Starship Asterisk*

APOD Robot wrote: ↑Sun Aug 13, 2023 4:06 am The Sombrero Galaxy in Infrared

recently recorded by the orbiting Spitzer Space Telescope

Rauf wrote: ↑Sun Aug 13, 2023 11:25 am The text seems a little outdated.

APOD Robot wrote: ↑Sun Aug 13, 2023 4:06 am The Sombrero Galaxy in Infrared

recently recorded by the orbiting Spitzer Space Telescope

Spitzer Space Telescope has retired, right? So it couldn't have possibly record data on this galaxy recently.

JimB wrote: ↑Sun Aug 13, 2023 8:28 am Beautiful image!

But it looks like the central region of this galaxy is pretty empty of stars - is this really the case?

Rauf wrote: ↑Sun Aug 13, 2023 11:25 am The text seems a little outdated.

APOD Robot wrote: ↑Sun Aug 13, 2023 4:06 am The Sombrero Galaxy in Infrared

recently recorded by the orbiting Spitzer Space Telescope

Spitzer Space Telescope has retired, right? So it couldn't have possibly record data on this galaxy recently.

AVAO wrote: ↑Sun Aug 13, 2023 12:15 pm

Rauf wrote: ↑Sun Aug 13, 2023 11:25 am The text seems a little outdated.

APOD Robot wrote: ↑Sun Aug 13, 2023 4:06 am The Sombrero Galaxy in Infrared

recently recorded by the orbiting Spitzer Space Telescope

Spitzer Space Telescope has retired, right? So it couldn't have possibly record data on this galaxy recently.

The fact that today's APOD is an evergreen or a repost from 2012 (viewtopic.php?t=27724) your question can be answered quickly. Unfortunately, it happens relatively often that the original APOD text is also adopted without making any adjustments.

By the way in this case, the title is also only 50 % correct, since the image shown is a composite of IR and the Hubble optical wavelenght.



https://www.spitzer.caltech.edu/image/s ... -sombrero

Chris Peterson wrote: ↑Sun Aug 13, 2023 1:14 pm

JimB wrote: ↑Sun Aug 13, 2023 8:28 am Beautiful image!

But it looks like the central region of this galaxy is pretty empty of stars - is this really the case?

It's an illusion. The central region is nothing but stars!

Universe Today wrote:

The Sombrero galaxy has a split personalty, according to recent observations by NASA’s Spitzer Space Telescope. Infrared imaging has revealed a hazy elliptical halo of stars enveloping a dual-structured inner disk; before this, the Sombrero galaxy was thought to be only disk-shaped.
...
Spitzer discerned that the flat disk within the galaxy is made up of two sections — an inner disk composed almost entirely of stars with no dust, and an outer ring containing both dust and stars.

Universe Today wrote:

“The Sombrero is more complex than previously thought,” said Dimitri Gadotti of the European Southern Observatory in Chile and lead author of the report. “The only way to understand all we know about this galaxy is to think of it as two galaxies, one inside the other.”

Although it might seem that the Sombrero is the result of a collision between two separate galaxies, that’s actually not thought to be the case. Such an event would have destroyed the disk structure that’s seen today; instead, it’s thought that the Sombrero accumulated a lot of extra gas billions of years ago when the Universe was populated with large clouds of gas and dust. The extra gas fell into orbit around the galaxy, eventually spinning into a flattened disk and forming new stars.

Ann wrote: ↑Sun Aug 13, 2023 5:35 pm ...
"Although it might seem that the Sombrero is the result of a collision between two separate galaxies, that’s actually not thought to be the case. Such an event would have destroyed the disk structure that’s seen today; instead, it’s thought that the Sombrero accumulated a lot of extra gas billions of years ago when the Universe was populated with large clouds of gas and dust. The extra gas fell into orbit around the galaxy, eventually spinning into a flattened disk and forming new stars."

De58te wrote: ↑Sun Aug 13, 2023 3:59 pm "The Sombrero Galaxy, also known as M104, spans about 50,000 light years across."

There seems to be some discrepancy with the Wikipedia Sombrero Galaxy article. And I quote; [The Sombrero Galaxy] has a D25 isophotal diameter of approximately 29.09 kiloparsecs (94,900 light-years),[1] making it slightly BIGGER in size than the Milky Way. unquote

johnnydeep wrote: ↑Sun Aug 13, 2023 8:31 pm

De58te wrote: ↑Sun Aug 13, 2023 3:59 pm "The Sombrero Galaxy, also known as M104, spans about 50,000 light years across."

There seems to be some discrepancy with the Wikipedia Sombrero Galaxy article. And I quote; [The Sombrero Galaxy] has a D25 isophotal diameter of approximately 29.09 kiloparsecs (94,900 light-years),[1] making it slightly BIGGER in size than the Milky Way. unquote

You beat me to it. I'll chalk it up to a repeat APOD and (hopefully) a more accurate recent reference for the diameter in Wikepedia (*). But if the Sombrero Galaxy really IS only 50 Kly in diameter, it makes it much less impressive in my view.

