Evidence for a nuclear radio jet and its structure down to ≲100 Schwarzschild radii in the center of the Sombrero galaxy (M 104, NGC 4594)
- INAF Istituto di Radioastronomia, via Gobetti 101, I-40129 Bologna (Italy)
- Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuo, Sagamihara 252-5210 (Japan)
- National Astronomical Observatory of Japan, Osawa, Mitaka, Tokyo 181-8588 (Japan)
- Academia Sinica Institute for Astronomy and Astrophysics, 11F Astronomy-Mathematics Building, National Taiwan University, No. 1, Roosevelt Road, Sec. 4, Taipei 10617, Taiwan R.O.C. (China)
The Sombrero galaxy (M 104, NGC 4594) is associated with one of the nearest low-luminosity active galactic nuclei (AGNs). We investigated the detailed radio structure of the Sombrero nucleus using high-resolution, quasi-simultaneous, multi-frequency, phase-referencing Very Long Baseline Array observations. We obtained high-quality images of this nucleus at seven frequencies, where those at 15, 24, and 43 GHz are the first clear very long baseline interferometry detections. At 43 GHz, the nuclear structure was imaged on a linear scale under 0.01 pc or 100 Schwarzschild radii, revealing a compact, high-brightness-temperature (≳ 3 × 10{sup 9} K) radio core. We discovered the presence of the extended structure emanating from the core on two sides in the northwest and southeast directions. The nuclear radio spectra show a clear spatial gradient, which is similar to that seen in more luminous AGNs with powerful relativistic jets. Moreover, the size and position of the core tend to be frequency dependent. These findings provide evidence that the central engine of the Sombrero is powering radio jets and the jets are overwhelming the emission from the underlying radiatively inefficient accretion flow over the observed frequencies. Based on these radio characteristics, we constrained the following physical parameters for the M 104 jets: (1) the northern side is approaching, whereas the southern one is receding; (2) the jet viewing angle is relatively close to our line-of-sight (≲ 25°); and (3) the intrinsic jet velocity is highly sub-relativistic (≲ 0.2c). The derived pole-on nature of the M 104 jets is consistent with the previous argument that this nucleus contains a true type II AGN, i.e., the broad line region is actually absent or intrinsically weak if the plane of the circumnuclear torus is perpendicular to the jet axis.
- OSTI ID:
- 22348564
- Journal Information:
- Astrophysical Journal, Vol. 779, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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