Abstract
We studied the spectral signature of different components of the diffuse X-ray background (DXB), including Local Hot Bubble, solar wind charge exchange, galactic halo, and typically ...unresolved point sources (galaxies and active galactic nuclei), in the direction of the Chandra Deep Field South using the 4 Ms XMM-Newton survey and Chandra 4 Ms Source Catalog. In this paper, we present our results showing how the different components contribute to the DXB below 1 keV. In particular, we have found that ∼6% of the emission at
3
4
keV (all-sky average value ≈3 × 10
−3
cm
−6
pc), which is typically associated with galactic halo (GH) and circumgalactic medium (CGM), is, in fact, due to emission from typically unresolved galaxies. We will discuss the effect that this has on our understanding of GH and CGM and to our understanding of the missing CGM baryons.
THE STRUCTURE OF THE LOCAL HOT BUBBLE Liu, W.; Chiao, M.; Collier, M. R. ...
Astrophysical journal/The Astrophysical journal,
01/2017, Letnik:
834, Številka:
1
Journal Article
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Odprti dostop
ABSTRACT Diffuse X-rays from the Local Galaxy (DXL) is a sounding rocket mission designed to quantify and characterize the contribution of Solar Wind Charge eXchange (SWCX) to the Diffuse X-ray ...Background and study the properties of the Local Hot Bubble (LHB). Based on the results from the DXL mission, we quantified and removed the contribution of SWCX to the diffuse X-ray background measured by the ROSAT All Sky Survey. The "cleaned" maps were used to investigate the physical properties of the LHB. Assuming thermal ionization equilibrium, we measured a highly uniform temperature distributed around kT = 0.097 keV 0.013 keV (FWHM) 0.006 keV (systematic). We also generated a thermal emission measure map and used it to characterize the three-dimensional (3D) structure of the LHB, which we found to be in good agreement with the structure of the local cavity measured from dust and gas.
Recent analyses of the fluctuations of the soft diffuse X-ray background (DXB) have provided indirect detection of a component consistent with the elusive warm-hot intergalactic medium (WHIM). In ...this work we use theoretical predictions obtained from hydrodynamical simulations to investigate the angular correlation properties of the WHIM in emission and assess the possibility of indirect detection with next-generation X-ray missions. Our results indicate that the angular correlation signal of the WHIM is generally weak but dominates the angular correlation function of the DXB outside virialized regions. Its indirect detection is possible but requires rather long exposure times 0.1-1 Ms, large (∼1°× 1°) fields of view and accurate subtraction of isotropic fore/background contributions, mostly contributed by Galactic emission. The angular correlation function of the WHIM, which turns out to be positive for θ < 5 arcmin, provides limited information on its spatial distribution. A satisfactory characterization of the WHIM in 3D can be obtained through spatially resolved spectroscopy. 1 Ms long exposures with next generation detectors will allow to detect ∼400 O vii+O viii X-ray emission systems that could be used to trace the spatial distribution of the WHIM. We predict that these observations will allow us to estimate the WHIM correlation function with high statistical significance out to ∼10 Mpc h
−1 and characterize its dynamical state through the analysis of redshift-space distortions. The detectable WHIM, which is typically associated with the outskirts of virialized regions rather than the filaments, has a non-zero correlation function with slope γ=−1.7 ± 0.1 and correlation length r
0= 4.0 ± 0.1 Mpc h
−1 in the range r= 4.5, 12 Mpc h
−1. Redshift-space distances can be measured to assess the dynamical properties of the gas that we predict to be typically infalling on to large virialized structures.
The Universe has evolved from an initial diffuse, uniform gas to a complex structure that includes both voids and high-density galaxy clusters connected by gaseous filaments, known as the Cosmic Web, ...and traced by 3D surveys of galaxies. The filamentary structure contains a significant fraction of the baryonic matter and is predicted to be mostly in the form of a moderately high temperature plasma, the Warm Hot Intergalactic Medium. Plasma at this temperature and ionization level emits mostly in soft X-rays. The filamentary structure, however, is hard to detect because the other sources contributing to the Diffuse X-ray Background are much brighter and, currently, there are very few reported detections of emission from the filaments. We report the first high-confidence level indirect detection of X-ray emission from the Warm Hot Intergalactic Medium. Applying the Power Spectrum Analysis to XMM-Newton and eROSITA data, we separated its contribution from other sources modeled in previous studies. Our result is in good agreement with numerical simulations and fills a critical gap in the picture of the large-scale structure of the Universe, in which filamentary gas, galaxies and dark matter interact and co-evolve.
