Martin G. Haehnelt

Publications (54)68.64 Total impact

• Article: A z=3.045 Lyman alpha emitting halo hosting a QSO and a possible candidate for AGN-triggered star-formation

  Michael Rauch, George D. Becker, Martin G. Haehnelt, Robert F. Carswell, Jean-Rene Gauthier
  [show abstract] [hide abstract]
  ABSTRACT: 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.
  02/2013;
• Article: Neutrino masses and cosmological parameters from a Euclid-like survey: Markov Chain Monte Carlo forecasts including theoretical errors

  Benjamin Audren, Julien Lesgourgues, Simeon Bird, Martin G. Haehnelt, Matteo Viel
  [show abstract] [hide abstract]
  ABSTRACT: We present forecasts for the accuracy of determining the parameters of a minimal cosmological model and the total neutrino mass based on combined mock data for a future Euclid-like galaxy survey and Planck. We consider two different galaxy surveys: a spectroscopic redshift survey and a cosmic shear survey. We make use of the Monte Carlo Markov Chains (MCMC) technique and assume two sets of theoretical errors. The first error is meant to account for uncertainties in the modelling of the effect of neutrinos on the non-linear galaxy power spectrum and we assume this error to be fully correlated in Fourier space. The second error is meant to parametrize the overall residual uncertainties in modelling the non-linear galaxy power spectrum at small scales, and is conservatively assumed to be uncorrelated and to increase with the ratio of a given scale to the scale of non-linearity. It hence increases with wavenumber and decreases with redshift. With these two assumptions for the errors and assuming further conservatively that the uncorrelated error rises above 2% at k = 0.4 h/Mpc and z = 0.5, we find that a future Euclid-like cosmic shear/galaxy survey achieves a 1-sigma error on Mnu close to 32 meV/25 meV, sufficient for detecting the total neutrino mass with good significance. If the residual uncorrelated errors indeed rises rapidly towards smaller scales in the non-linear regime as we have assumed here then the data on non-linear scales does not increase the sensitivity to the total neutrino mass. Assuming instead a ten times smaller theoretical error with the same scale dependence, the error on the total neutrino mass decreases moderately from sigma(Mnu) = 18 meV to 14 meV when mildly non-linear scales with 0.1 h/Mpc < k < 0.6 h/Mpc are included in the analysis of the galaxy survey data.
  10/2012;
• Article: On the rapid demise of Lyman-alpha emitters at z>7 due to the increasing incidence of optically thick absorption systems

  James S. Bolton, Martin G. Haehnelt
  [show abstract] [hide abstract]
  ABSTRACT: A variety of independent observational studies have now reported a significant decline in the fraction of Lyman-break galaxies which exhibit Ly-a emission over the redshift interval z=6-7. In combination with the strong damping wing extending redward of Ly-a in the spectrum of the bright z=7.085 quasar ULAS 1120+0641, this has strengthened suggestions that the hydrogen in the intergalactic medium (IGM) is still substantially neutral at z~7. Current theoretical models imply HI fractions as large as 40-90 per cent may be required to explain these data assuming there is no intrinsic evolution in the Ly-a emitter population. We propose that such large neutral fractions are not necessary. Based on a hydrodynamical simulation which reproduces the absorption spectra of high-redshift (z~6-7) quasars, we demonstrate that the opacity of the intervening IGM redward of rest-frame Ly-a can rise rapidly in average regions of the Universe simply because of the increasing incidence of absorption systems which are optically thick to Lyman continuum photons as the tail-end of reionisation is approached. Our simulations suggest these data do not require a large change in the IGM neutral fraction by several tens of per cent from z=6-7, but may instead be indicative of the rapid decrease in the typical mean free path for ionising photons expected during the final stages of reionisation.
  08/2012;
• Article: Extended and Filamentary Lyman Alpha Emission from the Formation of a Protogalactic Halo at z=2.63

