High signal-to-noise (S/N) observations of the QSO PKS 0405-123 (zem = 0.572) with the Cosmic Origins Spectrograph from 1134 to 1796 A with a resolution of 17 km s-1 are used to study the multi-phase partial Lyman limit system (LLS) at z = 0.16716 which has previously been studied using relatively low S/N spectra from STIS and FUSE. The LLS and an associated H I-free broad O VI absorber likely originate in the circumgalactic gas associated with a pair of galaxies at z = 0.1688 and 0.1670 with impact parameters of 116 h70-1 and 99 h70-1. The broad and symmetric O VI absorption is detected in the z = 0.16716 restframe with v = -278 +/- 3 km s-1, log N(O VI) = 13.90 +/- 0.03 and b = 52 +/- 2 km s-1. This absorber is not detected in H I or other species with the possible exception of N V . The broad, symmetric O VI profile and absence of corresponding H I absorption indicates that the circumgalactic gas in which the collisionally ionized O VI arises is hot (log T ~ 5.8-6.2). The absorber may represent a rare but important new class of low z IGM absorbers. The LLS has strong asymmetrical O VI absorption with log N(O VI) = 14.72 +/- 0.02 spanning a velocity range from -200 to +100 km s-1. The high and low ions in the LLS have properties resembling those found for Galactic highly ionized HVCs where the O VI is likely produced in the conductive and turbulent interfaces between cool and hot gas.
We explore the high spectral resolution X-ray data towards the quasar 3C273 to search for signals of hot ($\sim10^{6-7}$ K) X-ray-absorbing gas co-located with two established intergalactic FUV OVI absorbers. We analyze the soft X-ray band grating data of all XMM-Newton and Chandra instruments to search for the hot phase absorption lines at the FUV predicted redshifts. The viability of potential line detections is examined by adopting the constraints of a physically justified absorption model. The WHIM hypothesis is investigated with a complementary 3D galaxy distribution analysis, and by comp…
We examine how HI and metal absorption lines within low-redshift galaxy halos trace the dynamical state of circumgalactic gas, using cosmological hydrodynamic simulations that include a well-vetted heuristic model for galactic outflows. We categorize inflowing, outflowing, and ambient gas based on its history and fate as tracked in our simulation. Following our earlier work showing that the ionisation level of absorbers was a primary factor in determining the physical conditions of absorbing gas, we show here that it is also a governing factor for its dynamical state. Low-ionisation metal abso…
We report the discovery of a small galaxy system in the vicinity of the NeVIII absorber at z=0.20701 toward HE0226-4110. The galaxy system consists of two 0.25 L* disk galaxies and a 0.05 L* galaxy all within Δv < 300 km/s and rho< 200 h^{-1} physical kpc of the absorber. We consider various scenarios for the origin of the NeVIII absorption, including photo-ionized gas from a AGN, a starburst driven wind, a hot intragroup medium, hot gas in a galaxy halo, and a conductive front produced by cool clouds moving at high speed through a hot medium. We argue that the conductive front scenario is mos…
Observations of the QSO HE 0153-4520 (z-em = 0.450) with the Cosmic Origins Spectrograph (COS) from 1134 to 1796 A with a resolution of ~17 km/s and signal-to- noise per resolution element of 20 to 40 are used to study a multi-phase partial Lyman limit system (LLS) at z = 0.22601 tracing both cool and hot gas. FUSE observations of the Lyman limit break yield log N(H I) = 16.61(0.12, -0.17) The observed UV absorption lines of H I 1216 to 926, C III, C II, N III, N II, Si III, and Si II imply the existence of cool photoionized gas in the LLS with log U = -2.8\pm0.1 and log N(H) = 19.35\pm0.18, l…
We present a detailed analysis of the galaxy and group distributions around three reported X-ray absorption line systems in the spectrum of the quasar H2356-309. Previous studies associated these absorbers with known large-scale galaxy structures (i.e., walls and filaments) along the line of sight. Such absorption lines typically trace 10^{5-7} K gas, and may be evidence of the elusive warm-hot intergalactic medium (WHIM) thought to harbor the bulk of the low-redshift "missing baryons;" alternatively, they may be linked to individual galaxies or groups in the filaments. Here we combine existin…
