scholarly journals Probing inhomogeneity in the helium ionizing UV background

2019 ◽  
Vol 489 (1) ◽  
pp. 868-880 ◽  
Author(s):  
Sean Morrison ◽  
Matthew M Pieri ◽  
David Syphers ◽  
Tae-Sun Kim
Keyword(s):  
Optical Depth ◽  
Simultaneous Measurement ◽  
Large Scale ◽  
Neutral Hydrogen ◽  
Lyman Alpha ◽  
Quasar Spectra ◽  
Ionization Structure ◽  
Oxygen Excess ◽  
Uv Photons

ABSTRACT We present an analysis combining the simultaneous measurement of intergalactic absorption by hydrogen (${\rm {H\,\small {I}}}$), helium (${\rm {He\,\small {II}}}$), and oxygen (${\rm {O\,\small {VI}}}$) in UV and optical quasar spectra. The combination of the ${\rm {H\,\small {I}}}$ and ${\rm {He\,\small {II}}}$ Lyman-alpha forests through η (the ratio of column densities of singly ionized helium to neutral hydrogen) is thought to be sensitive to large-scale inhomogeneities in the extragalactic UV background. We test this assertion by measuring associated five-times-ionized oxygen (${\rm {O\,\small {VI}}}$) absorption, which is also sensitive to the UV background. We apply the pixel optical depth technique to ${\rm {O\,\small {VI}}}$ absorption in high and low η samples filtered on various scales. This filtering scale is intended to represent the scale of any coherent oxygen excess/deficit. We find a 2σ detection of an ${\rm {O\,\small {VI}}}$ opacity excess in the low η sample on scales of ∼10 cMpc for HE 2347-4342 at $\bar{z}\approx 2.6$, consistent with a large-scale excess in hard UV photons. However, for HS 1700 + 6416 at $\bar{z}\approx 2.5$ we find that the measured ${\rm {O\,\small {VI}}}$ absorption is not sensitive to differences in η. HS 1700 + 6416 also shows a relative absence of ${\rm {O\,\small {VI}}}$ overall, which is 6σ inconsistent with that of HE 2347-4342. This implies UV background inhomogeneities on ≳200 cMpc scales, hard UV regions having internal ionization structure on ∼10 cMpc scales, and soft UV regions showing no such structure. Furthermore, we perform the pixel optical depth search for oxygen on the ${\rm {He\,\small {II}}}$ Gunn-Peterson trough of HE 2347-4342 and find results consistent with post-${\rm {He\,\small {II}}}$-reionization conditions.

scholarly journals Neutral hydrogen in the post-reionization universe

2017 ◽  
Vol 12 (S333) ◽  
pp. 216-221
Author(s):  
Hamsa Padmanabhan
Keyword(s):  
Galaxy Evolution ◽  
Large Scale ◽  
Neutral Hydrogen ◽  
Lyman Alpha ◽  
Intensity Mapping ◽  
Best Fitting ◽  
Hydrodynamical Simulations ◽  
Intermediate Redshift ◽  
Intermediate Redshifts ◽  
The Universe

AbstractThe evolution of neutral hydrogen (HI) across redshifts is a powerful probe of cosmology, large scale structure in the universe and the intergalactic medium. Using a data-driven halo model to describe the distribution of HI in the post-reionization universe (z ∼ 5 to 0), we obtain the best-fitting parameters from a rich sample of observational data: low redshift 21-cm emission line studies, intermediate redshift intensity mapping experiments, and higher redshift Damped Lyman Alpha (DLA) observations. Our model describes the abundance and clustering of neutral hydrogen across redshifts 0 - 5, and is useful for investigating different aspects of galaxy evolution and for comparison with hydrodynamical simulations. The framework can be applied for forecasting future observations with neutral hydrogen, and extended to the case of intensity mapping with molecular and other line transitions at intermediate redshifts.

scholarly journals Large-scale simulations of H and He reionization and heating driven by stars and more energetic sources

