2,257 research outputs found
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Observational aspects of galactic accretion at redshift 3.3
We investigate the origin of extragalactic continuum emission and its
relation to the stellar population of a recently discovered peculiar z=3.344
Lyman alpha emitter. Based on an analysis of the broad-band colors and
morphology we find further support for the idea that the underlying galaxy is
being fed by a large-scale (L > 35 kpc) accretion stream. Archival HST images
show small scale (~5 kpc) tentacular filaments converging near a hot-spot of
star-formation, possibly fueled by gas falling in along the filaments. The
spectral energy distribution of the tentacles is broadly compatible with either
(1) non-ionizing rest-frame far-UV continuum emission from stars formed in an
60 million-year-old starburst; (2) nebular 2-photon-continuum radiation,
arising from collisional excitation cooling, or (3) a recombination spectrum
emitted by hydrogen fluorescing in response to ionizing radiation escaping from
the galaxy. The latter possibility simultaneously accounts for the presence of
asymmetric Lyman alpha emission from the large-scale gaseous filament and the
nebular continuum in the smaller-scale tentacles as caused by the escape of
ionizing radiation from the galaxy. Possible astrophysical explanations for the
nature of the tentacles include: a galactic wind powered by the starburst;
in-falling gas during cold accretion, or tails of interstellar medium dragged
out of the galaxy by satellite halos that have plunged through the main halo.
The possibility of detecting extragalactic 2-photon continuum emission in
space-based, broad-band images suggests a tool for studying the gaseous
environment of high redshift galaxies at much greater spatial detail than
possible with Lyman alpha or other resonance line emission
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Warm dark matter as a solution to the small scale crisis: New constraints from high redshift Lyman-α forest data
We present updated constraints on the free-streaming of warm dark matter
(WDM) particles derived from an analysis of the Lya flux power spectrum
measured from high-resolution spectra of 25 z > 4 quasars obtained with the
Keck High Resolution Echelle Spectrometer (HIRES) and the Magellan Inamori
Kyocera Echelle (MIKE) spectrograph. We utilize a new suite of high-resolution
hydrodynamical simulations that explore WDM masses of 1, 2 and 4 keV (assuming
the WDM consists of thermal relics), along with different physically motivated
thermal histories. We carefully address different sources of systematic error
that may affect our final results and perform an analysis of the Lya flux power
with conservative error estimates. By using a method that samples the
multi-dimensional astrophysical and cosmological parameter space, we obtain a
lower limit mwdm > 3.3 keV (2sigma) for warm dark matter particles in the form
of early decoupled thermal relics. Adding the Sloan Digital Sky Survey (SDSS)
Lya flux power spectrum does not improve this limit. Thermal relics of masses 1
keV, 2 keV and 2.5 keV are disfavoured by the data at about the 9sigma, 4sigma
and 3sigma C.L., respectively. Our analysis disfavours WDM models where there
is a suppression in the linear matter power spectrum at (non-linear) scales
corresponding to k=10h/Mpc which deviates more than 10% from a LCDM model.
