248 research outputs found
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
Disentangling the circumnuclear environs of Centaurus A: Gaseous Spiral Arms in a Giant Elliptical Galaxy
We report the existence of spiral arms in the recently formed gaseous and
dusty disk of the closest giant elliptical, NGC 5128 (Centaurus A), using high
resolution 12CO(2-1) observations of the central 3 arcmin (3 kpc) obtained with
the Submillimeter Array (SMA). This provides evidence that spiral-like features
can develop within ellipticals if enough cold gas exists. We elucidate the
distribution and kinematics of the molecular gas in this region with a
resolution of 4.4 x 1.9 (80 pc x 40 pc). The spiral arms extend from the
circumnuclear gas at a radius of 200 pc to at least 1 kiloparsec. The general
properties of the arms are similar to those in spiral galaxies: they are
trailing, the width is \sim 500 \pm 200 pc, and the pitch angle is 20 degrees.
From independent estimates of the time when the HI-rich galaxy merger occurred,
we infer that the formation of spiral arms happened on a time scale of less
than \sim10^8 yr. The formation of spiral arms increases the gas density and
thus the star formation efficiency in the early stages of the formation of a
disk.Comment: 13 pages, 4 Figures. Accepted for publication in ApJ
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