Broadband spectroscopy beyond 40 mm: prospects for terrestrial and spacebased platforms after Hersch

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Broadband spectroscopy beyond 40 mm
prospectsfor terrestrial and space-based
platforms after Herschel
Sensitive broad-band spectral surveys reveal the
history of the far-IR background galaxies

• Matt Bradford with the BLISS / SPICA teams
• June 2, 2006

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Overview

• Outline
• Motivation for wideband far-IR spectroscopy.
• Looking beyond Herschel --gt SPICA
• Opportunities with the cold telescope
• Sensitive spectroscopy
• BLISS instrument concepts and trades
• l35-600 microns R1000, excellent sensitivity
  -- optimized for point source spectroscopy in the
  spirit of the IRS.
• Z-Spec and new ground-based wideband submm / mm
  spectrographs -- the complement to ALMA.
• BLISS plans and teaming.

Spitzer IRS Spectra of ULIRGs Borys, Bradford,
Smith in prep
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Cosmic backgrounds The repository for all
energy released the recombination
UV / opt / near-IR
Far-IR / submm
Lagache, Puget Dole (2005), ARAA 43
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Far-IR background is being resolved into galaxies
Spitzer MIPS 24 mm Lockman Hole Egami et al.
(2004)
Spitzer MIPS Chandra Deep Field South 70 (23)
160 (7) Dole et al. (2004)
MAMBO / IRAM 30 m 1.3 mm 60 hours, 40
sources 10 of BG Bertoldi et al. (2000)
Carilli et al. (2001c, 2002b) Dannerbauer et
al. (2002) Voss (2002) Eales et al.
(2002) Greve et al (2005)
Dole et al. (2004)
Future observatories will resolve the bulk of the
background into individual sources, but How to do
meaningful follow up of these sources?
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Far-IR background will be accounted for
Dole et al. Stacking analysis based 24 on micron
positions
24 micron positions binned in flux
160 micron aggregate detections -- 66 of BG
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Follow-up options for far-IR / submm galaxies

• VLA position Keck multi object spectrograph
• efficient 102 sources in 2 years
• potentially rich astrophysically
• unreliable, not necessarily true
• Z-machines (Z-Spec etc)
• CO J2 to J6 reliable at 1e-20 W m-2
• SLOW 1 night / source on biggest single-dish
  telescopes
• no (or limited) dynamical info (mass)
• ALMA spectral imaging at 230 GHz
• CO J2 to J6 reliable at 1e-20 Wm-2
• kinematic and spatial information built in
• 1 hour, MDLF 5e-22, but 8x penalty for 8 GHz
  bandwidth 1.5e-21 effective MDLF (1 hour)
• only discrete atmospheric windows
• only molecular gas (primarily CO)
• Sensitive, wide-bandwidth far-IR spectroscopy
  from space
• Powerful transitions, reliable suite of lines
• 1 hour MDLF at or below 1e-20 W m-2
• Complete wavelength coverage 20 mm to 1 mm
• Atomic, ionized, and molecular ISM phases
  together

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SPICA -- the first large cryogenic observatory

• Space Infrared Telescope
• for Cosmology and
• Astrophysics
• Takao Nakagawa, PI
• Size 3.5 m (No Deployment)
• Temperature 4.5 K
• Stirling J-T closed cycle
• Facility heat lift
• at 1.7 K 10 mW
• Orbit L2 Halo
• Lifetime 5 years
• Launch 2013 by HIIA-202
• COOLED Telescope
• Optimized for Thermal IR (10-600 mm)
• Complementary with JWST, ALMA
• A major international mission
• European consortium developing ESI concepts

2006 May 22 SPICA predecessor Akari working well
Space Infrared Telescope for Cosmology and
Astrophysics -- ISAS / JAXA
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Herschel, SOFIA and ground based platforms are
are limited by emission from warm
telescopes.Ultimate limitation is photon noise
from the astrophysical backgrounds.Source
confusion is not a problem for R1000
spectroscopy.SPICA leads the way to SAFIR and
beyond temperature is more important than
aperture.Cold space telescope allows
high-redshift spectroscopy throughout the far-IR
SPICA with BLISS is a new frontier in the far-IR
Crosses show redshifted fine structure lines in
ULRGs Effect of finite detector NEP in yellow
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Far-IR lines are often the brightest features in
dusty galaxies

