Deep HST/PC imaging of a young elliptical radio galaxy at z=2.390

Details Deep HST/PC imaging of a young elliptical radio galaxy at z=2.390 Deep HST/PC imaging of a young elliptical radio galaxy at z=2.390

Dec 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aas...18510704w&link_type=abstract

American Astronomical Society, 185th AAS Meeting, #107.04; Bulletin of the American Astronomical Society, Vol. 26, p.1497

Astronomy and Astrophysics

Astronomy

Scientific paper

We present deep 6-hr HST/PC images in both the WFPC2 wide-V and I filters of the weak radio galaxy 53W002, a compact narrow-line object at z=2.390. These are among the first refurbished PC-images of a high redshift galaxy, and are nearly fully sampled at ~ 0.07'' FWHM resolution. We subtract series of point sources to constrain its weak AGN (<=550 pc at z=2.390 for H_o=50, q_o=0.5) to 26+/-7% of its total continuum in the I-band and 16+/-4% in the V-band. This unresolved component is surrounded by an extended envelope that follows an r(1/4) -law with effective radius r_e =~ 1.1'' (8.6 kpc), with a color gradient that indicates an aging stellar population of ~ 0.3 Gyr in the center to ~ 0.5 Gyr at ~ 9 kpc. 53W002 has a very blue feature 0.45'' (3.5 kpc) to the West, which is ~ 0.3 mag bluer than the galaxy's young stellar population, that shows a more streak-like structure in V (which contains redshifted C-IV) and is more uniform in I (which contains no strong emission lines). This ``cloud'' is aligned with the radio source and ground-based Ly-alpha image, but only on one side, and could be a combination of: (1) reflection of its AGN-light shining through a cone off an electron cloud and/or a dust screen, including Ly-alpha and C-IV emission lines from gas lit up by the cone. A cone is not seen to the East, so if AGN light is reflected on both sides, its far-side must be obscured by dust; or (2) a star-bursting region induced by the weak radio jet. Its bluer colors indicate that any such star-bursting region is <= 10(8) years old ( =~ the typical radio source life-time), younger than the galaxy's dynamical time scale, or it would have disappeared into the galaxy's r(1/4) profile. We conclude that the weak radio source 53W002 is likely a genuinely young elliptical galaxy that started forming stars <=0.3--0.5 Gyr before z=2.390, possibly induced by its weak and fading radio jet, and is just old enough to have developed a regular r(1/4) light-profile at z=2.390. This work was supported by HST grant GO-5308-01-94A from STScI, which is operated by AURA, Inc., under NASA contract NAS5-26555.

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