Radiation Fundamentals and Atomic and Molecular Clouds: (Single-Dish Observations) Youngung Lee Korea Astronomy and Space Science Institute

Size: px

Start display at page:

Download "Radiation Fundamentals and Atomic and Molecular Clouds: (Single-Dish Observations) Youngung Lee Korea Astronomy and Space Science Institute"

Hubert Ross
5 years ago
Views:

1 Radiation Fundamentals and Atomic and Molecular Clouds: (Single-Dish Observations) Youngung Lee Korea Astronomy and Space Science Institute

2 Contents 2

3 EMR emission mechanism Thermal emission blackbody radiation (continuum) free-free or bremstrahlung (continuum) Spectrum lines from atoms or molecules from HI; Lyman/Balmer/Paschen HI 21cm Non-thermal emission Synchrontron CO 2.6mm Gyrosynchrotron Maser

Black Body Radiation A black body is an idealized physical body

Bν = kt 2hv ( T ) hν / e 1200C 2 / c 1 temperature) emits

4 Black Body Radiation A black body is an idealized physical body that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence. A black body in thermal equilibrium (that is, 3at a 1000C constant Bν = kt 2hv ( T ) hν / e 1200C 2 / c 1 temperature) emits electromagnetic radiation called 525C black-body radiation. The radiation is emitted according to Planck's law, 200C

6 Wiens law

8 Free-free (bremstrahlung) EMR produced by the deceleration of a charged particle when deflected by another charged particle (in plasma) thermal 8

9 Synchrotron radiation EMR emitted when charged particles are accelerated radially Non-thermal 9

10 Gyrosynchrotron - Pulsar Non-thermal 10

11 Maser Non-thermal microwave amplification by stimulated emission of radiation 11

12 Black Body Radiation Planck showed using quantum mechanics that a black body would emit radiation of the form: radio B ν 2hv ( T ) hν / e 3 = kt 2 / c 1 Many stellar sources can usefully be approximated to be black bodies: hν kt >>1 hν <<1 kt B ( T ) ν 2hv 3 = hν / kt e 2 Wien s Approximation c 2 v B ( 2 T ) = ν 2 c kt thermal Rayleigh-Jeans Law 12

13 Spectrum lines from atoms or molecules thermal from HI; Lyman/Balmer/Paschen Later I ll talk about two spectral lines HI 21cm CO 2.6mm

14 Radiation Fundamentals: Specific intensity Flux density Luminosity Temperature(brightness)

15 Brightness and Flux Density Astronomers wants to measure the strength of radiation of a source as a function of direction on the sky and frequency. Needs some definitions Definition of specific intensity comes from the fact The number of photons falling on the plate per unit area per unit time per unit solid angle does not depend on the distance between the source and the observer. Brightness!!!

16 Specific Intensity (brightness, spectral radiance)??? dσ θ dω Infinitesimal surface area of a detector the angle between a "ray" of radiation and the normal to the surface Infinitesimal solid observer s position

17 Energy/time = Power

18 Specific Intensity (brightness) [W m -2 Hz -1 sr -1 ]

19 Specific Intensity (brightness, spectral radiance) dσ θ dω Infinitesimal surface area of a detector the angle between a "ray" of radiation and the normal to the surface Infinitesimal solid observer s position

20 Specific intensity is invariable Total Intensity [W m -2 sr -1 ]

21 Specific Intensity is not dependent on distance. But what about the flux density???

22 Flux density If a source is discrete, meaning that it subtends a well-defined solid angle, the spectral power received by a detector of unit projected area is called the source Flux Density for small angle

23 Flux density unit d = infinitesimal surface area (e.g., of a detector) [W [W m -2 mhz -2-1 Hz ster -1 ] -1 ] = the angle between a "ray" of radiation and the normal to the surface d d = infinitesimal solid angle measured at the observer's location [W Hz -1 ] Luminosity [W]

Example Sun s luminosity = how many light bulbs of 100W? Answer: Sun s luminosity = 3.83x10 33 erg/sec = 3.83 x 10 26 W Thus, sun = 3.

