part3 - Importance of the Interstellar Medium Gas has...

Info iconThis preview shows pages 1–6. Sign up to view the full content.

View Full Document Right Arrow Icon
Importance of the Interstellar Medium I Role in the star/gas cycle I facilitates ongoing star formation I repository for element buildup; integral for chemical evolution I Gas can cool, so its collapse is dissipational I Hot gas cold gas stars I Star formation cools spiral disks, leading to arm formation I Gas migrates inwards in the gravitational potential I Galactic disks are smaller than dark matter halos I Galaxies have steep density gradients I Galactic nuclei have high densities, including massive black holes I Gas has important diagnostic properties I Doppler effect reveals dynamics of Galaxy I Abundances show chemical evolution I Physical conditions can be found I Some emission lines are seen at cosmological distances I High-redshift absorption lines reveal galaxy birth & evolution I Can dominate the integrated spectral energy distribution I Dust: mid-IR to sub-mm I Hot ISM phase (and X-ray binaries): soft X-rays I HII regions and relativistic plasmas: cm-radio I Some emission lines (Ly α , [CII]) are major coolants J.M. Lattimer AST 346, Galaxies, Part 3
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Activity in the Interstellar Medium I ISM energized by stars I UV light ionizes atoms, dissociates molecules I photoelectric effect heats gas I SN shocks heat, ionize and accelerate gas I ISM is inhomogeneous with phases I Hot/warm/cold phases with similar pressures ( P = nkT 1 eV cm - 3 ) I Cloud and intercloud media with huge density contrasts (10 2 - 10 5 ) I Mass and metallicity exchange between phases I Cooling: hot warm cold stars I SN accelerate gas and rearrange phases (bubbles and fountains out of disk) I Tidal encounters and resulting starbursts I create bubbles I cycle gas into halos I convert spirals into ellipticals I Global distribution of ISM I colder phases confined closely to plane I hotter and turbulent phases are thicker I ISM in disk is thin at small radii and flares at large radii I ISM is locally complex I SN create superbubbles I between bubbles are cold, dense sheets I Equipartition in the ISM I Energy densities of all three gas phases, starlight, magnetic fields and cosmic rays are each 1 eV cm - 3 . J.M. Lattimer AST 346, Galaxies, Part 3
Background image of page 2
Structures in the Interstellar Medium I HII regions I Reflection nebulae I Dark nebulae I Photodissociation regions I Supernova remnants J.M. Lattimer AST 346, Galaxies, Part 3
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
HII Regions I Ionized H regions formed by O and B0-B1 stars with an abundance of photons with λ < 912 ˚ A . I n H 10 - 10 4 cm - 3 I T 10 4 K I Total mass 5 × 10 7 M ± I R 0 . 5 - 10 pc I Optical spectra dominated by H and He recombination and [OII], [OIII] and [NII] lines. I Strong sources of free-free radio emission and thermal emission from warm dust. I Signposts of massive star formation. NASA Richard Crisp J.M. Lattimer AST 346, Galaxies, Part 3
Background image of page 4
Reflection Nebulae I Bluish dusty nebulae reflect light of nearby stars later than B1.
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 6
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 01/25/2012 for the course AST 346 taught by Professor Lattimer during the Spring '11 term at SUNY Stony Brook.

Page1 / 52

part3 - Importance of the Interstellar Medium Gas has...

This preview shows document pages 1 - 6. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online