Giant Star-Forming Regions

Transcription

1 University of Heidelberg, Center for Astronomy Dimitrios A. Gouliermis & Ralf S. Klessen Lecture #1 Introduction & Overview Introduction to HII Regions In this Lecture Motivation for this Course Schedule of the Course Literature Historic Overview Overview of Physical Properties Classification of HII Regions Examples of Giant SF Regions 2

2 Motivation for the Course Giant Star-Forming (HII) Regions are regions where stars form, so they contribute significantly to the stellar populations of galaxies host the majority of young stellar clusters and associations regions of hot interstellar matter, so they are the laboratories for ISM gas processes studies are signposts of interactions between stars & the ISM 3 (tentative) Schedule of the Course Lect. 1 Lect. 2 Lect. 3 Lect. 4 Lect. 5 Lect. 6 Lect. 7 Lect. 8 Lect. 9 Lect. 10 Lect. 11 Lect. 12 Lect Oct-2012 Course Overview Motivation for the Course/Schedule; Overview of Physical Processes in HII Regions; Classification of HII regions 26-Oct-2012 Introduction to the Physics of the ISM I Phases of the ISM; Transitions; Introduction to cooling mechanisms 2-Nov-2012 Introduction to the Physics of the ISM II Gas Cooling & Heating; Collisional Excitation; Photo-ionization; Photo-electric heating 9-Nov-2012 Interstellar Dust Absorption & Scattering by particles; Interstellar Extinction; Infrared Emission 16-Nov-2012 Physical Processes in HII Regions I Radiative Processes; Strömgren Theory; Photo-ionization & Recombination of hydrogen; Dust 23-Nov-2012 Physical Processes in HII Regions II Thermal Properties; Heating and Cooling of HII Regions; Forbidden lines and Line Diagnostics 30-Nov-2012 Photodissociation regions (PDR) Ionization & Energy Balance; Dissociation of Molecular Hydrogen; Structure; Observations 7-Dec-2012 Stellar Feedback Processes Dynamics of the ISM; Ionization fronts; Expansion of HII regions; Stellar Winds and Supernovas 14-Dec-2012 Stellar Content of HII Regions I Massive Stellar Evolution; Mass-Loss; Rotation; Binary interaction; Spectral features of OB stars; Runaway stars - Stellar Cluster dynamics 21-Dec-2012 Stellar Content of HII Regions II Pre--Main-Sequence (PMS) Stars; Young Stellar Systems; Stellar Initial Mass Function; Age determination & History 11-Jan-2012 Star Formation (SF) Isothermal shperes and Jeans mass; Molecular Cores collapse; Protostars 18-Jan-2012 Star Formation PMS Stellar Evolution/Contraction; Characteristics of T Tauri stars; Herbig Ae/Be Stars; Multiple SF 25-Jan-2012 Summary Gas, Dust and Stars: Members of one eco-system; Up-to-date material on Giant HII Regions 4

3 Literature Resources Interstellar Medium and HII Regions G. B. Rybicki & A. P. Lightman Radiative Processes in Astrophysics (John Wiley & Sons Inc. 1978, 2004) L. Spitzer Jr. Physical Processes in the Interstellar Medium (John Wiley & Sons Inc. 1978, 2004) A. G. G. M. Tielens The Physics and Chemistry of the Interstellar Medium (Cambridge 2005) B. Draine Physics of the Interstellar and Intergalactic medium (Princeston Series in Astrophysics 2011) D. Osterbrock & G. Farland Astrophysics of nebulae & Active Galactic Nuclei (Uni Science Books 2006) 5 Literature Resources Stars & Star Formation K. S. de Boer & W. Seggewiss Stars and Stellar Evolution (EDP Science 2008) S. W. Stahler and F. Palla The Formation of Stars (WILEY-VCH 2004) N. Schulz The Formation and Early Evolution of Stars (Springer 2005, 2012) P. Bodenheimer Principles of Star Formation (Springer Verlag 2012) 6

4 Milky way starscape taken from Paranal.(ESO)" 7 Milky way starscape taken from Paranal.(ESO)" 8

5 Milky way starscape taken from Paranal.(ESO)" 9 10

6 Multi-wavelength observations different wavelengths provide different information. astronomer use the full electromagnetic spectrum radio: interstellar gas (line emission -> velocity information) sub-mm range: dust (thermal emission) infrared & optical: stars x-rays stars (coronae), supernovae remnants (very hot gas) γ-rays: supernovae remnants (radioactive decay, e.g. 26 Al), compact objects, merging of neutron stars (γ-ray burst) Carina with HST

7 14 HH 901/902 in Carina with HST Orion Giant Star-Forming Nebula Cluster Regions (ESO VLT) 15 15

8 16 Trapezium stars in the center of the ONC (HST, Johnstone et al. 1998) strong feedback: UV radiation from Θ1C Orionis affects star formation on all cluster scales 17 Trapezium stars in the center of the ONC (HST, Johnstone et al. 1998)

