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Blue-shifted Galaxies

  1. Oct 9, 2005 #1
    Blue-shifted Galaxies

    Why are the blue-shifted galaxies located pretty much in two directions in the sky about 180º apart? I got a list of blue-shifted galaxies from the NASA/IPAC EXTRAGALACTIC DATABASE (NED), http://nedwww.ipac.caltech.edu/index.html, and sorted them by their velocities. The faster they are approaching, the fewer there are in the regions about RA 100º and RA 300º.

    Is this NEC data base incomplete and there are blue-shifted galaxies in these regions waiting to be observed?

    Or is space in the directions with few blue-shifted galaxies expanding faster than that with lots of blue-shifted galaxies? This added expansion velocity would subtract from the approach velocity so they would not be very blue (or even be red-shifted) for moderate approach speeds.

    I understand blue-shifted galaxies are orbiting something else. Right now they are approaching, sometime in the past (or future) they were (will be) receding. Otherwise, if they'd been approaching us for the last 13 billion years, most of them would have already past us by, and become red-shifted galaxies.

    That NED data base is pretty big and it takes a while to sort out the blue-shifted entries. If you want to see my spread sheet and charts, send me an e-mail and I'll e-mail you the file. It's a lot smaller than the NED because I kept only those approaching at 100 kps or more.

    Paul Deichelbohrer
    paulanddiw@netscape.com
     
  2. jcsd
  3. Oct 10, 2005 #2

    Tide

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    I would guess that most of the blue shifted galaxies are part of our local group which is not necessarily spherically symmetric.
     
  4. Oct 30, 2005 #3

    Nereid

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    How many galaxies are in your speed <-100 km/s database/spreadsheet, Paulanddiw?
     
  5. Nov 1, 2005 #4
    Thanks for asking. I haven't kept very close watch on this thread. I have 659 galaxies with blue-shift velocity from -100 kps to -3586 kps (the largest speed (absolute)).
     
  6. Nov 2, 2005 #5

    Garth

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    Hi Paulanddiw!

    Are they near enough for distance determinations that are not dependent on Hubble expansion?

    Garth
     
  7. Nov 3, 2005 #6
    Garth:
    I'm just now understanding how profound that question is. The NED data I down loaded does not have any information on distance. I'm going to go back and try to find the answer to your question.
     
  8. Dec 13, 2009 #7
    There are almost 7000 blue-shifted galaxies listed the NED all-sky web site (see ref. 1,below) and I plotted them (a random sample), http://fittedplane.blogspot.com/2009...-are-more.html. I have an x-y plot of the Decl vs RA and also a plot of them on the celestial sphere (seen from the outside). Most of the blue shifted galaxies lie in a band in the southern hemisphere. The normal to the plane of the band points to RA 15.8°, Decl 75.5°. The band touches the equator around RA180° and dips to almost -30°.

    I made the x-y plot with Excel; I selected the sample randomly with Excel; I made the spherical plot with AutoCad; I calculated the plane with MathCad by fitting the galaxy's coods, x, to the equation:
    x • n = b where n is the normal to the plane and b is the plane's displacement below the orgin. I got b = -0.234.

    1 This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
    http://nedwww.ipac.caltech.edu/cgi-...0&obj_sort=RA+or+Longitude&zv_breaker=30000.0
     

    Attached Files:

    Last edited: Dec 13, 2009
  9. Dec 13, 2009 #8

    Chronos

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    All blue shifted galaxies are local. The hubble shift is not strong enough to overcome gravity at these distances.
     
  10. Dec 14, 2009 #9
    Most of those "galaxies" are really stars observed in the 2dFGRS.
     
  11. Dec 14, 2009 #10

    Chronos

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    Ack, matt o. you stole my thunder.
     
  12. Dec 16, 2009 #11
    Either that or Hubble was wrong... :eek: Maybe pulsars really are alien beacons then! Maybe worse... now is the BIG CRUNCH! *runs screaming*

    All kidding aside, it's what everyone has said or implied: part of the local group or stars as described by Matt.o and Chronos.
     
  13. Dec 16, 2009 #12
    Thanks for letting me know that 2dFGRS refers to a study of red-shifted galaxies done in Austrailia.

    But, I still don't understand your comment completely. Are you saying that the blue-shifted spots that I plotted are stars within the 2dFGRS galaxies. It seems that you are saying the the galaxies are red shifted, but, the "stars" that I plotted are seen within the corresponding galaxy disk.

    I didn't think stars were generally visible within galaxies. Also, I don't think stars can be distinguished from the galaxy itself with a radio telescope. (I believe the 2dFGRS used a radio telescope).

    Also, on the web site they talk about the shifting of balmer lines to determine the velocity. I don't think blue stars are blue because of shifting of balmer lines.

