The effects of dust on the photometric parameters of decomposed disks and bulges^⋆

¹ Jeremiah Horrocks Institute, University of Central Lancashire, PR1 2HE, Preston, UK
e-mail: bapastrav@uclan.ac.uk; cpopescu@uclan.ac.uk; aesansom@uclan.ac.uk
² Max Planck Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany
e-mail: Richard.Tuffs@mpi-hd.mpg.de

Received: 14 June 2013
Accepted: 31 July 2013

Abstract

We present results of a study to quantify the effects of dust on the derived photometric parameters of disk and bulges obtained from bulge-disk decomposition: scale-length, effective radius, Sérsic index, disk axis-ratio, and bulge-to-disk ratio. The dust induced changes in these parameters were obtained by fitting simulated images of composite systems (containing a disk and a bulge) produced using radiative transfer calculations. The simulations were fitted with the GALFIT 3.0.2 data analysis algorithm. Fits were done with both a combination of an exponential plus a variable-index Sérsic function as well as with a combination of two variable-index Sérsic functions. We find that dust is biasing the derived exponential scale-length of decomposed disks towards smaller values than would be otherwise derived if the galaxy were to have no bulge. Similarly, the derived bulge-to-disk ratio is biased towards smaller values. However, the derived axis-ratio of the disk is not changed in the decomposition process. The derived effective radius of decomposed disks of systems having exponential bulges is found to be less affected by dust when fits are done with two variable-index Sérsic functions. For the same type of fits dust is found to bias the value of the derived effective radius of decomposed disks towards lower values for systems having de Vaucouleurs bulges.