# MaNGA Resolved Stellar Populations

## Contact

Nell Byler
University of Washington
ebyler@astro.washington.edu

## Summary

This program targets nearby galaxies with existing HST imaging and high-quality color-magnitude diagrams selected from the ACS Nearby Galaxy Survey (ANGST, Dalcanton 2009). These galaxies are significantly closer than galaxies targeted in the main MaNGA sample, allowing for detailed studies of the resolved stellar populations. The comparison of spatially-matched observations of resolved stars and integrated light will be used to place empirical constraints on SPS models and assess spectral fitting techniques.

## Finding Targets

An object whose MANGA_TARGET3 value includes one or more of the bitmasks in the following table was targeted for spectroscopy as part of this ancillary target program. See SDSS bitmasks to learn how to use these values to identify objects in this ancillary target program.

Program (bit name) Bit number Target Description
ANGST 18 nearby galaxies with existing HST observations

## Description

Nearby galaxies (within ~4 Mpc) provide a unique opportunity to compare various methods of measuring star formation histories (SFHs) to the stellar fossil record. These galaxies are close enough to be resolved into individual stars, enabling the construction of color-magnitude diagrams (CMDs), but distant enough that their angular sizes are comparable to the current generation of IFU instruments, enabling the direct comparison of galaxy properties derived using CMD fitting and spectral fitting methods.

We will extract stellar photometry from the MaNGA footprint and model the CMD of those stars using MATCH (Dolphin 2002), solving for star formation history, the current star formation rate, and the history of chemical enrichment. We will co-add MaNGA spectra for the same region and fit the spectrum using “Prospector” (an SED-fitter using SPS models from FSPS; Conroy et al. 2009, also Johnson et al. 2013). With a set of properties from both CMD fitting and spectral fitting for matched spatial locations, the analysis follows two paths: First, we can test the general SPS model ingredients by comparing an observed MaNGA spectrum with a spectrum predicted from propagating a CMD-inferred SFH through FSPS. Second, we can probe fitting methodology by comparing the galaxy properties derived using CMD-fitting and spectral fitting.

The net data product will be a library of SFHs and matched spectra that can be used to asses the performance and robustness of SPS fitting methods for any code. This comparison links the complimentary approaches to stellar population studies from HST and SDSS and offers immediate applicability to the extensive body of research based on single-fiber galaxy spectra and broadband photometry from SDSS.

## Target Selection

The ancillary program observations target NGC 4163, a nearby dwarf galaxy (3 Mpc, MB = 13.66) with recent star formation. This galaxy has a relatively deep CMD, and the low dust content (AV~0.06) ensures a clean test of SFH-inference uncomplicated by dust-metallicity degeneracies. The MaNGA observations cover both the main body of the galaxy where the star formation is intense, as well as outer regions where star formation is less important.

## REFERENCES

Conroy, C. et al. 2009, ApJ, 699, 486.
Dalcanton, J.J., et al. 2009, ApJS, 183, 67
Dolphin, A.E., 2002, MNRAS, 332, 91.
Johnson, B. 2013, ApJ, 772, 8.