LOCAL BENCHMARKS FOR THE EVOLUTION OF MAJOR-MERGER GALAXIES—SPITZEROBSERVATIONS OF AK-BAND SELECTED SAMPLE

Abstract

We present Spitzer observations for a sample of close major-merger galaxy pairs (KPAIR sample) selected from 2MASS/SDSS-DR3 cross-matches. The goals are to study the star formation activity in these galaxies and to set a local bench mark for the cosmic evolution of close major mergers. The Spitzer KPAIR sample (27 pairs, 54 galaxies) includes all spectroscopically confirmed spiral-spiral (S+S) and spiral-elliptical (S+E) pairs in a parent sample that is complete for primaries brighter than K=12.5 mag, projected separations of 5 ≤ s ≤ 20h −1 kpc, and mass ratios ≤ 2.5. The Spitzer data, consisting of images in 7 bands (3.6, 4.5, 5.8, 8, 24, 70, 160µm), show very diversified IR emission properties. Compared to single spiral galaxies in a control sample, only spiral galaxies in S+S pairs show significantly enhanced specific star formation rate (sSFR=SFR/M), whereas spiral galaxies in S+E pairs do not. Furthermore, the SFR enhancement of spiral galaxies in S+S pairs is highly mass-dependent. Only those with M > ∼ 10 10.5 M show significant enhancement. Relatively low mass (M ∼ 10 10 M ) spirals in S+S pairs have about the same SFR/M compared -2to their counterparts in the control sample, while those with 10 11 M have on average a ∼ 3 times higher SFR/M than single spirals. There is evidence for a correlation between the global star formation activities (but not the nuclear activities) of the component galaxies in massive S+S major-merger pairs (the "Holmberg effect"). There is no significant difference in the SFR/M between the primaries and the secondaries, nor between spirals of SEP < 1 and those of SEP ≥ 1, SEP being the normalized separation parameter. The contribution of KPAIR galaxies to the cosmic SFR density in the local universe is only 1.7%, and amounts to ρ . KPAIR = 2.54 × 10 −4 (M yr −1 Mpc −3 ).

An investigation of star formation and dust attenuation in major mergers using ultraviolet and infrared data

“…This estimation is consistent with the one given by Dale et al (2005) using 24, 70, and 160 μm data (Xu et al 2010). The IR data of control galaxies are selected from Spitzer SWIRE fields (34 galaxies) and Spitzer SINGS samples (5 galaxies).…”

“…The patchy distribution of dust in these regions can strongly affect the light distribution and make this method of identification problematic, especially in ultraviolet (UV) bands (Burgarella et al 2001). Another disadvantage of this method is that the signature of the disturbed features becomes harder to detect as one goes deeper in space (Mo et al 2010;Xu et al 2010).…”

“…This method avoids the complex identification of morphological features, and thus is more objective. However, it suffers from biases such as (1) the projection effect; (2) lack of very close pairs owing to the limited resolution of the telescope; (3) lack of less luminous components given a certain magnitude limit ("missing the secondary"; Xu et al 2004Xu et al , 2010. A&A 548, A117 (2012) To reduce these biases, Xu et al (2010, hereafter Xu10) built a local sample of close pairs selected from near-infrared bands by carefully choosing the selection criteria and presented Spitzer observations for these galaxies.…”

GOODS-Herschel: the impact of galaxy-galaxy interactions on the far-infrared properties of galaxies

“…Many studies have extensively investigated this enhancement of SFA in paired galaxies Article published by EDP Sciences A60, page 1 of 10 (e.g., Condon et al 1982;Keel et al 1985;Kennicutt et al 1987;Barton et al 2000;Lambas et al 2003;Nikolic et al 2004;Alonso et al 2004;De Propris et al 2005;Geller et al 2006;Woods & Geller 2007;Li et al 2008;Ellison et al 2008;Knapen & James 2009;Perez et al 2009;Park & Choi 2009;Hwang et al 2010a;Xu et al 2010;Darg et al 2010;Patton et al 2011). In summary, the SFA of galaxies seems to strongly depend on the morphology and the mutual separation of galaxies in pairs.…”

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.…”