2020 ◽  
Vol 498 (4) ◽  
pp. 6083-6099 ◽  
Author(s):  
Marius B Eide ◽  
Benedetta Ciardi ◽  
Luca Graziani ◽  
Philipp Busch ◽  
Yu Feng ◽  
...  
Keyword(s):  
Large Scale ◽  
Neutral Hydrogen ◽  
Thomson Scattering ◽  
Ionization State ◽  
X Ray ◽  
Post Process ◽  
Hydrodynamical Simulation ◽  
Main Driver ◽  
Uv Photons ◽  
The One

ABSTRACT We present simulations of cosmic reionization and reheating from z = 18 to z = 5, investigating the role of stars (emitting soft UV-photons), nuclear black holes (BHs, with power-law spectra), X-ray binaries (XRBs, with hard X-ray dominated spectra), and the supernova-associated thermal bremsstrahlung of the diffuse interstellar medium (ISM, with soft X-ray spectra). We post-process the hydrodynamical simulation MassiveBlack-II (MBII) with multifrequency ionizing radiative transfer. The source properties are directly derived from the physical environment of MBII, and our only real free parameter is the ionizing escape fraction fesc. We find that, among the models explored here, the one with an escape fraction that decreases with decreasing redshift yields results most in line with observations, such as of the neutral hydrogen fraction and the Thomson scattering optical depth. Stars are the main driver of hydrogen reionization and consequently of the thermal history of the intergalactic medium (IGM). We obtain 〈xH ii〉 = 0.99998 at z = 6 for all source types, with volume-averaged temperatures $\langle \, T \rangle \sim 20\,000$ K. BHs are rare and negligible to hydrogen reionization, but conversely they are the only sources that can fully ionize helium, increasing local temperatures by ∼104 K. The thermal and ionization state of the neutral and lowly ionized hydrogen differs significantly with different source combinations, with ISM and (to a lesser extent) XRBs, playing a significant role and, as a consequence, determining the transition from absorption to emission of the 21-cm signal from neutral hydrogen.

scholarly journals Lyman Alpha Emitting Galaxies in the Nearby Universe

2015 ◽  
Vol 32 ◽  
Author(s):  
Matthew Hayes
Keyword(s):  
Interstellar Medium ◽  
Large Scale ◽  
Neutral Hydrogen ◽  
Emission Feature ◽  
Ultraviolet Continuum ◽  
Lyman Alpha ◽  
Alpha Emission ◽  
Multi Wavelength ◽  
Metal Abundances ◽  
Galaxy Population

AbstractThe Lyman alpha emission line (Lyα) of neutral hydrogen (Hi) is intrinsically the brightest emission feature in the spectrum of astrophysical nebulae, making it a very attractive observational feature with which to survey galaxies. Moreover as an ultraviolet resonance line, Lyα possesses several unique characteristics that make it useful to study the properties of the interstellar medium and ionising stellar population at all cosmic epochs. In this review, I present a summary of Lyα observations of galaxies in the nearby universe. By ultraviolet continuum selection, at the magnitudes reachable with current facilities, only ≈ 5% of the local galaxy population shows a Lyα equivalent width (WLyα) that exceeds 20 Å. This fraction increases dramatically at higher redshifts, but only in the local universe can we study galaxies in detail and assemble unprecedented multi-wavelength datasets. I discuss many local Lyα observations, showing that when galaxies show net Lyα emission, they ubiquitously also produce large-scale halos of scattered Lyα, that dominate the integrated luminosity. Concerning global measurements, we discuss how WLyα and the Lyα escape fraction (fLyαesc) are higher (WLyα ≳ 20 Å and fLyαesc ≳ 10%) in galaxies that represent the less massive and younger end of the distribution for local objects. This is connected with various properties, such that Lyα-emitting galaxies have lower metal abundances (median value of 12 + log(O/H) ~ 8.1) and dust reddening. However, the presence of galactic outflows/winds is also vital to Doppler shift the Lyα line out of resonance with the atomic gas, and high WLyα is found only among galaxies with winds faster than ~ 50 km s−1. The empirical evidence is then assembled into a coherent picture, and the requirement for star-formation-driven feedback is discussed in the context of an evolutionary sequence where the interstellar medium is accelerated and/or subject to hydrodynamical instabilities, which reduce the scattering of Lyα. Concluding remarks take the form of perspectives upon future developments, and the most pressing questions that can be answered by observation.

