The Origin and Evolution of Lyman-alpha Blobs in Cosmological Galaxy Formation Simulations
Benjamin Kimock, Desika Narayanan, Aaron Smith, Xiangcheng Ma, Robert Feldmann, Daniel Anglés-Alcázar, Volker Bromm, Romeel Dave, James E. Geach, Philip Hopkins, Dušan Kereš
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Submitted to ApJ; comments welcome. 23 pages, 21 figures
High-redshift Lyman-alpha blobs (LABs) are an enigmatic class of objects that have been the subject of numerous observational and theoretical investigations. It is of particular interest to determine the dominant power sources for the copious luminosity, as direct emission from HII regions, cooling gas, and fluorescence due to the presence of active galactic nuclei (AGN) can all contribute significantly. In this paper, we present the first theoretical model to consider all of these physical processes in an attempt to develop an evolutionary model for the origin of high-z LABs. This is achieved by combining a series of high-resolution cosmological zoom-in simulations with ionization and Lyman-alpha (Lya) radiative transfer models. We find that massive galaxies display a range of Lya luminosities and spatial extents (which strongly depend on the limiting surface brightness used) over the course of their lives, though regularly exhibit luminosities and sizes consistent with observed LABs. The model LABs are typically powered from a combination of recombination in star-forming galaxies, as well as cooling emission from gas associated with accretion. When AGN are included in the model, the fluorescence caused by AGN-driven ionization can be a significant contributor to the total Lya luminosity as well. We propose that the presence of an AGN may be predicted from the Gini coefficient of the blob's surface brightness. Within our modeled mass range, there are no obvious threshold physical properties that predict appearance of LABs, and only weak correlations of the luminosity with the physical properties of the host galaxy. This is because the emergent Lya luminosity from a system is a complex function of the gas temperature, ionization state, and Lya escape fraction.
Lyman alpha blobs - luminous, spatially extended emission-line nebulae, often lacking bright continuum counterparts - are common in dense environments at high redshift. Until recently, atmospheric absorption and filter technology have limited our knowledge of any similar objects at z<2. We use GALEX slitless spectroscopy to search for similar objects in the rich environments of two known cluster and supercluster fields at z=0.8, where the instrumental sensitivity peaks. The regions around Cl 1054-0321 and Cl 0023+0423 were each observed in slitless-spectrum mode for 10-19 ksec, with accompanyi…
We report the result from observations conducted with the Atacama Large Millimeter/submillimeter Array (ALMA) to detect [CII] 158 um fine structure line emission from galaxies embedded in one of the most spectacular Lyman-alpha blobs (LABs) at z=3.1, SSA22-LAB1. Of three dusty star-forming galaxies previously discovered by ALMA 860 um dust continuum survey toward SSA22-LAB1, we detected the [CII] line from one, LAB1-ALMA3 at z=3.0993+/-0.0004. No line emission was detected, associated with the other ALMA continuum sources or from three rest-frame UV/optical selected z_spec~3.1 galaxies within …
We present the discovery of a candidate of giant radio-quiet Lyman-alpha (Lya) blob (RQLAB) in a large-scale structure around a high-redshift radio galaxy (HzRG) lying in a giant Lya halo, B3 J2330+3927 at redshift z=3.087. We obtained Lya imaging around B3 J2330+3927 with Subaru/Suprime-Cam to search for Lya emitters (LAEs) and absorbers (LAAs) at redshift z=3.09+-0.03. We detected candidate 127 LAEs and 26 LAAs in the field of view of 31' x 24'. We found that B3 J2330+3927 is surrounded by a 130 kpc Lya halo and a large-scale (60 x 20 comoving Mpc) filamentary structure. The large-scale stru…
Lyman-$α$ blobs (LABs) are spatially extended nebulae of emission in the Ly$α$ line of hydrogen, seen at high redshifts$^{1,2}$, and most commonly found in the dense environment of star-forming galaxies$^{3,4}$. The origin of Ly$α$ emission in the LABs is still unclear and under debate$^{5}$. Proposed powering sources generally fall into two categories: (1) photoionization, galactic super-winds/outflows, resonant scattering of Ly$α$ photons from starbursts or active galactic nuclei (AGNs)$^{6,7,8,9,10}$ and (2) cooling radiation from cold streams of gas accreting onto galaxies$^{12}$. Here we …
