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Diffuse matter in the Universe: [Interplanetary medium] [Solar/Stellar neighborhood] InterStellar Medium (ISM) Milky Way and galaxies in general composition, physical conditions special locations (e.g. SFR) InterGalactic Medium (IGM) & IntraCluster Medium (ICM) origin, composition, physical conditions [The diffuse matter in the early Universe] Dopita & Sutherland: ''Astrophysics of the Diffuse Universe'', A&A Library, Springer Padmanabhan: '' Theoretical Astrophysics'', Vol I, Cambridge University Press Some info on the medium: it is mainly gas (atomic and/or molecular, often ionized), dust and DARK MATTER Condensed diffuse ISM ICM/IGM From Dopita & Sutherland: ISM in our and spiral galaxies (1): – disk distribution, with inhomogeneities – mostly gas and dust + DM. ISM in our and spiral galaxies (3): – – ISM in our and spiral galaxies (4): Multiwavelength image of the Spiral Galaxy Messier 101 Three color composite image of the nearby spiral galaxy M101. The green color represents emission from neutral hydrogen (HI), emitted at 21 cm. The HI observations are part of VLA The HI Nearby Galaxy Survey (THINGS) which is based at MPIA (image credit: Fabian Walter, MPIA). Blue shows UV emission due to recent (<108 yr) star formation as seen by the Galaxy Evolution Explorer (GALEX). Red indicates warm dust emission as traced by infrared emission at 24 microns as seen by SPITZER (image credit: Karl Gordon, Steward Observatory). ISM in our and spiral galaxies (4): Multiwavelength image of the Spiral Galaxy Messier 101 Three color composite image of the nearby spiral galaxy M101. The green color represents emission from neutral hydrogen (HI), emitted at 21 cm. The HI observations are part of VLA The HI Nearby Galaxy Survey (THINGS) which is based at MPIA (image credit: Fabian Walter, MPIA). Blue shows UV emission due to recent (<108 yr) star formation as seen by the Galaxy Evolution Explorer (GALEX). Red indicates warm dust emission as traced by infrared emission at 24 microns as seen by SPITZER (image credit: Karl Gordon, Steward Observatory). ISM in our and spiral galaxies (4): Left: optical image (HST) of M51 Right: CO(J 10) image of M51 Dust and molecular gas are projected on the same space, and trace the spiral structure of the galaxy. ISM in our and spiral galaxies (5): It accounts for about 510% of the total galaxy mass with higher fractions for the latest galaxy types. Its distribution/properties are function of distance from the galaxy center. HI (and dust) ISM in our and spiral galaxies (6): It may be converted into stars in particular locations (SFRegions) where cold molecular gas collapse; massive (proto)stars provide photons to ionize the debris, shocks are formed during the collapse ISM in our and spiral galaxies (7): Chemical composition: gas = H (90%), He(9%), ...(1%)[relative abundances: Cowie & Songaila ARAA1996, V. 24, p.499] Mg, Al, Na, K, Ca, Ti underabundant wrt the solar composition as atoms & molecules (cold) ions +electrons (hot) average number density = 1 cm3 quantum processes then line emission/absorption ~80% of the interstellar space filled with cold, high density atomic and molecular gas. denser clouds < 0.5% of space low density HI/H2 is in cold, mixed with other molecules (CO, HCN,NH3, H2O, CH3OH...) These regions may appear dark/luminous, depending on the observing wavelength (radio to the Xrays), physical condition (SFR, SNR, GMC, RN,...) and chemical composition ISM in our and spiral galaxies(8): Chemical composition(2): dust = graphite, silicates, olivine,... (~1% of the total ISM mass) temperatures in the range 30 to 100 K small sizes (few µm) effective absorber (v dependent reddening) of radiation with λ < of their typical size reradiates as a black body (bulk at IR wavelengths) fundamental for molecule formation molecules = in GMC, emit/absorb in the mm/submm range as a consequence of rotovibrational transitions (optical in electronic transitions) ISM phases: summary Hot Ionized