HI column density statistics of the cold neutral medium from absorption studies
arXiv:1911.09396 · doi:10.1093/mnras/stz3148
Abstract
Physical properties of the tiny scale structures in the cold neutral medium (CNM) of galaxies is a long-standing puzzle. Only a few lines of sights in our Galaxy have been studies with mixed results on the scale-invariant properties of such structures. Moreover, since these studies measure the variation of neutral hydrogen optical depth, they do not directly constrain the density structures. In this letter, we investigate the possibility of measuring the properties of density and spin temperature structures of the \HI from absorption studies of \HI. Our calculations show that irrespective of the thermal properties of the clouds, the scale structure of the \HI column density can be estimated, whereas, \HI absorption studies alone cannot shed much light on either the amplitude of the density fluctuations and their temperature structures. Detailed methodology and calculations with some fiducial examples are presented.
arXiv comment6 pages, 4 figures
References in corpus (25)
- THINGS: The HI Nearby Galaxy Survey
- Interstellar Turbulence I: Observations and Processes
- Velocity Modification of HI Power Spectrum
- Velocity Modification of Power Spectrum from Absorbing Medium
- Power Spectrum of the density of cold atomic gas in the Galaxy towards Cas A and Cygnus A
- The Small-scale Structure in Interstellar HI: A Resolvable Puzzle
- GHIGLS: HI mapping at intermediate Galactic latitude using the Green Bank Telescope
- The impact of stellar feedback on the density and velocity structure of the interstellar medium
- Probing interstellar turbulence in cirrus with deep optical imaging: no sign of energy dissipation at 0.01 pc scale
- The Turbulence Power Spectrum in Optically Thick Interstellar Clouds
- The Structure of the Cold Neutral ISM on 10-100 Astronomical Unit Scales
- Measuring the Alfvenic Nature of the Interstellar Medium: Velocity Anisotropy Revisited
- Atomic and Ionized Microstructures in the Diffuse Interstellar Medium
- The Scale Height of NGC 1058 Measured from its HI Power Spectrum
- Spatial and Temporal Variations in Small-Scale Galactic HI Structure Toward 3C~138
- Study of velocity centroids based on the theory of fluctuations in position-position-velocity space
- Multi-epoch HI line measurements of 4 southern pulsars
- Probing interstellar turbulence in spiral galaxies using HI power spectrum analysis
- HI anisotropies associated with radio-polarimetric filaments. Steep power spectra associated with cold gas
- HI 21 cm opacity fluctuations power spectra towards Cassiopeia A
- Tiny scale opacity fluctuations from VLBA, MERLIN and VLA observations of HI absorption toward 3C 138
- The \HI column density power spectrum of six nearby spiral galaxies
- The structure function of Galactic \HI opacity fluctuations on AU scales based on MERLIN, VLA and VLBA data
- Visibility moments and power spectrum of turbulence velocity
- A High Resolution Study of Carbon Radio Recombination Lines towards Cassiopeia A