Astronomers uncover properties of a molecular outflow feature in a nearby starburst galaxy

January 24, 2017 by Tomasz Nowakowski, Phys.org report
ALMA CO(1–0) observations of NGC 253. Credit: Walter et al., 2017.

(Phys.org)—An international team of astronomers led by Fabian Walter of the Max Planck Institute for Astronomy in Germany has revealed essential properties of a molecular outflow feature in the nearby starburst galaxy designated NGC253. The findings were presented in a paper published Jan. 18 on the arXiv pre-print repository.

NGC 253, also known as the Sculptor Galaxy, is an intermediate spiral starburst galaxy in the constellation Sculptor some 11 million away. The galaxy is one of the brightest spiral visible and also one of the dustiest. Due to its proximity and the fact that it is currently undergoing a period of intense star formation, it serves as one of the best laboratories to study starburst–driven galactic–scale winds in detail.

NGC 253 is known for the galactic wind emerging from its central area, which carries significant amounts of . In order to better characterize this emission, Walter and his team carried out a series of observations between November 2013 and August 2014 utilizing the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. This observational campaign allowed the researchers to uncover crucial properties of the studied molecular outflow.

"We present a detailed study of a molecular outflow feature in the nearby starburst galaxy NGC 253 using ALMA," the paper reads.

According to the study, NGC 253's most prominent outflow feature towards the south has a projected length of about 978 light years, a width of approximately 163 light years, and a velocity dispersion of 40 km s−1. The scientists note that its extent and dispersion are consistent with an ejection from the galaxy's disk starting about 1 million years ago.

The kinematics of the molecular gas in this feature show that the material is approaching us and is also accelerating. However, the astronomers were unable to determine whether or not the molecular mass entrained in the outflow will escape the galaxy, or be recycled to fuel later episodes of . More observations are required to draw final conclusions.

"The kinematics of the molecular gas are consistent with accelerating with a velocity gradient of 1 km s−1 pc−1, and at its last measurable point it approaches the escape velocity. (…) More sensitive ALMA observations will trace the outflow even further out, and will shed light on whether or not part of the ejected molecular material will escape the galaxy," the researchers wrote in the paper.

The team also discovered bright tracers of dense molecular gas like HCN, CN, HCO+, CS in the molecular outflow. Moreover, they found that line ratios HCN/CO measured in the outflow are high and consistent with ratios observed in the central starburst region of NGC253 and in other starbursts, while the HCN/CO line ratio in the galaxy's disk is significantly lower, which is typical for gas in the disks of nearby galaxies. The researchers concluded that this indicates that the dense molecular gas is retaining its properties in the process of its ejection from the central regions into the outflow.

Explore further: Starburst to star bust: Astronomers ID suspect behind dearth of high-mass galaxies

More information: Dense Molecular Gas Tracers in the Outflow of the Starburst Galaxy NGC 253, arXiv:1701.05040 [astro-ph.GA] arxiv.org/abs/1701.05040

Abstract
We present a detailed study of a molecular outflow feature in the nearby starburst galaxy NGC 253 using ALMA. We find that this feature is clearly associated with the edge of NGC 253's prominent ionized outflow, has a projected length of ~300 pc, with a width of ~50 pc and a velocity dispersion of ~40 km s^-1, consistent with an ejection from the disk about 1 Myr ago. The kinematics of the molecular gas in this feature can be interpreted (albeit not uniquely) as accelerating at a rate of 1 km s^-1 pc^-1. In this scenario, the gas is approaching escape velocity at the last measured point. Strikingly, bright tracers of dense molecular gas (HCN, CN, HCO+, CS) are also detected in the molecular outflow: We measure an HCN(1-0)/CO(1-0) line ratio of ~1/10 in the outflow, similar to that in the central starburst region of NGC 253 and other starburst galaxies. By contrast, the HCN/CO line ratio in the NGC 253 disk is significantly lower (~1/30), similar to other nearby galaxy disks. This strongly suggests that the streamer gas originates from the starburst, and that its physical state does not change significantly over timescales of ~1 Myr during its entrainment in the outflow. Simple calculations indicate that radiation pressure is not the main mechanism for driving the outflow. The presence of such dense material in molecular outflows needs to be accounted for in simulations of galactic outflows.

