Questions tagged [active-galaxy]

Questions regarding galaxies that host a compact, energetic core at the center characterized by non-stellar emission.

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Is the appearance of accretion disks of M87 and Sgr A* in EHT image, related to the nucleus being active or non-active?

I'm a newbie in this field so forgive me if I'm considering things wrong. As much as I can see, the newly published image of the Sgr A* looks pretty much the same as M87 released years ago. I'm ...
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0 votes
2 answers
52 views

What are the applications of cross matching astronomical catalogues?

Why do we cross match astronomical catalogues at different wavelengths? What information can we determine from combining the information from two catalogues? One of the applications I read was ...
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7 votes
1 answer
974 views

Why can't 'dead' galaxies start forming stars again if they merge with another, 'active' galaxy?

I heard Matthew O'Dowd mention on PBS Space-Time that dead galaxies cannot start re-forming stars even if they collect gas and/or dust from elsewhere, or even merge with another galaxy.... Why? And ...
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2 votes
1 answer
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Meaning of "blue continuum spectrum"?

The textbook Astrophysics in a Nutshell, talks about the "blue continuum spectrum" in relation to the spectrum of an AGN: I know that a continuum spectrum is caused by the interaction of a ...
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4 votes
0 answers
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Why do the Centaurus A radio jets have two "arms" each? (Event Horizon Telescope image)

Fig. 2: Image analysis of the final model: a, Model image corresponding to the image from Fig. 1 with a pixel size of 2 μas. Here, the tentative position of the jet apex is indicated with a circle. ...
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7 votes
1 answer
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Why is the Milky Way's SMBH inactive?

Our galaxy is not an active galactic nucleus (AGN). With so many stars and so much gas orbiting it, as explained here Central kiloparsec of Seyfert and inactive host galaxies: a comparison of two-...
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0 votes
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Searching for a modern AGN Catalog

I am searching for a simple, modern catalog of Active Galactic Nuclei. I expected a catalog similar to this or this, but instead found that they contain observed spectra instead of properties like the ...
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3 votes
1 answer
210 views

Do any particles in AGN jets escape the galaxy?

I have read, at http://www.thestargarden.co.uk/Black-holes.html for example, that whole stars can be ejected from certain galaxies. "These are thought to have been part of a binary star system ...
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2 votes
0 answers
21 views

Line Flux Ratios in Active galaxies

Good day to everyone. I wanted to know what is the importance of estimation of line flux ratios in active galaxies? What does it help in characterizing? As in Lyman $\alpha /$Carbon IV, or Mg II$/$...
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2 votes
1 answer
42 views

Optical emission line data archives

I am trying to do exhaustive optical emission line analysis of some active galaxies using archival data. What are some of the publically available data archives from where one could obtain optical ...
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4 votes
2 answers
102 views

How much light comes from quasars in an AGN?

From what I've been able to gather, the very bright spot at the center of galaxies is produced by both the central quasar and a dense cluster of millions of stars that surround it. How much of the ...
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3 votes
0 answers
29 views

The activity of the galactic nucleus is cyclic?

Are there observations/theoretical calculations that prove or disprove a cyclic activity of the galactic nucleus (I mean the nucleus is active than stops than become newly active with a time ...
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2 votes
0 answers
61 views

Radio loud AGN restarting as Radio Quiet AGN?

Is it possible for a Radio-loud object (eg., an FRI galaxy) to evolve into a Radio-quiet (eg., a Seyfert) source? Also, can this happen via AGN restart? That is, have there been instances where the ...
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2 votes
0 answers
25 views

Observed instances of massive gas inflow and AGN restart due to cluster-cluster merger?

Works such as Acreman et al. (2003) have demonstrated via simulations the possibility of gas being stripped off a galaxy due to interaction with a galaxy cluster. Have there been confirmed instances ...
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1 vote
0 answers
36 views

What is the O[III]/H$\alpha$ line ratio for Active Galactic Nuclei?

I have the H$\alpha$ line flux of an AGN and I am trying to calculate the Bolometric luminosity using it. Bolometric luminosity can be calculated from O[III] fluxes by $L_{\rm Bol} = 3500 L_{\rm O[III]...
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2 votes
1 answer
46 views

What is the mass and momentum of a relativistic jet?

Relativistic jets from accreting black holes are powerful radiation sources, but carries some ionized matter along. What are the estimates or observations of the mass or momentum flow in such jets?
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9 votes
1 answer
313 views

How are neutrinos produced in blazar jets?

