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NGC 4449: Close up of a Small Galaxy

Explanation: Grand spiral galaxies often seem to get all the glory. Their young, blue star clusters and pink star forming regions along sweeping spiral arms are guaranteed to attract attention. But small irregular galaxies form stars too, like NGC 4449, about 12 million light-years distant. Less than 20,000 light-years across, the small island universe is similar in size, and often compared to our Milky Way's satellite galaxy, the Large Magellanic Cloud (LMC). This remarkable Hubble Space Telescope close-up of the well-studied galaxy was reprocessed to highlight the telltale reddish glow of hydrogen gas. The glow traces NGC 4449's widespread star forming regions, some even larger than those in the LMC, with enormous interstellar arcs and bubbles blown by short-lived, massive stars. NGC 4449 is a member of a group of galaxies found in the constellation Canes Venatici. Interactions with the nearby galaxies are thought to have influenced star formation in NGC 4449.

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This is a beautiful and detailed picture of what was once the most common kind of galaxy in the universe: the massively starforming dwarf irregular galaxy.

Nowadays there is not very much "free gas" left in the universe, compared with what there once was. Most of it has already been used up to make stars. Also, black holes and their nasty jets put much of the remaining gas in a state of turbulence, particularly in large galaxy clusters dominated by huge ellipticals, so that this gas can't cool and condense and turn into new stars.

But once the galactic population of the universe was dominated by small starbursting galaxies like NGC 4449. Fascinatingly, this may be the second time over that NGC 4449 is a small starburst galaxy. Take a look at this SDSS picture of NGC 4449:

http://cosmo.nyu.edu/hogg/rc3/NGC_4449_UGC_7592_irg.jpg

This is a g-r-i (green-red-infrared) image of NGC 4449, which means that red emission nebulae are shown as green here. But please note the large, non-blue "envelope" of diffuse light that is seen around the bright blue clusters of young stars. What is that diffuse and non-blue light?

This is the light from many billion-year-old faint reddish stars. These stars were born in NGC 4449 billions of years ago, back when, perhaps, NGC 4449 was a violently starforming galaxy for the first time. The flamboyant bright blue stars of that first episode of starforming glory have died long ago, after living for what in cosmic time is merely a blink of an eye. But all the small red stars that were formed in that first burst of star formation still shine on like little lanterns in space.

As for today's APOD, it is a great image that really brings out the pink emission nebulae of the galaxy. Do take a look at the large version, too, and note how bright mostly blue stars can be found close to the emission nebulae. But other parts of the galaxy is dominated by much smaller, fainter, not so blue stars, which mostly belong to the faint old population.

Ann

My first post is a question on today's close up view.
Since this is irregular does it still have a black hole at the center
or is the shape the result of interaction with close neighbors

I'd just like to make a suggestion for a future APOD: Elliptical Galaxies. When I was young, it was unclear whether a round elliptical galaxy was really spherical, or was a discus shape seen face on. Similarly, it wasn't clear whether the oblong ones were really NFL football-shaped or that same discus seen at an angle. The old photos taken by the 200" Hale telescope in the 1950's showed these shapes better than newer CCD images that see deep into the core. How exactly do the stars move in ellipticals? An APOD that showed a cluster of ellipticals along with other types, like an image of the Virgo cluster, might be a good opportunity to answer these questions.

Jurgen wrote:My first post is a question on today's close up view.
Since this is irregular does it still have a black hole at the center
or is the shape the result of interaction with close neighbors

Since this is a dwarf galaxy, chances are that it doesn't have a black hole in its center. Dwarf galaxies can have central black holes, but it is probably not the rule. In any case, there is no sign of any particular activity in the center of NGC 4449, so if there is a black hole there, it is probably not responsible for setting off the fireworks of star formation in this galaxy. Massive star formation may itself distort a galaxy, because of extremely strong stellar winds from a number of massive stars, plus a large number of supernovae explosions.

The caption of today's APOD suggests that interaction with other galaxies may have triggered the strong star formation activity in NGC 4449.

Ann

larrygeary wrote:... When I was young, it was unclear whether a round elliptical galaxy was really spherical, or was a discus shape seen face on. ... How exactly do the stars move in ellipticals? ...

There's good solid info in Wikipedia about all types of galaxies, including Ellipticals. Here's a bit from that page, but there's lots more known and available there and elsewhere on the web.

The Hubble classification system rates elliptical galaxies on the basis of their ellipticity, ranging from E0, being nearly spherical, up to E7, which is highly elongated. These galaxies have an ellipsoidal profile, giving them an elliptical appearance regardless of the viewing angle. Their appearance shows little structure and they typically have relatively little interstellar matter. ... they are dominated by generally older, more evolved stars that are orbiting the common center of gravity in random directions.

As for a cluster featuring a giant elliptical, how about this image from the Hubble site ...
... along with some of what the Hubble site says about it:

This image from NASA's Hubble Space Telescope shows the diverse collection of galaxies in the cluster Abell S0740 that is over 450 million light-years away in the direction of the constellation Centaurus.

The giant elliptical ESO 325-G004 looms large at the cluster's center. The galaxy is as massive as 100 billion of our suns. Hubble resolves thousands of globular star clusters orbiting ESO 325-G004. Globular clusters are compact groups of hundreds of thousands of stars that are gravitationally bound together. At the galaxy's distance they appear as pinpoints of light contained within the diffuse halo.

