Post-starburst galaxies in SDSS-IV MaNGA

ABSTRACT Post-starburst galaxies, identified by their unusually strong Balmer absorption lines and weaker than average emission lines, have traditionally been selected based on their central stellar populations. Here we identify 360 galaxies with post-starburst regions from the MaNGA integral field survey and classify these galaxies into three types: 31 galaxies with central post-starburst regions (CPSB), 37 galaxies with off-centre ring-like post-starburst regions (RPSB), and 292 galaxies with irregular post-starburst regions (IPSB). Focusing on the CPSB and RPSB samples, and comparing their radial gradients in Dn4000, HδA, and W(H α) to control samples, we find that while the CPSBs have suppressed star formation throughout their bulge and disc, and there is clear evidence of rapid decline of star formation in the central regions, the RPSBs only show clear evidence of recently rapidly suppressed star formation in their outer regions and an ongoing central starburst. The radial profiles in mass-weighted age and stellar v/σ indicate that CPSBs and RPSBs are not simply different evolutionary stages of the same event, rather the CPSB galaxies are caused by a significant disruptive event, while the RPSB galaxies are caused by disruption of gas fuelling to the outer regions. Compared to the control samples, both CPSB and RPSB galaxies show a higher fraction of interactions/mergers, misaligned gas, or bars that might be the cause of the gas inflows and subsequent quenching.

Alternative classification diagrams for AGN-starburst galaxies

The aim of diagnostic diagrams is to classify galactic nuclei according to their photoionizing source using emission-line ratios, differentiating starburst regions from active galactic nuclei (AGN). However, the three traditional diagnostic diagrams can sometimes be ambiguous with regard to a single object. The main goal of the present work is to propose alternative diagnostic diagrams by using distinct combinations of emission lines ratios. We present these diagrams using data from the Sloan Digital Sky Survey. With these new diagrams, it is possible to better distinguish the ionizing source in nuclei of galaxies and also to study the parameters that are relevant when considering both kinds of objects, starbursts and AGN.

Formation of the twin galactic starburst regions NGC 6357 and NGC 6334

New CO J=1–0 observations with NANTEN and NANTEN2 reveal that extensive collisions between two molecular clouds at relative velocity of 15 km s−1 triggered the O star formation in the Galactic mini-starbursts NGC 6357 and NGC 6334. Correlated/anti-correlated gas distributions and intermediate velocity features between the two clouds lend support for the cloud-cloud collision scenario. The timescale of the collision and high-mass star formation is as short as less than 0.5 Myrs, suggesting rapid O star formation.

Gas accretion from halos to disks: observations, curiosities, and problems

Accretion of gas from the cosmic web to galaxy halos and ultimately their disks is a prediction of modern cosmological models but is rarely observed directly or at the full rate expected from star formation. Here we illustrate possible large-scale cosmic HI accretion onto the nearby dwarf starburst galaxy IC10, observed with the VLA and GBT. We also suggest that cosmic accretion is the origin of sharp metallicity drops in the starburst regions of other dwarf galaxies, as observed with the 10-m GTC. Finally, we question the importance of cosmic accretion in normal dwarf irregulars, for which a recent study of their far-outer regions sees no need for, or evidence of, continuing gas buildup.

Sturm und Drang: The turbulent, magnetic tempest in the Galactic center

The Galactic center central molecular zone (GCCMZ) bears similarities with extragalactic starburst regions, including a high supernova (SN) rate density. As in other starbursts like M82, the frequent SNe can heat the ISM until it is filled with a hot (∼ 4 × 107 K) superwind. Furthermore, the random forcing from SNe stirs up the wind, powering Mach 1 turbulence. I argue that a turbulent dynamo explains the strong magnetic fields in starbursts, and I predict an average B ∼70 μG in the GCCMZ. I demonstrate how the SN driving of the ISM leads to equipartition between various pressure components in the ISM. The SN-heated wind escapes the center, but I show that it may be stopped in the Galactic halo. I propose that the Fermi bubbles are the wind's termination shock.

Supernova Remnants in Starburst Regions

We study the evolution of SNRs in starburst regions taking into consideration the role of the high ambient pressure and the influence of gravitational forces from the stellar component within the shell of a SNR. On this basis, we discuss the connection between the radio, infrared, and gamma emissions from starburst regions.

The Effects of Binaries on Population Studies

We give an overview of the work that has been done in Brussels since 1997 on various aspects of population studies and the effects of binaries: stellar populations and supernova rates in regions where star formation is continuous and in starbursts, the expected spectral evolution of starburst regions, the chemical evolution of galaxies.