We present new spectroscopic observations of Lyman-$α$ (Ly$α$) Blob 2 ($z \sim$ 3.1). We observed extended Ly$α$ emission in three distinct regions, where the highest Ly$α$ surface brightness (SB) center is far away from the known continuum sources. We searched through the MOSFIRE slits that cover the high Ly$α$ SB regions, but were unable to detect any significant nebular emission near the highest SB center. We further mapped the flux ratio of the blue peak to the red peak and found it is anti-correlated with Ly$α$ SB with a power-law index of $\sim$ -0.4. We used radiative transfer models wi…
Utilizing {\it ab initio} ultra-high resolution hydrodynamical simulations, we investigate the properties of the interstellar and circum-galactic medium of Ly$α$ Blobs (LABs) at $z=3$, focusing on three important emission lines: Ly$α$ 1216Å, \heii 1640Å and \civ 1449Å. Their relative strengths provide a powerful probe of the thermodynamic properties of the gas when confronted with observations. By adjusting the dust attenuation effect using one parameter and matching the observed size-luminosity relation of LABs using another parameter, we show that our simulations can reproduce the observed \…
The intergalactic medium (IGM) is the dominant reservoir of baryons, delineates the large scale structure at low to moderate overdensities, and provides gas from which galaxies form and evolve. Simulations of a Cold Dark Matter (CDM) dominated universe predict that the IGM is distributed in a cosmic web of filaments, and that galaxies should form along and at the intersections of these filaments (Bond et al. 1994; Miralda-Escude et al. 1996). While observations of QSO absorption lines and the large scale distribution of galaxies have confirmed the CDM paradigm, the cosmic web has never been co…
Ly-alpha blobs (LABs) offer insight into the complex interface between galaxies and their circumgalactic medium. Whilst some LABs have been found to contain luminous star-forming galaxies and active galactic nuclei that could potentially power the Ly-alpha emission, others appear not to be associated with obvious luminous galaxy counterparts. It has been speculated that LABs may be powered by cold gas streaming on to a central galaxy, providing an opportunity to directly observe the `cold accretion' mode of galaxy growth. Star-forming galaxies in LABs could be dust obscured and therefore detec…
Extended nebulae of Ly-alpha emission ("Ly-alpha blobs") are known to be associated with overdense regions at high redshift. Here we present six large Ly-alpha blobs in a previously known protocluster with galaxy overdensity delta ~ 7 at z = 2.3; this is the richest field of giant Ly-alpha blobs detected to date. The blobs have linear sizes >~100 kpc and Ly-alpha luminosities of ~10^43 erg/s. The positions of the blobs define two linear filaments with an extent of at least 12 comoving Mpc; these filaments intersect at the center of one of the blobs. Measurement of the position angles of the bl…
We present new observations of Lyman-$α$ (Ly$α$) Blob 1 (LAB1) in the SSA22 protocluster region ($z$ = 3.09) using the Keck Cosmic Web Imager (KCWI) and the Keck Multi-object Spectrometer for Infrared Exploration (MOSFIRE). By applying matched filtering to the KCWI datacube, we have created a narrow-band Ly$α$ image and identified several prominent features. By comparing the spatial distributions and intensities of Ly$α$ and H$β$, we find that recombination of photo-ionized HI gas followed by resonant scattering is sufficient to explain all the observed Ly$α$/H$β$ ratios. We further decode the…
We report the discovery of 14 Lyman-alpha blobs (LABs) at z~0.3, existing at least 4-7 billion years later in the Universe than all other LABs known. Their optical diameters are 20-70 kpc, and GALEX data imply Ly-alpha luminosities of (0.4-6.3)x10^43 erg/s. Contrary to high-z LABs, they live in low-density areas. They are ionized by AGN, suggesting that cold accretion streams as a power source must deplete between z=2 and z=0.3. We also show that transient AGN naturally explain the ionization deficits observed in many LABs: Their Ly-alpha and X-ray fluxes decorrelate below 10^6 years because o…
Lyman-$α$ nebulae are usually found in massive environments at high redshift ($z > 2$). The origin of their Lyman-$α$ (Lya) emission remains debated. Recent polarimetric observations showed that at least some Lya sources are polarized. This is often interpreted as a proof that the photons are centrally produced, and opposed to the scenario in which the Lya emission is the cooling radiation emitted by gas heated during the accretion onto the halo. We suggest that this scenario is not incompatible with the polarimetric observations. In order to test this idea, we post-process a radiative hydrody…