Related Stories

Hubble sees a galaxy with a glowing heart

July 14, 2014

(Phys.org) —This view, captured by the NASA/ESA Hubble Space Telescope, shows a nearby spiral galaxy known as NGC 1433. At about 32 million light-years from Earth, it is a type of very active galaxy known as a Seyfert galaxy—a ...

Outflowing gas in ultraluminous galaxies

January 9, 2017

Galaxies evolve over billions of years in part through the activity of star formation and their supermassive nuclear black holes, and also by mergers with other galaxies. Some features of galaxies, in particular the strong ...

Hidden details revealed in nearby starburst galaxy

December 9, 2013

Using the new, high-frequency capabilities of the National Science Foundation's Robert C. Byrd Green Bank Telescope (GBT), astronomers have captured never-before-seen details of the nearby starburst galaxy M82. These new ...

Recommended for you

Lyman-alpha emission detected around quasar J1605-0112

February 20, 2018

Using the Multi Unit Spectroscopic Explorer (MUSE) instrument astronomers have discovered an extended and broad Lyman-alpha emission in the form of a nebula around the quasar J1605-0112. The finding is reported February 9 ...

'Ultramassive' black holes discovered in far-off galaxies

February 20, 2018

Thanks to data collected by NASA's Chandra X-ray telescope on galaxies up to 3.5 billion light years away from Earth, an international team of astrophysicists has detected what are likely to be the most massive black holes ...

61 comments

Adjust slider to filter visible comments by rank

Display comments: newest first

cantdrive85
1.6 / 5 (14) Jan 24, 2017
Nice study of this electric current, not that the paper at any point acknowledges this simple fact. Also, any mention of escape velocity is meaningless. What would be of greater value is trying to determine the galactic circuit to which this current connected.
Whydening Gyre
5 / 5 (12) Jan 24, 2017
Nice study of this electric current, not that the paper at any point acknowledges this simple fact.

(Sigh). IF it was "electric", it would have been mentioned..
Also, any mention of escape velocity is meaningless.

Why, pray tell...?
What would be of greater value is trying to determine the galactic circuit to which this current connected.

Sounds like you have it figured out - please elucidate...
jonesdave
4.4 / 5 (13) Jan 24, 2017
@cantthink,
Electric current my arse. Surely any half decent electric current would have ionised the gas, yes? Most of those molecules are neutral, and are not particularly 'excited'. You are only seeing the lower state ro-vibrational transition (1-0).
You people really need to learn some science, before you start commenting on it.
Chris_Reeve
Jan 24, 2017
This comment has been removed by a moderator.
Chris_Reeve
Jan 24, 2017
This comment has been removed by a moderator.
IMP-9
5 / 5 (9) Jan 24, 2017
there's an explanation of Marklund convection and the Lorentz force here ...


You didn't answer the question. Jonesdave asked why the current had not ionised the CO. He did not ask how could a plasma affect a neutral species, try answering the question.
barakn
4.6 / 5 (11) Jan 24, 2017
btw: This alternative explanation should certainly not be news by this point. I've spoken about Marklund convection on countless occasions here on physorg.

It's a crucial aspect of electrical cosmology, and to think that the astrophysical community probably does not even know about it yet is another brewing scandal.

