1,793 research outputs found
On the Uncertainties of Stellar Mass Estimates via Colour Measurements
Mass-to-light versus colour relations (MLCRs), derived from stellar
population synthesis models, are widely used to estimate galaxy stellar masses
(M) yet a detailed investigation of their inherent biases and limitations
is still lacking. We quantify several potential sources of uncertainty, using
optical and near-infrared (NIR) photometry for a representative sample of
nearby galaxies from the Virgo cluster. Our method for combining multi-band
photometry with MLCRs yields robust stellar masses, while errors in M
decrease as more bands are simultaneously considered. The prior assumptions in
one's stellar population modelling dominate the error budget, creating a
colour-dependent bias of up to 0.6 dex if NIR fluxes are used (0.3 dex
otherwise). This matches the systematic errors associated with the method of
spectral energy distribution (SED) fitting, indicating that MLCRs do not suffer
from much additional bias. Moreover, MLCRs and SED fitting yield similar
degrees of random error (0.1-0.14 dex) when applied to mock galaxies and,
on average, equivalent masses for real galaxies with M 10
M. The use of integrated photometry introduces additional uncertainty
in M measurements, at the level of 0.05-0.07 dex. We argue that using
MLCRs, instead of time-consuming SED fits, is justified in cases with complex
model parameter spaces (involving, for instance, multi-parameter star formation
histories) and/or for large datasets. Spatially-resolved methods for measuring
M should be applied for small sample sizes and/or when accuracies less than
0.1 dex are required. An Appendix provides our MLCR transformations for ten
colour permutations of the filter set.Comment: Accepted to MNRAS. 43 pages, 12 figures, 3 table
The Changing Nature of Pharmaceutical R&D - Opportunities for Asia?
During the 1990''s, the pharmaceutical R&D process has witnessed tremendous technological changes. The emergence of new tools like ''combinatorial chemistry'', ''high throughput screening'' and the in-creasing use of computer-aided in silico experiments has led to significant improvements of research efficiency. This paper discusses the economic impact of this trend. It is argued that the resulting radical improvements in R&D productivity have lowered the minimum efficient scale in pharmeceutical research. As a consequence, the main bottleneck in pharmaceutical research has shifted from the mechanical act of synthesising and screening a sufficient number of active compounds to scientific excellence. Empirical finding indicate that the latter can more easily be achieved in smaller, highly focused firms. Accordingly, the most efficient way to currently conduct pharmaceutical R&D may be a new ''division of labour'' in research between small, highly specialised firms conducting research and large firms focusing on the development, testing, and marketing or new drugs. This reopens a ''window of opportunity'' for Asian pharmaceutical firms who had lost out in the previous race to ever increasing size.economics of technology ;
The Determinants of Pharmaceutical R&D Expenditures: Evidence from Japan
During the past 20 years, the world pharmaceutical industry has experienced a dramatic increase in R&D intensity. We apply and extend a model developed by Grabowski and Vernon (2000) with a pooled data sample of the 15 publicly listed Japanese drug firms for the period 1987 to 1998. As in the reference paper, we find expected returns to be an important determinant of R&D spending in the Japanese drug industry, albeit considerably smaller than in the U.S., which is particularly obvious in the case of returns from newly introduced drugs. However, our results are sensitive to econometric model specification, in particular to controlling for serial correlation and to a dynamic specification of the baseline model. Likewise, estimates on financial constraints are sensitive to model specification, indicating that Japanese drug firms face small or no financial constraints. Our results are consistent with the general literature on R&D investment behaviour, yet raise some methodological questions with regard to the original study.R&D, investment, panel data estimation, pharmaceuticals, Japan
HST-COS Spectroscopy of the Cooling Flow in Abell 1795 - Evidence for Inefficient Star Formation in Condensing Intracluster Gas
We present far-UV spectroscopy from the Cosmic Origins Spectrograph on the
Hubble Space Telescope of a cool, star-forming filament in the core of Abell
1795. These data, which span 1025A - 1700A, allow for the simultaneous modeling
of the young stellar populations and the intermediate-temperature (10^5.5 K)
gas in this filament, which is far removed (~30 kpc) from the direct influence
of the central AGN. Using a combination of UV absorption line indices and
stellar population synthesis modeling, we find evidence for ongoing star
