Data analysis
Benjamin Winkel
Map observations (spectroscopy)
ESSEA 2010
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Map observations (spectroscopy)
Dec
e.g., Zig-Zag scanning
RA
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Map observations (spectroscopy)
N⨯
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Map observations (spectroscopy)
Brüns & Westmeier 2004
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Map observations (spectroscopy)
McClure-Griffiths et al. 2006
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●
But: objects in the
data cube not 3D!
ESSEA 2010
y
ue
nc
3D data structure
Fr
eq
●
Latitude
Data cubes
Longitude
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Data cubes
Movie...
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Data cubes: P-V diagrams
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Data cubes: P-V diagrams
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Data cubes: P-V diagrams
NGC 4395
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Image moments
Total intensity
Velocity field
Dispersion
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Image moments
ESSEA 2010
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Image moments
Total intensity
ESSEA 2010
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Image moments
Mean velocity
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Image moments
Dispersion
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Moments: bottlenecks
Mean velocity
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Moments: bottlenecks
Mean velocity
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Moments and data cubes
NGC 4395
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Noise and detections
When do we speak
of a detection?
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Noise and detections
Noise statistics
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Noise and detections
Noise statistics
ESSEA 2010
1σ - 68%
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Noise and detections
Noise statistics
ESSEA 2010
3σ - 99.6%
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Noise and detections
How to estimate the noise
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Noise and detections
How to estimate the noise
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Noise and detections
When do we speak
of a detection?
Answer: > 4-5σ
5σ
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Noise and detections
Signal might cover
multiple channels
→ Smoothing
5σ
Noise goes down with 1/sqrt of number
of averaged spectral channels
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Useful formulae
●
Can use Gaussians to fit emission lines
(also multiple components)
Mean velocity
Peak intensity
●
Velocity width (dispersion)
Often, the Full-Width Half-Maximum is used:
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Useful formulae
●
Column density
= Moment 1
→ Column density map follows directly
from the Moment 1 map
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Upper kinetic temperature limit (for HI)
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Useful formulae
Angular size of pixels
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Mass
Distance
Column density in pixel i
(of the column density map)
Problem: distance often unknown
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Thank you!
ESSEA 2010
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