  Michael Rauch, George D. Becker, Martin G. Haehnelt, Jean-Rene Gauthier, Wallace L. W. Sargent
  [show abstract] [hide abstract]
  ABSTRACT: We report the observation of a further asymmetric, extended Lyman alpha emitting halo at z=2.63, from our ultra-deep, long-slit spectroscopic survey of faint high redshift emitters, undertaken with Magellan LDSS3 in the GOODS-S field. The Lya emission, detected over more than 30 kpc, is spatially coincident with a concentration of galaxies visible in deep broad-band imaging. While these faint galaxies without spectroscopic redshifts cannot with certainty be associated with one another or with the Lya emission, there are a number of compelling reasons why they very probably form a Milky Way halo-mass group at the Lya redshift. A filamentary structure, possibly consisting of Lya emission at very high equivalent width, and evidence for disturbed stellar populations, suggest that the properties of the emitting region reflect ongoing galaxy assembly, with recent galaxy mergers and star formation occurring in the group. Hence, the Lya provides unique insights into what is probably a key mode of galaxy formation at high redshifts. The Lya emission may be powered by cooling radiation or spatially extended star formation in the halo, but is unlikely to be fluorescence driven by either an AGN or one of the galaxies. The spatial profile of the emission is conspicuously different from that of typical Lya emitters or Lyman break galaxies, which is consistent with the picture that extended emission of this kind represents a different stage in the galaxy formation process. Faint, extended Lya emitters such as these may be lower-mass analogues of the brighter Lya blobs. Our observations provide further, circumstantial evidence that galaxy mergers may promote the production and / or escape of ionizing radiation, and that the halos of interacting galaxies may be significant sources for ionizing photons during the epoch of reionization.
  06/2012;
• Article: Constraints on Massive Neutrinos from the CFHTLS Angular Power Spectrum

  Jun-Qing Xia, Benjamin R. Granett, Matteo Viel, Simeon Bird, Luigi Guzzo, Martin G. Haehnelt, Jean Coupon, Henry Joy McCracken, Yannick Mellier
  [show abstract] [hide abstract]
  ABSTRACT: We use the galaxy angular power spectrum at $z\sim0.5-1.2$ from the Canada-France-Hawaii-Telescope Legacy Survey Wide fields (CFHTLS-Wide) to constrain separately the total neutrino mass $\sum{m_\nu}$ and the effective number of neutrino species $N_{\rm{eff}}$. This survey has recently benefited from an accurate calibration of the redshift distribution, allowing new measurements of the (non-linear) matter power spectrum in a unique range of scales and redshifts sensitive to neutrino free streaming. Our analysis makes use of a recent model for the effect of neutrinos on the weakly non-linear matter power spectrum derived from accurate N-body simulations. We show that CFHTLS, combined with WMAP7 and a prior on the Hubble constant provides an upper limit of $\sum{m_\nu}<0.29\,$eV and $N_{\rm{eff}} =4.17^{+1.62}_{-1.26}$ (2$\,\sigma$ confidence levels). If we omit smaller scales which may be affected by non-linearities, these constraints become $\sum{m_\nu}<0.41\,$eV and $N_{\rm{eff}} =3.98^{+2.02}_{-1.20}$ (2$\,\sigma$ confidence levels). Finally we show that the addition of other large scale structures probes can further improve these constraints, demonstrating that high redshift large volumes surveys such as CFHTLS are complementary to other cosmological probes of the neutrino mass.
  03/2012;
• Source

  Available from: arxiv.org

  Article: Filamentary infall of cold gas and escape of Lyα and hydrogen ionizing radiation from an interacting high‐redshift galaxy★

