Lyman-alpha Flux Research Articles

Anatomy of an ionized bubble: NIRCam grism spectroscopy of the z=6.6 double-peaked Lyman-alpha emitter COLA1 and its environment

The increasingly neutral intergalactic gas at $z>6$ impacts the Lyman-alpha (Lyalpha ) flux observed from galaxies. One luminous galaxy, COLA1, stands out because of its unique double-peaked Lyalpha line at $z=6.6$, unseen in any simulation of reionization. Here, we present JWST/NIRCam wide-field slitless spectroscopy in a 21 arcmin2 field centered on COLA1. We find 141 galaxies spectroscopically selected through the doublet at $5.35<z<6.95$, with 40 of these sources showing Hbeta . For COLA1, we additionally detect $ as well as Hgamma . We measure a systemic redshift of $z=6.5917$ for COLA1, confirming the classical double-peak nature of the Lyalpha profile. This implies that it resides in a highly ionized bubble and that it is leaking ionizing photons with a high escape fraction of $f_ esc (LyC) =20$--$50$<!PCT!>, making it a prime laboratory to study Lyman continuum escape in the Epoch of Reionization. COLA1 shows all the signs of a prolific ionizer with a Lyalpha escape fraction of $81 Balmer decrement indicating no dust, a steep UV slope ($ UV 0.4$), and a star-formation surface density $ that of typical galaxies at similar redshift. We detect five galaxies in COLA1's close environment ($ z<0.02$). Exploiting the high spectroscopic completeness inherent to grism surveys, and using mock simulations that fully mimic the selection function, we show that the number of detected companions is very typical for a normal similarly UV-bright UV galaxy -- that is, the ionized bubble around COLA1 is unlikely to be due to an excessively large over-density. Instead, the measured ionizing properties suggest that COLA1 by itself might be powering the bubble required to explain its double-peaked Lyalpha profile ion 0.7$ pMpc), with only minor contributions from detected neighbors ($-19.5 UV

Inferring Intrinsic Stellar EUV and Lyman-Alpha Fluxes and Their Effects on Exoplanet Atmospheres

Inferring Intrinsic Stellar EUV and Lyman-Alpha Fluxes and Their Effects on Exoplanet Atmospheres

A Lyα Transit Left Undetected: the Environment and Atmospheric Behavior of K2-25b

Abstract K2-25b is a Neptune-sized exoplanet (3.45R ⊕) that orbits its M4.5 host with a period of 3.48 days. Due to its membership in the Hyades Cluster, the system has a known age (727 ± 75 Myr). K2-25b’s youth and its similarities with Gl 436b suggested that K2-25b could be undergoing strong atmospheric escape. We observed two transits of K2-25b at Lyα using HST/STIS in order to search for escaping neutral hydrogen. We were unable to detect an exospheric signature, but placed an upper limit of (R p /R ⋆)∣ Ly α < 0.56 at 95% confidence by fitting the light curve of the Lyα red wing, or < 1.20 in the blue wing. We reconstructed the intrinsic Lyα profile of K2-25 to determine its Lyα flux, and analyzed XMM-Newton observations to determined its X-ray flux. Based on the total X-ray and extreme ultraviolet irradiation of the planet (8763 ± 1049 erg s−1 cm−2), we estimated the maximum energy-limited mass-loss rate of K2-25b to be 10.6 − 6.13 + 15.2 × 10 10 g s−1 (0.56M ⊕ per 1 Gyr), five times larger than the similarly estimated mass-loss rate of Gl 436b (2.2 × 1010 g s−1). The photoionization time is about 3 hr, significantly shorter than Gl 436b’s 14 hr. A nondetection of a Lyα transit could suggest K2-25b is not significantly losing its atmosphere, or factors of the system are resulting in the mass loss being unobservable (e.g., atmosphere composition or the system’s large high-energy flux). Further observations could provide more stringent constraints.