Unlike the neutral gas density, which remains largely constant over redshifts of 0 < z < 5, the star formation density exhibits a strong redshift dependence, increasing from the present day before peaking at a redshift of z ~ 2.5. Thus, there is a stark contrast between the star formation rate and the abundance of raw material available to fuel it. However, using the ratio of the strength of the HI 21-cm absorption to the total neutral gas column density to quantify the spin temperature of the gas, it has recently been shown that its reciprocal may trace the star formation density. This would …
Thermally broadened Ly alpha absorbers (BLAs) offer an alternative method to highly-ionized metal lines for tracing the WHIM. We compile a catalog of reliable BLA candidates along seven AGN sight lines from a larger set of Lya absorbers observed by HST/STIS. We compare our measurements based on independent reduction and analysis of the data to those published by other research groups. Purported BLAs are grouped into probable (15), possible (48) and non-BLA (56) categories. We infer a line frequency (dN/dz)_BLA=18+-11, comparable to observed OVI absorbers. There is significant overlap between B…
We investigate the metallicity evolution and content of the intergalactic medium (IGM) and galactic halo gas from z=2->0 using 110-million particle cosmological hydrodynamic simulations. We focus on the detectability and physical properties of UV resonance metal-line absorbers observable with Hubble's Cosmic Origins Spectrograph (COS). We confirm that galactic superwind outflows are required to enrich the IGM to observed levels down to z=0 using three wind prescriptions contrasted to a no-wind simulation. Our favoured momentum-conserved wind prescription deposits metals closer to galaxies owin…
We report on the detection of two O VI absorbers separated in velocity by 710 km/s at z ~ 0.4 towards the background quasar SBS0957+599. Both absorbers are multiphase systems tracing substantial reservoirs of warm baryons. The low and intermediate ionization metals in the first absorber is consistent with an origin in photoionized gas. The O VI has a velocity structure different from other metal species. The Ly-alpha shows the presence of a broad feature. The line widths for O VI and the broad Ly-alpha suggest T = 7.1 x 10^5 K. This warm medium is probing a baryonic column which is an order of…
We investigate the physical state of HI absorbing gas at low redshift (z = 0.25) using a subset of cosmological, hydrodynamic simulations from the OWLS project, focusing in particular on broad (b_HI > 40 km/s) HI Lyman-Alpha absorbers (BLAs), which are believed to originate in shock-heated gas in the warm-hot intergalactic medium (WHIM). Our fiducial model, which includes radiative cooling by heavy elements and feedback by supernovae and active galactic nuclei, predicts that by z = 0.25 nearly 60 per cent of the gas mass ends up at densities and temperatures characteristic of the WHIM and we f…
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 10$^5$-10$^7$K. While the cooler phase of this gas has been observed using O VI and Ne VIII absorbers at 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 li…
O VI absorption is observed in a wide range of astrophysical environments, including the Local ISM, the disk and halo of the Milky Way, high-velocity clouds, the Magellanic clouds, starburst galaxies, the intergalactic medium, damped Lyman-alpha systems, and gamma-ray-burst host galaxies. Here a new compilation of 775 O VI absorbers drawn from the literature is presented, all observed at high resolution (instrumental FWHM<20 km/s) and covering the redshift range z=0-3. In galactic environments [log N(H I)>20], the mean O VI column density is shown to be insensitive to metallicity, taking a val…
We report a detection of an absorption line at ~44.8 Å in a > 500 ks Chandra HRC-S/LETG X-ray grating spectrum of the blazar H 2356-309. This line can be identified as intervening CV-Kα absorption, at z\approx0.112, produced by a warm (log T = 5.1 K) intergalactic absorber. The feature is significant at a 2.9σ level (accounting for the number of independent redshift trials). We estimate an equivalent hydrogen column density of log N_H=19.05 (Z/Zsun)^-1 cm^-2. Unlike other previously reported FUV/X-ray metal detections of warm-hot intergalactic medium (WHIM), this CV absorber lies in a region w…
