New redshift determinations for three 3C radio sources.
ATel #10021; V. Reynaldi (IALP - FCAGLP)
on 29 Jan 2017; 18:34 UT
Credential Certification: Victoria Reynaldi (vreynaldi@fcaglp.unlp.edu.ar)
I report the new redshift determinations of three radio sources 3C 196.1, 3C 268.2 and 3C 303.1 by using GMOS/Gemini North long-slit optical spectroscopy. The details of the observations are summarized in the following table (the B600 grating was used for the three observations):
Object | RA(J2000) | DEC(J2000) | Date of obs. | width-slit(arcsec) | PA(deg) | Exp.Time(sec)
3C 196.1 | 8:15:27.8 | -03:08:27 | Mar 2012 | 0.5 | 50 | 2560
3C 268.2| |12:00:59.1 | 31:33:28 | Feb 2011 | 0.5 | 165 | 2576
3C 303.1 | 14:43:14.5 | 77:07:28 | Feb 2012 | 1 | 145 | 2560
The three of the sources have extended regions of ionized gas that do not obey a spherical distribution. Rather than that, these Extended Emission-Line Regions (EELR) emerge near the central core and fade out toward the outskirts of the galaxy in a quite specific direction. The spectra were obtained with the slit oriented in such a direction (the Position Angle, PA, is measured from North to East).
The spectral range is 3300-5200A. The main feature in all the spectra is the [OIII]4959,5007 emission-line, followed by Hbeta and the (unresolved) [OII]3727 doublet. There also are important emission-lines from neon: [NeV]3424 (the bluest line in the spectra) and [NeIII]3869.
The following table shows the new redshift determinations, along with their error measurement (in parenthesis) in the second column. The redshifts of the sources, as they were known so far, and their references (as stated by NED, NASA/IPAC Extragalactic Database) are also listed.
Object | NEW REDSHIFT | redshift (NED) | NED Reference
3C 196.1 | 0.19753(2E-05 | 0.198 |Smith & Spinrad, 1980, PASP, 92, 553
3C 268.2 | 0.36280(3E-05) | 0.362 | Spinrad et al., 1985, PASP, 97, 932
3C 303.1 | 0.26862(3E-05) | 0.2704(6E-05) | Holt et al., 2008, MNRAS, 387, 639
Line-emission's centroids in Gemini spectra show wavelength displacements that do not correspond to the known redshifts. In order to be consistent with the last and more recent redshift calculation of these sources, the new redshifts were obtained by following the same method that Holt et al., 2008, MNRAS, 387, 639 employed in their work. The central spectrum was extracted with a 3 px (0.3 arcsec) aperture, then a new redshift was calculated by using all the emission-lines that could be fitted with just one Gaussian component, i.e. all the lines except [OIII]4959 and [OIII]5007. Once the Gaussian decomposition of these two line-profiles were obtained (up to three Gaussian components were needed) we identified the component whose wavelength displacement were consistent with our former redshift calculation. Then, the new redshift were recalculated by using all the lines available in each spectrum.