Given this limit, the corresponding "free-streaming mass" below which the mass
function may be suppressed is 2x10^8 Msun/h. There is thus very little room for
a contribution of the free-streaming of WDM to the solution of what has been
termed the small scale crisis of cold dark matter
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Probing the metallicity and ionization state of the circumgalactic medium at z ~ 6 and beyond with OI absorption
Low ionization metal absorption due to OI has been identified as an important
probe of the physical state of the inter-/circumgalactic medium at the tail-end
of reionization. We use here high-resolution hydrodynamic simulations to
interpret the incidence rate of OI absorbers at z~6 as observed by Becker et
al. (2011). We infer weak OI absorbers (EW > 0.1 A) to have typical HI column
densities in the range of sub-DLAs, densities of 80 times the mean baryonic
density and metallicities of about 1/500 th solar. This is similar to the
metallicity inferred at similar overdensities at z~3, suggesting that the metal
enrichment of the circumgalactic medium around low-mass galaxies has already
progressed considerably by z~6. The apparently rapid evolution of the incidence
rates for OI absorption over the redshift range 5<z<6 mirrors that of
self-shielded Lyman-Limit systems at lower redshift and is mainly due to the
rapid decrease of the meta-galactic photo-ionization rate at z>5. We predict
the incidence rate of OI absorbers to continue to rise rapidly with increasing
redshift as the IGM becomes more neutral. If the distribution of metals extends
to lower density regions, OI absorbers will allow the metal enrichment of the
increasingly neutral filamentary structures of the cosmic web to be probed
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A consistent determination of the temperature of the intergalactic medium at redshift (z) = 2.4
We present new measurements of the thermal state of the intergalactic medium
(IGM) at derived from absorption line profiles in the Ly
forest. We use a large set of high-resolution hydrodynamical simulations to
calibrate the relationship between the temperature-density (--)
relation in the IGM and the distribution of HI column densities, ,
and velocity widths, , of discrete Ly forest absorbers.
This calibration is then applied to the measurement of the lower cut-off of the
-- distribution recently presented by Rudie et al.
(2012). We infer a power-law -- relation,
, with a temperature at mean density,
and slope
. The slope is fully consistent with that advocated by
the analysis of Rudie et al (2012); however, the temperature at mean density is
lower by almost a factor of two, primarily due to an adjustment in the
relationship between column density and physical density assumed by these
authors. These new results are in excellent agreement with the recent
temperature measurements of Becker et al. (2011), based on the curvature of the
transmitted flux in the Ly forest. This suggests that the thermal state
of the IGM at this redshift is reasonably well characterised over the range of
densities probed by these methods
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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
Re-examining the case for neutral gas near the redshift 7 quasar ULAS J1120+0641
Signs of damping-wing absorption attenuating the Lyman α emission line of the first known z ∼ 7 quasar, ULAS J1120+0641, recently provided exciting evidence of a significantly neutral intergalactic medium (IGM). This long-awaited signature of reionization was inferred, in part, from a deficit of flux in the quasar's Lyman α emission line based on predictions from a composite of lower redshift quasars. The composite sample was chosen based on its C IV emission line properties; however, as the original study by Mortlock et al. noted, the composite contained a slight velocity offset in C IV compared to ULAS J1120+0641. Here we test whether this offset may be related to the predicted strength of the Lyman α emission line. We confirm the significant (∼10 per cent at rms) scatter in Lyman α flux for quasars of a given C IV velocity and equivalent width found by Mortlock et al. We further find that among lower redshift objects chosen to more closely match the C IV properties of ULAS J1120+0641, its Lyman α emission falls within the observed distribution of fluxes. Among lower redshift quasars chosen to more closely match in C IV velocity and equivalent width, we find that ULAS J1120+0641 falls within the observed distribution of Lyman α emission line strengths. This suggests that damping-wing absorption may not be present, potentially weakening the case for neutral gas around this object. Larger samples of z > 7 quasars may therefore be needed to establish a clearer picture of the IGM neutral fraction at these redshifts
Preclinical correction of human Fanconi anemia complementation group A bone marrow cells using a safety-modified lentiviral vector.
