scholarly journals The warm-hot circumgalactic medium around EAGLE-simulation galaxies and its detection prospects with X-ray and UV line absorption

2020 ◽  
Vol 498 (1) ◽  
pp. 574-598 ◽  
Author(s):  
Nastasha A Wijers ◽  
Joop Schaye ◽  
Benjamin D Oppenheimer
Keyword(s):  
Column Density ◽  
Extreme Ultraviolet ◽  
Gas Well ◽  
X Ray ◽  
Filling Phase ◽  
Circumgalactic Medium ◽  
Halo Masses ◽  
Collisional Ionization ◽  
Far Ultraviolet ◽  
Halo Gas

ABSTRACT 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 $\,{M}_{\rm {200c}}= 10^{11}$–$10^{14.5} \, \rm {M}_{\odot}$ 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 temperatures corresponding to the collisional ionization peak for each ion, and towards high metallicities. Gas well within the virial radius is mostly collisionally ionized, but around and beyond this radius, and for O vi, photoionization becomes significant. When presenting observables, we work with column densities, but quantify their relation with equivalent widths by analysing virtual spectra. Virial-temperature collisional ionization equilibrium ion fractions are good predictors of column density trends with halo mass, but underestimate the diversity of ions in haloes. Halo gas dominates the highest column density absorption for X-ray lines, but lower density gas contributes to strong UV absorption lines from O vi and Ne viii. Of the O vii (O viii) absorbers detectable in an Athena X-IFU blind survey, we find that 41 (56) per cent arise from haloes with $\,{M}_{\rm {200c}}= 10^{12.0}{-}10^{13.5} \, \rm {M}_{\odot}$. We predict that the X-IFU will detect O vii (O viii) in 77 (46) per cent of the sightlines passing $\,{M}_{\star }= 10^{10.5}{-}10^{11.0} \, \rm {M}_{\odot}$ galaxies within $100 \, \rm {pkpc}$ (59 (82) per cent for $\,{M}_{\star }\gt 10^{11.0} \, \rm {M}_{\odot}$). Hence, the X-IFU will probe covering fractions comparable to those detected with the Cosmic Origins Spectrograph for O vi.

scholarly journals The abundance and physical properties of O vii and O viii X-ray absorption systems in the EAGLE simulations

2019 ◽  
Vol 488 (2) ◽  
pp. 2947-2969 ◽  
Author(s):  
Nastasha A Wijers ◽  
Joop Schaye ◽  
Benjamin D Oppenheimer ◽  
Robert A Crain ◽  
Fabrizio Nicastro
Keyword(s):  
Column Density ◽  
Gas Absorption ◽  
Ionization State ◽  
Simple Estimate ◽  
X Ray ◽  
Density Distributions ◽  
Lower Column ◽  
Hydrodynamical Simulations ◽  
Halo Gas ◽  
X Ray Absorption

Abstract We use the EAGLE cosmological, hydrodynamical simulations to predict the column density and equivalent width distributions of intergalactic O vii ($E=574 \, \rm {eV}$) and O viii ($E=654 \, \rm {eV}$) absorbers at low redshift. These two ions are predicted to account for $40 \, \hbox{ per cent}$ of the gas-phase oxygen, which implies that they are key tracers of cosmic metals. We find that their column density distributions evolve little at observable column densities from redshift 1 to 0, and that they are sensitive to active galactic nucleus feedback, which strongly reduces the number of strong (column density $N \gtrsim 10^{16} \, \rm {cm}^{-2}$) absorbers. The distributions have a break at $N \sim 10^{16}\, \rm {cm}^{-2}$, corresponding to overdensities of ∼102, likely caused by the transition from sheet/filament to halo gas. Absorption systems with $N \gtrsim 10^{16} \, \rm {cm}^{-2}$ are dominated by collisionally ionized O vii and O viii, while the ionization state of oxygen at lower column densities is also influenced by photoionization. At these high column densities, O vii and O viii arising in the same structures probe systematically different gas temperatures, meaning their line ratio does not translate into a simple estimate of temperature. While O vii and O viii column densities and covering fractions correlate poorly with the H i column density at ${N}_{\rm {H}\, \rm {I}} \gtrsim 10^{15} \, \rm {cm}^{-2}$, O vii and O viii column densities are higher in this regime than at the more common, lower H i column densities. The column densities of O vi and especially Ne viii, which have strong absorption lines in the UV, are good predictors of the strengths of O vii and O viii absorption and can hence aid in the detection of the X-ray lines.

