454 research outputs found
Reanalysis of the spectrum of the z=10 galaxy
In a recent paper Pello et al. reported observations of a faint galaxy,
gravitationally lensed by the galaxy cluster Abell 1835. Deep J-band
spectroscopy revealed a weak emission line near 1.34 microns, detected in two
spectra with different central wavelengths. The line was interpreted as
Lyman-alpha at redshift z=10.0. This interpretation is supported by the
broad-band photometric spectral energy distribution, and by the location of the
galaxy close to the lens critical line for this redshift. We have reanalysed
the two spectra, just released from the data archive. Our analysis includes
allowance for wavelength shifts due to transverse drift of the object in the
slit. We do not detect a significant emission line at the reported location, or
nearby, at either grating setting, nor in the combined spectrum. We provide a
possible explanation for the reported detection as due to spurious positive
flux introduced in the sky-subtraction stage as a result of variable hot
pixels. We provide our final reduced 2D frame, and corresponding error array.Comment: 4 pages, 1 figure. To appear in A&A Letters. Added possible
explanation for reported emission line as due to variable hot pixel
The first detection of [OIII] emission from high-redshift damped Lyman-alpha galaxies
We present the detection of [OIII] emission lines from the galaxies
responsible for two high-redshift z>1.75 damped Lyman-alpha (DLA) absorption
lines. These are the first detections of rest-frame optical emission lines from
high-redshift DLA galaxies. Unlike the Lyman-alpha line, the [OIII] line
provides a measure of the systemic velocity of the galaxy. We compare the
[OIII] redshifts with the velocity profile of the low-ionisation metal lines in
these two absorbers, with the goal of distinguishing between the model of
Prochaska and Wolfe of DLA absorbers as large rapidly rotating cold thick
discs, and the standard hierarchical CDM model of structure formation, in which
DLAs arise in protogalactic fragments. We find some discrepancies with the
predictions of the former model. Furthermore the image of the DLA galaxy
towards Q2206-1958 shows a complex disturbed morphology, which is more in
accord with the hierarchical picture. We use the properties of the rest-frame
optical emission lines to further explore the question posed by Moller et al.:
are high-redshift DLA galaxies Lyman-break galaxies (LBGs) selected by gas
cross section? The measured velocity dispersions of the DLA galaxies are in
agreement with this picture, while the data on the [OIII] luminosities and the
velocity differences between the Lyman-alpha and [OIII] lines are inconclusive,
as there are insufficient LBG measurements overlapping in luminosity. Finally
we estimate the star formation rates in these two DLA galaxies, using a variety
of diagnostics, and include a discussion of the extent to which the [OIII] line
is useful for this purpose. (abridged)Comment: MNRAS, in press. 14 pages, 10 figure
Galaxy Counterparts of metal-rich Damped Lyman-alpha Absorbers - I: The case of the z=2.35 DLA towards Q2222-0946
We have initiated a survey using the newly commissioned X-shooter
spectrograph to target candidate relatively metal-rich damped Lyman-alpha
absorbers (DLAs). The spectral coverage of X-shooter allows us to search for
not only Lyman-alpha emission, but also rest-frame optical emission lines. We
have chosen DLAs where the strongest rest-frame optical lines ([OII], [OIII],
Hbeta and Halpha) fall in the NIR atmospheric transmission bands. In this first
paper resulting from the survey, we report on the discovery of the galaxy
counterpart of the z_abs = 2.354 DLA towards the z=2.926 quasar Q2222$-0946.
