The VIRUS-P Exploration of Nearby Galaxies (VENGA): spatially resolved gas-phase metallicity distributions in barred and unbarred spirals

Abstract

We present a study of the excitation conditions and metallicity of ionized gas (Z gas ) in eight nearby barred and unbarred spiral galaxies from the VIRUS-P Exploration of Nearby Galaxies (VENGA) survey, which provides high spatial sampling and resolution (median ∼ 387 pc), large coverage from the bulge to outer disc, broad wavelength range (3600-6800 Å), and medium spectral resolution (∼ 120 km s −1 at 5000 Å). Our results are: (1) We present high resolution gas excitation maps to differentiate between regions with excitation typical of Seyfert, LINER, or recent star formation. We find LINER-type excitation at large distances (3-10 kpc) from the centre, and associate this excitation with diffuse ionized gas (DIG). (2) After excluding spaxels dominated by Seyfert, LINER, or DIG, we produce maps with the best spatial resolution and sampling to date of the ionization parameter q, star formation rate, and Z gas using common strong line diagnostics. We find that isolated barred and unbarred spirals exhibit similarly shallow Z gas profiles from the inner kpc out to large radii (7-10 kpc or 0.5-1.0 R 25 ). This implies that if profiles had steeper gradients at earlier epochs, then the presentday bar is not the primary driver flattening gradients over time. This result contradicts earlier claims, but agrees with recent IFU studies. (3) The Z gas gradients in our z ∼ 0 massive spirals are markedly shallower, by ∼ 0.2 dex kpc −1 , than published gradients for lensed lower mass galaxies at z ∼ 1.5 − 2.0. Cosmologically-motivated hydrodynamical simulations best match this inferred evolution, but the match is sensitive to adopted stellar feedback prescriptions.

The lifecycle of molecular clouds in nearby star-forming disc galaxies

“…Hoopes et al 1996;Greenawalt 1998) or applying a fixed intensity threshold to remove all emission lower than a given value (e.g. Blanc et al 2009;Kaplan et al 2016). Including information about the spatial extent of HII regions can also help decomposing the emission into a diffuse background and compact sources (e.g.…”

The VIRUS-P Exploration of Nearby Galaxies (VENGA): the stellar populations and assembly of NGC 2903’s bulge, bar, and outer disc

“…One complication to the Balmer decrement method is that Hα/Hβ is a function of temperature and density and we assume that the emission is coming from a star-forming region. However, diffuse ionized gas (DIG) which has non-local origins, also contribute Hα (see Kaplan et al 2016 for how they dealt with DIG emission in a sample of VENGA galaxies). Figure 6 shows the extinction maps derived from both methods as well as the non extinctioncorrected Hα map of NGC 2903.…”

“…Next, we compare to observations of gas-phase metallicity radial gradients in the local universe. NGC 2903 is one of the galaxies that Kaplan et al (2016) studied. The authors found that seven out of the seven gas-phase metallicity indicators exhibit solar and super-solar values in the central region of NGC 2903, even reaching 0.4 dex above so-lar values.…”

Evidence for azimuthal variations of the oxygen-abundance gradient tracing the spiral structure of the galaxy HCG 91c

“…via the PINGS and CALIFA surveys; Rosales-Ortega et al 2010;Sánchez et al 2012bSánchez et al ,a, 2014 and VIRUS-P (e.g. via the VENGA survey; Blanc et al 2013;Kaplan et al 2016). This push is particularly interesting from a galaxy evolution perspective, as MUSE effectively allows the study of galaxies inside a wider range of environments, including that of compact groups and clusters, with unprecedented spatial resolution.…”