scholarly journals Features of the Soft X-ray Background and Implications for the EUV Background

1996 ◽  
Vol 152 ◽  
pp. 295-298
Author(s):  
C.R. Barber ◽  
R.S. Warwick
Keyword(s):  
Column Density ◽  
Extreme Ultraviolet ◽  
Significant Excess ◽  
Total Exposure ◽  
X Ray ◽  
Sky Survey ◽  
X Ray Background ◽  
Lockman Hole

A series of eight overlapping ROSAT PSPC observations situated in the Lockman hole region have been analysed in the 0.1 – 0.4 keV band. The total exposure of ~ 137 ks and the ultra-low interstellar column density make the data extremely suitable for studies of the diffuse signal. After excluding the contribution of bright discrete sources the remaining signal was examined on a scale of 20′. As expected the 0.1 – 0.4 keV signal exhibits a strong anticorrelation with column density. However, there is also evidence for significant excess fluctuations superimposed on this anticorrelation which may be attributable to some form of cloud structures within the hot ISM.The diffuse signal expected in the ROSAT WFC all-sky survey for this region is predicted and shown to be far in excess of that observed. The origin of the fluctuations in the soft X-ray background and their possible relevance to the Extreme-Ultraviolet background are discussed.

scholarly journals Recurring obscuration in NGC 3783

2018 ◽  
Vol 619 ◽  
pp. A112 ◽  
Author(s):  
J. S. Kaastra ◽  
M. Mehdipour ◽  
E. Behar ◽  
S. Bianchi ◽  
G. Branduardi-Raymont ◽  
...  
Keyword(s):  
Column Density ◽  
Extreme Ultraviolet ◽  
Galactic Nuclei ◽  
Seyfert Galaxies ◽  
Continuum Emission ◽  
X Ray ◽  
Transient Nature ◽  
Hardness Ratio ◽  
Ultraviolet Photons ◽  
The Continuum

Context. Obscuration of the continuum emission from active galactic nuclei by streams of gas with relatively high velocity (>1000 km s−1) and column density (>3 × 1025 m−2) has been seen in a few Seyfert galaxies. This obscuration has a transient nature. In December 2016 we witnessed such an event in NGC 3783. Aims. The frequency and duration of these obscuration events is poorly known. Here we study archival data of NGC 3783 in order to constrain this duty cycle. Methods. We use archival Chandra/NuSTAR spectra taken in August 2016. We also study the hardness ratio of all Swift XRT spectra taken between 2008 and 2017. Results. In August 2016, NGC 3783 also showed evidence of obscuration. While the column density of the obscuring material is ten times lower than in December 2016, the opacity is still sufficient to block a significant fraction of the ionising X-ray and extreme ultraviolet photons. From the Swift hardness ratio behaviour we find several other epochs with obscuration. Obscuration with columns >1026 m−2 may take place about half of the time. Also, in archival X-ray data taken by the Advanced Satellite for Cosmology and Astrophysics (ASCA) in 1993 and 1996 we find evidence of obscuration. Conclusions. Obscuration of the ionising photons in NGC 3783 occurs more frequently than previously thought. This may not always have been recognised due to low-spectral-resolution observations, overly limited spectral bandwidth or confusion with underlying continuum variations.

scholarly journals The ionic composition of the local absorber towards 3C 273

2020 ◽  
Vol 492 (4) ◽  
pp. 5634-5640
Author(s):  
Itay Gissis ◽  
Uria Peretz ◽  
Ehud Behar
Keyword(s):  
Column Density ◽  
Ionic Composition ◽  
Elemental Abundance ◽  
Ionized Gas ◽  
X Ray ◽  
Line Region ◽  
Collisional Ionization ◽  
X Ray Absorption ◽  
Absorption Features ◽  
Measure Distribution

