Slide 1 Andromeda galaxy M31Milky Way galaxy similar to M31.
Planck intermediate results. XXV. The Andromeda Galaxy as ... · The Andromeda Galaxy as seen by...
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Planck intermediate results. XXV. The Andromeda Galaxy as seen by Planck Jodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester Fig. 1: CMB subtraction in M31 Fig. 2: CMB-subtracted maps at all Planck bands. Fig. 3: The integrated SED of M31. Right: Fig. 4: Identifying the dust heating mechanisms. Fig. 5: SEDs of individual pixels. Fig. 6: Fitted dust parameters to the cold dust. Accurate CMB subtraction is important for M31 given the similarities in angular scales between M31 and the CMB. Fig. 1 shows the different Planck CMB maps in the M31 region, and the SMICA CMB-subtracted 217 GHz (1.38 mm) map. Fig. 2 shows the CMB-subtracted Planck maps. Planck has detected M31 in all wavebands and clearly resolves multiple spiral arms and sub-features at >100 GHz (<3 mm). A number of features are clearly visible, such as the outermost spiral arm structures at 545/857 GHz (550/350 μm; bottom-right of each panel), as well as NGC 205 and a bright background quasar. The integrated SED of M31, shown in Fig. 3, is well-fitted with a global dust temperature of 18.2 ± 1.0 K, a spectral index of 1.62 ± 0.11, and a significant amount of free-free emission at 20–60 GHz, which when converted into a star formation rate (SFR) agrees well with the Hα SFR of 0.4 M ⊙ yr −1 . We find a 2.3σ marginal detection of spinning dust emission, with a 30 GHz amplitude of 0.7 ± 0.3 Jy, compared to the ~1 Jy expected from Galactic AME- 100 μm ratios. We investigate the dust heating mechanism across M31. By comparing the colour ratios between Planck and Herschel bands with Spitzer 3.6 and 24 μm data, we find that dust dominating the longer wavelength emission (>0.3 mm) is heated by the diffuse stellar population (as traced by 3.6 μm emission), with the dust dominating the shorter wavelength emission heated by a mix of the old stellar population and star-forming regions (as traced by 24 μm emission). Fig. 4 shows the colour ratios for various bands (top row), and the fraction of the emission that is attributable to star formation in each colour ratio (bottom row) for the Planck and Herschel data; only the last ratio is dominated by the star-formation contribution. We also fit spectral energy distributions (SEDs) for individual 5′ pixels and quantify the dust properties across the galaxy, taking into account the different heating mechanisms. Two examples of these are shown in Fig. 5 for pixels in the nuclear region (top) and the northern edge of the 10 kpc ring (bottom). Red points are the flux densities measured in the pixels; blue points are the flux densities after rescaling using the colour ratios to only fit the cold dust contribution. In the nuclear region these two are the same; in the ring there is a difference between the two, which represents a decrease in temperature from 16.2 K to 15.5 K, and a 10 % increase in dust mass. The fitted dust parameters for the rescaled SEDs, with a fixed spectral index of 2.0, are shown in map form in Fig. 6. We find that there is a linear decrease in temperature with galactocentric distance for dust heated by the old stellar population, as would be expected, with temperatures ranging from around 22 K in the nucleus to 14 K outside of the 10 kpc