The Ly$α$ forest decomposed into Voigt profile components allow us to study clustering properties of the intergalactic medium and its dependence on various physical quantities. Here, we report the first detections of probability excess of low-z (i.e z<0.48) Ly$α$ absorber triplets over a scale of $r_\parallel\leq8$pMpc with a maximum amplitude of $8.76^{+1.96}_{-1.65}$ at a longitudinal separation of 1-2pMpc. We measure non-zero three-point correlation ($ζ=4.76^{+1.98}_{-1.67}$) only at this scale with reduced three-point correlation value of Q=$0.95^{+0.39}_{-0.38}$. The measured $ζ$ shows an increasing trend with increasing HI column density ($N_{HI}$) while Q does not show any $N_{HI}$ dependence. About 88% of the triplets contributing to $ζ$ (at z$\le0.2$) have nearby galaxies (whose distribution is known to be complete for 0.1L$_*$ at z<0.1 and for L$_*$ at z~0.25 and within 20' to the quasar sightlines) within a velocity separation of 500$kms^{-1}$ and a median impact parameter of 405pkpc. The measured impact parameters are consistent with appreciable number of triplets at z$\le0.2$ not originating from individual galaxies but tracing the underlying galaxy distribution. Frequency of occurrence of high-b absorbers in triplets (~85%) is a factor~3 higher than that found among the full sample (~32%). Using four different cosmological simulations, we quantify the effect of peculiar velocities, feedback effects and show that most of the observed trends are broadly reproduced. However, $ζ$ at small scales ($r_\parallel<1$pMpc) and b-dependence of $ζ$ in simulations are found inconsistent with the observations. This could either be related to the fact that none of these simulations reproduce the observed b-distribution and $N_{HI}$ distribution for $N_{HI}>10^{14}$cm$^{-2}$ self-consistently or to the widespread of signal-to-noise ratio in the observed data.
We analyze the sources of free electrons that produce the large dispersion measures, DM $\approx 300-1600$ (in units cm$^{-3}$ pc), observed toward fast radio bursts (FRBs). Individual galaxies typically produce DM $\sim 25-60$ cm$^{-3}$ pc from ionized gas in their disk, disk-halo interface, and circumgalactic medium. Toward an FRB source at redshift $z$, a homogeneous IGM containing a fraction $f_{\rm IGM}$ of cosmological baryons will produce DM $= (935~{\rm cm}^{-3}~{\rm pc}) f_{\rm IGM} \, h_{70}^{-1} I(z)$, where $I(z) = (2/3 Ω_m)[ \{ Ω_m(1+z)^3 + Ω_Λ \}^{1/2} - 1 ]$. A structured IGM of…
Due to their long mean free path, X-rays are expected to have an important impact on cosmic reionization by heating and ionizing the IGM on large scales, especially after simulations have suggested that Population III stars may form in pairs at redshifts as high as 20 - 30. We use the Pop III distribution and evolution from a self-consistent cosmological radiation hydrodynamics simulation of the formation of the first galaxies and a simple Pop III X-ray binaries model to estimate their X-ray output in a high density region larger than 100 comoving (Mpc)$^3$. We then combine three different met…
We present semi-analytical models of galactic outflows in high redshift galaxies driven by both hot thermal gas and non-thermal cosmic rays. Thermal pressure alone may not sustain a large scale outflow in low mass galaxies (i.e $M\sim 10^8$~M$_\odot$), in the presence of supernovae (SNe) feedback with large mass loading. We show that inclusion of cosmic ray pressure allows outflow solutions even in these galaxies. In massive galaxies for the same energy efficiency, cosmic ray driven winds can propagate to larger distances compared to pure thermally driven winds. On an average gas in the cosmic…
Aim. Our aim is to analyse the variance of the Inter-Galactic Medium transmission (IGM) by studying this parameter in the rest-frame UV spectra of a large sample of high redshift galaxies. Method. We make use of the VIMOS Ultra Deep Survey and the VANDELS public survey to have an insight into the far UV spectrum of $2.7<z<6$ galaxies. Using the SPARTAN fitting software, we estimate the IGM towards individual galaxies and then divide them in two sub-samples characterized by a transmission above or below the theoretical prescription. We create average spectra of combined VUDS and VANDELS data fo…
In this Letter, we constrain the dust-to-gas ratio in the intergalactic medium (IGM) at high redshifts. We employ models for dust in the local Universe to contrain the dust-to-gas ratio during the epoch of reionization at redshifts z ~ 6-10. The observed level of reddening of high redshift galaxies implies that the IGM was enriched to an intergalactic dust-to-gas ratio of less than 3% of the Milky Way value by a redshift of z=10.