ABSTRACT Hot ionized gas is observed in the local vicinity of our galaxy through spectral absorption features. The most common hypothesis is that this gas forms a halo surrounding our Milky Way, in collisional ionization equilibrium. In this paper, we investigate the elemental abundance of this hot and ionized local gas. We use a 2.4 Ms stacked X-ray spectrum of the bright blazar 3C 273 and probe the local absorption features. Using ion-by-ion fitting of the X-ray absorption lines, we derive the column density of each ionization species. Based on the column densities, we reconstruct the absorption measure distribution, namely the hydrogenic column density as a function of temperature. We report the elemental abundances of C, N, Ne, and Fe relative to solar O. Previous measurements of local X-ray emission lines in conjunction with the present column densities indicate a scale height of 1–80 kpc and hydrogen number density of 10−4–10−3 cm−3 for the hot ionized gas. Additionally, we detect He-like O lines from the quasar broad line region with velocities of 6400 ± 1500 km s−1.

scholarly journals The Diffuse Extreme Ultraviolet Background

1997 ◽  
Vol 166 ◽  
pp. 79-82
Author(s):  
John Vallerga ◽  
Jonathan Slavin
Keyword(s):  
Extreme Ultraviolet ◽  
Broad Band ◽  
Line Flux ◽  
Ionization Equilibrium ◽  
Significant Evidence ◽  
X Ray ◽  
Hot Plasma ◽  
Solar Abundances ◽  
Collisional Ionization

AbstractObservations of the diffuse EUV background towards 138 different directions using the spectrometers aboard the Extreme Ultraviolet Explorer satellite (EUVE) have been combined into a spectrum from 150Å to 730Å and represent an effective exposure of 18 million seconds. There is no significant evidence for any line flux from any source other than the geocorona. These results are inconsistent with the Wisconsin C and B broad-band surveys assuming the source is a logT = 5.8 – 6.1 hot plasma in ionization equilibrium with solar abundances, confirming the previous result of Jelinsky, Vallerga & Edelstein (1995) (hereafter Paper I) using an observation along the ecliptic with the same instrument. To make these results consistent with the previous broad-band surveys, the plasma responsible for the emission must either be depleted in Fe by a factor of ~ 6, be behind an absorbing slab of neutral H with a column of 2×l019cm−2, or not be in collisional ionization equilibrium (CIE). One particular non-CIE model (Breitschwerdt & Schmutzler, 1994) that explains the soft x-ray results is also inconsistent with this EUV data.

scholarly journals Ca II H&K stellar activity parameter: a proxy for extreme ultraviolet stellar fluxes

2020 ◽  
Vol 644 ◽  
pp. A67
Author(s):  
A. G. Sreejith ◽  
L. Fossati ◽  
A. Youngblood ◽  
K. France ◽  
S. Ambily
Keyword(s):  
Extreme Ultraviolet ◽  
Radiation Power ◽  
Optical Observations ◽  
Scaling Relations ◽  
Activity Parameter ◽  
X Ray ◽  
Atmospheric Escape ◽  
Direct Measurements ◽  
Nearby Stars ◽  
Far Ultraviolet

Atmospheric escape is an important factor shaping the exoplanet population and hence drives our understanding of planet formation. Atmospheric escape from giant planets is driven primarily by the stellar X-ray and extreme ultraviolet (EUV) radiation. Furthermore, EUV and longer wavelength UV radiation power disequilibrium chemistry in the middle and upper atmospheres. Our understanding of atmospheric escape and chemistry, therefore, depends on our knowledge of the stellar UV fluxes. While the far-ultraviolet (FUV) fluxes can be observed for some stars, most of the EUV range is unobservable due to the lack of a space telescope with EUV capabilities and, for the more distant stars, due to interstellar medium absorption. Therefore, it becomes essential to have an indirect means for inferring EUV fluxes from features observable at other wavelengths. We present here analytic functions for predicting the EUV emission of F-, G-, K-, and M-type stars from the log R′HK activity parameter that is commonly obtained from ground-based optical observations of the Ca II H&K lines. The scaling relations are based on a collection of about 100 nearby stars with published log R′HK and EUV flux values, the latter of which are either direct measurements or inferences from high-quality FUV spectra. The scaling relations presented here return EUV flux values with an accuracy of about a factor of three, which is slightly lower than that of other similar methods based on FUV or X-ray measurements.

