SIMBAD references

The properties of star-forming clouds at the edge of the galactic molecular disk (far-outer Galaxy: FOG) are analyzed. By adding data from the literature, we compare the inner- and outer Galaxy (separated at R=R₀=8.5kpc) cloud populations. Applying a radiation transfer model to multi-line CO observations of two FOG clouds, T_kin's between about 6K and 15K are derived, comparable to those of clouds at smaller R. A statistical analysis of T^*_A both of clouds without embedded heating sources, and of clouds associated with IRAS sources, confirms there is no evidence for a gradient in cloud temperatures across the Galaxy for R>8.5kpc. The column density of H₂, as derived from N(H₂)=XxW_CO(={Integral}T^*_Rdv), and the H₂ LTE column density show a reasonable agreement for X=2.3x10²⁰cm^–2(Kxkm/s)^–1 (derived for the inner Galaxy), if the LTE analysis takes into account a galactic gradient of (H₂/¹³CO). The average and median values of X=N_lte/{Integral}T^*_Rdv, 3.3±1.7 [1σ] and 2.9x10²⁰ respectively, then are within 30-45% of the inner Galaxy value. Due to saturation effects the average X increases from 3x10²⁰ (W_CO≤20) to 6x10²⁰cm^–2(Kxkm/s)^–1 (W_CO>35Kkm/s). Including data from the literature we have a sample of 204 molecular clouds with 3≲R≲20kpc. Assuming X=2.3x10²⁰ for all inner- and outer Galaxy clouds we find separate, nearly parallel relations in diagrams of logM_WCO versus logr_A and log{DELTA}v versus logr_A. Although part of the offset of a factor of 2 in r_A may be due to the difficulties related to the identification of inner Galaxy clouds, it may be mainly explained by inner Galaxy clouds having a higher density, or by a variation of X with R (or with mass). We find M_WCO∝ r_A^2.0 ± 0.1^ for all clouds, and {DELTA}v ∝ r_A^0.48 ±0.04^ (inner) and ∝ r_A^0.53 ±0.03^ (outer). Inner- and outer Galaxy clouds define a single relation in a diagram of logL_CO versus log{DELTA}v: L_CO∝ {DELTA}v^3.91 ±0.12^. This is in contrast to published results where an offset is found between clouds inside and outside the solar circle. We conclude that a diagram of CO luminosity versus line width is not a good instrument to determine whether there is a dependence of X on R. The mass spectrum for all outer Galaxy molecular clouds in the extended sample with M_WCO>3.75x10⁴ is dN/dM_WCO∝ M_WCO^{–1.62±0.04}. For all 204 clouds, the slope is -1.79±0.03. The average ratio of virial- to W_CO-mass of all clouds is 1.4±1.3 (1σ), with a possible dependency on R and/or mass: there are indications that the ratio increases for clouds at larger R, or for clouds of smaller mass, but the cloud-cloud variations are large. Most clouds in the sample could be in equilibrium through confinement by external pressure. All clouds can be made to be in virial equilibrium, by allowing X to change by a factor of 4 between R ≃4 and 20kpc. This would require the galactic abundance gradient to be steeper than what is expected from an extrapolation of the presently available data.