  Michael Rauch, George D. Becker, Martin G. Haehnelt, Jean-Rene Gauthier, Swara Ravindranath, Wallace L. W. Sargent
  [show abstract] [hide abstract]
  ABSTRACT: We present observations of a peculiar Lyα-emitting galaxy at redshift z = 3.344, discovered in a deep, blind spectroscopic survey for faint Lyα emitters with the Magellan II telescope in the Hubble Ultra Deep Field. The galaxy exhibits complex Lyα emission, including an extended, asymmetric component that is partially suppressed by damped Lyα absorption, and two spatially elongated, narrow emission features. Archival Hubble Space Telescope Advanced Camera for Surveys imaging shows evidence for tidal disruption of the stellar component. This V = 27 galaxy appears to give us unprecedented insight into two fundamental stages in the formation of structure at high redshift: the inflow of gas into ordinary galaxies, and the escape of ionizing radiation into the intergalactic medium. Neutral hydrogen, falling in partly in the form of a narrow filament, appears to emit fluorescent Lyα photons induced by the stellar ionizing flux escaping from the disturbed galaxy. The in-falling material may represent primary cold accretion or an interaction-triggered inflow. The rate of ionizing photons required by the observed Lyα emission is consistent with the rate of photons produced by the observed stellar population, with roughly 50 per cent of ionizing photons escaping from the immediate galaxy and encountering the in-falling gas. We briefly discuss cooling radiation and large-scale shocks as additional sources for Lyα and ionizing radiation in high-redshift galaxies, but find that stellar radiation is likely to be the dominant source of ionizing photons for most faint galaxies. The observational properties of the galaxy lend support to a picture where galaxy interactions facilitate the escape of both Lyα and ionizing radiation. We argue that galaxies like the present object may be common at high redshift. This galaxy may therefore be a late example of an interacting population of dwarf galaxies that contribute significantly to the reionization of the universe.
  Monthly Notices of the Royal Astronomical Society 11/2011; 418(2):1115 - 1126. · 4.90 Impact Factor
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  Available from: ArXiv

  Article: Improved measurements of the intergalactic medium temperature around quasars: possible evidence for the initial stages of He-II reionisation at z~6

  James S. Bolton, George D. Becker, Sudhir Raskutti, J. Stuart B. Wyithe, Martin G. Haehnelt, Wallace L. W. Sargent
  [show abstract] [hide abstract]
  ABSTRACT: We present measurements of the intergalactic medium (IGM) temperature within ~5 proper Mpc of seven luminous quasars at z~6. The constraints are obtained from the Doppler widths of Lyman-alpha absorption lines in the quasar near-zones and build upon our previous measurement for the z=6.02 quasar SDSS J0818+1722. The expanded data set, combined with an improved treatment of systematic uncertainties, yields an average temperature at the mean density of log (T_0/K) = 4.21 \pm 0.03 (\pm^0.06_0.07) at 68 (95) per cent confidence for a flat prior distribution over 3.2 < log (T_0/K) < 4.8. In comparison, temperatures measured from the general IGM at z~5 are ~0.3 dex cooler, implying an additional source of heating around these quasars which is not yet present in the general IGM at slightly lower redshift. This heating is most likely due to the recent reionisation of He-II in vicinity of these quasars, which have hard, non-thermal ionising spectra. The elevated temperatures may therefore represent evidence for the earliest stages of He-II reionisation in the most biased regions of the high-redshift Universe. The temperature as a function of distance from the quasars is consistent with being constant, log(T_0/K)~4.2, with no evidence for a line-of-sight thermal proximity effect. However, the limited extent of the quasar near-zones prevents the detection of He-III regions larger than ~5 proper Mpc. Under the assumption the quasars have reionised the He-II in their vicinity, we infer the data are consistent with an average optically bright phase of duration in excess of 10^6.5 yr. These measurements represent the highest-redshift IGM temperature constraints to date, and thus provide a valuable data set for confronting models of H-I reionisation.
  10/2011;
• Source

  Available from: ArXiv

  Article: Massive Neutrinos and the Non-linear Matter Power Spectrum

  Simeon Bird, Matteo Viel, Martin G. Haehnelt
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  ABSTRACT: We perform an extensive suite of N-body simulations of the matter power spectrum, incorporating massive neutrinos in the range M = 0.15-0.6 eV, probing the non-linear regime at scales k < 10 hMpc-1 at z < 3. We extend the widely used HALOFIT approximation to account for the effect of massive neutrinos on the power spectrum. In the strongly non-linear regime HALOFIT systematically over-predicts the suppression due to the free-streaming of the neutrinos. The maximal discrepancy occurs at k ~ 1 hMpc-1, and is at the level of 10% of the total suppression. Most published constraints on neutrino masses based on HALOFIT are not affected, as they rely on data probing the matter power spectrum in the linear or mildly non-linear regime. However, predictions for future galaxy, Lyman-alpha forest and weak lensing surveys extending to more non-linear scales will benefit from the improved approximation to the non-linear matter power spectrum we provide. Our approximation reproduces the induced neutrino suppression over the targeted scales and redshifts significantly better. We test its robustness with regard to changing cosmological parameters and a variety of modelling effects.
  09/2011;
• Article: Galactic winds and extended Lyα emission from the host galaxies of high column density quasi‐stellar object absorption systems

