Star Formation Rates for Starburst Galaxies From Ultraviolet, Infrared, and Radio Luminosities

Abstract

We present a comparison of star formation rates (SFR) determined from mid-infrared 7.7 µm PAH luminosity [SFR(PAH)], from 1.4 GHz radio luminosity [SFR(radio)], and from far ultraviolet luminosity [SFR(UV)] for a sample of 287 starburst galaxies with z < 0.5 having Spitzer IRS observations. The previously adopted relation log [SFR(PAH)] = log [νL ν (7.7 µm)] -42.57±0.2, for SFR in M ⊙ yr −1 and νL ν (7.7 µm) the luminosity at the peak of the 7.7 µm PAH feature in ergs s −1 , is found to agree with SFR(radio). Comparing with SFR(UV) determined independently from ultraviolet observations of the same sources with the GALEX mission (not corrected for dust extinction), the median log [SFR(PAH)/SFR(UV)] = 1.67, indicating that only 2% of the ultraviolet continuum typically escapes extinction by dust within a starburst. This ratio SFR(PAH)/SFR(UV) depends on infrared luminosity, with form log [SFR(PAH)/SFR(UV)] = (0.53±0.05)log [νL ν (7.7 µm)] -21.5±0.18, indicating that more luminous starbursts are also dustier. Using our adopted relation between νL ν (7.7 µm) and L ir , this becomes log [SFR(PAH)/SFR(UV)]= (0.53±0.05)log L ir -4.11±0.18, for L ir in L ⊙ . Only Blue Compact Dwarf galaxies show comparable or greater SFR(UV) compared to SFR(PAH). We also find that the ratio SFR(PAH)/SFR(UV) is similar to that in infrared-selected starbursts for a sample of Markarian starburst galaxies originally selected using optical classification, which implies that there is no significant selection effect in SFR(PAH)/SFR(UV) using starburst galaxies discovered by Spitzer. These results indicate that SFRs determined with ultraviolet luminosities require dust corrections by a factor of ∼ 10 for typical local starbursts but this factor increases to > 700 for the most luminous starbursts at z ∼ 2.5. Application of this factor explains why the most luminous starbursts discovered by Spitzer at z ∼ 2.5 are optically faint; with this amount of extinction, the optical magnitude of a starburst having f ν (7.7 µm) of 1 mJy should be V ∼ 25.6.

Analysis ofSpitzer-IRS spectra of hyperluminous infrared galaxies

“…After converting these fluxes into luminosities, we estimated the SFR using the relation obtained by Sargsyan & Weedman (2009): log SFR PAH = log λL SB λ (7.7 µm) − 42.57 ± 0.2,…”

“…(3) is calibrated with respect to the total 7.7 µm flux, including both components. In any case, the continuum contribution is typically just ∼10% of the total (Sargsyan & Weedman 2009). Since α 6 is close to unity in all our sources, the relative error of the SB contribution at 6 µm is high.…”

Mid-Infrared Spectral Indicators of Star Formation and Active Galactic Nucleus Activity in Normal Galaxies

“…This method yields considerably smaller EW values as it assigns a nonnegligible fraction of the PAH flux extracted by PAHFIT to the continuum. Figure 12 shows our EWs (Equation (3)) against the 6.2 μm PAH EWs computed by Sargsyan & Weedman (2009) for the SSGSS sample assuming a single Gaussian on a linear continuum between 5.5 μm and 6.9 μm. Their published sample is restricted to SF galaxies defined as having EW(6.2 μm) > 0.4 μm (Weedman & Houck 2009).…”

Multiwavelength study of 230 IRAS FSC galaxies

“…As shown in [23] the comparison of Star Formation Rates (SFR) measured in the infrared and ultraviolet can be used to derive an empirical estimate of extinction for the ultraviolet luminosity. For this purpose in [23], a sample of 287 SB galaxies with z < 0.5 was used having Spitzer IRS observations.…”

“…For this purpose in [23], a sample of 287 SB galaxies with z < 0.5 was used having Spitzer IRS observations. As an infrared flux the mid-infrared 7.7 m μ polycyclic aromatic hydrocarbon (PAH) luminosity [SFR(PAH)] was used.…”