20 research outputs found
A nearly constant CN/HCN line ratio in nearby galaxies: CN as a new tracer of dense gas
We investigate the relationship between CN N = 1 - 0 and HCN J = 1 - 0
emission on scales from 30 pc to 400 pc using ALMA archival data, for which CN
is often observed simultaneously with the CO J = 1 - 0 line. In a sample of 9
nearby galaxies ranging from ultra-luminous infrared galaxies to normal spiral
galaxies, we measure a remarkably constant CN/HCN line intensity ratio of 0.86
0.07 (standard deviation of 0.20). This relatively constant CN/HCN line
ratio is rather unexpected, as models of photon dominated regions have
suggested that HCN emission traces shielded regions with high column densities
while CN should trace dense gas exposed to high ultraviolet radiation fields.
We find that the CN/HCN line ratio shows no significant correlation with
molecular gas surface density, but shows a mild trend (increase of ~ 1.3 per
dex) with both star formation rate surface density and star formation
efficiency (the inverse of the molecular gas depletion time). Some starburst
and active galactic nuclei show small enhancements in their CN/HCN ratio, while
other nuclei show no significant difference from their surrounding disks. The
nearly constant CN/HCN line ratio implies that CN, like HCN, can be used as a
tracer of dense gas mass and dense gas fraction in nearby galaxies.Comment: Accepted to MNRAS; 21 pages, 12 figure
Stored in the archives: Uncovering the CN/CO intensity ratio with ALMA in nearby U/LIRGs
We present an archival Atacama Large Millimeter/submillimeter Array (ALMA)
study of the CN N = 1 - 0 / CO J = 1 - 0 intensity ratio in nearby (z < 0.05)
Ultra Luminous and Luminous Infrared Galaxies (U/LIRGs). We identify sixteen
U/LIRGs that have been observed in both CN and CO lines at 500 pc
resolution based on sixteen different ALMA projects. We measure the (CN
bright)/CO and (CN bright)/(CN faint) intensity ratios at an ensemble of
molecular clouds scales (CN bright = CN N = 1 - 0, J = 3/2 - 1/2; CN faint = CN
N = 1 - 0, J = 1/2 - 1/2 hyperfine groupings). Our global measured (CN
bright)/CO ratios range from 0.02-0.15 in LIRGs and 0.08-0.17 in ULIRGs. We
attribute the larger spread in LIRGs to the variety of galaxy environments
included in our sample. Overall, we find that the (CN bright)/CO ratio is
higher in nuclear regions, where the physical and excitation conditions favour
increased CN emission relative to the disk regions. 10 out of 11 galaxies which
contain well-documented active galactic nuclei show higher ratios in the
nucleus compared to the disk. Finally, we measure the median resolved (CN
bright)/(CN faint) ratio and use it to estimate the total integrated CN line
optical depth in ULIRGs ( 0.96) and LIRGs ( 0.23). The
optical depth difference is likely due to the higher molecular gas surface
densities found in the more compact ULIRG systems.Comment: Accepted to MNRAS; 18 pages, 9 figure
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Determination of the most suitable technology system for virtual touring at the National Museum of Denmark
This report documents the process by which a virtual touring system was designed for the National Museum of Denmark. The selection of the most suitable solution was made based on background research of various types of imaging technology as well as the specific desires and characteristics of the museum. The solutions consists of panoramic images, still images and relevant text to be presented on the museum's website. A prototype website was created on CD-ROM to demonstrate the system