X-ray morphology, kinematics, and geometry of the Eridanus soft X-ray enhancement

We present mosaics of X-ray intensity maps and spectral fit results for selected regions of the Eridanus soft X-ray enhancement (EXE), as well as kinematics of the X-ray-absorbing clouds in the EXE region and geometrical properties of this X-ray-emitting bubble. The work is based on pointed observations with the ROSAT Position Sensitive Proportional Counter, 21 cm observations with the NRAO 140 foot telescope at Green Bank and interstellar Na D line observations with the NOAO Coudé Feed telescope at Kitt Peak. The ROSAT pointed observations examine two regions of the EXE. The first is an X-ray absorption lane produced by an IR filament which is located at galactic coordinates of about (200°, -47°). The second is in the vicinity of the northern (galactic) boundary of the 1/4 keV EXE, at galactic coordinates of about (202°, -25°). Both our spatial and spectral analysis suggest that variations in emission measure and N_H are primarily responsible for the observed variations of the X-ray intensity. Using 100 μm intensities obtained from IRAS maps and N_H column densities obtained from our X-ray spectral fits, we find 100 μm/N_H ratios across the IR filament that are compatible with typical high-latitude values. Maps of the X-ray-absorbing clouds in the EXE region at 21 cm reveal that these clouds may belong to two different expanding systems, with one possibly associated with our Local Bubble and the other with the boundary of the EXE. Based on 21 cm data and Na D observations in the direction (l, b) ∼ (200°, -47°), our best estimate of the distance to the near side of the Orion-Eridanus bubble is 159 ± 16 pc. We estimate the center of the bubble in this direction to be about 226 pc away, with much larger uncertainty. The density and the thermal pressure found for this X-ray-emitting superbubble are 0.015 cm^-3 and 4.9 × 10⁴ cm^-3 K.