Subject: Comments on SWG document

From: Andrew Connolly

Submitted: Thu, 10 Jun 2004 11:25:27 -0400

Message number: 218 (previous: 217, next: 219 up: Index)

Michael,

A very nice piece of work. A couple of general and then specific
comments. Some of the typos at the end may have already been picked up.

cheers
Andy

1. General Comments:

  We refer to a number of additional surveys for which LSST will be the
  finding chart/followup for detected transients (GLAST, EXIST etc). To
  put the timelines in context for the LSST it would be useful to have a
  figure that has the expected timeframe for each of these surveys (and
  for the CFH Legacy projects, PanSTARRS etc) even if these numbers are
  fuzzy and evolve.

  For GLAST and EXIST are we suggesting that their timelines be tied to
  the LSST if we want temporal optical coverage during their missions?
  GLAST is projected for 2007 and EXIST 2010+ (I dont know their mission
  lengths). Does anyone know how much of their missions will intersect
  with the a projected LSST telescope.

  In most of the science cases we mention PanSTARRS but dont really
  state where the science cases stand when PS4 is complete. It seems
  from all of the sections that the 4 telescope PanSTARRS is the most
  relevant precursor project (it hits the time domain, covers a wide
  field and touches on many of the science goals). We will learn a lot
  from PS about how to do the survey and where to refine the science. It
  would be useful to address the leap in depth, areal coverage etc that
  LSST will make and what we think the science will be post-PS4. I know
  PanSTARRS have a series of DRMs for various science goals it would be
  interesting to get their perspective.

2. Specific Comments:

  Page 8: In the PHA section are we recommending more research into
  Tsunami as from the text we seem to say that we have little
  understanding of the correct damage model from Tsunami. 

  Page 14: The orbit linkage I think is in good shape from our
  prototypes on PS data but it is an interesting problem when we push
  into the noise (I'm not saying you change the wording)

  Page 20: and a couple of other places (e.g. Page 50). I think when we
  say photometric accuracy we should be clear and refer to accuracy of
  the photometric zeropoint and its variation across the sky as it is
  easy to confuse this with S/N requirements.

  Page 47, Section 7.4.3: It would be good to address Differential
  Chromatic Refraction (DCR) when talking about the shear
  systematics. Given the need to cover 15000 sq degrees we have to hit
  large airmasses and coadd data over a range of airmass. We will detect
  these effects (i.e. the shifts will be more than a pixel and source
  color dependent). Testing for the systematic would be straightforward
  as we know the direction of the effect but we should acknowledge that
  we will need to deal with this problem.

  Page 48, Section 7.4.5: I would like to add something like "While the
  required Gaussian dispersion in the photometric redshift relation of
  5-10\% in (1+z) is achievable from current ground-based surveys the
  requirements on the controlling the non-Gaussian tails of this
  dispersion are an order of magnitude more stringent than surveys
  currently achieve."

  What I mean is that I just finished some photoz simulations for the PS
  people that show that, at the limit of the survey, even at a S/N of 10
  in all bands that we get about 5% outliers in the redshift
  relations. Based on the weak lensing numbers I think we need to
  control these outliers to better than the 1% level to get the mean
  redshifts right. So this is going to be a real challenge for the
  tomography work - we are also finding this a challenge with the SDSS
  data.

  Page 49, Section 7.5.2: In the second paragraph it is not just the
  photometric accuracy that is critical it is the measurement of fluxes
  at faint magnitudes (in different passbands). Making a 0.5 mag error
  in the flux of one band due to poor deblending, cosmic rays etc is as
  big a problem as getting the zeropoint wrong (as these produce
  catastrophic redshift errors not just a small systematic
  offsets).

  Page 50, Section 7.5.4: the depth of the imaging surveys should
  include a S/N associated with these limits

  Page 51, first paragraph: It would be good to state that this is a
  fundamental question of how we measure magnitudes of galaxies at faint
  flux limits.

  Page 65, Section 9.3: For the extended science section; with LSST we
  can characterize galaxy clustering as a function of type, luminosity
  etc from z=0.5 to z=1.5. This should impact on clustering models,
  measures of bias and galaxy formation. Also LSST has some powerful
  implications for the Integrated Sachs Wolfe effect. A paper by Cooray,
  Huterer and Baumann has an interesting comparison of what you might
  get from ISW with the next generation of telescopes and how it
  complements the SNe and lensing measures (astro-ph/0304268). The
  errors on their ISW predictions are overly optimistic (by a factor of
  two at least) but the fact that they are almost orthogonal to the SNe
  is powerful. I'd be happy to send you a paragraph tomorrow if this is
  useful to you.

  Page 71, Data Systems: One additional point would be the need for the
  algorithm development to be done upfront for DCR, asteroid linkage,
  optimal coaddition of data, optimal photometry of faint sources etc.
  The are many algorithmic challenges ahead that we should be investing
  in - we talk a lot about the science and telescope but not too much
  about investing in the algorithm research that may end up being the
  limiting factor on the quality of the data products.

  Page 94: I like the statement on data access (Appendix D).  I'd like
  to see the data access statement moved to a more prominent place
  (e.g. maybe the first appendix). I think it is important we make this
  statement upfront as delivering the data rapidly to the public (after
  some verification phase) has to be one of the drivers (and
  requirements) for whomever builds the LSST. We should also add that
  the data has to be delivered with the metadata for understanding the
  selection functions (depth etc) associated with the catalog/database
  as a function of position on the sky (i.e. LSST must not just dump a
  catalog on the community it has to be a useful resource).


2. Layout + Typos:

   It could be just our printer at Pitt but having wider borders around
   the text would make it look better.

   Page 14: References wraps incorrectly on my version

   Page 21: References wraps incorrectly

   Page 25, last paragraph, first sentence: "A glimpse of the
   time-domain...."-> "The ongoing SDSS variability survey provides a
   glimpse of the time domain discoveries that will be made possible by
   the LSST"

   Page 43, Section 7.2.4, "constraints on nature of dark energy" ->
   "constraints on the nature of dark energy"

   Page 49, Section 7.5.2: I would prefer $r_{AB}$ as the nomenclature
   instead of ABmag or that we ensure that we specify in AB mags
   throughout the document.

   Page 49, Section 7.5.2, first para: "is adequate" -> "are adequate" 

   Page 51, Section 7.6, para 2: "At leat" -> "At least" and the remaining
   lines seem truncated.

LSST LSST LSST LSST LSST    Mailing List Server   LSST LSST LSST LSST LSST LSST
LSST
LSST  This is message 218 in the lsst-general archive, URL
LSST         http://www.astro.princeton.edu/~dss/LSST/lsst-general/msg.218.html
LSST         http://www.astro.princeton.edu/cgi-bin/LSSTmailinglists.pl/show_subscription?list=lsst-general
LSST  The index is at http://www.astro.princeton.edu/~dss/LSST/lsst-general/INDEX.html
LSST  To join/leave the list, send mail to lsst-request@astro.princeton.edu
LSST  To post a message, mail it to lsst-general@astro.princeton.edu
LSST
LSST LSST LSST LSST LSST LSST LSST LSST LSST LSST LSST LSST LSST LSST LSST LSST