A Powerful Ultra Steep Spectrum Radio Galaxy Having an Extremely Low Excitation Emission Line Spectrum

Details A Powerful Ultra Steep Spectrum Radio Galaxy Having an Extremely Low Excitation Emission Line Spectrum A Powerful Ultra Steep Spectrum Radio Galaxy Having an Extremely Low Excitation Emission Line Spectrum

Feb 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992a%26a...254...42g&link_type=abstract

Astronomy and Astrophysics, Vol.254, NO. FEB(I), P. 42, 1992

Astronomy and Astrophysics

Astrophysics

9

Scientific paper

In the course of our optical follow up of the Ooty sample of ultra-steep spectrum radio sources (USSRS), we have discovered an exceptionally interesting case of a classical double radio source of size ~14" and spectral index α = - 1.2 associated with a red galaxy at a modest redshift of z = 0.477. The galaxy exhibits gaseous wisps broadly coincident with the radio lobes. The optical spectrum is dominated by an emission line showing a very large rest-frame equivalent width of 350 A, a spatial extent of ~10" at the position angle of the radio structure, and a tilt with a maximum rest-frame velocity difference of ~760 km s^-1^. These properties, as well as the presence of the optical wisps suggest that the system is a product of a merger involving a gas-rich disk and a massive elliptical. Even though the object is relatively bright (V= 21.3), additional spectral lines could only be detected after a persistent, deep integration. These very faint features, identified with Hβ, [O III] λ5007, and H, K and G-band, have lead to an unambiguous interpretation of the dominant emission line as being [O II] λ3727. The detection of faint lines may have considerable relevance to some cases of radio galaxies for which extremely large redshifts (z > 3) have been inferred recently. The red colour of the galaxy, and the equivalent widths of the stellar absorption features suggest that the continuum of 1411-192 is dominated by an old stellar population. The physical conditions of the gas are similar to those of LINERS, with shock-heating as a possible ionization mechanism. The association of an "ultra-soil" emission line spectrum with such a powerful radio galaxy is intriguing.

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