This DLA is amongst the most metal-rich z>2 DLAs studied so far at comparable
redshifts and there is evidence for substantial depletion of refractory
elements onto dust grains. We measure metallicities from ZnII, SiII, NiII, MnII
and FeII of -0.46+/-0.07, -0.51+/-0.06, -0.85+/-0.06, -1.23+/-0.06, and
-0.99+/-0.06, respectively. The galaxy is detected in the Lyman-alpha, [OIII]
lambda4959,5007 Halpha emission lines at an impact parameter of about 0.8
arcsec (6 kpc at z_abs = 2.354). We infer a star-formation rate of 10 M_sun
yr^-1, which is a lower limit due to the possibility of slit-loss. Compared to
the recently determined Halpha luminosity function for z=2.2 galaxies the
DLA-galaxy counterpart has a luminosity of L~0.1L^*_Halpha. The emission-line
ratios are 4.0 (Lyalpha/Halpha) and 1.2 ([OIII]/Halpha). The Lyalpha line shows
clear evidence for resonant scattering effects, namely an asymmetric,
redshifted (relative to the systemic redshift) component and a much weaker
blueshifted component. The fact that the blueshifted component is relatively
weak indicates the presence of a galactic wind. The properties of the galaxy
counterpart of this DLA is consistent with the prediction that metal-rich DLAs
are associated with the most luminous of the DLA-galaxy counterparts.Comment: 9 pages, 7 figures. Accepted for publication in MNRA
ImpZ: a new photometric redshift code for galaxies and quasars
We present a combined galaxy-quasar approach to template-fitting photometric
redshift techniques and show the method to be a powerful one. The code (ImpZ)
is presented, developed and applied to two spectroscopic redshift catalogues,
namely the Isaac Newton Telescope Wide Angle Survey ELAIS N1 and N2 fields and
the Chandra Deep Field North. In particular, optical size information is used
to improve the redshift determination. The success of the code is shown to be
very good with Delta z/(1+z) constrained to within 0.1 for 92 per cent of the
galaxies in our sample. The extension of template-fitting to quasars is found
to be reasonable with Delta z/(1+z) constrained to within 0.25 for 68 per cent
of the quasars in our sample. Various template extensions into the far-UV are
also tested.Comment: 21 pages. MNRAS in press. Minor alterations to match MNRAS final
proo
Airway microstructure in idiopathic pulmonary fibrosis: assessment at hyperpolarized 3He diffusion-weighted MRI
Background
MRI with inhaled hyperpolarized helium 3 (3He) allows for functional and structural imaging of the lungs. Hyperpolarized gas diffusion-weighted (DW) MRI provides noninvasive and quantitative assessment of microstructural acinar changes in the lungs.
Purpose
To investigate whether microstructural imaging metrics from in-vivo hyperpolarized 3He DW MRI are sensitive to longitudinal changes in a cohort of participants with idiopathic pulmonary fibrosis (IPF) and to evaluate the reproducibility of these metrics and their correlation with existing clinical measures of IPF disease severity.
Materials and Methods
In this prospective study, 18 participants with IPF underwent 3He DW MRI at 1.5 T and 11 participants underwent an identical same-day examination for reproducibility assessment. Thirteen participants returned for 6- and 12-month follow-up examinations. Pulmonary function tests, including diffusing capacity of the lungs for carbon monoxide and forced vital capacity, were performed at each examination. The apparent diffusion coefficient (ADC) and stretched exponential modelâderived mean diffusive length scale (LmD) from DW MRI was compared with baseline CT fibrosis scores and pulmonary function tests by using Spearman rank correlation coefficient. Longitudinal changes in DW MRI and pulmonary function test measurements were assessed with Friedman tests and post hoc Dunn test.
Results
3He ADC and LmD were reproducible (mean Bland-Altman analysis bias, 0.002 cm2 · sec-1 and â1.5 ÎŒm, respectively). Elevated ADC and LmD regions qualitatively corresponded to fibrotic regions at CT. ADC and LmD correlated with diffusing capacity of the lungs for carbon monoxide (respectively: r = â0.56, P = .017; and r = â0.54, P = .02) and CT fibrosis score (respectively: r = 0.71, P = .001; and r = 0.65, P = .003). LmD increased by 12 ÎŒm after 12 months (P = .001) whereas mean ADC (P = .17), forced vital capacity (P = .12), and diffusing capacity of the lungs for carbon monoxide (P > .99) were not statistically different between examinations.
Conclusion
Helium 3 diffusion-weighted MRI-derived mean diffusive length scale demonstrates longitudinal changes in lungs affected by idiopathic pulmonary fibrosis
A new comprehensive set of elemental abundances in DLAs III. Star formation histories
We obtained comprehensive sets of elemental abundances for eleven damped
Ly-alpha systems (DLAs) at z_DLA=1.7-2.5. In Paper I of this series, we showed
for three DLA galaxies that we can derive their star formation histories and
ages from a detailed comparison of their intrinsic abundance patterns with
chemical evolution models. We determine in this paper the star formation
properties of six additional DLA galaxies. The derived results confirm that no
single star formation history explains the diverse sets of abundance patterns
in DLAs. We demonstrate that the various star formation histories reproducing
the DLA abundance patterns are typical of local irregular, dwarf starburst and
quiescent spiral galaxies. Independent of the star formation history, the DLAs
have a common characteristic of being weak star forming galaxies; models with
high star formation efficiencies are ruled out. All the derived DLA star
formation rates per unit area are moderate or low, with values between -3.2 <
log SFR < -1.1 M_sol yr^{-1} kpc^{-2}. The DLA abundance patterns require a
large spread in ages ranging from 20 Myr up to 3 Gyr. The oldest DLA in our
sample is observed at z_DLA=1.864 with an age estimated to more than 3 Gyr; it
nicely indicates that galaxies were already forming at z_f>10. But, most of the
DLAs show ages much younger than that of the Universe at the epoch of
observation. Young galaxies thus seem to populate the high redshift Universe at
z>2, suggesting relatively low redshifts of formation (z~3) for most
high-redshift galaxies. The DLA star formation properties are compared with
those of other high-redshift galaxies identified in deep imaging surveys with
the aim of obtaining a global picture of high-redshift objects.Comment: 19 pages, 11 figures, Accepted for publication in A&
Discovery of a compact gas-rich DLA galaxy at z = 2.2: evidences for a starburst-driven outflow
We present the detection of Ly-alpha, [OIII] and H-alpha emission associated
with an extremely strong DLA system (N(HI) = 10^22.10 cm^-2) at z=2.207 towards
the quasar SDSS J113520-001053. This is the largest HI column density ever
measured along a QSO line of sight, though typical of what is seen in GRB-DLAs.
