PACS PSF and PSF photometry

Transcription

1 PACS PACS and photometry Babar Ali (NHSC) - page 1

2 Introduction An often asked question. Can I perform photometry on PACS images? - page 2

3 Answer There are no tools within HIPE that allow fitted photometry. There is (so far) limited experience within the PACS team in using fitting techniques. Lower priority thus far This presentation will summarize: Unique issues for PACS photometry, and Summarize what s available and some preliminary investigations. - page 3

4 reference A comprehensive report provides detailed description and properties of the PACS beam profile. This report is publicly available from NHSC and HSC websites: may be downloaded from NHSC or HSC websites: - page 4

5 PACS PACS The best available for fitting is the Vesta. The Mars has the best details at radii > ~ 1 The best available radial profiles of the encircled energy are made from by combining Mars and Vesta profiles. Vesta - page 5 Mars

6 Unique to PACS PACS s are asymmetric. Rotation is important. PACS are distorted in the scan direction. Limited libraries are available. No tinytim like software. May be significant difference between blue and red sources. Astrometry drifts broaden the profile. Illustration of distortion at high scan speeds - page 6

7 Selecting for phtometry PACS If possible, derive the from your own data. Has scan distortion, rotation, and astrometric broadening unique to your images But, may have lower s/n than Vesta Use Vesta Rotate to match profile on your images. Use one with astrometry errors, or Convolve idealized. Select scan speed matching your observations. - page 7

8 fitting choices DAOPHOT (IDL version) Pros: Much used and fairly reliable Can do multi- fits in crowded regions Cons: Gaussian+lookup table s only. Cannot import. Constant background only -- doesn t work well in confused regions. Starfinder (IDL) Apex (C/C++, perl, standalone tool part of the Spitzer toolkit) Others? - page 8

9 Starfinder Works relatively easily with PACS images. Allows selection of from file, or define one from images. Source Finding parameters require significant tuning to avoid detecting spurious sources in regions with strong nebulosity. Noticeable remnants in fits for strong sources in high nebulosity regions. Display capabilities could use improvement. - page 9

10 The original photproject 70 µm map: IRDC in the middle with embedded point sources HII region to the south-east LBV shell to the north-west IDL Starfinder: detected stars after fitting using the rotated Vesta Some artificial sources in the LBV shell and the extended emission blobs. But all point sources visible by eye in the IRDC are detected. IDL Starfinder: background image With point sources removed... Starfinder results courtesy of H. Linz (MPIA) - page 10

11 Apex Very Spitzer specific standalone tool Requires significant tweaking of images and s to work with PACS data. Allows spatial filtering to handle complicated backgrounds But may affect s 50+ parameters - page 11

12 Apex results Vesta from image Source is faint. HPF MADmap Scanamorphos - page 12

13 Apex results Vesta from image HPF MADmap Scanamorphos Source of moderate brightness - page 13

14 Apex results Vesta from image Blended source HPF MADmap Scanamorphos - page 14

15 Apex results Vesta from image HPF MADmap Scanamorphos Best result: isolated point source - page 15

16 Apex results Vesta from image HPF MADmap Scanamorphos Another blended source. - page 16

17 photometry & recommendations Usually requires additional correction (recalibration) using aperture photometry results. To account for missing flux at large >~60 radii To account for systematics in spatial filtering by Apex To account for any normalization errors Always view residual images. - page 17