A Deep Photometric Study of M83 with the DuPont and Magellan Las Campanas Telescopes

(Above) Composite RGB mosaic of the M83 stellar halo from the Magellan 6.5m in V (blue) and I (red, green)

(Below) Deep coadded RGB image of M83 from the DuPont 100” telescope in R, V, and B filters.

Bryan Penprase (Pomona College), Barry Madore, Wendy Freedman (OCIW), and Ryan Quadri (Yale)

(Above) Closeup of M83 spiral arms in Magellan V and I filters, showing variations of stellar populations

(Below) Tricolor image of M83 in H-alpha, R and V filters, showing intense emission from HII regions

(Above) V band mosaic from Magellan after background subtraction and mosaicing with the SWARP program; (Below) same region as viewed in the I band before background subtraction.

Abstract:

The Galaxy M83 has been a target of an intensive observational campaign from Las Campanas and CTIO. Our program will help determine the relation between spiral structure and stellar populations, as well as the variation in nebular diagnostics from H-a, [O III], [S II], and other emission lines within M83. As part of the study we also will present deep photometry of the V-I colors and I magnitudes of the M83 stellar halo, to detect giant stars undergoing the Helium flash (Lee, Freedman and Madore 1991), which will enable an accurate distance estimate toward M83.

HST ACS Imaging of the Halo of M83

(Below, Top) Color Magnitude Diagram for the halo of M83. The tip of the red giant branch is apparent at approximately I=24.5

(Below, middle) Histogram of I magnitudes for the ACS photometry sample. The rise in star counts is caused by the detection of the red giant

stars in the M83 Halo.

(Above) Histogram of I magnitudes and convolution with Sobel kernel after Lee, Freedman and Madore (1991). The edge of the Red Giant Branch can be found, and since the absolute magnitude ITRGB = 4.0 the distance to M83 can be measured with a single photometric dataset.

Abstract:

The Galaxy M83 has been imaged with the HST ACS camera in the V and I (606W and 814W) filters to determine the stellar populations, magnitudes, and distance to the galaxy based on the tip of the red giant branch. Through accurate photometry of the halo stars, a distance modulus of I = MI-I = 28.5, which corresponds to a distance of 4.9 Mpc. The comparison of TRGB distances with Cepheid distances for M83 provides an important calibration of the Cepheid distance scales for a higher metallicity galaxy. Additional features of the ACS HST images are a population of blue stars, indicating a burst of star formation of approximately 1Gyr age, as well as a background cluster of galaxies.

(Above) Composite RGB mosaic of the M83 stellar halo from the HST ACS sci1 chip with V (blue) and I (red, green)

(Below) Composite RGB mosaic of the M83 stellar halo from the HST ACS sci2 chip, with slightly different stretch to show halo stars.

Bryan Penprase (Pomona College), Barry Madore (OCIW), and Wendy Freedman(OCIW)