303 research outputs found
Leucine-rich repeat kinase 2 (LRRK2): an update on the potential therapeutic target for Parkinson’s disease
Mutations in Leucine-rich repeat kinase 2 (LRRK2) are a risk factor for and a cause of sporadic and familial Parkinson’s disease (PD), respectively. These mutations are some of the most common genetic contributors to PD and render the kinase hyperactive. Increasingly within the past decade, there has been substantial effort investigating LRRK2 as a target for therapeutics in preclinical studies, and currently, small-molecule inhibitors and antisense oligonucleotides are being assessed in clinical trials as therapies to reduce the toxic hyperactivity of its kinase and/or reduce total levels of the protein in healthy individuals and people with PD
The Cuspy LINER Nucleus of the S0/a Galaxy NGC 2681
The nucleus of the bulge-dominated, multiply-barred S0/a galaxy NGC 2681 is
studied in detail, using high resolution Hubble Space Telescope FOC and NICMOS
imaging and FOS spectroscopy. The ionised gas central velocity dispersion is
found to increase by a factor ~2 when narrowing the aperture from R~1.5"
(ground) to R~0.1" (FOS). Dynamical modeling of these velocity dispersions
suggests that NGC 2681 does host a supermassive black hole (BH) for which one
can estimate a firm mass upper limit M_BH < 6*10^7 Solar Masses. This upper
limit is consistent with the relation between the central BH mass and velocity
dispersion M_BH - sigma known for other galaxies. The emission line ratios
place the nucleus of NGC 2681 among LINERs. It is likely that the emission line
region comes from a rather mild, but steady, feeding of gas to the central BH
in this galaxy. The inner stellar population lacks any measurable color
gradient (to a radius of 0.6 kpc) from the infrared to the ultraviolet,
consistently with FOC, FOS and IUE data, all indicating that this system
underwent a starburst ~1 Gyr ago that encompassed its whole interior, down to
its very center. The most likely source of such a widely-distributed starburst
is the dumping of tidally-extruded gas from a galaxy neighbor. If so, then NGC
2681 can be considered as the older brother of M82, seen face-on as opposed to
the edge-on view we have for M82.Comment: 25 pages, LaTeX, with 10 PostScript figures, to appear in The
Astrophysical Journa
Origin of Two Distinct Populations in Dwarf Spheroidal Galaxies
We study the chemical and kinematic properties of the first galaxies which
formed at a high redshift, using high resolution cosmological numerical
simulations, and compared them with the recent observational results for the
Sculptor dwarf spheroidal galaxy by Tolstoy et al., who found two distinct
stellar populations: the lower metallicity stars are more spatially extended
and possess a higher velocity dispersion than the higher metallicity stars. Our
calculations reproduce these observations as the result of a steep metallicity
gradient, within a single populations, induced by dissipative collapse of the
gas component. We also predict strong [N/O] enhancements in the lowest
metallicity stars in dwarf spheroidals, due to the preferential retention of
ejected gas from intermediate mass stars, compared to Type II supernovae.Comment: 11 pages, 10 figures, accepted for publication in Ap
Halos of Spiral Galaxies. III. Metallicity Distributions
(Abriged) We report results of a campaign to image the stellar populations in
the halos of highly inclined spiral galaxies, with the fields roughly 10 kpc
(projected) from the nuclei. We use the F814W (I) and F606W (V) filters in the
Wide Field Planetary Camera 2, on board the Hubble Space telescope. Extended
halo populations are detected in all galaxies. The color-magnitude diagrams
appear to be completely dominated by giant-branch stars, with no evidence for
the presence of young stellar populations in any of the fields. We find that
the metallicity distribution functions are dominated by metal-rich populations,
with a tail extending toward the metal poor end. To first order, the overall
shapes of the metallicity distribution functions are similar to what is
predicted by simple, single-component model of chemical evolution with the
effective yields increasing with galaxy luminosity. However, metallicity
distributions significantly narrower than the simple model are observed for a
few of the most luminous galaxies in the sample. It appears clear that more
luminous spiral galaxies also have more metal-rich stellar halos. The
increasingly significant departures from the closed-box model for the more
luminous galaxies indicate that a parameter in addition to a single yield is
required to describe chemical evolution. This parameter, which could be related
to gas infall or outflow either in situ or in progenitor dwarf galaxies that
later merge to form the stellar halo, tends to act to make the metallicity
distributions narrower at high metallicity.Comment: 20 pages, 8 figures (ApJ, in press
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Leucine-rich repeat kinase 2 (LRRK2): an update on the potential therapeutic target for Parkinson's disease.
