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If we want to check a QSO's lyman alpha narrow band image, could a ground based telescope do that?

I mean under the circumstance that its lyman alpha shifts to 3300A.

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questionhang
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  • Are you asking what is the bluest commercially available filter, or the bluest ever commissioned by a professional observatory to make special observations? The former might be feasible to answer, but I cannot imagine that the latter will be, short of someone happening to know every single filter available to astronomers at every facility. I also don't quite understand the reason for your question. People are imaging ly-alpha sources and studying them spectrographically, so yes that is feasible. But why are you qualifying the question for ly-alpha sources red-shifted to 3000 Angstroms? – Jeremy Apr 10 '14 at 20:33
  • There are only certain windows of visibility for ly-alpha due to the atmosphere, requiring satellite/probe observations for frequencies outside those windows. – Jeremy Apr 10 '14 at 20:37
  • Just want to do a narrow band photometry. I find Gemini-N (http://www.gemini.edu/?q=node/10420) has a poor response at 3300A and the u-band filter is no longer available now.What is the bluest commercially available filter？ As far as you know, what is the bluest ever commissioned by a professional observatory? – questionhang Apr 11 '14 at 01:26
  • Do you want to do photometry with your own equipment, or do you want to approach a facility to use theirs? Are you trying to source a filter for yourself (and if you find a place using a suitable filter, you will endeavour to also source one from where they did?) I think most U filters will be weak at 330nm. However, if you have special needs for a filter centred on 330nm, and you can fund it, I'm sure you could commission something... Who knows what others might have commissioned. – Jeremy Apr 11 '14 at 05:28
  • I find someone bought a suitable filter for their Keck observation. I know the absorption by the atmosphere at 3300A on the earth is large. If we want to get a 3300A narrow image,a space telescope,i.e. hst, is necessary? – questionhang Apr 11 '14 at 07:43
  • Yeah, 330nm is pretty much the starting point for visible light, given the blocking below that. Yes, to avoid that, a space telescope is required. That isn't to say that you cannot accomplish a lot with a standard U filter ground based, but you'll find that 330nm is about the lower point in the usable spectrum, rather than a point you can target easily. But there are ly-alpha targets redshifted to longer wavelengths than 330nm, if those are of special interest. – Jeremy Apr 12 '14 at 02:53
  • Can you identify an example target you are keen to measure? – Jeremy Apr 17 '14 at 20:41
  • a quasar with z=1.7 is ok. – questionhang Apr 18 '14 at 01:51
  • The atmosphere does not cut-off at 330nm. The transmission is still of order 50% (per airmass) (and of course depends on height), though it is dropping sharply towards shorter wavelengths but is still about 5% at 300nm. I guess that's why sunscreen is required. – ProfRob Dec 16 '14 at 12:32

1 Answers1

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You probably will have difficulty imaging Ly$\alpha$ from a z=1.7 quasar at 330nm.

Says P. Veron: The lower limit [z=1.8] is set by the ultraviolet transmission of the atmosphere... between 3300 and 3600Å.

Jeremy
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  • Yes, the lowest redshift in their table 1 is 1.7. However their surveys are spectroscopic, a redshift lower than 1.7 is OK too.They can use other lines except lyman alpha. – questionhang Apr 20 '14 at 13:38
  • And isn't it ly-a you wanted to image? – Jeremy Apr 20 '14 at 20:17
  • Of course we talk about this problem under the premise that 3300A falls in the wavelength range. I should say larger than 1.7. 3300A low a response at a CCD's blue edge. It is marginal and maybe be not feasible. I do not know whether it is worth a try. I need to know how much feasibility is left. – questionhang Apr 21 '14 at 01:27
  • Why not use the T17 telescope at iTelescope.net using the U filter, and image a target of interest. See how it comes out, maybe post the result here in an answer. – Jeremy Apr 21 '14 at 07:34
  • I tried to register but failed. U band is too wide. I need a narrow band image. sigh, maybe hst is necessary. – questionhang Apr 21 '14 at 12:20
  • If you'd still like to give those scopes a go, find them on Facebook and mention your registration problems - they are very helpful. So far you have only mentioned sensitivity at 330nm, so what bandwidth are you interested in? How wide do you want the passband of the filter? – Jeremy Apr 21 '14 at 19:54
  • You might like this: http://www.stevedawson.org/thesis/thesis.pdf – Jeremy Apr 22 '14 at 09:11
  • Do you know the equivalent width of the Ly$\alpha$? If it's broad enough, you may be able to use a filter with a few hundred angstrom passband. – Aaron Aug 22 '14 at 19:45
  • The issue doesn't appear to be whether a filter could be made, they don't seem to exist off the shelf because there is no point, as the atmosphere doesn't permit observations at the desired frequency – Jeremy Oct 17 '14 at 10:08