S7/S11

Interstellar dust in M51 from IRC
images
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
Outline
!  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
2
Fumi Egusa (ISAS/JAXA)
Introduction
3
Fumi Egusa (ISAS/JAXA)
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
!  InfraRed Camera
Models from GRASIL (Silva et al. 1998)
!  NIR
!  N3: star + neutral PAH
!  N4: star
!  MIR
!  S7: ionized PAH
!  S11: PAH
!  L15: hot dust + PAH
!  L24: warm dust (~100K)
5
Fumi Egusa (ISAS/JAXA)
Draine & Li (2007)
Data Reduction
6
Fumi Egusa (ISAS/JAXA)
Basic Data Reduction
Date
!  Datasets
!  Two pointed observations toward
M51
!  FoV covering almost the entire
M51 system
!  Data Reduction
!  Latest reduction toolkit
!  Neighbor dark frames
(Coadd dark frames from
neighbor (+/- 5 days)
pointings.)
7
Fumi Egusa (ISAS/JAXA)
Filters # of long
2006/12/16 N3, N4
4
S7, S11
12
L15
9
L24
12
2007/06/16
Super dark (left), self dark (middle), neighbor dark
(right) for MIR-L long exposure frames of M51.
Additional Data Reduction
!  Earth-shine Light Removal for L24
8
Fumi Egusa (ISAS/JAXA)
L24-long images after prepipeline -> after EL removal
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
9
Fumi Egusa (ISAS/JAXA)
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
11
Fumi Egusa (ISAS/JAXA)
S7
S11
L15
L24
Results
13
Fumi Egusa (ISAS/JAXA)
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)
14
Fumi Egusa (ISAS/JAXA)
!  Definition
!  Center: r < 30’’
!  Arm
!  filtered amplitude > 1
!  Inter-arm
!  filtered amplitude < -1
Inter-arm 2
Inter-arm 1
Flux Distribution
Center
Arm 1 2
Inter-arm 1 2
!  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
15
Fumi Egusa (ISAS/JAXA)
Arm/Inter-arm Contrast
!  A/I Ratio
!  Highest in L24
!  tracing warm dust around star
forming region in the arms
Region
S7
Center
25.26 24.54 29.69 40.58
Arm 1
4.67
4.25
4.85
6.19
!  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
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
!  Reflects the temperature
distribution in the galactic disk
16
Average flux [MJy/sr]
Fumi Egusa (ISAS/JAXA)
S11
L15
L24
Color Maps
!  Flux ratio based on S11
S7/S11
L15/S11
L24/S11
Flux > 5σ was used.
17
Fumi Egusa (ISAS/JAXA)
Color Maps
!  S7/S11
!  Sakon et al. (2007)
found S7/S11 > 1 in
the spiral arm of
NGC6946.
!  Similar trend found in
M51!
S7/S11
!  also high ratio in feathers
C
1.03 ± 0.09
!  mildly correlates with
A1 1.04 ± 0.14
L24
A2 1.09 ± 0.14
!  higher ionization fraction I1 0.95 ± 0.13
in HII regions?
I2 0.96 ± 0.13
18
Fumi Egusa (ISAS/JAXA)
S7/L15
Color Maps
!  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?
S7/L15
ISO LW3
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
19
Fumi Egusa (ISAS/JAXA)
Dust Models
!  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)
20
Fumi Egusa (ISAS/JAXA)
fixed: α=2 & Umax=1e6
S7/S11
Colors & Models
0.5%
2.5%
4.6%
increasing qPAH
Dust model
!  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)
21
Fumi Egusa (ISAS/JAXA)
γ
Umin
!  S7/S11>1 for arm
!  Large qPAH and/or small γ in
arm?
!  Large ionization fraction in arm?
Observational data
Models with γ=0
increasing Umin
increasing Umin
22
Fumi Egusa (ISAS/JAXA)
increasing qPAH
increasing qPAH
Colors & Models
Observational data, 1pix=3.7’’
!  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
Models (color=qPAH): γ=0-1, Umin=0.1-25
23
Fumi Egusa (ISAS/JAXA)
Color Maps
!  S11 Excess
!  In inter-arm regions
!  PAH formation?
S11/L15
increasing qPAH
24
Fumi Egusa (ISAS/JAXA)
increasing Umin
L15/S11
L24/S11
Contamination?
!  Stellar Continuum
!  ~10% in S7 and less in S11
Center
Arm1
Inter-arm1
!  [NeII] emission line
!  λ=12.81um, from
Spitzer IRS (Dale et al.
2009)
!  [NeII]/S11 = 1--3%
from 2MASS
Blackbody with 5000K
Position where the
flux measured
26
Fumi Egusa (ISAS/JAXA)
Summary
!  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?
27
Fumi Egusa (ISAS/JAXA)
!  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
ionization fraction v.s. dust
size (Li & Draine 2001)
Future Works
!  Dust Model
!  With larger qPAH and
Dale et al. (2005)
varying ionization fraction
!  Neutral PAH
stellar continuum
!  Strong emission at 3.3um
!  N3 (or IRAC1) can be
used?
!  foreground star
!  stellar continuum
!  elongated PSF for N3
28
Fumi Egusa (ISAS/JAXA)
N3
IRAC1