THE FAR-INFRARED FIR = IRAS region (60-100 micron) TIR = 8-1000 micron (1 micron = 1A/10^4) Silva et...
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Transcript of THE FAR-INFRARED FIR = IRAS region (60-100 micron) TIR = 8-1000 micron (1 micron = 1A/10^4) Silva et...
![Page 1: THE FAR-INFRARED FIR = IRAS region (60-100 micron) TIR = 8-1000 micron (1 micron = 1A/10^4) Silva et al. 1998 0.1 1 10 100 1000 Lambda (micron) Log λ L.](https://reader035.fdocument.pub/reader035/viewer/2022062304/56649eaa5503460f94bae6ce/html5/thumbnails/1.jpg)
THE FAR-INFRARED
FIR = IRAS region (60-100 micron)
TIR = 8-1000 micron (1 micron = 1A/10^4)
Silva et al. 1998
0.1 1 10 100 1000
Lambda (micron)
Log
λ L λ
(1
0^30
erg
s/s)
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THE FAR-INFRARED
Part of the luminosity of a galaxy is absorbed by interstellar dust and re-emitted in the IR (10-300 micron)
The most heavily extincted part of the stellar continuum is the UV – therefore the FIR emission can be a sensitive tracer of young stellar populations (and current SF)
Silva et al. 1998
0.1 1 10 100 1000
Lambda (micron)
Lambda (micron)
Log
λ L λ
(1
0^30
erg
s/s)
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THE FAR-INFRARED
Two contributions to the FIR emission:
a) young stars in starforming regions (warm, λ ~ 60 micron)
b) an “infrared cirrus” component (cooler, λ>100 micron), associated with more extended dust heated by the interstellar radiation field
Whenever
young stars dominate the UV-visible emission and
dust opacity is high
then a) dominates and the FIR is a good indicator of SFR
This is the case in Luminous and Ultraluminous Infrared Galaxies, and mostly works also in late-type starforming galaxies
In at least some of the early-type galaxies the FIR emission is due to older stars or AGNs, therefore in these the FIR emission is not a good tracer of SF
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THE SFR-FIR CALIBRATION“One” calibration based on spectrophotometric models and found :
a) Assuming the dust reradiates all the bolometric luminosity (!) (Optically thick case)
b) For starbursts (constant SFR) of ages < 10^8 yrs:
SFR(solar masses/yr) = 4.5 X 10-44 LFIR (ergs/s)
where LFIR is the luminosity integrated over 8-1000 micron
(Kennicutt 1998)
Most of other published calibrations within 30%.
In quiescent starforming galaxies, the contribution from older stars will tend to lower the coefficient above.
Keeping in mind that no calibration applies to all galaxy types and SFHs…
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Indicators of ongoing star-formation activity - Timescales
Emission lines < 3 x 107 yrs
UV-continuum emission it depends…
FIR emission < a few 10^7 (but…it depends on the dominant population of stars heating the dust)
Radio emission as FIR (?)
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LATE-TYPE STARFORMING GALAXIES
The FIR luminosity correlates with other SFR tracers such as the UV continuum and Halpha luminosities.
FIR
flu
x
Halpha flux
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MIR EMISSION AS A SFR INDICATOR
0.1 1 10 100 1000
Lambda (micron)
Log
λ L λ
(1
0^30
erg
s/s) Near-IR J,H,K bands
12000,16000,22000 A =
1.2, 1.6, 2.2 micron
Mid-IR 6-20 micron
Far-IR >25 micron (60-100)
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MIR EMISSION AS A SFR INDICATOR
In principle, complex relation between MIR emission and SFR:
continuum emission by warm small dust grains heated by young stars or an AGN
unidentified infrared bands (UIBs a family of features at 3.3, 6.2, 7.7, 8.6, 11.3, 12.7 micron) thought to result from C-C and C-H vibrational bands in hydrocarbons (large, carbon-rich molecules as polycyclic aromatic hydrocarbins, or PAHs?)