Yes, it was published in an obscure journal called Nature, I'm sure it was overlooked by every single astrophysicist on the planet.
Chris_Reeve
Jan 24, 2017
This comment has been removed by a moderator.
Chris_Reeve
Jan 24, 2017
This comment has been removed by a moderator.
barakn
3.8 / 5 (10) Jan 24, 2017
Please understand me that I am not exaggerating when I say that you should be spending more time asking questions and reading than arguing. This will enable you to better identify where the controversy occurs. If you do that, these discussions will be far more interesting for everybody.
Because arguing involves asking Chris_Reeve/HannesAlfven uncomfortable questions that he can't answer. It would be a lot easier for Chris if you asked yourself questions and not him.
Chris_Reeve
Jan 24, 2017
This comment has been removed by a moderator.
Chris_Reeve
Jan 24, 2017
This comment has been removed by a moderator.
IMP-9
4.4 / 5 (7) Jan 24, 2017
The current would have to have considerable velocity in order to ionize a neutral. This is called critical ionization velocity (CIV)


Does the air in a lightning strike reach tens of kilometers per second before the strike? No. Then how could it be ionised? Because CIV is not the only ionisation process.

We're talking about one structure with current flowing inside it, CIV is not relevant. Because of the current the charged species won't even be in velocity equilibrium so talking about a single velocity doesn't make any sense. If you were relying on CIV to provide all the ionisation in this situation then there would be no plasma because the ionisation energy of CO is pretty much the same as hydrogen. CO would actually dissociate before you had a plasma with CIV.

So that doesn't answer the question.
Hyperfuzzy
1 / 5 (5) Jan 24, 2017
The analysis has just begun. There can be no conclusions. We see an object. At what state relative to the center of mass of the entire object relative to us. Acceleration! Velocity? Temporal Position? Formation of such an object? Mirror image in time?

The hydrogen line defines speed, v is +/-! s = c Le/Lo. Each line defines it's near field. etc.
Benni
1 / 5 (11) Jan 24, 2017
@cantthink,
Electric current my arse. Surely any half decent electric current would have ionised the gas, yes? Most of those molecules are neutral, and are not particularly 'excited'. You are only seeing the lower state ro-vibrational transition (1-0).
You people really need to learn some science, before you start commenting on it.


Coming from a person who makes assassination threats against President Donald Trump as I repost his threat below from earlier in the day:

jonesdave5 / 5 (2) 6 hours ago
What might Trump mean for chemistry?

Don't know. Let's set fire to the b***ard, and find out.


Read more at: https://phys.org/...html#jCp

OK Physorg.......when will you make this guy history at this website. You want civil discourse about science, but making threats against the President of the United States is not an ON TOPIC discourse is it?
barakn
4.3 / 5 (6) Jan 24, 2017
I collect the best critique that's ever been lodged against modern science. If you're smart, you'll realize there is some value to having somebody like that around. -Chris_Reeve
Liar. I've been waiting for 4 years for a cogent response from you about your untenable belief that lavas can't saturate cameras in this thread: https://phys.org/...ars.html Go ahead, surprise me by responding with an intelligent argument.
Whydening Gyre
5 / 5 (3) Jan 25, 2017
The current would have to have considerable velocity in order to ionize a neutral. This is called critical ionization velocity (CIV)


The current? As in Electrical...?
Doesn't that (generally) run at the speed of light?
Don't you really mean "charge potential"?
RNP
5 / 5 (7) Jan 25, 2017
@Chris_Reeve
I collect the best critique that's ever been lodged against modern science. If you're smart, you'll realize there is some value to having somebody like that around.


Then enlighten us! You should have no trouble explaining how these currents and/or Marklund convection explain the position-velocity diagrams in the paper linked above (Figs. 2 and 6). These clearly show that the filaments contain matter flowing OUTWARD in opposite directions from the central body.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
bschott
5 / 5 (1) Jan 25, 2017
"Even if there is no external magnetic field, any small elements of current flowing in a plasma will tend to accumulate naturally into larger currents which generate their own magnetic fields and so preserve the filament of current.


Precisely what experiment proves this quote is valid and who are you quoting? I have never seen, read about or hallucinated a self stabilizing electric current...ever.

Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
RNP
4.3 / 5 (6) Jan 25, 2017
@Chris_Reeve
Unable to actually address any of the actual scientific questions/comments your posts have so far elicited, you resort to pure Gish gallop. Either enter into a scientific dialogue with at least one of your critics or continue to be seen as an evangelizing pseudo-scientist.
bschott
5 / 5 (2) Jan 25, 2017
What do you propose you are seeing in a novelty plasma globe?

A difference in electrical potential between the central electrode and the glass globe confining the inert gas surrounding it, visually manifesting as filaments when a temporary current pathway forms between the globe and the electrode due to the difference in potential. Have you ever seen a continuous filament in one of these? No.
Then at the bottom of your post you link to Birkeland who, never once, formed a plasma current with out a magnetic field source, and the actual definition of a Birkeland current is ionized particles travelling along lines of magnetic flux...not generating the flux lines the particles travel along.

EU theory put simply - Electricity happens, then everything else does. It's the easiest thing to prove if it is correct....there is a reason it's still just a theory.

And you never answered the question about the quote....
cantdrive85
1.7 / 5 (6) Jan 25, 2017
Not surprising, well understood EE concepts are considered "gish gallop" by those who kneel at the alter of the thought experiment diety and the "dark" entities.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
cantdrive85
1.7 / 5 (6) Jan 25, 2017
visually manifesting as filaments when a temporary current pathway forms between the globe and the electrode due to the difference in potential.

"Visually manifesting"?
Have you ever seen a continuous filament in one of these? No.

Definitions, relevance, and an understanding of time scales is obviously not your strong point.
Even that filament that lasts a few seconds in a plasma ball is a stable structure. Your belief these must be eternal to qualify as stable is your own problem, not the EU's. BTW, when these structures are scaled to cosmic proportions, the time factor must also be scaled to cosmic proportions.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
bschott
5 / 5 (3) Jan 25, 2017
Even that filament that lasts a few seconds in a plasma ball is a stable structure.

You just said this lasts 3 seconds and is stable...temporary does not = stable
Your belief these must be eternal to qualify as stable is your own problem,

Your claim is that the field the current creates is self stabilizing, therefore once a current is established it should never destabilize.
We are in very dark times for science when people cannot recognize the fundamental difference between conjecture and laboratory observations

So back to my question to you in my first post Chris...not answered yet you go on about how you can....
Definitions, relevance, and an understanding of time scales is obviously not your strong point.

Your perception of what the 3 things above entail is unique to you, and anyone stupid enough to support a theory that states "electricity happens, then everything does" .
As I said, easiest thing in the world to prove if it was correct.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
bschott
4.2 / 5 (5) Jan 25, 2017
What in the world are you talking about? These are indeed continuous filaments. They're not "visually manifesting" as anything other than what they are.

Now I see how you became an EU acolyte, the failure to read and understand a physical description of an event. Re read what I said is visually manifesting, "the difference in electrical potential"... lightening is a visual manifestation of this as well Chris. When a lightening bolt forms, does it self stabilize? "Continuous" is another word you may want to check your understanding of as far as what the word means... something cannot be described as both continuous and temporary. None of the fingers of plasma in your novelty globe last the entire time the electrode causes ionization...they move, kink, break apart and reform...none of this indicates stability.
We haven't even got to "force free currents" yet, I was going to ask for any verified example but I fear I will get the same response as I did to my first question.
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
bschott
5 / 5 (2) Jan 25, 2017
Nobody said that.

what you said that my first post was in response to:
"Even if there is no external magnetic field, any small elements of current flowing in a plasma will tend to accumulate naturally into larger currents which generate their own magnetic fields and so preserve the filament of current.

This means self sustaining.....
Your surprise follows from the fact that you've never had somebody actually explain these equations to you in normal English. The equations themselves are not at all new.

