Probing the thermal state of the intergalactic medium at z &gt; 5 with the transmission spikes in high-resolution  Ly α forest spectra

ABSTRACT We compare a sample of five high-resolution, high S/N Ly α forest spectra of bright 6 < z < ∼6.5 QSOs aimed at spectrally resolving the last remaining transmission spikes at z > 5 with those obtained from mock absorption spectra from the Sherwoodand Sherwood–Relics simulation 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 characterize 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 prominent in low temperature models of the IGM. The width distribution of the observed transmission spikes, which require high spectral resolution (≤ 8 km s−1) to be resolved, is reproduced for optically thin simulations with a temperature at mean density of T0 = (11 000 ± 1600, 10 500 ± 2100, 12 000 ± 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 z ∼ 5.3, the width distribution of the observed transmission spikes is consistent with the range of T0 caused by spatial fluctuations in the temperature–density relation.

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Tracing the 107 K warm–hot intergalactic medium with UV absorption lines

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2971 ◽

2020 ◽

Vol 499 (4) ◽

pp. 5230-5240

Author(s):

A Y Fresco ◽

C Péroux ◽

A Merloni ◽

A Hamanowicz ◽

R Szakacs

Keyword(s):

Galaxy Formation ◽

Spectral Resolution ◽

Column Density ◽

Intergalactic Medium ◽

High Spectral Resolution ◽

High Signal ◽

Gas Temperature ◽

X Ray ◽

Quasar Spectra ◽

Hydrodynamical Simulations

ABSTRACT Today, the majority of the cosmic baryons in the Universe are not observed directly, leading to an issue of ‘missing baryons’ at low redshift. Cosmological hydrodynamical simulations have indicated that a significant portion of them will be converted into the so-called warm–hot intergalactic medium (WHIM), with gas temperature ranging between 105 and 107 K. While the cooler phase of this gas has been observed using O vi and Ne viii absorbers at ultraviolet (UV) wavelengths, the hotter fraction detection relies mostly on observations of O vii and O viii at X-ray wavelengths. Here, we target the forbidden line of [Fe xxi] λ 1354 Å which traces 107 K gas at UV wavelengths, using more than 100 high-spectral resolution ($R\sim 49\, 000$) and high signal to noise VLT/UVES quasar spectra, corresponding to over 600 h of VLT time observations. A stack of these at the position of known Ly α absorbers lead to a 5σ limit of $\log [N\mathrm{([Fe\,{\small XXI}])]\lt }$17.4 (EWrest < 22 mÅ), three orders of magnitude higher than the expected column density of the WHIM $\log [N\mathrm{([Fe\,{\small XXI}])]\lt }$14.5. This work proposes an alternative to X-ray detected 107 K WHIM tracers, by targeting faint lines at UV wavelengths from the ground benefiting from higher instrumental throughput, enhanced spectral resolution, longer exposure times, and increased number of targets. The number of quasar spectra required to reach this theoretical column density with future facilities including 4MOST, ELT/HIRES, MSE, and the Spectroscopic Telescope appears challenging at present. Probing the missing baryons is essential to constrain the accretion and feedback processes that are fundamental to galaxy formation.

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Implications of the z > 5 Lyman-α forest for the 21-cm power spectrum from the epoch of reionization

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab2424 ◽

2021 ◽

Author(s):

Janakee Raste ◽

Girish Kulkarni ◽

Laura C Keating ◽

Martin G Haehnelt ◽

Jonathan Chardin ◽

...

Keyword(s):

Radiative Transfer ◽

Power Spectrum ◽

Intergalactic Medium ◽

Neutral Hydrogen ◽

Redshift Range ◽

Sky Temperature ◽

Conventional Models

Abstract Our understanding of the intergalactic medium at redshifts z = 5–6 has improved considerably in the last few years due to the discovery of quasars with z > 6 that enable Lyman-α forest studies at these redshifts. A realisation from this has been that hydrogen reionization could end much later than previously thought, so that large “islands” of cold, neutral hydrogen could exist in the IGM at redshifts z = 5–6. By using radiative transfer simulations of the IGM, we consider the implications of the presence of these neutral hydrogen islands for the 21-cm power spectrum signal and its potential detection by experiments such as hera, ska, lofar, and mwa. In contrast with previous models of the 21-cm signal, we find that thanks to the late end of reionization the 21-cm power in our simulation continues to be as high as $\Delta ^2_{21}=10~\mathrm{mK}^2$ at k ∼ 0.1 h cMpc−1 at z = 5–6. This value of the power spectrum is several orders of magnitude higher than that in conventional models considered in the literature for these redshifts. Such high values of the 21-cm power spectrum should be detectable by hera and ska1-low in ∼1000 hours, assuming optimistic foreground subtraction. This redshift range is also attractive due to relatively low sky temperature and potentially greater abundance of multiwavelength data.