ring. We have also used a variable spectral index to fit the data, and find that the spectral index traces the heating from the old stellar population rather than measuring the dust grain properties. A&A (submitted), arXiv:1407.5452 Right Ascension (J2000) Declination (J2000) +40:00 +41:00 +42:00 +43:00 28.4 GHz (10.5 mm) -3.75 -3.25 log(T RJ (K)) 44.1 GHz (6.8 mm) -4.0 -3.5 log(T RJ (K)) 70.4 GHz (4.3 mm) -4.0 -3.5 log(T RJ (K)) +40:00 +41:00 +42:00 +43:00 100 GHz (3.0 mm) -4.25 -3.75 log(T RJ (K)) 143 GHz (2.1 mm) -4.25 -3.75 log(T RJ (K)) 217 GHz (1.38 mm) -4.0 -3.5 log(T RJ (K)) 00:50 00:40 +40:00 +41:00 +42:00 +43:00 353 GHz (850 μm) -4.0 -3.5 log(T RJ (K)) 00:50 00:40 545 GHz (550 μm) -4.0 -3.5 -3.0 log(T RJ (K)) 00:50 00:40 857 GHz (350 μm) -4.0 -3.5 -3.0 log(T RJ (K)) Right Ascension (J2000) Declination (J2000) +40:00 +41:00 +42:00 +43:00 217 GHz (1.38 mm) No CMB subtraction -4.0 -3.5 log(T RJ (K)) 217 GHz (1.38 mm) CMB-subtracted -4.0 -3.5 log(T RJ (K)) +40:00 +41:00 +42:00 +43:00 SMICA CMB map -400 0 400 T CMB (μK) Commander CMB map -400 0 400 T CMB (μK) 00:50 00:40 +40:00 +41:00 +42:00 +43:00 SEVEM CMB map -400 0 400 T CMB (μK) 00:50 00:40 NILC CMB map -400 0 400 T CMB (μK) 10 0 10 1 10 2 10 3 10 4 1 10 100 1000 0.1 1 10 100 1000 Flux density (Jy) Frequency (GHz) Wavelength (mm) Synchrotron Free-free CMB Thermal dust AME Model Archival data Planck WMAP Herschel 00:50 00:40 Right Ascension (J2000) +40:00 +40:30 +41:00 +41:30 +42:00 +42:30 Declination (J2000) Surface Density 4.0 4.5 5.0 log(M O • kpc -2 ) 00:50 00:40 Right Ascension (J2000) Temperature 15 20 K 00:50 00:40 Right Ascension (J2000) χ 2 0.0 2.0 4.0 10 -1 10 0 10 1 10 2 100 1000 10000 10 100 1000 Flux density (Jy) Frequency (GHz) (b) 10 -1 10 0 10 1 10 2 100 1000 10000 10 100 1000 Flux density (Jy) Frequency (GHz) Wavelength (μm) (a) Right Ascension (J2000) Declination (J2000) +40:00 +40:30 +41:00 +41:30 +42:00 +42:30 S P857 /S P545 3.0 3.5 E SF /E Total (S P857 /S P545 ) 0.0 0.5 1.0 +40:00 +40:30 +41:00 +41:30 +42:00 +42:30 S H857 /S H600 2.5 3.0 E SF /E Total (S H857 /S H600 ) 0.0 0.5 1.0 +40:00 +40:30 +41:00 +41:30 +42:00 +42:30 S H1200 /S H857 2.0 2.5 E SF /E Total (S H1200 /S H857 ) 0.0 0.5 1.0 +40:00 +40:30 +41:00 +41:30 +42:00 +42:30 S H1870 /S H1200 1.0 2.0 E SF /E Total (S H1870 /S H1200 ) 0.0 0.5 1.0 +40:00 +40:30 +41:00 +41:30 +42:00 +42:30 S H3000 /S H1870 0.4 0.8 E SF /E Total (S H3000 /S H1870 ) 0.0 0.5 1.0 00:50 00:40 +40:00 +40:30 +41:00 +41:30 +42:00 +42:30 S S4280 /S H3000 0.2 0.4 00:50 00:40 E SF /E Total (S S4280 /S H3000 ) 0.0 0.5 1.0 This research was funded by an STFC Consolidated Grant (no. ST/L000768/1) and an ERC Starting (Consolidator) Grant (no. 307209). The Andromeda Galaxy (M31) is one of a few galaxies that has sufficient angular size on the sky to be resolved by Planck. We use colour ratios to investigate the dust heating method in M31, finding that the dust seen by Planck is heated by the diffuse stellar population. We fit SEDs to the individual pixels, measuring the dust temperature and mass before and after rescaling the SEDs to consider just the dust heated by the diffuse stellar population. We also measure the integrated SED, finding a large amount of free-free emission, and a 2.3σ marginal detection of AME. M. Peel, on behalf of the Planck Collaboration
Transcript of Planck intermediate results. XXV. The Andromeda Galaxy as ... · The Andromeda Galaxy as seen by...