  Luke A. Barnes, Martin G. Haehnelt, Edoardo Tescari, Matteo Viel
  [show abstract] [hide abstract]
  ABSTRACT: We present three-dimensional (3D) resonant radiative transfer simulations of the spatial and spectral diffusion of the Lyα radiation from a central source in the host galaxies of high column density absorption systems at z∼ 3. The radiative transfer simulations are based on a suite of cosmological galaxy formation simulations which reproduce a wide range of observed properties of damped Lyα absorption systems. The Lyα emission is predicted to be spatially extended up to several arcsec, and the spectral width of the Lyα emission is broadened to several hundred (in some case more than thousand) km s−1. The distribution and the dynamical state of the gas in the simulated galaxies are complex, the latter with significant contributions from rotation and both in- and out-flows. The emerging Lyα radiation extends to gas with column densities of NH I∼ 1018 cm−2 and its spectral shape varies strongly with viewing angle. The strong dependence on the central H i column density and the H i velocity field suggests that the Lyα emission will also vary strongly with time on time-scales of a few dynamical times of the central region. Such variations with time should be especially pronounced at times where the host galaxy undergoes a major merger and/or starburst. Depending on the pre-dominance of in- or out-flow along a given sightline and the central column density, the spectra show prominent blue peaks, red peaks or double-peaked profiles. Both spatial distribution and spectral shape are very sensitive to details of the galactic wind implementation. Stronger galactic winds result in more spatially extended Lyα emission and – somewhat counterintuitively – a narrower spectral distribution.
  Monthly Notices of the Royal Astronomical Society 08/2011; 416(3):1723 - 1738. · 4.90 Impact Factor
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  Available from: ArXiv

  Article: How neutral is the intergalactic medium surrounding the redshift z=7.085 quasar ULAS J1120+0641?

  James S. Bolton, Martin G. Haehnelt, Stephen J. Warren, Paul C. Hewett, Daniel J. Mortlock, Bram P. Venemans, Richard G. McMahon, Chris Simpson
  [show abstract] [hide abstract]
  ABSTRACT: The quasar ULAS J1120+0641 at redshift z=7.085 has a highly ionised near zone which is smaller than those around quasars of similar luminosity at z~6. The spectrum also exhibits evidence for a damping wing extending redward of the systemic Lya redshift. We use radiative transfer simulations in a cosmological context to investigate the implications for the ionisation state of the inhomogeneous IGM surrounding this quasar. Our simulations show that the transmission profile is consistent with an IGM in the vicinity of the quasar with a volume averaged HI fraction of f_HI>0.1 and that ULAS J1120+0641 has been bright for 10^6--10^7 yr. The observed spectrum is also consistent with smaller IGM neutral fractions, f_HI ~ 10^-3--10-4, if a damped Lya system in an otherwise highly ionised IGM lies within 5 proper Mpc of the quasar. This is, however, predicted to occur in only ~5 per cent of our simulated sight-lines for a bright phase of 10^6--10^7 yr. Unless ULAS J1120+0641 grows during a previous optically obscured phase, the low age inferred for the quasar adds to the theoretical challenge of forming a 2x10^9 M_sol black hole at this high redshift.
  06/2011;
• Source

  Available from: Swara Ravindranath

  Article: Filamentary Infall of Cold Gas and Escape of Lyman Alpha and Hydrogen Ionizing Radiation from an Interacting High-Redshift Galaxy

