APOD: IC 342: The Hidden Galaxy in... (2022 Feb 11)

[APOD Robot]

IC 342: The Hidden Galaxy in Camelopardalis

Explanation: Similar in size to large, bright spiral galaxies in our neighborhood, IC 342 is a mere 10 million light-years distant in the long-necked, northern constellation Camelopardalis. A sprawling island universe, IC 342 would otherwise be a prominent galaxy in our night sky, but it is hidden from clear view and only glimpsed through the veil of stars, gas and dust clouds along the plane of our own Milky Way galaxy. Even though IC 342's light is dimmed and reddened by intervening cosmic clouds, this sharp telescopic image traces the galaxy's own obscuring dust, young star clusters, and glowing pink star forming regions along spiral arms that wind far from the galaxy's core. IC 342 may have undergone a recent burst of star formation activity and is close enough to have gravitationally influenced the evolution of the local group of galaxies and the Milky Way.

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[VictorBorun]

is it just me or is there really a bar in the core?

[Chris Peterson]

is it just me or is there really a bar in the core?

I don't think there's a bar (and I don't find any classifications of this as barred). I think there's just a slightly asymmetric star forming region at or near the center that gives that impression. The arms still appear to start at the center, not off the tips of a bar.

[Ann]

is it just me or is there really a bar in the core?

Yes, it looks like there is a small bar there. IC 342 may be another of these "intermediate" spirals, which are intermediate between barred and non-barred spirals.

IC 342: The Hidden Galaxy in Camelopardalis
Image Credit & Copyright: Daniel Feller

NGC 1566: The Spanish Dancer Spiral Galaxy. Image Credit & Copyright: Mark Hanson and Mike Selby

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Wikipedia wrote about IC 342:

IC 342 (also known as Caldwell 5) is an intermediate spiral galaxy in the constellation Camelopardalis

It is interesting to compare IC 342 with another intermediate spiral galaxy, NGC 1566.

Wikipedia wrote about NGC 1566:

NGC 1566, sometimes known as the Spanish Dancer, is an intermediate spiral galaxy in the constellation Dorado...

The morphological classification of NGC 1566 is SAB(rs)bc, which indicates a spiral galaxy with a weak bar structure around the nucleus (SAB), an incomplete ring around the bar (rs), and showing moderate to loosely wound arms (bc). The spiral arms are strong and symmetrical...

The mass ratio of neutral hydrogen gas to the mass of the stars is 0.29, which is on the high side for a galaxy of this mass. Absolute luminosity is 3.7×1010 L_☉, and is calculated to contain 1.4×1010 M_☉ of H I...

NGC 1566 is an active galaxy with many features of a Seyfert type 1, although the exact type remains uncertain. It is one of the closest and brightest Seyfert galaxies. The mass of the supermassive black hole at the center is estimated at (1.3±0.6)×107 M_☉.

It's interesting to compare the appearance of these two galaxies. NGC 1566 looks a lot more massive to me. The elegant, symmetrical grand design (two-armed) spiral shape with inner arms studded with pink emission nebulas makes it look "dynamic" and "powerful", whatever I mean by that! ¯\_(ツ)_/¯

NGC 1566 might be brighter than the Milky Way. According to Wikipedia, the absolute luminosity of NGC 1566 is 3.7×1010 L_☉, whereas the absolute luminosity of the Milky Way might be described as

www.astro.utu.fi The total luminosity of the disk is about 1.2 x 10¹⁰ L_☉ while the luminosity of the spheroid is about 2 x 10⁹ L_☉

But that's an old source, so we should be skeptical. My impression is that astronomers have tended to upgrade the size, mass and luminosity of the Milky Way in recent years. However, it does appear as if the central black hole of NGC 1566 is more massive than Sgr A* in the Milky Way.

What I'm really getting at is this - IC 342 looks relatively small to me. Not very small, and it is probably larger than M33, the Triangulum galaxy. But it doesn't look very massive to me, because it is a bit too disorganized, with no (very) strong forces apparently pulling at it.

But it actually looks more impressive in infrared light! Here you can also see the bar very clearly.

IC 342 in infrared light. Credit: NASA/JPL-Caltech/J. Turner (UCLA)

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That's just my two cents!