The Relative Emission from Chromospheres and Coronae: Dependence on Spectral Type and Age

Extreme-ultraviolet and X-ray emissions from stellar coronae drive mass loss from exoplanet atmospheres, and ultraviolet emission from stellar chromospheres drives photo-chemistry in exoplanet atmospheres. Comparisons of the spectral energy distributions of host stars are, therefore, essential for understanding the evolution and habitability of exoplanets. The large number of stars observed with the MUSCLES, Mega-MUSCLES, and other recent HST observing programs has provided for the first time a large sample (79 stars) of reconstructed Lyman-alpha fluxes that we compare with X-ray fluxes to identify significant patterns in the relative emission from these two atmospheric regions as a function of stellar age and effective temperature. We find that as stars age on the main sequence, the emissions from their chromospheres and coronae follow a pattern in response to the amount of magnetic heating in these atmospheric layers. A single trendline slope describes the pattern of X-ray vs. Lyman-alpha emission for G and K dwarfs, but the different trendlines for M dwarf stars show that the Lyman-alpha fluxes of M stars are significantly smaller than warmer stars with the same X-ray flux. The X-ray and Lyman-alpha luminosities divided by the stellar bolometric luminosities show different patterns depending on stellar age. The L(Lyman-alpha)/L(bol) ratios increase smoothly to cooler stars of all ages, but the L(X)/L(bol) ratios show different trends. For older stars, the increase in coronal emission with decreasing T(eff) is much steeper than chromospheric emission. We suggest a fundamental link between atmospheric properties and trendlines relating coronal and chromospheric heating,

Notes on the correlation between sudden stratospheric warmings and solar activity

Abstract. A correlation between solar activity and normalized occurrence rate of sudden stratospheric warmings (SSWs) has been found. As a proxy for solar activity, the 10.7 cm solar radio flux has been used. In order to find the correlation, we derived a normalized occurrence rate of major sudden stratospheric warmings (MSSWs) based on both the ERA-40/ERA-Interim dataset and NCEP data. Based on this distribution, we calculated the correlation coefficient, which amounts to 0.63, with a significance of 90.68 %, for ERA-40/ERA-Interim, and 0.55 for the NCEP–NCAR-I reanalysis, with a significance of 83.80 %. Additionally, we calculate correlation coefficients for Lyman-alpha flux and sunspot numbers with the analogous method for the same period.

An Intercomparison of VLF and Sounding Rocket Techniques for Measuring the Daytime D Region Ionosphere: Theoretical Implications

AbstractWe compare the two approaches that have been used to measure the lowermost ionosphere, the measurement of the propagation of very low frequency (VLF) radio waves and the in situ sampling by sounding rockets. We focus on the altitude, latitude, and zenith angle variation of the electron density profiles inferred from these two observational techniques as compared with a theoretical photochemical model. Our results show that below 68–70 km, the VLF data and the model agree better with each other than with the sounding rocket profile. At the lowest altitudes, near 60 km, both the VLF data and the model show a greater electron density at higher latitudes, consistent with a cosmic ray flux that increases with latitude, whereas the limited rocket data show a maximum at the tropics. Above 68–70 km, the VLF data and the sounding rockets agree better and at tropical latitudes, the model fails to reproduce the observations. Specifically, the calculated electron density is lower than the data by up to a factor of 2. Possible reasons for the model deficit include underestimates of the solar Lyman alpha flux, the solar X‐ray flux and the mesospheric nitric oxide density. Once these three factors are mitigated, the model is in agreement with the observations between 60 and 80 km.