    Sorry for being so thick skulled.
    Thanks
     
  14. Dec 16, 2009 #13
    That's right. The 2dFGDR (or the 2-degree Galaxy Redshift Survey) was conducted at the Anglo-Australian Telescope just outside Coonabarabran, NSW.

    No, these are stars within our own galaxy. When selecting objects to observe in the 2dFGRS a catalogue was generated based on photographic plates. Ideally when doing a galaxy redshift survey, the initial catalogue will only contain galaxies. However, sometimes it is very difficult to tell the difference between a star and a galaxy, particularly for faint, small objects. This means that it is inevitable that the catalogue of objects you want to observe in the survey will have some objects in it that shouldn't be there, like stars. Consequently, you end up with a few stars in your final redshift survey.

    First off, the 2dFGRS was an optical spectroscopy survey. Spectra were collected for 400 objects at a time across a field of view of 2 degrees. The spectral range was ~300--900 nano-metres, i.e. stretching from violet to red in the visible spectrum (see wikipedia's entry on the visible spectrum for more). See the 2dF website for more information.

    Secondly, you are right that, in general, stars in external galaxies cannot be resolve by current telescopes. However, there are a few exceptions, like M31 where stars can be resolved by current telescopes. As an example of the work being done on M31, see this paper http://arxiv.org/abs/0901.0820.

    No, blue stars are blue because they are hot, and so their spectrum peaks at bluer wavelengths.
     
  15. Dec 16, 2009 #14

    ideasrule

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    I'd highly recommend removing your email address from your post. It's extremely easy, with even a little bit of programming skill, for spammers to write a web spider that searches for the character "@" and adds the email address to its spam list.
     
  16. Dec 16, 2009 #15

    DaveC426913

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    Your advice is a little more than 4 years late...
     
  17. Dec 17, 2009 #16
    The issue of resolving stars within our own galaxy also has a lot to do with the fact that we're on an outer arm, off the plane of our galaxy. That's not terribly relevent to this discussion, but plenty of stars along the view afforded by that position can be resolved. Of course, that's a tiny fraction, but it may be enough to resolve our own galactic center's black hole. Neat eh?
     
  18. Dec 18, 2009 #17

    ideasrule

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    I didn't realize this thread had been resurrected after 4 years (!!!!!). Aren't old threads supposed to be locked?
     
  19. Dec 20, 2009 #18
    Are you sure? The site is called the "NASA/IPAC EXTRAGALACTIC DATABASE". All of the "blue-shifted" entries the I found have a negative velocity that was determined by shifting of spectral lines.

    For example, how can you tell that 2dFGRS S805Z292 or 2dFGRS S433Z059 are stars instead of galaxies from looking at the informaton given in the site?

    If its just a few stars, like you say, my question about why it is claimed that there are only "about 100 blue-shifted galaxies" is still a good question.

    Thanks for putting up with my curiosity.
    Paul Deichelbohrer
     
  20. Dec 20, 2009 #19
    Again, this issue was resolved. All of those galaxies are within The Local Group (such as Andromeda). Another would be a star within another rotating spiral galaxy. Unless you're proposing The only possible exceptions would be relativistic beaming, and that is not what we're talking about here. The 2dFGRS study explicity states that MOST of the objects are galaxies. Most, not all. It was a broad survey, and it seems fair to assume that any blue-shifted objects were galaxies within the local group, stars rotating in a spiral arm towards us, or beaming.

    100 blue-shifted OBJECTS or "sightings" is a better description. So, yeah, maybe one of those objects is a physics defying galaxy moving against all expectations, but that's a bit of a leap, no?
     
  21. Dec 26, 2009 #20
    Yes, I am sure. The vast majority of the points you claim are blueshifted galaxies from the 2dFGRS are in fact stars which reside in our own galaxy. It matters not what the name of the website is that you chose your sample from, the point I was trying to make is that when selecting objects to observe spectroscopically, you can not select galaxies over stars 100 percent of the time due to limitations of the imaging used for selection.

    I can tell by the fact that they have blueshifts, and from my experience with these types of redshift surveys, which tells me that stars will sneak into your sample because of the imaging used to select the sample to be observed. Also, you can check the images and spectra for those objects by going to the website

    http://magnum.anu.edu.au/~TDFgg/Public/Release/Database/mSQLquery.shtml

    inputting the following text into the "WHERE" box

    name='TGS805Z292' AND extnum=0 OR name='TGS433Z059' and extnum=0

    and clicking the "next" button when the results load. Depending on the type of star, it should be pretty easy to distinguish it from a galaxy because of certain features in the shape of the spectrum.

    Well, when I said that I was talking about the entire survey, so when considering the entirety of the 2dFGRS, with its 250000-odd spectra, "a few" means thousands. Within your sample, the 2dFGRS objects are almost certainly all stars within our own galaxy.
     
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