Astronomers study giant molecular clouds in galaxy NGC 613

An international team of astronomers used the Atacama Large Millimeter/submillimeter Array (ALMA) to perform high-resolution observations of a nearby galaxy called NGC 613. The results of the observation campaign, published on May 30 on the preprint server arXiv, shed further light on the numerous giant molecular clouds at the center of this galaxy. Molecular clouds are huge complexes of interstellar gas and dust left over from the formation of galaxies, and are composed mainly of molecular hydrogen. Molecular clouds with more than 100,000 solar masses are called giant molecular clouds (GMCs). GMCs generally have diameters of 15 to 600 light years and are the coldest and densest parts of the interstellar medium. GMCs are the gas reservoirs where most star formation processes take place. Therefore, studying their life cycle and properties is crucial to advance our knowledge of galaxy formation and evolution. NGC 613 is a nearby barred spiral galaxy located about 57 million light-years away with a total stellar mass of about 45 billion solar masses. The galaxy has a bright core and a ring of star-forming cores. Previous observations of NGC 613 have revealed that NGC 613 hosts GMCs in and around its core ring. Recently, a group of astronomers led by Woorak Choi from Yonsei University in South Korea decided to use the ALMA telescope to take a closer look at these GMCs and study their properties. “NGC 613 was observed using the Atacama Large Millimeter/submillimeter Array on line 12CO(1-0) (geostationary frequency 115.271 GHz),” the researchers wrote.

Through ALMA observations, Choi’s team was able to identify 356 GMCs in NGC 613, 158 of which had spatial and spectral resolution. The size of the GMCs in this galaxy was found to be 49 to 244 light years, with a velocity dispersion ranging from 2 to 36 km/s. The molecular gas mass of the GMCs in the sample was estimated to be 3 to 50 million solar masses, and the surface density of molecular gas mass ranged from 100 to 6,000 solar masses/pc2. By comparing the GMCs of NGC 613 with those of the Milky Way disk and the Local Galaxy, the astronomers found that the GMCs of the studied galaxies are of comparable size. However, the GMCs described in the paper generally have larger velocity dispersions, molecular gas masses, and molecular gas mass surface densities. Analyzing the distribution of GMCs identified within NGC 613, scientists found that their size is similar in different regions of the galaxy. However, GMCs in the dust band of NGC 613 seem to have smaller gas molecular masses, velocity dispersions and surface densities of gas clumps than GMCs in other regions. The research team also found that GMCs in the arcs tend to have larger gas masses and gas mass surface densities than GMCs in other regions of NGC 613. According to the study, the studied giant molecular clouds are slightly bound by the influence of gravity, and GMCs in the arcs tend to have smaller virial parameters than GMCs in other regions of the galaxy. The obtained results also suggest that the characteristic cloud life of NGC 613’s GMCs is about 3 to 8 million years.

source: https://dx.doi.org/10.48550/arxiv.2405.19709