245 research outputs found
Galactic Archeology with 4MOST
4MOST is a new wide-field, high-multiplex spectroscopic survey facility for
the VISTA telescope of ESO. Starting in 2022, 4MOST will deploy more than 2400
fibres in a 4.1 square degree field-of-view using a positioner based on the
tilting spine principle. In this ontribution we give an outline of the major
science goals we wish to achieve with 4MOST in the area of Galactic Archeology.
The 4MOST Galactic Archeology surveys have been designed to address
long-standing and far-reaching problems in Galactic science. They are focused
on our major themes: 1) Near-field cosmology tests, 2) Chemo-dynamical
characterisation of the major Milky Way stellar components, 3) The Galactic
Halo and beyond, and 4) Discovery and characterisation of extremely metal-poor
stars. In addition to a top-level description of the Galactic surveys we
provide information about how the community will be able to join 4MOST via a
call for Public Spectroscopic Surveys that ESO will launch.Comment: To be published in "Rediscovering our Galaxy", IAU Symposium 334,
Eds. C. Chiappini, I. Minchev, E. Starkenburg, M. Valentin
The Pristine survey II: a sample of bright stars observed with FEROS
Extremely metal-poor (EMP) stars are old objects formed in the first Gyr of
the Universe. They are rare and, to select them, the most successful strategy
has been to build on large and low-resolution spectroscopic surveys. The
combination of narrow- and broad band photometry provides a powerful and
cheaper alternative to select metal-poor stars. The on-going Pristine Survey is
adopting this strategy, conducting photometry with the CFHT MegaCam wide field
imager and a narrow-band filter centred at 395.2 nm on the CaII-H and -K lines.
In this paper we present the results of the spectroscopic follow-up conducted
on a sample of 26 stars at the bright end of the magnitude range of the Survey
(g<=15), using FEROS at the MPG/ESO 2.2 m telescope. From our chemical
investigation on the sample, we conclude that this magnitude range is too
bright to use the SDSS gri bands, which are typically saturated. Instead the
Pristine photometry can be usefully combined with the APASS gri photometry to
provide reliable metallicity estimates.Comment: AN accepte
Constraints on mass loss and self-enrichment scenarios for the globular clusters of the Fornax dSph
Recently, high-dispersion spectroscopy has demonstrated conclusively that
four of the five globular clusters (GCs) in the Fornax dwarf spheroidal galaxy
are very metal-poor with [Fe/H]<-2. The remaining cluster, Fornax 4, has
[Fe/H]=-1.4. This is in stark contrast to the field star metallicity
distribution which shows a broad peak around [Fe/H]=-1 with only a few percent
of the stars having [Fe/H]<-2. If we only consider stars and clusters with
[Fe/H]<-2 we thus find an extremely high GC specific frequency, SN=400,
implying by far the highest ratio of GCs to field stars known anywhere. We
estimate that about 1/5-1/4 of all stars in the Fornax dSph with [Fe/H]<-2
belong to the four most metal-poor GCs. These GCs could, therefore, at most
have been a factor of 4-5 more massive initially. Yet, the Fornax GCs appear to
share the same anomalous chemical abundance patterns known from Milky Way GCs,
commonly attributed to the presence of multiple stellar generations within the
clusters. The extreme ratio of metal-poor GC- versus field stars in the Fornax
dSph is difficult to reconcile with scenarios for self-enrichment and early
evolution of GCs in which a large fraction (90%-95%) of the first-generation
stars have been lost. It also suggests that the GCs may not have formed as part
of a larger population of now disrupted clusters with an initial power-law mass
distribution. The Fornax dSph may be a rosetta stone for constraining theories
of the formation, self-enrichment and early dynamical evolution of star
clusters.Comment: 4 pages, 2 figures, accepted for A&A Letter
Draft Nuclear Genome, Complete Chloroplast Genome, and Complete Mitochondrial Genome for the Biofuel/ Bioproduct Feedstock Species Scenedesmus obliquus Strain DOE0152z
The green alga Scenedesmus obliquus is an emerging platform species for the industrial production of biofuels. Here, we report the draft assembly and annotation for the nuclear, plastid, and mitochondrial genomes of S. obliquus strain DOE0152z
The Rest-Frame Optical Luminosity Density, Color, and Stellar Mass Density of the Universe from z=0 to z=3
We present the evolution of the rest-frame optical luminosity density, of the
integrated rest-frame optical color, and of the stellar mass density for a
sample of Ks-band selected galaxies in the HDF-S. We derived the luminosity
