near infrared background radiation …...aug. 17, 2015, subaru telescope near infrared background...
TRANSCRIPT
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Aug. 17, 2015, Subaru Telescope
NEAR INFRARED BACKGROUND RADIATION OBSERVED BY AKARI
Hyung Mok Lee (Seoul National University)
In collaboration with T. Matsumoto (ASIAA), H. Seo (SNU), W. Jeong, J. Pyo (KASI), K. Wada, S. Oyabu, S. Matsuura (ISAS/JAXA), and more
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Aug. 17, 2015, Subaru Telescope
OUTLINE
• Introduction
• Fluctuation measurements with AKARI
• Monitor field
• NEP-deep field
• Origin
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Hauser & Dwek 2001, ARAA
BACKGROUND RADIATION OVER WIDE SPECTRAL RANGES
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Aug. 17, 2015, Subaru Telescope
COSMIC INFRARED BACKGROUND RADIATION (CIRB)
• Residual light in long exposure IR image after removal of contribution from all known sources
• Stars
• Galaxies
• Diffuse Galactic light
• Zodiacal light
• Issues
• Accuracy of measurement
• Origin4
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Aug. 17, 2015, Subaru Telescope
RELEVANT STUDIES
• COBE
• Hauser et al. (1998): excess emission in near to far IR
• Cambresy et al. (2001), Levenson et al. (2007): Existence of CIRB in NIR
• IRTS
• Matsumoto et al. (2005): spectrum from 1.6-4 micron
• Spitzer
• Kashlinsky et al. (2005, 2007, 2012): significant fluctuations at 100-300 arcsec scale
• More recently
• AKARI: Monitor Field (Matsumoto et al. 2011), NEP-Deep (Seo et al. 2015)
• CIBER: NEP area (Zemcov et al. 2014)
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Aug. 17, 2015, Subaru Telescope
CONTROVERSY
• Uncertainties in foreground Zodiacal Light
• TeV γ-ray Blazar spectrum favors no excess above the contributions from faint galaxies (Ahronian et al. 2005, Mazin & Raue 2007)
• Energetics: claimed background light means too much generation of Pop. III stars (Madau & Silk 2005)
• Large angular scale fluctuations6
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Aug. 17, 2015, Subaru Telescope
CAREFUL MEASUREMENT OF THE BACKGROUND RADIATION
• Kashlinsky et al. 2005 using Spitzer telescope data
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Aug. 17, 2015, Subaru Telescope
FLUCTUATION ANALYSIS OF SPITZER DATA
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Kashlinsky et.al 2007
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Aug. 17, 2015, Subaru Telescope
NEW MEASUREMENT WITH AKARI
• Cold shutter ⇒accurate determination of dark current
• Deep and Wide Surveys
• Wavelength coverage to shorter wavelength
• Other ancillary data available: optical, ground based high resolution near-IR, mid-IR
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Aug. 17, 2015, Subaru Telescope
FIELDS
• Observed areas
• Monitor field (Matsumoto et al. 2011)
• circular field with10 arcmin radius, used for the performance of the instruments
• NEP-Deep (Seo et al. 2015)
• Blank field survey area of ~0.6 sq. deg.
10NEP-Deep Monitor field
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Aug. 17, 2015, Subaru Telescope 11
Summary of Monitor Field Data
Band N2 (2.4㎛) N3 (3.2㎛) N4 (4.1㎛)
Pixel scale (〃)
Limitingmagnitude (AB)
21.7 21.4 20.7
1.46
10’ diameter (412pixel diameter)
Position (J2000)
Number ofimage frames
Integrated exposure time
RA 268.8500 DEC 66.6256
40
1776 sec 1732 sec 1243 sec
39 28
FOV ofstacked image
Observation14 pointed observation
(2006.9 – 2007.3)
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Aug. 17, 2015, Subaru Telescope 12
Stacked (original) images
※ The number in the scale bar is ADU scale.
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Aug. 17, 2015, Subaru Telescope
REMOVING FOREGROUND SOURCES
1. 2σ Clipping: Removing pixels above or below the average by 2σ. Repeat this process 10 times.
