HST/ACS Emission Line Imaging of Low Redshift 3CR Radio Galaxies I: The Data

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Tremblay, Grant R.
Chiaberge, Marco
Sparks, William B.
Baum, Stefi A.
Allen, Mark G.
Axon, David J.
Capetti, Alessandro
Floyd, David J. E.
Macchetto, F. Duccio
Miley, George K.
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Abstract
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We present 19 nearby (z<0.3) 3CR radio galaxies imaged at low- and high-excitation as part of a Cycle 15 Hubble Space Telescope snapshot survey with the Advanced Camera for Surveys. These images consist of exposures of the H-alpha (6563 \AA, plus [NII] contamination) and [OIII] 5007 \AA emission lines using narrow-band linear ramp filters adjusted according to the redshift of the target. To facilitate continuum subtraction, a single-pointing 60 s line-free exposure was taken with a medium-band filter appropriate for the target's redshift. We discuss the steps taken to reduce these images independently of the automated recalibration pipeline so as to use more recent ACS flat-field data as well as to better reject cosmic rays. We describe the method used to produce continuum-free (pure line-emission) images, and present these images along with qualitative descriptions of the narrow-line region morphologies we observe. We present H-alpha+[NII] and [OIII] line fluxes from aperture photometry, finding the values to fall expectedly on the redshift-luminosity trend from a past HST/WFPC2 emission line study of a larger, generally higher redshift subset of the 3CR. We also find expected trends between emission line luminosity and total radio power, as well as a positive correlation between the size of the emission line region and redshift. We discuss the associated interpretation of these results, and conclude with a summary of future work enabled by this dataset.
Comment: 18 pages, 12 figures, accepted for publication in ApJS
Keywords
Astrophysics - Cosmology and Nongalactic Astrophysics
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