density in the rest-frame U, B, and V-bands and found that the luminosity
density increases by a factor of 1.9+-0.4, 2.9+-0.6, and 4.9+-1.0 in the V, B,
and U rest-frame bands respectively between a redshift of 0.1 and 3.2. We
derived the luminosity weighted mean cosmic (U-B)_rest and (B-V)_rest colors as
a function of redshift. The colors bluen almost monotonically with increasing
redshift; at z=0.1, the (U-B)_rest and (B-V)_rest colors are 0.16 and 0.75
respectively, while at z=2.8 they are -0.39 and 0.29 respectively. We derived
the luminosity weighted mean M/LV using the correlation between (U-V)_rest and
log_{10} M/LV which exists for a range in smooth SFHs and moderate extinctions.
We have shown that the mean of individual M/LV estimates can overpredict the
true value by ~70% while our method overpredicts the true values by only ~35%.
We find that the universe at z~3 had ~10 times lower stellar mass density than
it does today in galaxies with LV>1.4 \times 10^{10} h_{70}^-2 Lsol. 50% of the
stellar mass of the universe was formed by $z~1-1.5. The rate of increase in
the stellar mass density with decreasing redshift is similar to but above that
for independent estimates from the HDF-N, but is slightly less than that
predicted by the integral of the SFR(z) curve.Comment: 19 pages, 12 figures, Accepted for Publication in the Dec. 20, 2003
edition of the Astrophysical Journal. Minor changes made to match the
accepted version including short discussions on the effects of clustering and
on possible systematic effects resulting from photometric redshift error
The satellites of the Milky Way – insights from semi-analytic modelling in a ΛCDM cosmology
We combine the six high-resolution Aquarius dark matter simulations with a semi-analytic galaxy formation model to investigate the properties of the satellites of Milky Way-like galaxies. We find good correspondence with the observed luminosity function, luminosity–metallicity relation and radial distribution of the Milky Way satellites. The star formation histories of the dwarf galaxies in our model vary widely, in accordance with what is seen observationally. Some systems are dominated by old populations, whereas others are dominated by intermediate populations; star formation histories can either be continuous or more bursty. Ram-pressure stripping of hot gas from the satellites leaves a clear imprint of the environment on the characteristics of a dwarf galaxy. We find that the fraction of satellites dominated by old populations of stars matches observations well. However, the internal metallicity distributions of the model satellites appear to be narrower than observed. This may indicate limitations in our treatment of chemical enrichment, which is based on the instantaneous recycling approximation. We find a strong correlation between the number of satellites and the dark matter mass of the host halo. Our model works best if the dark matter halo of the Milky Way has a mass of ∼8 × 1011 M⊙, in agreement with the lower estimates from observations, but about a factor of 2 lower than estimates based on the Local Group timing argument or abundance matching techniques. The galaxy that resembles the Milky Way the most also has the best-matching satellite luminosity function, although it does not contain an object as bright as the Large or Small Magellanic Cloud. Compared to other semi-analytic models and abundance matching relations we find that central galaxies reside in less massive haloes, but the halo mass–stellar mass relation in our model is consistent both with hydrodynamical simulations and with recent observations
The size evolution of galaxies since z~3: combining SDSS, GEMS and FIRES
We present the evolution of the luminosity-size and stellar mass-size
relations of luminous (L_V>3.4x10^10h_70^-2L_sun) and of massive
(M_*>3x10^10h_70^-2M_sun) galaxies in the last ~11 Gyr. We use very deep
near-infrared images of the Hubble Deep Field-South and the MS1054-03 field in
the J_s, H and K_s bands from FIRES to retrieve the sizes in the optical
rest-frame for galaxies with z>1. We combine our results with those from GEMS
at 0.2<z<1 and SDSS at z~0.1 to achieve a comprehensive picture of the optical
rest-frame size evolution from z=0 to z=3. Galaxies are differentiated
according to their light concentration using the Sersic index n. For less
concentrated objects, the galaxies at a given luminosity were typically ~3+-0.5
(+-2 sigma) times smaller at z~2.5 than those we see today. The stellar
mass-size relation has evolved less: the mean size at a given stellar mass was
\~2+-0.5 times smaller at z~2.5, evolving proportional to (1+z)^{-0.40+-0.06}.
