APOD: Messier 106 (2021 Apr 09)

[APOD Robot]

Messier 106

Explanation: Close to the Great Bear (Ursa Major) and surrounded by the stars of the Hunting Dogs (Canes Venatici), this celestial wonder was discovered in 1781 by the metric French astronomer Pierre Mechain. Later, it was added to the catalog of his friend and colleague Charles Messier as M106. Modern deep telescopic views reveal it to be an island universe - a spiral galaxy around 30 thousand light-years across located only about 21 million light-years beyond the stars of the Milky Way. Along with a bright central core, this stunning galaxy portrait, a composite of image data from amateur and professional telescopes, highlights youthful blue star clusters and reddish stellar nurseries tracing the galaxy's spiral arms. It also shows off remarkable reddish jets of glowing hydrogen gas. In addition to small companion galaxy NGC 4248 at bottom right, background galaxies can be found scattered throughout the frame. M106, also known as NGC 4258, is a nearby example of the Seyfert class of active galaxies, seen across the spectrum from radio to X-rays. Active galaxies are powered by matter falling into a massive central black hole.

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[Ann]

My immediate impression, when I looked at today's APOD, was that the picture is probably mostly Robert Gendler's own work, with no great contributions from NASA and Hubble. But now I think that the central part of today's APOD was indeed created from Hubble data.

M106. Image Credit: NASA, Hubble Legacy Archive, Kitt Peak National Observatory; Amateur Data & Processing Copyright: Robert Gendler.

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M106. NASA, ESA, the Hubble Heritage Team (STScI/AURA), and R. Gendler (for the Hubble Heritage Team). Acknowledgment: R. Jay GaBany

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The picture at right is very obviously a Hubble image, which has been processed by Robert Gendler, with some help from R. Jay GaBany. The picture at left looks much more like an amateur image.

Today's APOD may well be a composite of a an image of the central parts of M106, photographed by Hubble, and amateur data of the outer parts of the galaxy, gathered and processed by Robert Gendler.

Anyway. As for the galaxy itself, the most interesting thing about it is probably its water vapor megamasers. A maser is the microwave equivalent of a laser.

Wikipedia wrote:

M106 has a water vapor megamaser (the equivalent of a laser operating in microwave instead of visible light and on a galactic scale) that is seen by the 22-GHz line of ortho-H2O that evidences dense and warm molecular gas. These water vapors give M106 its characteristic purple color.[10] Water masers are useful to observe nuclear accretion disks in active galaxies. The water masers in M106 enabled the first case of a direct measurement of the distance to a galaxy, thereby providing an independent anchor for the cosmic distance ladder.

The description of water masers in M106 is too much math speak for me, but I do get this: Thanks to the water masers, astronomers have an independent way of measuring the distance to M106. It turns out to be 23.7 ± 1.5 million light-years, according to Wikipedia.

M. J. Reid, D. W. Pesce and A. G. Riess wrote:

We find the distance to NGC 4258 to be 7.576 +/- 0.082 (stat.) +/- 0.076 (sys.) Mpc. Using this as the sole source of calibration of the Cepheid-SN Ia distance ladder results in Ho = 72.0 +/- 1.9 km/s/Mpc, and in concert with geometric distances from Milky Way parallaxes and detached eclipsing binaries in the LMC we find Ho = 73.5 +/- 1.4 km/s/Mpc.

Now THAT is important! M106 has been used to nail down the Hubble constant, H₀, which gives us the rate of the expansion of the Universe! The M106 data tells us the the expansion rate of the Universe is around 72-73 km per second per Megaparsec. Okay, okay, I know, that's just the value for the nearby Universe, because the Hubble constant for the baby Universe, the one we detect as the CMB, the Cosmic Microwave Background, is more like 66-67 km/s/Mpc.

M106 is X-ray, optical, infrared and radio emission. Credit: X-ray: NASA/CXC/Caltech/P.Ogle et al; Optical: NASA/STScI & R.Gendler; IR: NASA/JPL-Caltech; Radio: NSF/NRAO/VLA.