24 Example Sun s luminosity = how many light bulbs of 100W? Answer: Sun s luminosity = 3.83x10 33 erg/sec = 3.83 x W Thus, sun = 3.83 x W-lightbulbs!!!! Homework: Assume that you are emitting all the energy 100% you are eating in everyday life, so of 3000 Kcal. Estimate your emitting power.

25 Example 2 Sun at 10GHz, T=5800K??? Calculate the specific intensity and luminosity

26 Example sun at 10GHz, T=5800K

27 Radiative Transfer Specific Intensity will change when radiation is absorbed or emitted, and this change of specific intensity is described by the equation of transfer.

28 Radiative Transfer Absorption coeff Emission coeff Equation of transfer

29 Radiative Transfer Absorption coeff [m -1 ] Emissivity [W m -3 Hz -1 ster -1 ]

30 Radiative Transfer

31 Radiative Transfer 3) Thermodynamic equilibrium (TE): If there is complete equilibrium of the radiation with its surroundings, the brightness distribution is described by the Planck function Kirchoff s law in TE

32 Absorption coeff to Optical depth [no unit]

33 partial integration;

34 for large optical depth

35 Black Body Radiation Planck showed using quantum mechanics that a black body would emit radiation of the form: intensity (power) radio B ν 2hv ( T ) hν / e 3 = kt 2 / c 1 Many stellar sources can usefully be approximated to be black bodies: hν kt >>1 hν <<1 kt B ν ( T ) 2hv c 3 = hν / kt e 2 Wien s Approximation 2 v Bν ( T ) = 2 cλ 2 kt temp (wavelength)freq Rayleigh-Jeans Law 36

36 Brightness Temperature (for cm, mm)

37 Practical Observations: 2 HI and H 2 Tb = λ Iν k 2 Clouds

38 Radio emission objects HI Atomic Cloud (21cm) Molecular Cloud (mm) Pulsar Outflow Disk, Jet Circumstellar Envelope Radio Galaxy, Quasar etc 39

39 T on T sky = T b beamsize

40 B68 12 CO

41 Doppler Shift line broadening Observed Spectrum 선폭변화 1.5 redshift blueshift Intensity broadening Doppler effect "Velocity"

42 Composition of the ISM Hydrogen is by far the most common element in the ISM Neutral (HI) Ionized (HII) Molecular (H 2 )

43 HI Cloud Van de Hulst (1944) predicted HI 21cm After WW II, HI observations toward the Galactic Plane started using radar antenna

44 HI 21cm emission (the most famous spectral line) Once per 10M yrs Spin flip 21cm (1.42 GHz)

45 Each HI cloud along a particular line of sight will be moving at a slightly different speed relative to us, meaning that the 21cm radiation emitted by the cloud will be Doppler shifted by a different amount when it arrives at radio telescope.

46 Our Galaxy HI map Oort and Kerr (1958) s = 1 s = 1/2 s = 1/2 e - s = 1/2 s = 1/2 p + s = 0 H The 21 cm line!! 48

47 HI Cloud HI 21cm line traces the distribution of the neutral hydrogen HI amount from intensity (T x v ) HI mass HI velocity along the line of sight due to differential rotation of the Galaxy Mean velocity range vary with longitude Rotation curve!

48 Rotation Curve from HI observation

49 HI Integrated Intensity map

50 HI clouds are useful ways to map out the structure of our Galaxy even in regions which do not contain large amounts of normal stars.

51 Cube data: Stack of spectra comprises a cube data B L v 53

52 L-V slice map from cube data L B V

53 L-V slice Galactic Plane

54 Molecular Clouds *birth place of all stars Giant Molecular Cloud (Complex) Dark Cloud (Complex), Globule Dense Core (Clump) Outflows/Jets Accretion Disks Circumstellar Envelope 56

55 MC to protostar to star 회전원반 아기별

56 Observation of MC H+H 2 : 90% He: 10% other < 1/1000 CO ( 12 CO, 13 CO, C 18 O etc) / H 2 :10-4 ~ 10-7 H 2 -collision energy excited CS (dense cores) HCN, NH 3 HCO + dust emission (heated by UV) Polarization Extinction mm FIR V/NIR 58