In this review, we will provide an update on the current status of drugs and other technologies that have emerged in recent years and provide an overview of their efficacy in ameliorating LRRK2 kinase activity and overall safety in animal models and humans. The growth of both target discovery and innovative drug design has sparked a lot of excitement for the future of how we treat Parkinson's disease. Given the immense focus on LRRK2 as a therapeutic target, it is expected within the next decade to determine its therapeutic properties, or lack thereof, for PD
Integrated Spectroscopy of Bulge Globular Clusters and Fields I. The Data Base and Comparison of Individual Lick Indices in Clusters and Bulge
We present a comprehensive spectroscopic study of the integrated light of
metal-rich Galactic globular clusters and the stellar population in the
Galactic bulge. We measure line indices which are defined by the Lick standard
system and compare index strengths of the clusters and Galactic bulge. Both
metal-rich globular clusters and the bulge are similar in most of the indices,
except for the CN index. We find a significant enhancement in the CN/ index
ratio in metal-rich globular clusters compared with the Galactic bulge. The
mean iron index of the two metal-rich globular clusters NGC 6528 and NGC
6553 is comparable with the mean iron index of the bulge. Index ratios such as
Mgb/, Mg2/, Ca4227/, and TiO/, are comparable in both stellar
population indicating similar enhancements in individual elements which are
traced by the indices. From the globular cluster data we fully empirically
calibrate several metallicity-sensitive indices as a function of [Fe/H] and
find tightest correlations for the Mg2 index and the composite [MgFe] index. We
find that all indices show a similar behavior with galactocentric radius,
except for the Balmer series, which show a large scatter at all radii. However,
the scatter is entirely consistent with the cluster-to-cluster variations in
the horizontal branch morphology.Comment: accepted for publication in A&A, 25 pages, incl. 10 figure
Why Are Radio-Galaxies Prolific Producers of Type Ia Supernovae?
An analysis of SNIa events in early type galaxies from the Cappellaro et al
(1999) database provides conclusive evidence that the rate of type Ia
Supernovae (SNe) in radio-loud galaxies is about 4 times higher than the rate
measured in radio-quiet galaxies, i.e. SNIa-rate SNu as compared to SNIa-rate SNu. The actual value of the
enhancement is likely to be in the range (P). This
finding puts on robust empirical grounds the results obtained by Della Valle &
Panagia (2003) on the basis of a smaller sample of SNe. We analyse the possible
causes of this result and conclude that the enhancement of SNIa explosion rate
in radio-loud galaxies has the same origin as their being strong radio sources,
but there is no causality link between the two phenomena. We argue that
repeated episodes of interaction and/or mergers of early type galaxies with
dwarf companions, on times-scale of about 1 Gyr, are responsible for inducing
both strong radio activity observed in 14% of early type galaxies and to
supply an adequate number of SNIa progenitors to the stellar population of
ellipticals.Comment: 26 pages+6 figures, ApJ, in pres
Integrated Spectroscopy of Bulge Globular Clusters and Fields. II. Implications for stellar population models and elliptical galaxies
Synthetic Lick indices (e.g. Mg_2, Fe, etc.) of Simple Stellar Population
(SSP) models are calibrated for the first time up to solar metallicity with a
sample of Milky Way globular clusters (GCs) which includes the metal rich GCs
of the Galactic bulge. This metallicity range is relevant to elliptical
galaxies. It is shown that the Bulge GCs and integrated light follow the same
correlation between Mg and Fe indices of elliptical galaxies, showing weaker Fe
indices at given Mg indices with respect to models that assume solar-scaled
abundances. This similarity is the robust empirical evidence for enhanced
alpha/Fe ratios in the stellar populations of elliptical galaxies, since the
globular clusters are independently known to be alpha-enhanced. The uniqueness
of this alpha-overabundance solution is checked by exploring the whole range of
