Astronomy and Astrophysics – Astrophysics
Scientific paper
2000-06-01
Astronomy and Astrophysics
Astrophysics
41 pages, 14 figures, Postscript version with high-resolution figures at ftp://ftp.aoc.nrao.edu/staff/dthilker/preprints
Scientific paper
10.1086/316852
We have developed a robust, automated method, hereafter designated HIIphot, which enables accurate photometric characterization of HII regions while permitting genuine adaptivity to irregular source morphology. HIIphot utilizes object-recognition techniques to make a first guess at the shapes of all sources then allows for departure from such idealized ``seeds'' through an iterative growing procedure. Photometric corrections for spatially coincident diffuse emission are derived from a low-order surface fit to the background after exclusion of all detected sources. We present results for the well-studied, nearby spiral M51 in which 1229 HII regions are detected above the 5-sigma level. A simple, weighted power-law fit to the measured H-alpha luminosity function (HII LF) above log L_H-alpha = 37.6 gives alpha = -1.75+/-0.06, despite a conspicuous break in the HII LF observed near L_H-alpha = 10^38.9. Our best- fit slope is marginally steeper than measured by Rand (1992), perhaps reflecting our increased sensitivity at low luminosities and to notably diffuse objects. HII regions located in interarm gaps are preferentially less luminous than counterparts which constitute M51's grand-design spiral arms and are best fit with a power-law slope of alpha = -1.96+/-0.15. We assign arm/interarm status for HII regions based upon the varying surface brightness of diffuse emission as a function of position throughout the image. Using our measurement of the integrated flux contributed by resolved HII regions in M51, we estimate the diffuse fraction to be approximately 0.45 -- in agreement with the determination of Greenawalt et al. (1998). Automated processing of degraded datasets is undertaken to gauge systematic effects associated with limiting spatial resolution and sensitivity.
Braun Robert
Thilker David A.
Walterbos Rene A. M.
No associations
LandOfFree
HIIphot: Automated Photometry of HII Regions Applied to M51 does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with HIIphot: Automated Photometry of HII Regions Applied to M51, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and HIIphot: Automated Photometry of HII Regions Applied to M51 will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-44580