Simple scaling relations between dark matter halos and baryons in a
hierarchical cosmogony predict a stronger (although consistent within the error
bars) than observed evolution of the stellar mass-size relation. The observed
luminosity-size evolution out to z~2.5 matches well recent infall model
predictions for Milky-Way type objects. For low-n galaxies, the evolution of
the stellar mass-size relation would follow naturally if the individual
galaxies grow inside-out. For highly concentrated objects, the situation is as
follows: at a given luminosity, these galaxies were ~2.7+-1.1 times smaller at
z~2.5 (or put differently, were typically ~2.2+-0.7 mag brighter at a given
size than they are today), and at a given stellar mass the size has evolved
proportional to (1+z)^{-0.45+-0.10}.Comment: Accepted for publication in ApJ. The new version includes several
improvements: much accurate size estimations and a better completeness and
robustness analysis. Tables of data are included. 29 pages and 14 figures
(one low resolution
A Substantial Population of Red Galaxies at z > 2: Modeling of the Spectral Energy Distributions of an Extended Sample
We investigate the nature of the substantial population of high-z galaxies
with Js-Ks>2.3 discovered as part of our FIRES survey. This colour cut
efficiently isolates z>2 galaxies with red rest-frame optical colors ("Distant
Red Galaxies" or DRGs). We select objects in the 2.5'x2.5' HDF-South (HDF-S)
and 5'x5' field around the MS1054-03 cluster; the surface densities at Ks<21
are 1.6+-0.6 and 1.0+-0.2 arcmin^-2. We discuss the 34 DRGs at 2<z<3.5: 11 at
Ks<22.5 in HDF-S and 23 at Ks<21.7 in the MS1054-03 field. We analyze the SEDs
constructed from our deep near-infrared (NIR) and optical imaging from the ESO
VLT and HST. We develop diagnostics involving I-Js, Js-H, and H-Ks to argue
that the red NIR colors of DRGs cannot be attributed solely to extinction and
require for many an evolved stellar population with prominent Balmer/4000A
break. In the rest-frame, the optical colours of DRGs fall within the envelope
of normal nearby galaxies and the UV colours suggest a wide range in star
formation activity and/or extinction. This contrasts with the much bluer and
more uniform SEDs of Lyman break galaxies (LBGs). From evolutionary synthesis
models with constant star formation, solar metallicity, Salpeter IMF, and
Calzetti et al. extinction law, we derive for the HDF-S (MS1054-03 field) DRGs
median ages of 1.7(2.0) Gyr, A_V = 2.7(2.4) mag, stellar masses 0.8(1.6)x10^11
Msun, M/L_V = 1.2(2.3) Msun/LVsun, and SFR = 120(170) Msun/yr. Models assuming
declining SFRs with e-folding timescales of 10Myr-1Gyr generally imply younger
ages, lower A_V's and SFRs, but similar stellar masses within a factor of two.
Compared to LBGs at similar redshifts and rest-frame L_V's, DRGs are older,
more massive, and more obscured for any given star formation history.
