Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.atnf.csiro.au/research/workshops/2013/astroinformatics/talks/Whiting-ASKAP-sourcefinding-Astroinformatics2013.pdf Дата изменения: Fri Dec 13 07:44:31 2013 Дата индексирования: Sat Mar 1 10:49:08 2014 Кодировка: Поисковые слова: trifid nebula

ASKAP Source Finding and Quality Evalua*on
Ma#hew Whi*ng
Credit: Alex Cherney/terrastro.com

CSIRO ASTRONOMY & SPACE SCIENCE


Data Flow in the ASKAP System

ASKAP Source Finding & Quality Evalua@on | Astroinforma@cs 2013 | December 13, 2013


ASKAP Science Processing Pipelines
Calibration Pipeline Services 16200 Channels (18.5kHz) ccalibrator Calibration Solution Calibration Data Service

Large-N (eg. Spectral Line) Imager Pipeline UV Data 16200 Channels (18.5kHz) Ingest Pipeline Small-N (e.g. Continuum) Imager Pipeline UV Data 300 Channels (1MHz) Imager (cimager) Images Source Finder/ Identifier Source Catalog Imager (cimager) Source Finder/ Identifier Source Catalog

Image Cube

Sky Model Service

Transient Detector Pipeline Transient Imager (cfimager) Transient Finder/Identifier Images Transient Detections Light Curve Service

~30 Channels (10MHz)

ASKAP Source Finding & Quality Evalua@on | Astroinforma@cs 2013 | December 13, 2013


The Duchamp astronomical source finder
Whi*ng (2012), MNRAS 421, 3242

Duchamp created to provide a publicly-
available source-
finder capable of searching three-
dimensional data
www.atnf.csiro.au/compu@ng/soNware/duchamp

Aim of Duchamp:

· Provide a generic source finding tool capable of searching 3D astronomical data · Emphasis on HI data, although more widely applicable · Deal with low signal-
to-
noise · Provide plenty of catalogue and graphical feedback · Various preprocessing techniques

ASKAP Source Finding & Quality Evalua@on | Astroinforma@cs 2013 | December 13, 2013


Selavy ­ a source-
finder for ASKAP
Whi*ng & Humphreys (2012) PASA 29, 371

ASKAP source finding challenges

· Large data sizes, especially spectral-
line: 1TB cubes · Large source counts in con@nuum: >60,000 sources per image · Survey science, so as reliable and complete as possible across en@re survey


Source finding pipelines largely developed, building on Duchamp library with extra func@onality
· Distributed processing · Gaussian fiZng for 2D images · More flexible threshold determina@on, responding to changes in sensi@vity


ASKAP Source finding working group

· Coordina@on of research effort across Science Teams · Provide feedback to ASKAP Compu@ng on source-
finding requirements · Provide specifica@ons of desired algorithms

ASKAP Source Finding & Quality Evalua@on | Astroinforma@cs 2013 | December 13, 2013


Duchamp vs Selavy ­ Gaussian fiYng
Solid & Dashed lines show ±1 and 3 sigma differences Dobed line shows average 5-
sigma threshold

Flux Ra@o: Detected / Model

"Detected flux" is total flux of fibed Gaussian, so recover full flux of component

Drop in flux since "detected flux" is just flux of detected pixels

Model flux
ASKAP Source Finding & Quality Evalua@on | Astroinforma@cs 2013 | December 13, 2013

Model flux


Mapping the noise across the field

ASKAP Source Finding & Quality Evalua@on | Astroinforma@cs 2013 | December 13, 2013


Source Catalogue Quality
ASKAP observa@ons will be calibrated with a Global Sky Model
· Distribu@on of known sources to some (bright) limit · Used for star@ng point of imaging

Should be able to do direct comparison of source catalogue with sky model and compare sources & parameters Similar applica@on in simula@ons, where en@re input sky is known Look at varia@on in posi@on, flux, size of components, as a func@on of posi@on, flux, size, etc Look at completeness and reliability (easier with simula@ons)
ASKAP Source Finding & Quality Evalua@on | Astroinforma@cs 2013 | December 13, 2013


Completeness & Reliability
Completeness
Red = high Purple = low

Reliability

Major Axis

Model flux
ASKAP Source Finding & Quality Evalua@on | Astroinforma@cs 2013 | December 13, 2013

Model flux


Source-
finder evalua*on

ASKAP Source Finding & Quality Evalua@on | Astroinforma@cs 2013 | December 13, 2013


Alterna*ve flux error analysis

Flux error

Rela@ve flux error [%]

ASKAP Source Finding & Quality Evalua@on | Astroinforma@cs 2013 | December 13, 2013


Diagnosing problems
Rela@ve flux error [%] Rela@ve flux error [%] Distance from field centre [deg] Distanstance f rfieldfielntre [treg] g] Dice from om ce d cende [de

Dis@nc@ve pabern in leN plot due to use of "equalised noise" image for parameterisa@on, where fluxes decrease towards edge of beams

ASKAP Source Finding & Quality Evalua@on | Astroinforma@cs 2013 | December 13, 2013


We acknowledge the Wajarri Yamatji people as the tradi8onal owners of the Observatory site.

Thank you
CSIRO Astronomy & Space Science Mabhew Whi@ng ASKAP Compu@ng t +61 2 9372 4683 E mabhew.whi@ng@csiro.au w www.atnf.csiro.au/projects/askap
CSIRO ASTRONOMY & SPACE SCIENCE