Rotation and stability of the circumnuclear gas disk in the Galactic Center potential by the ALMA CMZ Exploration Survey (ACES)

TL;DR

The paper constrains the GC gravitational potential using ACES data, showing that a nearly spherical potential best reproduces the CND's morphology and kinematics. It derives a rotation curve dominated by a central SMBH plus a cusp-like CMZ mass distribution, with $ ho_{ m mass} \\propto R^{-1.9}$ and $M(R)$ tracing a few million solar masses within a few parsecs. Stability analyses indicate tidal-Jeans suppression of fragmentation inside $R_T \approx 14$ pc and Toomre stability inside ~4 pc, implying suppressed star formation and a possible top-heavy IMF in the circumnuclear region. These results support a cusp-dominated mass model with limited inner-disk star formation and have implications for the GC's dynamical evolution and IMF in the CND.

Abstract

We investigated the gravitational potential and mass distribution in the Galactic Center by examining the morphology and kinematics of the circumnuclear gaseous disk revealed by the molecular line data from the ALMA CMZ Exploration Survey (ACES). We obtain an estimate of the shape of the potential {within the central $\sim 20$ pc} to reproduce the observed properties of the circumnuclear gas disk (CND) by simulating the motion of test particles for various axial ratios and show that the potential is approximately spherical. We construct a rotation curve by applying the terminal velocity method to the position-velocity diagrams, and calculate the mass distribution in the Galactic Center. The distribution of mass density is found to be of cusp type, approximated by $ρ_{\rm mass} \sim 1.56\times 10^5(R/1 {\rm pc})^{-1.9}~M_{\odot} {\rm pc}^{-3}$, where $R$ is the distance from the nucleus. We discuss the tidal effect caused by the gravitational potential that produces the rotation curve and show that the gas disk is stable against self-gravitational contraction within a critical radius of $ R_{\rm T}\sim 14 ~(ρ_{\rm gas}/10^5 {\rm H_2~cm^{-3}})^{-1/2}~{\rm pc}$. This suggests suppression of star formation and a top-heavy IMF in the circmunuclear region.

Figures (20)

• Figure 1: (A) Moment 0 maps of the central $0\deg.4\times 0\deg.1$ region around in the line by ACES. GLON and GLAT stand for $l$ and $b$, respectively. The structures discussed in the paper are illustrated. (B) Same, but in . (C) Longitudinal cross section of moment 0 map across . Note the central hole inside the CND, which is enlarged in figure \ref{['fig-hole']}. Sharp negative peak is due to absorption of the continuum from . (D) and (E) Moment 1 maps of and lines, respectively, in unit of m s$^{-1}$. Note the regular Galactic rotation with positive velocities at positive longitudes and negative velocities at negative longitudes. Alt text: Moment 0 maps, intensity cross section, and moment 1 maps in the and lines in the central $\pm 0\deg.1$ around .
• Figure 2: Close up of the moment 0 maps for the central $0\deg.05\times 0\deg.03$ region centered on . Note the "molecular hole" in the center. [Top] with contours every 2.5 . The blue mark indicates the position of at $(l,b)=-0\deg.055835,-0\deg.046110)$2022ApJ...940...15X. [2nd] Same, but in with contours every 1 . [3rd] Ratio of the HCN-to-CS moment 0 maps with contours of CS every 4 mJy beam$^{-1}$ km s$^{-1}$. [Bottom] Longitudinal cross section in line showing a hole of molecular gas inside $R \mathrel{ \vcenter{\m@th\f@size4 \ialign{$$\cr <\crcr{ } \sim\crcr}}} 1.5$ pc. The sharp negative peak at offset 0 is the absorption of the continuum emission from . Alt text: Moment 0 maps of the CND in and lines, and a cross section.
• Figure 3: [Top] Position-velocity diagrams of and H40$\alpha$ lines along the major axis of CND at position angle $70\deg$ (white dashed line in the top panel of figure \ref{['fig1']}) (width 10 pixels for CS, HCN, and 40 pix for H40$\alpha$). The horizontal axis is the offset from , positive to the east (left). [Bottom] PVD in CS by green overlaid with 40 by red. Alt text: PVD along the major axis of the CND.
• Figure 4: [Top left] Cross section of the moment 0 map from to SW at $PA=240\deg$ showing a clear cut of intensity inside the CND. [Top right, Bottom] Simulations for spherical, disk and bar potentials, respectively. The central deep hole is reproduced only by the spherical potential. Alt text: Cross section of moment 0 map across compared with the simulations.
• Figure 5: [1st panel] Moment 0 map of the minispiral in the 40 line. [2nd] Same, but with contours overlaid on the moment 0 map of the CND. [3rd] Overlay of LVD of the minispiral in 40 on LVD of CND in Ṫhe lines indicate Keplerian RC for the central black hole with a mass of $4\times 10^6\Msun$. [4th panel] Oblique projections of the 3D LBV 40 cube in violet from the longitude side superposed with that in the line in green. [5th] Same, but from latitude side. Alt text: Comparison of the minispiral with CND by moment 0 maps and LVDs in 40 and lines, and 3D projections of the LBV cubes.