• Suite of lines provides a reliable redshift
  template, perhaps the only method for very dusty
  sources.
• Fine structure and molecular lines dominate the
  gas cooling and enable subsequent star formation.
• Line ratios measure
• ? Gas mass, temperature, density
• ? UV field strength and hardness
• ? Metal abundances
• ? Starburst / AGN contributions
• ? Stellar type, starburst age.
• ? Degree of ISM processing
• Far-IR lines are subject to very little
  extinction, they probe the bulk of a galaxy.
• More local galaxies coming with Astro-F,
  Herschel, SOFIA.

J. Fischer et al. ISO LWS team 1999
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BLISS Instrument Architecture
Optimum sensitivity, large instantaneous band,
reliability more important than spatial mapping,
high spectral resolution

• Grating spectrometer is the best choice if
  background-limited detectors are available.
• 1st order ? octave of instantaneous bandwidth
• Good efficiency
• Fourier transform spectrometer (FTS) couples the
  full band to a single detector
• Sensitivity penalty relative to monochromator for
  perfect detectors
• Naturally accommodates 2-D spatial mapping
• Flexible observing modes
• Best option for detector-noise limited operation
• Fabry-Perot requires scanning for full spectral
  coverage
• Scanning time prohibits spectral surveys
• Heterodyne receivers subject to quantum noise
• NEPQN hn dn1/2 vs. NEPBG hn n (n1) dn1/2
  
• Also offer small bandwidth
• 10 GHz backend at 1 THz gives n / Dn 100

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Z-Spec a WAFIRS prototype for 195-305 GHz
INPUT FEEDHORN
Z-Spec Team JPL / Caltech M. Bradford J.
Bock B. Naylor J. Zmuidzinas H.
Nguyen Colorado J. Glenn J. Aguirre (also
NRAO) L. Earle ISAS / JAXA H. Matsuhara
GRATING ARC
Individually mounted SiN bolometers
Focal ARC
CSO, Mauna Kea
FRIDGE
3He RADIATION SHIELD
ADR
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Z-Spec approaching full functionality
HNC
C2H
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Z-Spec spectrum of M82

• 4800 sec total time
• 158/160 bolometers
• Sensitivities a factor of 2 from perfect
  background limit
• Lowest background, most sensitive bolometers
  deployed to date

• Plans
• 195-305 GHz line surveys in local LIRGS and
  ULIRGS
• high-redshift CO measurements of mm, submm
  selected sources.
• CO J4--8, z 0.4 to 2.5
• (Larger mm-wave telescopes, e.g. IRAM 30m, LMT)

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Suite of WaFIRS modules for BLISS on SPICA
Polarizer and dichroics couple a complete 40--600
micron spectrum from a point source
125 cm
SPICA f/6.9 beam

• 6 bands cover 40-600 microns, 2 positions on the
  sky gt 12 modules in total
• Challenge is to minimize aberrations in the
  system to provide R1000 or more
• Compact cross-dispersed echelle design an
  excellent fallback for the short wavelengths

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Sensitivity requirements for BLISS detectors
Detector requirements for BLISS / SPICA are
identical to those for spectroscopy with SAFIR,
SPIRIT, SPECS, any cold far-IR space
telescope Match or beat the photon noise from
the astrophysical backgrounds zodiacal and
galactic dust. A cold space telescope is a
unique environment with no appropriate
terrestrial or air- or balloon-borne observatory
testbeds. Even Herschel with its 80 K telescope
has backgrounds 10,000 times too high. Building
BLISS for SPICA pushes and demonstrates
technology for SAFIR and beyond. Nothing else
can.
4 K instrument AW 3 mm2, Dl/l 50 , e 10
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Technologies for BLISS detectors
Need few x 104 elements with NEP below 1e-18 W
Hz-1/2

