interstellar dust in m51 from irc images
TRANSCRIPT
Fumi Egusa (1), I. Sakon (2), T. Onaka (2), H. Matsuhara (1), K.
Arimatsu (1&2), T. Suzuki (1), T. Wada (1), the IRC team
1: ISAS/JAXA, 2: University of Tokyo
Interstellar dust in M51 from IRC images
Outline
Fumi Egusa (ISAS/JAXA) 2
! Introduction ! M51 -- nearby grand-design spiral galaxy ! Interstellar dust in MIR -- PAHs and warm dust
! Data Reduction ! With the latest reduction toolkit ! Additional procedures -- PSF correction, etc.
! Results ! Arm/Inter-arm ratio ! Colors & dust models
! Summary
M51! NGC5194/NGC5195
! Nearby (D=8.4Mpc) ! Face on (i=24deg) ! Grand-design spiral
structure ! Active star formation in
spiral arms ! Dust lanes along spiral
arms and in inter-arm regions
4 Fumi Egusa (ISAS/JAXA)
Interstellar Dust & AKARI IRC
5 Fumi Egusa (ISAS/JAXA) Draine & Li (2007)
! InfraRed Camera ! NIR
! N3: star + neutral PAH ! N4: star
! MIR ! S7: ionized PAH ! S11: PAH ! L15: hot dust + PAH ! L24: warm dust (~100K)
Models from GRASIL (Silva et al. 1998)
Basic Data Reduction! Datasets
! Two pointed observations toward M51
! FoV covering almost the entire M51 system
! Data Reduction ! Latest reduction toolkit ! Neighbor dark frames
Date Filters # of long 2006/12/16 N3, N4 4
S7, S11 12 2007/06/16 L15 9
L24 12
Super dark (left), self dark (middle), neighbor dark (right) for MIR-L long exposure frames of M51.
(Coadd dark frames from neighbor (+/- 5 days) pointings.)
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Additional Data Reduction! Earth-shine Light Removal for L24
L24-long images after prepipeline -> after EL removal 8 Fumi Egusa (ISAS/JAXA)
Additional Data Reduction! PSF Correction
! PSFs for MIR-S and -L provided by Arimatsu et al. (2011)
! FFT was used to correct the extended PSFs with different FWHM to a common 2D Gaussian PSF. ! FWHM=7.4’’ was
adopted. L24 long image before (left) and after (right) PSF correction
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Additional Data Reduction! Ghost Masking
! In MIR-S bands ! Cannot be fully removed
by the ghost model from Arimatsu et al. (2011) ! probably due to dependence
on color and position
! 15’’ around the ghost was masked.
10 Fumi Egusa (ISAS/JAXA) S11 before (top) and after (bottom) ghost masking
Final Images! Four MIR Bands
! Aligned ! WCS registered ! North-up ! 3.7’’/pix
! Ghost masked ! PSF corrected
! FWHM=7.4’’ ! Flux calibrated
! Tanabe et al. (2008)
! unit: MJy/sr
S7 S11
L15 L24
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Arm/Inter-arm Definition! Filter N3 image
! N3: shortest wavelength ! traces the stellar distribution
most among the IRC bands ! Procedures
! deproject to face-on view ! median filter to remove stars ! mask M51b out ! subtract azimuthal average at
each radius ! apply Wavelet analysis to
subtract components with 83’’ scale (c.f. Dumas et al. 2011)
! Definition ! Center: r < 30’’ ! Arm
! filtered amplitude > 1
! Inter-arm ! filtered amplitude < -1
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Inter-arm 2
Inter-arm 1
Flux Distribution! Histogram for Each Region
! Center peaks at large flux ! No significant difference between
Arm1&2 or Inter-arm1&2 ! Arm and Inter-arm peak at similar flux
but Arm has a tail in bright end
! Histogram for Each Band ! Highest contrast in L24 ! Lowest contrast in S11
Center Arm 1 2 Inter-arm 1 2
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Arm/Inter-arm Contrast
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! A/I Ratio ! Highest in L24
! tracing warm dust around star forming region in the arms
! Lowest in S11 ! including ~11um bands from
PAHs ! well correlates with the total FIR
(Onaka et al. 2007), i.e. represents total dust including colder component
! Reflects the temperature distribution in the galactic disk
Region S7 S11 L15 L24 Center 25.26 24.54 29.69 40.58 Arm 1 4.67 4.25 4.85 6.19 Arm 2 4.14 3.74 4.50 6.10 Inter-arm 1 1.32 1.38 1.53 1.64 Inter-arm 2 2.13 2.15 2.31 2.49 A/I 2.64 2.35 2.52 3.09
Average flux [MJy/sr]
Color Maps
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! Flux ratio based on S11 S7/S11 L15/S11 L24/S11
Flux > 5σ was used.