continuum emission from the photosphere of evolved stars
emission lines from the ionized interstellar gas
e.g. Genzel & Cesarsky ARAA 2000
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FROM MIR TO FIR
Empirical relation between MIR(typically 15micron) and FIR luminosities
Chary & Elbaz 2001: strong correlations between luminosity at 12 and 15micron and total IR luminosity (8-1000micron)
As it is done for calibrating OII vs Halpha…
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FROM MIR TO FIR
….much better correlated than with the B band (Chary & Elbaz 2001)
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FROM MIR TO FIR: ANOTHER METHOD
Infrared (8-1000micron) luminosities are interpolated between the MIR and the radio fluxes using best-fitting templates of various starbursts/starforming galaxies and AGNs. (e.g. Flores et al. 1999)
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SUBMILLIMITER OBSERVATIONS
Sampling the IR emission with 850micron fluxes (e.g. Hughes et al. 1998)
Negative K-corrections – the flux density of a galaxy at ~800micron with fixed intrinsic luminosity is expected to be roughly constant at all redshifts 1 < z < 10
While the Lyman break technique prefentially selects UV-bright starbursts, the submillimiter emission best identifies IR luminous starbursts. The approaches are complementary (debated relation between the two populations).
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Negative k-correction for sub-mm sources
Blain et al (2002) Phys. Rept, 369,111
K-correction is the dimming due to the (1+z) shifting of the wavelength band (and its width) for a filter with response S()
In the Rayleigh-Jeans tail of the dust blackbody spectrum, galaxies get brighter as they are redshifted to greater distance!
k(z) (1 z)F ()S()d
F ( 1z )S()d
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THE FIR-RADIO CORRELATION
Condon ARAA 1992
Van der Kruit 1971, 1973
Log LFIR
Log
L1
.49G
hz
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THE FIR-RADIO CORRELATION
Condon ARAA 1992
is surprising !!
For FIR: “warm” and “cirrus” contribution
Radio emission originates from complex and poorly understood physics of cosmic-ray generation and energy transfer:
Non-thermal component (synchrotron emission of relativistic electrons spiraling in a galaxy magnetic field)
Thermal component (free-free emission from ionized hydrogen in HII regions)
SNae
O, B stars
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THE FIR-RADIO CORRELATION
Condon ARAA 1992
Non-thermal
Thermal
is still surprising
α ~ 0.8
Due to difference in spectral shape, the relative contribution varies with frequency. At <5Ghz (1.4Ghz commonly used), non-thermal conponent dominates (90%) in luminous galaxies
α ~ 0.1
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Indicators of ongoing star-formation activity - Timescales
Emission lines < 3 x 107 yrs
UV-continuum emission it depends…
FIR emission < a few 10^7 (but…)
Radio emission as FIR (?)
(Could be higher: relativistic electrons have lifetimes ≤ 10^8 yr)
![Page 18: THE FAR-INFRARED FIR = IRAS region (60-100 micron) TIR = 8-1000 micron (1 micron = 1A/10^4) Silva et al. 1998 0.1 1 10 100 1000 Lambda (micron) Log λ L.](https://reader035.fdocument.pub/reader035/viewer/2022062304/56649eaa5503460f94bae6ce/html5/thumbnails/18.jpg)
2) SFR = 2.0 X 10-41 L([OII]) E(Hα) ergs/s
3) SFR = 1.4 X 10-28 Lnu ergs/s/Hz (L dust-corrected)
1) SFR = 0.9 X 10-41 L(Hα) E(Hα) ergs/s
4) SFR = 4.5 X 10-44 LFIR (ergs/s)
(Solar luminosities)
6) SUBMILLIMITRICO COME FIR
5)
7)
8)
erg/s
primaria
primaria
primaria
secondaria
secondaria
secondaria
secondaria
secondaria
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1 + z
SF
R (
Msu
n y
r-1 M
pc-3
)
Hopkins 2004
Evolution of SFR density with redshift, using a common obscuration correction where necessary. The points are color-coded by rest-frame wavelength as follows: Blue: UV; green: [O II]; red: H and H ; pink: X-ray, FIR, submillimeter, and radio. The solid line shows the evolving 1.4 GHz LF derived by
Haarsma et al. (2000). The dot-dashed line shows the least-squares fit to all the z < 1 data points, log( *)
= 3.10 log(1 + z) - 1.80. The dotted lines show pure luminosity evolution for the Condon (1989
) 1.4 GHz LF, at rates of Q = 2.5 (lower dotted line) and Q = 4.1 (upper dotted line). The dashed line
shows the "fossil" record from Local Group galaxies (Hopkins et al. 2001b).
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