The globular cluster system of NGC 1316

Abstract

Context. The light of the merger remnant NGC 1316 (Fornax A) is dominated by old and intermediate-age stars. The only sign of current star formation in this big galaxy is the HII region SH2, an isolated star cluster complex with a ring-like morphology and an estimated age of 0.1 Gyr at a galactocentric distance of about 35 kpc. A nearby intermediate-age globular cluster, surrounded by weak line emission and a few more young star clusters, is kinematically associated. The origin of this complex is enigmatic. Aims. We want to investigate the nature of this star cluster complex. The nebular emission lines permit a metallicity determination which can discriminate between a dwarf galaxy or other possible precursors. Methods. We used the Integrated Field Unit (IFU) of the VIMOS instrument at the Very Large Telescope of the European Southern Observatory in high dispersion mode to study the morphology, kinematics, and metallicity employing line maps, velocity maps, and line diagnostics of a few characteristic spectra. Results. The line ratios of different spectra vary, indicating highly structured HII regions, but define a locus of uniform metallicity. The strong-line diagnostic diagrams and empirical calibrations point to a nearly solar or even super-solar oxygen abundance. The velocity dispersion of the gas is highest in the region offset from the bright clusters. Star formation may be active on a low level. There is evidence for a large-scale disk-like structure in the region of SH2, which would make the similar radial velocity of the nearby globular cluster easier to understand. Conclusions. The high metallicity does not fit to a dwarf galaxy as progenitor. We favour the scenario of a free-floating gaseous complex having its origin in the merger 2 Gyr ago. Over a long period the densities increased secularly until finally the threshold for star formation was reached. SH2 illustrates how massive star clusters can form outside starbursts and without a considerable field population.

Dust and gas in the central region of NGC 1316 (Fornax A)

“…This corroborates the assumption that it is also not visible in NaI D. Serra et al (2019) find more HI emission outside the central region. This, among other sources, confirms the presence of HI in the star-forming region SH2 (Schweizer 1980;Richtler et al 2017).…”

Neutral hydrogen gas within and around NGC 1316

“…the extended emission-line region (EELR) south-west of NGC 1316 originally discovered by Mackie & Fabbiano (1998), which we detect at velocities 1730 -1820 km s −1 ; the star cluster complex SH2 south of NGC 1316 (Schweizer 1980;Richtler et al 2012Richtler et al , 2017) at 1680 km s −1 ; and an H i cloud just north of NGC 1316 at 1770 -1860 km s −1 (hereafter, C N,1 ).…”

“…The H i-bright region SH2, which consists of a ring-shaped collection of 100-Myr-old star clusters (M ∼ 10 6 M ; Richtler et al 2012Richtler et al , 2017, remains unresolved in our H i data both in velocity (at ∼ 1680 km s −1 ) and on the sky. The angular and velocity resolution of our data is insufficient to search for any low-column-density H i extension in the direction of an associated, intermediate-age globular cluster (∼ 15 to the south-west and ∼ 30 km s −1 offset in velocity; Richtler et al 2017). The H i mass of SH2 is 2.8 × 10 7 M , which dominates over the stellar mass by approximately an order of magnitude.…”

History and destiny of an emerging early-type galaxy

“…The data reduction is performed entirely with the PY3D data reduction package (Husemann et al 2013) that has been developed for fibre-fed IFUs as part of the Calar Alto Large Integral Field Area survey (CALIFA, Sánchez et al 2012). It has already been successfully used to reduce several VIMOS IFU data sets Woo et al 2014;Richtler et al 2017) and we follow the same scheme here, as briefly described below.…”