
For what the global physical properties are concerned (total mass,
mass-to-light ratios, etc.), we find systematic differences with those reported
in the literature by previous studies. Our analysis suggests that previous
results should be revisited; we show in fact that, if the literature data are
re-analysed in a consistent and homogeneous way, the properties obtained are in
agreement with those estimated for our sample.Comment: 31 pages, 25 figures, 10 tables. Accepted for publication on MNRAS.
Table references updated. Few minor corrections to the text applie
The Different Physical Mechanisms that Drive the Star-Formation Histories of Giant and Dwarf Galaxies
We present an analysis of star-formation and nuclear activity in galaxies as
a function of both luminosity and environment in the SDSS DR4 dataset. Using a
sample of 27753 galaxies at 0.00590% complete to Mr=-18.0 we
find that the EW(Ha) distribution is strongly bimodal, allowing galaxies to be
robustly separated into passive and star-forming populations about a value
EW(Ha)=2A. In high-density regions ~70% of galaxies are passive independent of
luminosity. In the rarefied field however, the fraction of passively-evolving
galaxies is a strong function of luminosity, dropping from ~50% for Mr<-21 to
zero by Mr~-18. Indeed for the lowest luminosity range covered (-18<Mr<-16)
none of the ~600 galaxies in the lowest density quartile are passive. The few
passively-evolving dwarf galaxies in field regions appear as satellites to
bright (~L*) galaxies. The fraction of galaxies with optical AGN signatures
decreases steadily from ~50% at Mr~-21 to ~0% by Mr~-18 closely mirroring the
luminosity-dependence of the passive galaxy fraction in low-density
environments. This result reflects the increasing importance of AGN feedback
with galaxy mass for their evolution, such that the star-formation histories of
massive galaxies are primarily determined by their past merger history. In
contrast, the complete absence of passively-evolving dwarf galaxies more than
~2 virial radii from the nearest massive halo (i.e. cluster, group or massive
galaxy) indicates that internal processes, such as merging, AGN feedback or gas
consumption through star-formation, are not responsible for terminating
star-formation in dwarf galaxies. Instead the evolution of dwarf galaxies is
primarily driven by the mass of their host halo, probably through the combined
effects of tidal forces and ram-pressure stripping.Comment: 29 pages, 11 figures. Accepted for publication in MNRA
Safety and feasibility of switching from phenytoin to levetiracetam monotherapy for glioma-related seizure control following craniotomy: a randomized phase II pilot study
Seizures are common in patients with gliomas, and phenytoin (PHT) is frequently used to control tumor-related seizures. PHT, however, has many undesirable side effects (SEs) and drug interactions with glioma chemotherapy. Levetiracetam (LEV) is a newer antiepileptic drug (AED) with fewer SEs and essentially no drug interactions. We performed a pilot study testing the safety and feasibility of switching patients from PHT to LEV monotherapy for postoperative control of glioma-related seizures. Over a 13-month period, 29 patients were randomized in a 2:1 ratio to initiate LEV therapy within 24 h of surgery or to continue PHT therapy. 6 month follow-up data were available for 15 patients taking LEV and for 8 patients taking PHT. In the LEV group, 13 patients (87%) were seizure-free. In the PHT group, 6 patients (75%) were seizure-free. Reported SEs at 6 months was as follows (%LEV/%PHT group): dizziness (0/14), difficulty with coordination (0/29), depression (7/14) lack of energy or strength (20/43), insomnia (40/43), mood instability (7/0). The pilot data presented here suggest that it is safe to switch patients from PHT to LEV monotherapy following craniotomy for supratentorial glioma. A large-scale, double-blinded, randomized control trial of LEV versus PHT is required to determine seizure control equivalence and better assess differences in SEs
A review of elliptical and disc galaxy structure, and modern scaling laws
A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their
models to describe the radial distribution of stars in `nebulae'. This article
reviews the progress since then, providing both an historical perspective and a
contemporary review of the stellar structure of bulges, discs and elliptical
galaxies. The quantification of galaxy nuclei, such as central mass deficits
and excess nuclear light, plus the structure of dark matter halos and cD galaxy
envelopes, are discussed. Issues pertaining to spiral galaxies including dust,
bulge-to-disc ratios, bulgeless galaxies, bars and the identification of
pseudobulges are also reviewed. An array of modern scaling relations involving
sizes, luminosities, surface brightnesses and stellar concentrations are
presented, many of which are shown to be curved. These 'redshift zero'
relations not only quantify the behavior and nature of galaxies in the Universe
today, but are the modern benchmark for evolutionary studies of galaxies,
whether based on observations, N-body-simulations or semi-analytical modelling.
