distant arcs and the Einstein radius

by Budgieye moderator

Do the usual rules about Einstein radius still hold when looking at objects at high z? The universe is smaller when we look back in time.

orange galaxy z=1.158

blue spot photoz= 3.06 0.070 arc-min away, or 4.2 arc-sec?

arc is greenish, so maybe it is z of 4.

Posted May 4, 2015 11:06 AM

by Capella05 moderator

According to what I have read - Yes, they do 😃

It is mass that causes the gravity wells around high mass objects, that can lead to lensing. I doubt the rules applied to mass in the 'earlier' universe are very different from today. If they were different, then it would have a impact on all the current models of star and galaxy formation.

Would love to have the opinion of a Scientist 😃

As for this galaxy - either it is more massive than it appears to be (unlikely - even taking dark matter into account) or the 'arc' at the lower 6 is unrelated.

Posted May 4, 2015 11:49 AM

by vrooje admin, scientist

The Universe is smaller at higher redshift, and because of this the way the apparent size of a galaxy changes as a function of redshift is a little non-intuitive. Galaxies of the same intrinsic physical size appear smallest at about redshift 1-2, and then start to appear larger as you go to really high redshift. It's a little jargony but the Wikipedia description of angular diameter distance may help.

But, as Capella05 says, the laws of physics still apply; there are certainly high-z gravitational lenses. I think Capella05 is better than I am at spotting lenses; I can't really see the arc you're talking about here! (Unless it's the blue bit at the very bottom of the image? I think I'd probably agree that's quite a high separation.)

Posted May 4, 2015 12:00 PM

by c_cld in response to Budgieye's comment.

@Budgieye

AGZ00083rr RA: 53.0970299, DEC: -27.8239085 (3h32m23.28718s, -27d49m26.0706s )

Looking at Ned, it seems you read

1 COMBO-17 30351 03h32m23.3s -27d49m26s G 1.158

2 GOODS-CDFS-MUSIC 07666 03h32m23.0s -27d49m24s 3.06 PHOT

but MUSIC 07666 is north of target 1 and can't be the blue spot in pic (assuming not flipped one).

Have a try at Aladin to find blue spot in south at ~1.69 arcsec, no visible arc only noise for me in BVI bands whatever stretch. 😃

or with GOODS Cutout Results http://archive.stsci.edu/eidol.php?POS=53.0970299+-27.8239085&resolver=Resolve&SIZE=4.&outputformat=HTML_Table

#no_lens

Posted May 4, 2015 3:12 PM

by c_cld in response to Budgieye's comment.

@Budgieye

Einstein Radius

No worries under HST imaging resolution power: see paper with Cecile as coauthor: http://arxiv.org/pdf/1206.3412.pdf "A seven square degrees survey for galaxy-scale gravitational lenses
with the HST imaging archive"

Posted May 4, 2015 5:35 PM

by Budgieye moderator in response to C_cld's comment.

Right on C_cld, I forgot that the galaxy was south of the equator, and the negative sign is important!

Posted May 4, 2015 10:57 PM

by Budgieye moderator in response to vrooje's comment.

Thank you Dr Simmons, So a lens arc should be thought of as being as the same redshift as the lensing galaxy, and won't be affected by the smaller size of the universe, where the lensed galaxy is located.

EDIT:

Summary for myself

Measuring distant lensed galaxies is that measurements is tricky when looking far back when the universe was smaller. It is like trying to measure the size of an insect when you have the ruler between you and the magnifying glass, instead of having the ruler near the insect. The size that you measure will be too big.

Posted May 4, 2015 11:02 PM

by c_cld in response to Budgieye's comment.

Lensed Einstein radius in extragalactic astronomy is proportional to angular-diameter distances ratio:

DAls / DAs

The symbols DAls, DAs are angular-diameter distances, respectively from lens to source and observer to source.

Angular diameter distance DAls is related to the transverse comoving distance by the formula

with the notations: DM transverse comoving distance, s source, l lens deflector

DAls = (DMs - DMl) / (1+zs)

You could do some numerical radius calculations with what is seen around a lens of constant deflector mass at z 0.5 and a lensed source varying from z 1.0 to 6.0 in flat curvature universe: not a big radius downsizing for Hubble resolving power!

example consider a radius 2" from source at z 1

z radius

1 2.0"

2 ~1.7"

3 ~1.2"

4 ~0.8"

5 ~0.5"

6 ~0.3"

😃

Posted May 18, 2015 2:39 PM