352 research outputs found
A sharp look at the gravitationally lensed quasar SDSS J0806+2006 with Laser Guide Star Adaptive Optics
We present the first VLT near-IR observations of a gravitationally lensed
quasar, using adaptive optics and laser guide star. These observations can be
considered as a test bench for future systematic observations of lensed quasars
with adaptive optics, even when bright natural guide stars are not available in
the nearby field. With only 14 minutes of observing time, we derived very
accurate astrometry of the quasar images and of the lensing galaxy, with 0.05
\arcsec spatial resolution, comparable to the Hubble Space Telescope (HST). In
combination with deep VLT optical spectra of the quasar images, we use our
adaptive optics images to constrain simple models for the mass distribution of
the lensing galaxy. The latter is almost circular and does not need any strong
external shear to fit the data. The time delay predicted for SDSS0806+2006,
assuming a singular isothermal ellipsoid model and the concordance cosmology,
is Delta t \simeq 50 days. Our optical spectra indicate a flux ratio between
the quasar images of A/B=1.3 in the continuum and A/B=2.2 in both the MgII and
in the CIII] broad emission lines. This suggests that microlensing affects the
continuum emission. However, the constant ratio between the two emission lines
indicates that the broad emission line region is not microlensed. Finally, we
see no evidence of reddening by dust in the lensing galaxy.Comment: 4 pages, Published in Astronomy and Astrophysics. Discussion slightly
expanded with respect to v1. Typos correcte
Deep optical spectroscopy of extended Lyman alpha emission around three radio-quiet z=4.5 quasars
We report the first results of a spectroscopic search for Lyman alpha,
envelopes around three z=4.5 radio-quiet quasars. Our observational strategy
uses the FORS2 spectrograph attached to the UT1 of the Very Large Telescope
(VLT) in the multi-slit mode. This allows us to observe simultaneously the
quasars and several PSF stars. The spectra of the latter are used to remove the
point-like quasar from the data, and to unveil the faint underlying Lyman
alpha, envelopes associated with the quasars with unprecedented depth. We
clearly detect an envelope around two of the three quasars. These envelopes
measure respectively 10" and 13" in extent (i.e. 67 kpc and 87 kpc). This is 5
to 10 times larger than predicted by the models of Haiman & Rees (2001) and up
to 100 times fainter. Our observations better agree with models involing a
clumpy envelope as in Alam & Miralda-Escude (2002) or Chelouche et al. (2008).
We find that the brighter quasars also have the brighter envelopes but that the
extend of the envelopes does not depend on the quasar luminosity. Although our
results are based on only two objects with a detected Lyman alpha, envelope,
the quality of the spatial deblending of the spectra lends considerable hope to
estimate the luminosity function and surface brightness profiles of high
redshift Lyman alpha, envelopes down to F= 2-3 10^{-21} erg/s/cm^2/A. We find
that the best strategy to carry out such a project is to obtain both
narrow-band images and deep slit-spectra.Comment: 8 pages, 5 figures, submitted to A&
Microlensing variability in the gravitationally lensed quasar Q2237+0305 = the Einstein Cross, I. Spectrophotometric monitoring with the VLT
We present the results of the first long-term (2.2 years) spectroscopic
monitoring of a gravitationally lensed quasar, namely the Einstein Cross
Q2237+0305. The goal of this paper is to present the observational facts to be
compared in follow-up papers with theoretical models to constrain the inner
structure of the source quasar. We spatially deconvolve deep VLT/FORS1 spectra
to accurately separate the spectrum of the lensing galaxy from the spectra of
the quasar images. Accurate cross-calibration of the 58 observations at
31-epoch from October 2004 to December 2006 is carried out with non-variable
foreground stars observed simultaneously with the quasar. The quasar spectra