Disentangling the galactic and intergalactic components in 313 observed Lyman-alpha line profiles between redshift 0 and 5
Observatori Astronòmic de la Universitat de València（瓦伦西亚大学天文台）；Departament d’Astronomia i Astrofísica, Universitat de València（瓦伦西亚大学天文学与天体物理学系）；Universität Heidelberg（海德堡大学）；Max Planck Institute for Astrophysics（马克斯·普朗克天体物理学研究所）；Tsinghua University（清华大学）；IFCA-CSIC/Universitat de València（坎塔布里亚物理研究所CSIC-瓦伦西亚大学联合单位）；Instituto de Física de Cantabria (CSIC-UC)（坎塔布里亚物理研究所）
We present redshift space two-point ($ξ$), three-point ($ζ$) and reduced three-point (Q) correlations of Ly$α$ absorbers (Voigt profile components having HI column density, $N_{\rm HI}>10^{13.5}$cm$^{-2}$) over three redshift bins spanning $1.7< z<3.5$ using high-resolution spectra of 292 quasars. We detect positive $ξ$ up to 8 $h^{-1}$ cMpc in all three redshift bins. The strongest detection of $ζ=1.81\pm 0.59$ (with Q$=0.68\pm 0.23$), is in $z=1.7-2.3$ bin at $1-2h^{-1}$ cMpc. The measured $ξ$ and $ζ$ values show an increasing trend with $N_{\rm HI}$, while Q remains relatively independent o…
We present a new flexible Bayesian framework for directly inferring the fraction of neutral hydrogen in the intergalactic medium (IGM) during the Epoch of Reionization (EoR, z~6-10) from detections and non-detections of Lyman Alpha (Ly$α$) emission from Lyman break galaxies (LBGs). Our framework combines sophisticated reionization simulations with empirical models of the interstellar medium (ISM) radiative transfer effects on Ly$α$. We assert that the Ly$α$ line profile emerging from the ISM has an important impact on the resulting transmission of photons through the IGM, and that these line p…
We decompose the Lyman-α (Lyα) forest of an extensive sample of 74 high signal-to-noise ratio and high-resolution quasar spectra into a collection of Voigt profiles. Absorbers located near caustics in the peculiar velocity field have the smallest Doppler parameters, resulting in a low-$b$ cutoff in the $b$-$N_{\text{HI}}$ set by the thermal state of intergalactic medium (IGM). We fit this cutoff as a function of redshift over the range $2.0\leq z \leq 3.4$, which allows us to measure the evolution of the IGM temperature-density ($T= T_0 (ρ/ ρ_0)^{γ-1}$) relation parameters $T_0$ and $γ$. We ca…
A late end to reionisation at redshift $z\simeq 5.3$ is consistent with observed spatial variations in the Ly$α$ forest transmission and the deficit of Ly$α$ emitting galaxies around extended Ly$α$ absorption troughs at $z=5.5$. In this model, large islands of neutral hydrogen should persist in the diffuse intergalactic medium (IGM) until $z\simeq 6$. We use a novel, hybrid approach that combines high resolution cosmological hydrodynamical simulations with radiative transfer to predict the incidence of strong 21 cm forest absorbers with optical depths $τ_{21}>10^{-2}$ from the diffuse IGM in t…
The thermal history of cosmic gas in the Dark Ages remains largely unknown. It is important to quantify the impact of relevant physics on the IGM temperature between $z=10$ and $z \sim 30$, in order to interpret recent and oncoming observations, including results reported by EDGES. We revisit the gas heating due to structure formation shocks in this era, using a set of fixed grid cosmological hydrodynamical simulations performed by three different codes. In all our simulations, the cosmic gas is predicted to be in multiphase state since $z>30$. The gas surrounding high density peaks gradually …
We present improved results of the measurement of the correlation between galaxies and the intergalactic medium (IGM) transmission at the end of reionisation. We have gathered a sample of $13$ spectroscopically confirmed Lyman-break galaxies (LBGs) and $21$ Lyman-$α$ emitters (LAEs) at angular separations $20'' \lesssim θ\lesssim 10'$ ($\sim 0.1-4$ pMpc at $z\sim 6$) from the sightlines to $8$ background $z\gtrsim 6$ quasars. We report for the first time the detection of an excess of Lyman-$α$ transmission spikes at $\sim 10-60$ cMpc from LAEs ($3.2σ$) and LBGs ($1.9σ$). We interpret the data …