  Michael Rauch, George D. Becker, Martin G. Haehnelt, Jean-Rene Gauthier, Swara Ravindranath, Wallace L. W. Sargent
  [show abstract] [hide abstract]
  ABSTRACT: We present observations of a peculiar Lyman alpha-emitting galaxy at redshift 3.344, discovered in a deep, blind spectroscopic survey for faint Lyman alpha emitters with the Magellan II telescope in the Hubble Ultra Deep Field (HUDF). The galaxy exhibits complex Lyman alpha emission, including an extended, asymmetric component that is partially suppressed by damped Lyman alpha absorption, and two spatially elongated, narrow emission features. Archival HST ACS imaging shows evidence for tidal disruption of the stellar component. This V=27 galaxy appears to give us unprecedented insights into two fundamental stages in the formation of structure at high redshift: the inflow of gas into ordinary galaxies, and the escape of ionizing radiation into the intergalactic medium. Neutral hydrogen, falling in partly in form of a narrow filament, appears to emit fluorescent Lyman alpha photons induced by the stellar ionizing flux escaping from the disturbed galaxy. The in-falling material may represent primary cold accretion or an interaction-triggered inflow. The rate of ionizing photons required by the observed Lyman alpha emission is consistent with the rate of photons produced by the observed stellar population, with roughly 50 percent of ionizing photons escaping from the immediate galaxy and encountering the in-falling gas. The observational properties of the galaxy lend support to a picture where galaxy interactions facilitate the escape of both Lyman alpha and ionizing radiation. We argue that galaxies like the present object may be common at high redshift. This galaxy may therefore be a late example of an interacting population of dwarf galaxies contributing significantly to the reionization of the universe.
  05/2011;
• Source

  Available from: Luke A. Barnes

  Article: Galactic Winds and Extended Lya Emission from the Host Galaxies of High Column Density QSO Absorption Systems

  Luke A. Barnes, Martin G. Haehnelt, Edoardo Tescari, Matteo Viel
  [show abstract] [hide abstract]
  ABSTRACT: We present 3D resonant radiative transfer simulations of the spatial and spectral diffusion of the Lya radiation from a central source in the host galaxies of high column density absorption systems at z ~ 3. The radiative transfer simulations are based on a suite of cosmological galaxy formation simulations that reproduce a wide range of observed properties of damped Lya absorption systems. The Lya emission is predicted to be spatially extended up to several arcsec, and the spectral width of the Lya emission is broadened to several hundred (in some case more than thousand) km/s. The distribution and the dynamical state of the gas in the simulated galaxies is complex, the latter with significant contributions from rotation and both in- and out-flows. The emerging Lya radiation extends to gas with column densities of N_HI ~ 10^{18} cm^{-2} and its spectral shape varies strongly with viewing angle. The strong dependence on the central \hi column density and the HI velocity field suggests that the Lya emission will also vary strongly with time on timescales of a few dynamical times of the central region. Such variations with time should be especially pronounced at times where the host galaxy undergoes a major merger and/or starburst. Depending on the pre-dominance of in- or out-flow along a given sightline and the central column density, the spectra show prominent blue peaks, red peaks or double-peaked profiles. Both spatial distribution and spectral shape are very sensitive to details of the galactic wind implementation. Stronger galactic winds result in more spatially extended Lya emission and - somewhat counterintuitively - a narrower spectral distribution.
  01/2011;
• Article: Faint resonantly scattered Lyα emission from the absorption troughs of damped Lyα systems at z∼ 3

  Michael Rauch, Martin G. Haehnelt
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  ABSTRACT: We demonstrate that the Lyα emission in the absorption troughs of a large sample of stacked damped Lyα absorption systems (DLAS) presented by Rahmani et al. is consistent with the spectral profiles and luminosities of a recently detected population of faint Lyα emitters at z∼ 3. This result supports the suggestion that the faint emitters are to be identified with the host galaxies of DLAS at these redshifts.
  Monthly Notices of the Royal Astronomical Society Letters 01/2011; 412(1):L55 - L57.
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  Available from: ArXiv

  Article: Measurements of the UV background at 4.6 < z < 6.4 using the quasar proximity effect