Other fuzzy elliptical galaxies dot the image. Some have evidence of a disk or ring structure that gives them a bow-tie shape. Several spiral galaxies are also present. The starlight in these galaxies is mainly contained in a disk and follows along spiral arms.

Rob

WikiSky: NGC 4449

APOD: Small Galaxy NGC 4449 (2007 May 03)
APOD: NGC 4449: Close-Up of a Small Galaxy (2007 Jul 10)

• (probably the same data set used in today's APOD)

Hubble Heritage: Stellar Fireworks Ablaze in NGC 4449 (2007 Jul 03)

That's a golden oldie, Rob. Thanks for the memories!

(And it's a good color picture, too. It's a three-color picture, a g-r-i picture.)

Ann

bystander wrote:WikiSky: NGC 4449

APOD: Small Galaxy NGC 4449 (2007 May 03)
APOD: NGC 4449: Close-Up of a Small Galaxy (2007 Jul 10)

• (probably the same data set used in today's APOD)

Hubble Heritage: Stellar Fireworks Ablaze in NGC 4449 (2007 Jul 03)

Bystander, when i clicked on "Stellar Fireworks Ablaze in NGC4449(2007 jul 03), i got an error page, in which there is a Hubble search engine. So i typed in the fireworks stuff and got a SMALL picture of something with an explanation. Is that what you linked to, or did you have a nice big picture of what they were calling "Fireworks" display??

Beyond wrote:Bystander, when i clicked on "Stellar Fireworks Ablaze in NGC4449(2007 jul 03), i got an error page, in which there is a Hubble search engine. So i typed in the fireworks stuff and got a SMALL picture of something with an explanation. Is that what you linked to, or did you have a nice big picture of what they were calling "Fireworks" display??

That's better than what I got when I clicked the link. This is what I see:

Error Trying to Access Specified Page

We are sorry you are experiencing problems. It appears this page's address was either mistyped or no longer exists. Please double check the page's address to make sure there was no misspelling. If you are still unsuccessful, please try searching for the page via our search engine.

Thank you for your patience

Go to the HUBBLE HERITAGE SITE Main Page.

Beyond wrote:Bystander, when i clicked on "Stellar Fireworks Ablaze in NGC4449(2007 jul 03), i got an error page, in which there is a Hubble search engine. So i typed in the fireworks stuff and got a SMALL picture of something with an explanation. Is that what you linked to, or did you have a nice big picture of what they were calling "Fireworks" display??

Indigo_Sunrise wrote:That's better than what I got when I clicked the link. This is what I see:

Error Trying to Access Specified Page

We are sorry you are experiencing problems. It appears this page's address was either mistyped or no longer exists. Please double check the page's address to make sure there was no misspelling. If you are still unsuccessful, please try searching for the page via our search engine.

Thank you for your patience

Go to the HUBBLE HERITAGE SITE Main Page.

OOPS! The url got doubled. It's been fixed, try again.

THAT's BETTER. Oops means you're human. Otto Posterman doesn't have THAT problem.

bystander wrote:WikiSky: NGC 4449

APOD: Small Galaxy NGC 4449 (2007 May 03)
APOD: NGC 4449: Close-Up of a Small Galaxy (2007 Jul 10)

• (probably the same data set used in today's APOD)

Hubble Heritage: Stellar Fireworks Ablaze in NGC 4449 (2007 Jul 03)

When I clicked on wikisky ngc 4449 it took forever to download and 6 of the pictures didn't come in.
Orin

I was wondering just how small this galaxy is, and larrygeary in a post up above would like to see a comparison, so I decided to scratch both itches at once. Here's an image I made up (from images available on Wikipedia) of three galaxies:
1 - M87, a supergiant elliptical galaxy with a diameter of perhaps 980 kly
2 - our neighbour M31 (aka Andromeda) roughly the same diameter as our Milky Way at about 140 kly
3 - the subject of this APOD, NGC 4449, which is about 20 kly in width

(NGC 4449 is the little splotch near the top-right corner of Andromeda's image.) The relative scale depends a lot on where you draw the "edge" of M87, of course, but I think I got within an order of magnitude.
Rob

Thanks, Rob! That really brings things into perspective.

Ann

The diameter of m32 is only 120 kly, not 980 kly. It is tremendously massive (and dense with stars) but not tremendously big:

http://seds.org/messier/m/m087.html

Guest wrote:

rstevenson wrote:
1 - M87, a supergiant elliptical galaxy with a diameter of perhaps 980 kly

The diameter of m32 is only 120 kly, not 980 kly.

Probably a typo.

Guest wrote:The diameter of m32 is only 120 kly, not 980 kly. It is tremendously massive (and dense with stars) but not tremendously big:

http://seds.org/messier/m/m087.html

The diameter of M32 may be 120 kly, but it was M87 I was picturing, and it is 980 kly, according to its Wikipedia page. But I may be misinterpreting a term. The Wiki page says "The extended stellar envelope of this galaxy reaches a radius of about 150 kpc (490 kly) ..." Perhaps "extended stellar envelope" is not equivalent to diameter?

Rob