78 research outputs found
Recommended from our members
A z = 3.045 Lyα emitting halo hosting a QSO and a possible candidate for AGN-triggered star formation
In this third paper in a series on the nature of extended, asymmetric Lyman
alpha emitters at z ~ 3 we report the discovery, in an ultra-deep, blind,
spectroscopic long-slit survey, of a Lyman alpha emitting halo around a QSO at
redshift 3.045. The QSO is a previously known, obscured AGN. The halo appears
extended along the direction of the slit and exhibits two faint patches
separated by 17 proper kpc in projection from the QSO. Comparison of the
2-dimensional spectrum with archival HST ACS images shows that these patches
coincide spatially with emission from a peculiar, dumbbell-shaped, faint
galaxy. The assumptions that the Lyman alpha emission patches are originating
in the galaxy and that the galaxy is physically related to the QSO are at
variance with photometric estimates of the galaxy redshift. We show, however,
that a population of very young stars at the redshift of the QSO may fit the
existing rest frame broad band UV photometry of the galaxy. If this scenario is
correct then the symmetry of the galaxy in continuum and Lyman alpha emission,
the extension of the QSO's Lyman alpha emission in its direction, and the
likely presence of a young stellar population in close proximity to a
(short-lived) AGN suggest that this may be an example of AGN feedback
triggering external star formation in high redshift galaxies
Recommended from our members
A new measurement of the intergalactic temperature at z ∼ 2.55–2.95
We present two measurements of the temperature–density relationship (TDR) of the intergalactic medium (IGM) in the redshift range 2.55 < z < 2.95 using a sample of 13 high-quality quasar spectra and high resolution numerical simulations of the IGM. Our approach is based on fitting the neutral hydrogen column density
NHI
and the Doppler parameter b of the absorption lines in the Lyα forest. The first measurement is obtained using a novel Bayesian scheme that takes into account the statistical correlations between the parameters characterizing the lower cut-off of the
b--NHI
distribution and the power-law parameters T0 and γ describing the TDR. This approach yields T0/103 K = 15.6 ± 4.4 and γ = 1.45 ± 0.17 independent of the assumed pressure smoothing of the small-scale density field. In order to explore the information contained in the overall
b--NHI
distribution rather than only the lower cut-off, we obtain a second measurement based on a similar Bayesian analysis of the median Doppler parameter for separate column-density ranges of the absorbers. In this case, we obtain T0/103 K = 14.6 ± 3.7 and γ = 1.37 ± 0.17 in good agreement with the first measurement. Our Bayesian analysis reveals strong anticorrelations between the inferred T0 and γ for both methods as well as an anticorrelation of the inferred T0 and the pressure smoothing length for the second method, suggesting that the measurement accuracy can in the latter case be substantially increased if independent constraints on the smoothing are obtained. Our results are in good agreement with other recent measurements of the thermal state of the IGM probing similar (over-)density ranges.MH acknowledges support by ERC ADVANCED GRANT 320596 ‘The Emergence of Structure during the epoch of Reionization’. GDB was supported by the National Science Foundation through grant AST-1615814. JSB acknowledges the support of a Royal Society University Research Fellowship. MTM thanks the Australian Research Council for Discovery Project grant DP130100568. This work made use of the DiRAC High Performance Computing System (HPCS) and the COSMOS shared memory service at the University of Cambridge. These are operated on behalf of the STFC DiRAC HPC facility. This equipment is funded by BIS National E-infrastructure capital grant ST/J005673/1 and STFC grants ST/H008586/1, ST/K00333X/1
Deuteronomy and Numbers
Four light isotopes - D, ^3He, ^4He and ^7Li - were produced by nuclear
reactions a few seconds after the big bang. New measurements of ^3He in the ISM
by Gloeckler and Geiss and of deuterium in high redshift hydrogen clouds by
Tytler and his collaborators provide further confirmation of big-bang
nucleosynthesis and new insight about the density of ordinary matter (baryons).Comment: 6 pages LaTeX with 1 eps Figur
A High Deuterium Abundance at z=0.7
Of the light elements, the primordial abundance of deuterium, (D/H)_p,
provides the most sensitive diagnostic for the cosmological mass density
parameter Omega_B. Recent high redshift (D/H) measurements are highly
discrepant, although this may reflect observational uncertainties. The larger
