The Mice at play in the CALIFA survey

Abstract

We present optical integral field spectroscopy (IFS) observations of the Mice, a major merger between two massive ( 10 11 M ) gas-rich spirals NGC 4676A and B, observed between first passage and final coalescence. The spectra provide stellar and gas kinematics, ionised gas properties, and stellar population diagnostics, over the full optical extent of both galaxies with ∼1.6 kpc spatial resolution. The Mice galaxies provide a perfect case study that highlights the importance of IFS data for improving our understanding of local galaxies. The impact of first passage on the kinematics of the stars and gas has been significant, with strong bars most likely induced in both galaxies. The barred spiral NGC 4676B exhibits a strong twist in both its stellar and ionised gas disk. The edge-on disk galaxy NGC 4676A appears to be bulge free, with a strong bar causing its "boxy" light profile. On the other hand, the impact of the merger on the stellar populations has been minimal thus far. By combining the IFS data with archival multiwavelength observations we show that star formation induced by the recent close passage has not contributed significantly to the total star formation rate or stellar mass of the galaxies. Both galaxies show bicones of high ionisation gas extending along their minor axes. In NGC 4676A the high gas velocity dispersion and Seyfert-like line ratios at large scaleheight indicate a powerful outflow. Fast shocks (v s ∼ 350 km s −1 ) extend to ∼6.6 kpc above the disk plane. The measured ram pressure (P/k = 4.8 × 10 6 K cm −3 ) and mass outflow rate (∼8−20 M yr −1 ) are similar to superwinds from local ultra-luminous infrared galaxies, although NGC 4676A only has a moderate infrared luminosity of 3 × 10 10 L . Energy beyond what is provided by the mechanical energy of the starburst appears to be required to drive the outflow. Finally, we compare the observations to mock kinematic and stellar population maps extracted from a hydrodynamical merger simulation. The models show little enhancement in star formation during and following first passage, in agreement with the observations. We highlight areas where IFS data could help further constrain the models.

NIHAO – VIII. Circum-galactic medium and outflows – The puzzles of H i and O vi gas distributions

“…Specifically, we recreate observations of gas velocity dispersion around edge-on discs. Wild et al (2014) proposed that heightened velocity dispersions perpendicular to the disc with respect to the velocity dispersion in the disc plane are evidence for bipolar outflows. We detect a signal in intermediate mass galaxies (10 ∼ < log M Halo / M ∼ < 11.5), though the ratio never exceeds two.…”

CALIFA, the Calar Alto Legacy Integral Field Area survey

“…This galaxy was observed in the time allocated to the main survey since it seemed worthwhile to cover the full "mice" merger. These data have been published in (Wild et al 2014).…”

“…The stellar dynamics together with detail analysis of the stellar populations revealed a tight relation between the initial mass function (IMF) and the local metallcity (Martín-Navarro et al 2015) and allowed us to dynamically constrain the shape of the IMF in early-type galaxies (Lyubenova et al 2016). vi) We explored in detail the impact of galaxy interactions on the enhancement of star-formation rates (SFR) and the ignition of galactic outflows (Wild et al 2014;Barrera-Ballesteros et al 2015b). vii) We studied the nature of the progenitors of SNe (Galbany et al 2014); viii) we explored star formation indicators for extended objects and the suitability of Hα as an SFR tracer (Catalán-Torrecilla et al 2015), as well as the spatially resolved SFR density across the Hubble sequence (González .…”

Central star formation and metallicity in CALIFA interacting galaxies

“…In this regard, IFS A&A 579, A45 (2015) observations of interacting galaxies are crucial for understanding whether the enhancement in the SFR is a global or a localized process. An example of the usefulness of such observations has been demonstrated by Wild et al (2014). From a detailed study of the Mice galaxies, they found that there is a moderate increment in the central SFR and no net enhancement in the global SFR.…”