Extracting Photometry from SPIRE Maps

Transcription

1 NHSC SPIRE Point Source Spectroscopy Webinar 21 March 2012 Extracting Photometry from SPIRE Maps David Shupe, Bernhard Schulz, Kevin Xu on behalf of the SPIRE ICC PACS

2 NHSC SPIRE Point Source Photometry Webinar 21 March 2012 SPIRE Point Source Photometry SPIRE Calibration and Map Units Fitting Functions to Point Sources Considerations for Aperture Photometry Source Extraction Summary: Checklists for Astronomers Demos of the HIPE Photometry Tools page # PACS

3 NHSC SPIRE Point Source Photometry Webinar 21 March 2012 SPIRE Point Source Photometry SPIRE Calibration and Map Units How Calibration is Defined Units and Beam Areas Fitting Functions to Point Sources Considerations for Aperture Photometry Source Extraction Summary: Checklists for Astronomers Demos of the HIPE Photometry Tools page # PACS

4 SPIRE calibra on is defined by the peak deflec on when scanning When a detector is scanned directly over a point source, the peak deflec on of the signal meline equals the brightness of the source. Scan of detector PSWE8 over Neptune, obsid

5 The meline- based defini on leads to some accoun ng correc ons 5 Units are in Janskys per beam Most so ware wants Jy/pixel or MJy/sr Map- making lowers the peaks rela ve to the melines Calibra on is for point source peaks Some detectors have bigger areas Calibra on is for nu*fnu = constant Color correc on for other spectral shapes

6 Use the fine- scale beam areas to convert Jy/beam to other units 6 The fine- scale beam areas were measured from Neptune maps with 1- arcsec pixels 250um: 423 sq arcsec 350um: 751 sq arcsec 500um: 1587 sq arcsec These values may change slightly in the near future (by a few percent) The convertimageunit task will change maps to Jy/pixel or MJy/sr

7 Divide peaks measured in maps by the pixeliza on correc on See Sec of the SPIRE Observer s Manual For nominal pixel sizes, divide by factors of: (250) (350) (500) Factor by which peak is lowered Curves obtained by integrating skybins/pixels over Gaussian approximations to the average beam Pixel size in arcseconds

8 Applying the Rela ve Gains equalizes the detector areas (instead of the peaks) Gains are provided in the SPIRE cal tree These gains are applied before destriping and map- making More details when we talk about Aperture Photometry 8

9 Single- detector Neptune maps show the gains reduce the spread in aperture photometry Neptune, Operational Day 168, PSW (250 microns) Timeline-fitting Number of Detectors in Flux Bin Aperture Photometry 9 Measured Flux (Jy) Aperture radius = 150 Aperture correction = 1.027

10 Color correc ons are described in the SPIRE Observers Manual & Data Reduc on Guide See Sec Mul ply by the value appropriate for your source For specific cases, compute your own correc on from the filter RSRFs Multiplicative Correction 250 Color Correction Factor vs. Assumed Source Spectral Index (Point Source) Source Spectral Index (in frequency)

11 NHSC SPIRE Point Source Photometry Webinar 21 March 2012 SPIRE Point Source Photometry SPIRE Calibration and Map Units Fitting Functions to Point Sources Peak-fitting techniques Estimating uncertainties Considerations for Aperture Photometry Source Extraction Summary: Checklists for Astronomers Demos of the HIPE Photometry Tools page # PACS

12 Peak- fi ng is recommended for point sources Fi ng Gaussians to melines is the best method for sources visible on the maps Jython script: bendosourcefit_v0.9.py Java task: melinesourcefi ertask Gaussian- fi ng on maps is serviceable as a second choice Java task: sourcefi ng Gaussian is good approxima on for radii up to (22, 30, 42) arcsec

13 To es mate the total uncertainty in flux, combine these terms in quadrature Uncertainty in the fi ed amplitude Includes the instrument and confusion noise (minimum of about 5 mjy) 7% of flux density for calibra on uncertainty 2% sta s cal reproducibility 5% absolute level of Neptune model (this term does not apply to SPIRE colors) 13

