arXiv subjects

Rieko Momose

Publications and source records attributed to Rieko Momose.

57 records · Page 4Linked to original sources

arXiv2011

Resolved Measurements of Xco in NGC 6946

We present the largest sample to date of giant molecular clouds (GMCs) in a substantial spiral galaxy other than the Milky Way. We map the distribution of molecular gas with high resolution and image fidelity within the central 5 kpc of the spiral galaxy NGC 6946 in the 12CO (J=1-0) transition. By combining observations from the Nobeyama Radio Observatory 45-meter single dish telescope and the Combined Array for Research in Millimeter Astronomy (CARMA) interferometer, we are able to obtain high image fidelity and accurate measurements of LCO compared with previous purely interferometric studies. We resolve individual giant molecular clouds (GMCs), measure their luminosities and virial masses, and derive Xco - the conversion factor from CO measurements to H2 masses - within individual clouds. On average, we find that Xco = 1.2 \times 10^20 cm-2 / (K km s-1), which is consistent within our uncertainties with previously derived Galactic values as well as the value we derive for Galactic GMCs above our mass sensitivity limit. The properties of our GMCs are largely consistent with the trends observed for molecular clouds detected in the Milky Way disk, with the exception of six clouds detected within \sim400 pc of the center of NGC 6946, which exhibit larger velocity dispersions for a given size and luminosity, as has also been observed at the Galactic center.

astro-ph.CO↗

arXiv2011

The Super-linear Slope of the Spatially-Resolved Star Formation Law in NGC 3521 and NGC 5194 (M51a)

We have conducted interferometric observations with CARMA and an OTF mapping with the 45-m telescope at NRO in the CO (J=1-0) emission line of NGC 3521. Combining these new data, together with CARMA+NRO45 data for M51a and archival SINGS H$α$, 24$μ$m, THINGS H I and GALEX FUV data for both galaxies, we investigate the empirical scaling law that connects the surface density of SFR and cold gas (the Schmidt-Kennicutt law) on a spatially-resolved basis. We argue that plausibly deriving SFR maps of nearby galaxies requires the diffuse stellar/dust background emission to be carefully subtracted. An approach to complete this task is presented and applied in our pixel-by-pixel analysis on both galaxies, showing that the controversial results whether the molecular S-K law is super-linear or basically linear is a result of removing or preserving the local background. In both galaxies, the power index of the molecular S-K law is 1.5-1.9 at the highest available resolution (230 pc), and decreases monotonically for decreasing resolution; while the scatter (mainly intrinsic) increases as the resolution becomes higher, indicating a trend for which the S-K law breaks down below some scale. Both quantities are systematically larger in M51a than in NGC 3521, but when plotted against the de-projected scale (δ_{dp}), they become highly consistent between the two galaxies, tentatively suggesting that the sub-kpc molecular S-K law in spiral galaxies depends only on the considered scale, without varying amongst spiral galaxies. A logarithmic function γ_{H_2}=-1.1 log[δ_{dp}/kpc]+1.4 and a linear relation σ_{H_2}=-0.2 [δ_{dp}/kpc]+0.7 are obtained through fitting to the M51a data, which describes both galaxies impressively well on sub-kpc scales. A larger sample of galaxies with better quality data are required to test the general applicability of these relations.

astro-ph.CO↗

arXiv2010

Star formation efficiency in the Barred Spiral Galaxy NGC 4303

We present new $^{12}$CO(J=1-0) observations of the barred galaxy NGC 4303 using the Nobeyama 45m telescope (NRO45) and the Combined Array for Research in Millimeter-wave Astronomy (CARMA). The H$α$ images of barred spiral galaxies often show active star formation in spiral arms, but less so in bars. We quantify the difference by measuring star formation rate and efficiency at a scale where local star formation is spatially resolved. Our CO map covers the central 2$\farcm$3 region of the galaxy; the combination of NRO45 and CARMA provides a high fidelity image, enabling accurate measurements of molecular gas surface density. We find that star formation rate and efficiency are twice as high in the spiral arms as in the bar. We discuss this difference in the context of the Kennicutt-Schimidt (KS) law, which indicates a constant star formation rate at a given gas surface density. The KS law breaks down at our native resolution ($\sim$ 250 pc), and substantial smoothing (to 500 pc) is necessary to reproduce the KS law, although with greater scatter.

astro-ph.CO↗