Response of noctilucent cloud brightness to daily solar variations

For the first time, long-term data sets of ground-based observations of noctilucent clouds (NLC) around the globe have been analyzed in order to investigate a response of NLC to solar UV irradiance variability on a day-to-day scale. NLC brightness has been considered versus variations of solar Lyman-alpha flux. We have found that day-to-day solar variability, whose effect is generally masked in the natural NLC variability, has a statistically significant effect when considering large statistics for more than ten years. Average increase in day-to-day solar Lyman-α flux results in average decrease in day-to-day NLC brightness that can be explained by robust physical mechanisms taking place in the summer mesosphere. Average time lags between variations of Lyman-α flux and NLC brightness are short (0–3 days), suggesting a dominant role of direct solar heating and of the dynamical mechanism compared to photodissociation of water vapor by solar Lyman-α flux. All found regularities are consistent between various ground-based NLC data sets collected at different locations around the globe and for various time intervals. Signatures of a 27-day periodicity seem to be present in the NLC brightness for individual summertime intervals; however, this oscillation cannot be unambiguously retrieved due to inevitable periods of tropospheric cloudiness.

Wandering in the Lyman-alpha forest: a study of dark matter-dark radiation interactions

The amplitude of large-scale matter fluctuations inferred from the observed Sunyaev-Zeldovich (SZ) cluster mass function and from weak gravitational lensing studies, when taken at face value, is in tension with measurements of the cosmic microwave background (CMB) and baryon acoustic oscillation (BAO). In this work, we revisit whether this possible discrepancy can be attributed to new interactions in the dark matter sector. Focusing on a cosmological model where dark matter interacts with a dark radiation species until the epoch of matter-radiation equality, we find that measurements of the Lyman-alpha flux power spectrum from the Sloan Digital Sky Survey provide no support to the hypothesis that new dark matter interactions can resolve the possible tension between CMB and large-scale structure (LSS). Indeed, while the addition of dark matter-dark radiation interactions leads to an improvement of 2Δ ln ℒ=12 with respect to the standard Λ cold dark matter (ΛCDM) model when only CMB, BAO, and LSS data are considered, the inclusion of Lyman-alpha data reduces the improvement of the fit to 2Δ ln ℒ=6 relative to ΛCDM . We thus conclude that the statistical evidence for new dark matter interactions (largely driven by the Planck SZ dataset) is marginal at best, and likely caused by systematics in the data. We also perform a Fisher forecast analysis for the reach of a future dataset composed of a CMB-S4 experiment combined with the Large Synoptic Survey Telescope galaxy survey. We find that the constraint on the effective number of fluid-like dark radiation species, Δ Nfluid, will be improved by an order of magnitude compared to current bounds.

Large-scale 3D mapping of the intergalactic medium using the Lyman α forest

Maps of the large-scale structure of the Universe at redshifts 2-4 can be made with the Lyman-alpha forest which are complementary to low redshift galaxy surveys. We apply the Wiener interpolation method of Caucci et al. to construct three-dimensional maps from sets of Lyman-alpha forest spectra taken from cosmological hydrodynamic simulations. We mimic some current and future quasar redshift surveys (BOSS, eBOSS and MS-DESI) by choosing similar sightline densities. We use these appropriate subsets of the Lyman-alpha absorption sightlines to reconstruct the full three dimensional Lyman-alpha flux field and perform comparisons between the true and the reconstructed fields. We study global statistical properties of the intergalactic medium (IGM) maps with auto-correlation and cross-correlation analysis, slice plots, local peaks and point by point scatter. We find that both the density field and the statistical proper- ties of the IGM are recovered well enough that the resulting IGM maps can be meaningfully considered to represent large-scale maps of the Universe in agreement with Caucci et al., on larger scales and for sparser sightlines than had been tested previously. Quantitatively, for sightline parameters comparable to current and near future surveys the correlation coefficient between true and reconstructed fields is r > 0.9 on scales > 30 h^-1 Mpc. The properties of the maps are relatively insensitive to the precise form of the covariance matrix used. The final BOSS quasar Lyman-alpha forest sample will allow maps to be made with a resolution of ~ 30 h^-1 Mpc over a volume of ~ 15 h^-3 Gpc^3 between redshifts 1.9 and 2.3.

