Oral Presentation

ALMA Sees the Heart of Perseus: Discovery of the Cold Gas Stream and Rotating Disk in NGC1275

Author(s): Hiroshi Nagai

Presenter: Hiroshi Nagai (NAOJ)

ALMA recently started to reveal the presence of massive cold molecular gas in the central galaxies in galaxy clusters. Many of them show filamentary structures with a possible inflow motion. These cold gas components may play an important role for the AGN feeding, but detailed morphology and kinematics within the central 100 pc were not clear because of the lack of angular resolution. We observed NGC1275 in the Perseus cluster, which is the nearby representative of central galaxies, using ALMA with unprecedented sensitivity and angular resolution in ALMA Cycle 5. In the previous observations, CO(2-1) emission was detected as radial filaments lying in the east-west direction. We resolved the inner filament and found that the filament cannot be represented by a simple infalling stream both morphologically and kinematically (Nagai et al. 2019). The observed complex nature of the filament resembles the cold gas structure predicted by recent numerical simulations of cold chaotic accretion. Within the central 100~pc, we detected a rotational disk of the molecular gas whose mass is 10^8 M_sun. This is the first evidence of the presence of massive cold gas disk on this spatial scale for BCGs. The disk rotation axis is approximately consistent with the axis of the radio jet on subpc scales (Nagai et al. 2014; Nagai et al. 2017). This probably suggests that the cold gas disk is physically connected to the innermost accretion disk which is responsible for jet launching. A crude estimate of cold gass accretion rate suggests that the cold accretion rate can be higher than Bondi accretion rate. Thus, the cold accretion can be a dominant accretion channel in this system. We also received data from our Cycle 6 observation in Band 6 with the longest baseline configuration. Preliminary analysis suggests that the HCN(3-2) and HCO+(3-2) emissions are detected with the angular resolution of (40 x 20) mas, which can resolve the Bondi radius of NGC1275. This new result will be also discussed in the presentation.