[ABRIDGED]Comment: Accepted for publication in the Astrophysical Journal. 27 pages, 14
b/w figure
Cost-effectiveness of tipranavir versus comparator protease inhibitor regimens in HIV infected patients previously exposed to antiretroviral therapy in the Netherlands
<p>Abstract</p> <p>Background</p> <p>This study compares the costs and effects of a regimen with ritonavir-boosted tipranavir (TPV/r) to a physician-selected genotypically-defined standard-of-care comparator protease inhibitor regimen boosted with ritonavir (CPI/r) in HIV infected patients that were previously exposed to antiretroviral therapy in the Netherlands.</p> <p>Methods</p> <p>We compared the projected lifetime costs and effects of two theoretical groups of 1000 patients, one receiving a standard of care regimen with TPV/r as a component and the other receiving a standard of care regimen with CPI/r. A 3-stage Markov model was formulated to represent three different consecutive HAART regimens. The model uses 12 health states based on viral load and CD4+ count to simulate disease progression. The transition probabilities for the Markov model were derived from a United States cohort of treatment experienced HIV patients. Furthermore, the study design was based on 48-week data from the RESIST-2 clinical trial and local Dutch costing data. Cost and health effects were discounted at 4% and 1.5% respectively according to the Dutch guideline. The analysis was conducted from the Dutch healthcare perspective using 2006 unit cost prices.</p> <p>Results</p> <p>Our model projects an accumulated discounted cost to the Dutch healthcare system per patient receiving the TPV/r regimen of €167,200 compared to €145,400 for the CPI/r regimen. This results in an incremental cost of €21,800 per patient. The accumulated discounted effect is 7.43 life years or 6.31 quality adjusted life years (QALYs) per patient receiving TPV/r, compared to 6.91 life years or 5.80 QALYs per patient receiving CPI/r. This translates into an incremental effect of TPV/r over CPI/r of 0.52 life years gained (LYG) or 0.51 QALYs gained. The corresponding incremental cost effectiveness ratios (iCERs) are €41,600 per LYG and €42,500 per QALY.</p> <p>Conclusion</p> <p>We estimated the iCER for TPV/r compared to CPI/r at approximately €40,000 in treatment experienced HIV-1 infected patients in the Netherlands. This ratio may well be in range of what is acceptable and warrants reimbursement for new drug treatments in the Netherlands, in particular in therapeutic areas as end-stage oncology and HIV and other last-resort health-care interventions.</p
Code Comparison in Galaxy Scale Simulations with Resolved Supernova Feedback: Lagrangian vs. Eulerian Methods
We present a suite of high-resolution simulations of an isolated dwarf galaxy
using four different hydrodynamical codes: {\sc Gizmo}, {\sc Arepo}, {\sc
Gadget}, and {\sc Ramses}. All codes adopt the same physical model which
includes radiative cooling, photoelectric heating, star formation, and
supernova (SN) feedback. Individual SN explosions are directly resolved without
resorting to sub-grid models, eliminating one of the major uncertainties in
cosmological simulations. We find reasonable agreement on the time-averaged
star formation rates as well as the joint density-temperature distributions
between all codes. However, the Lagrangian codes show significantly burstier
star formation, larger supernova-driven bubbles, and stronger galactic outflows
compared to the Eulerian code. This is caused by the behavior in the dense,
collapsing gas clouds when the Jeans length becomes unresolved: gas in
Lagrangian codes collapses to much higher densities than in Eulerian codes, as
the latter is stabilized by the minimal cell size. Therefore, more of the gas
cloud is converted to stars and SNe are much more clustered in the Lagrangian
models, amplifying their dynamical impact. The differences between Lagrangian
and Eulerian codes can be reduced by adopting a higher star formation
efficiency in Eulerian codes, which significantly enhances SN clustering in the
latter. Adopting a zero SN delay time reduces burstiness in all codes,
resulting in vanishing outflows as SN clustering is suppressed.Comment: accepted version by ApJ (including a new simulation in Appendix B
suggested by the referee
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