scholarly journals Properties of the circumgalactic medium in cosmic ray-dominated galaxy haloes

2020 ◽  
Vol 496 (4) ◽  
pp. 4221-4238 ◽  
Author(s):  
Suoqing Ji ◽  
T K Chan ◽  
Cameron B Hummels ◽  
Philip F Hopkins ◽  
Jonathan Stern ◽  
...  
Keyword(s):  
Cosmic Ray ◽  
Pressure Balance ◽  
Thermal Pressure ◽  
Star Forming ◽  
Circumgalactic Medium ◽  
Cool Gas ◽  
Field Lines ◽  
Halo Masses ◽  
Collisional Ionization ◽  
The Impact

ABSTRACT We investigate the impact of cosmic rays (CRs) on the circumgalactic medium (CGM) in FIRE-2 simulations, for ultra-faint dwarf through Milky Way (MW)-mass haloes hosting star-forming (SF) galaxies. Our CR treatment includes injection by supernovae, anisotropic streaming and diffusion along magnetic field lines, and collisional and streaming losses, with constant parallel diffusivity $\kappa \sim 3\times 10^{29}\, \mathrm{cm^2\ s^{-1}}$ chosen to match γ-ray observations. With this, CRs become more important at larger halo masses and lower redshifts, and dominate the pressure in the CGM in MW-mass haloes at z ≲ 1–2. The gas in these ‘CR-dominated’ haloes differs significantly from runs without CRs: the gas is primarily cool (a few ${\sim}10^{4}\,$ K), and the cool phase is volume-filling and has a thermal pressure below that needed for virial or local thermal pressure balance. Ionization of the ‘low’ and ‘mid’ ions in this diffuse cool gas is dominated by photoionization, with O vi columns ${\gtrsim}10^{14.5}\, \mathrm{cm^{-2}}$ at distances ${\gtrsim}150\, \mathrm{kpc}$. CR and thermal gas pressure are locally anticorrelated, maintaining total pressure balance, and the CGM gas density profile is determined by the balance of CR pressure gradients and gravity. Neglecting CRs, the same haloes are primarily warm/hot ($T\gtrsim 10^{5}\,$K) with thermal pressure balancing gravity, collisional ionization dominates, O vi columns are lower and Ne viii higher, and the cool phase is confined to dense filaments in local thermal pressure equilibrium with the hot phase.

scholarly journals The gas fractions of dark matter haloes hosting simulated ∼L⋆ galaxies are governed by the feedback history of their black holes

2019 ◽  
Vol 485 (3) ◽  
pp. 3783-3793 ◽  
Author(s):  
Jonathan J Davies ◽  
Robert A Crain ◽  
Ian G McCarthy ◽  
Benjamin D Oppenheimer ◽  
Joop Schaye ◽  
...  
Keyword(s):  
Dark Matter ◽  
Active Galactic Nucleus ◽  
Accretion Rate ◽  
Dark Matter Halo ◽  
X Ray ◽  
History Of ◽  
Halo Masses ◽  
Halo Gas ◽  
The Relationship ◽  
Gas Fractions

ABSTRACT We examine the origin of scatter in the relationship between the gas fraction and mass of dark matter haloes hosting present-day ∼L⋆ central galaxies in the EAGLE simulations. The scatter is uncorrelated with the accretion rate of the central galaxy’s black hole (BH), but correlates strongly and negatively with the BH’s mass, implicating differences in the expulsion of gas by active galactic nucleus feedback, throughout the assembly of the halo, as the main cause of scatter. Haloes whose central galaxies host undermassive BHs also tend to retain a higher gas fraction, and exhibit elevated star formation rates (SFRs). Diversity in the mass of central BHs stems primarily from diversity in the dark matter halo binding energy, as these quantities are strongly and positively correlated at fixed halo mass, such that ∼L⋆ galaxies hosted by haloes that are more (less) tightly bound develop central BHs that are more (less) massive than is typical for their halo mass. Variations in the halo gas fraction at fixed halo mass are reflected in both the soft X-ray luminosity and thermal Sunyaev–Zel’dovich flux, suggesting that the prediction of a strong coupling between the properties of galaxies and their halo gas fractions can be tested with measurements of these diagnostics for galaxies with diverse SFRs but similar halo masses.

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