Medium (HIM) [T= 106 ~ 107 K]: Warm Ionized Medium (WIM) [T ~ 104 K]: Warm Neutral Medium (WNM) [T= 100 ~ 10000 K]: Cold Neutral Medium (CNM) [T= 10 ~ 100 K]: ISM phases(1) temperature and density define the status of the ISM: Hot Ionized Medium (HIM) [T > 106 to 107 K]: ISM heated by shocks originated in SN esplosions. Initial cooling mainly via bremsstrahlung. Secondary process (at a later epoch): recombination (line emission from freebound transitions in the soft Xrays [CIV, OVI], boundbound in the optical [H, He,C, O]) (in SNR also synchrotron radio emission from freshly accelerated electrons) ISM phases(1bis): Hot Ionized Medium (HIM) [T > 106 to 107 K] in our galaxy: ROSAT allsky (soft) Xrays (0.12.2 keV), after removing point sources (from Snowden et al. 1997) ISM phases(2): Bok's globules in IC2944 Warm Ionized Medium (WIM) [T ~ 104 K]: – Around massive and hot stars (OB) capable of strong UV emission (also around galactic centres, where the UV radiation field is strong). OB associations are very often found in SFR (e.g. Orion). – Equilibrium between photo – ionization and recombination [T ~ 104 K] – Bremsstrahlung + line emission mainly of H and O [HII regions] – detectable via optical (line) and radio/IR/submm (bremsstrahlung continuum) ISM phases(3) Warm Neutral Medium (WNM) [T ~103 to 104 K]: low densities (0.1 cm3), mainly atomic H (HI) heated by diffuse UV and/or Xray radiation interaction of low energy Cosmic Rays detected via absorption of 21cm radiation (1) (opacity) ISM phases(3): Warm Neutral Medium (WNM) in spirals detected via emission of 21cm radiation (2) ISM phases(3) Herschel view of the Orion Nebula (FIR spectroscopy 160630 m) ISM phases(4) Cold Neutral Medium (CNM) [T= 10 ~ 100 K]: Neutral atomic hydrogen HI (densities 1 to 10 cm3, T= 100 K), often distributed on regions larger that those with stars Molecular hydrogen H2 (densities > 103 cm3, T= 10 K) CO,other molecules, in SFR (spiral arms and where interaction condensed matter) Revealed by mm/submm/radio observations (generally line emission) from Dame, Hartmann, & Thaddeus 2001 ISM phases: Cold Neutral Medium (CNM) in M31 ISM phases: Cold Neutral Medium (CNM) in M31 (with rotation curve info!) ISM phases: Cold Neutral Medium (CNM) in 3C31 q ISM phases: summary Hot Ionized Medium (HIM) [T= 106 ~ 107 K]: Warm Ionized Medium (WIM) [T ~ 104 K]: Warm Neutral Medium (WNM) [T= 100 ~ 10000 K]: Cold Neutral Medium (CNM) [T= 10 ~ 100 K]: ISM detectability we define the “Emission Measure” E.M. representing the amount of radiation emerging from a region (cloud) E.M.=∫ n2e dl which is usually averaged over the region of interest, with size l E.M.= 〈 ne 〉2 l Examples: Nova shell ejected from a WD when it becomes optically thin: ne ~ 107 cm3 ; l ~ 105 pc then E.M. ~ 109 pc cm6 Planetary nebula (ionized envelope of a dying star [from RG to WD]) ne ~ 104 cm3 ; l ~ 101 pc then E.M. ~ 107 pc cm6 HII region ne ~ 10 cm3 ; l ~ 102 pc then E.M. ~ 104 pc cm6 Diffuse (ionized) ISM ne ~ 0.1 cm3 ; l ~ 103 pc then E.M. ~ 10 pc cm6 The ISM planetary nebulae ISM in elliptical and irregular galaxies Earlytypes (elliptical galaxies) are known to posses much less gas and dust than latetypes (spiral galaxies) – result of formation process (?) – low star formation rates – different origin of ISM matter (from stellar mass loss: i.e. winds and SN explosions) – metal enrichment via stellar evolution In Irregulars the fraction of total mass in gas is higher than in spirals and ellipticals and the SFR is high (per unit mass). General consequence con “colors”: Ellipticals are generally redder than spirals Irregulars (and dwarfs) are bluer than spirals Large scale environment have strong influence on gas/dust content in galaxies (e.g. isolated – groups – clusters) The ISM in irregular galaxies Sextant A Ngc1427A The intergalactic medium(IGM / ICM): very hot (107108) and sparse The intergalactic medium(IGM / ICM): very hot (107108) and sparse The intergalactic medium(IGM / ICM): very hot (107108) and sparse nonthermal