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Register a new userEffective Opacity of the Intergalactic Medium from Galaxy Spectra Analysis
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We measure the effective opacity ($tau_{eff}$) of the Intergalactic Medium (IGM) from the composite spectra of 281 Lyman-Break Galaxies (LBGs) in the redshift range $2 lesssim z lesssim 3$. Our spectra are taken from the COSMOS Lyman-Alpha Mapping And Tomographic Observations (CLAMATO) survey derived from the Low Resolution Imaging Spectrometer (LRIS) on the W.M. Keck I telescope. We generate composite spectra in two redshift intervals and fit them with spectral energy distribution (SED) models composed of simple stellar populations. Extrapolating these SED models into the Ly$alpha$ forest, we measure the effective Ly$alpha$ opacity ($tau_{eff}$) in the $2.02 leq z leq 2.44$ range. At $z = 2.22$, we estimate $tau_{eff} = 0.159 pm 0.001$ from a power-law fit to the data. These measurements are consistent with estimates from quasar analyses at $z<2.5$ indicating that the systematic errors associated with normalizing quasar continua are not substantial. We provide a Gaussian Processes model of our results and previous $tau_{eff}$ measurements that describes the steep redshift evolution in $tau_{eff}$ from $z = 1.5 - 4$.
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We describe v02 of igmspec, a database of publically available ultraviolet, optical, and near-infrared spectra that probe the intergalactic medium (IGM). This database, a child of the specdb repository in the specdb github organization, comprises 403277 unique sources and 434686 spectra obtained with the worlds greatest observatories. All of these data are distributed in a single ~25 GB HDF5 file maintained at the University of California Observatories and the University of California, Santa Cruz. The specdb software package includes Python scripts and modules for searching the source catalog and spectral datasets, and software links to the linetools package for spectral analysis. The repository also includes software to generate private spectral datasets that are compliant with International Virtual Observatory Alliance (IVOA) protocols and a Python-based interface for IVOA Simple Spectral Access queries. Futu
Massive stars at redshifts z > 6 are predicted to have played a pivotal role in cosmological reionization as luminous sources of ultra-violet (UV) photons. However, the remnants of these massive stars could be equally important as X-ray luminous (L_X 1e38 erg/s) high-mass X-ray binaries (HMXBs). Because the absorption cross section of neutral hydrogen decreases sharply with photon energy (proportional to the inverse cube), X-rays can escape more freely than UV photons from the star-forming regions in which they are produced, allowing HMXBs to make a potentially significant contribution to the ionizing X-ray background during reionization. In this paper, we explore the ionizing power of HMXBs at redshifts z > 6 using a Monte Carlo model for a coeval stellar population of main sequence stars and HMXBs. Using the archetypal Galactic HMXB Cygnus X-1 as our template, we propose a composite HMXB spectral energy distribution consisting of black-body and power-law components, whose contributions depend on the accretion state of the system. We determine the time-dependent ionizing power of a combined population of UV-luminous stars and X-ray luminous HMXBs, and deduce fitting formulae for the boost in the populations ionizing power arising from HMXBs; these fits allow for simple implementation of HMXB feedback in numerical simulations. Based on this analysis, we estimate the contribution of high redshift HMXBs to the present-day soft X-ray background, and we show that it is a factor of ~100-1000 smaller than the observed limit. Finally, we discuss the implications of our results for the role of HMXBs in reionization and in high redshift galaxy formation.
The distribution of neutral hydrogen in the intergalactic medium (IGM) is currently explored at low-z by means of UV spectroscopy of quasars. We propose an alternative approach based on UV colours of quasars as observed from GALEX surveys. We built a NUV-selected sample of 9033 quasars with (FUV-NUV) colours. The imprint of HI absorption in the observed colours is suggested qualitatively by their distribution as a function of quasar redshift. Because broad band fluxes lack spectral resolution and are sensitive to a large range of N_HI a Monte Carlo simulation of IGM opacity is required for quantitative analysis. It was performed with absorbers randomly distributed along redshift and column density distributions, assumed to be a broken power law with index beta1 (10^15 < N_HI <10^17.2 cm^-2) and beta2 (10^17.2 < N_HI <10^19 cm^-2). The redshift distribution is proportional to the redshift evolution law of the number density of Lyman limit systems (LLS) per unit redshift as determined by spectroscopic surveys.The simulation is run with different assumptions on the spectral index alpha_nu of the quasar ionising flux. The fits between the simulated and observed distribution of colours require an LLS redshift density larger than that derived from spectroscopic counting. This result is robust in spite of difficulties in determining the colour dispersion other than that due to HI absorption. We provide arguments to retain alpha_nu = - 2, a value already extreme with respect to those measured with HST/COS. Further fitting of power law index beta1 and beta2 leads to a higher density by a factor of 1.7 (beta1 = -1.7, beta2 = -1.5), possibly 1.5 (beta1 = -1.7, beta2 = -1.7). Beyond the result in terms of density the analysis of UV colours of quasars reveals a tension between the current description of IGM opacity at low z and the published average ionising spectrum of quasars.
We study supernova-driven galactic outflows as a mechanism for injecting turbulence in the intergalactic medium (IGM) far from galaxies. To this aim we follow the evolution of a 10^13 Msun galaxy along its merger tree, with carefully calibrated prescriptions for star formation and wind efficiencies. At z~3 the majority of the bubbles around galaxies are old (ages >1Gyr), i.e. they contain metals expelled by their progenitors at earlier times; their filling factor increases with time reaching about 10% at z<2. The energy deposited by these expanding shocks in the IGM is predominantly in kinetic form (mean energy density of 1 mu eV cm^-3, about 2-3 x the thermal one), which is rapidly converted in disordered motions by instabilities, finally resulting in a fully developed turbulent spectrum whose evolution is followed through a spectral transfer function approach. The derived mean IGM turbulent Doppler parameter, b_t, peaks at z~1 at about 1.5 km/s with maximum b_t = 25 km/s. The shape of the b_t distribution does not significantly evolve with redshift but undergoes a continuous shift towards lower b_t values with time, as a result of bubble aging. We find also a clear trend of decreasing b_t with N_HI and a more complex dependence on R_s resulting from the age spread of the bubbles. We have attempted a preliminary comparison with the data, hampered by the scarcity of the latter and by the challenge provided by the subtraction of peculiar and thermal motions. Finally we comment on the implications of turbulence for various cosmological studies.
Baryonic feedback can significantly modify the spatial distribution of matter on small scales and create a bulk relative velocity between the dominant cold dark matter and the hot gas. We study the consequences of such bulk motions using two high resolution hydrodynamic simulations, one with no feedback and one with very strong feedback. We find that relative velocities of order $100 kms$ are produced in the strong feedback simulation whereas it is much smaller when there is no feedback. Such relative motions induce dipole distortions to the gas, which we quantify by computing the dipole correlation function. We find halo coordinates and velocities are systematically changed in the direction of the relative velocity. Finally, we discuss potential to observe the relative velocity via large scale structure, Sunyaev-Zeldovich and line emission measurements. Given the nonlinear nature of this effect, it should next be studied in simulations with different feedback implementations/strengths to determine the available model space.
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