We have shown that Lyman-$α$ blobs (LABs) may still exist even at $z\sim0.3$, about 7 billion years later than most other LABs known (Schirmer et al. 2016). Their luminous Ly$α$ and [OIII] emitters at $z\sim0.3$ offer new insights into the ionization mechanism. This paper focuses on the two X-ray brightest LABs at $z\sim0.3$, SDSS J0113$+$0106 (J0113) and SDSS J1155$-$0147 (J1155), comparable in size and luminosity to `B1', one of the best-studied LABs at $z \gtrsim$ 2. Our NuSTAR hard X-ray (3--30 keV) observations reveal powerful active galactic nuclei (AGN) with $L_{2-10{\;\rm keV}}=(0.5$--…
Lyman alpha blobs (LABs) are spatially extended lyman alpha nebulae seen at high redshift. The origin of Lyman alpha emission in the LABs is still unclear and under debate. To study their heating mechanism(s), we present Australia Telescope Compact Array (ATCA) observations of the 20 cm radio emission and Herschel PACS and SPIRE measurements of the far-infrared (FIR) emission towards the four LABs in the protocluster J2143-4423 at z=2.38. Among the four LABs, B6 and B7 are detected in the radio with fluxes of 67+/-17 microJy and 77+/-16 microJy, respectively, and B5 is marginally detected at 3…
We report the discovery of a multiply lensed Lyman-$α$ blob (LAB) behind the galaxy cluster AS1063 using the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope (VLT). The background source is at $z=$ 3.117 and is intrinsically faint compared to almost all previously reported LABs. We used our highly precise strong lensing model to reconstruct the source properties, and we find an intrinsic luminosity of $L_{\rm Lyα}$=$1.9\times10^{42}$ erg s$^{-1}$, extending to 33 kpc. We find that the LAB is associated with a group of galaxies, and possibly a protocluster, in agreement with…
We perform Lyman-alpha radiative transfer calculations for reproducing Lyman-alpha properties of star-forming galaxies at high redshifts. We model a galaxy as a halo in which the density distributions of Lyman-alpha sources and H I plus dust medium are described with exponential functions. We also consider an outflow of the medium that represents a momentum-driven wind in a gravitational potential well. We successfully reproduce both the spectra and the surface brightness profiles of eight star-forming galaxies at z =3-6 observed with MUSE using this outflowing halo model with Lyman-alpha scat…
Context: Lyman $α$ blobs (LABs) are large-scale radio-quiet Lyman $α$ (Ly$α$) nebula at high-$z$ that occur predominantly in overdense proto-cluster regions. Especially the prototypical SSA22a-LAB1 at $z=3.1$ has become an observational reference for LABs across the electromagnetic spectrum. Aims: We want to understand the powering mechanisms that drive the LAB to gain empirical insights into galaxy formation processes within a rare dense environment at high-$z$. Methods: LAB 1 was observed for 17.5h with the VLT/MUSE integral-field spectrograph. We produced optimally extracted narrow band ima…
The radio-quiet quasar Q2059-360 at redshift $z=3.08$ is known to be close to a small Lyman $α$ blob (LAB) and to be absorbed by a proximate damped Ly$α$ (PDLA) system. Here, we present the Multi Unit Spectroscopic Explorer (MUSE) integral field spectroscopy follow-up of this quasi-stellar object (QSO). Our primary goal is to characterize this LAB in detail by mapping it both spatially and spectrally using the Ly$α$ line, and by looking for high-ionization lines to constrain the emission mechanism. Combining the high sensitivity of the MUSE integral field spectrograph mounted on the Yepun tele…
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 u…
We present the Lensed Lyman-Alpha MUSE Arcs Sample (LLAMAS) selected from MUSE and HST observations of 17 lensing clusters. The sample consists of 603 continuum-faint (-23<M_UV<-14) lensed Lyman-alpha emitters (producing 959 images) with spectroscopic redshifts between 2.9 and 6.7. Combining the power of cluster magnification with 3D spectroscopic observations, we are able to reveal the resolved morphological properties of 268 Lyman-alpha emitters. We use a forward modelling approach to model both Lyman-alpha and rest-frame UV continuum emission profiles in the source plane and measure spatial…
We present statistical properties of diffuse Lyman-alpha halos (LAHs) around high-$z$ star-forming galaxies with large Subaru samples of Lyman-alpha emitters (LAEs) at $z=2.2$. We make subsamples defined by the physical quantities of LAEs' central Lyman-alpha luminosities, UV magnitudes, Lyman-alpha equivalent widths, and UV slopes, and investigate LAHs' radial surface brightness (SB) profiles and scale lengths $r_n$ as a function of these physical quantities. We find that there exist prominent LAHs around LAEs with faint Lyman-alpha luminosities, bright UV luminosities, and small Lyman-alpha …
