Research provides insights into molecular gas in the massive spiral galaxy NGC 5908

Research provides insights into molecular gas in the massive spiral galaxy NGC 5908
SDSS r-band image of the central 4′ × 4′ region of NGC 5908. The circles are the location of the IRAM 30m beams with the size indicating the beam size at 12CO J = 1−0 band. The black solid circles have twice the exposure time as the white solid ones. The two dashed circles (“8” and “9”) are taken in the 2018B semester, with “9” has an exposure time comparable to the black solid circles while “8” has much shorter exposure time. Most of the observations are along the dustlane, except for position “8” which is on the galactic center and slightly offset from the dustlane. The scale bar has a length of 20 kpc assuming a distance of d = 51.9 Mpc. Image credit: Li et al., 2019.

In a recently published research, which is part of a broader observational campaign focused on studying massive spiral galaxies, astronomers have investigated molecular lines of carbon monoxide and its isotopologues in NGC 5908. The study, detailed in a paper published April 10 on arXiv.org, sheds more light on properties of molecular gas in this galaxy, what could be helpful to better understand the evolution of such massive objects.

Massive , with few times greater than that of the Milky Way, often have relatively low star formation rates (SFRs), even lower than that of our home galaxy. This baffles astronomers, as it is impossible for these galaxies to build up such huge stellar mass with just continuous star formation at this SFR. Hence, some other mechanisms that influence galactic evolution are likely taking place in massive spiral galaxies.

In order to gain more insights on this topic, further research on overall content and spatial distribution of in galaxies of this type are required. Such studies could disclose how molecular gas builds up the stellar content of these massive objects.

With that aim in mind, a team of astronomers led by Jiang-Tao Li of University of Michigan, used the IRAM 30m millimeter radio telescope, located in Spain, to conduct observations of molecular lines of carbon monoxide and its isotopologues from NGC 5908. The target of the observational campaign, carried out under the Circum-Galactic Medium of MASsive Spirals (CGM-MASS) project, is a highly inclined massive spiral galaxy about 170 million light years away from the Earth, with a stellar mass of around 256 billion and SFR of approximately 3.81 solar masses per year.

"In this paper, we focus on the initial results from the IRAM 30m observations of NGC 5908, which has the highest-quality data and is the nearest galaxy in the CGM-MASS sample," the astronomers wrote in the paper.

The study found that the total mass of molecular gas in NGC 5908 is about 8.3 billion solar masses, while with the addition of atomic hydrogen, the total cool gas mass is at a level of 13 billion solar masses, which makes it one of the most massive isolated spiral galaxies. However, although these results confirm that the cool gas in NGC 5908 makes a significant contribution to the galaxy's gas budget, it is still far from sufficient to account for the galaxy's expected total baryon mass of around 2 trillion solar masses.

The observations also revealed that NGC 5908 has a dark matter halo with the mass of approximately 10 trillion solar masses. This, together with other results, indicates that NGC 5908 is one of the most massive spiral galaxies yet known in the local universe, and suggest that it evolved largely in isolation.

Furthermore, the researchers found that one of the studied molecular lines and the estimated gas temperature indicate a relatively weak star formation in NGC 5908. The results also suggest that radiative cooling of the hot circum-galactic medium (CGM) or any other external gas supplies are probably insufficient to compensate the gas consumed in star formation.

Therefore, analyzing all the results of IRAS observations, the researchers concluded that NGC 5908 is probably now at an early stage after the starburst, with plenty of leftover cool gas. "Since there is no signature of recent triggering of star formation (such as galaxy merger, gas transfer, or enhanced cooling of the CGM etc.), we conclude that NGC 5908 is not completely quiescent, and it may be in the early stage after the previous starburst, before the star formation is completely extinguished and the ejected gas cools and falls back to the galaxy," the astronomers wrote.


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More information: Jiang-Tao Li et al. Molecular Gas of the Most Massive Spiral Galaxies I: a Case Study of NGC 5908. arXiv:1904.05413 [astro-ph.GA].
arxiv.org/abs/1904.05413

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Citation: Research provides insights into molecular gas in the massive spiral galaxy NGC 5908 (2019, April 18) retrieved 16 September 2019 from https://phys.org/news/2019-04-insights-molecular-gas-massive-spiral.html
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Apr 18, 2019
This strangeness in NGC 5908

A spiral galaxy more massive than our own
With low star formation
with
10 trillion solar masses of the dark stuff
thats more than the mass NGC 5908 in the white stuff
and yet
it has a low star formation
a contradiction in terms
as
Sir Patrick Moore
would wonce say
Frankly I don't believe it

Apr 18, 2019
There are some very complicated issues of galaxy formation. Unfortunately, here is the same problem as with the stars. The origin of galaxies remains unclear, in spite of huge activity in the field. What the "formation" means? It means that we have the material that is assembling into galaxies.
https://www.acade...ome_From

Apr 18, 2019
well granny, the evidence is, what it is...

Until you invent better observational technology? We're stuck with the data we've acquired to date.

If you are concealing a better mousetrap?
The Chinese can supply you with better mice!

What is truly unbelievable?
Is the dunderheaded comment before yours!

Apr 18, 2019
Interesting. So this implies that AGNs aren't due to total mass- only dark matter mass, when the results are compared with those of this article: https://phys.org/...ark.html

Apr 18, 2019
This strangeness in NGC 5908
rrwillsj> well granny, the evidence is, what it is...

Until you invent better observational technology? We're stuck with the data we've acquired to date.

If you are concealing a better mousetrap?
The Chinese can supply you with better mice!

In this allusive quantum fluctuation world of this observation
of
This strangeness in NGC 5908
hath
befallen, this strangeness is in this textual scribing
as
when this dark stuff materialises
in these trillions of mass's of dark stuff
is when these textual scribing becometh confuseth
as
one can feel this exasperation in these textual scribing
the answer is there
it
is unravelling it from the trillions of mass's of this dark stuff
That is the problem

Apr 19, 2019
With 1 % active starburst galaxies at any given time, but observations suggesting that perhaps up to 50 % of galaxies are such at one time or other (have a starburst "hot" dark matter core distribution), I get the impression starbursts are typically long pulses. (Long times, since the supermassive black hole jets that seem to drive the gas outflow pulses/results from starbust gas infall can go long distances at each pulse.)

The 1/5 or 20 % matter/dark matter ratio is derived as the one that would be expected in an isolated galaxy, Planck 2018 gets the ratio 0.0244/0.120 = 0.203 between the energy densities [ https://arxiv.org...07.06209 ].

Nice!

Interesting. So this implies that AGNs aren't due to total mass- only dark matter mass, when the results are compared with those of this article: https://phys.org/...ark.html


I don't see that it can say that. But an astounding 99+ % of expected gas may be circulating outside the galaxy.

Apr 19, 2019
Starburst galaxies reminds me of ICEs of old cars: draw in gas, "ignite", push out gas, rinse and repeat.

Apr 19, 2019
I don't see that it can say that.
This article and paper don't, it's when they're combined with the other physorg article I linked that this becomes a viable conjecture. Maybe you should read the other article and then consider the linkage between the two.

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