Ann

[bystander]

is it just me or is there really a bar in the core?

I don't think there's a bar (and I don't find any classifications of this as barred). I think there's just a slightly asymmetric star forming region at or near the center that gives that impression. The arms still appear to start at the center, not off the tips of a bar.

Wikipedia calls it an intermediate spiral galaxy, somewhere between a spiral and a barred spiral.

[VictorBorun]

But it actually looks more impressive in infrared light! Here you can also see the bar very clearly.

IC 342 in infrared light. Credit: NASA/JPL-Caltech/J. Turner (UCLA)

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quite a macramé

[orin stepanek]

Look like a galaxy nestled behind hidden! Just my opinion!

I like this view of Andromeda! It Looks almost 3-D!

[Ann]

Click to view full size image

Look like a galaxy nestled behind hidden! Just my opinion!

Indeed, Orin, that's a distant background galaxy.

Ann

[Chris Peterson]

[float=][/float]

is it just me or is there really a bar in the core?

But it actually looks more impressive in infrared light! Here you can also see the bar very clearly.

Agreed, in IR it's much more apparent that there's some bar structure there.

[Star Searcher]

Anyone know what's causing stars near the corners to have off center red splotches? Is that due to red focusing differently on the sensor than blue and green?

[Chris Peterson]

Anyone know what's causing stars near the corners to have off center red splotches? Is that due to red focusing differently on the sensor than blue and green?

That effect is pretty small with this imaging setup, and would be corrected by focusing since each channel was collected separately (it's an issue with single-shot color, not with filtered channels). The fact that the red is offset in almost the same direction everywhere suggests a processing problem, although this kind of alignment error is unlikely with PixInsight.

I might guess it's related to the different channels having slightly different image scales. The telescope used was an SCT, and one with significant variation in tube length with temperature. With these optics, that changes both the focus and the focal length (and therefore image scale). Focus is correctable during imaging. Different scale can only be fixed during post processing, and might not have been done fully here.

[neufer]

is it just me or is there really a bar in the core?

But it actually looks more impressive in infrared light!
Here you can also see the bar very clearly.

Agreed, in IR it's much more apparent that there's some bar structure there.

Hubble Space Telescope image of the central region of IC 342, showing the central star cluster and surrounding dust lanes. ESA/Hubble

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Trifid Nebula H II region/nucleus

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<<Caldwell 5, also known as IC 342, is a spiral galaxy located approximately 11 million light-years from Earth.

This sparkling, face-on view of the center of the galaxy displays intertwined tendrils of glowing, rosy dust in spectacular arms that wrap around a brilliant blue core of hot gas and stars. This IC 342 core is a specific type of region called an H II nucleus — an area of atomic hydrogen that has become ionized. Such regions are energetic birthplaces of stars where thousands of stars can form over a couple million years. Each young, extremely hot, blue star emits ultraviolet light, further ionizing the surrounding hydrogen.

A relatively close galaxy, its face-on alignment makes it a prime target for possible supernova sightings, but so far, scientists have seen none. Caldwell 5 was discovered in the early 1890s by William Frederick Denning, a British amateur astronomer who had practically no formal scientific training yet still managed to achieve a great amount of success in astronomy (discovering several comets, publishing more than a thousand scholarly articles, and winning the Gold Medal of the Royal Astronomical Society).>>

[VictorBorun]

Hubble Space Telescope image of the central region of IC 342, showing the central star cluster and surrounding dust lanes. ESA/Hubble

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I tried to fit this "central region of IC 342, showing the central star cluster"

Field of view is 0.33 x 0.33 arcminutes
North is 10.2° left of vertical

with the APOD-posted pic, in vain

with Spitzer's IR "A Twisted Dust Web in the Galaxy IC 342" (did I say quite a macramé ? Sorry for wrong choice of words)
Field of view is 33.3 x 28.4 arcminutes
North is 139.1° left of vertical in vain

one Field of view is 100 times as big as the other! No good to fit

I still wonder if "the central star cluster" is the core with no bar at all or some other "central star cluster"

[Ann]

Hubble Space Telescope image of the central region of IC 342, showing the central star cluster and surrounding dust lanes. ESA/Hubble

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I tried to fit this "central region of IC 342, showing the central star cluster"

Field of view is 0.33 x 0.33 arcminutes
North is 10.2° left of vertical

with the APOD-posted pic, in vain

with Spitzer's IR "A Twisted Dust Web in the Galaxy IC 342" (did I say quite a macramé ? Sorry for wrong choice of words)
Field of view is 33.3 x 28.4 arcminutes
North is 139.1° left of vertical in vain

one Field of view is 100 times as big as the other! No good to fit

I still wonder if "the central star cluster" is the core with no bar at all or some other "central star cluster"

IC 342. Photo: Sean Curry.