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The long curved outflows from the core of M106 have been described as "anomalous arms". I guess they have something to do with the water masers of M106. Perhaps they are the water masers? At the very least, they are certainly visible in radio emission.

Ann

[Rob Gendler]

It appears to me that the image is not hot linked to a larger image

[brianbrengle@gmail.com]

I believe M106 has diameter greater than 30 thousand light years. I have found in other publications a diameter of 130,000 light years.

[Ann]

I believe M106 has diameter greater than 30 thousand light years. I have found in other publications a diameter of 130,000 light years.

Yes, that's what Wikipedia says:

Wikipedia wrote:

It is one of the largest and brightest nearby galaxies, similar in size and luminosity to the Andromeda Galaxy. The supermassive black hole at the core has a mass of (3.9±0.1)×107 M☉.

A diameter of 30,000 light-years, by contrast, would make M106 a quite small galaxy.

And Rob Gendler is right that the thumbnail APOD is not hotlinked to a larger image.

Ann

[Rob Gendler]

Here is a link to a higher resolution version of the APOD today.

http://www.robgendlerastropics.com/M106-NOAO-HST-L.html

[XgeoX]

Ann, thanks for downloading those stunning images!

Eric

[orin stepanek]

M106-NOAO-HST-1024c.jpg

Beautiful M106! I see the stars in the dust lanes; so a good view of
This galaxy! Looks like a lot of turmoil toward the center. Could
the black hole be going through a feeding frenzy?

[NCTom]

What is the chance of seeing an image like this annotated to note the various items in view such as types of galaxies, structural components of the central galaxy, and any other points of interest such faint star streams? The enlarged view is a treasure house of variety.

[neufer]

The long curved outflows from the core of M106 have been described as "anomalous arms". I guess they have something to do with the water masers of M106. Perhaps they are the water masers? At the very least, they are certainly visible in radio emission.

• Strong extragalactic water masers like M106/NGC 4258 are specifically located in dense (10⁸/cm³ to 10¹¹/cm³) warm (>300K) circumnuclear regions around the active galactic nuclei (AGN). It is thereby useful in accurately determining the mass of the central black hole

Water megamasers

<<Water masers stronger than galactic water masers, some of which are strong enough to be classified "mega" masers, may be described by the same luminosity function as galactic water masers. Strong extragalactic water masers are found in the circumnuclear regions around active galactic nuclei (AGN). The isotropic luminosities of these span a range of order one to a few hundred L_☉, and are found in nearby galaxies like Messier 51 (0.8 L_☉) and NGC 4258 (120 L_☉).

Water maser emission is observed primarily at 22 GHz, due to a transition between rotational energy levels in the water molecule. The upper state is at an energy corresponding to 643 kelvins about the ground state, and populating this upper maser level requires number densities of molecular hydrogen of order 10⁸ cm⁻³ or greater and temperatures of at least 300 kelvins. The water molecule comes into thermal equilibrium at molecular hydrogen number densities of roughly 10¹¹ cm⁻³, so this places an upper limit on the number density in a water masing region.

Black-hole mass plotted against velocity dispersion of stars in a galaxy bulge. Points are labelled by galaxy name; all points in this diagram are for galaxies that have a clear, Keplerian rise in velocity near the center, indicative of the presence of a central mass. The M–σ relation is shown in blue.

