2005ApJ...629..700N -
Astrophys. J., 629, 700-718 (2005/August-3)
Chandra detection of the first X-ray forest along the line of sight to Markarian 421.
NICASTRO F., MATHUR S., ELVIS M., DRAKE J., FIORE F., FANG T., FRUSCIONE A., KRONGOLD Y., MARSHALL H. and WILLIAMS R.
Abstract (from CDS):
We present the first ≥3.5 (conservative) or ≥5.8 σ (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 Mrk 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 Mrk 421, obtained following our two Target of Opportunity requests during two outburst phases (F0.5–2keV=40 and 60 mcrab; 1 crab=2x10–8 ergs/s/cm2). Columns of He-like oxygen and H-like nitrogen can be detected in the co-added LETG spectrum of Mrk 421 down to a sensitivity of N_OVII_≥8x1014/cm2 and N_NVII_≥1015/cm2, respectively, at a significance ≥3 σ. The two intervening WHIM systems that we detect have O VII and N VII columns of N_OVII_=(1.0±0.3)x1015/cm2, N_N VII_=(0.8±0.4)x1015/cm2 and N_OVII_=(0.7±0.3)x1015/cm2, N_NVII_=(1.4±0.5)x1015/cm2, respectively. We identify the closest of these two systems with an intervening WHIM filament at cz=3300±300 km/s. The second system, instead, at cz=8090±300 km/s, 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 H I Lyα system at cz=3046±12 km/s (Shull and coworkers) whose 3 σ maximal H I kinetic temperature, as derived from the observed line FWHM, is T≤1.2x105 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 far-ultraviolet (FUV) upper limits on the H I Lyα and the O VI_2s⟶2p_transitions with our measurements in the X-rays, we show that, for both filaments, equilibrium collisional ionization (with residual photoionization by both the diffuse UV and X-ray background and the beamed emission of Mrk 421 along our line of sight) provides acceptable solutions. These solutions define ranges of temperatures, metallicity ratios, and equivalent H column densities, which are in good agreement with the predictions of hydrodynamical simulations for the formation of large-scale structures in the universe. From the detected number of WHIM filaments along this line of sight we can estimate the number of O VII filaments per unit redshift with columns larger than 7x1014/cm2, dN_OVII/dz(NOVII≥7x1014)=67+88^–43, consistent, within the large 1 σ errors, with the hydrodynamical simulation predictions of dN_OVII/dz(NOVII_≥7x1014)=30. Finally, we measure a cosmological mass density of X-ray WHIM filaments Ωb=0.027+0.038–0.019x10[O/H]-1_^, consistent with both model predictions and the estimated number of ``missing'' baryons at low redshift.
Abstract Copyright:
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Journal keyword(s):
Galaxies: BL Lacertae Objects: Individual: Name: Markarian 421 - Galaxies: Intergalactic Medium - Galaxies: Quasars: Absorption Lines
Nomenclature:
Table 3: [NME2005] QSO J1104+3812 abs N.NNN N=2.
Simbad objects:
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