## Galactic Cirrus and Zodiacal Light

### 60 Kelvin 50 AU Dyson shell

\Large B(\lambda) = \LARGE { { 2 h c } \over { \lambda^3 \left( e^{ h c / \lambda k T } - 1 \right) } } = { { 4e19 ~ Jy / sr ~ {\mu}m^3 } \over { \lambda^3 \left( e^{ 240 {\mu} m / \lambda } - 1 \right) } }

This is for an infinite resolution imager - at large distances, the power is the image angular area divided by the pixel angular area. This scales the intensity way down for distant Dyson shells. If the ratio of shell intensity to background is H , the pixel size in arcseconds is px , the shell radius in AU is r , and the distance in parsecs is R , then the angular size A is:

A ~ = ~ \pi ( r / R )^2

H ~ = ~ px^2 / A = ( px ~ R / r ) ^2 / \pi

R ~ = ~ ( 50" / px ) \sqrt{ \pi H}

### Detectability

px is 90" (90 arcseconds) for IRAS, 12" for WISE, and .11" for JWST. It is 2.3" for Spitzer MIPS (Multiband Imaging Photometer for Spitzer) 24 μm (128x128 pixels) and 9.4" for Spitzer 70 μm (16x32 pixels).

R ~=~ 0.96 \sqrt{ H } for IRAS, 7.2 \sqrt{ H } for WISE, and 790 \sqrt{ H } for JWST. Of those three, only IRAS has sensors for wavelengths longer than 25 μm. R ~=~ 38 \sqrt{ H } for 24 μm Spitzer and 9.2 \sqrt{ H } for 70 μm Spitzer.

### Disk

Assume 3 pixels wide for identification of a disk. IRAS can "see" a 270" disk ( 100/270 = 0.37 pc away - nothing expected), WISE can see a disk (100/12 = 8.3 pc away ), etc:

 Pixel Image 1 MJy/sr 80 MJy/sr IRAS 90" 0.37 200 mJy/px 1.6 Jy/px WISE 12" 2.8 3.4 mJy/px 270 mJy/px Spitzer 24 μm 2.3" 14.5 124 μJy/px 9.8 mJy/px JWST 25 μm 0.11" 300 2.8 nJy/px 220 nJy/px

The graphs at the NASA site are not scaled, but they resemble logarithmic-scaled graphs in Kelsall, 1998, Figure 2. Units MJy/sr.

 Color Blue Blue Blue Blue Cyan Cyan Gren Gren Yelw Yelw Orng Orng Red Red Gray Gray Whit 4.9 μm 0.10 0.14 0.19 0.26 0.35 0.49 0.67 0.92 1.26 1.72 2.37 3.25 4.46 6.12 8.39 11.5 15.8 12 μm 1.58 2.02 2.58 3.29 4.21 5.37 6.86 8.77 11.2 14.3 18.3 23.3 29.8 38.1 48.7 62.2 79.4 25 μm 3.98 4.80 5.79 6.98 8.41 10.1 12.2 14.7 17.8 21.4 25.8 31.2 37.6 45.3 54.6 65.9 79.4 60 μm 1.00 1.31 1.73 2.27 2.99 3.92 5.16 6.78 8.91 11.7 15.4 20.2 26.6 35.0 46.0 60.4 79.4

Are these numbers too small?

The zodiac is highly inclined compared to the galaxy, but these plots show it intersecting near galactic center. This is fortunate if true - we are unlikely to distinguish a Dyson shell where the background is very dense (too confusing) or very thin (radially outwards, fewer candidates) - this puts two problem areas in the same place.

• frequency = 299792 GHz-μm/λ

• Ellis: Z zodiacal, C cirrus
• B 60K 100 AU 1-sun Dyson, full pixel
 Band(um) 12 μm 25 μm 60 μm 70 μm 100 μm frequency 25 THz 12 THz 5 THz 4.3 THz 3 THz Z nW/m²-sr 2800 1800 190 130 42 Z Jy-sr 1.12e7 1.5e7 3.8e6 3.0e6 1.4e6 are these numbers too large?? C nW/m²-sr 4.8 2.3 3.2 4.5 13 C Jy-sr 1.9e4 1.9e4 6.4e4 1.1e5 4.3e5 are these numbers too large?? B Jy-sr 4.8e7 1.7e11 3.5e12 3.9e12 4.0e12 B/(C+Z) 4.3 1.1e4 9.1e5 1.3e6 2.2e6 we may ignore zodiacal measurements H =B/C 2.5e3 8.9e6 5.5e7 3.5e7 9.3e6 assume measurements in galactic plane R IRAS pc 48 2900 7100 -- 2900 R WISE pc 360 21000 -- -- -- R Spitzer pc -- 110000 -- 54000 -- R JWST pc 40000 2400000 -- -- --

Question: In the very short wavelengths, does the presence of a shell block luminosity in a detectable way - a "round hole" in a uniform nebula?

CirrusZodiacal (last edited 2015-10-15 15:51:51 by KeithLofstrom)