We present simulations of Lyman-Alpha radiation transfer in an isolated disk galaxy with a turbulence sub-grid model, multi-phase interstellar medium and detailed star formation modelling. We investigate the influence of inclination on the observed Lyman-Alpha properties for different snapshots. The Lyman-alpha spectrum, equivalent width distribution and escape fractions vary significantly with the detailed morphology of the disk, leading to variations from one snapshot to another. In particular, we find that supernova-driven cavities near star-forming regions in the simulation can dominate th…
We exploit ALMA 870um observations to measure the star-formation rates (SFRs) of eight X-ray detected Active Galactic Nuclei (AGNs) in a z~3.1 protocluster, four of which reside in extended Ly-alpha haloes (often termed Ly-alpha blobs: LABs). Three of the AGNs are detected by ALMA and have implied SFRs of ~220-410~M_sun/yr; the non detection of the other five AGNs places SFR upper limits of <210 M_sun/yr. The mean SFR of the protocluster AGNs (~110-210 M_sun/yr) is consistent (within a factor of ~0.7-2.3) with that found for co-eval AGNs in the field, implying that galaxy growth is not signifi…
We report the detection of diffuse Lyman-alpha halos (LAHs) around star-forming galaxies at $z \sim 5.7$ by stacking 310 spectroscopically confirmed Lyman-alpha (LAEs). The majority of the LAEs are identified from our spectroscopic survey of galaxies at $z>5.5$. They are all located in well-studied fields with deep narrowband and broadband imaging data. We combine the LAE sample and its subsamples in the narrowband NB816 (i.e., the Lyman-alpha band) and $z$ band (i.e., the continuum band). By comparing the stacked objects with their corresponding point spread functions, we clearly detect exten…
[Abridged] With VLT/X-shooter, we obtain optical and NIR spectra of six Ly-alpha blobs at z~2.3. Using three measures --- the velocity offset between the Lya line and the non-resonant [OIII] or H-alpha line (Dv_Lya), the offset of stacked interstellar metal absorption lines, and the spectrally-resolved [OIII] line profile --- we study the kinematics of gas along the line of sight to galaxies within each blob center. These three indicators generally agree in velocity and direction, and are consistent with a simple picture in which the gas is stationary or slowly outflowing at a few hundred km/s…
We discuss new Keck/MOSFIRE spectroscopic observations of four luminous galaxies at z~7-9 selected to have intense optical line emission by Roberts-Borsani et al. (2016). Previous follow-up has revealed Lyman-alpha in two of the four galaxies. Our new MOSFIRE observations confirm that Lyman-alpha is present in the entire sample. We detect Lyman-alpha emission in COS-zs7-1, confirming its redshift as z=7.154, and we detect Lyman-alpha in EGS-zs8-2 at z=7.477, verifying a tentative detection presented in an earlier study. The ubiquity of Lyman-alpha in this sample is puzzling given that the IGM …
We present an analysis of HI Lyman-alpha emission in deep VLT/MUSE observations of two highly magnified and extended galaxies at z=3.5 and 4.03, including a newly discovered, almost complete Einstein ring. While these Lyman-alpha haloes are intrinsically similar to the ones typically seen in other MUSE deep fields, the benefits of gravitational lensing allows us to construct exceptionally detailed maps of Lyman-alpha line properties at sub-kpc scales. By combining all multiple images, we are able to observe complex structures in the Lyman-alpha emission and uncover small (~ 120 km/s in Lyman-a…
We present HIRES observations for 30 damped Lyman alpha systems, selected on the basis of their large metal column densities from previous, lower resolution data. The measured metal column densities for Fe, Zn, S, Si, Cr, Mn, and Ni are provided for these 30 systems. Combined with previously observed large metal column density damped Lyman alpha systems, we present a sample of 44 damped Lyman alpha systems observed with high resolution spectrographs (R~30000). These damped Lyman alpha systems probe the most chemically evolved systems at redshifts greater than 1.5. We discuss the context of our…
