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Register a new userThe igmspec Database of Public Spectra Probing the Intergalactic Medium
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J. Xavier Prochaska
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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
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We compare a sample of five high-resolution, high S/N Ly$alpha$ forest spectra of bright $6<z lesssim 6.5$ QSOs aimed at spectrally resolving the last remaining transmission spikes at $z>5$ 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, $1-F$, similar to the widely used Voigt profile fitting of the transmitted flux $F$ 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 ($leq $ 8 km/s) to be resolved, is reproduced for optically thin simulations with a temperature at mean density of $T_0= (11000 pm 1600,10500pm 2100,12000 pm 2200)$ K at $z= (5.4,5.6,5.8)$. 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 $zsim5.3$, the width distribution of the observed transmission spikes is consistent with the range of $T_0$ caused by spatial fluctuations in the temperature-density relation.
The intergalactic medium is expected to clump on scales down to $10^4-10^8$ M$_{odot}$ before the onset of reionization. The impact of these small-scale structures on reionization is poorly understood despite the modern understanding that gas clumpiness limits the growth of H II regions. We use a suite of radiation-hydrodynamics simulations that capture the $sim 10^4$ $M_odot$ Jeans mass of unheated gas to study density fluctuations during reionization. Our simulations track the complex ionization and hydrodynamical response of gas in the wake of ionization fronts. The clumping factor of ionized gas (proportional to the recombination rate) rises to a peak value of $5-20$ approximately $Delta t = 10$ Myr after ionization front passage, depending on the incident intensity, redshift, and degree to which the gas had been pre-heated by the first X-ray sources. The clumping factor reaches its relaxed value of $approx 3$ by $Delta t = 300$ Myr. The mean free path of Lyman-limit photons evolves in unison, being up to several times shorter in un-relaxed, recently reionized regions compared to those that were reionized much earlier. Assessing the impact of this response on the global reionizaton process, we find that un-relaxed gaseous structures boost the total number of recombinations by $approx 50$ % and lead to spatial fluctuations in the mean free path that persist appreciably for several hundred million years after the completion of reionization.
During reionization, the intergalactic medium is heated impulsively by supersonic ionization fronts (I-fronts). The peak gas temperatures behind the I-fronts, $T_mathrm{reion}$, are a key uncertainty in models of the thermal history after reionization. Here we use high-resolution radiative transfer simulations to study the parameter space of $T_mathrm{reion}$. We show that $T_mathrm{reion}$ is only mildly sensitive to the spectrum of incident radiation over most of the parameter space, with temperatures set primarily by I-front speeds. We also explore what current models of reionization predict for $T_mathrm{reion}$ by measuring I-front speeds in cosmological radiative transfer simulations. We find that the post-I-front temperatures evolve toward hotter values as reionization progresses. Temperatures of $T_mathrm{reion} = 17,000-22,000$ K are typical during the first half of reionization, but $T_mathrm{reion} = 25,000 - 30,000$ K may be achieved near the end of this process if I-front speeds reach $sim10^4$ km/s as found in our simulations. Shorter reionization epochs lead to hotter $T_mathrm{reion}$. We discuss implications for $z>5$ Ly$alpha$ forest observations, which potentially include sight lines through hot, recently reionized patches of the Universe. Interpolation tables from our parameter space study are made publicly available, along with a simple fit for the dependence of $T_mathrm{reion}$ on the I-front speed.
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 $z = 1.5 - 4$.
The recently discovered fast radio bursts (FRBs), presumably of extra-galactic origin, have the potential to become a powerful probe of the intergalactic medium (IGM). We point out a few such potential applications. We provide expressions for the dispersion measure and rotation measure as a function of redshift, and we discuss the sensitivity of these measures to the HeII reionization and the IGM magnetic field. Finally we calculate the microlensing effect from an isolate, extragalctic stellar-mass compact object on the FRB spectrum. The time delays between the two lensing images will induce constructive and destructive interference, leaving a specific imprint on the spectra of FRBs. With a high all-sky rate, a large statistical sample of FRBs is expected to make these applications feasible.
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