RCS2 J232727.6-020437: AN EFFICIENT COSMIC TELESCOPE ATz= 0.6986

We present a detailed gravitational lens model of the galaxy cluster RCS2 J232727.6-020437. Due to cosmological dimming of cluster members and ICL, its high redshift ($z=0.6986$) makes it ideal for studying background galaxies. Using new ACS and WFC3/IR HST data, we identify 16 multiple images. From MOSFIRE follow up, we identify a strong emission line in the spectrum of one multiple image, likely confirming the redshift of that system to $z=2.083$. With a highly magnified ($\mu\gtrsim2$) source plane area of $\sim0.7$ arcmin$^2$ at $z=7$, RCS2 J232727.6-020437 has a lensing efficiency comparable to the Hubble Frontier Fields clusters. We discover four highly magnified $z\sim7$ candidate Lyman-break galaxies behind the cluster, one of which may be multiply-imaged. Correcting for magnification, we find that all four galaxies are fainter than $0.5 L_{\star}$. One candidate is detected at ${>10\sigma}$ in both Spitzer/IRAC [3.6] and [4.5] channels. A spectroscopic follow-up with MOSFIRE does not result in the detection of the Lyman-alpha emission line from any of the four candidates. From the MOSFIRE spectra we place median upper limits on the Lyman-alpha flux of $5-14 \times 10^{-19}\, \mathrm{erg \,\, s^{-1} cm^{-2}}$ ($5\sigma$).

INTERSTELLAR HYDROGEN FLUXES MEASURED BY IBEX -LO IN 2009: NUMERICAL MODELING AND COMPARISON WITH THE DATA

In this paper, we perform numerical modeling of the interstellar hydrogen fluxes measured by IBEX-Lo during orbit 23 (spring 2009) using a state-of-the-art kinetic model of the interstellar neutral hydrogen distribution in the heliosphere. This model takes into account the temporal and heliolatitudinal variations of the solar parameters as well as non-Maxwellian kinetic properties of the hydrogen distribution due to charge exchange in the heliospheric interface. We found that there is a qualitative difference between the IBEX-Lo data and the modeling results obtained with the three-dimensional, time-dependent model. Namely, the model predicts a larger count rate in energy bin~2 (20-41 eV) than in energy bin~1 (11-21 eV), while the data shows the opposite case. We perform study of the model parameter effects on the IBEX-Lo fluxes and the ratio of fluxes in two energy channels. We shown that the most important parameter, which has a major influence on the ratio of the fluxes in the two energy bins, is the solar radiation pressure. The parameter fitting procedure shows that the best agreement between the model result and the data occurs in the case when the ratio of the solar radiation pressure to the solar gravitation, $\mu_0$, is 1.26$^{+0.06}_{-0.076}$, and the total ionization rate of hydrogen at 1 AU is $\beta_{E,0}=3.7^{+0.39}_{-0.35}\times 10^{-7}$~s$^{-1}$. We have found that the value of $\mu_0$ is much larger than $\mu_0=0.89$, which is the value derived from the integrated solar Lyman-alpha flux data for the period of time studied. We discuss possible reasons for the differences.

Using Lyman-αto detect galaxies that leak Lyman continuum

We propose to infer ionising continuum leaking properties of galaxies by looking at their Lyman-alpha line profiles. We carry out Lyman-alpha radiation transfer calculations in two models of HII regions which are porous to ionising continuum escape: 1) the so-called "density bounded" media, in which massive stars produce enough ionising photons to keep the surrounding interstellar medium transparent to the ionising continuum, i.e almost totally ionised, and 2) "riddled ionisation-bounded" media, surrounded by neutral interstellar medium, but with holes, i.e. with a covering factor lower than unity. The Lyman-alpha spectra emergent from these configurations have distinctive features: 1) a "classical" asymmetric redshifted profile in the first case, but with a small shift of the maximum of the profile compare to the systemic redshift (Vpeak < 150 km/s); 2) a main peak at the systemic redshift in the second case (Vpeak = 0 km/s), with, as a consequence, a non-zero Lyman-alpha flux bluewards the systemic redshift. Assuming that in a galaxy leaking ionising photons, the Lyman-alpha component emerging from the leaking star cluster(s) dominates the total Lyman-alpha spectrum, the Lyman-alpha shape may be used as a pre-selection tool to detect Lyman continuum (LyC) leaking galaxies, in objects with well determined systemic redshift, and high spectral resolution Lyman-alpha spectra (R >= 4000). The examination of a sample of 10 local starbursts with high resolution HST-COS Lyman-alpha spectra and known in the literature as LyC leakers or leaking candidates, corroborates our predictions. Observations of Lyman-alpha profiles at high resolution should show definite signatures revealing the escape of Lyman continuum photons from star-forming galaxies.

