In this the first of a series of Letters, we present a panchromatic data set in the Extended Groth Strip region of the sky. Our survey, the All-Wavelength Extended Groth Strip International Survey (AEGIS), aims to study the physical properties and evolutionary processes of galaxies at . It includes the following deep, wide-field imaging data sets: z ∼ 1 Chandra/ACIS X-ray, GALEX ultraviolet, CFHT/MegaCam Legacy Survey optical, CFHT/CFH12K optical, Hubble Space Telescope/ACS optical and NICMOS near-infrared, Palomar/WIRC near-infrared, Spitzer/IRAC mid-infrared, Spitzer/MIPS far-infrared, and VLA radio continuum. In addition, this region of the sky has been targeted for extensive spectroscopy using the Deep Imaging Multi-Object Spectrograph (DEIMOS) on the Keck II 10 m telescope. Our survey is compared to other large multiwavelength surveys in terms of depth and sky coverage.
A significant fraction (40% -50%) of baryons at the present epoch are predicted to be shock-heated to the warmhot intergalactic medium (WHIM) by our previous numerical simulations. Here we recompute the evolution of the WHIM with several major improvements: (1) galactic superwind feedback processes from galaxy and star formation are explicitly included; (2) major metal species (O v to O ix) are computed explicitly in a nonequilibrium way; and (3) mass and spatial dynamic ranges are larger by factors of 8 and 2, respectively, than in our previous simulations. We find the following: (1) Nonequilibrium calculations produce significantly different results than do ionization equilibrium calculations. (2) The abundance of O vi absorption lines based on nonequilibrium simulations with galactic superwinds is in remarkably good agreement with the latest observations, strongly validating our model, while the predicted abundances for O vii and O viii absorption lines appear to be lower than the still very uncertain observations. The expected abundances for O vi (as well as Ly ), O vii, and O viii absorption systems are in the range 50-100 per unit redshift at equivalent width EW = 1 km s À1 , decreasing to 10-20 per unit redshift at EW = 10 km s À1 , to one to three lines for O vii and O viii and negligible for O vi at EW > 100 km s À1 . (3) Emission lines, primarily O vi and Ly in the UVand O vii and O viii in soft X-rays, are potentially observable by future missions, and different lines provide complementary probes of the WHIM in the temperature-density-metallicity phase space. The number of emission lines per unit redshift that may be detectable by planned UV and soft X-ray missions are of order 0.1-1. Subject headingg s: cosmology: observations -intergalactic medium -large-scale structure of universe
We present the first ≥ 3.5σ (conservative) or ≥ 5.8σ (sum of lines significance) detection of two Warm-Hot Intergalactic Medium (WHIM) filaments at z > 0, which we find along the line of sight to the blazar Mkn 421. These systems are detected through highly ionized resonant metal absorption in high quality Chandra-ACIS and -HRC Low Energy Transmission Grating (LETG) spectra of Mkn 421, obtained following our two Target of Opportunity requests during two outburst phases (F 0.5−2keV = 40 and 60 mCrab;Columns of He-like oxygen and H-like nitrogen can be detected in the coadded LETG spectrum of Mkn 421 down to a sensitivity of N OV II ≥ 8 × 10 14 cm −2 and N N V II ≥ 10 15 cm −2 respectively, at a significance ≥ 3σ. The two intervening WHIM systems that we detect, have OVII and NVII columns of N OV II = (1.0 ± 0.3) × 10 15 cm −2 N N V II = (0.8 ± 0.4) × 10 15 cm −2 , and N OV II = (0.7 ± 0.3) × 10 15 cm −2 , N N V II = (1.4 ± 0.5) × 10 15 cm −2 respectively. We identify the closest of these two systems with an intervening WHIM filament at cz = 3300 ± 300 km s −1 . The second system, instead, at cz = 8090 ± 300 km s −1 , is identified with an intervening WHIM filament located ∼ 13 Mpc from the Blazar. The filament at cz = 3300±300 lies < ∼ 5 Mpc from a known HI Lyα system at cz = (3046±12) km s −1 (Shull et al., 1996) whose 3σ maximal HI kinetic temperature, as derived from the observed line FWHM, is T ≤ 1.2 × 10 5 K. This temperature is inconsistent with the temperature measured for the X-ray filament, so if the systems are related a multiphase WHIM is required.Combining UV and FUV upper limits on the HI Lyα and the OVI 2s→2p transitions, with our measurements in the X-rays, we show that, for both filaments,
Recent cosmological measurements indicate that baryons comprise about four per cent of the total mass-energy density of the Universe, which is in accord with the predictions arising from studies of the production of the lightest elements. It is also in agreement with the actual number of baryons detected at early times (redshifts z > 2). Close to our own epoch (z < 2), however, the number of baryons detected add up to just over half (approximately 55 per cent) of the number seen at z > 2 (refs 6-11), meaning that about approximately 45 per cent are 'missing'. Here we report a determination of the mass-density of a previously undetected population of baryons, in the warm-hot phase of the intergalactic medium. We show that this mass density is consistent, within the uncertainties, with the mass density of the missing baryons.
We report the detection of highly ionized gas at z $ 0 seen in resonant UV and X-ray absorption lines toward the z ¼ 0:03 blazar Mrk 421. A total of 13 X-ray and three UV lines were measured (or upper limits derived), including three lines in the O vii K series and K transitions from neon, carbon, and nitrogen. From the three O vii lines we derive a 2 Doppler parameter constraint of 24 km s À1 < b < 55 km s À1 . The FUSE spectrum shows strong Galactic low-velocity O vi k1032 absorption and a possible weak O vi high-velocity component (HVC). The Doppler parameter of the low-velocity O vi measured with FUSE is $3 higher than that derived from the O vii line ratios, indicating that the O vii and Galactic O vi arise in different phases. This velocity dispersion along with limits on the gas temperature and density from the X-ray line ratios (assuming a single phase with collisional ionization equilibrium plus photoionization) are all consistent with an extragalactic absorber. However, the O vii Doppler parameter is inconsistent with the high temperature required to produce the observed O vi HVC /O vii ratio, implying that the HVC is probably not related to the O vii. In addition, the O vi K line detected by Chandra implies a column density $4 times higher than the k1032 absorption. Although an extragalactic absorber is fully consistent with the measured column density ratios, a Galactic origin cannot be ruled out given the uncertainties in the available data.
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