114 research outputs found
The SINS survey of z~2 galaxy kinematics: properties of the giant star forming clumps
We have studied the properties of giant star forming clumps in five z~2
star-forming disks with deep SINFONI AO spectroscopy at the ESO VLT. The clumps
reside in disk regions where the Toomre Q-parameter is below unity, consistent
with their being bound and having formed from gravitational instability. Broad
H{\alpha}/[NII] line wings demonstrate that the clumps are launching sites of
powerful outflows. The inferred outflow rates are comparable to or exceed the
star formation rates, in one case by a factor of eight. Typical clumps may lose
a fraction of their original gas by feedback in a few hundred million years,
allowing them to migrate into the center. The most active clumps may lose much
of their mass and disrupt in the disk. The clumps leave a modest imprint on the
gas kinematics. Velocity gradients across the clumps are 10-40 km/s/kpc,
similar to the galactic rotation gradients. Given beam smearing and clump
sizes, these gradients may be consistent with significant rotational support in
typical clumps. Extreme clumps may not be rotationally supported; either they
are not virialized, or they are predominantly pressure supported. The velocity
dispersion is spatially rather constant and increases only weakly with star
formation surface density. The large velocity dispersions may be driven by the
release of gravitational energy, either at the outer disk/accreting streams
interface, and/or by the clump migration within the disk. Spatial variations in
the inferred gas phase oxygen abundance are broadly consistent with inside-out
growing disks, and/or with inward migration of the clumps.Comment: accepted Astrophys. Journal, February 9, 201
GMASS Ultradeep Spectroscopy of Galaxies at redshift z~2. I. The stellar metallicity
Context: Galaxy metallicities have been measured to redshift z~2 by gas-phase
oxygen abundances of the interstellar medium using the R23 and N2 methods.
Galaxy stellar metallicities provide crucial data for chemical evolution models
but have not been assessed reliably much outside the local Universe. Aims: We
determine the iron-abundance, stellar metallicity of star-forming galaxies
(SFGs) at redshift z~2, observed as part of the Galaxy Mass Assembly ultra-deep
Spectroscopic Survey (GMASS). Methods: We compute the equivalent width of a
rest-frame mid-ultraviolet, photospheric absorption-line index, the 1978 index
found to vary monotonically with stellar metallicity by Rix and collaborators.
We normalise and combine 75 SFG spectra from the GMASS survey to produce a
spectrum corresponding to a total integration time 1652.5 hours (and a
signal-to-noise ratio ~100 for our 1.5 angstrom binning) of FORS2 spectroscopic
observations at the Very Large Telescope. Results: We measure an
iron-abundance, stellar metallicity of log (Z/Zsolar) = -0.574+/-0.159 for our
spectrum representative of a galaxy of stellar mass 9.4 x 10^9 Msolar assuming
a Chabrier IMF. We find that the R04 model SFG spectrum for log (Z/Zsolar) =
-0.699 solar metallicity provides the best description of our GMASS coadded
spectrum. For similar galaxy stellar mass, our stellar metallicity is ~0.25 dex
lower than the oxygen-abundance, gas-phase metallicity quantified by Erb and
collaborators for UV-selected star-forming galaxies at z=2. Conclusions: We
conclude that we are witnessing the establishment of a light-element
overabundance in galaxies as they are being formed at redshift z~2. Our
measurements are reminiscent of the alpha-element enhancement seen in
low-redshift, galactic bulges and early-type galaxies. (Abridged)Comment: Accepted for publication in Astronomy and Astrophysics on 18 December
2007, 9 pages, 8 figures, aa.bst and aa.cls A&A style file
The Chandra COSMOS Survey: III. Optical and Infrared Identification of X-ray Point Sources
The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8 Ms, Chandra program that
has imaged the central 0.9 deg^2 of the COSMOS field down to limiting depths of
1.9 10^-16 erg cm^-2 s-1 in the 0.5-2 keV band, 7.3 10^-16 erg cm^-2 s^-1 in
the 2-10 keV band, and 5.7 10^-16 erg cm^-2 s-1 in the 0.5-10 keV band. In this
paper we report the i, K and 3.6micron identifications of the 1761 X-ray point
sources. We use the likelihood ratio technique to derive the association of
optical/infrared counterparts for 97% of the X-ray sources. For most of the
remaining 3%, the presence of multiple counterparts or the faintness of the
possible counterpart prevented a unique association. For only 10 X-ray sources
we were not able to associate a counterpart, mostly due to the presence of a
very bright field source close by. Only 2 sources are truly empty fields.
