13

As has now been corrected, BBC has misunderstood term "Seyfert flare", instead calling it a "Sifter flare". A "Seyfert flare", is not really a common term, but the authors refer to an energetic outburst from the type of active galaxies called Seyfert galaxies (after Carl Seyfert). Like a quasar, a Seyfert galaxy is powered by gas accretion onto a central, ...


10

Neutrinos are typically produced in AGN jets through what we refer to as hadronic processes. Protons are accelerated to relativistic speeds and interact with nearby photons. Depending on the particular type of AGN, there are a number of possible sources of these photons: Ambient light within the jet Emission from the accretion disk Photons from the broad ...


7

Yes, definitely. While some matter returns to the galaxy as a so-called "galactic fountain" (e.g. Biernacki & Teyssier 2018), some material is ejected at super-escape velocity, becoming part of the intergalactic medium. This is one of the mechanisms responsible for polluting the intergalactic medium (IGM) with metal-rich gas (i.e. elements ...


5

I think the answer to your question is 1) because of the general smaller probability of hosting an AGN with time, and 2) stochasticity. In general, the fraction of galaxies with active galactic nuclei (AGN) activity has decreased at least over the last 10 billion years, and is also lower for late type spirals, so the fact that the Milky Way and other local ...


4

Seyfert galaxies differ from other active galaxies (most notably quasars) in that their galactic nuclei are lower in luminosity compared to the rest of the galaxy. Quasars have nuclei that easily outshine the rest of the galaxy. Seyfert galaxies, on the other hand, host active nuclei that do not outshine the rest of the galaxy by the same amount. ...


3

A few sources come to mind to add to MAST and Sloan. Data releases from the SAMI Galaxy survey, which contain (or will eventually contain) emission line spectra for about 3500 galaxies. The papers for the first two releases can be found [here] and [here]. Another (smaller and older) dataset can be found at the Penn State Center for Astrophysics. It contains ...


3

I agree with your supervisor: If your paper is going to a peer-reviewed journal, you should cite peer-reviewed material. I also agree with you that the NASA version is clearer than the original figure, but if you're only going to refer to the image — i.e. not show a reproduction — I'm sure the reader can figure it out. Alternatively, you could create your ...


3

Yes of course, there are other forms apart from the four stated above. Basically you have just two kinds: the radio-quiet, and the radio-loud. But then again, there are two Seyferts Seyfert I, and Seyfert II Apart from Quasar, Blazar and Radio galaxy, we also have presently, BL Lac (Named after its prototype BL Lacarte (original member of Blazar type)),...


2

Addressing (2) and (3) first: In a case like this, your best option is to go straight to the source. In this case, that would be Blandford & Znajek (1977), the originators of the proposed mechanism. they have several figures regarding different magnetospheric structures depending on different magnetic fields. However, the most important one is Figure 1, ...


2

For starbursts, their star formation rates are best estimated by a combination of their ultraviolet and infrared emission. [O II] and [O III] as well as Hydrogen recombination lines can be used to estimate star formation, but like the UV, these suffer from extinction.


2

The frequency is related to the redshift by $$\frac{\nu_{\rm obs}}{\nu_{\rm emit}} = \frac{1}{1+z}$$ Another useful relation is the fact that, for any redshift, $$\frac{I_{\nu}}{\nu^3} = {\rm constant}$$ where $I_{\nu}$ is the specific radiative intensity. The specific count rate (counts per area per time per energy interval) is proportional to $I_{\nu}/\...


2

There is total confusion in the answers you refer to. Quasars were first defined because of their star-like appearance - quasi-stellar objects or QSOs. The fact that they are Galaxy-sized objects with point-like appearances means they are very luminous, dominated by central nuclear emission and far away (as confirmd by their high redshifts). It was later ...


2

Only a few percent of galaxies in the local universe have active galactic nuclei (e.g., Mishra & Dai 2020). The fraction with optically visible AGN (e.g., Seyfert nuclei) is lower than this, since in some galaxies only the X-ray or radio emission gets through the dust in the nuclear region of the galaxy. Even when the AGN is directly visible in optical ...


2

Active Galactic Nuclei (AGNs) are very luminous galactic nuclei. In Quasars, a type of an AGN, the nucleus outshines the host galaxy. Therefore the main source of radiation is the nucleus, not the stars and the host.


1

As Pela said in the comment, it is highly redshift dependent so there is no straight answer. "Some" is the safest option.


1

Answering the who is part of the question. Carl Seyfert (1911-1960) was a US astronomer. He is best known for his 1943 research paper on high-excitation line emission from the centers of some spiral galaxies, which are named Seyfert galaxies after him. Seyfert's Sextet, a group of galaxies, is also named after him.


1

I am not expert in that field, but I found a number and a reference: A paper by E. Memola et al. on Theoretical thermal X-ray spectra of relativistic MHD jets assumes a mass flow of $\dot{M}_{\rm jet}=10^{-8}M_\odot {\rm yr}^{−1}$ for a central object of $5 M_\odot$ The paper The theory and simulation of relativistic jet formation: towards a unified model ...


1

pc is the abbreviation for parsec, a common unit of distance objects outside the Solar system. In order to compress the scales, they have also taken the logarithm (to base 10) of the distances in parsecs. So the scale in the figure on the x-axis in the radial (r) direction from the central black hole spans from 1e-5 to 100 parsecs. The z-axis, which is ...


1

The consensus view is that Quasars are a type of AGN, and depending on precisely what meaning you put in "Quasar" it can also mean it is strictly a type defined by viewing angle. I think the consensus view also holds that viewing angle is the dominating factor for the typology, but there are other factors and it might spark a huge bikeshed debate ...


1

Blazar sequence Let's first look at which kind of sources are studied. Blazars are special type of radio-loud AGN. One of their special properties is that their spectral energy distributions (SED) form the so-called Blazar sequence. They all have a characteristic double peak SED and the position of the peaks mainly depend on their luminosity. The higher the ...


1

Metallicity and abundance Metallicity Without specifying a given metal, the term "metallicity" — abbreviated $Z$ — usually refers to the total metallicity of all elements, i.e. the mass fraction of all metals to the total mass of some ensemble of elements, e.g. a star, a cloud of gas, a galaxy, etc. (as usual, the term "metal" refers to all elements that ...


1

This question was asked more roughly 8 years ago, and for 2 years there is a review article around which I found worth mentioning and summarizing. The manuscript is called Redefining the torus: A unifying view of AGN in the infrared and sub mm and work of Sebastian Florian Hönig. Here an excerpt of the abstract: The advent of high-angular resolution IR and ...


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