* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Lecture 1
Survey
Document related concepts
Microplasma wikipedia , lookup
Indian Institute of Astrophysics wikipedia , lookup
Cosmic distance ladder wikipedia , lookup
Leibniz Institute for Astrophysics Potsdam wikipedia , lookup
Health threat from cosmic rays wikipedia , lookup
Gravitational lens wikipedia , lookup
Nucleosynthesis wikipedia , lookup
Planetary nebula wikipedia , lookup
Chronology of the universe wikipedia , lookup
Advanced Composition Explorer wikipedia , lookup
Cosmic microwave background wikipedia , lookup
Outer space wikipedia , lookup
Heliosphere wikipedia , lookup
H II region wikipedia , lookup
Astronomical spectroscopy wikipedia , lookup
Transcript
Lecture I History. Components of the ISM and pressure equilibrium. • What is the interstellar medium (ISM) • Why is the ISM important and interesting to study? • The discovery history of the interstellar medium (ISM) • An overview of the different components and gas phases that make up the ISM What is the ISM? • The ISM is the (baryonic) ’stuff’ between the stars, i.e. gas and dust. • It is NOT a single entity: its properties (i.e. density, temperature, kinematics and chemical abundances) vary greatly from place to place • http://www.eso.org/public/images/ eso0650a/zoomable/ Useful Units • pc = parsec = 206265AU = 3.086×1018cm • M⊙ = solar mass = 1.989×1030kg • L⊙ = solar luminosity =1.989×1033erg s-1 • eV = 1.602×10-12erg • Å = 10-8cm • Jansky = 10-23erg s-1 cm-2 Hz-1 What is the ISM? 12CO J=1-0 10 pc Extended ~ 10 pc scales low density ~ 102-103cm-3 1 kpc What is the ISM? 20 μm 10 pc 1 kpc What is the ISM? CS J=2-1 10 pc Compact ~ pc scales 4 6 -3 High density ~10 -10 cm 1 kpc What is the ISM? Critical density: The CO ladder spans the full density regime encountered in the molecular ISM CS(2-1) HCO+(1-0) Why is it important? • The Cosmic Blueprint Why is it important? • Galaxy formation and evolution Why is it important? • Galaxy formation and evolution Why is it important? IC 342 HI (atomic gas) THINGS 1 kpc Why is it important? IC 342 HI (atomic gas) THINGS 12CO J=1-0 (molecular gas) NRAO 12m 1 kpc Why is it important? IC 342 HI (atomic gas) THINGS 12CO J=1-0 (molecular gas) NRAO 12m Spitzer 70um IR emission (star formation) 1 kpc Historical Highlights ca. 1800: German/British astronomer William Herschel makes catalogue of bright patches in the sky, calls them ’nebulae’. Also discovered IR light. ca. 1860-1900: Margaret Lindsay (‘Herschel of the spectroscope’) and William Huggins, Irish/ English astronomer couple. Pioneers in the field of spectroscopy. William the first to take a spectrum of a planetary nebula (NGC6543). Noted that some bright patches (like the Orion Nebula) had pure emission spectra characteristic of gas while others (like the Andromeda Galaxy) had spectra reminiscent to that of stars. 1904: Discovery of the ISM by German astronomer Johannes F. Har tmann who noticed stationary CaII lines in the spectrum of the spectroscopic binary Ự Ori. Unclear whether the material is truly interstellar or circumstellar. 1919: Edward E Barnard (‘The man who never slept’), American astronomer. Made first catalogue of ‘dark nebulae’. Holes in the stellar distribution or obscuring dark matter? Historical Highlights 1913: Discovery of ‘Höhenstrahlung’ by Victor Hess, German Austrian physicist, using balloon born experiements. Shows that they cannot come from the Sun. 1927: ‘Höhenstrahlung’ is shown to be high energy charged particles by Dutch physicist J. Clay. Denoted Cosmic Rays. 1950s: Cosmic rays are shown to be heavy particles, i.e., protons and ử-particles. Post 1960: There are two types of cosmic rays: 1) Galactic Cosmic Rays (GCRs) and 2) Solar energetic particles (mainly protons). Normally ‘Cosmic Rays’ refers only to GCRs. The likely sources of GCRs are supernovae, active galactic nuclei, quasars and gamma ray bursts. So can originate in the Milky Way or even in other galaxies. We talk about primary (protons, ử-particles) and secondary (neutrons, pions, positrons, and muons) cosmic rays. Historical Highlights 1922: First observations of diffuse interstellar bands (DIBs) by American astronomer Mary Lea Heger (while graduate student at Lick Observatory!). 1934: Paul Merrill discovers many more DIBs and show unequivocally that their origin is interstellar. More than 250 DIBs known today. 1930: Rober Trumpler finds that the linear sizes of open clusters are systematically overestimated with distance, thus proving the existence of interstellar extinction by dust. 1933: Plaskett & Pearce finds that the CaII absorption line is stronger towards more distant stars, and concludes the absorption must be interstellar 1937-40: Discovery of the first interstellar molecule (CH) by Swings & Rosenfeld. This was based on optical spectra obtained by Dunham and Adams towards Oph. Historical Highlights 1944: “Henk” van der Hulst (while a student in Utrecht) predicts the existence of the 21cm hyperfine structure line of neutral interstellar hydrogen. 