scholarly journals Solar Irradiance Variability Due to Solar Flares Observed in Lyman-Alpha Emission

Solar Physics ◽  
2021 ◽  
Vol 296 (3) ◽  
Author(s):  
Ryan O. Milligan
Keyword(s):  
Solar Flares ◽  
Solar Spectrum ◽  
Neutral Hydrogen ◽  
Solar Limb ◽  
High Background ◽  
Superposed Epoch Analysis ◽  
Lyman Alpha ◽  
Alpha Emission ◽  
Epoch Analysis ◽  
Very High

AbstractAs the Lyman-alpha (Ly$\upalpha $ α ) line of neutral hydrogen is the brightest emission line in the solar spectrum, detecting increases in irradiance due to solar flares at this wavelength can be challenging due to the very high background. Previous studies that have focused on the largest flares have shown that even these extreme cases generate enhancements in Ly$\upalpha $ α of only a few percent above the background. In this study, a superposed-epoch analysis was performed on ≈8500 flares greater than B1 class to determine the contribution that they make to changes in the solar EUV irradiance. Using the peak of the 1 – 8 Å X-ray emission as a fiducial time, the corresponding time series of 3123 B- and 4972 C-class flares observed in Ly$\upalpha $ α emission by the EUV Sensor on the Geostationary Operational Environmental Satellite 15 (GOES-15) were averaged to reduce background fluctuations and improve the flare signal. The summation of these weaker events showed that they produced a 0.1 – 0.3% enhancement to the solar Ly$\upalpha $ α irradiance on average. For comparison, the same technique was applied to 453 M- and 31 X-class flares, which resulted in a 1 – 4% increase in Ly$\upalpha $ α emission. Flares were also averaged with respect to their heliographic angle to investigate any potential center-to-limb variation. For each GOES class, the relative enhancement in Ly$\upalpha $ α at the flare peak was found to diminish for flares that occurred closer to the solar limb due to the opacity of the line and/or foreshortening of the footpoints. One modest event included in the study, a C6.6 flare, exhibited an unusually high increase in Ly$\upalpha $ α of 7% that may have been attributed to a failed filament eruption. Increases of this magnitude have hitherto only been associated with a small number of X-class flares.

scholarly journals Hemispherical variance anomaly and reionization optical depth

2020 ◽  
Vol 499 (3) ◽  
pp. 3563-3570
Author(s):  
Márcio O’Dwyer ◽  
Craig J Copi ◽  
Johanna M Nagy ◽  
C Barth Netterfield ◽  
John Ruhl ◽  
...  
Keyword(s):  
Optical Depth ◽  
Large Scale ◽  
Cold Dark Matter ◽  
Signal To Noise Ratio ◽  
Cosmological Parameters ◽  
Temperature Data ◽  
Microwave Background ◽  
Parameter Uncertainties ◽  
Polarization Data ◽  
Best Fitting

ABSTRACT Cosmic microwave background (CMB) full-sky temperature data show a hemispherical asymmetry in power nearly aligned with the Ecliptic, with the Northern hemisphere displaying an anomalously low variance, while the Southern hemisphere appears consistent with expectations from the best-fitting theory, Lambda Cold Dark Matter (ΛCDM). The low signal-to-noise ratio in current polarization data prevents a similar comparison. Polarization realizations constrained by temperature data show that in ΛCDM the lack of variance is not expected to be present in polarization data. Therefore, a natural way of testing whether the temperature result is a fluke is to measure the variance of CMB polarization components. In anticipation of future CMB experiments that will allow for high-precision large-scale polarization measurements, we study how the variance of polarization depends on ΛCDM-parameter uncertainties by forecasting polarization maps with Planck’s Markov chain Monte Carlo chains. We show that polarization variance is sensitive to present uncertainties in cosmological parameters, mainly due to current poor constraints on the reionization optical depth τ, which drives variance at low multipoles. We demonstrate how the improvement in the τ measurement seen between Planck’s two latest data releases results in a tighter constraint on polarization variance expectations. Finally, we consider even smaller uncertainties on τ and how more precise measurements of τ can drive the expectation for polarization variance in a hemisphere close to that of the cosmic-variance-limited distribution.

