Densely targeting emission line dominated objects with NIRSPEC MSA

Notes on an obvious/crazy idea that has fermented in various people's brains,
and recently re-emerged from conversations involving Marijn Franx,
Daniel Eisenstein & HWR; these thoughts were floated at the
May 2016 NIRCAM-NIRSPEC meeting, with basically positive reception to the group there.


Conjecture: for emission-line dominated objects it is possible/sensible to open
many more shutters than the conservative "no overlapping spectra" targeting might suggest.
[For the time being, this pertains to NIRSPEC R=1.000 or higher resolution.]

Starting facts/assumption:
-- the spectra of most faint, high-z (z>~5-6) galaxies are emission line dominated.
-- the potentially most interesting ("PopIII") galaxies are emission line dominated
-- the # of targets that have potentially detectable emission lines in 10^(4-5) sec NIRSPEC
   exposures is far larger than the slit real estate budget, assuming no-spectral-overlap.
   [galaxies with broad-band magnitudes ~30 may well have strong, hence detectable lines...]
-- for emission line dominated spectra of (very) faint object, only a tiny portion of the spectral
   range therefore contains "significant" pixel.

Consequences:
-- the vast majority of detector pixels contains no "interesting" signal
-- many faint high-z emission line galaxy candidates will go un-targetted in
   any one deep NIRSPEC MSA setting.

Proposed remedy (to be taken as a though experiment, first):
open ALL shutters at focal plain locations that plausibly (according to NIRCAM photometry)
have high-z, presumably strong emission line targets.
[spectral overlap and chip gaps be damned for now.]
Let's take N~5 as a mental strwaman-plan.

[Nomenclature: dispersion runs along 'columns', slit runs along 'rows']
Let's presume that means we would have N shutters open in any one column (on N galaxies).
Advantages: N times more targets
Disadvantages:
  a)  N x higher sky background
  b)  "confusion of N overlapping spectra"

Addressing the disadvantages:
 on  a) How does the monochromatic surface brightness of emission lines (say, 10Msun/yr at z~6)
  compare to the background? I.e. are the cores of strong emission lines above/below the background.
  NB 1: compared to 'slitless' spectroscopy the background
  is still N/365 lower than slitless. [365 == # of shutters in dispersion direction]
  NB 2: the ensemble of open slits will inform us about the background

 on b) lines are narrow and sparse; if the continuum is negligible; the spectral signatures
 don't overlap. In principle there is some wavelength degeneracy
 (which line came through which slit); but this should be manageable, as long as there are
 no shutters open in the same column and adjacent/nearby rows.
on b): information on the continuum will be severely degraded;
 --> for emission-line dominated objects, there is little information in the continuum anyway;
 photometry will help

One specific approach is to target all objects that were done on R=100 mode, in R=1000, with disregard to overlap problems. The R=100 mode should break many of the degeneracy issues.
[Thanks to Chris W. for suggesting this.]

Basis of this: could one get Brant's and Christina's mock -data catalog, including their photo-z estimates?

Target assignment priorities for JWST MSA (NIRSPEC) Part I

after discussion in Victoria, May 2016, some notes on my thoughts
on the slit assignment from NIRSPEC MSA:

Let's presume, the plate solution is perfectly known and there are no failed shutters,
and we are interested in a 3-dither (no nods) mask design.

Let's presume we have a set of targets, with foremost attributes:
alpha,delta, size,flux,"scientific value", wavelength-range of highest interest (presuming we know z).

Let's presume, we want no spectral overlap; and we can neglect the issue of spectra
falling off the chip

The question is: what is the best combination of
a) telescope pointing (field center & orient)
b) target list

For a) we have in practice we have only 2 DOF, presuming the orient is given.
presumably these are fixed by the positions of very few "high-value" targets.
So a) and b) basically decouple.

Conjecture: in the limit that spectra cover the entire detector, the matter is simple:
in each slit position, one finds the "best available" object.
Complications foremost arise in defining which object is "best":
we need to define a merit function between
-- how intrinsically valuable is the target
-- how off-center (w.r.t. the micro shutter) should its centroid be;
   let's quantify this by a single number  log(S/N)-log(S/N_best),
  where S/N_best is defined as the S/N (given t_exp) we could get for
  a perfectly centered source with best sky subtraction.

Things to pre-compute:

Jan Rybitzki's Chempy projects

Just to commit to memory here is a discussion draft of Jan's papers
[from HWR - JR conversations; and DWH input]

Paper II or I :
  -- write-up of the basic model chempy (with thesis advisor Andreas Just).
  -- science bit: given a set of yields, how much can the abundances of
      a single star constrain the chempy parameters: the SFR, high-mass IMF slope,
      the SN-delay, the feed-back-mass-loading, the fraction of WD's that go SN Ia, and
     the gas inflow rate.
    [corollary: is having the age of a star helpful, if the star is not very old]
 -- implementation: take the Sun and Arcturus abundances and ages, and
    construct a chempy parameter pdf triangle plot.
-- consider taking the 'cosmic abundance' instead of Arcturus
-- consider different yield tables
-- discussion:
    explain why this fails..


Paper I or II:
   -- are the APOGEE data good enough to tell us which (published) yields tables are "best"
  -- Melissa will canonize the Hawkins et al accurate APOGEE abundances/ages to the
     RC sample of APOGEE; we then presume that abundance zero-point systematics
     are a sub-dominant error source
  -- Jan will try all 9 yield table (3x) combination to match the APOGEE RC sample
     (effectively marginalizing over the chempy params) and ask which fits best --> make Hogg happy
    [How much of this could be in paper I]
CHANGE of scope: use the ~30 abundance standards of Jofre et al 2016, to fix the field tables...
  that stays Paper III

Aside: can we ask what the set of [X/H] zero-point shifts in APOGEE can be, that would make
Arcturus, the Sun, and the cosmic standard likely??


Paper III:
   -- goal: the (varied?) chemical prehistories of all stars in the APOGEE sample
  -- use ensemble fit to tweak yield tables (see Paper II); we then assume both the
      yields and the abundance zero points to be "correct" (i.e. we won't marginalize)
  -- chempy has four parameters that may plausibly vary from star-to-star:
     the SFR, high-mass IMF slope (?), the feed-back-mass-loading, and
     the gas inflow rate.
  -- construct the pdf of these parameters for every single star in APOGEE;
     also exploit the ages for the stars we have..
  -- this enables:
      ** did the IMF vary as a function of time, of FeH?
      ** does the inferred mass-loading, or the inflow correlate with other properties
        (age, FeH, etc..)

CHANGE of scope: apply all of this to the ~30 abundance standards of Jofre et al 2016

Paper IV (Hogg)