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September events:
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Click here to download the detailed calendar for September 2001 in Adobe Acrobat format (151KB).
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Picture of the week:
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You can download the paper in Adobe Acrobat PDF format (635KB), recently submitted to the Astronomical Journal of the American Astronomical Society.
You need an advanced level of galactic astronomy to understand the paper (sorry that's the only way to keep them short) |
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Email me with suggestions, corrections, contributions.
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STATS
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| Did you know:
That the matter you are made of was once in the centre of a star? That our life-giving Sun will be the cause of our solar system extinction once it starts growing to become a red giant? |
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| Join our SETI team
It may be small and insignificant, but hey, we got to start from somewhere. |
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| Personal stats are here
Even if you don't want to join us, still don't let your computer's idle cycles to be wasted. Try to find the ET.
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| Some interesting links:
The AngloAustralian Observatory Heavens above: bright artificial satelites. |
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This site (like every other) is best viewed with: 
at 1024x768 It can be also viewed at a much slower pace using Netscape or IExplorer 4+ |
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Earth is not an ideal place to observe from. So close to our star, living in a giant bright Galaxy, our view of the universe is obstructed by our bright sky. The sky is so bright that even the nearby giant galaxy of Andromeda is extremely difficult to see with unaided eye. With the use of telescopes however, the light gathering power of which allow us to detect faint objects in the sky, we have been able to see galaxies and start thinking of them as the main constituents of the universe.
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| Up until ten years ago, all the scientific models that tried to explain our universe were based on a very simplistic (and wrong) assumption. That all galaxies are bright. In other words, people believed that what we see is what there is. New technologies, combined with explorations of spectrum regions other than the optical (like radio, submillimetre etc) allowed us to realise that what we see is actually only what we can see, not what is out there. In other words we may be well missing the vast majority of galaxies, which are too dim, and hence difficult to observe. | |||
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Now, galaxies can be dim for two reasons. First, they may be very distant and hence only very little light manages to reach earth. Second, they may be intrinsically dim. Such galaxies are usually small (dwarf) galaxies containing few stars. The property that characterises how dim a galaxy is, is called surface brightness. Surface brightness is independent of distance and has units of power per unit area. In astronomical terms (where we use the logarithmic scale of magnitudes for power and the angular size of the object on the sky) this translates to magnitudes per square arcsecond.
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| Low surface brightness galaxies are not yet understood. They may be formed as such, or they may be results of interactions with other galaxies. What is most amazing is that the largest galaxy known today is a low surface brightness galaxy. It has spiral structure and is almost 25 times larger than our own Milky Way. It is named Malin 1 after the astrophotographer's name, whose technique was used to enhance the image above the background sky. | |||
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What makes these galaxies so important, is their contribution to the total light/mass of the universe. Without taking them into account, we can add up all the baryonic mass of the universe and end up short by 90% of the dynamic mass. Baryons (protons and neutrons) are particles that constitute tha matter as we know it. The dynamic mass is calculated from the physics (motion) of the universe. For the universe to behave as it does we need 90% more mass than what we see. This "missing mass" is attributed to "dark matter", a substance of which we have no direct proof it exists. Dark matter has been introduced to avoid changing the physical models of the universe, and its existence is under constant debate.
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| It is a common belief that low surface brightness galaxies contain the highest quantities of dark matter. From dynamic behaviour of local dwarfs people believe that such galaxies have a ratio of mass to light higher than 100. That is the luminous mass (baryonic mass in stars) is 100 times less than the mass that causes the dynamic behaviour of these galaxies. Even though these galaxies are small, if their number is high, the contribution to the total light/mass may be significant. | |||
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The contribution to the total light of a group of galaxies such as our own Local Group is determined by the Luminosity Function of the Group. A flat luminosity function indicates that the bright giants contribute most to the total light. A steep end on the other hand shows an increasing contribution towards fainter galaxies. This obviously calls for high numbers of faint galaxies.
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| My personal research focuses on the Fornax Cluster of galaxies. Fornax is a nearby cluster rich in elliptical galaxies and centred on the giant elliptical NGC1399. Other prominent members include the NGC1365 spiral and NGC1398 irregular.
I have searched for low surface brightness galaxies in a strip in the southeast direction towards NGC1291, a peculiar galaxy non-member of Fornax. The data I use come from the 32" Schmidt telescope atop Cerro Tellolo (Chile). In my search for group member LSB galaxies I identified approximately 400 that follow the same distribution (exponential) of the 64 bright members, only in a much more extended fashion (about 4 times more extended than the bright galaxies). This indicates that these LSB galaxies follow the same clustering properties as their giant counterparts and are parts of the greater structure of the group. Although they do not fill the gaps, they certainly widen the filamentary structure of the universe. |
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With such high numbers, I conclude that these galaxies contribute to the total light of the cluster at least as much as the bright members. Considering that my data is still limited and my sample is not complete to extremely faint objects, the contribution I calculate is a conservative number with the tendency to increase.
To discuss about the mass contribution of this population is not as straight forward as the (directly measured) light. Still, with current believed mass to light ratios of 100 for such objects, this population may well account for the missing mass of the cluster!!! |
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| Even though this is a very optimistic and not at all verified conclusion, it indicates the importance of Low Surface Brightness galaxies and brings forward a much disregarded issue: that of selection effects. The fact that our observations and (especially) cataloguing of objects is constrained by selection effects that until the recent past were completely disregarded, is the cause of the mistaken view of the universe we used to (and still in some cases) have. I will not carry on to the matter but I will suggest the following as a hint to the problem:
Our view of the universe from a telescope is confined in a conical volume. Nearby objects are few due to the volume being small nearby and increasing with distance. As a parenthesis here, this is the reason why nearby extragalactic astronomy is more difficult than distant extragalactic astronomy. You need large areas of surveys to cover a volume large enough (end of parenthesis). On the other hand distant objects appear small and of high brightness (all their light is contained in a small area). Picking objects based on their size immediately will exclude objects that are too small (due to distance). Also, objects that are nearby maybe so large on the sky that we see right through them. Making a catalog (selecting) from this sample, as one can tell from above is not as straight forward as we may initially think. |
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Another interesting result was the detection of a large concentration of LSB galaxies around the isolated galaxy NGC1291. This may well be an LSB cluster, and there are scenaria that suggest isolated galaxies are accompanied by LSB satellites. This is an important issue as it explores LSB galaxies in environments different to the cluster environment I have been researching. Our team is now looking at the matter with new data on isolated galaxies we obtained this November from the JKT atop La Palma (Canary Islands, Spain).
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| The obvious thing to do after my first results is to check if they hold true on a new strip of data from Fornax Cluster. This time the data is of higher resolution and I use a different technique to obtain the properties of the galaxies. Still I expect to verify the results (even with lower numbers). I also have deeper images of the same area that I will use to define my completeness limit and check what I am missing (is there an even fainter population?). Further to that I have multicolour data to obtain additional properties of my sample (metalicity, star formation etc). This work will be soon completed so stay tuned.
You can download the paper recently submitted to the Astronomical Journal of the American Astronomical Society. |