The application of fast radio bursts (FRBs) as probes to investigate astrophysics and cosmology requires the proper modelling of the dispersion measures of Milky Way (${\rm DM_{MW}}$) and host galaxy (${\rm DM_{host}}$). ${\rm DM_{MW}}$ can be estimated using the Milky Way electron models, such as NE2001 model and YMW16 model. However, ${\rm DM_{host}}$ is hard to model due to limited information on the local environment of FRBs. In this paper, using 17 well-localized FRBs, we search for the possible correlations between ${\rm DM_{host}}$ and the properties of host galaxies, such as the redshi…
Above redshift 6, the dominant source of neutral hydrogen in the Universe shifts from localized clumps in and around galaxies and filaments to a pervasive, diffuse component of the intergalactic medium (IGM). This transition tracks the global neutral fraction of hydrogen in the IGM and can be studied, in principle, through the redshifted 21 cm hyperfine transition line. During the last half of the reionization epoch, the mean (global) brightness temperature of the redshifted 21 cm emission is proportional to the neutral fraction, but at earlier times (10 < z < 25), the mean brightness temperat…
We present a new method to directly measure the opacity from HI Lyman limit (LL) absorption k_LL along quasar sightlines by the intergalactic medium (IGM). The approach analyzes the average (``stacked'') spectrum of an ensemble of quasars at a common redshift to infer the mean free path (MFP) to ionizing radiation. We apply this technique to 1800 quasars at z=3.50-4.34 drawn from the Sloan Digital Sky Survey (SDSS), giving the most precise measurements on k_LL at any redshift. From z=3.6 to 4.3, the opacity increases steadily as expected and is well parameterized by MFP = (48.4 +/- 2.1) - (38.…
Ly$α$ forest absorption spectra decomposed into multiple Voigt profile components (clouds) allow us to study clustering of intergalactic medium (IGM) as a function of HI column density ($N_{\rm HI}$). Here, we explore the transverse three-point correlation ($ζ$) of these Ly$α$ clouds using mock triplet spectra obtained from hydrodynamical simulations at $z \sim 2$ on scales of 1-5 $h^{-1}$cMpc. We find $ζ$ to depend strongly on $N_{\rm HI}$ and scale and weakly on angle ($θ$) of the triplet configuration. We show that the "hierarchical ansatz" is applicable for scales $\ge~ 3h^{-1}$cMpc, and o…
We present a large spectroscopic campaign with Keck/MOSFIRE targeting Lyman-alpha emission (Ly$α$) from intrinsically faint Lyman-break Galaxies (LBGs) behind 12 efficient galaxy cluster lenses. Gravitational lensing allows us to probe the more abundant faint galaxy population to sensitive Ly$α$ equivalent width limits. During the campaign we targeted 70 LBG candidates with MOSFIRE Y-band, selected photometrically to cover Ly$α$ over the range $7<z<8.2$. We detect $S/N>5$ emission lines in 2 of these galaxies and find that they are likely Ly$α$ at $z=7.148\pm0.001$ and $z=7.161\pm0.001$. We pr…
The observed scatter in intergalactic Lyman-$α$ opacity at $z \lesssim 6$ requires large-scale fluctuations in the neutral fraction of the intergalactic medium (IGM) after the expected end of reionization. Post-reionization models that explain this scatter invoke fluctuations in either the ionizing ultraviolet background (UVB) or IGM temperature. These models make very different predictions, however, for the relationship between Lyman-$α$ opacity and local density. Here we test these models using Lyman-$α$ emitting galaxies (LAEs) to trace the density field surrounding the longest and most opa…
Cross-correlating 21cm with known cosmic signals will be invaluable proof of the cosmic origin of the first 21cm detections. As some of the widest fields available, comprising thousands of sources with reasonably known redshifts, narrow-band Lyman alpha emitter (LAE) surveys are an obvious choice for such cross-correlation. Here we revisit the 21cm -- LAE cross-correlation, relaxing the common assumption of reionization occurring in a pre-heated intergalactic medium (IGM). Using specifications from the Square Kilometre Array and the Subary Hyper Supreme-Cam, we present new forecasts of the 21c…
Revealing the cosmic reionisation history is at the frontier of extragalactic astronomy. The power spectrum of the cosmic microwave background (CMB) polarisation can be used to constrain the reionisation history. Here we propose a CMB-independent method using fast radio bursts (FRBs) to directly measure the ionisation fraction of the intergalactic medium (IGM) as a function of redshift. FRBs are new astronomical transients with millisecond timescales. Their dispersion measure (DM$_{\rm IGM}$) is an indicator of the amount of ionised material in the IGM. Since the differential of DM$_{\rm IGM}$…