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Long troughs in the Lyman-α forest below redshift 6 due to islands of neutral hydrogen

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3083 ◽

2019 ◽

Vol 491 (2) ◽

pp. 1736-1745 ◽

Cited By ~ 18

Author(s):

Laura C Keating ◽

Lewis H Weinberger ◽

Girish Kulkarni ◽

Martin G Haehnelt ◽

Jonathan Chardin ◽

...

Keyword(s):

High Resolution ◽

Radiative Transfer ◽

Neutral Hydrogen

ABSTRACT A long (110 cMpc h−1) and deep absorption trough in the Ly α forest has been observed extending down to redshift 5.5 in the spectrum of ULAS J0148+0600. Although no Ly α transmission is detected, Ly β spikes are present which has led to claims that the gas along this trough must be ionized. Using high-resolution cosmological radiative transfer simulations in large volumes, we show that in a scenario where reionization ends late (z ∼ 5.2), our simulations can reproduce troughs as long as observed. In this model, we find that the troughs are caused by islands of neutral hydrogen. Small ionized holes within the neutral islands allow for the transmission of Ly β. We have also modelled the Ly α emitter population around the simulated troughs, and show that there is a deficit of Ly α emitters close to the trough as is observed.

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Inhomogeneous He ii reionization in hydrodynamic simulations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1850 ◽

2020 ◽

Vol 496 (4) ◽

pp. 4372-4382 ◽

Cited By ~ 1

Author(s):

Phoebe Upton Sanderbeck ◽

Simeon Bird

Keyword(s):

Radiative Transfer ◽

Thermal State ◽

Computational Cost ◽

Spatial Inhomogeneity ◽

Intergalactic Gas ◽

Hydrodynamic Simulations ◽

Density Relation ◽

Free Parameters ◽

The Impact

ABSTRACT The reionization of the second electron of helium shapes the physical state of intergalactic gas at redshifts between 2 ≲ z ≲ 5. Because performing full in situ radiative transfer in hydrodynamic simulations is computationally expensive for large volumes, the physics of He ii reionization is often approximated by a uniform ultraviolet background model that does not capture the spatial inhomogeneity of reionization. We have devised a model that implements the effects of He ii reionization using semi-analytic calculations of the thermal state of intergalactic gas – a way to bypass a full radiative transfer simulation while still realizing the physics of He ii reionization that affects observables such as the Lyman α forest. Here, we present a publicly available code that flexibly models inhomogeneous He ii reionization in simulations at a negligible computational cost. Because many of the parameters of He ii reionization are uncertain, our model is customizable from a set of free parameters. We show results from this code in mp-gadget, where this model is implemented. We demonstrate the resulting temperature evolution and temperature–density relation of intergalactic gas – consistent with recent measurements and previous radiative transfer simulations. We show that the impact of He ii reionization gives rise to subtle signatures in the 1D statistics of the Lyman α forest at the level of several percent, in agreement with previous findings. The flexible nature of these simulations is ideal for studies of He ii reionization and future observations of the He ii Lyman α forest.

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Chasing the Tail of Cosmic Reionization with Dark Gap Statistics in the Lyα Forest over 5 < z < 6

The Astrophysical Journal ◽

10.3847/1538-4357/ac26c2 ◽

2021 ◽

Vol 923 (2) ◽

pp. 223

Author(s):

Yongda Zhu ◽

George D. Becker ◽

Sarah E. I. Bosman ◽

Laura C. Keating ◽

Holly M. Christenson ◽

...

Keyword(s):

Large Scale ◽

Intergalactic Medium ◽

Neutral Hydrogen ◽

Hydrodynamical Simulations

Abstract We present a new investigation of the intergalactic medium (IGM) near the end of reionization using “dark gaps” in the Lyα forest. Using spectra of 55 QSOs at z em > 5.5, including new data from the XQR-30 VLT Large Programme, we identify gaps in the Lyα forest where the transmission averaged over 1 comoving h −1 Mpc bins falls below 5%. Nine ultralong (L > 80 h −1 Mpc) dark gaps are identified at z < 6. In addition, we quantify the fraction of QSO spectra exhibiting gaps longer than 30 h −1 Mpc, F 30, as a function of redshift. We measure F 30 ≃ 0.9, 0.6, and 0.15 at z = 6.0, 5.8, and 5.6, respectively, with the last of these long dark gaps persisting down to z ≃5.3. Comparing our results with predictions from hydrodynamical simulations, we find that the data are consistent with models wherein reionization extends significantly below redshift six. Models wherein the IGM is essentially fully reionized that retain large-scale fluctuations in the ionizing UV background at z ≲6 are also potentially consistent with the data. Overall, our results suggest that signatures of reionization in the form of islands of neutral hydrogen and/or large-scale fluctuations in the ionizing background remain present in the IGM until at least z ≃ 5.3.

