Herschel’s view of
the Galactic Plane
and the Future
Chris Pearson (on behalf of Bruce Swinyard)
(Herschel SPIRE Post Operations Manager)
RAL Space, Rutherford Appleton Laboratory
Oxford Astrophysics, University of Oxford
The Open University
Herschel Space Observatory
•  ESA Cornerstone Space Mission
2009-2013
•  Large international collaboration
•  7.5m tall, 4m wide, 3.4 tonnes
•  Primary Mirror 3.5m
•  ~2500 litres of liquid Helium at 4K
•  3 Scientific Instruments
•  Infrared Wavelength 55 – 672 microns
•  Lifetime >3 years
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Herschel Space Observatory
SPIRE (250, 350, 500 microns)
Camera & FTS Spectrometer
PACS (70-160 microns)
Camera & IFU Spectrometer
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HIFI (157-625 microns)
Heterodyne Spectrometer
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Why Infrared, Why Herschel ?
Cosmic Background Radiation
Starlight reprocessed to infrared wavelengths
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The HiGal Project
HiGAL: Herschel Infrared Galactic Plane Survey
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The HiGal Project
HiGAL: Herschel Infrared Galactic Plane Survey
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The HiGal Project
HiGAL implemented three chunks:
HiGAL 1: +/-60o longitude from GC
HiGAL 2: 60o each side of GC
HiGAL 3: +/- 60o around AC
HiGAL-3
HiGAL-2
HiGAL-2
HiGAL-1
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The HiGal Project
HiGAL: Herschel Infrared Galactic Plane Survey
•  Herschel 5 band survey of the entire galactic plane
•  Latitude range of +/- 1o around the GP.
•  Bands centred on 70, 160, 250, 350 and 500 microns
•  Beam sizes 5.2, 12, 17, 25, 37 arcsec respectively.
•  Pixel sizes in maps are 6 arcsec as standard
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The HiGal Project
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Point Source Extraction
HiGAL: CUTEX algorithm
•  Uses differentiation of map in 4 directions
•  Tests for curvature & identifies “point” source by matching to expected PSF
•  Other algorithms tested – CUTEX is best at identifying sources in crowded
fields with complex diffuse emission (filaments)
•  Source extraction limits in a typical field were : 0.5, 1, 0.1, 0.1 and 2 Jy at
70 µm, 160 µm, 250 µm, 350 µm and 500 µm Four differential maps
Original map
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Sources clearly identified
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Catalogues
•  Catalogue created from HiGAL-1 sources
•  Attempted to cross correlate this with 2MASS (NIR), Glimpse (MIR), WISE
(MIR), MSX (MIR), Akari (MIR) and IRAS
•  Identified known YSOs and evolved objects in catalogue
•  Use as templates for colour-colour diagrams and source type separation
•  Final catalogue still in progress but has some 1000’s of candidate sources
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Source Segregation by Colour
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Model Fitting
•  Identified known AGBs – working mostly on C stars so far
•  Have distances to this so can correct J,H,K fluxes for extinction
•  Fit simple BB SED
•  Use DUSTY to predict mass loss
•  Initial results: relationship between colour temperature and mass loss
•  Full evolved object catalogue in a few months
Colour Temperature fit (Tc)
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Dusty model fità Mass loss (Ṁ)
Relationship Tc vs Ṁ
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Herschel LEGACY
•  Herschel observed ~ 1/10 of the entire sky!
•  37,000 individual science observations (23,400 hours)
•  www.cosmos.esa.int/web/herschel/science-archive
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Herschel LEGACY
•  Launch on 14 May 2009 …
•  … End of Helium on Operational Day 1447 on 29 April 2013
•  … last command 17 June 2013
•  … now in “parking” orbit
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WHATS NEXT ? FIRSPEX
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FIRSPEX
•  FIRSPEX is a joint ESA–CAS candidate small mission operating in THz
(>0.5 THz) frequency, submillimetre wavelength range.
•  Six band heterodyne receiver based on Schottky diode mixers cooled to
~100 K does NOT require cooling down to 4K
•  85 cm telescope
•  Cost effective space mission to deliver unique 3D maps of infrared sky.
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FIRSPEX
KEY SCIENCE QUESTIONS:
•  What is the origin and evolution of the Interstellar Medium in our Galaxy?
•  What determines the lifecycle of the interstellar Medium in the Milky Way?
•  What are the physical conditions of the gas clouds in our own Galaxy and
in Nearby Galaxies?
•  Is C+ a reliable tracer of Star Formation in the Universe?
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FIRSPEX
• Sun-synchronous orbit
• All-Sky survey in 6 months
• Multiple passes at poles
• 10 deg strip +/-5°on Galactic Plane (3800 sq. deg)
• Enhanced Surevy at Ecliptic Poles (2500 sq. deg.)
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FIRSPEX
COBE/FIRAS low resolution map in [CII], [NII] Bennett et al 1994
Spatial resolution 7° Spectral resolution: 1000 km/sec
Balloon-borne Infrared [CII] Explorer (BICE) Nakagawa 1998
Spatial resolution: 15 arcmin Spectral resolution : 175 km/sec
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FIRSPEX
FIRSPEX surveys will provide a census of the mass of the atomic, ionised and molecular gas.
Four tracers have been carefully selected to probe the ionised, atomic and molecular ISM:
•  [CII] 158µm (1.91 THz)
•  [NII] 205µm (1.46 THz)
•  [CI] 370 µm (890 GHz)
•  CO(6-5) 433µm (691 GHz)
Velocity resolutions of 0.5 – 1 km/s (1-3 MHz)
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FIRSPEX
PIs: D. Rigopoulou (UK) & J-S. Huang (NAOC)
Technical team:
RAL: B. Swinyard, B. Ellison, C. Pearson
PMO: Y. Gao, S-C. Shi, J. Hu
FIRSPEX Webpage:
http://astroweb1.physics.ox.ac.uk/~dar/FIR/firspex4.html
Sign up to support:
https://www2.physics.ox.ac.uk/far-infrared-spectroscopic-explorer-firspex
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WHATS NEXT ? SPICA
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SPICA
Three band grating spectrometer
•  Short wavelength 34-60 µm
•  Spectral resolution
•  Medium wavelength 60-110 µm
•  Low resolution mode – R~300
•  Long wavelength 110-210 µm
•  High resolution mode – R~3000
Limiting 5σ-1hr line flux sensitivity
Mode
SW band
MW band
LW band
Low R point source
/ x10-20 Wm-2
4.4
4.1
6.4
High R point source
/ x10-20 Wm-2
24
24
29
Mapping spectroscopy*
/ x10-20 Wm-2
98
50
42
Area mapped = 4 arcmin2
•  Values in brackets are performance with the beam splitter
•  saturation levels for this system will be ~20 Jy when observing point sources
• 
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END
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