Home > ALMA Jセミナー > 2021.3.29-2021.4.4


3月31日(水)15:00~16:00    ALMA-J seminar            zoom
Mar 31 Wed  



ALMA-J seminar
Regularly Scheduled/Sporadic
Every Wednesday
Date and time
2021 Mar. 31 15:00-16:00
Yusuke Miyamoto (NAOJ)
Atomic Carbon [C I] Mapping of the Nearby Galaxy M83
Atomic carbon (CI) has been proposed to be a global tracer of the molecular gas as a substitute for CO, however, its utility remains unproven. To evaluate the suitability of CI as the tracer, [CI] (3P1 −3 P0) (hereinafter [CI](1–0)) mapping observations, i.e., independent of CO brightness, and comparison of the distribution of [CI] and CO with H2 which is estimated by an independent method are essential. We performed [CI](1–0) mapping observations of the northern part of the nearby spiral galaxy M83 with the ASTE telescope and compared the distributions of [CI](1–0) with CO lines (CO(1–0), CO(3–2), and 13CO(1–0)), HI, and infrared (IR) emission (70, 160, and 250 μm). The [CI](1–0) distribution in the central region is similar to that of the CO lines, whereas [CI](1–0) in the arm region is distributed outside the CO. We examined the dust temperature, Tdust, and dust mass surface density, Σdust, by fitting the IR continuum spectrum distribution with a single-temperature modified blackbody. Assuming that dust and gas are well mixed and that a gas-to-dust ratio (GDR) is fixed in the atomic and molecular phases, cold molecular gas distribution, Σmol, can be estimated from Σdust by subtracting the atomic gas contribution. We solved GDR and CO-to-H2 conversion factor in a self-consistent way and found a much better consistency of the integrated intensity of CO(1–0) with the distribution of Σmol than that of [CI](1–0). Although the molecular gas mass in the whole area estimated from dust, CO, and [CI] is consistent within error, [CI](1–0) tends to underestimate the mass especially in the low Tdust region. Our results indicate that the atomic carbon is a photodissociation product of CO, and consequently, compared to CO(1–0), [CI](1–0) is less reliable in tracing the bulk of ”cold” molecular gas in the normal galactic disk.

Hiroshi Nagai, Xing Lu

Home > ALMA Jセミナー > 2021.3.29-2021.4.4

Return to page top