[ (*) EDIT: the reference for the diameter in Wikipedia is rather old:
"NASA/IPAC Extragalactic Database". Results for M104. Retrieved 2008-07-09." ]

Some more info: from https://esahubble.org/images/opo0328a/, the FOV of the image below is 9.57 x 5.36 arcminutes, which, assuming the distance of 30 Mly is correct, makes the real extent of the image at that distance out to be 87500 x 46700 ly. (I used the calculator at https://www.1728.org/angsize.htm.) So, the diameter of the bulk of what we can see here a lot closer to 50000 ly than it is to 100000 ly. There goes the majesty of the otherwise totally awesome Sombrero! <sigh>

Click to view full size image

Ann wrote: ↑Mon Aug 14, 2023 5:04 am

johnnydeep wrote: ↑Sun Aug 13, 2023 8:31 pm

De58te wrote: ↑Sun Aug 13, 2023 3:59 pm "The Sombrero Galaxy, also known as M104, spans about 50,000 light years across."

There seems to be some discrepancy with the Wikipedia Sombrero Galaxy article. And I quote; [The Sombrero Galaxy] has a D25 isophotal diameter of approximately 29.09 kiloparsecs (94,900 light-years),[1] making it slightly BIGGER in size than the Milky Way. unquote

You beat me to it. I'll chalk it up to a repeat APOD and (hopefully) a more accurate recent reference for the diameter in Wikepedia (*). But if the Sombrero Galaxy really IS only 50 Kly in diameter, it makes it much less impressive in my view.

[ (*) EDIT: the reference for the diameter in Wikipedia is rather old:
"NASA/IPAC Extragalactic Database". Results for M104. Retrieved 2008-07-09." ]

Some more info: from https://esahubble.org/images/opo0328a/, the FOV of the image below is 9.57 x 5.36 arcminutes, which, assuming the distance of 30 Mly is correct, makes the real extent of the image at that distance out to be 87500 x 46700 ly. (I used the calculator at https://www.1728.org/angsize.htm.) So, the diameter of the bulk of what we can see here a lot closer to 50000 ly than it is to 100000 ly. There goes the majesty of the otherwise totally awesome Sombrero! <sigh>

Click to view full size image

Thanks, Johnny! Interestingly, a 2003 Hubblesite caption of a portrait of M104 claims that the diameter of this galaxy is 50,000 ly, but a recent (2021) NASA caption says nothing about the diameter of M104.

I was going to ask someone to calculate the size of M104 based on its apparent size on the sky and its distance. Let's see, Johnny, you calculated the diameter of the APOD at a distance of 30 million light-years, not the size of the visible diameter of the galaxy?

Okay. According to Wikipedia, the apparent size of M104 is 9′ × 4′ — I assume that means 9 x 4 arcminutes? How big is a thing whose apparent diameter is 9 x 4 arcminutes at a distance of 30 million light-years?

Wikipedia talks about the isophotal diameter of M104. This apparently refers to the distance at which the surface brightness of a galaxy drops below a certain value. But take a look at this ESA/Hubble portrait of M104:

M104. Credit: NASA/ESA and The Hubble Heritage Team (STScI/AURA)

---

We see no signs that the galaxy, so to speak, gradually drops off beyond the well-defined dust lane. M104 appears to end abruptly at the outer edge of the dust lane, as if this dust lane was a piece of string keeping the contents of a parcel safe inside its wrapping. So to find the diameter of M104, it should be enough to calculate the size of the dust lane.

Unless, of course, James Webb is going to show us that M104 is much, much wider than the dust lane fooled us to believe. And indeed, even the old Spitzer Telescope showed us that the the old stellar population of M104 extended beyond the dust lane. Note that the false color blue haze of starlight extends slightly beyond the red-colored dust lane in the APOD:

M104 in infrared light by Spitzer. Credit: Credit: R. Kennicutt (Steward Obs.) et al., SSC, JPL, Caltech, NASA

---

I'd like to add that Wikipedia says that the isophotal diameter of the Milky Way is smaller than that of M104, corresponding to 26.8 ± 1.1 kiloparsecs (87,400 ± 3,590 light-years) versus 29.09 kiloparsecs (94,900 light-years) for M104.

Okay!! I have found the source for the claim that the diameter of M104 is almost 100.000 light-years. It's the NED database. If you scroll down almost to the bottom, you will find QUICK-LOOK ANGULAR & PHYSICAL DIAMETERS for MESSIER 104.

Here it says that the K (infrared) diameter of M104 is 32.32 kiloparsecs. That does indeed correspond to about 100,000 light-years. And the B diameter for M104 is 29.09 kiloparsecs (or 94,900 light-years), according to NED.

Ann

Some more info: from https://esahubble.org/images/opo0328a/, the FOV of the image below is 9.57 x 5.36 arcminutes, which, assuming the distance of 30 Mly is correct, makes the real extent of the image at that distance out to be 87500 x 46700 ly.

I was going to ask someone to calculate the size of M104 based on its apparent size on the sky and its distance. Let's see, Johnny, you calculated the diameter of the APOD at a distance of 30 million light-years, not the size of the visible diameter of the galaxy?

