New hot dog in the sky: Astronomers discover a galaxy obscured by hot dust

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Optical spectrum of W1904+4853 obtained at the Palomar Observatory. Credit: Li et al., 2023.

An international team of astronomers reports the detection of a new galaxy obscured by hot dust (DOG). The galaxy, which has received the WISE designation J190445.04+485308.9, was found to have a relatively low redshift of 0.415, making it the first confirmed low-redshift hot DOG. The finding was presented in a paper published May 23 in the arXiv prepress server.

Quasars are galaxies with extremely energetic active galactic nuclei (AGN). Hot DOGS are a rare type of obscured hyperluminous quasars identified by Wide-field Infrared Survey Explorer (WISE), specifically classified to be detected by their dust emission. Compared to typical dust-obscured galaxies, hot DOGs are significantly redder in the WISE passbands due to their emission of hotter AGN-heated dust, and have much higher bolometric luminosities.

Recently, a team of astronomers led by Guodong Li of the University of the Chinese Academy of Sciences in Beijing, China detected another quasar of this rare type. Analyzing data from WISE and various ground-based telescopes, they found a new hyperluminous and highly obscured AGN and designated it WISE J190445.04+485308.9 (or W1904+4853 for short).

“Its well-sampled spectral energy distribution (SED) is dominated by infrared dust emission, although broad emission lines are detected in the optical spectra. These features suggest that W1904+4853 contains an actively growing supermassive black hole hidden in its dusty cocoon, resembling the observed properties of hot dust-obscured galaxies (hot DOGs), a population previously identified only at z > 1.0,” the researchers explained.

According to the study, W1904+4853 has a stellar mass of about 30 billion solar masses and its bolometric luminosity is 11 trillion solar luminosities. The supermassive black hole (SMBH) of W1904+4853 is assumed to be accreting near the Eddington limit.

Astronomers found that the emission of infrared dust contributes about 99% of W1904+4853’s bolometric luminosity, dominating the total energy output of this galaxy. The total mass of dust was calculated to be about 50 million solar masses, while the temperature of the dust was estimated to reach 539 K. The researchers assume that in the case of W1904+4853, the dust near the AGN is heated by the accretion of SMBH to hotter temperatures than other infrared luminous galaxies.

By analyzing the spectral energy distribution (SED) of W1904+4853, the study authors found that the galaxy is surprisingly dominated by the young stellar population, with a star formation rate at the level of 45 solar masses per year. This star formation appears to contribute only 8% t of the far-infrared luminosity, further supporting the scenario where the infrared dust emission is fueled by AGN.

The search also found ionized gas leaks from W1904+4853’s obscured central AGN. The outflow mass was found to be an order of magnitude less than the host galaxy’s ongoing star formation rate, which, according to the researchers, suggests that the outflow power has not yet been fully deployed to eject star material. star formation. of the system.

“Even if it’s blue-shifted and lopsided [O III] The emission provides evidence of an outflow, we estimate to be an order of magnitude lower than the star formation rate, indicating that the current obscured AGN activity at the center has not yet produced a significant feedback on star formation activity of the host galaxy,” the astronomers say. concluded.

More information:
Guodong Li et al, Discovery of a galaxy obscured by hot low-redshift dust, arXiv (2023). DOI: 10.48550/arxiv.2305.13739

About the magazine:
arXiv

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