arXiv subjects

S. Komugi

Publications and source records attributed to S. Komugi.

7 recordsLinked to original sources

arXiv2021

A Giant Molecular Cloud Catalog in the Molecular Disk of the Elliptical Galaxy NGC 5128 (Centaurus A)

We present the first census of giant molecular clouds (GMCs) complete down to 10$^6 M_{\odot}$ and within the inner 4 kpc of the nearest giant elliptical and powerful radio galaxy, Centaurus A. We identified 689 GMCs using CO(1--0) data with 1" spatial resolution ($\sim 20$ pc) and 2 km/s velocity resolution obtained with the Atacama Large Millimeter/submillimeter Array (ALMA). The $I$(CO)-$N$(H$_2$) conversion factor based on the virial method is $X_{\rm CO}$ = $(2 \pm 1 )\times10^{20}$ cm$^{-2}$(K km/s)$^{-1}$ for the entire molecular disk, consistent with that of the disks of spiral galaxies including the Milky Way, and $X_{\rm CO}$ = $(5 \pm 2)\times10^{20}$ cm$^{-2}$(K km/s)$^{-1}$ for the circumnuclear disk (CND, within a galactocentric radius of 200 pc). We obtained the GMC mass spectrum distribution and find that the best-truncated power-law fit for the whole molecular disk, with index $γ\simeq -2.41 \pm 0.02$ and upper cutoff mass $\sim 1.3 \times 10^{7} M_{\odot}$, is also in agreement with that of nearby disk galaxies. A trend is found in the mass spectrum index from steep to shallow as we move to inner radii. Although the GMCs are in an elliptical galaxy, the general GMC properties in the molecular disk are as in spiral galaxies. However, in the CND, large offsets in the line-width-size scaling relations ($\sim$ 0.3 dex higher than those in the GMCs in the molecular disk), a different $X_{\rm CO}$ factor, and the shallowest GMC mass distribution shape ($γ= -1.1 \pm 0.2$) all suggest that there the GMCs are most strongly affected by the presence of the AGN and/or shear motions.

astro-ph.GA↗

arXiv2014

ASTE observations in the 345 GHz window towards the HII region N113 of the Large Magellanic Cloud

N113 is an HII region located in the central part of the Large Magellanic Cloud (LMC) with an associated molecular cloud very rich in molecular species. Most of the previously observed molecular lines cover the frequency range 85-270 GHz. Thus, a survey and study of lines at the 345 GHz window is required in order to have a more complete understanding of the chemistry and excitation conditions of the region. We mapped a region of 2.5' x 2.5' centered at N113 using the Atacama Submillimeter Telescope Experiment in the 13CO J=3-2 line with an angular and spectral resolution of 22" and 0.11 km/s, respectively. In addition, we observed 16 molecular lines as single pointings towards its center. For the molecular cloud associated with N113, from the 13CO J=3-2 map we estimate LTE and virial masses of about 1x10^4 and 4.5x10^4 M_sun, respectively. Additionally, from the dust continuum emission at 500 micron we obtain a mass of gas of 7x10^3 M_sun. Towards the cloud center we detected emission from: 12CO, 13CO, C18O (3-2), HCN, HNC, HCO+, C2H (4-3), and CS (7-6); being the first reported detection of HCN, HNC, and C2H (4-3) lines from this region. The CS (7-6) which was previously tentatively detected is confirmed in this study. By analyzing the HCN, HNC, and C2H, we suggest that their emission may arise from a photodissociation region (PDR). Moreover, we suggest that the chemistry involving the C2H in N113 can be similar to that in Galactic PDRs. Using the HCN J=4-3, J=3-2, and J=1-0 lines in a RADEX analysis we conclude that we are observing very high density gas, between some 10^5 and 10^7 cm-3.

astro-ph.GA↗

arXiv2012

Giant Molecular Clouds and Star Formation in the Tidal Molecular Arm of NGC 4039

The properties of tidally induced arms provide a means to study molecular cloud formation and the subsequent star formation under environmental conditions which in principle are different from quasi stationary spiral arms. We report the properties of a newly discovered molecular gas arm of likely tidal origin at the south of NGC 4039 and the overlap region in the Antennae galaxies, with a resolution of 1"68 x 0"85, using the Atacama Large Millimeter/submillimeter Array science verification CO(2-1) data. The arm extends 3.4 kpc (34") and is characterized by widths of ~ 200 pc (2") and velocity widths of typically \DeltaV ~ 10-20 km/s . About 10 clumps are strung out along this structure, most of them unresolved, with average surface densities of Σ_gas ~ 10-100 Msun pc^{-2}, and masses of (1-8) x 10^6 Msun. These structures resemble the morphology of beads on a string, with an almost equidistant separation between the beads of about 350 pc, which may represent a characteristic separation scale for giant molecular associations. We find that the star formation efficiency at a resolution of 6" (600 pc) is in general a factor of 10 higher than in disk galaxies and other tidal arms and bridges. This arm is linked, based on the distribution and kinematics, to the base of the western spiral arm of NGC 4039, but its morphology is different to that predicted by high-resolution simulations of the Antennae galaxies.