Okay. According to Wikipedia, the apparent size of M104 is 9′ × 4′ — I assume that means 9 x 4 arcminutes? How big is a thing whose apparent diameter is 9 x 4 arcminutes at a distance of 30 million light-years?

Coordinates
Position (RA): 12 39 59.29
Position (Dec): -11° 37' 21.89"
Field of view: 9.57 x 5.36 arcminutes
Orientation: North is 5.0° right of vertical

johnnydeep wrote: ↑Mon Aug 14, 2023 12:19 pm
So, yes, I assumed the FOV data at the esahubble.org link was for the square extent of the image, not for the galaxy that happens to be in it. Here's how it presented that data:

Coordinates
Position (RA): 12 39 59.29
Position (Dec): -11° 37' 21.89"
Field of view: 9.57 x 5.36 arcminutes
Orientation: North is 5.0° right of vertical

So, what's the correct interpretation here? Is the angular FOV measurement of the image rectangle as I took it to be, or is it of the galaxy shown in it? I had assumed that unless otherwise stated, the FOV of a particular image from a particular telescope is always of the total rectangular extent of it, since that is presumably precisely known, and independent of distance.

Chris Peterson wrote: ↑Mon Aug 14, 2023 1:35 pm

johnnydeep wrote: ↑Mon Aug 14, 2023 12:19 pm
So, yes, I assumed the FOV data at the esahubble.org link was for the square extent of the image, not for the galaxy that happens to be in it. Here's how it presented that data:

Coordinates
Position (RA): 12 39 59.29
Position (Dec): -11° 37' 21.89"
Field of view: 9.57 x 5.36 arcminutes
Orientation: North is 5.0° right of vertical

So, what's the correct interpretation here? Is the angular FOV measurement of the image rectangle as I took it to be, or is it of the galaxy shown in it? I had assumed that unless otherwise stated, the FOV of a particular image from a particular telescope is always of the total rectangular extent of it, since that is presumably precisely known, and independent of distance.

I've never seen FOV refer to anything other than the physical extents of the image. Not any structure within the image. (The angular extent of anything in the image is also precisely known and independent of distance, of course... but that isn't reasonably labeled "FOV".)

Chris Peterson wrote: ↑Sun Aug 13, 2023 1:14 pm

JimB wrote: ↑Sun Aug 13, 2023 8:28 am Beautiful image!

But it looks like the central region of this galaxy is pretty empty of stars - is this really the case?

It's an illusion. The central region is nothing but stars!

Ann wrote: ↑Sun Aug 13, 2023 5:35 pm
But the Sombrero Galaxy has not formed any new stars in a long time, and it is a very yellow galaxy. Let's compare the (blurry) GALEX picture of M104 with a somewhat less blurry GALEX picture of the Andromeda Galaxy. In these pictures, blue means hot stars that radiate far ultraviolet light, like B- och O-type stars, and yellow means cool stars that radiate near ultraviolet light, like F, G, K and M-type stars.

M104 GALEX.png

M104 in ultraviolet light by GALEX.

Andromeda Galaxy GALEX.png

The Andromeda Galaxy in ultraviolet light by GALEX.

Even though Andromeda is a quite yellow galaxy, its blue population of hot OB stars shows up very clearly in the GALEX image. In the GALEX picture of M104, however, we strain to see any traces of blue. It is safe to say that if there are any hot OB stars in M104, they are very few and far between.

Ann

MarkBour wrote: ↑Tue Aug 15, 2023 12:02 am

Chris Peterson wrote: ↑Sun Aug 13, 2023 1:14 pm

JimB wrote: ↑Sun Aug 13, 2023 8:28 am Beautiful image!

But it looks like the central region of this galaxy is pretty empty of stars - is this really the case?

It's an illusion. The central region is nothing but stars!

Thanks, Chris. When I look at this flat image, a 2-dimensional elliptical region, or oval, appears to be the main illuminated area. And you're pointing out that what we might mistake for a "glow" in empty space, is actually the effect of a vast number of stars that are too far away to be distinguished into points. And what seems the almost obvious mental interpretation is that these stars actually inhabit a 3-D ellipsoid, or somewhat "squashed sphere" shape in space. I think the overall shape is what about everyone would have guessed immediately, but it's very interesting to imagine the vast number of stars that fill this region and together create the "glow". Perhaps one can even determine the number of stars from measurements of this overall glow, though I am not thinking of trying that.

What I am most curious about today is the dark ring -- the galaxy's singular dust lane. I have a basic question about it. When we see such a dust lane, can we surmise much about its origin? Is it the debris from one or more prior generations of stars that have exploded? If so, why would it be in this position for this galaxy? Why wouldn't it form the same shape as the distribution of stars, and be all over the place?

MarkBour wrote: ↑Tue Aug 15, 2023 12:02 am
What I am most curious about today is the dark ring -- the galaxy's singular dust lane. I have a basic question about it. When we see such a dust lane, can we surmise much about its origin? Is it the debris from one or more prior generations of stars that have exploded? If so, why would it be in this position for this galaxy? Why wouldn't it form the same shape as the distribution of stars, and be all over the place?