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NGC 5905 & 5908 and many more galaxies (dime store deep field)
NGC 5905 & 5908 and many more galaxies (dime store deep field)
What started as a random target that I acquired while waiting for something else to peek above the horizon, turned into an interesting study of StarXterminator. Because it just loves to gobble up very small galaxies in prodigious quantities!
This image was 2x drizzled and cropped. Those galaxies are on the small side for my FOV.
When I applied StarXterminator to the master luminance image, I noticed that it removed a few galaxies. When I looked closer, it turned out that StarXterminator removed not a few but probably 100+ tiny galaxies. Then I noticed how many of them are on this image. Way, way more than I've ever expected for such a short integration time! Every speck on the starless image is a galaxy.
Naturally, I had to investigate. I made a hand-crafted mask. It took me about 2 hours, because I had to compare my image with scientific DSS data. The mask looks like this:
That allowed me to prepare a proper starless version but with all those tiny galaxies preserved- and there are hundreds of them! You can find it, as well as a monochrome inverted version among image revisions. It's worth to zoom in and take a tour.
I had to process this image in a less invasive way than I would otherwise do, because I wanted to preserve the integrity of the data. So it's not as aesthetically pleasing as it could otherwise be, but that's not the whole point here.
************************************************************************************
A few words about the two galaxies:
NGC 5905
A spiral galaxy with a very distinct bar, type SB(r)b, located 160 million light years away. It seems small - 4.0' x 2.6', but it is a huge galaxy with a diameter of 190,000 light years.
It is one of the very few galaxies in which a large X-ray flare occurred, as observed by ROSAT (a space telescope recording soft X-rays and far ultraviolet). The emissions were recorded during the first round of ROSAT observations, after two years they faded by two orders of magnitude.This type of flare occurs in Seyfert galaxies, which have an extremely bright core due to a supermassive, active black hole. However, NGC5905 shows no signs of such activity. It is therefore the only galaxy without an active core in which this type of flare occurred.
The sources of this phenomenon that have been considered include a supernova in the dense interstellar medium, gravitational lensing, X-ray emissions following a gamma-ray burst, or instabilities in the accretion disk around a black hole. However, these hypotheses are unlikely. The source of this phenomenon is probably a tidal disruption of a star by a black hole.
NGC 5908
A very massive SBb type galaxy, a barred spiral, but we are looking at it edge-on. It is about 500,000.00 light years away from NGC5905.
Its high mass is contrasted by a very low rate of new star formation - about 3.81 solar masses (MS) per year. This means that it must have been much higher in the past. The 30-meter IRAM radio telescope has measured the cold molecular gas, of which there is about 8.3 billion MS in this galaxy. Add to this about 13 billion solar masses of atomic hydrogen. This means that it is one of the most massive spiral galaxies known. The total mass of baryonic matter is estimated at 2 trillion solar masses and the (theoretical) dark matter halo would have a mass of about 10 trillion solar masses.
This galaxy has probably never had any significant gravitational interactions with other galaxies. It is therefore a good specimen for conducting galactic archaeology. Observations indicate that there are two main populations of stars – older ones in the center and younger, more metallic ones in the disk. Very low rate of new star formation mentioned above is probably due to the effects of the first, intensive phase of star formation, which took place shortly after the formation of the galaxy itself. The radiation from the new stars led to the “blowing off” of cold gas and the star formation process stopped. This galaxy may be approaching the end of this quiescent phase. The next stage may be the slow infall of the ejected cold gas back into the galaxy, that could fuel a new star formation period.
Sources:
https://doi.org/10.1017/9781316995303.089
https://theskylive.com/sky/deepsky/ngc5908-object
https://phys.org/news/2019-04-insights-molecular-gas-massive-spiral.html
https://arxiv.org/abs/1904.05413
https://arxiv.org/abs/1304.2235
https://arxiv.org/abs/astro-ph/9901008
This image was 2x drizzled and cropped. Those galaxies are on the small side for my FOV.
When I applied StarXterminator to the master luminance image, I noticed that it removed a few galaxies. When I looked closer, it turned out that StarXterminator removed not a few but probably 100+ tiny galaxies. Then I noticed how many of them are on this image. Way, way more than I've ever expected for such a short integration time! Every speck on the starless image is a galaxy.
Naturally, I had to investigate. I made a hand-crafted mask. It took me about 2 hours, because I had to compare my image with scientific DSS data. The mask looks like this:
That allowed me to prepare a proper starless version but with all those tiny galaxies preserved- and there are hundreds of them! You can find it, as well as a monochrome inverted version among image revisions. It's worth to zoom in and take a tour.
I had to process this image in a less invasive way than I would otherwise do, because I wanted to preserve the integrity of the data. So it's not as aesthetically pleasing as it could otherwise be, but that's not the whole point here.
************************************************************************************
A few words about the two galaxies:
NGC 5905
A spiral galaxy with a very distinct bar, type SB(r)b, located 160 million light years away. It seems small - 4.0' x 2.6', but it is a huge galaxy with a diameter of 190,000 light years.
It is one of the very few galaxies in which a large X-ray flare occurred, as observed by ROSAT (a space telescope recording soft X-rays and far ultraviolet). The emissions were recorded during the first round of ROSAT observations, after two years they faded by two orders of magnitude.This type of flare occurs in Seyfert galaxies, which have an extremely bright core due to a supermassive, active black hole. However, NGC5905 shows no signs of such activity. It is therefore the only galaxy without an active core in which this type of flare occurred.
The sources of this phenomenon that have been considered include a supernova in the dense interstellar medium, gravitational lensing, X-ray emissions following a gamma-ray burst, or instabilities in the accretion disk around a black hole. However, these hypotheses are unlikely. The source of this phenomenon is probably a tidal disruption of a star by a black hole.
NGC 5908
A very massive SBb type galaxy, a barred spiral, but we are looking at it edge-on. It is about 500,000.00 light years away from NGC5905.
Its high mass is contrasted by a very low rate of new star formation - about 3.81 solar masses (MS) per year. This means that it must have been much higher in the past. The 30-meter IRAM radio telescope has measured the cold molecular gas, of which there is about 8.3 billion MS in this galaxy. Add to this about 13 billion solar masses of atomic hydrogen. This means that it is one of the most massive spiral galaxies known. The total mass of baryonic matter is estimated at 2 trillion solar masses and the (theoretical) dark matter halo would have a mass of about 10 trillion solar masses.
This galaxy has probably never had any significant gravitational interactions with other galaxies. It is therefore a good specimen for conducting galactic archaeology. Observations indicate that there are two main populations of stars – older ones in the center and younger, more metallic ones in the disk. Very low rate of new star formation mentioned above is probably due to the effects of the first, intensive phase of star formation, which took place shortly after the formation of the galaxy itself. The radiation from the new stars led to the “blowing off” of cold gas and the star formation process stopped. This galaxy may be approaching the end of this quiescent phase. The next stage may be the slow infall of the ejected cold gas back into the galaxy, that could fuel a new star formation period.
Sources:
https://doi.org/10.1017/9781316995303.089
https://theskylive.com/sky/deepsky/ngc5908-object
https://phys.org/news/2019-04-insights-molecular-gas-massive-spiral.html
https://arxiv.org/abs/1904.05413
https://arxiv.org/abs/1304.2235
https://arxiv.org/abs/astro-ph/9901008
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