CI and CO in nearby galaxy centers: the bright galaxies NGC1068 (M77), NGC2146, NGC3079, NGC4826 (M64), and NGC7469

TL;DR

This study models the circumnuclear molecular gas in five bright galaxy centers using multi-line CO and [CI] observations, revealing diverse physical conditions and significantly lower CO-to-H2 conversion factors than the standard value.

Contribution

It provides detailed modeling of molecular gas properties in nearby galaxy centers, highlighting variations and lower conversion factors compared to the Milky Way.

Findings

High kinetic temperatures (125-150 K) in NGC2146 and NGC3079.

Very high gas densities (0.3-1.0 x 10^5 cm^-3) in NGC2146, NGC3079, and NGC7469.

H2 masses are about 1-2% of the dynamical mass within the central kiloparsecs.

Abstract

Maps and measurements of the J=1-0, J=2-1, J=3-2, J=4-3 12CO, the J=1-0, J=2-1, and J=3-2 13CO lines in the central arcminute squared of NGC1068, NGC2146, NGC3079, NGC4826, and NGC7469, as well as 492 GHz [CI] maps in three of these are used to model the circumnuclear molecular gas in these galaxies. In all five objects, the bright CO concentrations mapped have line intensities that require two distinct gas components for satisfactory fits. The physical condition of the molecular gas differs from galaxy to galaxy. High kinetic temperatures of 125-150 K occur in NGC2146 and NGC3079. Very high densities of 0.3-1.0 x 10**5 cm**-3 occur in NGC2146, NGC3079, and NGC7469. The CO to H2 conversion factor X is typically an order of magnitude less than the `standard' value in the Solar Neighborhood. The molecular gas is constrained within radii between 0.9 and 1.5 kpc from the nuclei. Within these radii, H2 masses are typically 1.2-2.5 x 10**8 M(sun). The exception is the (relatively nearby) merger NGC4826 with R=0.3 kpc, and M = 3 x 10**7 M(sun). In all five galaxies, the H2 mass is typically about one per cent of the dynamical mass in the same region.