The Structure and Ionization of the Extended Emission-Line Filaments Surrounding the QSO MR 2251-178
Abstract
New and deep high spatial resolution images of the QSO MR 2251-178 in the [O II] λ3727, [O III] λ5007, and Hα emission lines together with VLA radio maps are presented. The VLA radio maps show MR 2251-178 as a weak extended radio source with a double-sided radio jet structure, i.e., Fanaroff-Riley class I galaxy. Also the nearby galaxy G1 located to the north at a projected distance of 75 kpc has been detected at both 6 and 20 cm as an unresolved source at the present resolution. The quasar MR 2251-178 is a unique example of weak radio source showing an extended system of emission-line filaments surrounding it. The size, luminosity, excitation conditions, and mass of the ionized gas is similar to that detected around very powerful radio sources at low and high redshift. Circumnuclear emission-line gas is detected for the first time in [O II] λ3727 and [O III] λ5007. This ionized gas is located at distances between 3 and 6 kpc from the nucleus and is consistent with gas directly ionized by the central nonthermal source. These regions are strongly concentrated around the radio axis in the same way as is observed in some nearby Seyfert galaxies and high-redshift radio galaxies. Two new systems of Hα filaments are also observed for the first time. These systems are located at distances of 30 kpc and 50 kpc to the east of the MR 2251-178 nucleus and have a circular filamentary structure with a total size of almost 70 kpc and 100 kpc, respectively. An upper limit of 9.3 x 10^9^ M_sun_ and 2.1 x 10^10^ M_sun_ has been derived for the amount of ionized gas in these filaments. Several high-excitation emission-line filaments have been detected in the [O III] λ5007 emission line around MR 2251-178 forming, together with the Hα filaments, a ring structure at a radial distance of 50 kpc. The upper limit for the mass in these filaments is 2 x 10^9^ M_sun_ and the ionization parameter is similar to that found in the extended emission line regions (EELR) around nearby radio galaxies. Two possible scenarios consistent with the observations are outlined. One is the interaction between MR 2251-178 and the galaxy G1. The second one considers MR 2251-178 and the system of filaments as the merger result of a giant elliptical with a smaller disk galaxy.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 1990
- DOI:
- 10.1086/168847
- Bibcode:
- 1990ApJ...356..389M
- Keywords:
-
- Emission Spectra;
- Forbidden Transitions;
- Galactic Structure;
- Gas Ionization;
- Oxygen Spectra;
- Quasars;
- Galactic Nuclei;
- H Alpha Line;
- Hot Stars;
- Radio Jets (Astronomy);
- Stellar Envelopes;
- Very Large Array (Vla);
- Astrophysics;
- GALAXIES: INTERACTIONS;
- GALAXIES: INDIVIDUAL ALPHANUMERIC: MR 2251-178;
- GALAXIES: NUCLEI;
- QUASARS;
- RADIO SOURCES: GALAXIES