are further decomposed into a continuum component and several broad emission
lines to infer the variations of these spectral components. We find prominent
microlensing events in the quasar images A and B, while images C and D are
almost quiescent on a timescale of a few months. The strongest variations are
observed in the continuum of image A. Their amplitude is larger in the blue
(0.7 mag) than in the red (0.5 mag), consistent with microlensing of an
accretion disk. Variations in the intensity and profile of the broad emission
lines are also reported, most prominently in the wings of the CIII] and center
of the CIV emission lines. During a strong microlensing episode observed in
June 2006 in quasar image A, the broad component of the CIII] is more highly
magnified than the narrow component. In addition, the emission lines with
higher ionization potentials are more magnified than the lines with lower
ionization potentials, consistent with the results obtained with reverberation
mapping. Finally, we find that the V-band differential extinction by the lens,
between the quasar images, is in the range 0.1-0.3 mag.Comment: 16 pages, 16 figures, A&A accepted, corrected Fig. 1
Spectroscopy of extended Ly\alpha\ envelopes around z=4.5 quasars
What are the frequency, shape, kinematics, and luminosity of Ly\alpha\
envelopes surrounding radio-quiet quasars at high redshift, and is the
luminosity of these envelopes related to that of the quasar or not? As a first
step towards answering these questions, we have searched for Ly\alpha\
envelopes around six radio-quiet quasars at z~4.5, using deep spectra taken
with the FORS2 spectrograph attached to the UT1 of the Very Large Telescope
(VLT). Using the multi-slit mode allows us to observe several point spread
function stars simultaneously with the quasar, and to remove the point-like
emission from the quasar, unveiling the faint underlying Ly\alpha\ envelope
with unprecedented depth. An envelope is detected around four of the six
quasars, which suggests that these envelopes are very frequent. Their diameter
varies in the range 26<d<64 kpc, their surface brightness in the range
3x10^{-19}<\mu<2x10^{-17} erg/s/cm^2/arcsec^2, and their luminosity in the
range 10^{42}<L(Ly\alpha)<10^{44} erg/s. Their shape may be strongly
asymmetric. The Ly\alpha\ emission line full width at half maximum (FWHM) is
900<FWHM<2200 km/s and its luminosity correlates with that of the broad line
region (BLR) of the quasar, with the notable exception of BR2237-0607, the
brightest object in our sample. The same holds for the relation between the
envelope Ly\alpha\ luminosity and the ionizing luminosity of the quasar. While
the deep slit spectroscopy presented in this paper is very efficient at
detecting very faint Ly\alpha\ envelopes, narrow-band imaging is now needed to
measure accurately their spatial extent, radial luminosity profile, and total
luminosity. These observables are crucial to help us discriminate between the
three possible radiation processes responsible for the envelope emission: (i)
cold accretion, (ii) fluorescence induced by the quasar, and (iii) scattering
of the BLR photons by cool gas.Comment: 10 pages, 5 figures, accepted for publication in Astronomy &
Astrophysic
COSMOGRAIL: the COSmological MOnitoring of GRAvItational Lenses III. Redshift of the lensing galaxy in eight gravitationally lensed quasars
Aims: We measure the redshift of the lensing galaxy in eight gravitationally
lensed quasars in view of determining the Hubble parameter H_0 from the time
delay method.
Methods: Deep VLT/FORS1 spectra of lensed quasars are spatially deconvolved
in order to separate the spectrum of the lensing galaxies from the glare of the
much brighter quasar images. A new observing strategy is devised. It involves
observations in Multi-Object-Spectroscopy (MOS) which allows the simultaneous
observation of the target and of several PSF and flux calibration stars. The
advantage of this method over traditional long-slit observations is a much more
reliable extraction and flux calibration of the spectra.
