Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.mrao.cam.ac.uk/~bn204/mk2/publications/2005/MidIRSocorroNov05.pdf Äàòà èçìåíåíèÿ: Wed Nov 25 23:11:03 2009 Äàòà èíäåêñèðîâàíèÿ: Thu Apr 8 13:21:10 2010 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: m 44

Toward a Quantitative Understanding of Mid-IR Emission from Galaxies
Bojan Nikolic Paul Alexander, Marcel Clemens, Malcolm Longair, Dominic Ford and Garret Cotter
bnikolic@nrao.edu

NRAO - Charlottesville and Green Bank

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 1


Scope
Using mid-IR obser vations to learn about:
· Energetics of galaxies (star formation / SMBH accretion) · The conditions in the interstellar medium in active galaxies · Astrophysics of dust

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 2


Outline
· Introduction · Modelling mid-IR emission from galaxies · Application of the models to a statistical sample · Two case studies: Moderate starburst NGC 520 Intense starburst Ar p 220 · Conclusions

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 3


Intro

Figure: Composite spectrum of M82, [Kennicutt et al.(2003)]

· Mid-IR: 3 µm­30 µm
Socorro 2005: Mid-IR Emission from Galaxies ­ p. 4


Why Mid-IR?
Mid-IR compared to other tracers of star-formation: UV-light, H-recombination lines, far-IR, sub-mm, radio continuum

Advantages

Disadvantages

· More information · Less extinction than

· More extinction than

far-IR/sub-mm

optical/near-IR

· High resolution · Large format detectors

· Most power comes out in

far- not mid-IR

· More complex physics

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 5


Physics of far and mid IR emission
· Far-IR: treat as an bolometric measure of energy release in

galaxy.

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 6


Physics of far and mid IR emission
· Far-IR: treat as an bolometric measure of energy release in

galaxy.

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 6


Physics of far and mid IR emission
· Far-IR: treat as an bolometric measure of energy release in

galaxy.

· Shape of the far-IR spectrum constrains the relative

geometr y of dust and heating sources.

· Mid-IR: dominated by ver y small transiently heated grains

(including PAHs). For purely transiently heated grains, emission determined purely by the proper ties of the grain and hardness of the heating spectrum.

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 6


° Example: a grain in equilibrium (200 A)
10-
14

10

-7

10- )
-1

16 -1

10 S /U (W m3 sr 1 2 5 10 20 50 100 200 )

-8

S (W sr

10-

18

10

-9

10

-20

10

-10

10 10-
22

-11

10 (µm) 10
-17

-12

1

2

5

10

20

50

100

200

(µm)
1 · 10-
7

10-

19

S /U (W m3 sr

S (W sr

-1

-1

)

10-

18

5 · 10-

8

)

2 · 10-

8

10-

20

1

2

5

10

20

50

100

200

1 · 10-

8

1

2

5

10

20

50

100

200

(µm)

(µm)

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 7


° Example: a transiently heated grain (5 A)
10
-18

10

-11

10 )
-1

-20 -1

S (W sr

10

-22

S /U (W m3 sr 1 2 5 (µm) 10 20 50

) 10
-24

10

-12

10

-13

10

-26

10

-14

10

-28

10

-15

1
-11

2

5 (µm)

10

20

50

10 10 10 10 10 10 10

-21

10

-22 -1

)

-24

S /U (W m3 sr 1 2 5 (µm) 10 20 50

-23

S (W sr

-1

)
-25 -26 -27

10

-12

10

-13

10

-14

10

-15

1

2

5 (µm)

10

20

50

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 8


Modelling mid-IR emission from galaxies

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 9


Modelling mid-IR emission from galaxies
Starburst mass and age Geometry of the stars and dust Dust mo del parameters

starburst99: Stellar p opulation synthesis Radiative transfer Dust Mo del

Dust absorption cross section

Emission sp ectrum

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 10


Stellar heating: Starburst99
10
49

10

48

L (W)

10

47

10

46

10

45

10

44

1 · 10

3

2 · 103

(° A)

5 · 10

3

1 · 104

Luminosity of a starburst of mass 106 M

and age 5 Myr and 50 Myr.