One of the major hurdles for the development of gene therapy for Fanconi anemia (FA) is the increased sensitivity of FA stem cells to free radical-induced DNA damage during ex vivo culture and manipulation. To minimize this damage, we have developed a brief transduction procedure for lentivirus vector-mediated transduction of hematopoietic progenitor cells from patients with Fanconi anemia complementation group A (FANCA). The lentiviral vector FancA-sW contains the phosphoglycerate kinase promoter, the FANCA cDNA, and a synthetic, safety-modified woodchuck post transcriptional regulatory element (sW). Bone marrow mononuclear cells or purified CD34(+) cells from patients with FANCA were transduced in an overnight culture on recombinant fibronectin peptide CH-296, in low (5%) oxygen, with the reducing agent, N-acetyl-L-cysteine (NAC), and a combination of growth factors, granulocyte colony-stimulating factor (G-CSF), Flt3 ligand, stem cell factor, and thrombopoietin. Transduced cells plated in methylcellulose in hypoxia with NAC showed increased colony formation compared with 21% oxygen without NAC (P<0.03), showed increased resistance to mitomycin C compared with green fluorescent protein (GFP) vector-transduced controls (P<0.007), and increased survival. Thus, combining short transduction and reducing oxidative stress may enhance the viability and engraftment of gene-corrected cells in patients with FANCA
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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
The photoheating of the intergalactic medium in synthesis models of the UV background
We compare cosmological hydrodynamical simulations combined with the
homogeneous metagalactic UV background (UVB) of Haardt & Madau (2012) (HM2012)
to observations of the Lyman-alpha forest that are sensitive to the thermal and
ionization state of the intergalactic medium (IGM). The transition from
optically thick to thin photoheating predicted by the simple one-zone,
radiative transfer model implemented by HM2012 predicts a thermal history that
is in remarkably good agreement with the observed rise of the IGM temperature
at z~3 if we account for the expected evolution of the volume filling factor of
HeIII. Our simulations indicate that there may be, however, some tension
between the observed peak in the temperature evolution and the rather slow
evolution of the HeII opacities suggested by recent Hubble Space Telescope/COS
measurements. The HM2012 UVB also underpredicts the metagalactic hydrogen
photoionization rate required by our simulations to match the observed opacity
of the forest at z>4 and z<2
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First Constraints on Fuzzy Dark Matter from Lyman-α Forest Data and Hydrodynamical Simulations
We present constraints on the masses of extremely light bosons dubbed fuzzy dark matter (FDM) from Lyman- forest data. Extremely light bosons with a de Broglie wavelength of ~ 1 kpc have been suggested as dark matter candidates that may resolve some of the current small scale problems of the cold dark matter model. For the first time, we use hydrodynamical simulations to model the Lyman- flux power spectrum in these models and compare it to the observed flux power spectrum from two different data sets: the XQ-100 and HIRES/MIKE quasar spectra samples. After marginalization over nuisance and physical parameters and with conservative assumptions for the thermal history of the intergalactic medium (IGM) that allow for jumps in the temperature of up to 5000 K, XQ-100 provides a lower limit of 7.1 × 10 eV, HIRES/MIKE returns a stronger limit of 14.3 × 10 eV, while the combination of both data sets results in a limit of 20 × 10 eV (2σ C.L.). The limits for the analysis of the combined data sets increases to 37.5 × 10 eV (2σ C.L.) when a smoother thermal history is assumed where the temperature of the IGM evolves as a power law in redshift. Light boson masses in the range 1–10 × 10 eV are ruled out at high significance by our analysis, casting strong doubts that FDM helps solve the “small scale crisis” of the cold dark matter models.VI is supported by US NSF grant AST-1514734. VI also thanks M. McQuinn for useful discussions, and IAS, Princeton, for hospitality during his stay where part of this work was completed. MV is supported by INFN/PD51 Indark and by the ERC Grant 257670- cosmoIGM and by PRIN-INAF ”2012 ”The X-Shooter sample of 100 quasar spectra at z ~ 3.5”. JSB is supported by a Royal Society URF. MGH is supported by the FP7 ERC Grant Emergence-320596 and the Kavli Foundation. GB is supported by the NSF under award AST-1615814. Simulations were performed at the University of Cambridge with Darwin-HPCS and COSMOS, operated on behalf of the STFC DiRAC facility (funded by BIS National E-infrastructure capital grant ST/J005673/1 and STFC grants ST/H008586/1, ST/K00333X/1)
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