A Historical Perspec ve on the Interstellar Medium
John Dickey University of Tasmania
IAU GA XXVIII -- SpS 12 27 August 2012
Pre-modern Era: late 1800's – 1950:
Herschel's lists of light and dark nebulae were reobserved and photographed, some were analysed as HII regions.
General obscura on and reddening of distant -1 stars were measured: Av kpc . and dust cloud sizes and numbers were determined.
Spectral lines including molecular lines were detected from interstellar clouds. Barnard 1903 Ap. J. 17, 77. Barnard 1903 Ap. J. 17, 77. Barnards Loop (Orion) by Drew Sullivan, APOD 2009-02-24 Johannes Hartmann 1904 Ap. J. 19, 268 Detec on of Ca absorp on lines with a constant radial velocity very different from the changing velocity of the background star, δ Orionis, a binary system. Comstock, G.C. 1904, A.J. 24, 139. Washburn Obs., Univ. Wisconsin Kapteyn, J. C. 1909, Ap. J. 29, 46.
Jacobus Kapteyn Groningen Univ.
m Kapteyn's result: AV = 0.016 / 10 pc m -1 modern value: AV = 1.8 kpc Shapley, H. 1918 PASP 30, 42. Shapley, H. 1918 PASP 30, 42. Trumpler 1930 PASP 42, 214. Viktor Ambartsumian
On the Radia ve Equilibrium of a Planetary Nebula 1932 MNRAS 93, 50.
late 1930's work: Tracing interstellar clouds through obscura on – varying star density. background: Barnard 68 FORS Team VLT APOD 2012-01-12 Ambartsumian, V. Reviews of Modern Physics 30, 944 (1958). NGC 6823 from the CFHT (astronomy picture of the day 2004-10-4) Ap.J. 112, 380 (1950) Equilibrium between ioniza on and recombina on sets the radius of the ionized region around an O star. 1939 Ap. J. 89, 526. from StrÖmgren's memoir 1983 ARAA 21, 1.
IC 1396 POSS II composite by Davide De Mar n APOD 2005-09-08 Dunham 1937 PASP 49, 26. Stellar absorp on lines 1949 Ap. J. 109, 354. from molecules CH, CH+, and CN compared with Ca H and K lines
Note: Adams was following up detec ons from 1936 by Beals (DAO). 1952, BAIN 11, 459. Early Modern Era: late 1951 – 1977:
21-cm line maps show en re Milky Way ISM extent and velocity field.
Molecular lines show GMC distribu on.
ISM temperatures determined and explained.
Galac c Halo proposed, coronal gas detected.
SNR effects on the ISM studied and incorporated.
background Crab Nebula Hale 200" telescope David Kaplan van de Hulst, Muller, and Oort 1954 BAIN 12, 117. Longitude-velocity diagram of the 21- cm line as measured with the Kootwijk dish 1952-53.
Spectral line predicted by van de Hulst (1945), detected nearly simultaneously in 1951 by Ewen & Purcell, Muller & Oort,and Pawsey. Oort, Kerr, & Westerhout, 1958 MNRAS 118, 3790. Oort, Kerr, & Westerhout, 1958 MNRAS 118, 3790. Spitzer 1956, Ap. J. 124, 20. Clark, B.G. 1965 Ap. J. 142, 1398.
Absorp on in the 21-cm line spectra taken with a spectral line system on the Owens Valley interferometer.
The striking difference between the widths of the emission and absorp on lines shows that the atomic gas is in two thermal phases with very different temperatures. Field, Goldsmith & Habing 1969, Ap. J. 155, 149.
Dalgarno & McCray 1972 ARAA 10, 375 Gould & Salpeter 1963, Ap. J. 138, 393.
H2 detected by Copernicus satellite (Carruthers 1970 Ap J Le . 161, L81) Parker 1966, Ap. J. 145, 811. Barre , Meeks, & Weinreb 1964, Astron. J. 69, 134.
Detec on of the OH molecule in absorp on at 1667 MHz using an autocorrela on spectrometer. 1970, Ap. J. 141, L43 1983 Highlights of Astronomy 6, 681. all sky maps of so x-rays
130 eV - 188 eV
160 eV - 284 eV Data from the Copernicus orbi ng uv-observatory. background simeis 147 by Nobuhiko Miki
Recent Years (1978 – today) themes:
Disk-Halo Connec on (super-shells and chimneys)
Magneto-ionic Turbulence Tracers and theory
Dust temperatures and PAH emission (IRAS – Herschel)
Tiny Scale Structure (VLBA)
Star Forma on in Ac on (HST – ALMA) background: Herschel's Cyg X (Hennemann and Mo e) APOD 2012-05-17
Conclusions: • We stand on the shoulders of giants. • At any given me, some of the facts are wrong. • Scien sts' most important work is some mes an aside. Tarantula Nebula 30 Dor from the Hubble Space Telescope