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

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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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
Astrophysics - Cosmology and Nongalactic Astrophysics