model ingredients. We argue that the standard models reproduce the Mg-Fe
correlation at low metallicities because the stellar templates used in the
synthesis are the alpha-enhanced stars of the galactic Halo. These same models,
however, fail to recover the Mg-Fe pattern of Bulge clusters and ellipticals at
high metallicities because the high-metallicity templates are disk stars, which
are not alpha-enhanced. The new SSP models by Thomas, Maraston & Bender (2002)
which incorporate the dependence on alpha/Fe reproduce the Mg and Fe indices of
GCs at all metallicities, with alpha/Fe=+0.3, which is in agreement with
spectroscopic abundance determinations. The Balmer indices (Hbeta, Hdelta,
Hgamma) are very well calibrated, provided the Horizontal Branch morphology is
taken into account. In particular, we reproduce the Balmer lines of NGC 6388
and NGC 6441, which are metal-rich GCs with a tail of warm Horizontal Branch
stars. {Abridged}Comment: 19 pages, 13 figures, Astronomy and Astrophysics in press. Only minor
changes after the referee repor
The H Beta Index as an Age Indicator of Old Stellar Systems: The Effects of Horizontal-Branch Stars
The strength of the H index has been computed for the integrated
spectra of model globular clusters from the evolutionary population synthesis.
These models take into account, for the first time, the detailed systematic
variation of horizontal-branch (HB) morphology with age and metallicity. Our
models show that the H index is significantly affected by the presence
of blue HB stars. Because of the contribution from blue HB stars, the H
does not monotonically decrease as metallicity increases at a given age.
Instead, it reaches a maximum strength when the distribution of HB stars is
centered around 9500 K, the temperature where the H index becomes
strongest. Our models indicate that the strength of the H index
increases as much as 0.75 {\AA} due to the presence of blue HB stars.
The comparison of the recent Keck observations of the globular cluster system
in the Milky Way Galaxy with those in giant elliptical galaxies, NGC 1399 and
M87, shows a systematic shift in the H against metallicity plane. Our
models suggest that this systematic difference is understood if the globular
cluster systems in giant elliptical galaxies are several billion years older,
in the mean, than the Galactic counterpart. Further observations of globular
cluster systems in the external galaxies from the large ground-based telescopes
and space UV facilities will enable to clarify whether this difference is
indeed due to the age difference or other explanations are also possible.Comment: 21 pages, 8 figures, Accepted for publication in the Astronomical
Journal, August 2000 issue, Postscript files are available at
http://csaweb.yonsei.ac.kr/~hclee/Hbet
Globular Clusters in the Magellanic Clouds.II: IR-Array Photometry for 12 Globulars and Contributions to the Integrated Cluster Light
We report the results of the observations in the JHK bands of 12 globular
clusters in the LMC, and present CMDs down to K=16 for about 450 stars. We
merge the data with the BV ones presented in paper I and use the merged data to
study the evolution of integrated magnitudes and colours of SSPs. We find that
the AGB contributes about 60 percent of integrated clusters light in K, while
the contribution from RGB is correlated with the age of the cluster. The age at
which the first appearance of the RGB takes place depends on the models adopted
ranging from about 600 Myr in the "classical" models to about 1.5 Gyr with the
"overshooting" models. Both models give the same fractional contribution of the
RGB to the cluster light, in agreement with the Fuel Consumption Theorem. The
overall picture is consistent with the early conclusions of Persson et al. 1983
and Frogel et al. 1990 that J-K colour is driven by AGB stars, V-K is
controlled by AGB and RGB stars and B-V is partially influenced by the whole
population redder than the RGB clump, but is strongly dependent on the fading
and reddening of the TO stars with age.Comment: 26 pages, 15 figures available on request, uuencoded compressed
postscript file with tables included, BAP 08-1994-021-OA
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