A Wavelet Analysis of the RC- FIR-CO Correlation in the LMCastronomy.swin.edu.au/.../Talks_files/ahughes_radioFIR_Nagoya05.pdf · A Wavelet Analysis of the RC-FIR-CO Correlation in

A Wavelet Analysis of the RC-FIR-CO Correlation in the LMC

Annie HughesSwinburne University/ATNF

Tony Wong, Lister Staveley-Smith, Ron Ekers, Miroslav Filipovic

NANTEN team Juergen Ott, Erik Muller, Sarah Maddison

Outline

•  Introduction to Wavelet Analysis •  The Radio-FIR Correlation in the LMC

•  A Molecular Gas Connection?

•  Molecular Gas in the Inner LMC

Annie Hughes, Nagoya University, November 2005

Wavelet Analysis

•  convolve image with family of self-similar basis functions that depend on scale & location

• generate basis functions by dilation and translation of “mother wavelet”

•  general case of Fourier transform, using localised oscillatory function

•  astronomy applications: point source removal, time series analysis, comparing structure on different scales


The Pet Hat Wavelet

€

ˆ ψ (ka) =cos2 π

2log2

ka2π

0

€

:π < ka < 4π

€

: ka < π ,ka > 4π

Annie Hughes, Nagoya University, November 2005 Frick et al. (2001)

•  we used the “Pet Hat” wavelet (Frick et al. 2001)

The Pet Hat Wavelet

5 kλ ~ 20”


Frick et al. (2001)

•  a family of annuli in the Fourier plane that isolate structure on different scales

Wavelet Filtered Images

Wavelet Power Spectrum


€

W (a, x ) = w(a) f ( ′ x )ψ*( ′ x − x

a−∞

∞

∫−∞

∞

∫ )d x

€

E(a) = W (a, x ) 2(x1 ,x2 )∑

Wavelet Power Spectrum


Wavelet Cross-Correlation


Wavelet Cross-Correlation


€

rw (a) =W1(a,

x )W2(a,

x )∑∑

E1(a)E2(a)[ ]12

Example

rpx = 0.02


Yun,

Red

dy &

Con

don

2001

The Radio-FIR Correlation

Pierini et al. 2003

LMC


A Star Formation Model?

High Correlation! FIR

Hot stars

Heating

Warm Dust

UV UV

SN

SNR

ISM Shocks Particle

Acceleration

CR Synchrotron

Magnetic Field

Molecular clouds

Stars form

Radio

courtesy Ron Ekers


Models

•  star formation models - optically thin, optically thick (e.g. Völk et al. 1989)

•  hydrostatic midplane pressure (Murgia et al. 2005)

•  B-ρgas coupling (Hoernes et al. 1998) - via MHD turbulence? (Groves et al. 2003)


•  cosmic ray chemistry (e.g. Bettens 1998)

A Local Correlation

• Orion: total FIR vs non-thermal 13cm radiobreakdown at ~300pc? (Boulanger & Perault 1988)

•  LMC: total FIR vs total 6cm radiobreakdown at ~70pc around HII regions? (Xu et al. 1992)

• M31: warm/cold/total FIR vs thermal/nonthermal/total 6cmvalid down to ~1kpc (Hoernes et al. 1998)


LMC data

1.4GHz: resolution ~ 40as

courtesy LSS (ATCA/Parkes)


100 µm: resolution ~ 90as

courtesy Jason Surace (IRAS/IPAC)

HI: resolution ~ 60as

LMC data

1.4GHz: resolution ~ 40as

courtesy LSS (ATCA/Parkes) Kim et al. 2003 (ATCA/Parkes)


2.5 2.5 0.25 0.25 kpc

Results

•  RC-FIR correlation clearly better than for other cold gas tracers on smaller scales

•  rp > 0.75 for scales larger than ~30pc

LMC subregions


•  is result dominated by brightest regions?

SR8: 32% (1.4GHz) 45% (60um)

SR6 + SR7 + SR8 + SR11 = 56% (1.4GHz) = 72% (60um)

8

13

6

4

10 11

7

Thermal or nonthermal?


Thermal Fraction


€

S4.8S1.4

= fthν 4.8ν1.4

−0.1

+ fnon− thν 4.8ν1.4

αnon−th

Niklas et al. (1997)

€

αnon− th = −0.7

α = 0.96

Subregion 8


32%

45%

fth~1

Subregion 8


Subregion 6


7%

9%

fth~0.85

α = 0.69

Subregion 6


Subregion 10


5%

3%

fth~0.56

α = 0.40

Subregion 10


A Characteristic Scale?


13

8

11

12

6

9

3

4

15 5

7

10

14

1

2

€

αnon− th = −0.7For

Regions with high thermal fraction show better correlation at smaller scales

A Molecular Connection?


• Murgia et al (2005) propose “RC-FIR-CO correlation”

• 24 BIMA-SONG galaxies

• “The global correlations between CO-RC, FIR-RC, and FIR-CO are comparably tight…”

• “For CO-bright galaxies, the CO-RC correlation is as tightly correlated as the global value on linear scales above 100pc…”



• RC, FIR and CO emission regulated by hydrostatic pressure, modified by large-scale (spiral arms) and small-scale (star formation) effects

• FIR: stall radius of HII regions

• CO: molecular gas fraction

• RC: equipartition of turbulent and magnetic energy + observed radial dependence of CRE density



• No explicit dependence on star formation

• Characteristic scale of RC-FIR-CO correlation is pressure scale height of the galactic disk

• Can we investigate in LMC with NANTEN CO data?

continuum


CO


courtesy N. Mizuno (NANTEN)

Subregion 8


35%

15%

Subregion 6


8%

10%

Subregion 10


6%

5%

Conclusions & Caveats

•  local radio-FIR correlation in the LMC is excellent but may be dominated by thermal-FIR correlation

•  local correlation with cold gas is poorer

• characteristic scale? (40/200pc)

• high thermal fraction in the LMC


• central 1.2 kpc

• 12CO(J=1-0)

• Mopra telescope: OTF,

0.2km/s, 30”

• See Erik’s talk for

technical details

Inner LMC Survey


Motivations


• Relationship between atomic and molecular gas, focussing on internal dynamical effects

• Boring?

• “LMC is dwarf galaxy that rotates like a solid body”

A Big Mess?

Motivations


•  Molecular gas associated with L-component?

•  Compact central mass? 2x108 M within ~240pc

•  Offset stellar bar (and counter-rotating stellar core)?

•  Radial variation of CO(J=2-1)/CO(J=1-0) ratio?

•  Plus… many molecular clouds in the inner LMC have not been studied in detail

•  Includes SF and non-SF molecular clouds

Preliminary Results


Preliminary Results

Preliminary Results

Preliminary Results

Arigato gozaimasu

Documents

A Wavelet Analysis of the RC- FIR-CO Correlation in the LMCastronomy.swin.edu.au/.../Talks_files/ahughes_radioFIR_Nagoya05.pdf · A Wavelet Analysis of the RC-FIR-CO Correlation in