9 Star formation rate

So far this is the largest H$_\alpha$ catalogue of HCG galaxies having H$_\alpha$calibrated fluxes. Such a sample constitutes a powerful tool to perform quantitative analysis on the recent star formation rate inside HCG galaxies. We have derived the SFR for the galaxies of our sample using the results of Kennicutt (1983), which relate the SFR to H$_\alpha$ luminosity through the relation:

$${\rm SFR(total)}= \frac{L({\rm H}_\alpha)} {1.12\ 10^{41}~{\rm erg~s}^{-1}} M_\odot~{\rm yr}^{-1}$$ (16)

where a Salpeter initial mass function with an upper mass cutoff of 100 $M_\odot$ has been assumed. SFR inferred from luminosities for the 73 galaxies detected and for 22 upper limits estimated is shown in Table 10 as follows:
Column 1: Name of detected galaxies;
Column 2: SFR inferred from isophotal luminosities $L_{\rm iso}$ corrected for Galactic Extinction, SFR$_{\rm iso}$ (2);
Column 3: SFR inferred from isophotal luminosities, corrected for both Galactic and Internal Extinction, SFR$_{\rm iso}$ (3);
Column 5: name of galaxies for which we have computed the upper limits;
Column 6: SFR inferred from upper limit to luminosity, corrected for Galactic Extinction, SFR$_{\rm ul}$ (2);
Column 7: SFR inferred from upper limit to luminosity, corrected for both Galactic and Internal Extinction, SFR$_{\rm ul}$ (3).

In Fig. 5 we show the distribution of SFR$_{\rm iso}$ computed taking into account (dotted line) and without taking into account (solid line) Internal Extinction. The two distributions are quite similar, as confirmed also by a Kolmogorov-Smirnov test.

  

Figure 5: Distribution of SFR for the 73 detected galaxies derived from $L_{\rm iso}$. The solid histogram represents the SFR$_{\rm iso}$ (2) and the dotted histogram represents the SFR$_{\rm iso}$ (3) (see Table 10). The width of each bin is 0.1 [$M_\odot$ yr-1]