• TES Bolometers with SQUID MUX
• complete spectral coverage, response set by
  filter stack
• excellent optical efficiency (80) and stability
• time domain SQUID mux being fielded on SCUBA 2
  (104 pix TES)
• requires modifications to accommodate BLISS NEPs
• lower power dissipation at cold stage
• RF filter between detectors and SQUIDs to
  prevent back action heating detectors
• limited dynamic range
• DR hn/8kT 60--1000 at BLISS wavelengths
• requires 50mK base temperature to mitigate
  thermal noise
• GeGa photoconductors
• 1.5 K operating temperature
• large dynamic range
• conventional readouts, flight proven (at higher
  NEPs than BLISS requirements)
• non-uniform spectral response, and no response
  beyond 205 mm
• low optical efficiency (20-25)
• nonlinear behavior
• bulk materials are susceptible to cosmic rays
• Other approaches

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Record NEP achieved with leg-isolated SiN !
Measured NEP 4x10-19 W/Hz1/2 at 220mK
Extrapolates to 5x10-20 W/Hz1/2 at 50 mK, good
for BLISS grating
4 SiN beams 8.3 mm x 3 mm x 0.5 mm
G96 fW/K.
NEP0.51 aW/ÖHz.
Kenyon, LeDuc, Day
Rtes4.6mW
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Sensitive spectroscopy can go deeper than
continuum confusion limit
In one 30 arcsec BLISS - SPICA beam..
BLISS noise floor 1e-20 Wm-2
Surrogate spectrum -- line templates can be
extracted via local templates
Continuum from tens of galaxies, most well-below
confusion limit at long wavelengths
Bradford Chapman in prep
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Sensitive spectroscopy can go deeper than
continuum confusion limit
In another 30 arcsec BLISS - SPICA beam..
8 far-IR galaxies
Redshift log L log f 350 mJy 0.377
9.4 -0.29 1.07 10.58 -0.226
0.669 10.14 -0.154 1.43 11
-0.105 3.344 12.05 -0.07
2.809 12.21 0.252 1.365 11.33
0.257 1.452 11.71 0.556
BLISS noise floor 1e-20 Wm-2
Bradford Chapman in prep
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Thank you
BLISS - SPICA study team
Matt Bradford (JPL) PI, Andrew Blain
(Caltech), Jamie Bock (JPL), Peter Day (JPL),
Jackie Fischer (NRL), Jay Frogel (AURA),
Jason Glenn (Colorado), Martin Harwit
(Cornell), George Helou (Caltech / IPAC), David
Hollenbach (NASA Ames), Warren Holmes (JPL),
Kent Irwin (NIST), Michael Kaufman (CSUSJ /
Ames), Dan Lester (Texas), Matt Malkan
(UCLA), Hideo Matsuhara (ISAS / JAXA), Toshio
Matsumoto (ISAS / JAXA), Gary Melnick
(Harvard), Takao Nakagawa (ISAS / JAXA) SPICA
PI, Hien Nguyen (JPL), Takashi Onaka (Tokyo),
Hiroshi Shibai (Nagoya U.), Lisa
Storrie-Lombardi (Caltech / IPAC), Erick Young
(Arizona), Scott Chapman (Caltech), Gordon
Stacey (Cornell), Motohide Tamura (NAOJ),
Mark Wolfire (Maryland), Harold Yorke (JPL),
Jonas Zmuidzinas (Caltech)
US astronomers Stay tuned for SPICA science
workshop September in Pasadena
Representatives from Japanese SPICA
Consortium BLISS Science / Technology Working
Group (Co-Is) Advisory Committee (Co-Is
Collaborators)
Industrial Partners Ball Aerospace, Boulder,
CO Swales Aerospace, Pasadena, CA
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Mapping Speeds -- FTS comparable to single-pixel
grating
Time is time to survey 1 square degree to depth
of 1e-20 Wm2 (5s) FTS also solves TES dynamic
range problem, enables higher R
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Arp 220 -- prodigous starformation in the nearby
ULIRG is powered by a massive molecular gas
reservoir

• A case study for other local ULIRGs, high-z dusty
  galaxies
• A host of small abundant molecules have their
  fundamental rotational transitions in the far-IR.
• n0 1 / (Moment of Inertia)
• OH, CH
• HD
• H20
• NH, HN3
• Bright far-IR continuum gives molecular
  absorption
• Direct column density measure.
• Pumps masers

