810 research outputs found
HST/ACS Photometry of Old Stars in NGC 1569: The Star Formation History of a Nearby Starburst
(abridged) We used HST/ACS to obtain deep V- and I-band images of NGC 1569,
one of the closest and strongest starburst galaxies in the Universe. These data
allowed us to study the underlying old stellar population, aimed at
understanding NGC 1569's evolution over a full Hubble time. We focus on the
less-crowded outer region of the galaxy, for which the color-magnitude diagram
(CMD) shows predominantly a red giant branch (RGB) that reaches down to the red
clump/horizontal branch feature (RC/HB). A simple stellar population analysis
gives clear evidence for a more complicated star formation history (SFH) in the
outer region. We derive the full SFH using a newly developed code, SFHMATRIX,
which fits the CMD Hess diagram by solving a non-negative least squares
problem. Our analysis shows that the relative brightnesses of the RGB tip and
RC/HB, along with the curvature and color of the RGB, provide enough
information to ameliorate the age-metallicity-extinction degeneracy. The
distance/reddening combination that best fits the data is E(B-V) = 0.58 +/-
0.03 and D = 3.06 +/- 0.18 Mpc. Star formation began ~ 13 Gyr ago, and this
accounts for the majority of the mass in the outer region. However, the initial
burst was followed by a relatively low, but constant, rate of star formation
until ~ 0.5-0.7 Gyr ago when there may have been a short, low intensity burst
of star formation.Comment: 50 pages, including 17 figures. Accepted for publication in A
Intra-host evolution of multiple genotypes of hepatitis C virus in a chronically infected patient with HIV along a 13-year follow-up period
AbstractThe intra-host evolutionary process of hepatitis C virus (HCV) was analyzed by phylogenetic and coalescent methodologies in a patient co-infected with HCV-1a, HCV-2a, HCV-3a and human immunodeficiency virus (HIV) along a 13-year period.Direct sequence analysis of the E2 and NS5A regions showed diverse evolutionary dynamics, in agreement with different relationships between these regions and the host factors.The Bayesian Skyline Plot analyses of the E2 sequences (cloned) yielded different intra-host evolutionary patterns for each genotype: a steady state of a “consensus” sequence for HCV-1a; a pattern of lineage splitting and extinction for HCV-2a; and a two-phase (drift/diversification) process for HCV-3a.Each genotype evolving in the same patient and at the same time presents a different pattern apparently modulated by the immune pressure of the host.This study provides useful information for the management of co-infected patients and provides insights into the mechanisms behind the intra-host evolution of HCV
Feedback in the local LBG Analog Haro 11 as probed by far-UV and X-ray observations
We have re-analyzed FUSE data and obtained new Chandra observations of Haro
11, a local (D_L=88 Mpc) UV luminous galaxy. Haro 11 has a similar far-UV
luminosity (10^10.3 L_\odot), UV surface brightness (10^9.4 L_\odot kpc^-2),
SFR, and metallicity to that observed in Lyman Break Galaxies (LBGs). We show
that Haro 11 has extended, soft thermal (kT~0.68 keV) X-ray emission with a
luminosity and size which scales with the physical properties (e.g. SFR,
stellar mass) of the host galaxy. An enhanced alpha/Fe, ratio of ~4 relative to
solar abundance suggests significant supernovae enrichment. These results are
consistent with the X-ray emission being produced in a shock between a
supernovae driven outflow and the ambient material. The FUV spectra show strong
absorption lines similar to those observed in LBG spectra. A blueshifted
absorption component is identified as a wind outflowing at ~200-280 km/s.
OVI\lambda\lambda1032,1038 emission, the dominant cooling mechanism for coronal
gas at T~10^5.5 K is also observed. If associated with the outflow, the
luminosity of the OVI emission suggests that <20% of the total mechanical
energy from the supernovae and solar winds is being radiated away. This implies
that radiative cooling through OVI is not significantly inhibiting the growth
of the outflowing gas. In contradiction to the findings of Bergvall et al 2006,
we find no convincing evidence of Lyman continuum leakage in Haro 11. We
conclude that the wind has not created a `tunnel' allowing the escape of a
significant fraction of Lyman continuum photons and place a limit on the escape
fraction of f_{esc}<2%. Overall, both Haro 11 and a previously observed LBG
analogue VV 114, provide an invaluable insight into the X-ray and FUV
properties of high redshift LBGs.Comment: Accepted for publication in ApJ, 40 pages, 17 figure
LBT/MODS spectroscopy of globular clusters in the irregular galaxy NGC 4449
We present intermediate-resolution (R1000) spectra in the
3500-10,000 A range of 14 globular clusters in the magellanic irregular
galaxy NGC 4449 acquired with the Multi Object Double Spectrograph on the Large
Binocular Telescope. We derived Lick indices in the optical and the
CaII-triplet index in the near-infrared in order to infer the clusters' stellar
population properties. The inferred cluster ages are typically older than
9 Gyr, although ages are derived with large uncertainties. The clusters
exhibit intermediate metallicities, in the range
[Fe/H], and typically sub-solar []
ratios, with a peak at . These properties suggest that i) during the
first few Gyrs NGC 4449 formed stars slowly and inefficiently, with galactic
winds having possibly contributed to the expulsion of the -elements,
and ii) globular clusters in NGC 4449 formed relatively "late", from a medium
already enriched in the products of type Ia supernovae. The majority of
clusters appear also under-abundant in CN compared to Milky Way halo globular
clusters, perhaps because of the lack of a conspicuous N-enriched,
second-generation of stars like that observed in Galactic globular clusters.