Making use of the large number of X-ray sources, we update the "classic locus"
of AGN and define a new locus containing 90% of the AGN in the survey with full
band luminosity >10^42 erg/s. We present the linear fit between the total i
band magnitude and the X-ray flux in the soft and hard band, drawn over 2
orders of magnitude in X-ray flux, obtained using the combined C-COSMOS and
XMM-COSMOS samples. We focus on the X-ray to optical flux ratio (X/O) and we
test its known correlation with redshift and luminosity, and a recently
introduced anti-correlation with the concentration index (C). We find a strong
anti-correlation (though the dispersion is of the order of 0.5 dex) between C
and X/O, computed in the hard band, and that 90% of the obscured AGN in the
sample with morphological information live in galaxies with regular morphology
(bulgy and disky/spiral), suggesting that secular processes govern a
significant fraction of the BH growth at X-ray luminosities of 10^43- 10^44.5
erg/s.Comment: 21 pages, 17 figures, 4 tables; accepted for publication in ApJS. The
catalog is available at the urls listed in the pape
Ubiquitous outflows in DEEP2 spectra of star-forming galaxies at z=1.4
Galactic winds are a prime suspect for the metal enrichment of the
intergalactic medium and may have a strong influence on the chemical evolution
of galaxies and the nature of QSO absorption line systems. We use a sample of
1406 galaxy spectra at z~1.4 from the DEEP2 redshift survey to show that
blueshifted Mg II 2796, 2803 A absorption is ubiquitous in starforming galaxies
at this epoch. This is the first detection of frequent outflowing galactic
winds at z~1. The presence and depth of absorption are independent of AGN
spectral signatures or galaxy morphology; major mergers are not a prerequisite
for driving a galactic wind from massive galaxies. Outflows are found in
coadded spectra of galaxies spanning a range of 30x in stellar mass and 10x in
star formation rate (SFR), calibrated from K-band and from MIPS IR fluxes. The
outflows have column densities of order N_H ~ 10^20 cm^-2 and characteristic
velocities of ~ 300-500 km/sec, with absorption seen out to 1000 km/sec in the
most massive, highest SFR galaxies. The velocities suggest that the outflowing
gas can escape into the IGM and that massive galaxies can produce
cosmologically and chemically significant outflows. Both the Mg II equivalent
width and the outflow velocity are larger for galaxies of higher stellar mass
and SFR, with V_wind ~ SFR^0.3, similar to the scaling in low redshift
IR-luminous galaxies. The high frequency of outflows in the star-forming galaxy
population at z~1 indicates that galactic winds occur in the progenitors of
massive spirals as well as those of ellipticals. The increase of outflow
velocity with mass and SFR constrains theoretical models of galaxy evolution
that include feedback from galactic winds, and may favor momentum-driven models
for the wind physics.Comment: Accepted by ApJ. 25 pages, 17 figures. Revised to add discussions of
intervening absorbers and AGN-driven outflows; conclusions unchange
On the Origin of the Galaxy Star-Formation-Rate Sequence: Evolution and Scatter
We use a semi-analytic model for disk galaxies to explore the origin of the
time evolution and small scatter of the galaxy SFR sequence -- the tight
correlation between star-formation rate (SFR) and stellar mass (M_star). The
steep decline of SFR from z~2 to the present, at fixed M_star, is a consequence
of the following: First, disk galaxies are in a steady state with the SFR
following the net (i.e., inflow minus outflow) gas accretion rate. The
evolution of the SFR sequence is determined by evolution in the cosmological
specific accretion rates, \propto (1+z)^{2.25}, but is found to be independent
of feedback. Although feedback determines the outflow rates, it shifts galaxies
along the SFR sequence, leaving its zero point invariant. Second, the
conversion of accretion rate to SFR is materialized through gas density, not
gas mass. Although the model SFR is an increasing function of both gas mass
fraction and gas density, only the gas densities are predicted to evolve
significantly with redshift. Third, star formation is fueled by molecular gas.