We investigate the origin and physical properties of OVI absorbers at low redshift (z = 0.25) using a subset of cosmological, hydrodynamical simulations from the OverWhelmingly Large Simulations (OWLS) project. Intervening OVI absorbers are believed to trace shock-heated gas in the Warm-Hot Intergalactic Medium (WHIM) and may thus play a key role in the search for the missing baryons in the present-day Universe. When compared to observations, the predicted distributions of the different OVI line parameters (column density, Doppler parameter, rest equivalent width) from our simulations exhibit …
We present analysis of two O VI absorbers at redshift z_{abs} = 0.227, detected in the spectra of two closely spaced QSO sightlines (Q 0107-025 A and B), observed with the Cosmic Origins Spectrograph (COS) on board the Hubble Space Telescope (HST). At the same redshift, presence of a single bright (~ 1.2 L*) galaxy at an impact parameter of ~ 200 kpc (proper) from both the sightlines was reported by Crighton et al. (2010). Using detailed photoionization models we show that the high ionization phases of both the O VI absorbers have similar ionization conditions (e.g. log U ~ -1.1 to -0.9), chem…
Ultraviolet observations of the QSO 3C 263 (zem = 0.652) with COS and FUSE reveal O VI absorption systems at z = 0.06342 and 0.14072 . WIYN multi-object spectrograph observations provide information about the galaxies associated with the absorbers. The multi-phase system at z = 0.06342 traces cool photoionized gas and warm collisionally ionized gas associated with a L ~ 0.31L* compact spiral emission line galaxy with an impact parameter of 63 kpc. The cool photoionized gas in the absorber is well modeled with log U ~ -2.6, log N(H) ~17.8, log n(H) ~ -3.3 and [Si/H] = -0.14\pm0.23. The collisio…
With high resolution (0.46kpc/h), adaptive mesh-refinement Eulerian cosmological hydrodynamic simulations we compute properties of O VI and O VII absorbers from the warm-hot intergalactic medium (WHIM). Our new simulations are in broad agreement with previous simulations, with ~40% of the intergalactic medium being in the WHIM at z=0. It is found (1) The amount of gas in the WHIM at temperature below and above 10^6K is about equal within uncertainties. (1) Our simulations are in excellent agreement with observed properties of O VI absorbers, with respect to the line incidence rate and Doppler …
IGM metal absorption lines observed in z>6 spectra offer the opportunity to probe early feedback processes, the nature of enriching sources, and the topology of reionization. We run high-resolution cosmological simulations including galactic outflows to study the observability and physical properties of 5 ions (C II, C IV, O I, Si II, Si IV) in absorption between z=8->5. We apply three cases for ionization conditions: Fully neutral, fully reionized, and a patchy model based on the flux from the nearest galaxy. We find that our simulations broadly fit available z~5-6 IGM metal-line data, althou…
At z<1 a large fraction of the baryons is thought to reside in diffuse gas that has been shock-heated to high temperatures (log T=5-6). Absorption by the 770.41, 780.32 Å doublet of NeVIII in quasar spectra represents a unique tool to study this elusive warm-hot phase. We have developed an analytic model for the properties of NeVIII absorbers that allows for an inhomogeneous metal distribution. Our model agrees with the predictions of a simulation from the OWLS project indicating that the average line-of-sight metal-filling fraction within the absorbing gas is low (c_L~0.1). Most of the NeVIII…
We propose to trace the dynamical motion of a shearing hot spot near the SgrA* source through a dynamical image reconstruction algorithm, StarWarps. Such a hot spot may form as the exhaust of magnetic reconnection in a current sheet near the black hole horizon. A hot spot that is ejected from the current sheet into an orbit in the accretion disk may shear and diffuse due to instabilities at its boundary during its orbit, resulting in a distinct signature. We subdivide the motion to two distinct phases; the first phase refers to the appearance of the hot spot modelled as a bright blob, followed…
We present results from the analysis of a multiphase O VI - broad Ly-alpha absorber at z = 0.19236 in the HST/COS spectrum of PG 1121+422. The low and intermediate ionization metal lines in this absorber have a single narrow component, whereas the Ly-alpha has a possible broad component with b(HI) $\sim 71$ km/s. Ionization models favor the low and intermediate ions coming from a $T \sim 8,500$ K, moderately dense photoionized gas with near solar metallicities. The weak O VI requires a separate gas phase that is collisionally ionized. The O VI coupled with BLA suggests $T \sim 3.2 \times 10^5$…