Using the cluster velocities, we infer the dynamical mass of NGC 4449 inside
2.88 kpc to be M(2.88 kpc)=. We
also report the serendipitous discovery of a planetary nebula within one of the
targeted clusters, a rather rare event.Comment: Accepted for publication in MNRAS; corrected typo in author lis
Hubble Space Telescope study of resolved red giant stars in the outer halos of nearby dwarf starburst galaxies
[abridged] Aims. We observed the outer parts of NGC 1569 and NGC 4449, two of
the closest and strongest dwarf starburst galaxies in the local universe, to
characterize their stellar density and populations, and obtain new insights
into the structure, formation, and evolution of starburst galaxies and galaxy
halos. Methods. We obtained HST/WFPC2 images between 5 and 8 scale radii from
the center, along the intermediate and minor axes. We performed point-source
photometry to determine color magnitude diagrams of I vs. V-I. We compared the
results at different radii, including also our prior HST/ACS results for more
centrally located fields. Results. We detect stars in the RGB and TP-AGB
(carbon star) phases in all outer fields, but not younger stars such as those
present at smaller radii. The RGB star density profile is well fit by either a
de Vaucouleurs profile or a power-law profile, but has more stars at large
radii than a single exponential. To within the uncertainties, there are no
radial gradients in the RGB color or carbon-to-RGB-star ratio at large radii.
Conclusions. The galaxies have faint outer stellar envelopes that are not
tidally truncated within the range of radii addressed by our study. The density
profiles suggest that these are not outward extensions of the inner disks, but
are instead distinct stellar halos. This agrees with other work on galaxies of
similar morphology. The presence of such halos is consistent with predictions
of hierarchical galaxy formation scenarios. The halos consist of
intermediate-age/old stars, confirming the results of other studies that have
shown the starburst phenomenon to be very centrally concentrated. There is no
evidence for stellar-population age/metallicity gradients within the halos
themselves.Comment: 13 pages, 13 figures and 2 tables. Accepted for publication in A&
The CB2 Agonist β-Caryophyllene in Male and Female Rats Exposed to a Model of Persistent Inflammatory Pain
Cannabinoids help in pain treatment through their action on CB1 and CB2 receptors. β-caryophyllene (BCP), an ancient remedy to treat pain, is a sesquiterpene found in large amounts in the essential oils of various spice and food plants such as oregano, cinnamon, and black pepper. It binds to the CB2 receptor, acting as a full agonist. Sex differences in the BCP-induced analgesic effect were studied by exposing male and female rats to a persistent/repeated painful stimulation. To simulate treatment of a repeated inflammatory condition, after the first formalin injection (FT1; 50 μl, 2.5%), rats received BCP per os for 7 days at two dosages: 5 and 10 mg/kg dissolved in olive oil (OIL). The control group was treated with OIL for 7 days. On day 8, the formalin test was repeated (FT2) with a lower formalin concentration (50 μl, 1%). During the first and second formalin tests, pain-induced responses (licking, flexing, and paw jerk) and spontaneous behaviors were recorded and analyzed. In the FT1 (before the beginning of treatment with BCP), females displayed higher pain responses than did males in terms of flexing duration during the first part of the test (I phase and interphase), while during the second part (II phase early and late) males showed higher levels than did females in licking duration. In the FT2, the pain responses generally decreased in the BCP groups in a dose-dependent manner (i.e., greater effect of BCP10), with a more pronounced reduction in males than in females; moreover, the pain responses remained high in the OIL groups and in the female BCP5 group. In conclusion, long-term intake of BCP appears to be able to decrease pain behaviors in a model of repeated inflammatory pain in both sexes, but to a greater degree in males
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