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 11


Dust Model
Want:
· Dust absor ption cross section · Emission from dust given a heating spectrum

Need to consider :
· Three types of dust grains: silicate, graphitic and PAHs. · Absor ption cross section: For PAHs use empirical cross section For others Mie theor y · Transient heating: Single temperature no longer appropriate; must

calculate the probability distribution of grain energies. Also must know the heat capacities of grains over a wide range of energies.
Socorro 2005: Mid-IR Emission from Galaxies ­ p. 12

· The full size distribution of each family of grains


Polycyclic Aromatic Hydrocarbons

Pyrene

Phenanthrene Triphenylene

Coronene has a radius of 3.5 å­ about the smallest par ticles included in the models.
Coronene
Images source: Wikipedia

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 13


PAH cross sections
10-
18
10
-16

C-C

C-H

/NC (cm2 /C)

C 10
-22

abs

10-

19

/NC (cm2 /C)

10

-18

10

-20

0.01

0. 1

1 (µm)

10

100

1000

10

-20

C

abs

10-

22

2

5

10 (µm)

C-H

10-

21

20

Cross section of ionised and neutral PAHs
Socorro 2005: Mid-IR Emission from Galaxies ­ p. 14


PAH cross sections
· The cross section is a strong function of neutral/ionised

state. Ionisation of grains a function of T /ne : for PDRs ionisation typically hight to complete (Draine & Li 2001).

· Fudge factors to reconcile the strength of the features with

astronomical obser vations. Adjustable parameters in the present models are E62 , E77 and E86 . Fitting to diffuse galactic emission suggests E62 = 3.0, E77 = 2.0 and E86 = 2.0. assumed.

· Hydrogenisation? Here, complete hydrogenisation is

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 15


Grain size distributions
Best fit size distributions to the Galactic diffuse ISM [Weingar tner & Draine(2001)]: RV = 3.1, Galactic metallicity.

100

100

a4 dngr /da (cm3 )

10

a4 dngr /da (cm3 )
-1 H

10

-1 H

1029 n

0.1 0.001 0.01 a (µm) 0.1 1

1029 n

1

1

0.1 0.001 0.01 a (µm) 0. 1 1

Size distribution of silicate grains

Size distribution of carbonaceous grains (graphitic spheres and PAHs)

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 16


Radiative transfer

Heating radiation radiative transfer

Dust emission radiative transfer

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 17


Some basic results

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 18


Mid-IR as a SFR tracer
10
28

10 L (W Hz
-1

26

) 10
24

10

22

10

-1

10

0

10

1

10

2 -1

10 )

3

10

4

10

5

(M yr

Peak specific luminosities of the 3.3 µm (dotted line), 7.7 µm (full line) and 11.3 µm (dashed line) emission features as functions of the star-formation rate ( ). The starburst age was 108 yr, column density 10
22

cm

-2

and shell radius 100pc.

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 19


Mid-IR as a SFR tracer
10
28

10 L (W Hz
-1

26

) 10
24

10

22

10

-1

10

0

10

1

10

2 -1

10 )

3

10

4

10

5

(M yr

Peak specific luminosity of the 7.7 µm emission feature (full line) and 24 µm continuum (dashed line) as functions of the star-formation rate ( ). The starburst age was 10 8 yr, column density 10
22

cm

-2

and shell radius 100pc.

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 19


Observed mid-IR / SFR correlation

Correlations between mid-IR (features and continuum) and SFRs (estimated from radio continuum and H), [Wu et al.(2005)]. Based on the Spitzer first look survey.

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 20


Comparison of model vs observation
Shell radius 100 pc
1013 1012 1011 1010 109 108 106 10
7

1013 1012 1011 1010 109 108 107 108 L
H

109 /L

1010

1011

L (24 mµ)/L

L (8 mµ)/L

106

10

7

108 L
H

109 /L

1010

1011

Model 8 µm dust luminosity (broken line) as function of H luminosity compared to the best fitting line of [Wu et al.(2005)] (solid line).

Model 24 µm dust luminosity (broken line) as function of H luminosity compared to the best fitting line of [Wu et al.(2005)].

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 21


Comparison of model vs observation
Shell radius 500 pc
1013 1012 1011 1010 109 108 106 10
7

1013 1012 1011 1010 109 108 107 108 L
H

109 /L

1010

1011

L (24 mµ)/L

L (8 mµ)/L

106

10

7

108 L
H

109 /L

1010

1011

Model 8 µm dust luminosity (broken line) as function of H luminosity compared to the best fitting line of [Wu et al.(2005)] (solid line).

Model 24 µm dust luminosity (broken line) as function of H luminosity compared to the best fitting line of [Wu et al.(2005)].

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 21


Comparison of model vs observation
Shell radius 2 kpc
1013 1012 1011 1010 109 108 106 10
7

1013 1012 1011 1010 109 108 107 108 L
H

109 /L

1010

1011

L (24 mµ)/L

L (8 mµ)/L

106

10

7

108 L
H

109 /L

1010

1011

Model 8 µm dust luminosity (broken line) as function of H luminosity compared to the best fitting line of [Wu et al.(2005)] (solid line).

