The K-band luminosity functions of super star clusters in luminous infrared galaxies, their slopes and the effects of blending

Abstract

Super star clusters (SSCs) are typically found in interacting galaxies and trace an extreme form of star-formation. We present a K-band study of SSC candidates in a sample of local luminous infrared galaxies (LIRGs) using two adaptive optics instruments (VLT/NACO and Gemini/ALTAIR/NIRI). In addition to facilitating SSC detections in obscured environments, this work introduces SSC studies in hosts with higher star-formation rates (SFRs) than most previous studies. We find that the luminosity functions (LFs) of the clusters are reasonably well-fitted by a single power-law with the values of the index α ranging between 1.5 to 2.4 with an average value of α ≈ 1.9. This value appears to be less steep than the average α ≈ 2.2 in normal spiral galaxies. Due to the host galaxy distances involved (median D L ∼ 70 Mpc) blending effects have to be taken into account, and are investigated using Monte Carlo simulations of blending effects for LFs and a photometric SSC analysis of the wellstudied Antennae system which is artificially redshifted to distances of our sample. While blending tends to flatten LFs our analyses show that ∆α is less than ∼ 0.1 in our sample. The simulations also show that in the luminosity range, M K < −13, considered in this work the extracted SSC luminosities are generally dominated by a single dominant star cluster rather than several knots of SF. We present resolutionand distance-dependent SSC surface density confusion limits and show how blending rates and aperture sizes affect the LFs. The smallest possible apertures should be used in crowded regions.

Star formation and AGN activity in a sample of local luminous infrared galaxies through multiwavelength characterization

“…Finally, we did not find any correlation between the radio and near-IR total luminosities, nor between the radio to near-IR ratio maps and the position of the known SSCs in these galaxies (Randriamanakoto et al 2013b). …”

“…The extreme CCSN rate and SFR of IRAS 18293-3413, together with the controversy on its merger stage and its extremely steep spectrum (α = −1.73 ± 0.70, see section 4.4), turns it into an interesting case, likely hosting a very rich starburst. This is supported by the detection of hundreds of super star clusters (SSCs) in the field of IRAS 18293-3413 (Randriamanakoto et al 2013b). We note however, the lower SN rate derived with a previous simpler model (1 SN yr −1 ; Mattila et al 2007a).…”

“…Data from ALTAIR/NIRI come from a multi-epoch survey intended for the detection and study of nuclear core-collapse supernovae (CCSNe We reduced the near-IR data using standard IRAFbased tasks, including flat-fielding and sky subtraction, and created the final images by average-combining individual frames from different epochs after having shifted them to a common reference. A detailed description of the reduction process of the ALTAIR/NIRI and NACO/VLT data is presented in Randriamanakoto et al (2013b), while GeMS/GSAOI data are part of the SUNBIRD survey (Kool et al 2016, in prep.). In multi-epoch data, we found no evidence of variability among the different individual epochs above 2-σ.…”

“…We then added the WCS information in the FITS header of our targets using these intermediate images (see Randriamanakoto et al 2013b, for details). We estimate the astrometry calibration uncertainty to be 0.15 .…”

Shutting down or powering up a (U)LIRG? Merger components in distinctly different evolutionary states in IRAS 19115−2124 (the Bird)

“…These could be very young Super Star Clusters, or Young Massive Clusters, or at least complexes thereof, as is often seen in nearby gas-rich galaxy mergers or other intense massive star-formation regions (Randriamanakoto et al 2013;Väisänen et al 2014, and references therein). K-band adaptive optics imaging showed a number of point-like sources in this galaxy, concentrating on the side facing the larger galaxy.…”