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Water megamasers may be used to provide accurate distance determinations to distant galaxies. Assuming a Keplerian orbit, measuring the centripetal acceleration and velocity of water maser spots yields the physical diameter subtended by the maser spots. By then comparing the physical radius to the angular diameter measured on the sky, the distance to the maser may be determined. This method is effective with water megamasers because they occur in a small region around an AGN, and have narrow linewidths. This method of measuring distances is being used to provide an independent measure of the Hubble constant that does not rely upon use of standard candles. The method is limited, however, by the small number of water megamasers known at distances within the Hubble flow. This distance measurement also provides a measurement of the mass of the central object, which in this case is a supermassive black hole. Black hole mass measurements using water megamasers is the most accurate method of mass determination for black holes in galaxies other than the Milky Way. The black hole masses that are measured are consistent with the M-sigma relation, an empirical correlation between stellar velocity dispersion in galactic bulges and the mass of the central supermassive black hole.>>

[Ann]

What is the chance of seeing an image like this annotated to note the various items in view such as types of galaxies, structural components of the central galaxy, and any other points of interest such faint star streams? The enlarged view is a treasure house of variety.

I'll do my best...

M106. NASA, ESA, the Hubble Heritage Team (STScI/AURA), and R. Gendler (for the Hubble Heritage Team). Acknowledgment: J. GaBany.

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M106 annotated.png

This is what the annotations mean:

1 and 2: Anomalous arms emerging from the nuclear region of M106. They are bright in X-rays, radio emission and possibly hydrogen alpha (because of the red color).

3: Bright yellow center, with a brilliant core. All really large spiral galaxies have them.

4: The yellow bulge of M106. All major spiral galaxies have them, too (with perhaps an extremely few exceptions). The bulge is yellow, because all the stars in there are old and yellow and red. But there are fewer stars in the bulge than in the nuclear region, so the bulge is not as bright as the nucleus.

5: Very bright region of star formation. The brilliant young stars inside are still completely hidden by their pink-glowing hydrogen alpha birth cloud, so this is a very young region of star formation.

6 Another very bright, but slightly older region of star formation. The brilliant blue stars inside have burst through their pink birth cloud.

7: A still bright, but even older cluster of massive blue stars. The pink birth cloud has been completely dispersed by the stars' powerful stellar winds.

8: An even older region of star formation. Practically all the really bright and massive stars have already died here, most of them in supernova explosions. But huge numbers of more modest stars like Vega and Sirius remain, giving the region a pale bluish hue.

You may say it's an ex-parrot, or an ex-region of star formation, because there is no star-forming life in it. It's dead.

I didn't annotate any dust lanes. They are important, and all major spiral galaxies have them. In an optical image, the dust lanes will look dark brown. They look brown because interstellar matter, which is a mixture of a lot of gas and small amounts of dust particles, mostly made of silicates and ices, concentrate in the dust lanes and make them look dark.

Dust lanes are also typically sites of star formation. In my annotated image, 5, 6 and 7 are all young clusters that were born from the matter that gets concentrated in dust lanes. But please note that long stretches of dust don't contain any young clusters or pink nebulas at all.

Ann

[Ann]

Oh, and if we want to, we may note that the cluster that I marked as number 6 is a particularly energetic and interesting cluster.

M106 annotated.png

Composite image of M106 in X-ray, optical, infrared and radio emission. Credit: X-ray: NASA/CXC/Caltech/P.Ogle et al; Optical: NASA/STScI & R.Gendler; IR: NASA/JPL-Caltech; Radio: NSF/NRAO/VLA

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M106 is radio emission, color-coded as purple. Note the the relatively bright purple spot at lower left. That is the bright star cluster that I marked as number 6. Credit: NSF/NRAO/VLA.

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M106 in infrared light, color-coded as red. We can see the bright cluster 'number 6' at lower left. Credit: NASA/JPL-Caltech."

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If you go to this page and download one of the larger versions of Chandra's composite image of M106, you can find out what parts of the galaxies are bright in what wavelengths. I'd say that point sources that are bright in radio only, or in X-rays only, are probably not sources in M106 itself, at least not if they are found in the disk or the "normal arms". In those cases, I'd say that they are most likely distant background sources, like radio galaxies or quasars.

But "source 6" is a point source that is bright in both optical, radio and infrared light, which means that powerful things are going on in there!