(D/H) values, which imply a low Omega_B and require the Universe to be
dominated by non-baryonic matter (dynamical studies indicate a higher total
density parameter), cause problems for galactic chemical evolution models since
they have difficulty in reproducing the large decline down to the lower
present-day (D/H). Conversely, low (D/H) values imply an Omega_B greater than
derived from ^7Li and ^4He abundance measurements, and may require a deuterium
abundance evolution that is too low to easily explain. Here we report the first
measurement at intermediate redshift, where the observational difficulties are
smaller, of a gas cloud with ideal characteristics for this experiment. Our
analysis of the z = 0.7010 absorber toward 1718+4807 indicates (D/H) = 2.0 +/-
0.5 x 10^{-4} which is in the high range. This and other independent
observations suggests there may be a cosmological inhomogeneity in (D/H)_p of
at least a factor of ten.Comment: 6 pages, 1 figur
Metals in the z ~ 3 intergalactic medium: Results from an ultra-high signal-to-noise ratio UVES quasar spectrum
In this work, we investigate the abundance and distribution of metals in the
intergalactic medium (IGM) at through the
analysis of an ultra-high signal-to-noise ratio UVES spectrum of the quasar
HE0940-1050. In the CIV forest, our deep spectrum is sensitive at
to lines with column density down to and in 60
per cent of the considered redshift range down to . In our sample,
all HI lines with show an associated CIV absorption.
In the range , 43 per cent of HI lines has an
associated CIV absorption. At , the detection rates
drop to per cent, possibly due to our sensitivity limits and not to an
actual variation of the gas abundance properties. In the range , we observe a fraction of HI lines with detected CIV a factor of 2
larger than the fraction of HI lines lying in the circum-galactic medium (CGM)
of relatively bright Lyman-break galaxies hosted by dark matter haloes with
M. The comparison of our results with
the output of a grid of photoionization models and of two cosmological
simulations implies that the volume filling factor of the IGM gas enriched to a
metallicity should be of the order of
percent. In conclusion, our results favour a scenario in which metals are found
also outside the CGM of bright star-forming galaxies, possibly due to pollution
by lower mass objects and/or to an early enrichment by the first sources.MV is supported by the ERC Starting Grant ‘cosmoIGM’ and PD51 INDARK grant. TSK acknowledges funding support from the ERC Starting Grant ‘cosmoIGM’, through grant GA-257670. MH was supported by the ERC Advanced Grant 320596 ‘The Emergence of Structure during the epoch of Reionisation’. PB is supported by the INAF PRIN-2014 grant ‘Windy black holes combing galaxy evolution’. Parts of this research were conducted by the Australian Research Council Centre of Excellence for All-sky Astrophysics (CAASTRO), through project number CE110001020.This is the final version of the article. It first appeared from Oxford University Press via http://dx.doi.org/10.1093/mnras/stw216
Probing the thermal state of the intergalactic medium at z > 5 with the transmission spikes in high-resolution Ly α forest spectra
We compare a sample of five high-resolution, high S/N Ly forest
spectra of bright QSOs aimed at spectrally resolving the
last remaining transmission spikes at with those obtained from mock
absorption spectra from the Sherwood and Sherwood-Relics suites of
hydrodynamical simulations of the intergalactic medium (IGM). We use a profile
fitting procedure for the inverted transmitted flux, , similar to the
widely used Voigt profile fitting of the transmitted flux at lower
redshifts, to characterise the transmission spikes that probe predominately
underdense regions of the IGM. We are able to reproduce the width and height
distributions of the transmission spikes, both with optically thin simulations
of the post-reionization Universe using a homogeneous UV background and full
radiative transfer simulations of a late reionization model. We find that the
width of the fitted components of the simulated transmission spikes is very
sensitive to the instantaneous temperature of the reionized IGM. The internal
structures of the spikes are more prominant in low temeperature models of the
IGM. The width distribution of the observed transmission spikes, which require
high spectral resolution ( 8 km/s) to be resolved, is reproduced for
optically thin simulations with a temperature at mean density of K at . This is weakly
dependent on the slope of the temperature-density relation, which is favoured
to be moderately steeper than isothermal. In the inhomogeneous, late