14 NHSC SPIRE Point Source Photometry Webinar 21 March 2012 SPIRE Point Source Photometry SPIRE Calibration and Map Units Fitting Functions to Point Sources Considerations for Aperture Photometry Applying the relative gains Aperture corrections Source Extraction Demos of the HIPE Photometry Tools page # PACS

15 The rela ve gains may be applied using a Useful Script, or the SPIA 15 SPIRE official pipeline scripts applyextendedemissiongains op on SPIRE Useful Script: Photometer Baseline Removal and Destriper Example is at the end (5 th one) spialevel2 task Rela ve gains are applied by default In the last 2 cases, the original Level 1 melines are le untouched The point- source calibra on s ll based on peaks The best of both worlds: meline- fi ng on Level 1, and aperture photometry on maps

16 Official aperture correc ons are now in the SPIRE Data Reduc on Guide! 16 Available in the online HIPE 8 docs h p://herschel.esac.esa.int/hcss- doc- 8.0/load/spire_drg/html/ ch05s07.html Not in the docs that come with HIPE 8.1 Values in Photometry Recipe: (250μm) 22 radius, sky (350μm) 30 radius, sky (500μm) 42 radius, sky Uncertain es at 5% level

17 NHSC SPIRE Point Source Photometry Webinar 21 March 2012 SPIRE Point Source Photometry SPIRE Calibration and Map Units Fitting Functions to Point Sources Considerations for Aperture Photometry Source Extraction Inside HIPE: DAOPhot & Sussextractor DAOPhot Demo Summary: Checklists for Astronomers Demos of the HIPE Photometry Tools page # PACS

18 Two source extractors are available within HIPE 18 sourceextractordaophot Algorithms from IDL AstroLib FIND for detec on APER for photometry (not PSF- fi ng!) sourceextractorsussextractor Sussextractor algorithm (Savage & Oliver 2007) Flux density is peak of smoothed image Good for detec ng sources

19 The simplest opera on of extractors uses the FWHM of each band Averages for nominal pixels: 250um: 18.2 arcsec 350um: 24.9 arcsec 500um: 36.3 arcsec You can supply your own PRF image The fine- scale beam areas are needed (or the images must be converted) (423, 751, 1587) sq arcsec 19

20 Correc ons are s ll needed for extractor outputs For sourceextractordaophot, need an aperture correc on appropriate to radius supplied For sourceextractorsussextractor, the correc on seems to be flux- dependent A nice combina on for sources 20 mjy and brighter, is to use Sussextractor for detec on and meline- fi ng for the photometry (see demo) 20

21 NHSC SPIRE Point Source Photometry Webinar 21 March 2012 SPIRE Point Source Photometry SPIRE Calibration and Map Units Fitting Functions to Point Sources Considerations for Aperture Photometry Source Extraction Summary: Checklists for Astronomers Demos of the HIPE Photometry Tools page # PACS

22 Checklist for meline- fi ng photometry q Use the Level 1 melines without rela ve gains applied q Perform first- order baseline correc on q Supply a star ng posi on q Run the bendosourcefit or the melinesourcefi ngtask q Apply color correc on as needed 22

23 Checklist for fi ng on the map q Use the map made without rela ve gains applied q Run the sourcefi ng task q Divide by the pixeliza on correc on q Apply color correc on as needed 23

24 Checklist for aperture photometry 24 q Make the map with rela ve gains applied (destriping recommended also) q Convert to Jy/pixel using convertimageunit task q Run the annularskyaperturephotometry task q Apply an appropriate aperture correc on q Apply color correc on as needed

25 NHSC SPIRE Point Source Photometry Webinar 21 March 2012 SPIRE Point Source Photometry SPIRE Calibration and Map Units Fitting Functions to Point Sources Considerations for Aperture Photometry Source Extraction Summary: Checklists for Astronomers Demos of the HIPE Photometry Tools page # PACS

26 Demos of the photometry tools in HIPE Fi ng Gaussians on the map (Bernhard) Timeline- fi ng of Gaussians (Bernhard) Aperture Photometry (Kevin) Source detec on with Sussextractor combined with meline- fi ng (David) 26