Space Warps Talk

The colours of lensing and lensed galaxies

  • Budgieye by Budgieye moderator

    The lensed galaxy is always more distant than the lensing galaxy.

    If a galaxy is lensed, it's colour stays the same.

    Here is a simplified view of the distance of galaxies, and how the colour changes as the galaxies are more distant and the light is redshifted.

    enter image description here

    z=6 is about 9/10 of the way across the Universe.


  • Budgieye by Budgieye moderator


    L2S J08544-0121 has been proved to be a strong gravitational lens. Lens z=0.35, lensed z=1.27


    The lensing galaxy has a redshift of z=0.3514. It is a typical white elliptical, made yellow by its redshift.

    The distant lensed galaxy has a redshift of z=1.27 The blue colour of the lensed galaxy shows that it is star-forming, with many large short-lived stars going supernova, producing lots of hot oxygen (OII).

    The main arc is at 5" from the center of the lensing galaxy

    There is a small yellow elliptical galaxy with z=0.3517, which is near the blue arc. This small elliptical may be slightly further away from us than the main elliptical.

    The counter arc, the small blue arc to the north, is further away from the center than the main arc.

    There is another galaxy being lensed too, as shown by the outer arc at 8" with unknown redshift.

    A simple lens model of an elliptical galaxy did not explain the lens. They looked for other sources that might interfere with the path of the light. A luminosity map was constructed, and another area of mass near the nucleus was added to the model. The dwarf satellite did not have any effect on the model.

    A New Window of Exploration in the Mass Spectrum:

    Strong Lensing by Galaxy Groups in the SL2S

    Limousin et al 2009

    SL2S J08544-0121 at z spec =0:351
    The strong lensing deflector is populated by a single bright galaxy whose ellip-
    ticity and position angle equals 0.3 and 255 degrees, respec-
    tively. The luminosity contours are elongated in the east-west
    direction and define a position angle consistent with that of the
    bright galaxy. We also find the position angle of the SIE halo
    21 degrees, Section 5) to be consistent with that of the bright
    Note (Fig.
    ) that the innermost luminosity contour at 10

    encompass the SL system but also two bright galax-
    ies located
    east from the SL system, making this light
    distribution bimodal. This is the only group for which the lumi-
    nosity distribution is not clearly dominated by the lens, making
    this configuration rather exceptional: the large Einstein radius
    ) points toward a massive structure associated with this
    lens, but the luminosity distribution is found bimodal. This sug-
    gest a dynamically young structure in the process of formation.
    This bright galaxy has a spectroscopic redshift measured from
    Keck of 0.3514. We detect two multiply imaged systems: the
    brightest one is perturbed by a small satellite galaxy whose red-
    shift is equal to 0.3517 (FORS 2); and the outer one is seen on
    the ACS colour image (Fig.
    ). Note how the northern counter
    image is found much further (
    ) than the main arc (
    suggesting a strong contribution from the external shear ...

    Strong lensing as a probe of the mass distribution beyond the Einstein radius. Mass and light in SL2S J08544-0121, a galaxy group at z = 0.35

    M. Limousin, E. Jullo, J. Richard, R. Cabanac, S. H. Suyu, A. Halkola, J.-P. Kneib, R. Gavazzi, S. Soucail
    Published in A&A, 2010, v.524, p.95

    enter image description here

    Here is the Hubble image

    enter image description here

    The lens presents a typical elliptical spectrum at z = 0.35

    with prominent H and K Ca II lines, 4000 Å break, and G band.

    The spectrum of the arc shows a strong emission line at 8454 Å, resolved in a doublet separated by
    5 Å . The [OII] emission gives us an unambiguous redshift determination of

    z = 1.268

    enter image description here

    Anyone got anything to add?


  • Budgieye by Budgieye moderator

    Which objects are nearby, and which are distant?

    enter image description here , with several #quad #quasars from the Spotters Guide added at the bottom.

    enter image description here

    Redshift z=0.000 They are in our own Milky Way galaxy. Stars are round with sharp edges and often overexposed in the middle, though distant ones are fuzzy.

    Remove them from the picture.

    enter image description here

    Redshift 0.01 to 0.1 These are "nearby galaxies". They are white or blue. Nearby blue irregular galaxies are larger than distant blue star-forming galaxies. Remove them.

    enter image description here

    Redshift z=0.1 to 0.8 These are the yellow, orange and red galaxies. They would look the same as nearby galaxies, but their colour has been redshifted. We can't see most galaxies if they are further away that 0.8, their colour has been shifted to infrared, and we would need an infrared telescope, like the planned James Webb Telescope.

    enter image description here

    z> 0.8 But we can still see blue star-forming galaxies, both lensed and not lensed. We can see blue and yellow quasars. Lensing does not affect the colour of the lensed galaxy, just the brightness and position. Star-forming and quasars galaxies have lots of visible light due to the amount of UV (ultraviolet) light they produce, which is not so easily redshifted. Remove up to z=2 and..

    enter image description here

    Redshift z=4.5, 9/10 of the way across the Universe. There is just the yellow quasar remaining , the most distant object in the image.