We present observations of a giant Lyman-alpha blob in the SSA22 proto-cluster at z=3.1, SSA22-LAB1, taken with the Atacama Large Millimeter/submillimeter Array (ALMA). Dust continuum, along with [C II]158um, and CO(4-3) line emission have been detected in LAB1, showing complex morphology and kinematics across a ~100 kpc central region. Seven galaxies at z=3.0987-3.1016 in the surroundings are identified in [C II] and dust continuum emission, with two of them potential companions or tidal structures associated with the most massive galaxies. Spatially resolved [C II] and infrared luminosity ra…
In this work, we propose an improved approach to reconstruct the three-dimensional intergalactic medium from observed Lyman-$α$ forest absorption features. We present our new method, the Optimized Reconstruction with Constraints on Absorption (ORCA), which outperforms the current baseline Wiener Filter (WF) when tested on mock Lyman Alpha forest data generated from hydrodynamical simulations. We find that both reconstructed flux errors and cosmic web classification improve substantially with ORCA, equivalent to 30-40\% additional sight-lines with the standard WF. We use this method to identify…
The Nilsson et al. (2006) Lyman-alpha nebula has often been cited as the most plausible example of a Lyman-alpha nebula powered by gravitational cooling. In this paper, we bring together new data from the Hubble Space Telescope and the Herschel Space Observatory as well as comparisons to recent theoretical simulations in order to revisit the questions of the local environment and most likely power source for the Lyman-alpha nebula. In contrast to previous results, we find that this Lyman-alpha nebula is associated with 6 nearby galaxies and an obscured AGN that is offset by $\sim$4"$\approx$30…
It has been well established in the local universe that galaxy properties differ based on the large-scale environment in which they reside. As luminous Lyman-alpha nebulae have been shown to trace overdense environments at z~2-3, comparing the properties of galaxies within Lyman-alpha nebulae systems to those in the field can provide insight into how and when locally-observed trends between galaxy properties and environment emerged. Six Lyman-alpha nebulae were discovered at z~2.3 in a blind search of the GOODS-S extragalactic field, a region also covered by the 3D-HST spectroscopic survey. Ut…
We examine the Mg II 2796, 2803 Angstrom, Lyman alpha, and nebular line emission in five bright star-forming galaxies at 1.66<z<1.91 that have been gravitationally lensed by foreground galaxy clusters. All five galaxies show prominent Mg II emission and absorption in a P Cygni profile. We find no correlation between the equivalent widths of Mg II and Lyman alpha emission. The Mg II emission has a broader range of velocities than do the nebular emission line profiles; the Mg II emission is redshifted with respect to systemic by 100 to 200 km/s. When present, Lyman alpha is even more redshifted.…
The spatial and kinematic distribution of warm gas in and around the Coma Cluster is presented through observations of Lyman-alpha absorbers using background QSOs. Updates to the Lyman-alpha absorber distribution found in Yoon et al. (2012) for the Virgo Cluster are also presented. At 0.2-2.0 R_vir of Coma we identify 14 Lyman-alpha absorbers (N_HI = 10^{12.8-15.9} cm^-2) towards 5 sightlines and no Lyman-alpha absorbers along 3 sightlines within 3\sigmav_coma. For both Coma and Virgo, most Lyman-alpha absorbers are found outside the virial radius or beyond 1\sigmav consistent with them largel…
We present new Atacama Large Millimeter/Submillimeter Array (ALMA) 850um continuum observations of the original Lyman-alpha Blob (LAB) in the SSA22 field at z=3.1 (SSA22-LAB01). The ALMA map resolves the previously identified submillimeter source into three components with total flux density S_850 = 1.68+/-0.06 mJy, corresponding to a star formation rate of ~150 M_sun/yr. The submillimeter sources are associated with several faint (m~27 mag) rest-frame ultraviolet sources identified in Hubble Space Telescope Imaging Spectrograph (STIS) clear filter imaging (~5850A). One of these companions is …
We present the results of a high-spatial-resolution study of the line emission in a sample of z=3.1 Lyman-Alpha-Emitting Galaxies (LAEs) in the Extended Chandra Deep Field-South. Of the eight objects with coverage in our HST/WFPC2 narrow-band imaging, two have clear detections and an additional two are barely detected (~2-sigma). The clear detections are within ~0.5 kpc of the centroid of the corresponding rest-UV continuum source, suggesting that the line-emitting gas and young stars in LAEs are spatially coincident. The brightest object exhibits extended emission with a half-light radius of …