This absorption system also classifies as ultrastrong MgII system with
W2796_r=3.6 A. The mean metallicity of the gas ([Zn/H]=-1.1) and dust depletion
factors ([Zn/Fe]=0.72, [Zn/Cr]=0.49) are consistent with (and only marginally
larger than) the mean values found in the general QSO-DLA population. The
[OIII]-Ha emitting region has a very small impact parameter with respect to the
QSO line of sight, b=0.1", and is unresolved. From the Ha line, we measure
SFR=25 Msun/yr. The Ly-a line is double-peaked and is spatially extended. More
strikingly, the blue and red Ly-a peaks arise from distinct regions extended
over a few kpc on either side of the star-forming region. We propose that this
is the consequence of Ly-a transfer in outflowing gas. The presence of
starburst-driven outflows is also in agreement with the large SFR together with
a small size and low mass of the galaxy (Mvir~10^10 Msun). From the stellar UV
continuum luminosity of the galaxy, we estimate an age of at most a few 10^7
yr, again consistent with a recent starburst scenario. We interpret the data as
the observation of a young, gas rich, compact starburst galaxy, from which
material is expelled through collimated winds powered by the vigorous star
formation activity. We substantiate this picture by modelling the radiative
transfer of Ly-a photons in the galactic counterpart. Though our model (a
spherical galaxy with bipolar outflowing jets) is a simplistic representation
of the true gas distribution and velocity field, the agreement between the
observed and simulated properties is particularly good. [abridged]Comment: 15 pages, 18 figures, 4 tables, accepted for publication in Astronomy
and Astrophysic
Of mongooses and mitigation: ecological analogues to geoengineering
Anthropogenic global warming is a growing environmental problem resulting from unintentional human intervention in the global climate system. If employed as a response strategy, geoengineering would represent an additional intentional human intervention in the climate system, with the intent of decreasing net climate impacts. There is a rich and fascinating history of human intervention in environmental systems, with many specific examples from ecology of deliberate human intervention aimed at correcting or decreasing the impact of previous unintentionally created problems. Additional interventions do not always bring the intended results, and in many cases there is evidence that net impacts have increased with the degree of human intervention. In this letter, we report some of the examples in the scientific literature that have documented such human interventions in environmental systems, which may serve as analogues to geoengineering. We argue that a high degree of system understanding is required for increased intervention to lead to decreased impacts. Given our current level of understanding of the climate system, it is likely that the result of at least some geoengineering efforts would follow previous ecological examples where increased human intervention has led to an overall increase in negative environmental consequences
Xenon ventilation MRI in difficult asthma; initial experience in a clinical setting
Background: Hyperpolarised gas MRI can be used to assess ventilation patterns. Previous studies have shown the image derived metric of ventilation defect percent (VDP) to correlate with FEV1/FVC and FEV1 in asthma.
Objectives: To explore the utility of hyperpolarised xenon-129 (129Xe) ventilation MRI in clinical care and examine its relationship with spirometry and other clinical metrics in people seen in a severe asthma service.
Methods: 26 people referred from a severe asthma clinic for MRI scanning were assessed by contemporaneous 129Xe MRI and spirometry. A sub-group of 18 patients also underwent reversibility testing with spirometry and MRI. Quantitative MRI measures of ventilation were calculated; VDP and the ventilation heterogeneity index (VHI), and compared to spirometry, ACQ7 and blood eosinophil count. Images were reviewed by a multidisciplinary team.
Results: VDP and VHI correlated with FEV1, FEV1/FVC and FEF25â75% but not with ACQ7 or blood eosinophil count. Discordance of MRI imaging and symptoms and/or pulmonary function tests also occurred, prompting diagnostic re-evaluation in some cases.
Conclusion Hyperpolarised gas MRI provides a complementary method of assessment in people with difficult to manage asthma in a clinical setting. When used as a tool supporting clinical care in a severe asthma service, occurrences of discordance between symptoms, spirometry and MRI scanning indicate how MRI scanning may add to a management pathway
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