Tag Archive | Rings

Live Chat: Galactic Rings, Secular Evolution and The Good Old Days

GdV 3D morphological classification

It’s amazing what happens when you actually publicize your live chat in advance. We got so many questions, we decided to spend the entire chat just discussing them, and we still didn’t finish!

Partly that’s because we had a surprise guest appearance from the esteemed Ron Buta, who came in just after we had talked about some of the details covered in his Galaxy Morphology article (his Figure 3 is shown in the image). Ron worked with Gérard de Vaucouleurs — aka GdV — and told us some amusing stories about trying to take photometric* observations of dwarf galaxies, and about how GdV’s wife used to disagree with his morphologies, at one point looking over his shoulder and proclaiming, “no, there’s no ring”. I rather liked that story as it’s a reminder that anyone can spot patterns in galaxy images.

We’ll try to answer those questions on the previous blog post that we didn’t get to there — but in the meantime, here’s the video:

Left to right: Ron Buta & Bill Keel, Karen Masters, Kevin Schawinski, Brooke Simmons (me). Toward the end (not shown on the thumbnail), Kyle Willett arrived just in time to answer a question about the status of the latest Galaxy Zoo classification set.

We made ample use of the jargon gong on ourselves, but we may not have managed to define all the terms Ron used. We’ll try to do so in this post — if we’ve missed any please say so in the comments!

*photometry = precise quantitative measurements of the brightness of objects in the sky. You need very good observing conditions to take photometric measurements, which many (but not all) astronomical projects require.

Update: Now in podcast form:

Download MP3 file

From Blob to Collisional Ring

This week’s OOTW features this object (below) from Tsering’s OotD posted on the 26th of June.

AHZ30000yv SDSS Version

AHZ30000yv from Sloan's view

As Tsering showed, this seemingly uninteresting blob on the SDSS turns into this in Hubble Zoo:


AHZ30000yv from Hubble's view

This is AHZ30000yv, a wonderful collisional ring galaxy! I love seeing the huge differences between the SDSS and Hubble images, the reason why Hubble can see more is because it’s out of the way of the Earth’s atmosphere, so even though Hubble is actually smaller than the the Sloan telescope (Hubble’s mirror is 2.4 meters and the Sloan telescope’s mirror is 2.5) it can see further, taking us visually back to when the universe was around half its current age and making me very happy indeed!

This ring galaxy has a Z (redshift) of 1.432, so we’re seeing it as it was 9.15 billion years ago, just under 5 billion years after the big bang! So how did this galaxy end up as a collisional ring? The ring formed after another smaller galaxy punched through the centre of the galaxy, creating masses of hot young blue stars in the process through all the gravitational disruption.

And I have to quote this lovely post by Budgieye from the comments on Tsering’s OotD 😀 :

It is fun looking at the difference.
There must be lots of UV light coming from it, otherwise nothing would be visible at all on SDSS.  At that distance, the ordinary blue light from the stars would be redshifted off the limits of the SDSS detector for far red light.
A nice addition to
Colours of Galaxies in SDSS : Redshift chart