scholarly journals Limits to Ionization-parameter Mapping as a Diagnostic of Hii Region Optical Depth

2021 ◽  
Vol 923 (1) ◽  
pp. 78
Author(s):  
Amit N. Sawant ◽  
Eric W. Pellegrini ◽  
M. S. Oey ◽  
Jesús López-Hernández ◽  
Genoveva Micheva
Keyword(s):  
Optical Depth ◽  
Strong Dependence ◽  
Light Flux ◽  
Emission Lines ◽  
Ionization State ◽  
Hii Region ◽  
Parameter Mapping ◽  
Ionization Structure ◽  
The Galaxy ◽  
Ionization Parameter

Abstract We employ ionization-parameter mapping (IPM) to infer the optical depth of H ii regions in the northern half of M33. We construct [O iii]λ5007/[O ii]λ3727 and [O iii]λ5007/[S ii]λ6724 ratio maps from narrowband images continuum-subtracted in this way, from which we classify the H ii regions by optical depth to ionizing radiation, based on their ionization structure. This method works relatively well in the low-metallicity regime, 12 + log ( O / H ) ≤ 8.4 , where [O iii]λ λ4959, 5007 is strong. However, at higher metallicities, the method breaks down due to the strong dependence of the [O iii]λ λ4959, 5007 emission lines on the nebular temperature. Thus, although O++ may be present in metal-rich H ii regions, these commonly used emission lines do not serve as a useful indicator of its presence, and hence the O ionization state. In addition, IPM as a diagnostic of optical depth is limited by spatial resolution. We also report a region of highly excited [O iii] extending over an area ∼1 kpc across and [O iii]λ5007 luminosity of 4.9 ± 1.5 × 1038 erg s−1, which is several times higher than the ionizing budget of any potential sources in this portion of the galaxy. Finally, this work introduces a new method for continuum subtraction of narrowband images based on the dispersion of pixels around the mode of the diffuse-light flux distribution. In addition to M33, we demonstrate the method on C iii]λ1909 imaging of Haro 11, ESO 338-IG004, and Mrk 71.

scholarly journals Eurasia large-scale hazes in summer 2016

2019 ◽  
Vol 55 (3) ◽  
pp. 41-51
Author(s):  
G. I. Gorchakov ◽  
S. A. Sitnov ◽  
A. V. Karpov ◽  
I. A. Gorchakova ◽  
R. A. Gushchin ◽  
...  
Keyword(s):  
Spatial Distribution ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Radiative Forcing ◽  
Large Scale ◽  
Empirical Distribution ◽  
Growth Period ◽  
Maximum Growth ◽  
Qualitative Change ◽  
Smoke Aerosol

Using maximum aerosol optical depth (MAOD) spatial distribution formation technique the optically dense haze expansion scales in period from 15 to 31 July 2016 over Eurasia are estimated in during great Siberian smoke haze (SSH) with the area 16 mln km2 about, smog over the Northern China Plain (2 mln km2), dust haze in Takla Makan desert (0.8 mln km2) and hazes in India and Pakistan (1 mln km2 approximately). Empirical distribution function (EDF) MAOD is received which is approximated by linear function of MAOD logarithm. Aerosol optical depth (AOD) spatial distribution at wavelength 550 nm in SSH is analyzed. Total smoke aerosol mass assessment in SSH (3.2 mln tons) is evaluated. Smoke aerosol (SA) mass during maximum growth period from 22 July to 26 July 2016 over Siberia (50°-70°, 60°-120 °E) was equal 2 mln tons approximately. Aerosol index (AI) temporal variability is illustrated visually SA composition qualitative change in SSH during long-range transport. It is shown that AI variations are correlated with AOD variations. Aerosol radiative forcing (ARF) at the top and the bottom of the atmosphere over Siberia from 22 July to 26 July 2016 is estimated (average ARF are equal –68 and –98 W/m2). EDF AOD and EDF ARF at the top of the atmosphere are approximated by exponential and power function of AOD correspondingly.

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