Color Maps
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! S7/S11 ! Sakon et al. (2007)
found S7/S11 > 1 in the spiral arm of NGC6946.
! Similar trend found in M51! ! also high ratio in feathers ! mildly correlates with
L24 ! higher ionization fraction
in HII regions?
S7/S11 C 1.03 ± 0.09 A1 1.04 ± 0.14 A2 1.09 ± 0.14 I1 0.95 ± 0.13 I2 0.96 ± 0.13
Color Maps
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! S7/L15 ! No global trend ! ISO LW2 (7um) & LW3
(15um) ! Sauvage et al. (1996) report
small LW2/LW3 in the arm ! only for the brightest HII
regions? ISO LW3
S7/L15
S7/L15 C 0.86 ± 0.08 A1 0.98 ± 0.20 A2 0.90 ± 0.23 I1 0.91 ± 0.20 I2 0.89 ± 0.16
Dust Models
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! Draine & Li (2007) ! Composition
! carbonaceous (incl. PAH) ! silicate
! Abundance ! PAH fraction=0.5--4.6% ! ionization fraction fixed
! Radiation field ! U=1 for solar neighborhood
from Mathis et al. (1983)
fixed: α=2 & Umax=1e6
Colors & Models
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! S7/S11 ! Large qPAH, large S7/S11 ! Large γ, small S7/S11 (large
contribution from large U) ! S7/S11 ~ const. for Umin <
100 (and smaller for larger Umin)
! S7/S11>1 for arm ! Large qPAH and/or small γ in
arm? ! Large ionization fraction in arm?
S7/S
11
increasing qPAH
Dust model γ Umin
0.5% 2.5% 4.6%
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Observational data Models with γ=0
incr
easin
g q PA
H
increasing Umin
increasing Um
in
increasing qPAH
Colors & Models
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! Color-color Diagram ! Observational data
and models not consistent?
! Excess in S11 (& S7 perhaps)
! PAH fraction need to be > 4.6%? ! but the ratio is large
in inter-arm regions
Observational data, 1pix=3.7’’
Models (color=qPAH): γ=0-1, Umin=0.1-25
Color Maps
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! S11 Excess ! In inter-arm regions ! PAH formation?
L24/S11
increasing Umin
increasing qPAH
L15/S11
S11/
L15
Contamination?
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! Stellar Continuum ! ~10% in S7 and less in S11
! [NeII] emission line ! λ=12.81um, from
Spitzer IRS (Dale et al. 2009)
! [NeII]/S11 = 1--3%
Center Arm1 Inter-arm1
Blackbody with 5000K from 2MASS
Position where the flux measured
Summary
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! M51 IRC Images ! Arm/Inter-arm contrast
! Smallest in S11 ! Largest in L24
! Colors ! S7/S11>1 in arms
! large qPAH, small γ ! large ionization fraction
! S11/L15>1 in inter-arm ! even larger qPAH? ! low ionization fraction?
! Dust in M51 ! PAH ionization
! fixed models cannot explain the observational data.
! more ionized PAHs in arms and more neutral PAHs in inter-arm regions
Future Works
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! Dust Model ! With larger qPAH and
varying ionization fraction
! Neutral PAH ! Strong emission at 3.3um ! N3 (or IRAC1) can be
used? ! foreground star ! stellar continuum ! elongated PSF for N3
N3 IRAC1
Dale et al. (2005)
stellar continuum
ionization fraction v.s. dust size (Li & Draine 2001)