# What new instruments “so sensitive that we can see (large circumgalactic winds) have only been on telescopes for a few years”?

The Rhodes College press release Prof. David Rupke and Team of Astrophysicists Make Major New Discovery About Galaxy Evolution links to

and references the new Nature paper A 100-kiloparsec wind feeding the circumgalactic medium of a massive compact galaxy (viewable in arXiv)

and includes the video below, in which Prof. Rupke says near the end after about 03:43:

While I’m hopeful that it’s the tip of the iceberg, and that we will find many other galaxies in which we see these large winds extending into the circum-galactic medium, but of course we have to go out and look.

These new instruments that are so sensitive that we can see these things have only been on telescopes for a few years.

There’s more galaxies that we haven’t looked at than we have.

The last sentence (taken by itself) is probably an understatement :-)

Question: What "...new instruments so sensitive that we can see these things have only been on telescopes for a few years"? I'm guessing that "instruments on telescopes" means these are image sensors or imaging spectrometers on visible or IR telescopes on the ground, and not related to radio telescopes, but that's just a guess.

Figure 1 The giant galactic wind surrounding the massive, compact galaxy Makani, observed by emission from the [O II] line at λ=3726 A and 3729 A. The colour scale and white contours show observed-frame surface brightness, and the axes are labeled in kiloparsecs from the galaxy nucleus. Contours are 2–16% of peak flux, spaced by factors of 2. A rest-frame V-band image of the galaxy (Hubble Space Telescope/WFC3 F814W filter) is superimposed on the center of the [O II] image taken with KCWI at the Keck II telescope. The small circle at the centre illustrates the radius of the compact core (400 pc). North is up and east is to the left.

• The simple answer is probably “high spatial and spectral resolution integral field unit spectrographs on 8–10 m telescopes”, such as the KCWI (on Keck) they used for this study (another likely candidate would be MUSE on the Very Large Telescope). – Peter Erwin May 23 at 8:41
• @PeterErwin I've been poking through the links, and the 2nd one (Astronomy Community) mentions "KCWI was designed specifically to be very sensitive to faint gas far from galaxies, using highly reflective image slicers (seen in the image at right)." Searching for "KCWI slicer" I found more of them here www2.keck.hawaii.edu/inst/kcwi Then I noticed that galaxy image has a hole in the middle right where it's supposed to be the brightest per the video, which reminds me further of "faint gas far from galaxies". Maybe it's the particularly clean image slicing that makes this possible? – uhoh May 23 at 9:24
• I know that people are using MUSE for similar studies, so I don't think it's anything unique to the KCWI design. (Image slicing is one of the standard techniques for IFUs; MUSE uses it as well.) – Peter Erwin May 23 at 10:52
• The "hole in the middle" of the galaxy image is not actually real. If you look at the paper, you'll see this description in the caption for Figure 1: "A rest-frame V -band image of the galaxy (Hubble Space Telescope/WFC3 F814W filter) is superimposed on the center of the [O II] image taken with KCWI at the Keck II telescope." This is clearly a negative image, so the "black" center of the galaxy is actually bright in V. Figure 3a shows the [O II] emission without the HST image, and you can see that the central region of the galaxy is actually very bright. – Peter Erwin May 23 at 10:58
• I'll note that earlier in the video, he specifically says, "Theres a really good instrument on there [Keck], that is a new instrument, that is one of the best of its kind in the world" and then goes on talk about applying for time to use it, and how they finally got good data for one galaxy. So he clearly means KCWI and things like it. – Peter Erwin May 23 at 12:20