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Take a look at the picture of IC 342 by Sean Curry. As you can see, the core of the galaxy is bright and overexposed, and we can't see any details in it. (But we can indeed see that there appears to be star formation in the bar to the left and right of the nucleus - note the pink splotches.)

Anyway. My guess is that Hubble is showing us exactly the part of IC 342 that is overexposed in Sean Curry's image. In other words, I think that the dust lanes that can be seen in the Hubble image are invisible in Curry's image because the light from the center is so bright. I also think that what we see as the bar of IC 342 in Curry's image is outside the field of Hubble's camera.

So, we are looking at the innermost core of IC 342 in the Hubble image. Note right at the center a yellow-white spot with soft edges. I think that this is "the nucleus proper", where a (probably smallish) central black hole might be hiding. The bright star cluster surrounding it is an intense ring of star formation surrounding the nucleus.

Ann

[VictorBorun]

I think that this is "the nucleus proper", where a (probably smallish) central black hole might be hiding. The bright star cluster surrounding it is an intense ring of star formation surrounding the nucleus.

I made in vain an attempt to put Hubble’s "the very central region of the galaxy"

0.33 x 0.33 arcminutes

into Spitzer's IR "Twisted Dust Web"

33.3 x 28.4 arcminutes

using coordinates. I may be wrong, but the coordinates seem not precise enough to allow the fitting

[Ann]

I think that this is "the nucleus proper", where a (probably smallish) central black hole might be hiding. The bright star cluster surrounding it is an intense ring of star formation surrounding the nucleus.

I made in vain an attempt to put Hubble’s "the very central region of the galaxy"

0.33 x 0.33 arcminutes

into Spitzer's IR "Twisted Dust Web"

33.3 x 28.4 arcminutes

using coordinates. I may be wrong, but the coordinates seem not precise enough to allow the fitting

Click to view full size image

No, Victor, the Hubble image shows us the exact center of IC 342, the very brightest part of the galaxy (where your black "x" is).

Ann

[VictorBorun]

No, Victor, the Hubble image shows us the exact center of IC 342, the very brightest part of the galaxy (where your black "x" is).

1) why would not they call the core a core, why "central cluster"
2) why does it look just like a forming stellar cluster blowing a surrounding bubble? No hint to a massive black hole

[Ann]

No, Victor, the Hubble image shows us the exact center of IC 342, the very brightest part of the galaxy (where your black "x" is).

1) why would not they call the core a core, why "central cluster"
2) why does it look just like a forming stellar cluster blowing a surrounding bubble? No hint to a massive black hole

I think they do mean "a cluster in the core" when they call it a "central cluster".

I also think that IC 342 probably has a rather small central black hole, which is not at all active. We can't see such a black hole. Typically, the nucleus of a galaxy is just very luminous.

The very center of the Milky Way, with a vortex surrounding
Sgr A*. Image credit: NASA/JPL-Caltech/ESA/CXC/STScI

Take a look at the picture above, which shows the very center of the Milky Way. You can see the vortex surrounding the central black hole of our galaxy, Sgr A*. It is possible that the vortex is just a "whirlwind" of some kind, but you can also see that there are very many stars surrounding the vortex. You can see, too, that apart from the vortex, there is no special giveaway to show that there is a 4 million Solar mass black hole here.

So I really think that the "central cluster" of IC 342 is a cluster that is all but "hugging" the central black hole. If indeed IC 342 even has a central black hole. I would guess that it does, but Local Group spiral galaxy M33 apparently doesn't.

Wikipedia wrote:

Unlike the Milky Way and Andromeda galaxies, the Triangulum Galaxy does not appear to have a supermassive black hole at its center.