Gonzalez-Alfonso et al., and the ISO LWS
instrument team (2004)
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This interesting half of the luminosity has been
difficult to observe

• Atmosphere is opaque and warm
• Reduces transmission
• Introduces loading
• Far-IR /submm detector technology also behind
  optical / near-IR

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Suite of WaFIRS modules for BLISS on SPICA
BLISS WaFIRs suite fits comfortably within SPICA
instrument envelope 2.5 m by 50 cm
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BLISS FTS option fallback for higher-NEP
detectors

• 2 optical benches.
• Cool optics to 1.8 K with the SPICA 3He cooler
  for the long-wavelength channels.
• Telescope reimaging optics required )not shown)
• Modulation is naturally provided as part of the
  scan

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Suite of WaFIRS modules for BLISS on SPICA

• Two beams on the sky, separated by 5 arcmin (10
  beams longest l)
• 2x6 12 modules total
• If bolometers, then all are cooled to 60 mK --
  cold mass of 15 kg
• Can be cooled with continuous ADR (see Warren
  Holmes)
• Some modulation is required for bolometers (
  0.1 Hz)
• Would like to chop from one spectrometer bank to
  the other

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WaFIRS spectrometer module schematiccurved
grating in parallel plate waveguide

• Propagation confined in parallel-plate waveguide
• 2-D Geometry
• Stray light eliminated
• Curved grating diffracts and focuses
• Efficient use of space
• No additional optical elements

H.A. Rowland, 1883, Phil. Mag 16 K.A. McGreer,
1996, IEEE Phot. Tech. 8
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BLISS FTS option fallback for higher-NEP
detectors
Approach Divide the full BLISS band into 8
arrays. Build 4 Mach-Zehnder FTS modules, each
with 2 arrays
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BLISS 50 mK cooler concept -- continuous ADR w/
intercept
Continuous operation decreases peak power to
cryocooler

• Coolers Operated Serially
• Intercept Heat Pump Magnetizes at 1.8K, Cools to
  lt0.3K
• Intercept Heat Cooler Operated at Constant
  Temperature
• Detector Heat Pump Magnetizes at 0.3K and Cools
  to lt0.1K
• Detector Cooler Operated at Constant Temperature

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2
3
4
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M82 a nearby starburst demonstrates the
utility of far-IR fine structure lines

• ISO LWS Grating
• 7 fine structure lines
• HII regions
• ne 250 cm-3
• PDRs
• n 103.3,
• G0 102.8
• CII from PDRs (75)
• and HII regions (25)
• Model 3-5 Myr starburst with 100 M? cutoff
• Starburst mass
• 0.5-1.3x108 M?
• -gt 1/2 the total gas mass is involved in the
  starburst!

Colbert, Malkan et al. the LWS instrument team
1998
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Sensitive far-IR platform offers potential for
Pop III
High-opacity dust tracers immediately in first
supernova remnants

• Dust shell produced in the death of one star will
  be heated by the companion and radiate in the
  silicate features at 10 and 18 microns.
• With their high opacity and broad width, the
  silicate features may be our best opportunity to
  detect the first metals (Harwit 2004).
• At redshifts from 10--30, these features will be
  observed in the far-IR and submillimeter with
  fluxes of 10-20 (z1)-2 W m-2 . This is at the
  threshold of BLISS-SPICAs capability.
• Transition from Pop III to Pop II ?
• An opportunity for theorists / modelers

Silicate emission in QSOs with Spitzer IRS. Hao
et al (IRS team - Cornell) 2005
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A large cold telescope and the far-IR
meaningful diagnostics at high-z
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Stigmatic design minimizes aberrations

• Each facet positioned to provide perfect
  performance at two frequencies
• Each grating is completely custom
• Challenge is to minimize aberrations in the
  system to provide R1000 or more

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Spitzer has demonstrated sensitive high-z
spectroscopy with a cold telescope
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Fundamental limits for far-IR spectroscopy are
set by solar-system galactic dust
COBE DIRBE team Fixsen, Arendt, Hauser, Dwek,
Kelsall, Mather et al.