Star Formation Histories of the LEGUS Spiral Galaxies. I. The Flocculent Spiral NGC 7793^∗

Abstract

We present a detailed study of the flocculent spiral galaxy NGC 7793, part of the Sculptor group. By analyzing the resolved stellar populations of the galaxy, located at a distance of ∼ 3.7 Mpc, we infer for the first time its radial star formation history (SFH) from Hubble Space Telescope photometry, thanks to both archival and new data from the Legacy ExtraGalactic UV Survey. We determine an average star formation rate (SFR) for the galaxy portion covered by our F555W and F814W data of 0.23 ± 0.02 M /yr over the whole Hubble time, corresponding to a total stellar mass of (3.09 ± 0.33) × 10 9 M in agreement with previous determinations. Thanks to the new data extending to the F336W band, we are able to analyze the youngest stellar populations with a higher time resolution. Most importantly, we recover the resolved SFH in different radial regions of the galaxy; this shows an indication of a growing trend of the present-to-past SFR ratio, increasing from internal to more external regions, supporting previous findings of the inside-out growth of the galaxy.

The Age Dependence of Mid-infrared Emission around Young Star Clusters

“…NGC 4449 and NGC 3738 are found to have approximately constant SFHs in the last 200 Myr (Cignoni et al 2018(Cignoni et al , 2019Sacchi et al 2018). Sacchi et al (2019) also reported that the SFH of NGC 7793, which contributes 40% of our final sample (see Table 1), is not bursty and suggests inside-out star formation in this galaxy. Further discussion can be found in Appendix B, where we demonstrate that complex stellar populations are still needed to explain the observations of some of our sources.…”

The dependence of the hierarchical distribution of star clusters on galactic environment

“…It is part of the Sculptor group, and is one of the closest galaxies in the LEGUS sample. It is characterized by diffuse, broken spiral arms with no bar, a very faint central bulge, and a relatively low star formation rate Sacchi et al (2019). study the star formation history of this galaxy using LEGUS data, whileGrasha et al (2017a,b) study the spatial and temporal TPCF of its star clusters.…”

A Multi-Wavelength Study of Star Formation in 15 Local Star-Forming Galaxies

“…The photometry in Carignan (1985) as well as the measurements in Figure A28 show little to no color gradient across the galaxy. The SED-derived radial SFH of NGC 7793 (Figure A29) shows how NGC 7793 has a roughly constant SFH over its lifetime with the exception of the small bulge region, as mentioned in Section 5.1 and in Sacchi et al (2019). The similar results among all annuli included in the radial analysis suggests that the continuous SFH was experienced across the galaxy, and not limited to either the inner or outer regions.…”

“…Another galaxy from our sample that has had its CMD-derived SFH computed was NGC 7793 in Radburn- Smith et al (2012) and Sacchi et al (2019). Both of their results suggest that about 80% of the galaxy's stars were formed within the last 8 Gyr and 40% within the last 4 Gyr.…”