Gas and star formation in minor mergers: Molecular gas feeding the central starbursts in NGC 1614 and the Medusa merger Sabine König, S. Aalto (Chalmers), J. Gallagher (Univ. of Wisconsin), S. Muller (Chalmers), R. Beswick (Univ. of Manchester), E. Jütte (AIRUB), L. Lindroos (Chalmers) IRAM France Sabine König Gas and star formation in minor mergers 1
M INOR MERGERS WITH MINOR AXIS DUST LANES minor mergers: gas brought in by disturbing companion galaxy generally at large radii in merger remnant (Bournaud et al. 2005) gas returning from tidal tails often forms rings (e.g. polar, appearing as dust lanes when seen edge-on) How are polar rings/dust lanes physically and dynamically coupled to the gas reservoirs at the centers of minor mergers? Sabine König Gas and star formation in minor mergers F IGURE : Minor axis dust lane minor mergers NGC 1614 (top) and NGC 4194 (the Medusa merger, bottom). 2
NGC 1614 minor axis dust lane minor merger d = 64 Mpc L IR 3 10 11 L (LIRG) LINER and starburst activity starburst ring detected in different tracers (e.g. Pa, radio continuum, PAHs, H K imaging) Sabine König Gas and star formation in minor mergers 3
MOLECULAR GAS IN NGC 1614 CO 1 0 central kpc elongated CO structure associated with foreground dust lane (Olsson et al. 2010) CO 2 1 asymmetric ring ( 10 9 M, W/E mass ratio 2.7:1) Sabine König Gas and star formation in minor mergers 4
THE STARBURST RING FIGURE: H K image of the central 8 8 of NGC 1614 (left, Alonso-Herrero et al. 2001), and the 5 GHz radio continuum as seen by the VLA and MERLIN (right, Olsson et al. 2010). 300 pc radius ring in H K and radio continuum Sabine König Gas and star formation in minor mergers 5
TRACERS OF STAR FORMATION Pa 8GHz continuum Pa & radio continuum inside the molecular gas ring (CO) Sabine König Gas and star formation in minor mergers 6
ANNULAR PROFILES profiles centered with respect to center of Pa ring CO 2 1 has no central peak radio continuum & Pa aligned quite well, but inside the CO ring CO distribution shows strong asymmetry of the ring FIGURE: Comparison of the distribution of Pa (b), 12 CO 2 1 (c ) 8.4 GHz (d, X-band), 5 GHz (e, C-band) and 1.4 GHz emission (f, L-band) in the molecular gas ring of NGC 1614. Sabine König Gas and star formation in minor mergers 7
F EEDING THE RING F IGURE : Overlay of CO 2 1 (left) and CO 1 0 (right) integrated intensity emission on top of HST F435W image on different scales. CO gas distributions well correlated with dust lanes feeding of the ring via the dust lanes Sabine König Gas and star formation in minor mergers 8
PV DIAGRAM Northern extended gas follows solid body rotation of the ring. Sabine König Gas and star formation in minor mergers 9
GIANT MOLECULAR ASSOCIATIONS (GMAS) GMA diameter dispersion mass [ ] [km s 1 ] [M ] GMAs on the ring: GMA 4 0.6 1.0 61 ± 6 5.70 10 7 GMA 6 0.6 0.9 64 ± 4 9.74 10 7 GMA 7 0.8 1.1 38 ± 4 5.97 10 7 GMA 8 1.3 0.8 73 ± 5 9.36 10 7 GMA 9 0.6 1.2 54 ± 5 5.98 10 7 GMA 10 0.5 0.7 40 ± 5 4.96 10 7 average 259 ± 24 pc 55 ± 5 6.95 10 7 GMAs off the ring: GMA 1 0.6 1.1 57 ± 7 8.29 10 7 GMA 2 1.1 0.5 31 ± 4 1.64 10 7 GMA 3 0.8 1.1 53 ± 3 6.23 10 7 GMA 5 1.8 0.6 48 ± 5 3.70 10 7 average 273 ± 20 pc 47 ± 5 4.97 10 7 Sabine König Gas and star formation in minor mergers 10
GMA FORMATION no GMAs in the dust lane formation in situ smaller GMCs funneled along dust lanes umbilical cords molecular ring crowding in merger potential cloud-cloud collisions dissipation of excess E kin coagulation of individual GMCs form GMAs see also M 51 (Koda et al. 2009) & IC 342 (Hirota et al. 2011) FIGURE: Toy model for the formation of the molecular gas ring and the GMAs in the ring in NGC 1614. Sabine König Gas and star formation in minor mergers 11
THE MEDUSA MERGER (NGC 4194) E+S minor axis dust lane minor merger d = 39 Mpc L FIR 8.5 10 10 L starburst activity + small AGN contribution very efficient star formation - comparable to ULIRGs Sabine König Gas and star formation in minor mergers 12
MOLECULAR GAS IN THE MEDUSA FIGURE: 12 CO 1 0 (left, Aalto et al. 2000) and 12 CO 2 1 emission (right, König et al. 2014). Sabine König Gas and star formation in minor mergers 13
THE "EYE OF THE MEDUSA" radius 320 pc mass 4 10 8 M bulk of the CO south of the kinematical center northern tip of the ring -> molecular gas associated with the nucleus (radio continuum) radio continuum at the center of the Eye -> caused by SN explosions Sabine König Gas and star formation in minor mergers 14
FEEDING THE CENTRAL STARBURST CO: indications for streaming motions gas coming in via the dust lanes gas pile up in the central potential (crowding) burst of star formation SNe explosions gas driven outwards molecular shell Sabine König Gas and star formation in minor mergers 15
S UMMARY /C ONCLUSIONS molecular gas reservoirs associated with dust lanes in both minor mergers 1614: gas associated with star formation, Medusa: gas away from it molecular gas rings (circumnuclear vs. off-nucleus) feeding of the rings via the dust lanes Sabine König Gas and star formation in minor mergers 16
THANK YOU! Sabine König Gas and star formation in minor mergers 17