Results: For the first time we measure the redshift of the lensing galaxy in
three multiply-imaged quasars: SDSS J1138+0314 (z=0.445), SDSS J1226-0006
(z=0.517), SDSS J1335+0118 (z=0.440), and we give a tentative estimate of the
redshift of the lensing galaxy in Q 1355-2257 (z=0.701). We confirm four
previously measured redshifts: HE 0047-1756 (z=0.407), HE 0230-2130 (z=0.523),
HE 0435-1223 (z=0.454) and WFI J2033-4723 (z=0.661). In addition, we determine
the redshift of the second lensing galaxy in HE 0230-2130 (z=0.526). The
spectra of all lens galaxies are typical for early-type galaxies, except for
the second lensing galaxy in HE 0230-2130 which displays prominent [OII]
emission.Comment: 9 pages, 19 figures, accepted for publication in A&
Unravelling the interrelationships between ecosystem services and human wellbeing in the Bangladesh delta
Coupled social and ecological systems need to be understood from a dynamic perspective in order to operationalise complexity concepts, such as tipping points, for sustainable ecosystem management. In this study, we strive to achieve this type of conceptual understanding through the analysis of the relationships (e.g. strength, nonlinearity) between the trends of ecosystem services (ES) and human wellbeing (HWB) between 1960 and 2010 in the south-west Bangladesh delta using generalized additive and logistic regression models. We use sequential principal components analysis to investigate the connectedness within the social–ecological system as a measure of resilience. We also use published literature to help develop a system dynamic framework in order to investigate how ES and HWB are interlinked. Overall, our results support previous work, which depicts that material wellbeing (basic materials for a good life) having a strong relationship with provisioning services, which in turn, show a weak relationship with the quality of life (security and health). Moreover, our analysis confirms the ‘Environmentalist’s Paradox’ that HWB has increased despite the deterioration in ES. However, our results suggest that provisioning services are not the only important reason for the increases in observed HWB, as these have also been substantially influenced by technology and capital investment (aid and subsidy). In addition, worsening trends in regulation services and in ‘slow’ variables such as climate suggest that the resilience of the overall social-ecological system is decreasing. Such changes may have severe consequences if they continue, for example, if temperatures exceed the upper physiological limits of key provisioning services (e.g. rice, fish) in the Bangladesh delta. These indicators all suggest that although in terms of HWB the deltaic social–ecological system may be successfully adapting to environmental change, it may also be close to transgressing critical ecological boundaries in the near future
Impacts of rising temperatures and farm management practices on global yields of 18 crops
Understanding the impact of changes in temperature and precipitation on crop yields is a vital step in developing policy and management options to feed the world. As most existing studies are limited to a few staple crops, we implemented global statistical models to examine the influence of weather and management practices on the yields of 18 crops, accounting for 70% of crop production by area and 65% by calorific intake. Focusing on the impact of temperature, we found considerable heterogeneity in the responses of yields across crops and countries. Irrigation was found to alleviate negative implications from temperature increases. Countries where increasing temperature causes the most negative impacts are typically the most food insecure, with the lowest calorific food supply and average crop yield. International action must be coordinated to raise yields in these countries through improvement and modernization of agricultural practices to counteract future adverse impacts of climate change
A systematic map of research exploring the effect of greenspace on mental health
The past 35 years has seen an accumulation of empirical evidence suggesting a positive association between greenspace and mental health. Existing reviews of evidence are narrow in scope, and do not adequately represent the broad range of disciplines working in this field. This study is the first systematic map of studies investigating greenspace effects on mental health. A total of 6059 papers were screened for their relevance, 276 of which met inclusion criteria for the systematic map.The map revealed several methodological limitations hindering the practical applications of research findings to public health. Critically, the majority of studies used cross-sectional mental health data which makes causal inference about greenspace effects challenging. There are also few studies on the micro-features that make up greenspaces (i.e., their “quality”), with most focussing only on “quantity” effects on mental health. Moreover, few studies adopted a multi-scale approach, meaning there is little evidence about at which spatial scale(s) the relationship exists. A geographic gap in study location was also identified, with the majority of studies clustered in European countries and the USA.Future research should account for both human and ecological perspectives of “quality” using objective and repeatable measures, and consider the potential of scale-dependent greenspace effects to ensure that management of greenspace is compatible with wider scale biodiversity targets. To establish the greenspace and metal health relationship across a life course, studies should make better use of longitudinal data, as this enables stronger inferences to be made than more commonly used cross-sectional data
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