We studied the spectral signature of different components of the Diffuse X-ray Background (DXB), including Local Hot Bubble (LHB), Solar Wind Charge Exchange (SWCX), Galactic Halo, and typically ...unresolved point sources (galaxies and AGN), in the direction of the Chandra Deep Field South (CDFS) using the 4 Ms XMM-Newton survey and Chandra 4 Ms Source Catalog. In this paper, we present our results showing how the different components contribute to the DXB below 1 keV. In particular, we have found that ~6% of the emission at 3/4 keV (all-sky average value ~ 3\(\times10^{-3}\) cm\(^{-6}\)pc), which is typically associated with Galactic Halo (GH) and Circum-galactic medium (CGM) is, in fact, due to emission from typically unresolved galaxies. We will discuss the effect that this has on our understanding of GH and CGM, and to our understanding of the missing CGM baryons.
In the past years significant efforts have been focused on describing the evolution and structure of the Universe. One of the big open questions in cosmology is “Where is the baryonic mass”? We know ...from various surveys that the number of detected baryons in the Universe at present days is much smaller than predicted by the standard big-bang nucleosynthesis model and measured by the detailed observation of the Lyman-α forest at redshift z=2. Hydrodynamical simulations indicate that a large fraction of the baryons today is expected to be in a “warm-hot” (10 5-107 K) filamentary gas, distributed in the intergalactic medium. This gas, if exists, should be highly ionized and observable only in the soft x-ray and UV bands. The first part of my project is dedicated to studying the evolution of the baryonic mass in the intergalactic medium using the output of hydrodynamic simulations. In the second part I use the same simulations to predict the x-ray flux from the Warm-Hot Intergalactic Medium (WHIM), its distribution in space and its spectral properties. The primary motivation of this investigation is the construction and launch of a dedicated mission to detect and study the properties of the intergalactic medium and the missing baryons. What I found is that, depending on the model, in the 0.37-0.925 keV energy band the WHIM is between 3% and 20% of the Diffuse X-Ray Background, and comes mostly from filaments between redshift 0.1 and 0.8. The filaments have typical angular size of a few arc minutes, which requires an detector angular resolution of 2' or less. Since the identification of the WHIM is possible only from emission lines, we need a detector with energy resolution in the order of 4 eV or less. Another critical issue is the detector background which needs to be less than 10-3 counts s -1 eV-1 in order to detect the weak signal from the WHIM.
Shadow observations are the only way to observe emission from the galactic halo (GH) and/or the circumgalactic medium (CGM) free of any foreground contamination from local hot bubble (LHB) and solar ...wind charge exchange (SWCX). We analyzed data from a shadow observation in the direction of the high latitude, neutral hydrogen cloud MBM 16 with \Suzaku. We found that all emission can be accounted for by foreground emission from LHB and SWCX, plus power law emission associated with unresolved point sources. The GH/CGM in the direction of MBM 16 is negligible or inexistent in our observation, with upper limits on the emission measure of 9.5x10^{-4} pc cm^{-6} (90% C.L.), at the lowest end of current estimates.
We use numerical simulations to predict the soft X-ray (0.4-0.6 keV) and Sunyaev-Zeldovich signal (at 150 GHz) from the large scale structure in the Universe and then compute 2-point statistics to ...study the spatial distribution and time evolution of the signals. The average X-ray signal predicted for the WHIM is in good agreement with observational constraints that set it at about 10% of the total Diffuse X-ray Background. The characteristic angle computed with the Autocorrelation Function is of the order of some arcminutes and becomes smaller at higher redshift. The power spectrum peak of the SZ due to the WHIM is at l~10000 and has amplitude of ~0.2 muK^2, about one order of magnitude below the signal measured with telescopes like Planck, ACT, and SPT. Even if the high-redshift WHIM signal is too weak to be detected using X-rays only, the small-scale correlation between X-ray and SZ maps is dominated by the high-redshift WHIM. This makes the analysis of the SZ signal in support of X-rays a promising tool to study the early time WHIM.
We have used the angular Autocorrelation Function (AcF) in a pointing with Chandra's ACIS-S instrument. However, we determined that the contribution of Chandra's background below 1 keV is too high to ...achieve reasonable sensitivity.
Hydrodynamic simulations predict that a significant fraction of the gas in the current Universe is in the form of high temperature, highly ionized plasma emitting and absorbing primarily in the soft ...X-ray and UV bands, dubbed the Warm-Hot Intergalactic Medium (WHIM). Its signature should be observable in red-shifted emission and absorption lines from highly ionized elements. To determine the expected WHIM emission in the soft X-ray band we used the output of a large scale hydrodynamic SPH simulation to generate images and spectra with angular resolution of 14'' and energy resolution of 1 eV. The current biggest limit of any hydrodynamic simulation in predicting the X-ray emission comes from metal diffusion. In our investigation, by using four different models for the WHIM metallicity we have found a strong dependence of the emission on the model used, with differences up to almost an order of magnitude. For each model we have investigated the redshift distribution and angular scale of the emission, confirming that most photons come from redshift z<1.2 and that the emission has a typical angular scale of less than a few arcminutes. We also compared our simulations with the few currently available observations and found that, within the variation of the metallicity models, our predictions are in good agreement with current constraints on the WHIM emission, and at this time the weak experimental constraints on the WHIM emission are not sufficient to exclude any of the models used.
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