Baseline Specifications of Near-IR Instruments

We define three levels of possible instruments for Subaru GLAO.

1. Wide-Field Near-IR Imager
2. Wide-Field NIR Imager and Multi-Object Spectrograph
3. Multi-Object Integral Field Spectrograph

Subaru Next-Gen AO working group has been studying the feasibility of "2. Wide-Field NIR Imager and Multi-Object Spectrograph". There are some possible optical designs to achieve > 10 arcmin φ FoV, and further opt-mechanical feasibility study is necessary.

Because the cost of Wide-Field NIR Imager and MOS or Multi-Object Integral Field Spectrograph would be very large (more than 10M USD), there's a possibility that we only have a budget for imager. So we would like to ask speakers and participants whether the wide-field spectroscopic capability is really essential for your science cases.

Note that MOIRCS, the current NIR imaging and multi-object spectrograph for Subaru Telescope has relatively wide FoV (4' x 7') and fine spatial sampling (0.117"/pix). MOIRCS could be used with the GLAO. See Comparison with other NIR instruments.

We should also think that in the early 2020s when the Subaru GLAO and the new instrument are on-sky, TMT will start operation as well. The science cases for this instrument should be unique to Subaru Telescope (not being achieved by TMT).

See Questions to speakers.

Wavelength	0.8μm - 2.5μm
Plate Scale	0.10"	See *1 below
FoV	13.6' x 13.6'	See *1 below
Detectors	4 Teledyne H4RGs (4 x 4096 x 4096 pixels)
Filters	Broad-band and Narrow-band filters

*1: See the following table for alternative sets of plate scale and FoV. Note that under typical condition we assume FWHM of GLAO-corrected FWHM for point sources would be ∼0.2" in K-band. See Specifications of GLAO.

Plate Scale ("/pix)	FoV for 4 H4RG (arcmin2)
0.07	9.6 x 9.6
0.09	12.3 x 12.3
0.10	13.6 x 13.6

Sensitivities

Limiting mag. for one hour on-source exposure, for point sources. In Vega magnitudes.

	New Inst.	MOIRCS	Mag. difference
J-band	24.6	24.0	0.6
H-band	23.9	23.2	0.7
Ks-band	23.7	22.8	0.9

Wavelength	0.8μm - 2.5μm
Plate Scale	0.10"	See *1 below
FoV	13.6' x 13.6'	See *1 below
Detectors	4 Teledyne H4RGs (4 x 4096 x 4096 pixels)
Filters	Broad-band and Narrow-band filters
MOS	Multi Slit Mask	See *2 below
λ Dispersion	∼3000	See *3 below

*1: See the following table for alternative sets of plate scale and FoV. Note that under typical condition we assume FWHM of GLAO-corrected FWHM for point sources would be ∼0.2" in K-band. See Specifications of GLAO.

Plate Scale ("/pix)	FoV for 4 H4RG (arcmin2)
0.07	9.6 x 9.6
0.09	12.3 x 12.3
0.10	13.6 x 13.6

*2: We have not made design study of the MOS mask exchange system. The size of a mask can be as large as 400 mm in diameter (cf. MOIRCS mask size is ∼90mm) and we do not have any feasible plan to implement MOS exchanger. There could be some restrictions of either the size of the mask or the operation of MOS (e.g., one mask per night).
The maximum multiplicity of slitlets would be ∼ 100 - 150.

*3: Preliminary specifications of grisms:

Band	Wavelength	Resolution
Y	0.95-1.15	2700
J	1.1-1.4	2800
H	1.5-1.8	2800
K	2.0-2.4	2800

Sensitivities

Similar to sensitivities for imaging, we can expect sensitivity improvement (about 0.6 - 0.9 mag.) in spectroscopic observations by narrowing the slit width (for point sources).

Another candidate of the instrument is Multi-Object Integral Field Spectrograph. We have not studied the technical feasibility of such an instrument. Below is an example of possible specifications of the instrument, based on VLT/KMOS with slight modifications for GLAO (note that KMOS is not connected to any AO systems).

Wavelength	0.8μm - 2.5μm
Spatial Sampling	0.125"	See *4 below
FoV per IFU	1.75" x 1.75"	See *4 below
Number of IFUs	24 (TBD)
Detectors	3-4 H2RGs? (TBD)
Patrol Area	∼ 13'
λ Dispersion	∼3000	TBD
Imaging Capability	No

*4: matrix of sampling / FoV per IFU. Here we assume image slicer type IFU, and each IFU has 14 slices (as it does in KMOS).

Spatial Sampling	FoV per IFU
0.1"	1.4" x 1.4"
0.125"	1.75" x 1.75"
0.15"	2.1" x 2.1"
0.20"	2.8" x 2.8"

Multi-object IFU can be a very large instrument, and like KMOS it would be difficult to have imaging capability as well. In such case, if we do not alter the Cassegrain interface of the telescope, we could use MOIRCS as the imager (0.117"/pix, 4'x7' FoV if there's no change in the shape of the secondary mirror).