Episodic star formation in a group of LAEs at z = 5.07

Abstract We are undertaking a search for high-redshift low-luminosity Lyman Alpha sources in the SHARDS (Survey for High-z Absorption Red and Dead Sources) survey. Among the pre-selected Lyman Alpha sources two candidates were spotted, located 3.19 arcsec apart, and tentatively at the same redshift. Here, we report on the spectroscopic confirmation with Gran Telescopio Canarias of the Lyman Alpha emission from this pair of galaxies at a confirmed spectroscopic redshifts of z=5.07. Furthermore, one of the sources is interacting/merging with another close companion that looks distorted. Based on the analysis of the spectroscopy and additional photometric data, we infer that most of the stellar mass of these objects was assembled in a burst of star formation 100 Myr ago. A more recent burst (2 Myr old) is necessary to account for the measured Lyman Alpha flux. We claim that these two galaxies are good examples of Lyman Alpha sources undergoing episodic star formation. Besides, these sources very likely constitute a group of interacting Lyman Alpha emitters (LAEs).

THE INTRINSIC EXTREME ULTRAVIOLET FLUXES OF F5 V TO M5 V STARS

Extreme ultraviolet (EUV) radiations (10--117 nm) from host stars play important roles in the ionization, heating, and mass loss from exoplanet atmospheres. Together with the host star's Lyman-alpha and far-UV (117--170 nm) radiation, EUV radiation photodissociates important molecules, thereby changing the chemistry in exoplanet atmospheres. Since stellar EUV fluxes cannot now be measured and interstellar neutral hydrogen completely obscures stellar radiation between 40 and 91.2 nm, even for the nearest stars, we must estimate the unobservable EUV flux by indirect methods. New non-LTE semiempirical models of the solar chromosphere and corona and solar irradiance measurements show that the ratio of EUV flux in a variety of wavelength bands to the Lyman-alpha flux varies slowly with the Lyman-alpha flux and thus with the magnetic heating rate. This suggests and we confirm that solar EUV/Lyman-alpha flux ratios based on the models and observations are similar to the available 10--40 nm flux ratios observed with the EUVE satellite and the 91.2--117 nm flux observed with the FUSE satellite for F5 V--M5 V stars. We provide formulae for predicting EUV flux ratios based on the EUVE and FUSE stellar data and on the solar models, which are essential input for modelling the atmospheres of exoplanets.

DEEP LBT/LUCI SPECTROSCOPY OF AN Lyα EMITTER CANDIDATE AT z ≃ 7.7

We present deep spectroscopic observations of a Lyman-alpha emitter (LAE) candidate at z ~ 7.7 using the infrared spectrograph LUCI on the 2 x 8.4m Large Binocular Telescope (LBT). The candidate is the brightest among the four z ~ 7.7 LAE candidates found in a narrow-band imaging survey by Krug et al. 2012. Our spectroscopic data include a total of 7.5 hours of integration with LBT/LUCI and are deep enough to significantly (3.2-4.9 sigma) detect the Lyman-alpha emission line of this candidate, based on its Lyman-alpha flux 1.2 x 10^{-17} erg s^{-1} cm^{-2} estimated from the narrow-band photometry. However, we do not find any convincing signal at the expected position of its Lyman-alpha emission line, suggesting that this source is not an LAE at z ~ 7.7. The non-detection in this work, together with the previous studies of z ~ 7.7 LAEs, puts a strong constraint on the bright-end Lyman-alpha luminosity function (LF) at z ~ 7.7. We find a rapid evolution of the Lyman-alpha LF from z ~ 6.5 to 7.7: the upper limit of the z ~ 7.7 LF is more than 5 times lower than the z ~ 6.5 LF at the bright end (f > 1.0 x 10^{-17} erg s^{-1} cm^{-2}, or L > 6.9 x 10^{42} erg s^{-1}). This is likely caused by an increasing neutral fraction in the IGM that substantially attenuates Lyman-alpha emission at z ~ 7.7.

