The properties of the star-forming interstellar medium at z = 0.84-2.23 from HiZELS : mapping the internal dynamics and metallicity gradients in high-redshift disc galaxies.

We present adaptive optics assisted, spatially resolved spectroscopy of a sample of nine Hα-selected galaxies at z = 0.84-2.23 drawn from the HiZELS narrow-band survey. These galaxies have star formation rates of 1-27 M⊙ yr-1 and are therefore representative of the typical high-redshift star-forming population. Our ˜kpc-scale resolution observations show that approximately half of the sample have dynamics suggesting that the ionized gas is in large, rotating discs. We model their velocity fields to infer the inclination-corrected, asymptotic rotational velocities. We use the absolute B-band magnitudes and stellar masses to investigate the evolution of the B-band and stellar-mass Tully-Fisher relationships. By combining our sample with a number of similar measurements from the literature, we show that, at fixed circular velocity, the stellar mass of star-forming galaxies has increased by a factor of 2.5 between z = 2 and 0, whilst the rest-frame B-band luminosity has decreased by a factor of ˜ 6 over the same period. Together, these demonstrate a change in mass-to-light ratio in the B band of Δ(M/LB)/(M/LB)z=0 ˜ 3.5 between z = 1.5 and 0, with most of the evolution occurring below z = 1. We also use the spatial variation of [N II]/Hα to show that the metallicity of the ionized gas in these galaxies declines monotonically with galactocentric radius, with an average Δ log(O/H)/ΔR = -0.027 ± 0.005 dex kpc-1. This gradient is consistent with predictions for high-redshift disc galaxies from cosmologically based hydrodynamic simulations

Tramp Novae Between Galaxies in the Fornax Cluster: Tracers of Intracluster Light

We report the results of a survey for novae in and between the galaxies of the Fornax cluster. Our survey provides strong evidence that intracluster novae exist and that they provide a useful, independent measure of the intracluster light in Fornax. We discovered six strong nova candidates in six distinct epochs spanning eleven years from 1993 to 2004. The data were taken with the 4m and the 1.5m telescopes at CTIO. The spatial distribution of the nova candidates is consistent with $\sim$16-41% of the total light in the cluster being in the intracluster light, based on the ratio of the number of novae we discovered in intracluster space over the total number of novae discovered plus a simple completeness correction factor. This estimate is consistent with independent measures of intracluster light in Fornax and Virgo using intracluster planetary nebulae. The accuracy of the intracluster light measurement improves with each survey epoch as more novae are discovered.Comment: 30 pages, 10 figures, accepted for publication in the Astrophysical Journal (Sep 9, 2004). Version 2: Added references. Full resolution versions of figures 1-7 and 10 can be found at http://astrowww.phys.uvic.ca/~neill/fnx

The Thermal Memory of Reionization History

The recent measurement by WMAP of a large electron scattering optical depth tau_e = 0.17 +- 0.04 is consistent with a simple model of reionization in which the intergalactic medium (IGM) is ionized at redshift z ~ 15, and remains highly ionized thereafter. Here, we show that existing measurements of the IGM temperature from the Lyman-alpha forest at z ~ 2 - 4 rule out this ``vanilla'' model. Under reasonable assumptions about the ionizing spectrum, as long as the universe is reionized before z = 10, and remains highly ionized thereafter, the IGM reaches an asymptotic thermal state which is too cold compared to observations. To simultaneously satisfy the CMB and forest constraints, the reionization history must be complex: reionization begins early at z >~ 15, but there must have been significant (order unity) changes in fractions of neutral hydrogen and/or helium at 6 < z < 10, and/or singly ionized helium at 4 < z < 10. We describe a physically motivated reionization model that satisfies all current observations. We also explore the impact of a stochastic reionization history and show that a late epoch of (HeII --> HeIII) reionization induces a significant scatter in the IGM temperature, but the scatter diminishes with time quickly. Finally, we provide an analytic formula for the thermal asymptote, and discuss possible additional heating mechanisms that might evade our constraints.Comment: 10 pages, submitted to ApJ, new references, additional discussion on earlier work and partial HeII reionizatio

The HeII Lyman alpha forest and the thermal state of the IGM

Recent analyses of the intergalactic UV background by means of the HeII Lyman alpha forest assume that HeII and HI absorption features have the same line widths. We omit this assumption to investigate possible effects of thermal line broadening on the inferred HeII/HI ratio eta and to explore the potential of intergalactic HeII observations to constrain the thermal state of the IGM. Deriving a simple relation between the column density and the temperature of an absorber we develop a procedure to fit the parameters of a power law temperature-density relation and eta simultaneously. In an alternative approach the temperature of an absorber, eta, and the redshift scale of eta variations are estimated simultaneously. Tests with artificial data show that well-constrained results can be obtained only if the signal-to-noise ratio in the HeII forest is S/N > 20. Thus, it is impossible to give an estimate of the temperature-density relation with the HeII data available at present (S/N ~5). However, we find that only 45% of the lines in our sample favor turbulent line widths. Furthermore, the inferred eta values are on average about 0.05 dex larger if a thermal component is taken into account, and their distribution is 46% narrower in comparison to a purely turbulent fit. Therefore, variations of eta on a 10% level may be related to the presence of thermal line broadening. The apparent correlation between the strength of the HI absorption and the eta value, which has been found in former studies, essentially disappears if thermal broadening is taken into account. In the redshift range 2.58 < z < 2.74 towards the quasars HE2347-4342 and HS1700+6416 we obtain eta ~ 100. (abridged)Comment: accepted for publication by A&A, 11 pages, 13 figure