2. Subtraction of outer part of point source using carefully modeled PSF
3. Subtraction of outer part of extended sources identified by CFHT optical catalogue. Their Flamingo images (higher spatial resolution
at K band) are convolved with AKARI PSF and subtracted.4. In order to make contribution of identified sources negligible, we
masked a layer of one pixel around masked region.5. For sources that are not masked in step 1 but for which step 2 or
3 were applied, we masked 8 neighboring pixels around the center of these objects.
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Aug. 17, 2015, Subaru Telescope 14
Images after 2σ clipping
※ The number in the color bar is ADU scale.
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Aug. 17, 2015, Subaru Telescope 15
Final images
2.4 μm, 39.8% 3.2 μm, 39.3 % 4.1 μm , 36.8 %
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Aug. 17, 2015, Subaru Telescope
FLUCTUATION ANALYSIS • Absolute level of the CIRB is difficult to determine because of
uncertainties in diffuse component (especially Zodiacal light)
• Fluctuation analysis is another powerful method since diffuse component is thought to be rather smooth (Kashlinsky et al. 2007)
⇒ Typical fluctuation flux =
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Aug. 17, 2015, Subaru Telescope
OUR RESULTS: POWER SPECTRA
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Upper: skyLower: Dark
Straight: shot noise due to unresolved galaxies
Excess powers at > 100 arcsec
Matsumoto, Seo, Lee, et al. (2011)
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Aug. 17, 2015, Subaru Telescope
PIXEL CORRELATION BETWEEN DIFFERENT BANDS
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Correlation coefficient ~ 0.8
Correlation coefficient ~ 0.5
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Aug. 17, 2015, Subaru Telescope
SPECTRUM OF FLUCTUATING COMPONENT
• Average value of power at 100”<θ<300”
• Rayleigh Jeans like blue spectrum ( ∝ λ-3)
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λ-3
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Aug. 17, 2015, Subaru Telescope
COMPARISON WITH OTHER MEASUREMENTS
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Aug. 17, 2015, Subaru Telescope
LARGER ANGULAR SCALE STUDY: NEP-DEEP FIELD
• Large portion (~60%) of NEP-Deep survey area was affected by earthshine. We excluded such area.
212.4 μm 3.2 μm
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Aug. 17, 2015, Subaru Telescope
CORRECTION FOR THE INSTRUMENTAL EFFECTS
• MUXbleed caused sudden changes in background: we corrected it by fitting the average background to the linear function
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Aug. 17, 2015, Subaru Telescope
FLUCTUATION SPECTRA
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• Noise power was obtained by computing the fluctuation power for the difference images of two subsets of stacked images
• True fluctuation was obtained by quadratically subtracting the powers of mosaic and the subset
• Excess fluctuation power over all angular scales
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Aug. 17, 2015, Subaru Telescope
CORRECTION FOR INSTRUMENTAL AND SYSTEMATIC EFFECTS
• The computed power can be affected by
• Masking: too much masking could cause artificial fluctuations (mode coupling)
• Map making procedure: adjustment of background level of adjacent images (map-making transfer)
• Finite beam size: smear out fluctuations in small angular scale (beam transfer)
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P̃2(q) = M(q)T (q)B(q)P2(q)
Mode couplingmap making transfer
True power
beam transfer
Computed power
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Aug. 17, 2015, Subaru Telescope 25
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Aug. 17, 2015, Subaru Telescope
ESTIMATED FLUCTUATION SPECTRA
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• Excess fluctuation power over shot noise up to ~1000 arcsec.
• Smooth continuation from Monitor Field Results
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Aug. 17, 2015, Subaru Telescope
• DGL: Scattered stellar light• FIR Emission: Thermal emission⇒DGL and FIR emission should be well correlated
DIFFUSE GALACTIC LIGHT (DGL)?
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AKARI 90 μm image at Monitor field (Matsuura et al. 2010)
No correlation between NIR and FIR!
Monitor field
NEP-Deep field
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Aug. 17, 2015, Subaru Telescope
CLUSTERING OF FAINT GALAXIES AT Z=2~3?