For example, it is shown that some of the recently discovered compact
elliptical galaxies at 1.5 < z < 2.5 may be the bulges of modern disc galaxies.Comment: Condensed version (due to Contract) of an invited review article to
appear in "Planets, Stars and Stellar
Systems"(www.springer.com/astronomy/book/978-90-481-8818-5). 500+ references
incl. many somewhat forgotten, pioneer papers. Original submission to
Springer: 07-June-201
Correlates of women's cancer screening and contraceptive knowledge among female emergency department patients
<p>Abstract</p> <p>Background</p> <p>Lack of knowledge regarding preventive health services for women might impede campaigns to expand these services in the emergency department setting. For 18–55-year-old English-speaking women visiting an urban emergency department, we aimed to: (1) Ascertain their knowledge regarding the applicability, purpose, and recommended intervals of three women's cancer screening and three contraceptive methods; and (2) Determine if patient age, race/ethnicity, medical insurance status, and current or recent usage of these methods are associated with greater or lesser knowledge about them.</p> <p>Methods</p> <p>Emergency department-based survey on recent or current usage and knowledge about Pap smears, breast self-examinations, mammograms, condoms, birth control, and emergency contraception. Analyses included calculation of summary statistics and creation of multivariable logistic regression models.</p> <p>Results</p> <p>Of 1,100 patients eligible for the study, 69.9% agreed to participate. Most of the participants were < age 35, white, single (never married and no partner), Catholic, and had private medical insurance. Participant's recent or current usage of a particular cancer screening or contraceptive method varied by type of method: Pap smear within the past year (69.1%), breast self-exam within the past month (45.5%), mammogram within the past year (65.7% for women age 45–55), condom usage during every episode of sexual intercourse (15.4%), current usage of birth control pills (17.8%), and ever use of emergency contraception (9.3%). The participants correctly answered 87.9% of all survey questions about condoms, 82.5% about birth control pills, 78.5% about breast self-exams, 52.9% about Pap smears, 35.4% about mammograms, and 25.0% about emergency contraception. In multivariable logistic regression models, survey participants who had private medical insurance and those who recently or currently used a given screening or contraceptive method had a greater odds of correctly answering all questions about each cancer screening or contraceptive method.</p> <p>Conclusion</p> <p>Although these female ED patients demonstrated strong knowledge on some women's cancer screening and contraceptive methods, there were several areas of knowledge deficit. Women without private medical insurance and those who have not used a particular cancer screening or contraceptive method demonstrated less knowledge. Reduced knowledge about women's cancer screening and contraceptive methods should be considered during clinical encounters and when instituting or evaluating emergency department-based initiatives that assess the need for these methods.</p
Central mass-to-light ratios and dark matter fractions in early-type galaxies
Dynamical studies of local ETGs and the Fundamental Plane point to a strong
dependence of M/L ratio on luminosity (and stellar mass) with a relation of the
form . The "tilt" may be caused by various
factors, including stellar population properties, IMF, rotational support,
luminosity profile non-homology and dark matter (DM) fraction. We evaluate the
impact of all these factors using a large uniform dataset of local ETGs from
Prugniel & Simien (1997). We take particular care in estimating the stellar
masses, using a general star formation history, and comparing different
population synthesis models. We find that the stellar M/L contributes little to
the tilt. We estimate the total M/L using simple Jeans dynamical models, and
find that adopting accurate luminosity profiles is important but does not
remove the need for an additional tilt component, which we ascribe to DM. We
survey trends of the DM fraction within one effective radius, finding it to be
roughly constant for galaxies fainter than , and increasing
with luminosity for the brighter galaxies; we detect no significant differences
among S0s and fast- and slow-rotating ellipticals. We construct simplified
cosmological mass models and find general consistency, where the DM transition
point is caused by a change in the relation between luminosity and effective
radius. A more refined model with varying galaxy star formation efficiency
suggests a transition from total mass profiles (including DM) of faint galaxies
distributed similarly to the light, to near-isothermal profiles for the bright
galaxies. These conclusions are sensitive to various systematic uncertainties
which we investigate in detail, but are consistent with the results of dynamics
studies at larger radii.Comment: 21 Pages, 19 figures, accepted for publication on MNRAS. Version
including revisions after the referee's report and an updated list of
reference