SPIRE FTS spectral maps - Herschel

On-line spectroscopy
workshop SPIRE FTS spectral maps
Ivan Valtchanov, Herschel Science Centre
ESAC, ESA
1
24 Apr 2014
Outline
• Identifying SPIRE FTS spectral maps in the HSA
and downloading some data
• Follow selected topics from SPIRE DRG sections
7.7 and 7.11
• How spectral maps are done and how to modify their WCS or
the gridding algorithm.
• Experimenting with the different gridding algorithms.
• Walkthrough on extracting 1-d spectra, background/off
subtraction, cube line fitting script, extracting a point-source
calibrated spectrum, comparing with the photometer…
2
Must read!
•
The SPIRE Handbook (instrument observing modes,
calibration…)
•
The SPIRE Data Reduction Guide (data structure,
processing, reprocessing, many details and cookbooks)
•
•
•
•
Swinyard et al. (2014) => FTS calibration
Wu et al. (2013) => Semi-extended correction tool
Makiwa et al. (2013) => FTS beams
Benielli et al. (2014) => FTS mapping Check the public wiki on SPIRE http://herschel.esac.esa.int/twiki/bin/view/Public/SpireCalibrationWeb
3
Get the data from
the HSA
!
1342204919 (FTS)
1342239930 (Phot)
4
Get the data from
the HSA
!
1342204919 (FTS)
1342239930 (Phot)
Submit request:
Have to be logged in!
5
1. After getting an e-mail from the archive, download the
tar.gz file in a convenient place.
!
2. Un-tar the file in a convenient place.
!
3. (optional) delete the tar.gz file
!
3. Start HIPE
6
HIPE, Navigator view: go to the
place where you did tar xvzf ...
Double-click on this will
open the observation
context in HIPE
7
That’s all: the spectral map is in HIPE and we can start
looking at the data and the spectra.
Maybe rename the
variable:
8
Inspect the obsContext: general info,
thumbnails, level-2 (cubes)
9
Extract level-2 cubes and open them (double click by
default) in the Spectrum Explorer
10
the basics
Intermediate
2 arcmin!
diameter
Full spatial coverage
11
How to see where the
spectra are?
• Demo script #1: full and intermediate spatial sampling. • Introduce the preCube
12
full SSW
intermediate SSW
13
preCube
• Collection of all spectra as spectrum2d
• Visualise it: p = preCube.spectrum2d =>
Spectrum Explorer
• Remove noisy spectra, noisy detectors,
clipped spectra, etc… see section 7.7.3 in
SPIRE DRG.
14
Gridding algorithms
• nearest neighbour
• naive
• convolution
• gridding spireProjection(spc=preCube,wcs=wcs,projectionType=“ “)
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Default: naive gridding
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Coverage: NaNs
white: 12 spectra
light green: 8
dark green: 4
Try it out
• Demo #2:
• using naive projection
• using fixed kernel width
• using an array of kernels
• using gridding method
17
New map and coverage
No NaNs with convolution
or gridding
18
Which projection type
to use?
•
Default is naive projection, but
there are problems:
•
NaNs, unweighted mean of
spectra.
•
Convolution projection is good
for SSW => Gaussian beam is a
good approximation but not so
good for SLW (see Makiwa et al. 2013)
•
Gridding projection (HIFI) is
quite similar to the
Convolution.
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Convolve the map to a
reference beam
• Demo #3: convolve to the largest SSW
beam => the convolution kernel kernel(v) = SQRT(refBeam^2 - beamSsw(v)^2)
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Make the map with
different WCS
• Demo #4: custom made WCS as input to
spireProjection
• stitch together SSW and SLW spectra
from the same pixel
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Cube analysis
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Subtract foreground/
background from a cube
• Demo #5: • use a pixel from the cube
• use an off-position observation (map or
sparse).
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Cube line fitting
• Demo #6: run the useful script
• how to get the continuum subtracted
cube?
• check the line maps
• how to make line maps ratio?
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Compare with the
photometer
• Important notes:
• specMatchPhot() currently (HIPE v12) works only for point
sources. • SPIRE Handbook (eq. 5.18) provides the
framework
•
Photometer map assumptions: vSv=const.,
extended source calibration (MJy/sr)
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Example for M82
•
Make the photometer map with the same WCS as
the SSW cube (needs photometer map reprocessing from level-1,
including extended gains and converted to extended
units of MJy/sr)
•
Apply Eq. 5.18 from the SPIRE Handbook to each
SSW spaxel => derive the 250 µm synthetic
photometry.
•
Compare the two maps (with caveats)
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The End
(of the beginning)
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Download Report