plasma (contours) synchrotron emission cluster wide H field shock acceleration at cluster periphery thermal plasma (colors) elliptical shape ⇨ unrelaxed no counterpart to the SE extended radio emission Brunetti et al. 2009, Nature End of description of the ISM (and ICM) ATOMIC (molecular) SPECTRA Atomic spectra basic concepts Energy levels as according to quantum mechanics “orbits” correspond to different energies Radiative process (emission/absorption) during quantum transition must obey to firm selection rules Ground (fundamental) state as minimum electron energy also defines the ionization energy (e.g. for H atom 13.6 eV [UV photons]) Atomic spectra basic concepts (2) Quantum numbers: n – main number 1,2,3,.... defines the energy and the size of the “orbit” 2 n an = ao ao = 0.53 A Z l – azimutal number (angular momentum, related to eccentricity) 0,1,2,..., n1 l 1 b 2 1 − e = = ≤1 n a m – magnetic number (orbit orientation in case of magnetic field) l,l+1,...,0,...l1,l at a given main number (n), there is a tiny difference in energy between levels with different combination of l,m this is not true (first order) for hydrogen, where there is a high degree of energy degeneracy (fine structure) further extremely small energy structures (hyperfine structure) can be defined by the spin number – s (±1/2) contrary to classical theory of charges in motion, the electrons do not radiate in their curved orbits, except during a “transition” Atomic spectra basic concepts (3) Hydrogen: easiest example to study lines between various energy levels: if RH is Rydberg constant, the frequency v of a photon emitted/absorbed during a transition between two levels m and n is 2 RH nm = = c RH 4 2 e m e 3 h c 1 m2 − 1 n2 = 1.1⋅10 cm− 1 Hz 5 ; n m 0 ⇒ with increasing n, lines get closer to a limiting frequency v=cRH/m2 ⇒ if m is large, lines of different series start at very close frequencies and produce a spectrum similar to a continuum emission (but it is not!) [hydrogenlike atoms – He+, Li++, Be+++ – are obtained attributing the energy En at each “level”] En = − Z 2 R H hc n 2 n ,l Atomic spectra basic concepts (3b) Hydrogen transitions in terms of energy: Ry hmn = = 22 e4 me 2 h c Ry 1 n2 − = 13.6 eV 1 m2 eV called 1 Rydberg ; m n 0 For a given pair of quantum numbers, decay and excitation can either produce (emission) or cancel (absorption) photons at the appropriate frequency/energy Atomic spectra Hydrogen transitions obey to well known selection rules: n, l, m, Atomic spectra Hydrogen: Grotrian diagrams UV, visible, IR Atomic spectra Hydrogen: main series Atomic spectra Hydrogen at visual wavelengths 397 434 486 656 410 Atomic spectra typical spectra of stars for an extremely detailed spectrum of the sun see http://chinook.kpc.alaska.edu/~ifafv/lecture/fraunhofer.htm Molecular spectra(1): Molecules have 3–D structures capable to oscillate around the equilibrium distance, and may also change their rotation axis/velocity moving through energy levels defined by quantum mechanics electronic (~eV energies, optical) Electrons in individual atoms may move to a different energy level vibrational (~0.1 – 0.01 eV, IR) n is the vibrational quantum number 2 2 ho 1 1 E n= n ho − n 2 2 4De 2 ho E n1 − E n = ho − n 1 2De With the quantum harmonic oscillator, the energy between adjacent levels is constant, hv0. With the Morse potential, the energy between adjacent levels decreases with increasing n as is seen in nature. It fails at the value of n where En+1 − En is calculated to be zero or negative. The Morse potential is a good approximation for the vibrational fine structure at n values below this limit. Molecular spectra (2): rotational (~meV, submm, mm & cm wavelengths) rotational levels lie within vibrational levels The rotational quantum number J is related to the moment of inertia I, to the distance r and to the rotational energy Erot: 2 J J 1 = 2 8 I r E rot 2 h I = m1 r 21 m2 r 22 Molecular spectrum: rotatiotal transitions Molecular spectrum: NIR & MIR, from vibrational transitions