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Modelling high-resolution transmission spectra of the ultra-hot jupiter wasp-76b with 3D Monte-Carlo radiative transfer

10.5194/epsc2020-1118 ◽

2020 ◽

Author(s):

Joost Wardenier ◽

Vivien Parmentier ◽

Graham Lee

Keyword(s):

Monte Carlo ◽

High Resolution ◽

Radiative Transfer ◽

Cross Correlation ◽

Circulation Model ◽

High Spectral Resolution ◽

Cloud Formation ◽

Time Varying ◽

Hot Jupiters ◽

3D Monte Carlo

<div class="c-message_kit__gutter"> <div class="c-message_kit__gutter__right" data-qa="message_content"> <div class="c-message_kit__blocks c-message_kit__blocks--rich_text"> <div class="c-message__message_blocks c-message__message_blocks--rich_text"> <div class="p-block_kit_renderer" data-qa="block-kit-renderer"> <div class="p-block_kit_renderer__block_wrapper p-block_kit_renderer__block_wrapper--first"> <div class="p-rich_text_block" dir="auto"> <div class="p-rich_text_section">Ultra-hot Jupiters are tidally-locked gas giants with two chemical regimes: on the scorching dayside molecular species are dissociated and metals are ionised, while the permanent nightside is cool enough for cloud formation to occur. This means that the abundances of particular chemical species, such as iron, will exhibit a sharp gradient across the terminator region, which can be probed by transmission spectroscopy. We present a state-of-the-art 3D Monte-Carlo radiative transfer framework, adapted from Lee et al. (2017, 2019), that allows for the 3D modelling of high-resolution spectra of ultra-hot Jupiters. We use this tool to post-process the output of the SPARC/MITgcm global circulation model, with the aim to better understand how inhomogeneous chemistry, clouds and Doppler shifts due to atmospheric dynamics impact the appearance of a transit spectrum and its cross-correlation signal.</div> <div class="p-rich_text_section">&#160;</div> <div class="p-rich_text_section">In this talk, we apply our model to the transit of WASP-76b, for which Ehrenreich et al. (2020) recently presented a time-varying iron signature at high spectral resolution. The observation suggests that iron condenses on the nightside of the planet. We show that different parts of the limb lead to very different cross-correlation signals and we show that the relative contributions from the east and west limb change during the transit, resulting in a time-varying cross-correlation signal. Finally, we explore different atmospheric scenarios for WASP-76b and we demonstrate that the occurrence of iron condensation, combined with the specific time-varying geometry during the transit, can quantitatively reproduce the Ehrenreich et al. (2020) result.</div> </div> </div> </div> </div> </div> </div> </div> <div class="c-message_actions__container c-message__actions" role="group" aria-label="Message shortcuts" data-qa="message-actions">&#160;</div>

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A coma-free super-high resolution optical spectrometer using 44 high dispersion sub-gratings

Scientific Reports ◽

10.1038/s41598-020-80307-z ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Hua-Tian Tu ◽

An-Qing Jiang ◽

Jian-Ke Chen ◽

Wei-Jie Lu ◽

Kai-Yan Zang ◽

...

Keyword(s):

High Resolution ◽

Spectral Resolution ◽

Wavelength Region ◽

Ultra Violet ◽

High Spectral Resolution ◽

Visible Range ◽

High Dispersion ◽

Charge Coupled Device ◽

Wide Range ◽

High Resolution Spectrometer

AbstractUnlike the single grating Czerny–Turner configuration spectrometers, a super-high spectral resolution optical spectrometer with zero coma aberration is first experimentally demonstrated by using a compound integrated diffraction grating module consisting of 44 high dispersion sub-gratings and a two-dimensional backside-illuminated charge-coupled device array photodetector. The demonstrated super-high resolution spectrometer gives 0.005 nm (5 pm) spectral resolution in ultra-violet range and 0.01 nm spectral resolution in the visible range, as well as a uniform efficiency of diffraction in a broad 200 nm to 1000 nm wavelength region. Our new zero-off-axis spectrometer configuration has the unique merit that enables it to be used for a wide range of spectral sensing and measurement applications.

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Physics and modes of star cluster formation

Proceedings of the International Astronomical Union ◽

10.1017/s1743921309990834 ◽

2009 ◽

Vol 5 (S266) ◽

pp. 29-34

Author(s):

Matthew R. Bate

Keyword(s):

Radiative Transfer ◽

Magnetic Fields ◽

Cluster Formation ◽

Star Cluster ◽

Hydrodynamical Simulations ◽

Made In

AbstractI review the progress made in understanding the physics and modes of star cluster formation through the use of direct self-gravitating hydrodynamical simulations, including those that have recently been performed incorporating radiative transfer and magnetic fields.

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