1949: Hall & Hiltner find a correlation between the polarisation of starlight and reddening, which is evidence of aligned dust grains and thus magnetic fields. 1953-57: Shklovsky suggests that the Crab nebula is powered by synchrotron radiation. Confirmed the following year by Russian astronomers. Searches for Zeeman splitting of the 21cm line suggested by Bolton & Wild. 1951: Detection of 21cm line by Ewen & Purcell using home-build radio detector. Beat Oort & Muller to it. HI is seen everywhere in the sky. 1954: First maps of the HI distribution in the Milky Way by Hulst, Muller & Oort. The Galactic disk is estimated to contain 5ₒ109M⊙ of atomic gas (ca. 10% of the entire mass of the disk). Average density <n> ≈ 1cm-3. Historical Highlights 1960-70s: First radio detections of interstellar molecules, pioneered by C. H. Townes. Interstellar OH masers discovered by Weinreb et al. (1963). First detection of polyatomic molecules (NH3) in space (Cheung 1968). Millimetre observations of the Orion Nebula leads to the first detection of CO J=1-0 in space (Wilson, Jefferts & Penzias 1970). CO is found to be an abundant constituent of the interstellar medium in the Galaxy (Zuckerman & Palmer 1974). 1973: George Carruthers, inventor of UV the camera and spectrograph, detects UV lines of H2 using sounding rockets to fly detectors above the Earths atmosphere. Incontrovertible proof that H2 exists in the interstellar medium. 1975: First extragalactic detection of CO at millimetre wavelengths using the 36feet NRAO telescope on Kitt Peak (Rickard et al. 1975). 1970-80s: First maps of the Galactic distribution of CO. A picture of the molecular versus atomic gas distribution in the Galaxy emerges. Historical Highlights 1983: The Infrared Astronomical Satellite (IRAS). First ever space-born observatory to carry out an all-sky survey at IR wavelengths. UK, US, NL mission. IRAS all-sky map Full sky survey at 12, 60, 100μm Groundbreaking observations of cirrus clouds, dust properties and the Milky Way’s core Discovered a dust disk around Vega, possibly proto planetary system. Discovered a new population of dustenshrouded IR-luminous galaxies 1990-91: Cosmic Background Explorer (COBE). NASA mission which mapped the temperature and temperature anisotropies of the cosmic microwave background. Also produced maps the CO, [NII], and [CII] emission distribution in our Galaxy. 1995-98: Infrared Space Observatory (ISO). An ESA/JAXA/NASA mission designed to study the Universe at 2.5-40μm. With its spectroscopic capableties in the mid- and far-IR, ISO sheds new light on: The nature and composition of grains (silicates and ices) and PAHs H2 lines as probes of shocks and photodissociation regions IR dark clouds The excitation of gas in starburst galaxies and active galactic nuclei in the local universe ISO Antennae Galaxies ISO: 15μm (red)+ 7μm (blue) image Optical COBE All-sky Maps in [CII]158 and [NII]205 Historical Highlights SWAS 13CO J=1-0 and 5-4, and [CI]609μm maps of Orion A 1998-2006: The Submillimetre Wave Astronomy Satellite (SWAS) and ODIN. Pointed observations of H2O, H218O, O2, CI and 13CO lead to new insight into chemistry, composition and collapse of star forming clouds. 2007: Launch of Far-Ultraviolet Space Explore (FUSE). 2003-now: Spitzer Space Telescope Car ries three instr uments: IRAC, IRS and MIPS. M u c h h i g h e r s e n s i t i v i t y, mapping speed than ISO and much higher angular resolution than IRAS. First large scale FIR maps of clouds at high angular resolution Leads to a revolution in our ability to study gas and dust in n e a r b y a s we l l a s d i s t a n t galaxies Uncovers tens of thousands of distant dust obscured galaxies IRS spectra of nearby IR-luminous galaxies IRAC image (red) of nearby galaxy Historical Highlights 2009-2013: Herschel Space Observatory. Highly successful ESA mission. Was co-launched with Planck. A quantum leap forward in far-IR and sub millimetre studies of gas and dust in our own galaxy as well as in other galaxies - from our cosmic backyard to the edge of the observable universe Left behind an astounding data archive much of which is still not fully explored 2011-now: The Atacama Large Millimeter/sub-millmeter Array. A groundbreaking facility: 56 submillimeter antennase working in unison as an interferometer Continuous coverage from 83GHz to 1000GHz Very high spectral resolution: 0.1km/s Very high angular resolution: down to 0.01” Small instantaneous field of view: 10-20”