formation, with the youngest stars having ages of 7.5 +/- 2.0 Myr and
metallicities of 0.4 +/- 0.2 Zsun. The latter is consistent with the local
metallicity of the intracluster medium. We detect the O VI (1038) line,
measuring a flux of 4.0 +/- 0.9 x 10^-17 erg s^-1 cm^-2. The O VI (1032) line
is redshifted such that it is coincident with a strong Galactic H2 absorption
feature, and is not detected. The measured O VI (1038) flux corresponds to a
cooling rate of 0.85 +/- 0.2 (stat) +/- 0.15 (sys) Msun/yr at ~10^5.5 K,
assuming that the cooling proceeds isochorically, which is consistent with the
classical X-ray luminosity-derived cooling rate in the same region. We measure
a star formation rate of 0.11 +/- 0.02 Msun/yr from the UV continuum,
suggesting that star formation is proceeding at 13 +/- 3% efficiency in this
filament. We propose that this inefficient star formation represents a
significant contribution to the larger-scale cooling flow problem.Comment: 6 pages, 4 figures. Accepted for publication in ApJ Letter
The Next Generation Virgo Cluster Survey (NGVS). XVIII. Measurement and Calibration of Surface Brightness Fluctuation Distances for Bright Galaxies in Virgo (and Beyond)
We describe a program to measure surface brightness fluctuation (SBF)
distances to galaxies observed in the Next Generation Virgo Cluster Survey
(NGVS), a photometric imaging survey covering of the Virgo cluster
in the bandpasses with the Canada-France Hawaii Telescope. We
describe the selection of the sample galaxies, the procedures for measuring the
apparent -band SBF magnitude , and the calibration of the absolute
as a function of observed stellar population properties. The
multi-band NGVS data set provides multiple options for calibrating the SBF
distances, and we explore various calibrations involving individual color
indices as well as combinations of two different colors. Within the color range
of the present sample, the two-color calibrations do not significantly improve
the scatter with respect to wide-baseline, single-color calibrations involving
. We adopt the calibration as reference for the present
galaxy sample, with an observed scatter of 0.11 mag. For a few cases that lack
good photometry, we use an alternative relation based on a combination
of and colors, with only a slightly larger observed scatter of
0.12 mag. The agreement of our measurements with the best existing distance
estimates provides confidence that our measurements are accurate. We present a
preliminary catalog of distances for 89 galaxies brighter than
mag within the survey footprint, including members of the background M and W
Clouds at roughly twice the distance of the main body of the Virgo cluster. The
extension of the present work to fainter and bluer galaxies is in progress.Comment: ApJ accepte
The infall of the Virgo elliptical galaxy M60 toward M87 and the gaseous structures produced by Kelvin-Helmholtz instabilities
We present Chandra observations of hot gas structures, characteristic of gas stripping during infall, in the Virgo cluster elliptical galaxy M60 (NGC4649) located 1 Mpc east of M87. 0.5−2 keV Chandra X-ray images show a sharp leading edge in the surface brightness 12.4±0.1 kpc north and west of the galaxy center in the direction of M87 characteristic of a merger cold front due to M60's motion through the Virgo ICM. We measured a temperature of 1.00±0.02 keV for abundance 0.5Z⊙ inside the edge and 1.37+0.35−0.19 keV for abundance 0.1Z⊙ in the Virgo ICM free stream region. We find that the observed jump in surface brightness yields a density ratio of 6.44+1.04−0.67 between gas inside the edge and in the cluster free stream region. If the edge is a cold front due solely to the infall of M60 in the direction of M87, we find a pressure ratio of 4.7+1.7−1.4 and Mach number 1.7±0.3. For 1.37 keV Virgo gas we find a total infall velocity for M60 of 1030±180 kms−1. We calculate the motion in the plane of the sky to be 1012+183−192 km−1 implying an inclination angle ξ=11±3 degrees. Surface brightness profiles show the presence of a faint diffuse gaseous tail. We identify filamentary, gaseous wing structures caused by the galaxy's motion through the ICM. The structure and dimensions of these wings are consistent with simulations of Kelvin-Helmholtz instabilities as expected if the gas stripping is close to inviscid
Stripped elliptical galaxies as probes of ICM physics : III. Deep Chandra observation of NGC 4552 - Measuring the viscosity of the intracluster medium