Model 24 µm dust luminosity (broken line) as function of H luminosity compared to the best fitting line of [Wu et al.(2005)].

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 21


How impor tant is the column density?
1 0. 5

0. 2
max

F /F

0. 1 0.05

0.02 0.01 10

19

1020

10

21

10 n (cm
-2

22

10

23

10

24

)

Normalised strengths of the 3.3 µm (dotted line), 7.7 µm (full line) and 11.3 µm (dashed line) emission features as functions of column density. Normalization is to the maximum possible if all of the exciting radiation is absorbed but no dust re-absorption occurs.

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 22


Evolution with starburst age
10
37

10

36

L (W)

10

35

10

34

10

33

10

32

5

10 (µm)

20

Mid-infrared luminosity spectra of a 107 M

starburst at three times from the

star-formation epoch: 5 â 106 yr, 30 â 106 yr and 100 â 106 yr

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 23


Evolution with starburst age
2 1 0. 5
SB ,dust

/L L

0. 2 0. 1 0.05

0.02 0.01 5 10 (µm) 20

As before but normalised by the total starburst luminosity

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 23


Sample Mid-IR spectra
50 50

20

20

)

-1

S (MJy sr

10

S (MJy sr 4 6 8 10 (µm) 12 14 16

-1

)

10

5

5

4

6

8

10 (µm)

12

14

16

NGC 2798
10 5
-1

NGC 3351

)

S (MJy sr

Spitzer Near Galaxies Legacy Survey: nu2

clear IRS spectra of (a random subsample
1

of) spiral galaxies.
4 6 8 10 (µm) 12 14 16

0.5

NGC 7793

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 24


Sample Mid-IR spectra (trend with luminosity)

Figure by [Peeters(2004)]: Collection of ISO mid-infrared spectra shown sor ted by luminosity.

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 25


Case study: NGC 520

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 26


NGC 520

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 27


NGC 520: imaging

R-band image (from [Xu(2000)]) overlaid with mid-infrared contours (from ISO ).

K -band image (from [Kotilainen(2001)]) overlaid with mid-infrared contours (from ISO ).
Socorro 2005: Mid-IR Emission from Galaxies ­ p. 28


MICHELLE imaging of NGC 520
7.9 µm and 9.7 µm filters

(a) 7.9µm filter (Speak = 109 mJy arcsec-2 ); (b) 9.7µm filter (no firm detection, Speak = 28 mJy arcsec-2 );
Socorro 2005: Mid-IR Emission from Galaxies ­ p. 29


MICHELLE imaging of NGC 520
11.6 µm and 12.5 µm filters

(c) 11.6µm filter (Speak = 44 mJy arcsec-2 ); (d) 12.5µm filter (Speak = 80 mJy arcsec-2 );
Socorro 2005: Mid-IR Emission from Galaxies ­ p. 29


NGC 520 in the Radio

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 30


About NGC 520
· Mid-infrared imaging: The majority of emission from a disk-like region around

400 pc in radius. Ver y weak emission in the filter covering the silicate absor ption band.

· Near-infrared H recomb-lines: SFR rate about 7 M yr-1 .

· Radio obser vations: Also indicate a SFR of 7 M yr

Obscuring column density 6.2 â 10
-1

22

cm

-2

.

, confined within the

mid-ir/molecular disk region.

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 31


NGC 520 model
20 10 5 2 F (Jy) 1 0.5 0.2 0.1 0.05 0.02 5 10 20 (µm) 50 100 200

Standard dust model, 7 M yr

-1

Full line: ISO -CVF spectroscopy

, shell radius 400 pc, column density 6.2 â 10

22

cm

-2

.

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 32


NGC 520 model: column density
20 10 5 2 F (Jy) 1 0.5 0.2 0.1 0.05 0.02 5 10 20 (µm)
22

50
-2

100

200

Column density: 6.2 â 10

cm

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 33


NGC 520 model: column density
20 10 5 2 F (Jy) 1 0.5 0.2 0.1 0.05 0.02 5 10 20 (µm)
22

50
-2

100

200

Column density: 2 â 10

cm

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 33


NGC 520 model: column density
20 10 5 2 F (Jy) 1 0.5 0.2 0.1 0.05 0.02 5 10 20 (µm)
22

50
-2

100

200

Column density: 18 â 10

cm

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 33


NGC 520 model: shell radius
20 10 5 2 F (Jy) 1 0.5 0.2 0.1 0.05 0.02 5 10 20 (µm) 50 100 200

Shell radius 400 pc.