• Spectrum of red dwarf galaxies is red at near infrared (Chary et al. 2008)
• Expected fluctuation of galaxies fainter than Ks(Vega)>21 mag : 0.03 nW m-2sr-1 at 600”
• AKARI observation at 2.4 μm: nW m-2 sr-1 • Estimated fluctuation power is lower than
observed
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--------------Spectrum of fluctuating emission
Chary et al. 2008
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Aug. 17, 2015, Subaru Telescope
POP III STARS?
• Difficulty in explaining the TeV γ-ray spectra
• γ-ray photons experience inverse compton scattering with IR background radiation
• However, intrinsic spectra of TeV γ-ray galaxies are not known.
• Too much metal production (Madau & Silk 2005)
• Absolute level uncertain
• Collapse into black hole? 29
⌦⇤ ⇡ 0.045⌦B
✓FJ
2.5nW/m2/sr�1
◆
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Aug. 17, 2015, Subaru Telescope
HIGH-Z GALAXIES (INCLUDING POP III STARS)?
• Background flux level can be explained by combination of low and high-z galaxies
• However, fluctuations at 100-1000 arctic cannot be explained by ‘known’ components
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flux
fluctuation
Yue et al. 2012
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Aug. 17, 2015, Subaru Telescope
INTRA HALO LIGHT (IHL)
• Diffuse light in intracluster has been found (IHL or ICL)
• The fraction and origin of IHL are not well known: accretion or in-situ
• IHL becomes an interesting component in understanding the formation and evolution of galaxies
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Mihos et al. (2005), Virgo
Presotto et al. (2014), MACS1206
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Aug. 17, 2015, Subaru Telescope
IHL AS SOURCE OF IR BACKGROUND• Larger fluctuation means
strong clustering
• Clusters are known to show strong clustering than galaxies
• Angular scale distance varies slowly from z>1
• Larger fluctuation is expected from
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Aug. 17, 2015, Subaru Telescope
LARGE SCALE FLUCTUATION FROM SPITZER
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Kashlinsky et al. 2012Shot Noise
Known galaxies fainter than detection limits
Blue: High-z ΛCDM
Red: Total
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Aug. 17, 2015, Subaru Telescope
INTRA-HALO LIGHT (IHL) AND OBSERVED FLUCTUATIONS
• IHL may be able to account for most of the fluctuation at 10-100 arcmin.
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Zemcov et al. (2014), CIBER
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Aug. 17, 2015, Subaru Telescope
WHAT ELSE DO WE NEED?
• Current measurement extends to ~1 degree
• Recent analysis of IRTS data by Matsumoto et al. (private comm.) shows excess power up to ~40 degree (tentative)
• Such a large scale structure due to the same component?
• Very local?
• MIRIS will filll the gap of 1-10 degree fluctuations
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Aug. 17, 2015, Subaru Telescope
MIRIS CONCEPT
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• Optics8cm aperture, F2 Refractive optics
• Picnic array: 51.6” pixel scale, 3.67
o x 3.67
o
• Telescope is passively cooled by radiation to ~180K
• Mission period: Nov. 2013 - early 2015
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Aug. 17, 2015, Subaru Telescope
COSMIC NEAR-INFRARED BACKGROUND: MIRIS OBSERVATION
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§ I & H bands§ NEP (North Ecliptic Pole): > 10o x 10o
(FOV = 3.67o x 3.67o)
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Aug. 17, 2015, Subaru Telescope
SUMMARY• Unambiguous detection of Cosmic Infrared Background (CIRB) from various
surveys• Spitzer: GOODS , UDS, EGS• AKARI’s Monitor field and NE-Deep field• CIBER: NEP
• Excess powers 100-1000 arc second• Nearly Rayleigh-Jeans SED with possible peak around ~ 1.8 μm • Difficult to explain with zodiacal light, diffuse galactic light or low-z faint galaxies• Possible explanations
• Pop III stars, and epoch of reionization? Maybe difficult• IHL appears to be a viable candidate
• Future• Measurements at larger angular scale (~up to 10 degrees) and spectrum will
help to understand the origin38