Neutrino signatures on the high-transmission regions of the Lyman $\boldsymbol {\alpha }$ forest

We quantify the impact of massive neutrinos on the statistics of low density regions in the intergalactic medium (IGM) as probed by the Lyman-alpha forest at redshifts z=2.2--4. Based on mock but realistic quasar (QSO) spectra extracted from hydrodynamic simulations with cold dark matter, baryons and neutrinos, we find that the probability distribution of weak Lyman-alpha absorption features, as sampled by Lyman-alpha flux regions at high transmissivity, is strongly affected by the presence of massive neutrinos. We show that systematic errors affecting the Lyman-alpha forest reduce but do not erase the neutrino signal. Using the Fisher matrix formalism, we conclude that the sum of the neutrino masses can be measured, using the method proposed in this paper, with a precision smaller than 0.4 eV using a catalog of 200 high resolution (S/N~100) QSO spectra. This number reduces to 0.27 eV by making use of reasonable priors in the other parameters that also affect the statistics of the high transitivity regions of the Lyman-alpha forest. The constraints obtained with this method can be combined with independent bounds from the CMB, large scale structures and measurements of the matter power spectrum from the Lyman-alpha forest to produce tighter upper limits on the sum of the masses of the neutrinos.

COMPUTING INTRINSIC LYα FLUXES OF F5 V TO M5 V STARS

The Lyman-alpha emission line dominates the far-ultraviolet spectra of late-type stars and is a major source for photodissociation of important molecules including H2O, CH4, and CO2 in exoplanet atmospheres. The incident flux in this line illuminating an exoplanet's atmosphere cannot be measured directly as neutral hydrogen in the interstellar medium (ISM) attenuates most of the flux reaching the Earth. Reconstruction of the intrinsic Lyman-alpha line has been accomplished for a limited number of nearby stars, but is not feasible for distant or faint host stars. We identify correlations connecting the intrinsic Lyman-alpha flux with the flux in other emission lines formed in the stellar chromosphere, and find that these correlations depend only gradually on the flux in the other lines. These correlations, which are based on HST spectra, reconstructed Lyman-alpha line fluxes, and irradiance spectra of the quiet and active Sun, are required for photochemical models of exoplanet atmospheres when intrinsic Lyman-alpha fluxes are not available. We find a tight correlation of the intrinsic Lyman-alpha flux with stellar X-ray flux for F5 V to K5 V stars, but much larger dispersion for M stars. We also show that knowledge of the stellar effective temperature and rotation rate can provide reasonably accurate estimates of the Lyman-alpha flux for G and K stars, and less accurate estimates for cooler stars.

