| Name: | Atharva Bagul |
| Affiliation: | IISER Bhopal |
| Conference ID : | ASI2023_404 |
| Title : | Cygnus A Obscuring Torus: Ionized, Atomic or Molecular? |
| Authors : | Atharva Bagul, Patrick Ogle, Robert Antonucci, Philip Maloney, Enrique Lopez Rodriguez |
| Mode of Presentation: | Poster |
| Abstract Category : | Extragalactic Astronomy |
| Abstract : | The prototypical powerful FR II radio galaxy Cygnus A fits extremely well into the quasar/radio galaxy unified model: high polarization with an angle almost perpendicular to the radio jet and polarized flux showing broad permitted lines. It has been claimed that ionized gas in the torus reveals a very clear torus shape via Bremmstrahlung emission. We rule out the later with an energetic argument and constrain the molecular and atomic gas properties with existing observations. The atomic absorption against the core has been shown to match the X-ray column only if the spin temperature is an implausible T_s = 1x10^6 K. This points to a molecular medium for the X-ray column log(N_h [cm^-2]) ~ 23.5. Yet no low-J CO absorption is detected to sensitive limits. The non-detection is surprising given that this powerful radio galaxy hosts a luminous, dust-obscured active nucleus and copious warm molecular hydrogen. These conditions suggest a detectable level of emission. Furthermore, the torus X-ray column density suggests detectable absorption. We explore various possibilities to explain the lack of a signature from cold CO. Specifically, the radiative excitation by the radio core renders low-J CO absorption below current sensitivities, and the high-J levels are well-populated and conducive to producing absorption. We test this hypothesis using archival Herschel/SPIRE FTS observations of Cygnus A of high-J CO lines (14 >= J >= 4 transitions). Still, high-J CO lines are not detected but the limits are inconclusive. ALMA observations near its high-frequency limit can be critical to obtaining the signature of the molecular line of the torus of Cygnus A. |