We present results from a deep (200 ks) Chandra observation of the early-type galaxy NGC 4552 (M89) which is falling into the Virgo cluster. Previous shallower X-ray observations of this galaxy showed a remnant gas core, a tail to the South of the galaxy, and twin `horns' attached to the northern edge of the gas core [machacek05a]. In our deeper data, we detect a diffuse, low surface brightness extension to the previously known tail, and measure the temperature structure within the tail. We combine the deep Chandra data with archival XMM-Newton observations to put a strong upper limit on the diffuse emission of the tail out to a large distance (10×the radius of the remnant core) from the galaxy center. In our two previous papers [roediger15a,roediger15b], we presented the results of hydrodynamical simulations of ram pressure stripping specifically for M89 falling into the Virgo cluster and investigated the effect of ICM viscosity. In this paper, we compare our deep data with our specifically tailored simulations and conclude that the observed morphology of the stripped tail in NGC 4552 is most similar to the inviscid models. We conclude that, to the extent the transport processes can be simply modeled as a hydrodynamic viscosity, the ICM viscosity is negligible. More generally, any micro-scale description of the transport processes in the high-β plasma of the cluster ICM must be consistent with the efficient mixing observed in the stripped tail on macroscopic scales
Stripped elliptical galaxies as probes of ICM physics: I. Tails, wakes, and flow patterns in and around stripped ellipticals
Elliptical cluster galaxies are progressively stripped of their atmospheres
due to their motion through the intra-cluster medium (ICM). Deep X-ray
observations reveal the fine-structure of the galaxy's remnant atmosphere and
its gas tail and wake. This fine-structure depends on dynamic conditions
(galaxy potential, initial gas contents, orbit through the host cluster),
orbital stage (early infall, pre-/post-pericenter passage), and ICM plasma
properties (thermal conductivity, viscosity, magnetic field structure). We aim
to disentangle dynamic and plasma effects in order to use stripped ellipticals
as probes of ICM plasma properties. This first paper of a series investigates
the hydrodynamics of progressive gas stripping by means of inviscid
hydrodynamical simulations. We distinguish a long-lasting initial relaxation
phase and a quasi-steady stripping phase. During quasi-steady stripping, the
ICM flow around the remnant atmosphere resembles the flow around solid bodies,
including a `deadwater' region in the near wake. Gas is stripped from the
remnant atmosphere predominantly at its sides via Kelvin-Helmholtz
instabilities. The downstream atmosphere is largely shielded from the ICM wind
and thus shaped into a tail. Observationally, both, this `remnant tail' and the
stripped gas in the wake can appear as a `tail', but only in the wake can
galactic gas mix with the ambient ICM. While the qualitative results are
generic, the simulations presented here are tailored to the Virgo elliptical
galaxy M89 (NGC 4552) for the most direct comparison to observations. Papers II
and III of this series describe the effect of viscosity and compare to Chandra
and XMM-Newton observations, respectively.Comment: ApJ, in press. 19 pages, 13 figures. Clarifications added, text
restructured. Conclusions unchange
Stripped elliptical galaxies as probes of ICM physics: II. Stirred, but mixed? Viscous and inviscid gas stripping of the Virgo elliptical M89
Elliptical galaxies moving through the intra-cluster medium (ICM) are
progressively stripped of their gaseous atmospheres. X-ray observations reveal
the structure of galactic tails, wakes, and the interface between the galactic
gas and the ICM. This fine-structure depends on dynamic conditions (galaxy
potential, initial gas contents, orbit in the host cluster), orbital stage
(early infall, pre-/post-pericenter passage), as well as on the still
ill-constrained ICM plasma properties (thermal conductivity, viscosity,
magnetic field structure). Paper I describes flow patterns and stages of
inviscid gas stripping. Here we study the effect of a Spitzer-like temperature
dependent viscosity corresponding to Reynolds numbers, Re, of 50 to 5000 with
respect to the ICM flow around the remnant atmosphere. Global flow patterns are
independent of viscosity in this Reynolds number range. Viscosity influences
two aspects: In inviscid stripping, Kelvin-Helmholtz instabilities (KHIs) at
the sides of the remnant atmosphere lead to observable horns or wings.
Increasing viscosity suppresses KHIs of increasing length scale, and thus
observable horns and wings. Furthermore, in inviscid stripping, stripped
galactic gas can mix with the ambient ICM in the galaxy's wake. This mixing is
suppressed increasingly with increasing viscosity, such that viscously stripped
galaxies have long X-ray bright, cool wakes. We provide mock X-ray images for
different stripping stages and conditions. While these qualitative results are
generic, we tailor our simulations to the Virgo galaxy M89 (NGC 4552), where
Re~ 50 corresponds to a viscosity of 10% of the Spitzer level. Paper III
compares new deep Chandra and archival XMM-Newton data to our simulations.Comment: ApJ in press. 16 pages, 16 figures. Text clarified, conclusions
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