  Alexander P. Calverley, George D. Becker, Martin G. Haehnelt, James S. Bolton
  [show abstract] [hide abstract]
  ABSTRACT: We present measurements of the ionising ultraviolet background (UVB) at z ~ 5-6 using the quasar proximity effect. The fifteen quasars in our sample cover the range 4.6 < z_q < 6.4, enabling the first proximity effect measurements of the UVB at z > 5. The metagalactic hydrogen ionisation rate, Gamma_bkg, was determined by modelling the combined ionisation field from the quasar and the UVB in the proximity zone on a pixel-by-pixel basis. The optical depths in the spectra were corrected for the expected effect of the quasar until the mean flux in the proximity region equalled that in the average Ly-alpha forest, and from this we make a measurement of Gamma_bkg. A number of systematic effects were tested using synthetic spectra. Noise in the flux was found to be the largest source of bias at z ~ 5, while uncertainties in the mean transmitted Ly-alpha flux are responsible for the largest bias at z ~ 6. The impacts of large-scale overdensities and Lyman limit systems on Gamma_bkg were also investigated, but found to be small at z > 5. We find a decline in Gamma_bkg with redshift, from log(Gamma_bkg) = -12.15 $\pm$ 0.16 at z ~ 5 to log(Gamma_bkg) = -12.84 $\pm$ 0.18 at z ~ 6 (1 sigma errors). Compared to UVB measurements at lower redshifts, our measurements suggest a drop of a factor of five in the HI photoionisation rate between z ~ 4 and z ~ 6. The decline of Gamma_bkg appears to be gradual, and we find no evidence for a sudden change in the UVB at any redshift that would indicate a rapid change in the attenuation length of ionising photons. Combined with recent measurements of the evolution of the mean free path of ionising photons, our results imply decline in the emissivity of ionising photons by roughly a factor of two from z ~ 5 to 6, albeit with significant uncertainty due to the measurement errors in both Gamma_bkg and the mean free path. Comment: 22 pages, 19 figures, 5 tables; accepted for publication in MNRAS
  11/2010;
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  Available from: ArXiv

  Article: Faint Resonantly Scattered Lyman Alpha Emission from the Absorption Troughs of Damped Lyman Alpha Systems at z ~ 3

  Michael Rauch, Martin G. Haehnelt
  [show abstract] [hide abstract]
  ABSTRACT: We demonstrate that the Lyman alpha emission in the absorption troughs of a large sample of stacked damped Lyman alpha absorption systems (DLAS) presented by Rahmani et al (2010) is consistent with the spectral profiles and luminosities of a recently detected population of faint Lyman alpha emitters at z ~ 3. This result supports the suggestion that the faint emitters are to be identified with the host galaxies of DLAS at these redshifts. Comment: 3 pages, 1 eps figure
  11/2010;
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  Available from: ArXiv

  Article: Detection of Extended He II Reionization in the Temperature Evolution of the Intergalactic Medium

  George D. Becker, James S. Bolton, Martin G. Haehnelt, Wallace L. W. Sargent
  [show abstract] [hide abstract]
  ABSTRACT: We present new measurements of the temperature of the intergalactic medium (IGM) derived from the Lyman-alpha forest over 2.0 < z < 4.8. The small-scale structure in the forest of 61 high-resolution QSO spectra is quantified using a new statistic, the curvature, and the conversion to temperature calibrated using a suite of hydrodynamic simulations. At each redshift we focus on obtaining the temperature at an optimal overdensity probed by the Lyman-alpha forest, T(Delta), where the temperature is nearly a one-to-one function of the curvature regardless of the slope of the temperature-density relation. The median 2-sigma statistical uncertainty in these measurements is 8 per cent, though there may be comparable systematic errors due to the unknown amount of Jeans smoothing in the IGM. We use our T(Delta) results to infer the temperature at the mean density, T0. Even for a maximally steep temperature-density relation, T0 must increase from ~8000 K at z ~ 4.4 to >~12000 K at z ~ 2.8. This increase is not consistent with the monotonic decline in T0 expected in the absence of He II reionization. We therefore interpret the observed rise in temperature as evidence of He II reionization beginning at z >~ 4.4. The evolution of T0 is consistent with an end to He II reionization at z ~ 3, as suggested by opacity measurements of the He II Lyman-alpha forest, although the redshift at which T0 peaks will depend somewhat on the evolution of the temperature-density relation. These new temperature measurements suggest that the heat input due to the reionization of He II dominates the thermal balance of the IGM over an extended period with Delta_z >~ 1. Comment: 19 pages, 15 figures, accepted to MNRAS
  08/2010;
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  Available from: Luke A. Barnes

