Infrared Background - Revision history

Rebull at 18:47, 13 May 2011

2011-05-13T18:47:44Z

Rebull at 20:42, 22 January 2010

2010-01-22T20:42:45Z

Rebull at 20:42, 22 January 2010

2010-01-22T20:42:12Z

Rebull at 20:41, 22 January 2010

2010-01-22T20:41:49Z

Rebull: /* Zodiacal Light */

2010-01-22T20:40:39Z

Zodiacal Light

Rebull at 20:40, 22 January 2010

2010-01-22T20:40:04Z

Rebull at 20:37, 22 January 2010

2010-01-22T20:37:50Z

New page

=Introduction=

Sources of background noise in the infrared can be very different than those for optical astronomy. The structure of the background effectively increases its noise contribution above what would be calculated based on the flux contributed by all of the sources in a region. The structure contributes directly to the variance of the background as it would be measured by aperture or PSF-fitting photometry extraction software, for example.

==[[Confusion| Source Confusion]]==
Source confusion itself is a source of background noise, and this is covered on a different page.

==Zodiacal Light==
Optical astronomers do not often worry about Zodiacal light, but thermal emission from what is in essence our own remnant dust disk is a source of IR background. Scattered sunlight dominates this component of background at wavelengths shorter than 3.5 microns; at longer wavelengths, thermal emission from the particles themselves dominates this component. See the plot below for an indication of sky brightness as a function of wavelength; see the Solar System Science Overview for images of the zodiacal light.

==Interstellar cirrus==
Emission from the interstellar medium dominates the sky brightness at wavelengths longer than 70 microns at high galactic latitudes, shifting to 45 microns at galactic latitudes around 10 degrees. In the galactic plane, the interstellar medium dominates at all wavelengths with a minimum around 20 microns. See the plot below for an indication of sky brightness as a function of wavelength.

==Cosmic Background==
This is not the IR portion of the CMBR, but rather the integrated light of unresolved galaxies.

{| border="1"
|[[image:leinert.gif]]
| This plot is from Leinert et al, 1998, A&ASS, 127, 1 This is an overview of the sky brightness outside the lower terrestrial atmosphere at high ecliptic and galactic latitudes. Of course, Spitzer will not be affected by airglow, and of course the brightness of the non-terrestrial components are a function of galactic and ecliptic latitude.
|}

=IR Background and Spitzer=

At mid and low ecliptic latitudes, zodiacal light is the dominant source of background for IRAC, IRS, and MIPS 24 microns. The zodiacal background is very significant for the 8 micron channel in IRAC, and in fact sets the upper limit to exposure times by consuming the detector well depth. At mid and low galactic latitudes, the interstellar medium dominates, especially for the MIPS 160 microns. Use Spot (see below) to interactively calculate background estimates for targets. Source confusion is more difficult to quantify, but could be important, depending on where you are looking, which wavelength you use, and what exposure time you select. See the confusion page for some additional references for confusion limits as they apply to Spitzer.

@@ Line 11: / Line 11: @@
 {| border="1"
 |[[image:cobezodi.jpg]]
-| COBE/DIRBE image of the infrared sky. The S-shaped blue streak is the zodiacal light in the plane of our Solar System.
+| COBE/DIRBE image of the infrared sky, in Galactic projection. The S-shaped blue streak is the zodiacal light in the plane of our Solar System.
 |}

@@ Line 10: / Line 10: @@
 {| border="1"
-|[[image:cobezodi.gif]]
+|[[image:cobezodi.jpg]]
 | COBE/DIRBE image of the infrared sky. The S-shaped blue streak is the zodiacal light in the plane of our Solar System.
 |}

@@ Line 7: / Line 7: @@
 ==Zodiacal Light==
-Optical astronomers do not often worry about Zodiacal light, but thermal emission from what is in essence our own remnant dust disk is a source of IR background. Scattered sunlight dominates this component of background at wavelengths shorter than 3.5 microns; at longer wavelengths, thermal emission from the particles themselves dominates this component. See the plot below for an indication of sky brightness as a function of wavelength; you can find pictures of the Zodiacal light elsewhere on line or in astronomy textbooks.
+Optical astronomers do not often worry about Zodiacal light, but thermal emission from what is in essence our own remnant dust disk is a source of IR background. Scattered sunlight dominates this component of background at wavelengths shorter than 3.5 microns; at longer wavelengths, thermal emission from the particles themselves dominates this component. See the plot below for an indication of sky brightness as a function of wavelength; you can find more pictures of the Zodiacal light elsewhere on line or in astronomy textbooks.
 ==Interstellar cirrus==

← Older revision		Revision as of 20:40, 22 January 2010
Line 23:		Line 23:
	=IR Background and Spitzer=		=IR Background and Spitzer=

−	At mid and low ecliptic latitudes, zodiacal light is the dominant source of background for IRAC, IRS, and MIPS 24 microns. The zodiacal background is very significant for the 8 micron channel in IRAC, and in fact sets the upper limit to exposure times by consuming the detector well depth. At mid and low galactic latitudes, the interstellar medium dominates, especially for the MIPS 160 microns. Use Spot ~~(see below)~~ to interactively calculate background estimates for targets. Source confusion is more difficult to quantify, but could be important, depending on where you are looking, which wavelength you use, and what exposure time you select. See the ~~confusion~~ page for some additional references for confusion limits as they apply to Spitzer.	+	At mid and low ecliptic latitudes, zodiacal light is the dominant source of background for IRAC, IRS, and MIPS 24 microns. The zodiacal background is very significant for the 8 micron channel in IRAC, and in fact sets the upper limit to exposure times by consuming the detector well depth. At mid and low galactic latitudes, the interstellar medium dominates, especially for the MIPS 160 microns. Use Spot to interactively calculate background estimates for targets. Source confusion is more difficult to quantify, but could be important, depending on where you are looking, which wavelength you use, and what exposure time you select. See the [[Confusion]] page for some additional references for confusion limits as they apply to Spitzer.

@@ Line 3: / Line 3: @@
 Sources of background noise in the infrared can be very different than those for optical astronomy. The structure of the background effectively increases its noise contribution above what would be calculated based on the flux contributed by all of the sources in a region. The structure contributes directly to the variance of the background as it would be measured by aperture or PSF-fitting photometry extraction software, for example.
-==[[Confusion| Source Confusion]]==
+=[[Confusion| Source Confusion]]=
 Source confusion itself is a source of background noise, and this is covered on a different page.
-==Zodiacal Light==
+=Zodiacal Light=
 Optical astronomers do not often worry about Zodiacal light, but thermal emission from what is in essence our own remnant dust disk is a source of IR background. Scattered sunlight dominates this component of background at wavelengths shorter than 3.5 microns; at longer wavelengths, thermal emission from the particles themselves dominates this component. See the plot below for an indication of sky brightness as a function of wavelength; you can find more pictures of the Zodiacal light elsewhere on line or in astronomy textbooks.
@@ Line 15: / Line 15: @@
-==Interstellar cirrus==
+=Interstellar cirrus=
 Emission from the interstellar medium dominates the sky brightness at wavelengths longer than 70 microns at high galactic latitudes, shifting to 45 microns at galactic latitudes around 10 degrees. In the galactic plane, the interstellar medium dominates at all wavelengths with a minimum around 20 microns. See the plot below for an indication of sky brightness as a function of wavelength.
-==Cosmic Background==
+=Cosmic Background=
 This is not the IR portion of the CMBR, but rather the integrated light of unresolved galaxies.