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

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 MNRA

Resolving the high redshift Lyman-alpha forest in smoothed particle hydrodynamics simulations

We use a large set of cosmological smoothed particle hydrodynamics (SPH) simulations to examine the effect of mass resolution and box size on synthetic Lya forest spectra at 2 \leq z \leq 5. The mass resolution requirements for the convergence of the mean Lya flux and flux power spectrum at z=5 are significantly stricter than at lower redshift. This is because transmission in the high redshift Lya forest is primarily due to underdense regions in the intergalactic medium (IGM), and these are less well resolved compared to the moderately overdense regions which dominate the Lya forest opacity at z~2-3. We further find that the gas density distribution in our simulations differs significantly from previous results in the literature at large overdensities (\Delta>10). We conclude that studies of the Lya forest at z=5 using SPH simulations require a gas particle mass of M_gas \leq 2x10^5 M_sol/h, which is >8 times the value required at z=2. A box size of at least 40 Mpc/h is preferable at all redshifts.Comment: 5 pages, 5 figures, 2 tables, accepted by MNRA

The Evolution of Optical Depth in the Ly-alpha Forest: Evidence Against Reionization at z~6

We examine the evolution of the IGM Ly-alpha optical depth distribution using the transmitted flux probability distribution function (PDF) in a sample of 63 QSOs spanning absorption redshifts 1.7 < z < 5.8. The data are compared to two theoretical optical depth distributions: a model distribution based on the density distribution of Miralda-Escude et al. (2000) (MHR00), and a lognormal distribution. We assume a uniform UV background and an isothermal IGM for the MHR00 model, as has been done in previous works. Under these assumptions, the MHR00 model produces poor fits to the observed flux PDFs at redshifts where the optical depth distribution is well sampled, unless large continuum corrections are applied. However, the lognormal optical depth distribution fits the data at all redshifts with only minor continuum adjustments. We use a simple parametrization for the evolution of the lognormal parameters to calculate the expected mean transmitted flux at z > 5.4. The lognormal optical depth distribution predicts the observed Ly-alpha and Ly-beta effective optical depths at z > 5.7 while simultaneously fitting the mean transmitted flux down to z = 1.6. If the evolution of the lognormal distribution at z < 5 reflects a slowly-evolving density field, temperature, and UV background, then no sudden change in the IGM at z ~ 6 due to late reionization appears necessary. We have used the lognormal optical depth distribution without any assumption about the underlying density field. If the MHR00 density distribution is correct, then a non-uniform UV background and/or IGM temperature may be required to produce the correct flux PDF. We find that an inverse temperature-density relation greatly improves the PDF fits, but with a large scatter in the equation of state index. [Abridged]Comment: 45 pages, 16 figures, submitted to Ap

Semi-analytic Simulations of Galactic Winds: Volume Filling Factor, Ejection of Metals and Parameter Study

We present a semi-analytic treatment of galactic winds within high resolution, large scale cosmological N-body simulations of a LCDM Universe. The evolution of winds is investigated by following the expansion of supernova driven superbubbles around the several hundred thousand galaxies that form in an approximately spherical region of space with diameter 52 Mpc/h and mean density close to the mean density of the Universe. We focus our attention on the impact of winds on the diffuse intergalactic medium. Initial conditions for mass loss at the base of winds are taken from Shu, Mo and Mao (2003). Results are presented for the volume filling factor and the mass fraction of the IGM affected by winds and their dependence on the model parameters is carefully investigated. The mass loading efficiency of bubbles is a key factor to determine the evolution of winds and their global impact on the IGM: the higher the mass loading, the later the IGM is enriched with metals. Galaxies with 10^9 < M_* < 10^10 M_sun are responsible for most of the metals ejected into the IGM at z=3, while galaxies with M_* < 10^9 M_sun give a non negligible contribution only at higher redshifts, when larger galaxies have not yet assembled. We find a higher mean IGM metallicity than Lyalpha forest observations suggest and we argue that the discrepancy may be explained by the high temperatures of a large fraction of the metals in winds, which may not leave detectable imprints in absorption in the Lyalpha forest.Comment: 18 pages, 15 figures. Major changes in the model. Manuscript with high resolution figures available upon request. MNRAS in pres

Radio Afterglows of Gamma-Ray Bursts and Hypernovae at High Redshift, and their Potential for 21-cm Absorption Studies

We investigate the radio afterglows of gamma-ray bursts (GRBs) and hypernovae (HNe) at high redshifts and quantify their detectability, as well as their potential usefulness for 21 cm absorption line studies of the intergalactic medium (IGM) and intervening structures. We examine several sets of source and environment model parameters that are physically plausible at high redshifts. The radio afterglows of GRBs would be detectable out to z ~ 30, while the energetic HNe could be detectable out to z ~ 20 even by the current Very Large Array (VLA). We find that the 21 cm absorption line due to the diffuse neutral IGM is difficult to detect even by the proposed Square Kilometer Array (SKA), except for highly energetic sources. We also find that the 21 cm line due to collapsed gas clouds with high optical depth may be detected on rare occasions.Comment: 36 pages, 12 figures, 1 table, accepted for publication in Ap