Ann

[johnnydeep]

Only visible in the larger image, I noticed an ovoid blur with a brilliant point-like center off to the lower left. What is it? A far off elliptical? Local small companion? Or optical artifact?

Click to view full size image

[NCTom]

Thanks Ann for the detailed info. Like johnnydeep I am also curious about those structures that seem independent of Messier 106, scattered around its perimeter and in some cases obviously far behind it. For those of us who do not have the astronomical background some of the rest of you have, these extra explanations allow us to revisit the cosmos in ways we have not had in decades.

[alter-ego]

Only visible in the larger image, I noticed a ovoid blur with a brilliant point-like center off to the lower left. What is it? A far off elliptical? Local small companion? Or optical artifact?

Click to view full size image

UGC 7356 -- Galaxy

It's distance is ≈21MLy to 25MLy, could be a satellite.
It's morphology is somewhat questionable. It is listed as a dwarf elliptical (dE) or highly irregular (Im)

[Ann]

Only visible in the larger image, I noticed a ovoid blur with a brilliant point-like center off to the lower left. What is it? A far off elliptical? Local small companion? Or optical artifact?

Click to view full size image

UGC 7356 -- Galaxy

It's distance is ≈21MLy to 25MLy, could be a satellite.
It's morphology is somewhat questionable. It is listed as a dwarf elliptical (dE) or highly irregular (Im)

It is a weird object.

UGC 7356 SDSS.png

UGC 7356 according to SDSS.

UGC 7356 Gendler.png

UGC 7356 according to Rob Gendler.

The object is roughly spherical. It appears to be "the same brightness all over", except for its bright nucleus. It is completely featureless, except for the red objects inside it, which in my opinion are almost certainly distant background galaxies. It could be a puff of smoke, if the nucleus wasn't there. Or is it a nucleus? I'm going to guess that it is, because it is so perfectly centrally located inside this featureless blob.

Nucleated dwarf galaxy NGC 4323. Photo: SDSS.

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Nucleated dwarf galaxy NGC 4323 interacting with large spiral galaxy M100 at a distance of about 55 light-years. Photo: David Malin.

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So I'm going to use David Malin's expression and call it a "nucleated dwarf". He used that word for galaxy NGC 4323, a (possible) companion of large spiral galaxy M100. But the nucleus of UGC 7356 looks much brighter, at least to the rest of the galaxy, than the nucleus of NGC 4323.

Also note that NGC 4323 is a much, much more "substantial" galaxy than UGC 7356. NGC 4323 is about one and a half magnitudes brighter than UGC 7356, even though it is about twice as far away.

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Note that if you are going to google NGC 4323 you may have some trouble finding it, because the galaxy has often been referred to as NGC 4322. But the object listed as NGC 4322 is actually a star.

Ann

[johnnydeep]

Only visible in the larger image, I noticed a ovoid blur with a brilliant point-like center off to the lower left. What is it? A far off elliptical? Local small companion? Or optical artifact?

Click to view full size image

UGC 7356 -- Galaxy

It's distance is ≈21MLy to 25MLy, could be a satellite.
It's morphology is somewhat questionable. It is listed as a dwarf elliptical (dE) or highly irregular (Im)

Thank you, alter-ego (and Ann!). Simbad to the rescue once again, along with Ann's further exposition. I've since found this short phys.org article about the same image as the APOD, which also mentions M106's two companions: https://phys.org/news/2021-03-image-sta ... holas.html

Accompanying Messier 106 is a pair of dwarf galaxies belonging to the same galaxy group. The loose collection of stars and dust visible in the bottom-right of this image is the small irregular galaxy NGC 4248. Another small galaxy—UGC 7356—lies to the lower-left of Messier 106 and is dwarfed by its larger neighbor. Messier 106 and its companions are framed by a variety of objects, from foreground stars to background galaxies. Stars from our own galaxy stud the image, easily identified by the criss-cross diffraction patterns surrounding them. In the background, distant galaxies litter the image, some of them visible through the tenuous disk of Messier 106.