57 H 2 H H No transition at radio freq 12 CO Rotation/vibration transition at mm J= mm

58 C O

59 CO 2.6mm 1.3mm 61

6mm 13 CO, CS Emission from denser regions C O N(CO) ~ N(H 2 ) x 10-4 N( 13 CO) ~

60 H 2 H H No transition at radio freq 12 CO Rotation/vibration transition at mm J= mm 13 CO, CS Emission from denser regions C O N(CO) ~ N(H 2 ) x 10-4 N( 13 CO) ~ N(H 2 ) x 2x10-6 N(CS) ~ N(H 2 ) x 5x10-7 great tool to trace MC CO: Vibration, Rotation transition ν J=1-0 = GHz (2.6 mm) A 1-0 = s -1 (~4 months) 62

61 Detection of Molecules CH, CN (optical absorption line) * * Hartmann Ca II (1904) CH + (1941) Shklovski (1952), Townes (1957) CO, OH, HCN Weinreb (1963) OH lines Chang et al. (1968) NH 3, H 2 O Snyder et al. (1969) H 2 CO FUV band : H 2 (1970), CO (1971) from (hot stars) Wilson et al. (1970) CO 2.6mm (OMC) : study of MCs started!! More than 100 molecules found 63

62 GMC size : 100 pc density : 10 2 cm -3 mass : solar masses observation : CO lines T K : 10~100 K B : 5 ~20 µg active star formation 66

63 CO 2.6 mm FIR 100µm (IPAC ISSA) 68

64 Molecular gas was found to be ubiquitous! Started Galactic Plane Survey using CO lines

12 CO (1-0) Galactic plane surveys Galactic latitude (degree) Galactic longitude (degree) FCRAO UM/SB NANTEN Southern limit name D beam grid covered area longitude range rms Columbia 1.2m 8.

65 12 CO (1-0) Galactic plane surveys Galactic latitude (degree) Galactic longitude (degree) FCRAO UM/SB NANTEN Southern limit name D beam grid covered area longitude range rms Columbia 1.2m b < (complete) K UM/SB 14m b < 1 (inner Galaxy) K OGS 14m < b < 5.5 (outer Galaxy) K NANTEN 4m b < (220<L< 60) K Nagoya 4m b < (60<L< 220) K

66 12 CO Complete Survey of the Galactic Plane Dame, Hartmann & Thaddeus (2001) Excellent calibration Complete survey of the MW molecular disk 488,000 spectra 7200 deg2 Grid; Nyquist 1/4 deg Distribution, spiral arms, kinematics Dust/HI emission comparison Limitations 8.7 arcmin resolution 12 CO: opacity >>1 1.2m dish!

Galactic Latitude 20 0 0-20 180 150 120 90 60 30 0 330-30 300-60 270-90 -120 240-150 210-180 Galactic Longitude 300 200 0.0 0.5 1.0 1.5 2.

67 Galactic Latitude Galactic Longitude log Wco (K km/s) LSR Velocity (km s -1 ) L o c a l Arm -200 G. C. Non-circular motions Expanding 3-kpc Arm Galactic Longitude log Ico (K-deg)

68 Molecular Clouds in Our Galaxy has been completed but more and more survey is going on. Why? Need higher resolution survey; Astronomers want to see them more clearly!! *Higher resolution with better sensitivity!

69 5.5 FCRAO Outer Galaxy Survey (OGS; 1998) (QUARRY 50 /50 first subarcminute full-sampling survey, 1.7M spectra largest 12 CO) B L 102 Primary Results Confinement of CO to spiral arm features to much more sensitive limits (Heyer & Terebey 1998); 0.5K, 330 deg2 Equilibrium State of GMCs (Heyer et al. 2001) Universality of Turbulence (Brunt 2003; Heyer & Brunt 2004) HI Self-Absorption-CO Connection (Gibson et al. 2000)

70 Survey Beamsize comparison CO(1-0) LMT Nobeyama IRAM 개 CfA 1.2m Nagoya/NANTEN 4m Bell-Lab 7m TRAO/FCRAO 14m 1deg 2 45 개 500 개 1300 개 5200 개

