Oral comunication
C. Pappalardo
Abstract
The extremely large telescopes commissioned for the next decade will open a new window in the comprehension of the formation and evolution of galaxies. In this context, important information about the physical processes involved will come from spectroscopy, since a spectrum contains crucial information about the stellar and gas emission, chemistry, and kinematics. Spectral analysis has shown to be reliable in many aspects and led to the discovery of important relations driving the galaxy evolution at different epochs. With the increase of technical capabilities different spectral analysis tools have been proposed to the scientific community in order to extract such parameters (STECKMAP, FireFly, FADO, VESPA and many others). But still, many biases and inconsistencies in the results are present, in some case leading to different results. The current state of the art of this technique suffers large uncertainties when leading with a relevant parameter driving the evolution of galaxies: the star formation history. In this presentation, a comparative study for some of these spectral fitting tools is performed, focusing on the discrepancies between the different approaches. Using the evolutionary stellar population code REBETIKO, a set of different mock spectra, with different SNR, and star formation histories are produced. These spectra are analyzed with three different tools: STARLIGHT, FADO and STECKMAP, to investigate at which SNR values each method is able to reproduce the input parameters. Each code uses a different method to extract the best fit, allowing the possibility to disentangle possible biases introduced in the analysis. STECKMAP reproduces quite well the spectra and the star formation history of the mock data, even if for some particular model a secondary peak appears. This double peak is due to a bad spectral coverage within the time bin of the secondary peak since the proposed spectral synthesis population basis does not have a sufficient number of spectra covering that specific time bin. Moreover, we note that the typical double peak is on average shifted towards the younger or the older time bin. This introduces an interesting feature because the oldest time bin corresponds to a stellar population with high weight in terms of total mass and low weight in terms of total light, while the young one has a low weight in terms of mass but high weight in terms of light. This trend can have different origins: for example, these secondary peaks are particularly evident when considering stellar populations at an epoch where the nebular emission is still relevant. In those cases, FADO reproduces better the trend for both nebular and stellar continuum emission, confirming that at these stages of star formation the nebular emission must be properly taken into account. Where nebular emission is not negligible, the results obtained with methods taking into account such a component are more reliable, and this can be very important when moving at higher redshift, where the stellar populations are young. In particular, this is true for starburst systems, where a huge amount of stars are forming almost at the same epoch. This is an important aspect to take into account the future facilities, which will provide the community with high-resolution spectra of galaxies at redshift 3-4 and even higher. For these objects, it is important to quantify these effects, as the emission due to the ionized gas can be very high compared to the emission of the stellar continuum.
XXIX Encontro Nacional de Estudantes de Astronomia
Lisboa, Portugal
2019 September