We study the heating of the intergalactic medium (IGM) surrounding high redshift star forming galaxies due to cosmic rays (CR). We take into account the diffusion of low energy cosmic rays and study the patchiness of the resulting heating. We discuss the case of IGM heating around a high redshift minihalo ($z\sim 10\hbox{--}20$, M$\sim 10^5\hbox{--}10^7$ M$_\odot$),and put an upper limit on the diffusion coefficient $D\le 1\times 10^{26}$ cm$^2$ s$^{-1}$ for the heating to be inhomogeneous at $z\sim 10$ and $D\le 5\hbox{--}6 \times 10^{26}$ cm$^2$ s$^{-1}$ at $z\sim 20$. For typical values of …
The production and distribution of metals in the diffuse intergalactic medium (IGM) have implications for galaxy formation models and the baryon (re)cycling process. The relative abundance of metals in high versus low-ionization states has also been argued to be sensitive to the Universe's reionization history. However, measurements of the background metallicity of the IGM at z~4 are sparse and in poor agreement with one another, and reduced sensitivity in the near-IR renders detecting individual metal absorbers nearly impossible. We present a new clustering-based technique that enables the de…
The ultraviolet background (UVB) emitted by quasars and galaxies governs the ionization and thermal state of the intergalactic medium (IGM), regulates the formation of high-redshift galaxies, and is thus a key quantity for modeling cosmic reionization. The vast majority of cosmological hydrodynamical simulations implement the UVB via a set of spatially uniform photoionization and photoheating rates derived from UVB synthesis models. We show that simulations using canonical UVB rates reionize and, perhaps more importantly, spuriously heat the IGM, much earlier z ~ 15 than they should. This prob…
Recent studies have derived quasar luminosity functions (QLFs) at various redshifts. However, the faint side of the QLF at high redshifts is still too uncertain. An accurate estimate of the survey completeness is essential to derive an accurate QLF for use in studying the luminosity-dependent density evolution of the quasar population. Here we investigate how the luminosity dependence of quasar spectra (the Baldwin effect) and the attenuation model for the inter-galactic medium (IGM) affect the completeness estimates. For this purpose, we revisit the completeness of quasar surveys specifically…
The correlation between neutral Hydrogen (HI) in the intergalactic medium (IGM) and galaxies now attracts great interests. We select four fields which include several coherently strong Ly$α$ absorption systems at $z\sim2.2$ detected by using background quasars from the whole SDSS/(e)BOSS database. Deep narrow-band and $g$-band imaging are performed using the Hyper Suprime-Cam on the Subaru Telescope. We select out 2,642 Ly$α$ emitter (LAE) candidates at $z=2.177\pm0.023$ down to the Ly$α$ luminosity of $L_{\text{Ly}α}\approx 2 \times 10^{42} {\rm erg~s}^{-1}$ to construct the galaxy overdensit…
We demonstrate the redshift-evolution of the spectral profile of H i Lyman-alpha (Lyα) emission from star-forming galaxies. In this first study we pay special attention to the contribution of blueshifted emission. At redshift z = 2.9-6.6, we compile spectra of a sample of 229 Lyα-selected galaxies identified with the Multi-Unit Spectroscopic Explorer at the Very Large Telescope, while at low-z (< 0.44) we use a sample of 74 ultraviolet-selected galaxies observed with the Cosmic Origin Spectrograph onboard the Hubble Space Telescope. At low-z, where absorption from the intergalactic medium (IGM…
The distribution of neutral hydrogen in the intergalactic medium (IGM) is currently explored at low-z by means of UV spectroscopy of quasars. We propose an alternative approach based on UV colours of quasars as observed from GALEX surveys. We built a NUV-selected sample of 9033 quasars with (FUV-NUV) colours. The imprint of HI absorption in the observed colours is suggested qualitatively by their distribution as a function of quasar redshift. Because broad band fluxes lack spectral resolution and are sensitive to a large range of N_HI a Monte Carlo simulation of IGM opacity is required for qua…