  Article: Faint extended Lyα emission due to star formation at the centre of high column density QSO absorption systems

  Luke A. Barnes, Martin G. Haehnelt
  [show abstract] [hide abstract]
  ABSTRACT: We use detailed Lyα radiative transfer calculations to further test the claim of Rauch et al. that they have detected spatially extended faint Lyα emission from the elusive host population of damped Lyα absorption systems (DLAs) in their recent ultra-deep spectroscopic survey. We investigate the spatial and spectral distribution of Lyα emission due to star formation at the centre of DLAs, and its dependence on the spatial and velocity structure of the gas. Our model simultaneously reproduces the observed properties of DLAs and the faint Lyα emitters, including the velocity width and column density distribution of DLAs and the large spatial extent of the emission of the faint emitters. Our modelling confirms previous suggestions that DLAs are predominately hosted by dark matter (DM) haloes in the mass range 109.5–1012 M⊙, and are thus of significantly lower mass than those inferred for L* Lyman Break Galaxies (LBGs). Our modelling suggests that DM haloes hosting DLAs retain up to 20 per cent of the cosmic baryon fraction in the form of neutral hydrogen, and that star formation at the centre of the haloes is responsible for the faint Lyα emission. The scattering of a significant fraction of the Lyα emission to the observed radii, which can be as large as 50 kpc or more, requires the amplitude of the bulk motions of the gas at the centre of the haloes to be moderate. The observed space density and size distribution of the emitters together with the incidence rate of DLAs suggests that the Lyα emission due to star formation has a duty cycle of ∼25 per cent.
  Monthly Notices of the Royal Astronomical Society 03/2010; 403(2):870 - 885. · 4.90 Impact Factor
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  Available from: ArXiv

  Article: The effect of neutrinos on the matter distribution as probed by the Intergalactic Medium

  Matteo Viel, Martin G. Haehnelt, Volker Springel
  [show abstract] [hide abstract]
  ABSTRACT: We present a suite of full hydrodynamical cosmological simulations that quantitatively address the impact of neutrinos on the (mildly non-linear) spatial distribution of matter and in particular on the neutral hydrogen distribution in the Intergalactic Medium (IGM), which is responsible for the intervening Lyman-alpha absorption in quasar spectra. The free-streaming of neutrinos results in a (non-linear) scale-dependent suppression of power spectrum of the total matter distribution at scales probed by Lyman-alpha forest data which is larger than the linear theory prediction by about 25% and strongly redshift dependent. By extracting a set of realistic mock quasar spectra, we quantify the effect of neutrinos on the flux probability distribution function and flux power spectrum. The differences in the matter power spectra translate into a ~2.5% (5%) difference in the flux power spectrum for neutrino masses with Sigma m_{\nu} = 0.3 eV (0.6 eV). This rather small effect is difficult to detect from present Lyman-alpha forest data and nearly perfectly degenerate with the overall amplitude of the matter power spectrum as characterised by sigma_8. If the results of the numerical simulations are normalized to have the same sigma_8 in the initial conditions, then neutrinos produce a smaller suppression in the flux power of about 3% (5%) for Sigma m_{\nu} = 0.6$ eV (1.2 eV) when compared to a simulation without neutrinos. We present constraints on neutrino masses using the Sloan Digital Sky Survey flux power spectrum alone and find an upper limit of Sigma m_{\nu} < 0.9$ eV (2 sigma C.L.), comparable to constraints obtained from the cosmic microwave background data or other large scale structure probes. Comment: 38 pages, 21 figures. One section and references added. JCAP in press
  03/2010;
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  Available from: ArXiv

