dustlane elliptical with gravitational lensing

by liometopum

I think this might be one of those rare dustlane ellipticals. Massive enough to create gravitational lensing.
A zoo of dusty ellipticals provides evidence for merging galaxies

(It is also on SDSS, and I placed it in the comparison collection.)

Posted April 10, 2015 7:57 PM

by ElisabethB moderator

Did you see my comments to the left ?

Gorgeous galaxy, gorgeous dustlane, but definitely no lensing here ! And not sure this is an elliptical either ! Sorry !

Posted April 10, 2015 8:22 PM

by liometopum

Dustlane ellipticals are merged galaxies. This galaxy is a merger. You can see the massive tidal trails at about 5:00. The object at 6:30 is a likely tidal remnant. There is a lot of star formation at 6:00, and 12:00, both areas in line with the dustlane.

The elongated core suggests that the cores of the colliding galaxies have not yet merged, and that is supported by the presence of the tidal region, already mentioned. Thus a dustlane elliptical may not look like a normal elliptical. I think we are seeing this after the merger, but before the merger is complete, and thus there is distortion visible.

A merger of two large galaxies could give enough mass to allow gravitational lensing. The object at 19:00 may be a local tidal remnant though.

That is my argument for it. This galaxy needs to be noted for the experts to examine.

Posted April 10, 2015 11:48 PM

by Capella05 moderator in response to liometopum's comment.

Dustlane ellipticals are merged galaxies.

Elliptical galaxies do not have any discernible features. To be classified as an Elliptical galaxy they must be void of dust lanes, bars, spiral arms etc... So this is more likely to be a lenticular or disk galaxy.

I agree that this galaxy has most likely been involved in a few mergers in the past, but I am thinking it is more likely that the galaxy is subsuming closer satellite galaxies than interacting with a galaxy of similar mass.

Having said that, the tidal bridge to the lower right is interesting. Only a wider image will give us answers 😃

If you would like some more information on Galaxy Morphology - I would suggest this paper from Ronald J. Buta

As for gravitational lensing - No.

If you would like a more comprehensive answer on why the answer is No- let me know. But at 1am in the morning I need my sleep.

Posted April 11, 2015 12:32 AM

by JeanTate

I agree with liometopum that this is, very likely, a late-stage merger. As such, it does not make much sense to try to force it into an elliptical vs disk galaxy dichotomy.

The two 2010 GZ papers on mergers are good reads re the difficulties and limits of working out the nature of the galaxies involved in a late-stage merger: Galaxy Zoo: the fraction of merging galaxies in the SDSS and their morphologies (Darg+ 2010) and Galaxy Zoo: the properties of merging galaxies in the nearby Universe - local environments colours masses star formation rates and AGN activity (also Darg+ 2010) (both links are to the ADS abstract page, from the main Zooniverse Publications page).

Posted April 11, 2015 1:32 AM

by JeanTate in response to Capella05's comment.

Reading Buta is always a pleasure ...

Elliptical galaxies do not have any discernible features. To be classified as an Elliptical galaxy they must be void of dust lanes, bars, spiral arms etc... So this is more likely to be a lenticular or disk galaxy.

Here's Buta (p77, my bold):

There are several categories of interaction and merger-driven morphologies. A dustlane elliptical is an E or E-like galaxy showing lanes of obscuring dust (Fig. 2.68). Minor axis, major axis, and misaligned lanes are found. Whether these should be classified as ‘ellipticals’ or not was controversial, as de Vaucouleurs had once quipped: ‘If an elliptical shows dust, then it’s not an elliptical’. Bertola (1987) established dustlane Es as a class of interacting galaxies where a small gas-rich companion undergoes a minor merger with a more massive E galaxy (Oosterloo et al. 2002). The current general view of these objects is to call them ‘dustlane early-type galaxies’ (or dustlane ETGs; Kaviraj et al. 2011).

I'm not 100% sure, but "Kaviraj et al. 2011" is actually the GZ paper "Galaxy Zoo: dust and molecular gas in early-type galaxies with prominent dust lanes" (Kaviraj+ 2012)

Posted April 11, 2015 12:55 PM

by Capella05 moderator

My rebuttal - from the same source.

Elliptical galaxies are smooth, amorphous systems with a continuously declining brightness distribution and no breaks, inflections, zones, or structures, as well as no sign of a disk.

If you disagree take it up with the author, not myself.

Posted April 11, 2015 1:18 PM

by JeanTate in response to Capella05's comment.

The universe does not care what classifications we give to parts of it. And morphological classifications - of galaxies - are useful to the science of astronomy in part because they provide clues (evidence) to inform the development of theories (models, etc) concerning the underlying physics.

Decades of study of the morphology of galaxies has shown that a rigid 'elliptical vs disk' dichotomy does not square with the observed reality; in particular, where galaxies appear to be interacting, morpholical descriptions such as 'dustlane elliptical' and 'dustlane early-type galaxies' seem to pertinent, as Buta summarizes in the section of his paper from which the quote I posted comes.

From the OP:

I think this might be one of those rare dustlane ellipticals.

And the source cited (an astrobites commentary on a paper titled "Galaxy Zoo: Dust lane early-type galaxies are tracers of recent, gas-rich minor mergers") includes this:

Dust lane ETGs are elliptical galaxies with dust lane features

But perhaps a more interesting discussion can be had around this, also from the OP:

Massive enough to create gravitational lensing.

Is there a lower threshold, a galaxy whose mass is so low that gravitational lensing is not possible? Are ellipticals, simply because they are ellipticals (whether they have dustlanes or not), more likely to be gravitational lenses than other mrophological types of galaxy? Or does the presence of a dustlane in an elliptical strongly suggest that it is massive enough that gravitational lensing is likely?

I think these are all good questions, and I think we should thank liometopum for her comments, because it allows us to start a discussion on this fascinating topic.

Posted April 11, 2015 1:49 PM

by liometopum

Here is another dustlane elliptical. This dustlane is equatorial.

AGZ0007yzo

z(spectroscopic) 0.5190

name: PEARS 34967 or TKRS 6961

Notice that it too has tidal debris. And, like TKRS 2974, is surrounded by an array of objects (ok... not lensing- I agree). The similar distribution of objects around the galaxy is noteworthy.

TKRS 6961