FMOS & (vs?) PFS
Subaru Fiber Multi-Object
Prime Focus Spectrograph”s”
Naoyuki TAMURA
Subaru Instrument Astronomer(Subaru Telescope, NAOJ)
1. Overview of FMOS
2. Spectroscopic survey of galaxies
3. Key specs to science & some technical issues
4. Summary

What is Subaru FMOS?
A couple of years ago, when we were struggling hard for
its integration and commissioning, I saw a number ofpeople who did not know FMOS, but knew WFMOS …

For details, please visit our section in the Subaru web site:
http://subarutelescope.org/Observing/Instruments/FMOS

“FMOS”: Fibre Multi Object Spectrograph
2 x NIRspectrographs

IRS1

Prime focus
unit (“PIR”)★ Subaru M1 8.2ｍ
★ 400 fibers in the30’ diameter FoV★ NIR (0.9-1.8µm)
spectroscopy

Unique combination
as a multi-object
spectrograph
Fiber positioner “Echidna”

IRS2

Fiber positioning

InfraRed Spectrograph
200 fibers are fed to each spectrograph (IRS1 & IRS2).
OH suppression by the mask mirror“LowR”: R~500 (w/ VPH), “HighR”: R~2200 (w/o VPH)

History & current status of Subaru FMOS
1997?: Project started.
 1999: Tamura joined FMOS (optical design, fiber experiment, etc)
 Apr 2002: Tamura moved to Durham (development of fiber cable &fiber connector, cryogenic tests of VPH gratings)
 2005?: FMOS parts integration & commissioning started in Hawaii.
 Dec 2005: Tamura moved to Subaru.
• Dec 2007: Engineering observation started.
• May 2008: Engineering first light.
• Mar 2009: Performance verification started.
• May 2010: Open use started (IRS1 LR only).
- 21 nights (8 programs + GTO) completed.
- No serious troubles on the FMOS side.

• Feb 2011: IRS2 LR will also be available.
• Sep 2011?: IRS1 HR will be in operation.
• Feb 2012?: IRS2 HR will become available.

Data from FMOS engineering observation
HαHβ?

[OIII]
4959, 5007

[OIII]

CBS
IRS1-LR
1.5 hHαBackgroundTo take “snapshots” of the universe and characterize the galaxy
popula:on at each of them, spectroscopic informa:on is necessary.
Redshi', star‐forming ac4vity, AGN ac4vity, abundance, stellar age, etc

Background
Properties of galaxies & AGNs are found “different” at highredshift in various aspects, especially at z>1, from those at z=0.
Imaging survey  Galaxy sample  Follow-up spectroscopy
How could one make sure that a “complete” galaxy sample
is constructed with no significant missing population?
(Conselice et al. 2003)(Reddy et al. 2008)

Background
Existing/on-going surveys:
SDSS, DEEP2, COSMOS, VVDS, SXDS, K20, GMASS, …
Why can we not yet fully understand galaxy evolution
by looking at the data from these surveys?
Any missing pieces, especially in spectroscopy?
• “Redshift desert”• Optically faint (red) objects
Dusty red & old red
 Massive survey in NIR with FMOS, with better
statistics over a wide area of sky.
(but probably limited to emission-line objects)
Nothing missing in relatively bright blue populations?
Which piece(s) will be addressed by SuMIRe/PFS?

To have a “complete” view of galaxy population
How about a magnitude (or mass) limited survey with enoughsensitivity to quiescent galaxies & those with weak-emission
lines due to dust extinction?

Cimatti et al. (2008)

“UDSz”: An ESO large programGMASS

Courtesy of Ross McLure, Henry Pearce(Edinburgh), UDSz teamWhy non-active population in the active era?
• Galaxies (massive?) that already assembled.
• Formation of red sequence: Nature or nurture.
• Characterizing “green valley” population• Elucidating star formation histories of galaxies:- Continuous, short-term burst-like, or sporadic.
- Physics of mass acquisition:
Accretion, interaction. etc- Roles of AGN activities

Key specs to science• Fiber density• Field coverage

How big can thesample be at the end?
Survey speed?

Which features• Spectral coverage, resolution can be accessed?

• System throughput (as a function of λ)Even to study composite spectra, redshift needs
to be determined for individual galaxies.

• Strategy of sky subtraction

PFS: High resolution option?
Butterfly mirror
system?
By rotating two mirrors
at once, more than one
gratings with different
spectral resolutions may
be accommodated.

Hastings et al. (2010)(See also Bernstein et al.
2002)

PFS: High resolution option?
A switching layer (3 x 1 in the example shown below) toselect fibers for use & keep more space on the detector
allowing cross dispersion

PFS: High resolution option?
A switching layer (3 x 1 in the example shown below) toselect fibers for use & keep more space on the detector
allowing cross dispersion

Subaru Flexibly Addressable
Integral Field Spectrographs(SuFAIFS)(Exploiting fiber optical switch)~ A preliminary proposal for future instrumentation ~Naoyuki Tamura (Subaru)
J. R. Allington-Smith, G. J. Murray, “DFS” collaboration(Centre for Advanced Instrumentation, Durham Univ., UK)(2010/08/31, an internal meeting at Subaru)

nxCourtesy ofAllington-Smith(Durham, UK)n x m switch made from 3
layers of n x 1 switches
Any NO = m points in the fieldof NI = n2 points can be routed
to the output with a down-selection
factor, F = n2/m
Example shown: n = 6, m = 3
with contiguous field (red) so
NI = 36, NO = 3, F = 6
Durham Univ. (& Tamura from Subaru) havebeen working with an industrial partner to
optimize a telecom device (single mode) for
astronomy (multi-mode) with high throughput.

(1 x m) x n(1 x n) xmGoal of SuFAIFS
Allows a ﬂexible selec:on of regions for spectroscopy
among the 2D array of available spaxels on a focal plane,
given a limita:on in mul:plicity of spectrograph(s).
E.g. Number of spaxels to be routed to spectrographs = 64.

Both will be in choice on SuFAIFS – Let’s be even cleverer!?
MOS+IFS (w/ op4mal shape)  Diverse Field Spectroscopy (DFS)

01 2301 230 12 301 23
45 6745 674 56 745 67
8 9 A B 8 9 A B 8 9A B 8 9 A B
CD E FCD E FCD E FCD E F
01 230 12 30 12 301 2345 674 56 74 56 745 67
8 9 A B 8 9A B 8 9A B 8 9 A B
CD E FCD E FCD E FCD E F
01 2301 230 12 301 2345 6745 674 56 745 67
8 9 A B 8 9 A B 8 9A B 8 9 A B
CD E FCD E FCD E FCD E F
01 230 12 30 12 301 2345 674 56 74 56 745 67
8 9 A B 8 9A B 8 9A B 8 9 A B
CD E FCD E FCD E FCD E F

Observation
control

Telescope focus

Either Cs or
Ns is OK.
Selected regions

Primary feed
SwitcherSpectrograph feed

Recorded spectra

Spectrographs
PFS spectrographs
can be an option?
Spectrograph slit

Murray, Allington-Smith (2009)
Poppett, Allington-Smith, Murray (2010)

Summary
FMOS is working in a good condition.
Clear identification of missing piece(s) in the existing/on-goingsurveys that would be addressed by SuMIRe/PFS to better
understand galaxy evolution.
To make a “snapshot” of a redshift with a “complete” view ofgalaxy population, surveys sensitive enough also to quiesecent
galaxies would be critical.
Fiber optical switch may be a key technology for high resolution
option, making PFS more versatile in its spectral domain.