  Article: A first direct measurement of the intergalactic medium temperature around a quasar at z=6

  James S. Bolton, George D. Becker, J. Stuart B. Wyithe, Martin G. Haehnelt, Wallace L. W. Sargent
  [show abstract] [hide abstract]
  ABSTRACT: The thermal state of the intergalactic medium (IGM) provides an indirect probe of both the HI and HeII reionisation epochs. Current constraints on the IGM temperature from the Lya forest are restricted to the redshift range 2<z<4.5, limiting the ability to probe the thermal memory of HI reionisation toward higher redshift. In this work, we present the first direct measurement of the IGM temperature around a z=6 quasar by analysing the Doppler widths of Lya absorption lines in the proximity zone of SDSS J0818+1722. We use a high resolution (R= 40000) Keck/HIRES spectrum in combination with detailed numerical modelling to obtain the temperature at mean density, T_0=23600\pm^5000_6900K (\pm^9200_9300K) at 68 (95) per cent confidence assuming a prior probability 13500K<T_0<38500 K following HI and HeII reionisation. This enables us to place an upper limit on the redshift of HI reionisation, z_H, within 33 comoving Mpc of SDSS J0818+1722. If the quasar reionises the HeII in its vicinity, then in the limit of instantaneous reionisation we infer z_H<9.0 (11.0) at 68 (95) per cent confidence assuming photoheating is the dominant heat source and that HI reionisation is driven by ionising sources with soft spectra, typical of population II stars. If the HI and HeII in the IGM around SDSS J0818+1722 are instead reionised simultaneously by a population of massive metal-free stars, characterised by very hard ionising spectra, we obtain a tighter upper limit of z_H<8.4 (9.4). Initiating reionisation at higher redshifts produces temperatures which are too low with respect to our constraint unless the HI ionising sources or the quasar itself have spectra significantly harder than typically assumed. Comment: 15 pages, 9 figures, accepted to MNRAS
  01/2010;
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  Available from: Luke A. Barnes

  Article: A joint model for the emission and absorption properties of damped Lyα absorption systems

  Luke A. Barnes, Martin G. Haehnelt
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  ABSTRACT: The recently discovered population of ultra-faint extended line emitters, with fluxes of a few times 10−18 erg s−1 cm−2 at z∼ 3, can account for the majority of the incidence rate of damped Lyα systems (DLAs) at this redshift if the line emission is interpreted as Lyα. We show here that a model similar to that proposed by Haehnelt, Steinmetz & Rauch (2000), which reproduces the incidence rate and kinematics of DLAs in the context of Λ cold dark matter models for structure formation, also reproduces the size distribution of the new population of faint Lyα emitters for plausible parameters. This lends further support to the interpretation of the emission as Lyα, as well as the identification of the emitters with the hitherto elusive population of DLA host galaxies. The observed incidence rate of DLAs together with the observed space density and size distribution of the emitters suggest a duty cycle of ∼0.2–0.4 for the Lyα emission from DLA host galaxies. We further show that Lyα cooling is expected to contribute little to the Lyα emission for the majority of emitters. This leaves centrally concentrated star formation at a rate of a few tenths M⊙ yr−1, surrounded by extended Lyα haloes with radii up to 30–50 kpc, as the most plausible explanation for the origin of the emission. Both the luminosity function of Lyα emission and the velocity width distribution of low ionization absorption require that galaxies inside dark matter (DM) haloes with virial velocities ≲50–70 km s−1 contribute little to the incidence rate of DLAs at z∼ 3, suggesting that energy and momentum input due to star formation efficiently removes gas from these haloes. Galaxies with DM haloes with virial velocities of 100–150 km s−1 appear to account for the majority of DLA host galaxies. DLA host galaxies at z∼ 3 should thus become the building blocks of typical present-day galaxies like our Milky Way.
  Monthly Notices of the Royal Astronomical Society 07/2009; 397(1):511 - 519. · 4.90 Impact Factor