But if M33 doesn't have a supermassive black hole at its center, why does the center look bright? It could be, frankly, because there is a very big star cluster smack dab in the center!

www.syfy.com wrote:

Interestingly, the central region of M33 looks like it underwent a burst of star formation in the past, about 70 million years ago, which created some hundred million stars or more. That would explain why the core looks so bright.

Our giant galactic neighbor Andromeda also has a population of young blue stars very near its core:

Michele Diodati of medium.com wrote:

Young Blue Stars in the Andromeda Core

In 2005, astronomers identified the source of a mysterious blue light right in the center of our neighbor, the Andromeda Galaxy (M31). It was a disk of young blue stars in the middle of a population of ancient stars

Ann

[VictorBorun]

So, how to tell at glance a galaxy core center including a massive black hole from a new open stellar cluster 100 thousand times less massive?

My guess is to look at colors.
The number of blue super giants in a galaxy core center matches the number of red dwarfs in a new open stellar cluster, but the color tells the difference

Now I wonder what a few most bright stars in the Hidden Galaxy's center may be. Are they stars at all? Maybe they are men of the hour Hubble telescope was taking that picture?

[Ann]

So, how to tell at glance a galaxy core center including a massive black hole from a new open stellar cluster 100 thousand times less massive?

My guess is to look at colors.
The number of blue super giants in a galaxy core center matches the number of red dwarfs in a new open stellar cluster, but the color tells the difference

Now I wonder what a few most bright stars in the Hidden Galaxy's center may be. Are they stars at all? Maybe they are men of the hour Hubble telescope was taking that picture?

I don't think that the visible colors in a typical photo of the core of a galaxy taken with almost any telescope except Hubble will reveal the blue stars in the core. At least not if the camera settings, exposure times etc are not specifically chosen to reveal details in the core only. The core is typically so much brighter than the rest of the galaxy that you are going to overexpose the core if you try to get a good picture of the disk and spiral arms of the galaxy.

In any case, there is almost always a lot of yellow light in the core from huge numbers of old stars. The way I understand it, stars have formed in the core of a galaxy over billions of years, and stars may also have migrated there. Any predominantly old population of stars is going to be predominantly yellow. But the huge numbers of old stars in the core doesn't mean there can't be young blue clusters there, too.

Galaxy M100. Photo: ESO and the FORS instrument on ESO’s Very Large Telescope at Paranal Observatory in Chile. The core is overexposed.

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M100 photo taken by Hubble. We can see the colors of the core.
https://www.nasa.gov/feature/goddard/2017/messier-100

Compare the two pictures of galaxy M100. The picture on the left was taken with ESO's Very Large Telescope, while the picture at right was taken with Hubble. As you can see, the core of M100 is overexposed in the ESO image, but we can see colors in it in the Hubble picture.

(Admittedly we can also see the colors of the core of M100 in this SDSS/Giuseppe Donatiello image.)

The core of galaxy M94 by Hubble.

Galaxy M94 by R. Jay GaBany. The field of view is much larger here than in the image at left, and we see much more of the galaxy. The core therefore looks much smaller. Note that there are two blue rings visible in GaBany's image, but the Hubble image only shows us the inner blue ring.

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A galaxy with an interesting core is M94. The blue ring surrounding the core is quite large, and can be seen with other telescopes than Hubble. Interestingly, you can see that the color of the star field inside the blue ring is not the same everywhere. Closer to the blue ring, the star field is slightly greenish, which suggests that there is a significant amount of "intermediately aged" stars here, or in other words: This part of the center of M94 is not completely dominated by old stars. But further in, the color of the core is all "old and yellow", until we get to the nucleus itself, which is too overexposed even for Hubble.

Could there be a blue star cluster extremely close to the core of M94, a cluster that we can't see because the nucleus is too overexposed? I guess there could be.

Another very interesting galaxy is NGC 3081:

This Hubble image shows us an outer blue ring and an inner blue ring of NGC 3081, as well as a 'knotty' core. https://cdn.spacetelescope.org/archives/images/large/potw1423a.jpg

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The same Hubble image processed by Steve Byrne.