No evidence for Lyman emission in spectroscopy of z &gt; 7 candidate galaxies

We present Gemini/GNIRS spectroscopic observations of 4 z-band (z~7) dropout galaxies and VLT/XSHOOTER observations of one z-band dropout and 3 Y-band (z~8-9) dropout galaxies in the Hubble Ultra Deep Field, which were selected with Wide Field Camera 3 imaging on the Hubble Space Telescope. We find no evidence of Lyman-alpha emission with a typical 5-sigma sensitivity of 5X10^-18erg/cm^2/s, and we use the upper limits on Lyman-alpha flux and the broad-band magnitudes to constrain the rest-frame equivalent widths for this line emission. Accounting for incomplete spectral coverage, we survey 3.0 z-band dropouts and 2.9 Y-band dropouts to a Lyman-alpha rest-frame equivalent width limit > 120Ang (for an unresolved emission line); for an equivalent width limit of 50Ang the effective numbers of drop-outs surveyed fall to 1.2 z-band drop-outs and 1.5 Y-band drop-outs. A simple model where the fraction of high rest-frame equivalent width emitters follows the trend seen at z=3-6.5 is inconsistent with our non-detections at z=7-9 at the ~ 1-sigma level for spectrally unresolved lines, which may indicate that a significant neutral HI fraction in the intergalactic medium suppresses the Lyman-alpha line in z-drop and Y-drop galaxies at z > 7.

MEAN-FLUX-REGULATED PRINCIPAL COMPONENT ANALYSIS CONTINUUM FITTING OF SLOAN DIGITAL SKY SURVEY Lyα FOREST SPECTRA

Continuum fitting is an important aspect of Lyman-alpha forest science, since errors in the estimated optical depths scale with the fractional continuum error. However, traditional methods of estimating continua in noisy and moderate-resolution spectra (S/N < 10 pixel^-1 and R ~ 2000, respectively, such as SDSS) using power-law extrapolation or the mean spectrum, achieve no better than ~ 10-15% RMS accuracy. To improve on this, we introduce mean-flux regulated/principal component analysis (MF-PCA) continuum fitting. In this technique, PCA fitting is carried out redwards of the quasar Lyman-alpha line in order to provide a prediction for the shape of the Lyman-alpha forest continuum. The slope and amplitude of this continuum prediction is then corrected using external constraints for the Lyman-alpha forest mean-flux. From tests on mock spectra, we find that MF-PCA reduces the errors to 8% RMS in S/N ~ 2 spectra, and < 5% RMS in spectra with S/N > 5. The residual Fourier power in the continuum is decreased by a factor of a few in comparison with dividing by the mean continuum, enabling Lyman-alpha flux power spectrum measurements to be extended to ~2x larger scales. Using this new technique, we make available continuum fits for 12,069 z>2.3 Lyman-alpha forest spectra from SDSS DR7 for use by the community. This technique is also applicable to future releases of the ongoing BOSS survey, which is obtaining spectra for ~ 150,000 Lyman-alpha forest spectra at low signal-to-noise (S/N ~ 2).

Fluctuations in the high-redshift Lyman-Werner and Lyα radiation backgrounds

We use a new method to model fluctuations of the Lyman-Werner (LW) and Lyman-alpha radiation backgrounds at high redshift. At these early epochs the backgrounds are symptoms of a universe newly lit with its first stars. LW photons (11.5-13.6 eV) are of particular interest because they dissociate molecular hydrogen, the primary coolant in the first minihalos. By using a variation of the halo model, we efficiently generate power spectra for any choice of radiation background. We find that the LW power spectrum typically traces the matter power spectrum at large scales but turns over at the scale corresponding to the effective `horizon' of LW photons (~100 comoving Mpc), unless the sources are extremely rare. The series of horizons that characterize the Lyman-alpha flux profile shape the fluctuations of that background in a similar fashion, though those imprints are washed out once one considers fluctuations in the brightness temperature of the 21-cm signal. The Lyman-alpha background strongly affects the redshifted 21-cm signal at just about the time the LW background begins to dissociate molecular hydrogen, so measuring that background's properties will reveal important information about the transition from early Population III stars to more normal stars. Around this time we find that fluctuations in the LW background are weak; the fractional standard deviation is less than ~0.5 on scales > 10 cMpc, only rising to be of order unity on scales < 1 cMpc. This should not lead to substantial spatial fluctuations in molecular hydrogen content, except at the earliest times. Even then, most halos form far from other sources, so the transition from star formation in low-mass to high-mass halos is rather homogeneous across the universe.