The Opacity of Nearby Galaxies from Counts of Background Galaxies: II. Limits of the Synthetic Field Method

Abstract

Recently, we have developed and calibrated the Synthetic Field Method (SFM) to derive the total extinction through disk galaxies. The method is based on the number counts and colors of distant background field galaxies that can be seen through the foreground object, and has been successfully applied to NGC 4536 and NGC 3664, two late-type galaxies located, respectively, at 16 and 11 Mpc. Here, we study the applicability of the SFM to HST images of galaxies in the Local Group, and show that background galaxies cannot be easily identified through these nearby objects, even with the best resolution available today. In the case of M 31, each pixel in the HST images contains 50 to 100 stars, and the background galaxies cannot be seen because of the intrinsic granularity due to strong surface brightness fluctuations. In the LMC, on the other hand, there is only about one star every six linear pixels, and the lack of detectable background galaxies results from a ``secondary'' granularity, introduced by structure in the wings of the point spread function. The success of the SFM in NGC 4536 and NGC 3664 is a natural consequence of the reduction of the intensity of surface brightness fluctuations with distance. When the dominant confusion factor is structure in the PSF wings, as is the case of HST images of the LMC, and would happen in M 31 images obtained with a 10-m diffraction- limited optical telescope, it becomes in principle possible to improve the detectability of background galaxies by subtracting the stars in the foreground object. However, a much better characterization of optical PSFs than is currently available would be required for an adequate subtraction of the wings. Given the importance of determining the dust content of Local Group galaxies, efforts should be made in that direction.

arXiv comment45 pages, 10 Postscript figures

References in corpus (14)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• High Redshift Galaxies in the Hubble Deep Field. Color Selection and Star Formation History to z=4
• A Simple Model for the Absorption of Starlight by Dust in Galaxies
• The Hubble Deep Field: Observations, Data Reduction, and Galaxy Photometry
• Toward High-Precision Astrometry with WFPC2. I. Deriving an Accurate PSF
• Distance to M31 With the HST and Hipparcos Red Clump Stars
• The Panchromatic Starburst Intensity Limit At Low And High Redshift
• The Top Ten List of Gravitational Lens Candidates from the HST Medium Deep Survey
• Tracing the Dynamics of Disk Galaxies with Optical and IR Surface Photometry: Color Gradients in M99
• Evolution in the Clustering of Galaxies to r = 26 (TAPIR GRP-390)
• HST Observations of the Field Star Population in the Large Magellanic Cloud
• The Opacity of Nearby Galaxies from Colors and Counts of Background Galaxies: I. The Synthetic Field Method and its Application to NGC 4536 and NGC 3664
• The HST Medium Deep Survey Cluster Sample: Methodology and Data
• Galactic Extinction from Colors and Counts of Field Galaxies in WFPC2 Frames: An Application to GRB 970228

Cited by in corpus (10)

• The Opacity of Spiral Galaxy Disks IV: Radial Extinction Profiles from Counts of Distant Galaxies seen through Foreground Disks
• The Opacity of Spiral Galaxy Disks III: Automating the "Synthetic Field Method"
• The Opacity of Spiral Galaxy Disks VI: Extinction, stellar light and color
• The Opacity of Spiral Galaxy Disks V: dust opacity, HI distributions and sub-mm emission
• The Occulting Galaxy Pair UGC 3995; Dust properties from HST and CALIFA data
• Galaxy And Mass Assembly (GAMA) Blended Spectra Catalog: Strong Galaxy-Galaxy Lens and Occulting Galaxy Pair Candidates
• Gaps in the cloud cover? Comparing extinction measures in spiral disks
• The Opacity of Spiral Galaxy Disks VIII: Structure of the Cold ISM
• The Opacity of Spiral Galaxy Disks VII: the accuracy of galaxy counts as an extinction probe
• The Opacity of Spiral Galaxy Disks IX; Dust and Gas Surface Densities