9 Fly through Orion Nebula Cluster (NASA animation) 18 WS Lecture 1 NGC 602 in the LMC: Hubble Heritage Image

10 30 Doradus in LMC

11 Orion, NGC 3603, 30 Doradus (Zinnecker & Yorke 2007) comparison of size 22 Abundances, scaled to H atoms element atomic number abundance hydrogen H deuterium 1 H helium He carbon C nitrogen N 7 90 oxygen O neon Ne sodium Na 11 2 magnesium Mg aluminium Al 13 3 silicium Si sulfur S calcium Ca 20 2 iron Fe nickel Ni 28 2 Taurus hydrogen is by far the most abundant element (more than 90% in number). 23

12 ionization dissociation NGC 3329: Hubble Heritage Image NGC 3329: Hubble Heritage Image 24 A V HII HI H 2 density / column density increases A V denotes the extinction, the attenuation of radiation due to absorption (mostly on dust grains) 25

13 The multi-phase ISM 26 Historic Overview of HII Regions HII regions are Emission-Line Nebulae as opposed to 'diffuse nebulae with merely a continuum spectrum. The element Nebulium was postulated in 1864 by W. Huggins to explain strange emission lines. In1927 I. S. Bowen showed that these lines are coming from forbidden transitions at low densities. B. Strömgren in 1939 set the basis for understanding the physics of HII regions 27

14 Typical Emission Spectrum From Magrini et al. 2005, Astronomy & Astrophysics, Vol. 433, pp Overview of Physical Processes Extreme UV radiation from a star ionizes and heats the surrounding gas. Hydrogen can be ionized by photons more energetic than 13.6 ev (912 Å or Hz). Recombination of electrons with protons leads to neutralization. The balance between photo-ionization and radiative recombination determines the degree of ionization. 29

15 Atomic hydrogen emission spectrum 30 The Strömgren Theory NGC 602 in the LMC: Hubble Heritage Image NGC 3329: Hubble Heritage Image 31

16 Ionization Balance Densities Ionization n H : neutral H n p : proton n e : electron n = n p + n H : Total n p n e (H is neutral) N(ν): Photon intensity Recombination rate α H (ν): Ionization cross-section β A (Te): Recombination rate coefficient ν T : Threshold frequency α H (ν) ~ ν -3 β A (T e ) = <αv> 32 Ionization Balance Recombination is slow (~100 yr for ρ 10 3 cm 3 ), while e-e collisions occur on ~30 sec timescales. The excess energy over the ionization potential is carried away by the photo-electron as kinetic energy. Electrons collisions exchange energy leading to Maxwell velocity distribution (Thermal emission). Thermal electrons excite low-lying levels of trace species. Downward radiative transitions cool the nebula. This energy balance sets the temperature of the gas. 33

17 Classification of HII Regions From Franco, Kurtz & Garcia-Segura 2003, Reviews in Modern Astronomy, Vol. 16, pp

18 Peters et al. (2010a,b,c) 37 Peters et al. (2010a,b,c) Morphology of HII region depends on viewing angle 38

19 influence of B on disk evolution in disk around high-mass stars, fragmentation is reduced but rarely fully suppressed see Peters et al. (2011), Hennebelle et al. (2011), Seifried et al. (2011) Peters et al. (2011) 39 How a Giant HII Regions looks like Schematic of a Giant SF Region with a supper-bubble 40

20 41 Carina with HST (tentative) Schedule of the Course Lect. 1 Lect. 2 Lect. 3 Lect. 4 Lect. 5 Lect. 6 Lect. 7 Lect. 8 Lect. 9 Lect. 10 Lect. 11 Lect. 12 Lect Oct-2012 Course Overview Motivation for the Course/Schedule; Overview of Physical Processes in HII Regions; Classification of HII regions 26-Oct-2012 Introduction to the Physics of the ISM I Phases of the ISM; Transitions; Introduction to cooling mechanisms 2-Nov-2012 Introduction to the Physics of the ISM II Gas Cooling & Heating; Collisional Excitation; Photo-ionization; Photo-electric heating 9-Nov-2012 Interstellar Dust Absorption & Scattering by particles; Interstellar Extinction; Infrared Emission 16-Nov-2012 Physical Processes in HII Regions I Radiative Processes; Strömgren Theory; Photo-ionization & Recombination of hydrogen; Dust 23-Nov-2012 Physical Processes in HII Regions II Thermal Properties; Heating and Cooling of HII Regions; Forbidden lines and Line Diagnostics 30-Nov-2012 Photodissociation regions (PDR) Ionization & Energy Balance; Dissociation of Molecular Hydrogen; Structure; Observations 7-Dec-2012 Stellar Feedback Processes Dynamics of the ISM; Ionization fronts; Expansion of HII regions; Stellar Winds and Supernovas 14-Dec-2012 Stellar Content of HII Regions I Massive Stellar Evolution; Mass-Loss; Rotation; Binary interaction; Spectral features of OB stars; Runaway stars - Stellar Cluster dynamics 21-Dec-2012 Stellar Content of HII Regions II Pre--Main-Sequence (PMS) Stars; Young Stellar Systems; Stellar Initial Mass Function; Age determination & History 11-Jan-2012 Star Formation (SF) Isothermal shperes and Jeans mass; Molecular Cores collapse; Protostars 18-Jan-2012 Star Formation PMS Stellar Evolution/Contraction; Characteristics of T Tauri stars; Herbig Ae/Be Stars; Multiple SF 25-Jan-2012 Summary Gas, Dust and Stars: Members of one eco-system; Up-to-date material on Giant HII Regions 42