Deepest Ever Deep Field. Where Are The Limits of James Webb?

We all know the Hubble Deep Field as one of the most important astronomy images of all time. But when will we get a similar attempt from Webb? What will we be able to get from it and what are the limits of JWST? Finding out with Dr Viraj Pandya from NASA.

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00:00 Intro
01:43 Galaxy classification
08:20 Hubble's observations and biases
19:53 Breadstick galaxies
31:07 Wen JWST Deep Field
43:58 What is the limit of Webb
52:03 Final thoughts

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[frasercain]

A note from Viraj,

"I just saw your video from our interview and think it's fantastic! Thank you so much again. It seems many of your viewers were interested in the planning of future JWST deep field surveys (based on the video title) but that is not my current interest/expertise -- it is something I'd like to help with in a few years after I get a permanent faculty-level position (fingers crossed). But right now, as an early career researcher, thanks to the work of many others who dedicated lots of time to the planning of surveys like CEERS, I have the privilege of focusing my time on thinking deeply about galaxy formation using these amazing observations and by developing new theoretical models (like what we discussed in the first half of the video).

I highly recommend getting someone from the JADES team on your podcast -- they are at the current frontier of JWST deep fields so will know much more than me about what is and isn't possible over the next few years (as I said, I'm focused on the science itself). They've already surveyed areas including and surrounding the Hubble Deep Fields North and South. As discussed in section 4.1 and Table 1 of Eisenstein+23 (arXiv:2306.02465), some of their deepest imaging in any particular pointing and in any single filter is of order ~10 hours which is a factor of ~5 lower than the deepest single pointing (in a single filter) from the latest "Hubble Legacy Field" (Whitaker+19). And yet as Figure 5 from Eisenstein+23 beautifully shows, this ~10 hour JWST imaging is already much more sensitive than the deepest single ~65 hour Hubble Legacy Field imaging (at a similar wavelength). There is also another "JADES Origins Deep Field" (Eisenstein+23, arXiv:2310.12340) whose deepest single pointing (in a single filter) may approach or even exceed the deepest single-pointing, single-filter HDF images with 50+ hours. On top of this, they are investing a significant chunk of time on spectroscopy -- I discussed the importance of spectroscopy in the first half of the video for, e.g., constraining the kinematics of stars/gas in low-mass high-redshift elongated galaxies. You can probably extrapolate what will be possible for JWST Deep Fields over the ~15-20 year lifetime of JWST based on the incredible work that JADES has done.

I also wanted to clarify that I mis-spoke at ~37:30. The HST-CANDELS program was ~2 months total of observing time but that was split among 5 fields, and there is nuance in the depth of individual pointings (in individual filters) in any individual field. In other words, not all tiles for the mosaic in a single field have the same exposure time. For GOODS-S and GOODS-N (which contain the HDF-S and HDF-N, respectively), some of the deepest imaging is indeed ~50+ hours in a single pointing (in a single filter). For the wider (shallower) parts of CANDELS in the UDS, EGS and COSMOS fields, the depth drops to a few hours at most in a single tile with a single filter. This nuance is important because it can be confusing to say that a deep field was "100s or 1000s" of hours -- indeed, the latest Hubble Legacy Field in GOODS-S (containing HUDF) has a total exposure time of 6.3 Megasec ~ 1750 hours, but what's more useful from a practical point of view is to quote the *range* of exposure times in a single filter over the full survey area (as nicely shown in Figure 1 of Whitaker+19). For example, the original Hubble Deep Field was 140 hours (Table 5 of Williams+96) but that was split into ~30-40 hour images in four different filters -- this was unprecedentedly deep in individual filters and only feasible because they didn't do a mosaic (effectively just a single tile/pointing)."

Sincerely,
Viraj

[anthonythomas]

Normally interviews like these don't really captivate me but, Fraser does a really good job with the questions that he asks that I can't stop listening, it also helps when you have really interesting guests like Dr Pandya. I can't wait for the next one.

[ianlockett]

This was a fantastic interview. You can tell Dr. Pandya loves and is excited about his work.

[donporter]

That's the first time I've heard somebody being interviewed saying "thanks. It's been a lot of fun." For an esteemed scientist to say that to you greatly impresses me. Congratulations Fraser!! And greetings from Thailand.

[picksalot]

You are hitting home run after home run with your interviews. The guests are highly knowledgeable, are great communicators, topics are very interesting, and you're asking high quality questions. I think you're doing a wonderful job and sincerely thank you for bringing such high quality Science for presentation on YT. 👏

[lyledal]

Dr. Pandya's food analogies absolutely work for me! 🤣

Thanks for these interviews, Fraser. Please, never get tired of doing them!

[tonywells]

These recent interviews are awesome and your questions and reasoning are great. Well done Fraser.

[colchiandragon]

The exposure length limits due to background light is addressed in a JWST Science Working Group paper titled The Scientific Capabilities of the James Webb Space Telescope. It is available on-line as a pdf.

[Poult]

The Hubble Deep field, as wonderful as it is, only took 100 hrs, not thousands.
However, I love these interviews. Great to get the insights of experts actually working on and with these projects. 👍

[gregansen]

Great interview and interviewee, yes. Impressive when someone successfully conveys their visualisation of dynamics.

[markboccaccio]

This discussion with Viraj is so interesting . Cain is a GREAT Interviewer, and the discussion is deep but so clear. Thank you for doing this!

[sebastianwrites]

I liked Viraj's attitude... just straight up admitted when he didn't know something, and then demonstrated interest in the question?

[markboccaccio]

Fraser Cain is such a great choice for explaining the Hubble and James Webb ultra deep field images. His sentences are clear and informative. I’m glad he is our guide!

[bobh]

I've never commented before, but had to for this. Viraj was far and away one of the best interviews I've seen - wonderfully knowledgeable, thoughtful, and so interesting. And Fraser excellent as always. Thanks for all you do, and hoping for a follow-up interview with Viraj someday!

[sandeepgodolo]

Great you tube with a great subject. Definitely the best work on Galaxies I have seen so far

[tune]

Thank you Fraser for asking that question! I wanted to ask the questions at 42:25 and the question at 44:25. That is what I want to know!

[Corvaire]

I agree with Fraser.

If waiting for Roman to come online and having that ability to do a wider range view prior to a James Webb deep field, this will allow for a better targeting range for Webb to deep field and whether a longer/shorter exposure is needed.

JW has plenty of science to do before that decision is needed. Besides, they can do both w/a shorter exposure now and after Roman is alive, proceed w/a longer more targeted exposure then.

[RogerCouture-rd]

Another great interview, "Deepest Ever Deep Field", that I could not stop listening to! It would be most helpful to my limited, linear mind, to see pictures flashed up on objects being discussed, e.g. Hubble deep field view, bread stick galaxies, 15 red shift galaxies, and even such 'mundane' things as Red Dwarf, Blue stars?, edge on elliptical galaxy, etc, etc....

[sulljoh]

Loved it as usual. It's sometimes hard to click on these instead of some anger-inducing drama. But I'm always happy that I clicked

[MistSoalar]

This is a great interview. Thank you Fraser and Dr. Pandya.