astro-ph.CO↗

arXiv2012

The Schmidt-Kennicutt Law of Matched-Age Star Forming Regions; Pa-alpha Observations of the Early-Phase Interacting Galaxy Taffy I

In order to test a recent hypothesis that the dispersion in the Schmidt-Kennicutt law arises from variations in the evolutionary stage of star forming molecular clouds, we compared molecular gas and recent star formation in an early-phase merger galaxy pair, Taffy I (UGC\ 12915/UGC\ 12914, VV\ 254) which went through a direct collision 20 Myr ago and whose star forming regions are expected to have similar ages. Narrow-band Pa-alpha image is obtained using the ANIR near-infrared camera on the mini-TAO 1m telescope. The image enables us to derive accurate star formation rates within the galaxy directly. The total star formation rate, 22.2 M_sun/yr, was found to be much higher than previous estimates. Ages of individual star forming blobs estimated from equivalent widths indicate that most star forming regions are ~7 Myr old, except for a giant HII region at the bridge which is much younger. Comparison between star formation rates and molecular gas masses for the regions with the same age exhibits a surprisingly tight correlation, a slope of unity, and star formation efficiencies comparable to those of starburst galaxies. These results suggest that Taffy I has just evolved into a starburst system after the collision, and the star forming sites are at a similar stage in their evolution from natal molecular clouds except for the bridge region. The tight Schmidt-Kennicutt law supports the scenario that dispersion in the star formation law is in large part due to differences in evolutionary stage of star forming regions.

astro-ph.CO↗

arXiv2011

Temperature Variations of the Cold Dust in the Triangulum Galaxy M33

We present wide-field 1.1 mm continuum imaging of the nearby spiral galaxy M 33, conducted with the AzTEC bolometer camera on ASTE. We show that the 1.1 mm flux traces the distribution of dust with T ~20 K. Combined with far-infrared imaging at 160um, we derive the dust temperature distribution out to a galactic radius of ~7 kpc with a spatial resolution of ~100 parsecs. Although the 1.1 mm flux is observed predominantly near star forming regions, we find a smooth radial temperature gradient declining from ~20 K to ~13 K, consistent with recent results from the Herschel satellite. Further comparison of individual regions show a strong correlation between the cold dust temperature and the Ks band brightness, but not with the ionizing flux. The observed results imply that the dominant heating source of cold dust at few hundred parsec scales are due to the non-OB stars, even when associated with star forming regions.

astro-ph.GA↗

arXiv2009

AKARI Far-Infrared All Sky Survey

We demonstrate the capability of AKARI for mapping diffuse far-infrared emission and achieved reliability of all-sky diffuse map. We have conducted an all-sky survey for more than 94 % of the whole sky during cold phase of AKARI observation in 2006 Feb. -- 2007 Aug. The survey in far-infrared waveband covers 50 um -- 180 um with four bands centered at 65 um, 90 um, 140 um, and 160 um and spatial resolution of 3000 -- 4000 (FWHM).This survey has allowed us to make a revolutionary improvement compared to the IRAS survey that was conducted in 1983 in both spatial resolution and sensitivity after more than a quarter of a century. Additionally, it will provide us the first all-sky survey data with high-spatial resolution beyond 100 um. Considering its extreme importance of the AKARI far-infrared diffuse emission map, we are now investigating carefully the quality of the data for possible release of the archival data. Critical subjects in making image of diffuse emission from detected signal are the transient response and long-term stability of the far-infrared detectors. Quantitative evaluation of these characteristics is the key to achieve sensitivity comparable to or better than that for point sources (< 20 -- 95 [MJy/sr]). We describe current activities and progress that are focused on making high quality all-sky survey images of the diffuse far-infrared emission.

astro-ph.GA↗

arXiv2008

Molecular Gas Distribution in Barred and Non-Barred Galaxies along the Hubble Sequence

We present results from a survey of 12CO(J=1-0) spectra obtained for the central regions of 68 nearby galaxies at an angular resolution of 16 arcseconds using the Nobeyama Radio Observatory 45m telescope, aimed at characterizing the properties of star forming molecular gas. Combined with similar resolution observations in the literature, the compiled sample set of 166 galaxies span a wide range of galactic properties. NGC 4380, which was previously undetected in CO, was detected. This initial paper of a series will focus on the data and the gaseous properties of the samples, and particularly on the degree of central concentration of molecular gas in a range of morphological types, from early (S0/Sa) to late (Sd/Sm) galaxies with and without bars. The degree of molecular central concentration in the central kiloparsec, compared to the central several kiloparsecs of galaxies, is found to vary smoothly with Hubble type, so that early type galaxies show larger central concentration. The comparison of barred and non-barred galaxies within early and late type galaxies suggest that difference in Hubble type, representing the effect of bulges, is the more important factor in concentrating gas into the central regions than bars.

astro-ph↗