Planck intermediate results. XXV. The Andromeda Galaxy as seen by PlanckJodrell Bank Centre for Astrophysics, School of Physics and Astronomy, The University of Manchester
Fig. 1: CMB subtraction in M31
Fig. 2: CMB-subtracted maps at all Planck bands.
Fig. 3: The integrated SED of M31.
Right: Fig. 4: Identifying the dust heating mechanisms.
Fig. 5: SEDs of individual pixels.
Fig. 6: Fitted dust parameters to the cold dust.
Accurate CMB subtraction is important for M31 given the similarities in angular scales between M31 and the CMB. Fig. 1 shows the different Planck CMB maps in the M31 region, and the SMICA CMB-subtracted 217 GHz (1.38 mm) map.
Fig. 2 shows the CMB-subtracted Planck maps. Planck has detected M31 in all wavebands and clearly resolves multiple spiral arms and sub-features at >100 GHz (<3 mm). A number of features are clearly visible, such as the outermost spiral arm structures at 545/857 GHz (550/350 µm; bottom-right of each panel), as well as NGC 205 and a bright background quasar.
The integrated SED of M31, shown in Fig. 3, is well-fitted with a global dust temperature of 18.2 ± 1.0 K, a spectral index of 1.62 ± 0.11, and a significant amount of free-free emission at 20–60 GHz, which when
converted into a star formation rate (SFR) agrees well with the Hα SFR of 0.4 M⊙ yr−1. We find a 2.3σ marginal detection of spinning dust emission, with a 30 GHz amplitude of 0.7 ± 0.3 Jy, compared to the ~1 Jy expected from Galactic AME- 100 µm ratios.
We investigate the dust heating mechanism across M31. By comparing the colour ratios between Planck and Herschel bands with Spitzer 3.6 and 24 µm data, we find that dust dominating the longer wavelength emission ( ︎>0.3 mm) is heated by the diffuse stellar population (as traced by 3.6 µm emission), with the dust dominating the shorter wavelength emission heated by a mix of the old stellar population and star-forming regions (as traced by 24 µm emission).
Fig. 4 shows the colour ratios for various bands (top row), and the fraction of the emission that is attributable to star formation in each colour ratio (bottom row) for the Planck and Herschel data; only the last ratio is dominated by the star-formation contribution.
We also fit spectral energy distributions (SEDs) for individual 5′ pixels and quantify the dust properties across the galaxy, taking into account the different heating mechanisms. Two examples of these are shown in Fig. 5 for pixels in the nuclear region (top) and the northern edge of the 10 kpc ring (bottom). Red points are the flux densities measured in the pixels; blue points are the flux densities after rescaling using the colour ratios to only fit the cold dust contribution. In the nuclear region these two are the same; in the ring there is a difference between the two, which represents a decrease in temperature from 16.2 K to 15.5 K, and a 10 % increase in dust mass.
The fitted dust parameters for the rescaled SEDs, with a fixed spectral index of 2.0, are shown in map form in Fig. 6. We find that there is a linear decrease in temperature with galactocentric distance for dust heated by the old stellar population, as would be expected, with temperatures ranging from around 22 K in the nucleus to 14 K outside of the 10 kpc ring. We have also used a variable spectral index to fit the data, and find that the spectral index traces the heating from the old stellar population rather than measuring the dust grain properties.
