China-Chile Proposal

China-Chile Joint Research Fund 2016

Project presentation

• Title: :Star Formation History of Galaxies in Different Environments from MaNGA Spectra

• Abstract (<1000 words):

In the present–day galaxy population, it is well known that there is a strong relation between the properties of galaxies and their stellar masses and environments (Peng et al., 2010, 2012). However, the relative importance of secular evolution (nature) over nurture is not yet clear. Separating the effects of interaction–driven evolution in the observed galaxy properties is not trivial.

- MaNGA spectra and galaxy properties

- SED modelling

- Experience of the team working with MaNGA data

- Experience of the team working together and how this research funding would help in the development of the projects

- Implementation and involvement of Chile researches on MaNGA

• Area of Research: Galaxies

• Names of project PI and Co-Is and their institutions:

Médéric Boquien(1) (PI), Shiyin Shen(2) (PI), Maria Argudo-Fernández(1) (Co-I),

Fangting Yuan(2) (Co-I), Jun Yin(2) (Co-I), Ruixiang Chang(2) (Co-I), Lei Hao(2) (Co-I)

1. - University of Antofagasta, Chile
2. - Shanghai Astronomical Observatory, Chinese Academy of Sciences, China

Scientific Justification

(less than 8 single-spaced pages, including text, graphics, tables and references).

Galaxy evolution in the era of the SDSS–IV and MaNGA surveys

Whereas the universe was incredibly homogeneous 300,000 years after the Big Bang, as shown by the cosmic microwave background, it is now highly heterogeneous: a large fraction of the baryonic matter is concentrated in galaxies, the basic astronomical ecosystems in which stars form, evolve, and die. This means that to understand why the universe we see around us is so diverse, we need to understand how the first galaxies formed from primordial gas and how they grew and changed over time, generating the variety of structures we observe in nearby galaxies.

The appearance of galaxies ultimately depends on the properties of their stellar populations: age, mass, chemical composition, etc. As stars form, evolve and die they produce dust and inject vast amounts of metals in the interstellar medium, which have a direct impact on the formation of new stars, shielding and cooling molecular clouds. In case of intense feedback from young, massive stars, star formation can even be quenched altogether. In other words, star formation is the fundamental process governing the formation and evolution of galaxies.

The Sloan Digital Sky Survey (SDSS) has provided us with spectra for a vast number of low redshift galaxies, yielding for each of them information about their star formation, metallicity, and kinematics. However, this information is limited to a single spatial position at the galaxy’s center. This means that this treasure trove of data unfortunately gives us only very limited information on the structure of gradients in galaxies, which would reveal how galaxies have grown over cosmic times. Integral field unit (IFU) observations enable a leap forward: they provide us with an added dimension to the information available for each galaxy. Clues to the nature of the physical processes that drive star formation in galaxies are encoded in the map.

With the advent of the spatially resolved spectroscopy, from integral field spectroscopy (IFS) data and the multi–band images with good spatial coverage from the ultraviolet with GALEX to the infrared with WISE, new observational results are available to explore galaxy assembly models (Pérez et al., 2013; Sánchez-Blázquez et al., 2014; Pan et al., 2015). To elucidate how galaxies grow with time, one needs to recover the SFH, both in space and time, for individual galaxies. In practice, the SFH of a galaxy is determined by finding the most plausible combination of evolved single stellar populations (SSP) that matches its observed spectrum or SED, the so–called “fossil record method”.

MaNGA (Mapping Nearby Galaxies at Apache Point Observatory, Bundy et al. 2016) is an IFS survey designed to investigate the internal kinematic structure and composition of gas and stars in an unprecedented sample of 10,000 nearby galaxies. The survey is one of three core programs in the fourth–generation Sloan Digital Sky Survey (SDSS–IV) that began on 2014 July 1. In previous SDSS programs the observing mode was from a single fiber spectrum. To overcome this limitation and provide spatially resolved spatial maps, MaNGA has adopted a new strategy by bundling fibers together (see Figure 1).