reionization, full radiative transfer simulations where islands of neutral
hydrogen persist to , the width distribution of the observed
transmission spikes is consistent with the range of caused by spatial
fluctuations in the temperature-density relation
Constraining the magnetic field on white dwarf surfaces; Zeeman effects and fine structure constant variation
ABSTRACT
White dwarf (WD) atmospheres are subjected to gravitational potentials around 105 times larger than occur on Earth. They provide a unique environment in which to search for any possible variation in fundamental physics in the presence of strong gravitational fields. However, a sufficiently strong magnetic field will alter absorption line profiles and introduce additional uncertainties in measurements of the fine structure constant. Estimating the magnetic field strength is thus essential in this context. Here, we model the absorption profiles of a large number of atomic transitions in the WD photosphere, including first-order Zeeman effects in the line profiles, varying the magnetic field as a free parameter. We apply the method to a high signal-to-noise, high-resolution, far-ultraviolet Hubble Space Telescope/Space Telescope Imaging Spectrograph spectrum of the WD G191−B2B. The method yields a sensitive upper limit on its magnetic field of B &lt; 2300 G at the 3σ level. Using this upper limit, we find that the potential impact of quadratic Zeeman shifts on measurements of the fine structure constant in G191−B2B is 4 orders of magnitude below laboratory wavelength uncertainties.</jats:p
The Cosmological Baryon Density from the Deuterium Abundance at a redshift z = 3.57
We present a measurement of the deuterium to hydrogen ratio in a quasar
absorption system at redshift z = 3.57 towards QSO 1937-1009. We use a two
component fit, with redshifts determined from unsaturated metal lines, to fit
the hydrogen and deuterium features simultaneously. We find a low value of D/H
= 2.3 \pm 0.6 \times 10^{-5}, which does not agree with other measurements of
high D/H (Songaila et al. 1994, Carswell et al. 1994). The absorption system is
very metal poor, with metallicities less than 1/100 solar. Standard models of
chemical evolution show the astration of deuterium is limited to a few percent
from primordial for systems this metal-poor, so we believe our value represents
the primordial one. Using predictions of standard big-bang nucleosynthesis and
measurements of the cosmic microwave background, our measurement gives the
density of baryons in units of the critical density, , where H_0 = 100 h km s^{-1] Mpc^{-1}.Comment: 10 pages, 2 Figures, also available at http://nately.ucsd.edu/ ;
submitted to Natur
Migration experiences, employment status and psychological distress among Somali immigrants: a mixed-method international study
Background:
The discourse about mental health problems among migrants and refugees tends to focus on adverse pre-migration experiences; there is less investigation of the environmental conditions in which refugee migrants live, and the contrasts between these situations in different countries. This cross-national study of two samples of Somali refugees living in London (UK) and Minneapolis, Minnesota, (USA) helps to fill a gap in the literature, and is unusual in being able to compare information collected in the same way in two cities in different countries.
Methods:
There were two parts to the study, focus groups to gather in-depth qualitative data and a survey of health status and quantifiable demographic and material factors. Three of the focus groups involved nineteen Somali professionals and five groups included twenty-eight lay Somalis who were living in London and Minneapolis. The quantitative survey was done with 189 Somali respondents, also living in London and Minneapolis. We used the MINI International Neuropsychiatric Interview (MINI) to assess ICD-10 and
Results:
The overall qualitative and quantitative results suggested that challenges to masculinity, thwarted aspirations, devalued refugee identity, unemployment, legal uncertainties and longer duration of stay in the host country account for poor psychological well-being and psychiatric disorders among this group.
Conclusion:
The use of a mixed-methods approach in this international study was essential since the quantitative and qualitative data provide different layers and depth of meaning and complement each other to provide a fuller picture of complex and multi-faceted life situations of refugees and asylum seekers. The comparison between the UK and US suggests that greater flexibility of access to labour markets for this refugee group might help to promote opportunities for better integration and mental well-being
- …