A&A (submitted), arXiv:1407.5452
Right Ascension (J2000)
Decl
inatio
n (
J2000)
+40:00
+41:00
+42:00
+43:00
28.4 GHz (10.5 mm)
-3.75 -3.25log(TRJ (K))
44.1 GHz (6.8 mm)
-4.0 -3.5log(TRJ (K))
70.4 GHz (4.3 mm)
-4.0 -3.5log(TRJ (K))
+40:00
+41:00
+42:00
+43:00
100 GHz (3.0 mm)
-4.25 -3.75
log(TRJ (K))
143 GHz (2.1 mm)
-4.25 -3.75log(TRJ (K))
217 GHz (1.38 mm)
-4.0 -3.5log(TRJ (K))
00:50 00:40
+40:00
+41:00
+42:00
+43:00
353 GHz (850 µm)
-4.0 -3.5log(TRJ (K))
00:50 00:40
545 GHz (550 µm)
-4.0 -3.5 -3.0log(TRJ (K))
00:50 00:40
857 GHz (350 µm)
-4.0 -3.5 -3.0log(TRJ (K))
Right Ascension (J2000)
De
clin
atio
n (
J20
00
)
+40:00
+41:00
+42:00
+43:00
217 GHz (1.38 mm)No CMB subtraction
-4.0 -3.5log(TRJ (K))
217 GHz (1.38 mm)CMB-subtracted
-4.0 -3.5log(TRJ (K))
+40:00
+41:00
+42:00
+43:00
SMICA CMB map
-400 0 400TCMB (µK)
Commander CMB map
-400 0 400TCMB (µK)
00:50 00:40
+40:00
+41:00
+42:00
+43:00
SEVEM CMB map
-400 0 400TCMB (µK)
00:50 00:40
NILC CMB map
-400 0 400TCMB (µK)
100
101
102
103
104
1 10 100 1000
0.1 1 10 100 1000
Flux
den
sity
(Jy)
Frequency (GHz)
Wavelength (mm)
Synchrotron
Free-free
CMB
Thermal dust
AME
ModelArchival dataPlanckWMAPHerschel
00:50 00:40Right Ascension (J2000)
+40:00
+40:30
+41:00
+41:30
+42:00
+42:30
Decl
inatio
n (
J2000)
Surface Density
4.0 4.5 5.0log(MO •
kpc-2)
00:50 00:40Right Ascension (J2000)
Temperature
15 20K
00:50 00:40Right Ascension (J2000)
χ2
0.0 2.0 4.0
10-1
100
101
102
100 1000 10000
10 100 1000
Flu
x d
en
sity
(Jy
)
Frequency (GHz)
Wavelength (µm)
(b)
10-1
100
101
102
100 1000 10000
10 100 1000
Flu
x d
en
sity
(Jy
)
Frequency (GHz)
Wavelength (µm)
(a)
Right Ascension (J2000)
Decl
inatio
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J2000)
+40:00
+40:30
+41:00
+41:30
+42:00
+42:30
SP545/SP353
3.5 4.0
ESF/ETotal (SP545/SP353)
0.0 0.5 1.0
+40:00
+40:30
+41:00
+41:30
+42:00
+42:30
SP857/SP545
3.0 3.5
ESF/ETotal (SP857/SP545)
0.0 0.5 1.0
+40:00
+40:30
+41:00
+41:30
+42:00
+42:30
SH857/SH600
2.5 3.0
ESF/ETotal (SH857/SH600)
0.0 0.5 1.0
+40:00
+40:30
+41:00
+41:30
+42:00
+42:30
SH1200/SH857
2.0 2.5
ESF/ETotal (SH1200/SH857)
0.0 0.5 1.0
+40:00
+40:30
+41:00
+41:30
+42:00
+42:30
SH1870/SH1200
1.0 2.0
ESF/ETotal (SH1870/SH1200)
0.0 0.5 1.0
+40:00
+40:30
+41:00
+41:30
+42:00
+42:30
SH3000/SH1870
0.4 0.8
ESF/ETotal (SH3000/SH1870)
0.0 0.5 1.0
00:50 00:40
+40:00
+40:30
+41:00
+41:30
+42:00
+42:30
SS4280/SH3000
0.2 0.4
00:50 00:40
ESF/ETotal (SS4280/SH3000)
0.0 0.5 1.0
This research was funded by an STFC Consolidated Grant (no. ST/L000768/1) and an ERC Starting (Consolidator) Grant (no. 307209).
The Andromeda Galaxy (M31) is one of a few galaxies that has sufficient angular size on the sky to be resolved by Planck. We use colour ratios to investigate the dust heating method in M31, finding that the dust seen by Planck is heated by the diffuse stellar population. We fit SEDs to the individual pixels, measuring the dust temperature and mass before and after rescaling the SEDs to consider just the dust heated by the diffuse stellar population. We also measure the integrated SED, finding a large amount of free-free emission, and a 2.3σ marginal detection of AME.
M. Peel, on behalf of the Planck Collaboration
