EI2GYB > ASTRO 19.11.25 12:45l 56 Lines 4798 Bytes #200 (0) @ WW
BID : 47735_EI2GYB
Subj: Y1 is an ultra-luminous infrared galaxy, ALMA observations
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Y1 is an ultra-luminous infrared galaxy, ALMA observations reveal
Using the Atacama Large Millimeter/submillimeter Array (ALMA), an international team of astronomers has inspected a distant galaxy designated MACS0416_Y1. Results of the observations, presented Nov. 11 on the arXiv pre-print server, indicate that MACS0416_Y1 is an ultra-luminous infrared galaxy.
With infrared luminosities of over one trillion solar luminosities and star formation rates between 100 and 1,000 solar masses per year, ultra-luminous infrared galaxies (ULIRGs) are the most intensely star-forming galaxies in the local universe. Hence, finding new galaxies of this type could be important for improving the understanding of star formation and evolution.
Distant star-forming galaxy
At a redshift of 8.31, MACS0416_Y1 (or Y1 for short) was first identified as a bright Lyman-break galaxy (LBG) behind the galaxy cluster MACS J0416.1?2403. In general, LBGs are high-redshift star-forming galaxies exhibiting a significant drop in flux at wavelengths shorter than the Lyman limit (121.6 nm).
Previous observations of Y1 have suggested that it could be an archetypal example of a low-metallicity galaxy with a small but warm dust component. Recently, a group of astronomers led by Tom Bakx of the Chalmers University of Technology in Sweden, decided to employ ALMA in order to shed more light on the nature of this galaxy, by inspecting mainly its dust emission.
"Using ALMA Band 9 observations at 671 GHz, we aim to measure the dust temperature of Y1 by characterizing its short-wavelength dust emission," the researchers write.
New ULIRG on the block
The observations found that Y1 has a high dust temperature-of about 91 K. Its dust mass was estimated to be 1.4 million solar masses. The infrared luminosity of Y1 was measured to be around one trillion solar luminosities, while its star-formation rate (SFR) was calculated to be at a level of 173 solar masses per year.
Therefore, the obtained results indicate that Y1 is an ultra-luminous infrared galaxy. Given that the unobscured SFR of Y1 is 14 solar masses per year, this makes it an ULIRG with a relatively high obscured fraction of star formation when compared to other galaxies of this type at lower redshift.
The study found that the contrast between carbon and oxygen emission of Y1 implies an ionized gas region outflowing from this galaxy with a velocity of around 100 km/s. This outflowing cloud traces the ultraviolet emission from Y1.
Covered by dust
According to the paper, results of the study suggest the existence of obscured stellar components of Y1 that are missed by the ultraviolet observations. This may mean that the dust is only partially covering the ultraviolet-emitting regions, and/or that dust and ultraviolet-emitting regions are dissociated on scales smaller than about 650 light years.
"This source is an extreme example of dust-obscured star formation contributing strongly to the cosmic build-up of stellar mass, which can only be revealed through direct and comprehensive observations in the (sub)mm regime," the authors of the study conclude.
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