The equations do not predict self sustaining currents, so my "surprise" stems from your lack of understanding of the physics of a sustained electric current or plasma current and what is required to maintain one for any timescale...which would be a magnetic field geometry tailored to do just that. The EU claim that electricity does this by itself gets trashed in the lab every time when people require a plasma current.

bschott
5 / 5 (3) Jan 25, 2017
The stability that is referred to relates to the CYLINDRICAL structure of the filament -- not the temporal duration or any of these other things. The stability naturally follows from the geometry which is detailed in these posts.

Stability in physics refers that which does not decay, if something is stable its form is maintained until an interaction disrupts it's stability.
If there is some confusion here it is that you want to redefine the meaning of "stability" in physics so that even a temporary structure such as a filament in a plasma chamber can be labeled as stable despite the fact the it cannot maintain itself...like an electron or proton. (stable particles). "Stable" cannot be used to describe a temporary structure...because of the definition of the word stable...you insist it can...sheesh indeed!
Chris_Reeve
Jan 25, 2017
This comment has been removed by a moderator.
cantdrive85
1 / 5 (4) Jan 25, 2017
Well bshott, you have yet to answer how those magical bowls get magnetized without an electric current. And if magnetism is an inherent property, why then did the magnetic field collapse precisely when Maxwell opened the circuit? Wait, I forgot, you're of the opinion that Maxwell was a quack and his field equations are meaningless and the entirety of our modern electronic society is merely an accident being that EE's have such a skewed understanding of EM theory with their belief that electro and magnetism are intimate hand maidens.
cantdrive85
1 / 5 (4) Jan 25, 2017
This conversation is dumb.

Well, it does involve magic bowl guy.
IMP-9
5 / 5 (5) Jan 25, 2017
I'm not even sure where the confusion is at this point.


I'm not sure how I can state it any more clearly. When there's a current the charged species are not in velocity equilibrium (that's how current works) so you cannot define a single velocity between the charged particles and the neutrals. It's not a gas and a plasma coming together as in CIV.

What role does the observed behavior of laboratory plasmas play in this thought process?


What? It's an experimental fact that CIV isn't the only ionisation process, e.g Townsend Avalanche, photoionisation. Most lab experiments won't use CIV to get the plasma going either. Perhaps instead of deflecting completely you could just answer the question.

The ionization does not have to even be occurring near the filament.


That's not what was asked. The question that was asked was why has this electric current not ionised the CO. Please try answering the question.
bschott
5 / 5 (5) Jan 25, 2017
The movement of the charged particles obviously creates the very magnetic field which you claim is missing.

Find one...just one experiment demonstrating a self aligning plasma current which then generates a field that stabilizes itself and I will never bad mouth the EU again. Because, ya see....in every experiment we as a species have done where we created a plasma current, every single one required a magnetic field geometry to align the particles and confine the current...every....single...one.
@IQ85 - we aren't discussing a theory regarding the magnetic moment/field geometry around stable SA particles (bowl talk)...we are discussing the easiest theory in the world to prove as correct...if it only was. Get it through your hollow head, no plasma current exists unless it has magnetic flux to follow or a magnetic boundary to confine it...this is physics that happens billions of times a day....you cannot provide a single example of your claim occurring but once.
Whydening Gyre
5 / 5 (4) Jan 25, 2017
This is why it's such a mistake to thoughtlessly apply fluids-based models throughout a plasma universe.

If the fluid models account for variable densities - they're not a mistake or thoughtless...
jonesdave
3 / 5 (2) Jan 25, 2017
@cantthink,
Electric current my arse. Surely any half decent electric current would have ionised the gas, yes? Most of those molecules are neutral, and are not particularly 'excited'. You are only seeing the lower state ro-vibrational transition (1-0).
You people really need to learn some science, before you start commenting on it.


Coming from a person who makes assassination threats against President Donald Trump as I repost his threat below from earlier in the day:

jonesdave5 / 5 (2) 6 hours ago
What might Trump mean for chemistry?

Don't know. Let's set fire to the b***ard, and find out.