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 34


NGC 520 model: shell radius
20 10 5 2 F (Jy) 1 0.5 0.2 0.1 0.05 0.02 5 10 20 (µm) 50 100 200

Shell radius 1 kpc.

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 34


NGC 520 model: shell radius
20 10 5 2 F (Jy) 1 0.5 0.2 0.1 0.05 0.02 5 10 20 (µm) 50 100 200

Shell radius 100 pc.

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 34


NGC 520 model: grain destruction
20 10 5 2 F (Jy) 1 0.5 0.2 0.1 0.05 0.02 5 10 20 (µm) 50 100 200

Smallest grain size 3.5 å

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 35


NGC 520 model: grain destruction
20 10 5 2 F (Jy) 1 0.5 0.2 0.1 0.05 0.02 5 10 20 (µm) 50 100 200

Smallest grain size 5 å

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 35


NGC 520 model: grain destruction
20 10 5 2 F (Jy) 1 0.5 0.2 0.1 0.05 0.02 5 10 20 (µm) 50 100 200

Smallest grain size 6 å

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 35


NGC 520 model: grain destruction
20 10 5 2 F (Jy) 1 0.5 0.2 0.1 0.05 0.02 5 10 20 (µm) 50 100 200

Smallest grain size 7 å

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 35


NGC 520 model: grain destruction
20 10 5 2 F (Jy) 1 0.5 0.2 0.1 0.05 0.02 5 10 20 (µm) 50 100 200

Smallest grain size 10 å

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 35


Case study II: Arp 220

HST/NICMOS [Thomson et al]

UKIRT/MICHELLE

SFR: 120 M yr-1 ; Mid-IR emission radius 150 pc; gas col. dens. 12 â 1022 cm-2 .
Socorro 2005: Mid-IR Emission from Galaxies ­ p. 36


Arp 220 model
100

10

1 F (Jy) 0. 1 0.01 0.001 5 10 20 (µm) 50 100 200

Smallest grain size 3.5 å

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 37


Arp 220 model
100

10

1 F (Jy) 0. 1 0.01 0.001 5 10 20 (µm) 50 100 200

Smallest grain size 6 å

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 37


Arp 220 model
100

10

1 F (Jy) 0. 1 0.01 0.001 5 10 20 (µm) 50 100 200

Smallest grain size 20 å

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 37


Arp 220 model
100

10

1 F (Jy) 0. 1 0.01 0.001 5 10 20 (µm) 50 100 200

Smallest grain size 35 å

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 37


Conclusions
· A physical framework for modelling the mid-IR emission

from galaxies. Can directly relate the proper ties of the heating source (starburst), dust and geometr y to obser vations. emission and star-formation rates. Suggests dust absorbing from young stars is not directly associated with the parent molecular clouds.

· Validated on the obser ved correlations between mid-IR

· Applied to a moderate and an intense starburst (NGC 520

and Ar p 220) Proper ties of dust must be changing! Destruction of small grains plausible.

· The 3.3 µm PAH feature often overlooked but ver y useful.

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 38


Supplementary

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 39


SF in Arp 220
500
1 · 10
10

5 · 10

9

)
-1

(M yr

M (M )

200

2 · 10 1 · 10

9

100
9

50 1 · 10

6

2 · 10

6

5 · 10

6

1 · 10

7

t (yr)

2 · 10

7

5 · 10

7

1 · 10

8

5 · 108 1 · 10

6

2 · 10

6

5 · 10

6

1 · 10

7

t (yr)

2 · 10

7

5 · 10

7

1 · 10

8

Modelling H-recombination, bolometric luminosity and radio luminosity of Arp 220 as due to a continuous star burst

Modelling H-recombination, bolometric luminosity and radio luminosity of Arp 220 as due to an instantaneous star burst

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 40


Bibliography

References
[Kennicutt et al.(2003)] Kennicutt R. C., et al., 2003, PASP, 115, 928 [Kotilainen(2001)] Kotilainen, 2001, A&A, 366, 439 [Peeters(2004)] Peeters, 2004, ApJ, 613, 986 [Weingar tner & Draine(2001)] Weingar tner J. C., Draine B. T., 2001, ApJ, 548, 296 [Wu et al.(2005)] Wu H., et al., 2005, ApJ, 632, L79 [Xu(2000)] Xu, 2000, ApJ, 541, 644

Socorro 2005: Mid-IR Emission from Galaxies ­ p. 41