FLAMINGO: Tracing the co-evolution of hot gas and black holes in galaxy groups and clusters
Astrophysics Research Institute, Liverpool John Moores University（利物浦约翰摩尔斯大学天体物理研究所）；Institute for Computational Cosmology, Department of Physics, University of Durham（杜伦大学物理学院计算宇宙学研究所）；Leiden Observatory, Leiden University（莱顿大学莱顿天文台）；Lorentz Institute for Theoretical Physics, Leiden University（莱顿大学洛伦兹理论物理研究所）
The first systematic study of the warm gas (T=10^4-5 K) distribution across a galaxy cluster is presented using multiple background QSOs to the Virgo Cluster. We detect 25 Lya absorbers (N_HI = 10^13.1-15.4 cm^-2) in the Virgo velocity range toward 9 of 12 QSO sightlines observed with Cosmic Origin Spectrograph, with a cluster impact parameter range of 0.36-1.65 Mpc (0.23-1.05R_vir). Including 18 Lya absorbers previously detected by STIS or GHRS toward 7 of 11 background QSOs in and around the Virgo Cluster, we establish a sample of 43 absorbers towards a total of 23 background probes for stud…
We report on the detection of Ne VIII in the HST/Cosmic Origins Spectrograph spectrum of the intervening absorption system at z = 0.495096 towards PKS 0405-123. The high S/N COS spectrum also covers absorption from H I, C III, O III, O IV and O VI associated with this multiphase system. The Ne VIII is detected with high significance in both lines of the doublet, with integrated column densities of log Na(Ne VIII 770) = 13.96 +/- 0.06 dex and log Na(Ne VIII 780) = 14.08 +/- 0.07 dex. We find the origin of Ne VIII consistent with collisionally ionized gas at T ~ 5 x 10^5 K with a large baryonic …
Thermally-broadened Lya absorbers (BLAs) offer an alternate method to using highly-ionized metal absorbers (OVI, OVII, etc.) to probe the warm-hot intergalactic medium (WHIM, T=10^5-10^7 K). Until now, WHIM surveys via BLAs have been no less ambiguous than those via far-UV and X-ray metal-ion probes. Detecting these weak, broad features requires background sources with a well-characterized far-UV continuum and data of very high quality. However, a recent HST/COS observation of the z=0.03 blazar Mrk421 allows us to perform a metal-independent search for WHIM gas with unprecedented precision. Th…
Matter distribution in the environment of galaxy clusters, from their cores to their connected cosmic filaments, must be in principle related to the underlying cluster physics and it evolutionary state. We aim to investigate how radial and azimuthal distribution of gas is affected by cluster environments, and how it can be related to cluster mass assembly history. Radial physical properties of gas (velocity, temperature, and density) is first analysed around 415 galaxy cluster environments from IllustrisTNG simulation at z = 0 (TNG300-1). Whereas hot plasma is virialised inside clusters (< R20…
Recent searches for the hosts of high-redshift ($z \sim 4$) damped Ly$α$ absorbers (DLAs) have detected bright galaxies at distances of tens of kpc from the DLA. Using the FIRE-2 cosmological zoom simulations, we argue that these relatively large distances are due to a predominantly cool and neutral inner circumgalactic medium (CGM) surrounding high-redshift galaxies. The inner CGM is cool because of the short cooling time of hot gas in $\lesssim10^{12}$ Msun halos, which implies that accretion and feedback energy are radiated quickly, while it is neutral due to the high volume densities and c…
We report a bimodality in the azimuthal angle distribution of gas around galaxies as traced by MgII absorption: Halo gas prefers to exist near the projected galaxy major and minor axes. The bimodality is demonstrated by computing the mean azimuthal angle probability distribution function using 88 spectroscopically confirmed MgII absorption-selected galaxies [W_r(2796)>0.1A] and 35 spectroscopically confirmed non-absorbing galaxies [W_r(2796)<0.1A] imaged with HST and SDSS. The azimuthal angle distribution for non-absorbers is flat, indicating no azimuthal preference for gas characterized by W_…
We perform a series of cosmological simulations using Enzo, an Eulerian adaptive-mesh refinement, N-body + hydrodynamical code, applied to study the warm/hot intergalactic medium. The WHIM may be an important component of the baryons missing observationally at low redshift. We investigate the dependence of the global star formation rate and mass fraction in various baryonic phases on spatial resolution and methods of incorporating stellar feedback. Although both resolution and feedback significantly affect the total mass in the WHIM, all of our simulations find that the WHIM fraction peaks at …
