Wednesday, 14th December at 2.00pm @ JAC

ABSTRACT: We have investigated the optical properties of 4248 infrared galaxies (IRGs) by positionally matching data from the IRAS and SDSS DR3. Our sample includes 3 hyper luminous infrared galaxies (L >10^13Lsun) and 178 ultra luminous infrared galaxies (10^12Lsun < L < 10^13Lsun ). Our findings are as follows:

(i) more IR luminous galaxies tend to have a smaller local galaxy density, being consistent with the picture where luminous IRGs are created by the merger-interaction of galaxies that happens more often in lower density regions;

(ii) the fractions of AGN increase as a function of Lir;

(iii) there is a good correlation between Lir and L[OIII] for AGNs, suggesting that both of the parameters can be a good estimator of the total power of AGNs;

(iv) a good correlation is found between Lir and the optically estimated star formation rate (SFR) for star-forming galaxies, suggesting that Lir is a good indicator of galaxy SFR. However, caution is needed when the SFR is estimated using Lir, i.e., high SFR galaxies selected by Lir are frequently merger/interaction, whereas high SFR galaxies selected by their optical emission are often normal spiral or Magellanic-cloud like irregular galaxies.

(v) more IR luminous galaxies have a slightly larger H-alpha/H-beta ratio;

(vi) more IR luminous galaxies have a more centrally-concentrated morphology, being consistent with the morphological appearance of galaxy-galaxy merger remnants. Optical images of ultra/very luminous infrared galaxies also show frequent signs of merger/interaction.

(vii) comparison with the SED synthesis models indicate that the majority of luminous infrared galaxies (L > 10^11Lsun) may be in a post-starburst phase, sharing a similar (but not the same) merger/interaction origin with E+A galaxies.