麻豆淫院

Argentinian astronomers have employed the upgraded Giant Metrewave Radio Telescope (uGMRT) to perform high-resolution radio observations of a nearby spiral galaxy designated NGC 4527. Results of the observational campaign, July 2 on the arXiv preprint server, shed more light on the nature of this galaxy, suggesting that it hosts an active galactic nucleus.

Discovered in 1783, NGC 4527 is an edge-on spiral galaxy in the constellation Virgo, at a distance of some 49 million light years. It has an estimated size of 104,000 light years and is classified as a starburst galaxy due to its high infrared luminosity (about 26 billion solar luminosities) and star formation rate at a level of three solar masses per year.

Previous observations of NGC 4527 have detected three supernovae on the galaxy's disk, providing evidence of recent massive star formation activity. Moreover, it turned out that the nuclear region of NGC 4527 harbors a massive molecular gas reservoir and exhibits kinematic signatures of a gravitationally unstable disk. However, this galaxy has an unusually low star formation efficiency when compared to classic starburst galaxies like M 82 and NGC 253.

These peculiar properties of NGC 4527 suggest that it may be in a "pre-starburst" phase, where gas accumulation precedes an imminent star formation burst. A team of astronomers led by Camila Ailen Galante of the National University of La Plata in Buenos Aires, Argentina, decided to further investigate this matter using uGMRT.

"This paper presents new radio continuum observations of NGC 4527 using the upgraded Giant Metrewave Radio Telescope (uGMRT) at 700 MHz (Band-4) and 1,230 MHz (Band5), complemented by archival infrared and X-ray data," the researchers wrote.

Galante's team managed to explore the large-scale emissions and the central region of NGC 4527. It turned out that on a large scale, the radio emission at 700 and 1,230 MHz follows the stellar disk, with no evidence of a radio halo. The spectral index values across the disk point to the presence of polycyclic aromatic hydrocarbons (PAHs).

When it comes to the central region of NGC 4527, the observations identified three compact radio sources. One of them was found at the center of the galaxy and exhibits a non-thermal spectral index. The two other sources appear to be symmetrically located along the galaxy's major axis at a projected distance of approximately 1,300 light years, and they both display relatively flat spectral indices. The collected data also indicate PAH destruction in the more energetic zones of the galaxy.

The astronomers concluded that the observed properties of NGC 4527 suggest that it contains a circumnuclear star-forming ring. Furthermore, they noted that the PAH destruction, non-thermal radio emission and also the recent detection of X-rays in the central region of this galaxy can be explained by the presence of an active galactic nucleus (AGN).

"Moreover, the AGN scenario offers a plausible mechanism for the formation of the circumnuclear ring: if the accretion flow is鈥攐r was鈥攕uper-Eddington and driving a dense wind that fails to escape the galaxy's gravitational potential, the fallback of material onto the disk could inject fresh gas a few hundred parsecs from the center, triggering star formation in a ring-like structure," the researchers explained.

However, the authors of the paper underlined that variability studies and higher-resolution observations of the innermost central region of NGC 4527 are required in order to confirm the presence of an AGN.

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