We use the EAGLE (Evolution and Assembly of GaLaxies and their Environments) cosmological simulation to study the distribution of baryons, and far-ultraviolet (O VI), extreme-ultraviolet (Ne VIII) and X-ray (O VII, O VIII, Ne IX, and Fe XVII) line absorbers, around galaxies and haloes of mass $\mathrm{M}_{200c}=10^{11}$-$10^{14.5}\,\mathrm{M}_{\odot}$ at redshift 0.1. EAGLE predicts that the circumgalactic medium (CGM) contains more metals than the interstellar medium across halo masses. The ions we study here trace the warm-hot, volume-filling phase of the CGM, but are biased towards temperat…
For low-redshift cosmology and galaxy formation rates, it is important to account for all the baryons synthesized in the Big Bang. Although galaxies and clusters contain 10% of the baryons, many more reside in the photoionized Lyman-alpha forest and shocked-heated warm-hot intergalactic medium (WHIM) at T = 10^5 to 10^7 K. Current tracers of WHIM at 10^5 to 10^6 K include the O VI 1032, 1038 absorption lines, together with broad Lyman-alpha absorbers (BLAs) and EUV/X-ray absorption lines from Ne VIII, O VII, and O VIII. We improve the O VI baryon surveys with corrections for oxygen metallicity…
We present analyses of the physical conditions in the z=0.22496 and z=0.22638 multi-phase O VI absorption systems detected in the ultraviolet HST/STIS and FUSE spectra of the quasar H1821+643. Both absorbers are likely associated with the extended halo of a ~2L* Sbc-Sc galaxy situated at a projected distance of ~116 kpc from the sight line. The z=0.22496 absorber is detected in C II, C III, C IV, O III, O VI, Si II, Si III and H I at > 3 sigma significance. The low and intermediate ions in this absorber are consistent with an origin in photoionized gas with [Si/H] and [C/H] of -0.6 dex. In con…
Highly ionized, z=0 metal absorption lines detected in the X-ray spectra of background active galactic nuclei (AGNs) provide an effective method to probe the hot ($T\sim10^6$ K) gas and its metal content in and around the Milky Way. We present an all-sky survey of the $K_α$ transition of the local O VII absorption lines obtained by Voigt-profile fitting archival XMM-Newton observations. A total of 43 AGNs were selected, among which 12 are BL Lac-type AGNs, and the rest are Seyfert 1 galaxies. At above the $3σ$ level the local O VII absorption lines were detected in 21 AGNs, among which 7 were …
We investigate the nature of gas accretion onto haloes and galaxies at z=2 using cosmological hydrodynamic simulations run with the moving mesh code AREPO. Implementing a Monte Carlo tracer particle scheme to determine the origin and thermodynamic history of accreting gas, we make quantitative comparisons to an otherwise identical simulation run with the smoothed particle hydrodynamics (SPH) code GADGET-3. Contrasting these two numerical approaches, we find significant physical differences in the thermodynamic history of accreted gas in haloes above 10^10.5 solar masses. In agreement with prev…
We report results from multi-epoch X-ray observations of the polar-scattered Seyfert 1 galaxy ESO 323-G77. The source exhibits remarkable spectral variability from months to years timescales. The observed spectral variability is entirely due to variations of the column density of a neutral absorber towards the intrinsic nuclear continuum. The column density is generally Compton-thin ranging from a few times 10$^{22}$ cm$^{-2}$ to a few times 10$^{23}$ cm$^{-2}$. However, one observation reveals a Compton-thick state with column density of the order of 1.5 $\times$ 10$^{24}$ cm$^{-2}$. The obse…
We present a detection of a broad Ly-alpha absorber (BLA) with a matching O VI line in the nearby universe. The BLA is detected at z = 0.01028 in the high S/N spectrum of Mrk 290 obtained using the Cosmic Origins Spectrograph. The Ly-alpha absorption has two components, with b(HI) = 55 +/- 1 km/s and b(HI) = 33 +/- 1 km/s, separated in velocity by v ~ 115 km/s. The O VI, detected by FUSE at z = 0.01027, has a b(OVI) = 29 +/- 3 km/s and is kinematically well aligned with the broader HI component. The different line widths of the BLA and OVI suggest a temperature of T = 1.4 x 10^5 K in the absor…
