Utilizing the Atacama Large Millimeter/sub-millimeter Array (ALMA), a collaborative team of astronomers has conducted a detailed examination of NGC 613, a nearby barred spiral galaxy. The findings, published on May 30 on the arXiv preprint server, provide significant insights into the giant molecular clouds (GMCs) populating the galaxy's center.
Molecular clouds are expansive regions of interstellar gas and dust, predominantly made up of molecular hydrogen. These clouds are remnants from the galaxy formation era. When molecular clouds surpass 100,000 solar masses, they are classified as giant molecular clouds (GMCs). Typically, GMCs span 15 to 600 light years and represent the densest and coldest segments of the interstellar medium.
GMCs play a crucial role as the primary sites of star formation. Therefore, understanding their lifecycle and attributes is essential for unraveling the mysteries surrounding galaxy formation and evolution.
Situated about 57 million light years away, NGC 613 boasts a stellar mass of approximately 45 billion solar masses. It is characterized by a bright core and a star-forming nuclear ring. Earlier studies identified GMCs in and around this nuclear ring. To delve deeper into these GMCs, astronomers led by Woorak Choi from Yonsei University in South Korea employed ALMA for high-resolution observations.
“NGC 613 was observed in the 12CO(1-0) line (rest frequency 115.271 GHz) using the Atacama Large Millimeter/sub-millimeter Array,” the researchers stated in their paper.
The ALMA data enabled the identification of 356 GMCs in NGC 613, with 158 being both spatially and spectrally resolved. These GMCs varied in size from 49 to 244 light years and exhibited velocity dispersions between 2 and 36 km/s. Their molecular gas masses ranged from 0.3 to 50 million solar masses, and their gas mass surface densities spanned 100 to 6,000 solar masses per square parsec.
Comparative analysis with GMCs in the Milky Way and Local Group galaxies revealed that those in NGC 613 have similar sizes but generally larger velocity dispersions, molecular gas masses, and gas mass surface densities.
Investigating the spatial distribution of GMCs within NGC 613, the researchers noted that the sizes were consistent across different regions. However, GMCs in the dust lanes exhibited smaller molecular gas masses, velocity dispersions, and gas mass surface densities compared to those in other regions. Conversely, GMCs in the arcs had larger gas masses and gas mass surface densities.
The study concluded that the GMCs in NGC 613 are marginally gravitationally bound. Moreover, those in the arcs displayed smaller virial parameters than GMCs in other regions. The research also suggested that the typical lifespan of GMCs in NGC 613 ranges between 3 and 8 million years.
This detailed study of NGC 613's GMCs not only enhances our understanding of star formation processes but also contributes to the broader knowledge of galactic evolution. The high-resolution observations from ALMA continue to be instrumental in uncovering the complex dynamics of galaxies.