I was watching the press release about measuring neutrinos and gamma rays from a distant blazar. One of the presenters mentioned that the neutrinos are associated with very high energy protons caught ...
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3 votes
1 answer
209 views

What fraction of galaxies host active galactic nuclei?

I've been saying "some". I can't find a reference for a particular percentage. This seems to address the question to some extent; https://arxiv.org/abs/astro-ph/0108389 would "roughly 1%" be in the ...
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9 votes
2 answers
2k views

Who is Seyfert, and what is "the so-called Seyfert flare"?

The BBC's Milky Way's centre exploded 3.5 million years ago says: A cataclysmic energy flare ripped through our galaxy, the Milky Way, about 3.5 million years ago, a team of astronomers say. They say ...
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1 vote
1 answer
81 views

Regions and size of an AGN

In this diagram of the regions and approximate scale of an AGN: which is from this paper, what do the x and y scales log(z/pc) and ...
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3 votes
0 answers
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Number of obscured AGN compared to unobscured AGN

Urry and Padovani 1995 proposed a unified model for Active Galactic Nuclei, which has since been recognised as a good model for AGN. If AGN are randomly oriented, then I'd expect there to be more ...
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4 votes
2 answers
309 views

Are quasars simply AGNs that are viewed from a particular angle?

I found the picture below in an answer to the post "Was the Milky Way ever a quasar". The picture is published on a website belonging to "NASA/IPAC Extragalactic Database". In the answer that has 16 "...
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3 votes
0 answers
48 views

What is the relationship between AGN and [OIII]

I read that we can observe [OIII] from AGNs but what processes in AGNs produces these lines why we can use them to trace or tell if that galaxy is active or not?
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3 votes
1 answer
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An image for the unified model of AGN

In a paper I'm writing, I've referenced an image I got from the NASA site at https://fermi.gsfc.nasa.gov/science/eteu/agn/ regarding the Unified Model of AGN. I captioned it ...
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6 votes
1 answer
125 views

What experiment does this "Tracing the History of Starlight" video try to explain?

The YouTube video Tracing the History of Starlight with NASA's Fermi Mission describes observation by the Fermi gamma ray telescope of EBL (extragalactic background light) gamma rays from 2,000 ...
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0 votes
1 answer
326 views

How to shift an AGN X-ray spectrum to rest frame

I have limited information to shift a spectrum (in the X-ray 0.5-10 keV bandpass) from redshift $z=2$ to the rest frame. I have a plot of normalized (photon) counts s$^{−1}$ keV$^{−1}$ as a function ...
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3 votes
1 answer
190 views

How can ionized emission line flux decrease as a function of increasing metallicity or abundance?

The chemical evolution of galaxies is an important way to learn about their formation and stellar/gaseous constituents. Many galaxies show narrow emission lines at optical wavelengths (3500-9000 ...
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6 votes
1 answer
596 views

How does an accreting black hole acquire magnetic fields?

There is actually a similar question on this site: Can magnetism escape a black hole?, however the answers do not focus on accretion, which is my main concern, so I start a new one. In Kip Thorne's ...
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3 votes
1 answer
442 views

What is a Seyfert galaxy?

I know Seyfert galaxies are types of active galaxies, but I do not understand what separates them from other types of active galaxies. Are they brighter/not as bright as other types of active ...
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4 votes
0 answers
127 views

Spectral analysis of AGN (velocity dispersion of galaxy absorption, doppler shifts)

I was wondering what parameters I need to know/measure to calculate the velocity dispersion of a galaxy, specifically an AGN. Also, I have spectra where there are blueshifted and redshifted ...
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3 votes
1 answer
71 views

What are possible methods of discerning a starburst AGN composite galaxy?

I'm currently working on an independent project that involves discerning starburst galaxies that are themselves within active galaxies. I would assume radio observations would be best to discern star ...
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5 votes
1 answer
109 views

Structure of the torus of the Active Galactic Nucleus

How much do we know about the structure of the torus surrounding the Active Galactic Nucleus (AGN)? Is the shape defined or still under speculations? And are there different structures for this torus ...
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2 votes
1 answer
154 views

Classification of Active Galaxies

I've read that there are 4 distinct although related forms of AGs : Seyferts, Quasars, Radio and Blazars. Are there any other forms possible? Also do these forms ever intermix to give something new?
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