4. Radial density profile and integrated photometry
The radial density profile of SagDIG has been obtained by counting stars in circular concentric annuli from the apparent optical center of the galaxy. Fig. 8 shows the results. It is apparent from this figure that the galaxy vanishes at , the background level corresponding to about 0.016 stars arcsec-2. From the nearby companion field that we have taken, a similar but slightly lower value of 0.013 stars arcsec-2 is obtained.
Subtracting the former value of the background to the density profile, an exponential law has been fitted to the region , which results in a scale length of or 140 pc.
Total integrated magnitudes and colours have also been obtained. To reduce the effects of foreground contamination, we have first remove all the stars with and . The sky level has been approximated by a 2-dimension polynomial, using regions with few stars near the edges of the images. Then, integrated photometry of SagDIG has been performed with increasing circular apertures. The galaxy magnitude in each band has then been measured as the asymptotic value of the derived growth curve. The colour has been determined as the difference of total magnitudes in each band. The results are and .
Fig. 9 shows the CMDs for 2 circular regions centered in the galaxy center and radii 60" and 120", respectively. It visualizes the relative contribution of SagDIG and foreground stars for increasing radial distances.
© European Southern Observatory (ESO) 1999
Online publication: December 2, 1999