Read more at: https://phys.org/...html#jCp

OK Physorg.......when will you make this guy history at this website. You want civil discourse about science, but making threats against the President of the United States is not an ON TOPIC discourse is it?


Benni, do us a favour: F**k off, yes?
jonesdave
3 / 5 (2) Jan 25, 2017
This conversation is dumb.

Well, it does involve magic bowl guy.


Jeez, thick or what?
jonesdave
3 / 5 (2) Jan 25, 2017
I see Reeve is back again. Still putting out this Velikovskian woo, yes? Seen Wal the f***wit lately? How is his electric comet woo getting on? How many more lies is he going to tell to his scientifically challenged followers? How much more evidence against his woo is he going to ignore? Are you thick as pig**it idiots going to buy it all again? Answer; yes, of course you are! You always do.
Here is the reason; you are all scientifically illiterate. No ifs, no buts; you are all as thick as pig**it. End of story. Wouldn't know science if it bit you on the a**e.
jonesdave
3 / 5 (2) Jan 25, 2017
Re: "Unable to actually address any of the actual scientific questions/comments your posts have so far elicited, you resort to pure Gish gallop. Either enter into a scientific dialogue with at least one of your critics or continue to be seen as an evangelizing pseudo-scientist."

Is this a form letter?

What a joke.


No,idiot, it's what you do. In case you haven't noticed, science is actually beyond you. And the idiot Thornhill. And the idiot Talbott. Et bleeding cetera. You just make sh*t up as you go along. Nothing to do with science. Never has been, never will be.
jonesdave
3 / 5 (2) Jan 25, 2017

@Benni the BURKE,
OK Physorg.......when will you make this guy history at this website. You want civil discourse about science, but making threats against the President of the United States is not an ON TOPIC discourse is it?


I only suggested setting fire to the cnut as an experiment. Let's see what happens. Maybe, during the autopsy, we'll find a brain cell. You never know.
jonesdave
3 / 5 (2) Jan 25, 2017
btw: This alternative explanation should certainly not be news by this point. I've spoken about Marklund convection on countless occasions here on physorg.

It's a crucial aspect of electrical cosmology, and to think that the astrophysical community probably does not even know about it yet is another brewing scandal.

When the experts try so hard to ignore controversies, eventually they stop being the experts.


Idiot. There is, yet again, no controversy. Only in the feeble minds that make up your silly cult (think I spelled that right). It doesn't exist, understand? It is like your "insects fell from Venus to Earth" BS. Nobody takes it seriously. For good reason. That reason being - you lot are as thick as pigs**t.
jonesdave
3 / 5 (2) Jan 25, 2017
@Reeve the liar,
Honestly, I'm one of the few people here who actually provides sourced quotes....


Where is your convection? Why so many craters? Why such a thick crust? Why so few volcanos? Et bleeding cetera. You are a liar, and a gobsh*te. Sorry, can't put it more nicely than that. Start answering some questions, woo boy.
cantdrive85
1 / 5 (3) Jan 26, 2017
jonesdumb, I know it will be nearly impossible for you, but try and leave the lowbrow vulgarities and name calling out of it. You're emotional again, you take your dementia meds?
MultiverseFilament
not rated yet Feb 03, 2017
"It's a crucial aspect of electrical cosmology, and to think that the astrophysical community probably does not even know about it yet is another brewing scandal."
When the experts try so hard to ignore controversies, eventually they stop being the experts.
Truth .. it is.
And more than that, no one has a corner on the truth, we are all connected, electrically. Thoughts thunk and being thought are not a demonstration of intelligence but in a filtering of the river, the great river of all thoughts thunk.. and so a new 'genius' may enlighten, with each a generator of this spark of thoughts..
My thoughts received say that this is matter creation, as those gases were created, but a spark of lights that coalesced into the falling magnetism, by the 'drop' of electric charge across the coils, inducing the secondary and tertiary.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.