Multi-wavelength observations of a nearby multi-phase interstellar cloud
Résumé
Aims: High-resolution spectroscopic observations (UV HST/STIS and optical) are used to characterize the physical state and velocity structure of the multiphase interstellar medium seen towards the nearby (170 pc) star HD 102065. The star is located behind the tail of a cometary-shaped, infrared cirrus-cloud, in the area of interaction between the Sco-Cen OB association and the Local Bubble.
Methods: We analyze interstellar components present along the line of sight by fitting multiple transitions from a group of species all at once. We identify four groups of species: (1) molecules (CO, CH, CH^+), (2) atoms (C i, S i, Fe i) with ionization potential lower than H i, (3) neutral and low-ionized states of atoms (Mg i, Mg ii, Mn ii, P ii, Ni ii, C ii, N i and O i) with ionization potential larger than H i and (4) highly-ionized atoms (Si iii, C iv, Si iv). The absorption spectra are complemented by H i, CO and C ii emission-line spectra, H2 column-densities derived from FUSE spectra, and IRAS images.
Results: Gas components of a wide range of temperatures and ionization states are detected along the line of sight. Most of the hydrogen column-density is in cold, diffuse, molecular gas at low LSR velocity. This gas is mixed with traces of warmer molecular gas traced by H2 in the J > 2 levels, in which the observed CH+ must be formed. We also identify three distinct components of warm gas at negative velocities down to -20 km s-1. The temperature and gas excitation are shown to increase with increasing velocity shift from the bulk of the gas. Hot gas at temperatures of several 105 K is detected in the most negative velocity component in the highly-ionized specie. This hot gas is also detected in very strong lines of less-ionized species (Mg ii, Si ii* and C ii^*) for which the bulk of the gas is cooler.
Conclusions: We relate the observational results to evidence for dynamical impact of the Sco-Cen stellar association on the nearby interstellar medium. We propose a scenario where the infrared cirrus cloud has been hit a few 105 yr ago by a supernova blast wave originating from the Lower Centaurus Crux group of the Sco-Cen association. The observations provide detailed information on the interplay between ISM phases in relation with the origin of the Local and Loop I bubbles.
Methods: We analyze interstellar components present along the line of sight by fitting multiple transitions from a group of species all at once. We identify four groups of species: (1) molecules (CO, CH, CH^+), (2) atoms (C i, S i, Fe i) with ionization potential lower than H i, (3) neutral and low-ionized states of atoms (Mg i, Mg ii, Mn ii, P ii, Ni ii, C ii, N i and O i) with ionization potential larger than H i and (4) highly-ionized atoms (Si iii, C iv, Si iv). The absorption spectra are complemented by H i, CO and C ii emission-line spectra, H2 column-densities derived from FUSE spectra, and IRAS images.
Results: Gas components of a wide range of temperatures and ionization states are detected along the line of sight. Most of the hydrogen column-density is in cold, diffuse, molecular gas at low LSR velocity. This gas is mixed with traces of warmer molecular gas traced by H2 in the J > 2 levels, in which the observed CH+ must be formed. We also identify three distinct components of warm gas at negative velocities down to -20 km s-1. The temperature and gas excitation are shown to increase with increasing velocity shift from the bulk of the gas. Hot gas at temperatures of several 105 K is detected in the most negative velocity component in the highly-ionized specie. This hot gas is also detected in very strong lines of less-ionized species (Mg ii, Si ii* and C ii^*) for which the bulk of the gas is cooler.
Conclusions: We relate the observational results to evidence for dynamical impact of the Sco-Cen stellar association on the nearby interstellar medium. We propose a scenario where the infrared cirrus cloud has been hit a few 105 yr ago by a supernova blast wave originating from the Lower Centaurus Crux group of the Sco-Cen association. The observations provide detailed information on the interplay between ISM phases in relation with the origin of the Local and Loop I bubbles.