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 λ (10^30 ergs/s)

2. 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) Log λ L λ (10^30 ergs/s)

3. 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

4. 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 L FIR (ergs/s) where L FIR 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…

5. Indicators of ongoing star-formation activity - Timescales Emission lines < 3 x 10 7 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 (?)

6. LATE-TYPE STARFORMING GALAXIES The FIR luminosity correlates with other SFR tracers such as the UV continuum and Halpha luminosities. FIR flux Halpha flux

7. MIR EMISSION AS A SFR INDICATOR 0.1 1 10 100 1000 Lambda (micron) Log λ L λ (10^30 ergs/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)

8. 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

9. 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…

10. FROM MIR TO FIR ….much better correlated than with the B band (Chary & Elbaz 2001)

11. 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)

12. 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).

13. 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!

14. THE FIR-RADIO CORRELATION Condon ARAA 1992 Van der Kruit 1971, 1973 Log L FIR Log L 1.49Ghz

15. 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

16. 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

17. Indicators of ongoing star-formation activity - Timescales Emission lines < 3 x 10 7 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)

18. 2) SFR = 2.0 X 10 -41 L([OII]) E(H α ) ergs/s 3) SFR = 1.4 X 10 -28 L nu ergs/s/Hz (L dust-corrected) 1) SFR = 0.9 X 10 -41 L(H α ) E(H α ) ergs/s 4) SFR = 4.5 X 10 -44 L FIR (ergs/s) (Solar luminosities) 6) SUBMILLIMITRICO COME FIR 5) 7) 8) erg/s primaria secondaria

19. 1 + z SFR (M sun yr -1 Mpc -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).200019892001b