We present IRAM PdBI observations of the CO(3-2) and CO(5-4) line transitions from a Ly-alpha blob at z~2.7 in order to investigate the gas kinematics, determine the location of the dominant energy source, and study the physical conditions of the molecular gas. CO line and dust continuum emission are detected at the location of a strong MIPS source that is offset by ~1.5" from the Ly-alpha peak. Neither of these emission components is resolved with the 1.7" beam, showing that the gas and dust are confined to within ~7kpc from this galaxy. No millimeter source is found at the location of the Ly…
We use high-resolution cosmological hydrodynamical AMR simulations to predict the characteristics of La emission from the cold gas streams that fed galaxies in massive haloes at high redshift. The La luminosity in our simulations is powered by the release of gravitational energy as gas flows from the intergalactic medium into the halo potential wells. The UV background contributes only <20% to the gas heating. The La emissivity is due primarily to electron-impact excitation cooling radiation in gas ~2x10^4K. We calculate the La emissivities assuming collisional ionisation equilibrium (CIE) at …
Lecture notes for 8 lectures on the `Physics of Lyman alpha Radiative Transfer', given at the 46th Saas-Fee winter school held in Les Diablerets, Switzerland on March 13-19 2016. These lectures aimed at offering basic insights into Lyman alpha (Lya) radiative processes including emission processes and Lya radiative transfer, and highlighting some of the physics associated with these processes. The notes include derivations in greater detail than what was discussed during the lectures.
We report the detection of the most luminous high-redshift Lyman Alpha Emitting galaxy (LAE) yet seen, with log L(Ly alpha) = 43.9 ergs/s. The galaxy -- COSMOS Lyman alpha 1, or COLA1 -- was detected in a search for ultra-luminous LAEs with Hyper Suprime-Cam on the Subaru telescope. It was confirmed to lie at z = 6.593 based on a Lyman alpha line detection obtained from followup spectroscopy with the DEIMOS spectrograph on Keck2. COLA1 is the first very high-redshift LAE to show a multi-component Lyman alpha line profile with a blue wing, which suggests that it could lie in a highly ionized re…
The Mg II 2796,2803 doublet is often used to measure interstellar medium absorption in galaxies, thereby serving as a diagnostic for feedback and outflows. However, the interpretation of Mg II remains confusing, due to resonant trapping and re-emission of the photons, analogous to Lyman Alpha. Therefore, in this paper, we present new MMT Blue Channel Spectrograph observations of Mg II for a sample of 10 Green Pea galaxies at z~0.2-0.3, where Lyman Alpha was previously observed with the Cosmic Origins Spectrograph on Hubble Space Telescope. With strong, (mostly) double-peaked Lyman Alpha profil…
The inhomogeneous cosmological reionization process leaves tangible imprints in the intergalactic medium down to z=4-5. The Lyman-alpha forest flux power spectrum provides a potentially powerful probe of the epoch of reionization. With the existing SDSS I/II quasar sample we show that two cosmological reionization scenarios, one completing reionization at z=6 and the other at z=9, can be distinguished at ~7 sigma level by utilizing Lyman alpha forest absorption spectra at z=4.5+-0.5, in the absence of other physical processes that may also affect the Lyman alpha flux power spectrum. The redshi…
We compare the low redshift (z ~ 0.1) Lyman-alpha forest from hydrodynamical simulations with data from the Cosmic Origin Spectrograph (COS). We find tension between the observed number of lines with b-parameters in the range 25-45 km/s and the predictions from simulations that incorporate either vigorous feedback from active galactic nuclei or that exclude feedback altogether. The gas in these simulations is, respectively, either too hot to contribute to the Lyman-alpha absorption or too cold to produce the required line widths. Matching the observed b-parameter distribution therefore require…
This review summarizes our current understanding of the outer heliosphere and local interstellar medium (LISM) inferred from observations and modeling of interplanetary Lyman-$α$ emission. The emission is produced by solar Lyman-alpha photons (121.567 nm) backscattered by interstellar H atoms inflowing to the heliosphere from the LISM. Studies of Lyman-alpha radiation determined the parameters of interstellar hydrogen within a few astronomical units from the Sun. The interstellar hydrogen atoms appeared to be decelerated, heated, and shifted compared to the helium atoms. The detected decelerat…
