Astronomers take a closer look at a nearby dwarf active galactic nucleus

Astronomers take a closer look at a nearby dwarf active galactic nucleus
Left panel: large-scale image of NGC 4395 at R-band (Cook et al 2014). Right panels: optical (top) and K-band (bottom) continuum images obtained from the GMOS and NIFS data cubes, respectively. Credit: Brum et al., 2019.

An international team of astronomers has conducted optical and spectroscopic observations of the dwarf galaxy NGC 4395 that contains an active galactic nucleus (AGN). The observations, described in a paper published March 19 on arXiv.org, allowed the researchers to take a closer look at this dwarf AGN, what could provide essential insights into the nature of this object.

AGNs are compact regions at the center of galaxies, more luminous than surrounding galaxy light. They are very energetic due either to the presence of a black hole or star formation activity at the core of the galaxy.

AGNs in local dwarf galaxies offer an excellent opportunity to study relatively small supermassive black holes (SMBHs). By conducting detailed analysis of the gas kinematics ionization structure and gas morphology in such dwarfs, astronomers could gather crucial information about evolution of small SMBHs.

Located some 14.3 million light years away, NGC 4395 is an example of a nearby known to harbor an AGN. It is perceived as a great candidate to investigate the nature of a dwarf AGN, as its proximity allows telescopes to take a close look at its .

That is why a group of astronomers led by Carine Brum of Federal University of Santa Maria in Brazil decided to perform optical and near-infrared integral field spectroscopic observations of the inner region of NGC 4395. For this purpose, they employed the Gemini Multi-Object Spectrograph (GMOS) and the Gemini Near-infrared Integral Field Spectrograph (NIFS), both mounted on the Gemini North Telescope in Hawaii.

The allowed the researchers to estimate the properties of ionized and molecular gas in NGC 4395. In particular, optical and near-infrared emission-line flux distributions uncovered an elongated structure at about 78 light years west of the nucleus.

"The line emission peaks at the nucleus but is also extended in a blob at 1.'2 (24 pc) west of the nucleus," the astronomers wrote in the paper.

Gas in this blob is blueshifted by approximately 30 km/s compared to the surrounding material. This, according to the researchers, suggests that the gas flowing toward the nucleus at a rate of about 0.00032 solar masses per year. However, the origin of the inflowing material is uncertain. The scientists assume that it may be an ongoing minor merger of a gas-rich small galaxy, or the accretion of a low-metallicity cosmic cloud.

Furthermore, the authors of the paper estimated that the bolometric luminosity of the AGN in NGC 4395 is about 99 duodecillion erg/s, and the mass of the central black hole is approximately 250,000 solar masses. They also calculated that the mass within the radius of about 32.6 from the nucleus is around 770,000 , most likely due to the presence of a young nuclear stellar cluster in this region.

All in all, the results of the study allowed the researchers to find out that NGC 4395 differs from typical Seyfert due to the lower mass inflow rate and due to the fact that gas inflow in the studied galaxy seems to be undergoing a minor merger or accretion event.


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More information: Carine Brum et al. A close look at the dwarf AGN of NGC 4395: optical and near-IR integral field spectroscopy. arXiv:1903.08083 [astro-ph.GA]. arxiv.org/abs/1903.08083

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Apr 01, 2019
Gas in this blob is blueshifted by approximately 30 km/s compared to the surrounding material. This, according to the researchers, suggests that the gas flowing toward the nucleus at a rate of about 0.00032 solar masses per year. However, the origin of the inflowing material is uncertain.

Gosh, is it again left to me to point out the obvious assumption? The blob may be ejected therefrom and approaching us from the near side. Are astronomers really just that stupid? Or is merger mania just too entrenched. And if the blob really is from an external source, why has it not consolidated over the billions of years into a star? Obvious questions for merger maniacs to consider. Instead, they just recite the common mantra.

Apr 01, 2019
Gosh, is it again left to me to point out the obvious assumption? The blob may be ejected therefrom and approaching us from the near side. Are astronomers really just that stupid? Or is merger mania just too entrenched. And if the blob really is from an external source, why has it not consolidated over the billions of years into a star? Obvious questions for merger maniacs to consider. Instead, they just recite the common mantra.


Gosh, is it again left to a crank to totally fail to understand the paper?

The velocity fields derived for all emission lines are similar, presenting blueshifts of up to 30 km s^−1 to the east side of the nucleus and similar redshifts to the west at distances smaller than 1′′ from the nucleus.


In other words, for the hard of thinking, the galaxy is not quite face-on. Therefore the infalling material will be blue or redshifted depending on which side of the nucleus you are observing.

Apr 01, 2019
In search of black holes and dark matter astrophysicists are relying on indirect observations. It would seem that the measurement of the event horizon of a black hole directly would be a direct evidence. However, by the nature of a horizon, any real measurement of the event horizon will be indirect. The Event Horizon Telescope will get picture of the silhouette of the Sgr A* which is due to optical effects of spacetime outside of the event horizon. The result will be determined by the simple quality of the resulting image that does not depend on the properties of the spacetime within the image. So, it will be also indirect and an existence of BH is a hypothesis.
https://www.acade...ilky_Way

Apr 01, 2019
So, it will be also indirect and an existence of BH is a hypothesis.


Rubbish. And stop posting the same garbage time after time.

Apr 02, 2019
@Castrogiovanni,

I'm glad I'm not the only one to notice that @v_p always posts the same rubbish. I think it's a cut & paste job -- I seem to recall seeing it somewhere else, not connected with @v_p. Just another troll. Why do some people -- they show up on every site -- have trouble with the idea of a black hole?

@Tux,

I think the astronomers know their jobs. I think you don't. One reason the stuff may not be consolidated into a star is that maybe it hasn't been around long enough. Or maybe because it's being disrupted by a SMBH -- that's more than enough to keep something from turning into a star. It would likely turn me into spaghetti before it flattened my spaghettificated remains. It takes push, not pull, to turn something into a star -- enough stuff has to be pushed together before there's enough pull to bring more stuff in. Being pulled by a SMBH will disrupt that quite well.

Apr 08, 2019
" @v_p always posts the same rubbish".

Yes, it is some vanity press texts, not peer reviewed papers that can be discussed for usefulness.

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