HERSCHEL OBSERVATIONS OF MAJOR MERGER PAIRS AT z = 0: DUST MASS AND STAR FORMATION

Abstract

We present Herschel PACS and SPIRE far-infrared (FIR) and submillimeter imaging observations for a large K-band selected sample of 88 close major-merger pairs of galaxies (H-KPAIRs) in 6 photometric bands (70, 100, 160, 250, 350, and 500 μm). Among 132 spiral galaxies in the 44 spiral-spiral (S+S) pairs and 44 spiral-elliptical (S+E) pairs, 113 are detected in at least 1 Herschel band. The star formation rate (SFR) and dust mass (M dust ) are derived from the IR SED fitting. The mass of total gas (M gas ) is estimated by assuming a constant dust-to-gas mass ratio of 0.01. Star-forming spiral galaxies (SFGs) in S+S pairs show significant enhancements in both specific star formation rate (sSFR) and star formation efficiency (SFE), while having nearly the same gas mass compared to control galaxies. On the other hand, for SFGs in S+E pairs, there is no significant sSFR enhancement and the mean SFE enhancement is significantly lower than that of SFGs in S+S pairs. This suggests an important role for the disk-disk collision in the interaction-induced star formation. The M gas of SFGs in S+E pairs is marginally lower than that of their counterparts in both S+S pairs and the control sample. Paired galaxies with and without interaction signs do not differ significantly in their mean sSFR and SFE. As found in previous works, this much larger sample confirms that the primary and secondary spirals in S+S pairs follow a Holmberg effect correlation on sSFR.

Major-Merger Galaxy Pairs at Z = 0: Dust Properties and Companion Morphology

“…We have omitted the E+E option from further study as they do not represent a likely candidate for star formation enhancements due to lower relative ISM abundance. The KPAIR sample has been refined in an effort to understand the star forming properties in the observing campaigns of Xu et al (2010) and Cao et al (2016) resulting in the current H-KPAIR sample examined in this paper. Cao et al (2016) demonstrate the spirals in S+S pairs show significant enhancement in sSFR and star formation efficiency (SFE) while spirals in S+E pairs do not exhibit these enhancements.…”

“…We describe the sample characteristics chosen to examine the dust properties in these close major merger pairs populations and their relation to the star formation properties presented in Cao et al (2016). Cao et al (2016) present the Far-Infrared (FIR) data used in the present analysis but concentrate on the derivation of SFR and dust mass as an indication of gas content with the fitting models of Draine & Li (2007) (DL07).…”

“…Here as in Cao et al (2016) we begin with the Herschel subset (H-KPAIRS) sample developed by further restricting the selection of pairs with three criteria : 1) keep only pairs where both pair members have spectroscopically confirmed redshifts to avoid false pairs, 2) remove elliptical+elliptical pairs to facilitate the study of star forming galaxies, and 3) keep only pairs with recession velocity v>2000 km s −1 . The resulting H-KPAIR sample contains 88 galaxy pairs (44 are Spiral +Spiral (S+S) and 44 are Spiral + Elliptical (S+E)) with a median redshift z∼0.04.…”

“…Cao et al (2016) present the Far-Infrared (FIR) data used in the present analysis but concentrate on the derivation of SFR and dust mass as an indication of gas content with the fitting models of Draine & Li (2007) (DL07). In this present work we take the further steps of adding the near and mid-infrared data to the analysis in order to understand the PAH contribution fractions and dust characteristics such as incident radiation intensity for both the pair and control samples.…”

“…The KPAIR sample has been refined in an effort to understand the star forming properties in the observing campaigns of Xu et al (2010) and Cao et al (2016) resulting in the current H-KPAIR sample examined in this paper. Cao et al (2016) demonstrate the spirals in S+S pairs show significant enhancement in sSFR and star formation efficiency (SFE) while spirals in S+E pairs do not exhibit these enhancements. Xu et al (2012) also found no significant sSFR enhancement in massive S+E pairs at any redshift.…”