Research

Stellar Populations in Galaxy Bars

Bars as non-axisymmetric structures have been shown to greatly impact the distribution of stars, gas and angular momentum in galaxies. By studying stellar populations in the central parts of barred galaxies we are able to learn about processes during bar formation and bar evolution. A number of studies have been focused on the impact of bars on the radial gradients, but studies on the azimuthal changes of stellar populations are relatively scarce and have mainly been focussed on massive nearby strongly-barred galaxies.

In a first study, we use MUSE observation with high spatial resolution from the TIMER project to present detailed maps of star formation histories in bars of 9 nearby galaxies. We compare our data to the AURIGA state-of-the-art cosmological zoom-in simulations of barred galaxies and show that our MUSE observations can be explained by the dynamical influence of the bar on stellar populations with different ages and kinematic properties.

For more details, see Neumann+2020, A&A, 637, A56: Stellar populations across galaxy bars in the TIMER project.

In a second study, we increase the sample size by two orders of magnitude and investigate the azimuthal variations of stellar populations in a sample of 1,000 barred galaxies from the MaNGA survey. We find that bars are of higher stellar mass density and are more metal-rich than the inner discs at the same radii. The differences increase with total stellar mass of the galaxy and distance below the star-forming main sequence. Stellar ages show a variety of bar to inter-bar contrasts, with no consistent trend.

For more details, see Neumann+2024, MNRAS, submitted: Azimuthal Variations of Stellar Populations in Barred Galaxies.

Star Formation in Galaxy Bars

Star formation in galactic bar environments is still a poorly understood process. About half of all nearby barred galaxies show signatures of ongoing star formation along the bar, while the other half presents itself with a curious absence of star formation. Despite the presence of cold molecular gas observed as radial flows along the edge of the bar towards the galaxy centre, the local environment seems to be able to suppress star formation. Simulations indicate that a combination of shear and turbulence within the fast-flowing gas might be responsible. However, it is not clear how star-forming bars fit into this picture. In this work, for the first time, we quantify the spatially resolved star formation rate in 16 bars with MUSE data from the CARS survey and relate it to other bar and galaxy properties.

For more details, see  Neumann+2019, A&A, 627, A26: CARS: Comparative analysis of the structural properties of star-forming and non-star-forming galaxy bars.

See also Fraser-McKelvie+2020, MNRAS, 495, 4158F (incl. Neumann), where the morphology of Hɑ in a large sample of bars is classified into four different categories and it becomes clear that star-forming bars are mostly found in low-mass galaxies, and Kim+2024, ApJ, in press (including Neumann), where the impact of shear and shocks on star formation in bars is investigated.

Spatially Resolved Stellar Populations and Scaling Relations in 10,010 Galaxies in the MaNGA Survey

Stars are fossil records of galaxy evolution that save snapshots of the mass budget and chemical composition of a galaxy across cosmic time. Unveiling and unraveling the details of stellar populations is a powerful tool to understand physical processes of galaxy evolution. Large-scale IFU surveys such as SDSS-IV/MaNGA offer the unique opportunity for a statistically sound exploration of the spatial distribution of stellar populations across a large range of galaxy masses and morphologies.

In this study, we use the Firefly (link) full spectral fitting code to fit 2×3.7 million spectra across all 10,010 galaxies of the MaNGA survey employing two different stellar population libraries: MILES (Maraston & Strömbäck 2011) and MaStar (Maraston et al. 2020) to derive parameters such as stellar ages, metallicities, masses and remnant masses, star formation rates, full star formation histories and dust attenuation. The whole catalogue is publicly available here (https://www.sdss.org/dr17/manga/manga-data/manga-firefly-value-added-catalog).

For more details, see Neumann+2022, MNRAS, 513, 5988-6012,: The MaNGA FIREFLY value added catalogue: resolved stellar populations of 10 010 nearby galaxies.

Based on  the MaNGA Firefly Catalogue, we conduct a study to understand what drives the build-up of stellar metallicity locally in galaxies. Our study goes beyond the well-known  global mass-metallicity relation and radial metallicity gradients by providing a statistically sound exploration of local relations between stellar metallicity [Z/H], stellar surface mass density Σ⁎ and galactocentric distance in the global mass-morphology plane. We find a significant resolved mass density-metallicity relation rΣ⁎ZR for galaxies of all types and masses. The spread of the relation is mainly attributed to different radial distances. In particular, we find that at fixed Σ⁎ metallicity increases with radius.

For more details, see  Neumann+2021, MNRAS, 508, 4844-4857: SDSS-IV MaNGA: drivers of stellar metallicity in nearby galaxies.

Galaxy Bulge Classification Combining Photometry and Spectroscopy as part of the CALIFA Survey

The definition of a galaxy bulge is ambiguous. It has once been used to describe central ellipsoidal-like structures that stick out of the galactic disc and add light to the inwards extrapolation of the exponential disc. These are so-called “classical bulges”. But bulges can be many things and many of them are actually rather discy and rotation dominated, sometimes referred to as “pseudo bulges”. In this work we combined photometry with spectroscopy to deliver a variety of bulge classification criteria and improve their final classification.

For more details, see  Neumann+2017, A&A, 604, A30: A combined photometric and kinematic recipe for evaluating the nature of bulges using the CALIFA sample.



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