the h Ⅰ source finding pipeline sofia and its performance

InternationalCentre forRadioAstronomyResearch

The H Ⅰ Source Finding Pipeline SoFiA and its Performance on

ASKAP Early Science DataTobias Westmeier (ICRAR / UWA)

Pune, 06 / 02 / 2017 The H Ⅰ Source Finding Pipeline SoFiA 2

Overview of SoFiA


Overview of SoFiA

Source Finding Application

H Ⅰ source finding and parameterisation pipeline for SKA pathfinderand precursor surveys

Paolo SerraTobias WestmeierNadine GieseRussell JurekThijs van der HulstAttila Popping

Thank you to our users for their valuable feedback!

Benjamin WinkelLars FlöerMartin MeyerBärbel KoribalskiLister Staveley-SmithHélène Courtois

Contributors programmers:


Overview of SoFiA

Command-line interface


Overview of SoFiA

Graphical user interface


Overview of SoFiA

https://github.com/SoFiA-Admin/SoFiA/wiki

SoFiA wiki on GitHub

Help documentationTest data cube

https://github.com/SoFiA-Admin/SoFiA/wiki


SoFiA’s Algorithms



Source finding

Modular structure → multiple SF algorithms

Smooth + Clip(P. Serra)

Characterised Noise H Ⅰ(Jurek 2012)

2D–1D Wavelet(Flöer & Winkel 2012)

Basic Threshold

S+C

2D–1D

CNHI

Thresh

http://adsabs.harvard.edu/abs/2012PASA...29..251J

http://adsabs.harvard.edu/abs/2012PASA...29..244F



Noise normalisation

Noise variation known numerically→ Provide weights cube

Noise variation known analytically→ Specify analytic function

Noise variation unknown→ Enable automatic local noise scaling

ATCA mosaicof 32 pointings

Noise variationacross mosaic



Reliability calculation

Measure parameters of positive and negative sources

Serra, Jurek & Flöer (2012)

http://adsabs.harvard.edu/abs/2012PASA...29..296S



Reliability calculation

Compare densities in N–dimensional parameter space→ Reliability ≡ T / (T + F ) = (P − N ) / P → threshold

Measure parameters of positive and negative sources

Serra, Jurek & Flöer (2012)

http://adsabs.harvard.edu/abs/2012PASA...29..296S


Using SoFiA


Using SoFiA

SoFiA is…

…a collection of powerful and versatile source finding and parameterisation algorithms

SoFiA is not…

…a magic bo that automatically turns a data cube into a fully complete and reliable source catalogue


Using SoFiA

SoFiA’s default settings

Defaultsettings

Fine-tunesettings

Test on(sub-)cube

Processfull cubeOK ?

YesNo

Rule of thumb: Never ever use them!

Never rely on SoFiA’s default settings under any circumstances!


You are dealingwith point sources

Using SoFiA

You are dwith point

Don’t apply spatialsmoothing…

Consider using theCNHI algorithm…

…as it would decrease your S / N

…as it was designed for point sources

✔

✘Example


You are dealingwith extended sources

Using SoFiA

You are dealiwith extended

Apply spatial smoothingon multiple scales…

Don’t use theCNHI algorithm…

…as it will optimise your S / N

…as it was designed for point sources

✘

✔Example


You are dealingwith resolved objects

Using SoFiA

You are dealwith resolved

There’s no need torun a source finder…

You can still makeuse of SoFiA…

…as the source is plainly visible

…e.g. for generating source masks

✔

✘Example


You are haunted bycalibration artefacts

Using SoFiA

You are hauncalibration ar

Improve yourdata calibration…

Apply SoFiA’s noisescaling algorithm…

…to get rid of the artefacts

…to correct for your local noise level

✔

✔Example


Your data cubeis 23 GB in size

Using SoFiA

Your data cis 23 GB in

Split the data intomanageable chunks…

Optimise your settingson a small sub-cube…

…to process them separately

…before running SoFiA on the full cube

✔

✔Example


Early ASKAP Data


Early ASKAP Data

WALLABY pilot observations

H Ⅰ channel map, beam 9

IC 5201

Antennas: 12

Frequency:1.4 GHz

Bandwidth:48 MHz

Field:NGC 7232

Beams:36

ASKAP core

Mk Ⅱ PAF


Early ASKAP Data


Creation of galaxy models

in GIPSY

Convolution with ASKAP

beam (51″ × 43″)

Injection of 384 galaxies into emission-free ASKAP sub-cube

Running of SoFiA on

model cube


Early ASKAP Data


Single channel of mask cube

Sources rather extended and elongated

Similar orientation angles


Early ASKAP Data


Single channel (≈ 4 km/s)


Early ASKAP Data


Single channel (≈ 4 km/s) Sum over 1024 channels (≈ 4,000 km/s)

Continuum residuals and their sidelobes


Early ASKAP Data


Position error

Peak flux density error

Integrated flux error

Position error:≲ FWHM

Peak flux dens. error:positive bias dueto noise, as expected

Integrated flux error:all over the place

Use higher flux threshold of 5 σ instead of 3 σ


Early ASKAP Data


Problem:

Dilemma:

Low thresholdartefacts

High thresholdpartial detections

Galaxies split into multiple detectionsor only partially detected

Accurate calibration and continuum subtraction of utmost importance

→ Potential challenge for phased array feeds


Concluding Remarks


Concluding Remarks

Further information

GitHub project

Tutorial

Paper

https://github.com/SoFiA-Admin/SoFiA/

https://github.com/SoFiA-Admin/SoFiA/wiki/SoFiA-Tutorial

Serra, Westmeier, Giese, et al., 2015, MNRAS, 448, 1922

E-mail to [email protected] with “subscribe” in the e-mail body (subject will be ignored)

Mailing list


https://github.com/SoFiA-Admin/SoFiA/wiki/SoFiA-Tutorial

http://adsabs.harvard.edu/abs/2015MNRAS.448.1922S

mailto:[email protected]?subject=No%20subject


http://adsabs.harvard.edu/abs/2015MNRAS.448.1922S


Concluding Remarks

SoFiA mini-workshopAims:

▶ Assist participants with source finding ▶ on their own data cubes▶ Get feedback from users on how to ▶ improve SoFiA

Time and location:▶ Thu–Fri, 9–17 h, E-Lab

Organisers:▶ Thijs van der Hulst▶ Attila Popping▶ Tobias Westmeier

Programme:

Thursday 09:00 Introduction 09:30 SoFiA tutorial 11:00 Morning tea 11:30 Practical source finding 13:00 Lunch break 14:30 Practical source finding 16:00 Afternoon tea 16:30 Discussion & feedback

Friday 09:00 Practical source finding (subject to demand)

Please try to install SoFiA before the workshop▶ https://github.com/SoFiA-Admin/SoFiA/


the h Ⅰ source finding pipeline sofia and its performance

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