Since the molecular gas fraction increases monotonically with increasing gas
density, the model predicts strong evolution in the molecular gas fractions,
increasing by an order of magnitude from z=0 to z~2. On the other hand, the
model predicts that the effective surface density of atomic gas is ~10 M_sun
pc^{-2}, independent of redshift, stellar mass or feedback. Our model suggests
that the scatter in the SFR sequence reflects variations in the gas accretion
history, and thus is insensitive to stellar mass, redshift or feedback. The
large scatter in halo spin contributes negligibly, because it scatters galaxies
along the SFR sequence. An observational consequence of this is that the
scatter in the SFR sequence is independent of the size (both stellar and
gaseous) of galaxy disks.Comment: 24 pages, 19 figures, accepted to MNRAS, minor changes to previous
versio
The Impact of cold gas accretion above a mass floor on galaxy scaling relations
Using the cosmological baryonic accretion rate and normal star formation
efficiencies, we present a very simple model for star-forming galaxies (SFGs)
that accounts for the mass and redshift dependencies of the SFR-Mass and
Tully-Fisher relations from z=2 to the present. The time evolution follows from
the fact that each modelled galaxy approaches a steady state where the SFR
follows the (net) cold gas accretion rate. The key feature of the model is a
halo mass floor M_{min}~10^{11} below which accretion is quenched in order to
simultaneously account for the observed slopes of the SFR-Mass and
Tully-Fischer relations. The same successes cannot be achieved via a
star-formation threshold (or delay) nor by varying the SF efficiency or the
feedback efficiency. Combined with the mass ceiling for cold accretion due to
virial shock heating, the mass floor M_{min} explains galaxy "downsizing",
where more massive galaxies formed earlier and over a shorter period of time.
It turns out that the model also accounts for the observed galactic baryon and
gas fractions as a function of mass and time, and the cosmic SFR density from
z~6 to z=0, which are all resulting from the mass floor M_{min}. The model
helps to understand that it is the cosmological decline of accretion rate that
drives the decrease of cosmic SFR density between z~2 and z=0 and the rise of
the cosmic SFR density allows us to put a constraint on our main parameter
M_{min}~10^{11} solar masses. Among the physical mechanisms that could be
responsible for the mass floor, we view that photo-ionization feedback (from
first in-situ hot stars) lowering the cooling efficiency is likely to play a
large role.Comment: 19pages, 14 figures, accepted to ApJ, updated reference
Microbial ligand costimulation drives neutrophilic steroid-refractory asthma
Funding: The authors thank the Wellcome Trust (102705) and the Universities of Aberdeen and Cape Town for funding. This research was also supported, in part, by National Institutes of Health GM53522 and GM083016 to DLW. KF and BNL are funded by the Fonds Wetenschappelijk Onderzoek, BNL is the recipient of an European Research Commission consolidator grant and participates in the European Union FP7 programs EUBIOPRED and MedALL. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewedPublisher PD
“Medically unexplained” symptoms and symptom disorders in primary care: prognosis-based recognition and classification
Background: Many patients consult their GP because they experience bodily symptoms. In a substantial proportion of
cases, the clinical picture does not meet the existing diagnostic criteria for diseases or disorders. This may be because
symptoms are recent and evolving or because symptoms are persistent but, either by their character or the negative
results of clinical investigation cannot be attributed to disease: so-called “medically unexplained symptoms” (MUS).
MUS are inconsistently recognised, diagnosed and managed in primary care. The specialist classification systems
for MUS pose several problems in a primary care setting. The systems generally require great certainty about
presence or absence of physical disease, they tend to be mind-body dualistic, and they view symptoms from a
narrow specialty determined perspective. We need a new classification of MUS in primary care; a classification
that better supports clinical decision-making, creates clearer communication and provides scientific underpinning
of research to ensure effective interventions.
Discussion: We propose a classification of symptoms that places greater emphasis on prognostic factors.
