Galaxy Zoo Talk

LBG question

  • ramberts by ramberts

    Why are a lot of the LBG with specZ > 2 green and not red like other far away objects? Is this instrumental or something to do with the light they emit, disturbance with other galaxies, illumination from other galaxies?

    I think this is an example

    LBG

    EIS J033231.42-274621.6 03h32m31.4s -27d46m21s arcmin : .004 2.223000 SpecZ is an LBG

    MUSYC CDFS-6202 03h32m31.5s -27d46m23s arcmin : 0.033 2.225000 1LIN is the red one I believe

    Almost all of the examples from this survey on the High RS thread that are LBG's are green, the rest are red.

    Posted

  • Budgieye by Budgieye moderator

    http://talk.galaxyzoo.org/#/subjects/AGZ000873c

    Posted

  • JeanTate by JeanTate

    Please excuse my ignorance, but what's an "LBG"?

    Posted

  • ramberts by ramberts

    Lyman break galaxy. They are galaxies that are visible at certain wavelengths but not others and the lyman break is one of the most successful methods of finding high z galaxies. Far away green peas, similar anyways lots of starforming. Ive seen examples that are blue, red but almost all green.

    Posted

  • ramberts by ramberts

    Here is a quasar and lbg, better example at very high z. Top lbg z=4.146, bottom is quasar z = 3.66

    http://talk.galaxyzoo.org/?&&&_ga=1.4085488.1310713284.1428668940#/subjects/AGZ0007yqt

    lbg
    quasar
    http://talk.galaxyzoo.org/?_ga=1.42638757.1877800780.1427850640#/subjects/AGZ00087io

    Posted

  • JeanTate by JeanTate in response to ramberts's comment.

    Thanks.

    May I ask, where did you read that "SpecZ is an LBG"?

    Your original question:

    Why are a lot of the LBG with specZ > 2 green and not red like other far away objects?

    may be able to be answered by reference to the spectrum itself (together with knowledge of the mapping of filters to color map in the JPEG/PNG images displayed here).

    Posted

  • Budgieye by Budgieye moderator

    The main peak of radiation that we see from a quasar is the Lyman alpha peak, which is the highest energy which hydrogen can produce. Lyman-alpha is very short wave, which our telescopes can't detect, but it has been redshifted to blue, green or even red.

    Most of the galaxies we observe are spirals and ellipticals, which don't produce high energy radiation, and so the blue colour they emit gets redshifted into red by z=3 or so. At that distance, quasars still have their Lyman-alpha radiation redshifted only to green.

    Here was my latest chart, while I waited for more red galaxies to be posted. I haven't seen many quasars. Post more green galaxies! and bright red galaxies!

    z=1 quasars blue?, clumpy galaxies are blue, spirals are blue, ellipticals are red

    z=2 quasars blue?, clumpy galaxies are blue, spirals are blue, ellipticals are red

    z=3 quasars blue?, clumpy galaxies are blue, spirals are green, ellipticals are red

    z=4 quasars green?, clumpy galaxies are blue, spirals are red, ellipticals are lost by redshifting?

    z=5 quasars green?, clumpy galaxies are green?, spirals are red?

    z=6 quasars green? clumpy galaxies are red?, spirals are lost by redshifting?

    z=7 quasars red? clumpy galaxies are red

    z=8 quasars red? clumpy galaxies are red (published image)

    z=9 quasars red? clumpy galaxies lost due to redshifting.

    z=10 undetectable by Hubble, must wait for James Webb telescope to see them.

    This chart is done without looking up references , and could be totally wrong.

    Redshifts of GOODS full-depth galaxies http://talk.galaxyzoo.org/#/boards/BGZ0000001/discussions/DGZ0001cyg work in progress

    Saturday February 27, 2010 More hydrogen emission and quantum stuff http://www.galaxyzooforum.org/index.php?topic=277301.msg436944#msg436944

    If you look at the Galaxy Redshift Chart from SDSS http://talk.galaxyzoo.org/#/boards/BGZ0000001/discussions/DGZ0000ulp?page=2 , you will see that quasars are the objects that survive redshifting. This chart is for SDSS, but the same principles apply and the spectral charts still useful. Hubble can just go a bit further than SDSS, Hubble can go to 8, SDSS can only go to 5.

    CANDELS and GOODS wils have slightly different colours.

    I was wondering what an LBG was, so thank you Jean for asking. I thought if I waited several days, the answer might come to me.

    Posted

  • ramberts by ramberts

    Ill try to find more examples, theres some i havent posted because photoz measurements can vary so much with distant galaxies.

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  • Budgieye by Budgieye moderator

    I am wondering why we find so few distant galaxies, I mean greater than z=3. Is it because the software doesn't select them, or doesn't see them? or doesn't measure them properly, as you suggest. Or do the distant galaxies have to be very bright and we don't see the dimmer ones? Are they too small, and we dismiss them as random red pixels?

    The research is supposed to be targeted at looking a clumpy galaxies, so maybe that is what we are seeing [edit: being shown]

    Posted

  • ramberts by ramberts in response to Budgieye's comment.

    I've seen a lot of data in NED that is out of range of our pictures that I think your right...galaxies that are Z>5 that are .1 arc min away or more away, just out of sight. But I also think it might have to do with out of date measurements. I haven't seen any newer redshift data than 2011 if you look at the link of "redshift data points." Most are between 2004-2011, and you have to look at it to see what the newest measurements are. NED primary is often 2004 data, when all data afterwards shows redshift data that looks more accurate. I've posted some examples, a red, disturbed galaxy can show .04, but when you look at it, that's 2004 data, and there is 8 data points at 2005-2011 that show z >2. I have some examples that looks like they could be very far away in the high RS thread with no measurements, but that is almost like picking a needle out of a haystack, just because it looks like z>4 haha. Also, they are extremely rare with z>4, LBG's need to have something close by that illuminates it like a quasar, I read an article about that...not sure about quasars. I do know the furthest galaxies, a large majority are found by the lyman break method (which I'm still trying to understand more, reading is helping but a lot of the scientific writings are pretty complicated!)

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  • ramberts by ramberts in response to JeanTate's comment.

    Hey Jean, I was shortening the spectroscopic z measurement into SpecZ, ones that are over 2 seem to be green more often than not from these surveys, but I think it has to do with the color filters being used...been reading some stuff, LBG's are only visible in red, blue or green filters. A lot of the things I've read are a tad over my head because of the scientific terminology, trying to get a grasp of it, might look at some free open courseware stuff so I can understand the journal papers better.

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