As you can see, NGC 3081 has an outer blue ring, an inner blue ring and a "knotty" core. Could there be more star clusters inside that knotty core? Yes, I find it likely.

And take a look at galaxy NGC 1300:

The bulge, bar and core of NGC 1300. Image Credit: Hubble Heritage Team, ESA, NASA

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The core of NGC 1300. Note the blue star clusters. Source: Researchgate, uploaded by Richard de Grijs.

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There are definitely young blue star clusters in the core of NGC 1300. Okay, so why was it so much easier for Hubble to photograph the star clusters in the core of IC 342 than in all these other galaxies?

Uhmm... because IC 342 is so much closer to us than the other galaxies here?

Ann

[neufer]

IC 342. Photo: Sean Curry.

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Take a look at the picture of IC 342 by Sean Curry. As you can see, the core of the galaxy is bright and overexposed, and we can't see any details in it. (But we can indeed see that there appears to be star formation in the bar to the left and right of the nucleus - note the pink splotches.)

Anyway. My guess is that Hubble is showing us exactly the part of IC 342 that is overexposed in Sean Curry's image. In other words, I think that the dust lanes that can be seen in the Hubble image are invisible in Curry's image because the light from the center is so bright. I also think that what we see as the bar of IC 342 in Curry's image is outside the field of Hubble's camera.

So, we are looking at the innermost core of IC 342 in the Hubble image. Note right at the center a yellow-white spot with soft edges. I think that this is "the nucleus proper", where a (probably smallish) central black hole might be hiding. The bright star cluster surrounding it is an intense ring of star formation surrounding the nucleus.

Click to play embedded YouTube video.

[Ann]

I just found a video about M95, which has a remarkable core with a lot of star formation. But first, let's look at two pictures of M95, one where you don't see the star formation in the core, and one where you do:

M95 with an overexposed core. Photo: ESO.

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The sharp eye of Hubble reveals a brilliant blue ring of intense star formation around the core of M95. Image: ESA/Hubble.

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Click to play embedded YouTube video.

In this video, Dr. Maggie Lieu talks specifically about the core of M95 and what causes the intense star formation there. One thing she points out is that M95 does not have an AGN (an active galactic nucleus), or in other words: The central black hole of M95 is not active and is not emitting a jet. That may be important, because jets from AGNs tend to suppress star formation. The intense star formation is also not caused by a lopsided mass distribution in the core of M95.

Instead, the cause of the extreme star formation may be a feedback loop caused by the stars themselves, and by the way the massive stars recycle the existing star forming material through supernovas, strong stellar winds and photon pressure.

Ann

[VictorBorun]

do I get it right: an old galactic core, not a an active galactic nucleus, is rich with stars and thin with interstellar gas/plasma medium.
Moreover it's rich with large star, supergiants and black holes.
Those things tend to sink into the center and the red dwarfs, rogue planets, dust particles and gas molecules/atoms/ions tend to soar out of the core.
The most interacting, viscous component is gas, so what gas is shedded by stars in the core is quickly centrifuged out of the core.

[Ann]

do I get it right: an old galactic core, not a an active galactic nucleus, is rich with stars and thin with interstellar gas/plasma medium.
Moreover it's rich with large star, supergiants and black holes.
Those things tend to sink into the center and the red dwarfs, rogue planets, dust particles and gas molecules/atoms/ions tend to soar out of the core.
The most interacting, viscous component is gas, so what gas is shedded by stars in the core is quickly centrifuged out of the core.

Not all galactic cores are rich in star formation. The core of the Milky Way isn't. There are two great clusters close to Sgr A*, the Quintuplet Cluster and the Arches Cluster, which are full of massive young stars, and there are other OB stars there as well, but they are not inside clusters. As for Andromeda, it has a disk of bluish stars very close to its core, but to my knowledge, it has no young clusters there.

When a star goes supernova, some of the gas that is violently expelled may compress other gas clouds in the vicinity and prompt them to collapse into stellar cores, starting the cycle of star formation again. But I don't think that things are generally "centrifuged" out of galactic cores, unless there is an active black hole with an accretion disk there. Because if there is, a jet will be emitted and things will really fly out of the core.

More things will likely fall into the core than be jettisoned out of it.

Ann