Prognosis-based classification aims to categorise the patient’s risk of ongoing symptoms, complications, increased
healthcare use or disability because of the symptoms. Current evidence suggests several factors which may be
used: symptom characteristics such as: number, multi-system pattern, frequency, severity. Other factors are:
concurrent mental disorders, psychological features and demographic data. We discuss how these characteristics may
be used to classify symptoms into three groups: self-limiting symptoms, recurrent and persistent symptoms, and
symptom disorders. The middle group is especially relevant in primary care; as these patients generally have reduced
quality of life but often go unrecognised and are at risk of iatrogenic harm. The presented characteristics do not
contain immediately obvious cut-points, and the assessment of prognosis depends on a combination of several factors.
Conclusion: Three criteria (multiple symptoms, multiple systems, multiple times) may support the classification into
good, intermediate and poor prognosis when dealing with symptoms in primary care. The proposed new classification
specifically targets the patient population in primary care and may provide a rational framework for decision-making in
clinical practice and for epidemiologic and clinical research of symptoms
Gas Accretion and Galactic Chemical Evolution: Theory and Observations
This chapter reviews how galactic inflows influence galaxy metallicity. The
goal is to discuss predictions from theoretical models, but particular emphasis
is placed on the insights that result from using models to interpret
observations. Even as the classical G-dwarf problem endures in the latest round
of observational confirmation, a rich and tantalizing new phenomenology of
relationships between , , SFR, and gas fraction is emerging both in
observations and in theoretical models. A consensus interpretation is emerging
in which star-forming galaxies do most of their growing in a quiescent way that
balances gas inflows and gas processing, and metal dilution with enrichment.
Models that explicitly invoke this idea via equilibrium conditions can be used
to infer inflow rates from observations, while models that do not assume
equilibrium growth tend to recover it self-consistently. Mergers are an overall
subdominant mechanism for delivering fresh gas to galaxies, but they trigger
radial flows of previously-accreted gas that flatten radial gas-phase
metallicity gradients and temporarily suppress central metallicities. Radial
gradients are generically expected to be steep at early times and then
flattened by mergers and enriched inflows of recycled gas at late times.
However, further theoretical work is required in order to understand how to
interpret observations. Likewise, more observational work is needed in order to
understand how metallicity gradients evolve to high redshifts.Comment: Invited review to appear in Gas Accretion onto Galaxies, Astrophysics
and Space Science Library, eds. A. J. Fox & R. Dav\'e, to be published by
Springer. 29 pages, 2 figure
The zCOSMOS-SINFONI Project I: Sample Selection and Natural-Seeing Observations
The zCOSMOS SINFONI project is aimed at studying the physical and kinematical
properties of a sample of massive z~1.4-2.5 star-forming galaxies, through
SINFONI near-IR integral field spectroscopy (IFS), combined with the
multi-wavelength information from the zCOSMOS (COSMOS) survey. The project is
based on 1 hour of natural-seeing observations per target, and Adaptive Optics
(AO) follow-up for a major part of the sample, which includes 30 galaxies
selected from the zCOSMOS/VIMOS spectroscopic survey. This first paper presents
the sample selection, and the global physical characterization of the target
galaxies from multicolor photometry, i.e., star formation rate (SFR), stellar
mass, age, etc. The Halpha integrated properties such as, flux, velocity
dispersion, and size, are derived from the natural-seeing observations, while
the follow up AO observations will be presented in the next paper of this
series. Our sample appears to be well representative of star-forming galaxies
at z~2, covering a wide range in mass and SFR. The Halpha integrated properties
of the 25 Halpha detected galaxies are similar to those of other IFS samples at
the same redshifts. Good agreement is found among the SFRs derived from Halpha
luminosity and other diagnostic methods, provided the extinction affecting the
Halpha luminosity is about twice that affecting the continuum. A preliminary
kinematic analysis, based on the maximum observed velocity difference across
the source, and on the integrated velocity dispersion, indicates that the
sample splits nearly 50-50 into rotation-dominated and velocity
dispersion-dominated galaxies, in good agreement with previous surveys.Comment: 41 pages, 21 figures, 7 tables. Accepted for publication in the
Astrophysical Journa
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