71 Beamsize & Grid 12 CO Survey MINI : 9 / 8 NANTEN : 170 / 8 /4 UM-SB: 50 / 3 OGS 50 / 50 extended OGS 50 /22 13 CO Survey Bell Lab : 100 / 3 NANTEN : 170 / 8 GRS: 50 /22 TRAO: 50 / 50 Superbeam ¼ deg 77

72 spatial resolution beam size = 1.2λ/D λ : wavelength D : Diameter 78

73 4 CfA 1.2 m CO Survey (Dame et al. 2001) 7,500 spectra 9 3 Galactic Latitude Galactic Longitude 4 3 Part of FCRAO 14-m CO Survey (Heyer et al. 1998) log Wco (K km/s) 1,700,000 spectra 50 Galactic Latitude Galactic Longitude log Wco (K km/s) 79

Merits of 13 CO lines Optically thinner:

74 Merits of 13 CO lines Optically thinner: abundance ~1/50 of 12 CO Transparent observations for most of lines of sight Ubiquitous as 12 CO emission in the Galactic plane Clearer identification of clouds Tracing dense clumps more physical parameters 12 CO 2.6 mm 13 CO 2.7 mm

75 13 CO(1-0) Galactic plane surveys TRAO OGS (ongoing) name D beam grid covered area longitude range rms Bell Lab 7m b < 1 (1/3 of GP) K BU/FCRAO 14m b < 1 (1 st Quadrant) K (GRS) NANTEN 4m b < 1 (?)?

near-far ambiguity Infrared Dark Cloud Distribution (Simon et al. 2006; Jackson et al.

76 BU-FCRAO Galactic Ring Survey (GRS; Jackson et al. 2006) L 18 o ~56 o, B -1 o ~1 o 50 beam, 22 grid Established HI selfabsorption to discriminate near-far ambiguity Infrared Dark Cloud Distribution (Simon et al. 2006; Jackson et al. 2008) GMCs Properties with HII regions (Andersson et al. 2009) Reduced surface density of GMCs with respect to SRBY (Heyer et al. 2009) 9 UM-SB(50 3 ) GRS(50 /22 )

77 Column Density in Taurus using 12 CO and 13 CO cubes (Goldsmith et al. 2010)

78 Data Reduction 1. Few 100s spectra can be reduced one by by one. 2. Few 1000s spectra? How about millions of spectra? New method needed ; CLASS-GILDAS IRAF twod-longslit- background

79 composite spectra image 은위 (b ) statistics 은경 (l ) A fast reduction method; Background 속도 cleaning ( v ) process

80 Fast reduction using IRAF task twod-longslit-background High rejection & (low rejection) Any polynomial order Number of iteration Rejection radius (in pixel unit) Interactive or batch job B L V

81 1d reduction; Slice 156 B Vel IRAF twod-longslitbackground (rejection skill!!!)

82 T VLSR

83 Double peak case T VLSR

84 After background subtraction; Slice 156 B Vel

85 W( 13 CO) TOGS +1 B L 108.5

86 TOGS (after reduction)

87 他파장他파장자료자료 other data cube 대용량 database 자료 reduction GP survey Questions Desire New fact Fine obs. comparison analysis New information 새로운요구 새로운요구새로운요구 New questions model/simulation paper

88 Dying stars squirt out enriched gas which in turn explode Molecular Clouds Meanwhile, clouds of primordial gas are constantly raining down. The enriched gas clouds collapse to form new stars

89 B ν We started with blackbody radiation spectral lines 2hv ( T ) hν / e 3 = kt 2 / c 1 Atomic & Molecular Star Formation Study

90 Dying stars squirt out enriched gas which in turn Thanks explode for your attention! Molecular Clouds

Gas 1: Molecular clouds

Gas 1: Molecular clouds > 4000 known with masses ~ 10 3 to 10 5 M T ~ 10 to 25 K (cold!); number density n > 10 9 gas particles m 3 Emission bands in IR, mm, radio regions from molecules comprising H,