Colors and color gradients in bulges of galaxies

Historically, galactic bulges are thought to be elliptical galaxy-like objects sitting in the middle of a generally larger disk. There are, however, more and more claims that some bulges are much more similar to disks. John Kormendy has named these bulges pseudo-bulges. In this paper I discuss some recent integral field spectroscopy of the SAURON collaboration on a sample of 24 Sa and Sab galaxies. Using their 2-dimensional maps of the stellar velocity, velocity dispersion, a...

The origins of the bulge and disc components of galaxies are of primary importance to understanding galaxy formation. Here bulge-disc decomposition is performed simultaneously in B- and R-bands for 922 bright galaxies in 8 nearby (z < 0.06) clusters with deep redshift coverage using photometry from the NOAO Fundamental Plane Survey. The total galaxy colours follow a universal colour-magnitude relation (CMR). The discs of L_* galaxies are 0.24 magnitudes bluer in $B-R$ than bu...

This work presents the structural decomposition of a sample of 11 disk galaxies, which span a range of different morphological types. The U, B, V, R, and I photometric information given in Paper I (color and color-index images and luminosity, ellipticity, and position-angle profiles) has been used to decide what types of components form the galaxies before carrying out the decomposition. We find and model such components as bulges, disks, bars, lenses and rings.

We analyse colours of the nuclear regions of intermediate redshift disk galaxies, with the aim of obtaining empirical information of relative ages of bulges and disks at 0.1 < z < 1.3. We work with an apparent-diameter limited parent sample of 248 galaxies from the HST Groth Strip Survey. We apply a conservative criterion to identify bulges and potential precursors of present-day bulges based on nuclear surface brightness excess above the exponential profile of the outer part...

We present first results from an on-going survey of the stellar populations of the bulges and inner disks of spirals at various points along the Hubble sequence. In particular, we are investigating the hypotheses that bulges of early-type spirals are akin to (and may in fact originally have been) intermediate-luminosity ellipticals while bulges of late-type spirals are formed from dynamical instabilities in their disks. Absorption-line spectroscopy of the central regions of S...

We present near-infrared (NIR) surface photometry of a sample of 14 early-type spirals with observed rotation curves. In this first paper, we report the results of two-dimensional parametric and non-parametric decompositions to separate the bulge and disk components; the parametric bulge is modeled with a generalized exponential law of integer index n, and the disk with a simple exponential. We find that the derived bulge parameters, for a given galaxy, vary systematically wi...

We present a study of the broadband UBV color profiles for 257 Sbc barred and non-barred galaxies. In our sample, the color gradients are negative (reddish inward) in approximately 59% of the objects, are almost null in 27%, and are positive in 14%, considering only the face-on galaxies, which represent approximately 51% of the sample. We have also found that barred galaxies are over-represented among the objects having null or positive gradients, indicating that bars act as ...

In an ongoing effort to study the formation and evolution of galactic bulges we have investigated the position of 19 bulges of type S0-Sbc on the fundamental plane (FP). We find that bulges, both in B and K band, lie close to but slightly below the FP defined by ellipticals and S0s, i.e. are slightly brighter. There are hints that bulges of later morphological type are situated below the other bulges in our sample. The FP results are consistent with the picture, obtained from...

We study the photometric parameters of the bulges of galaxies of different Hubble types including ellipticals, lenticulars, early and late type spirals and early type dwarf galaxies. Analyzing the distributions of various photometric parameters, and two- and three-dimensional correlations between them, we find that there is a difference in the correlations exhibited by bright (M_K < -22) and faint bulges, irrespective of their Hubble type. Importantly, the bright bulges, whic...

An observational survey of stars selected from the region of sky in the direction of the Galactic bulge is presented. We discuss the choice of tracer populations for this study. Digitised UK Schmidt plate photometry, calibrated with CCD photometry, is obtained in 18 regions over the bulge. Stars are selected for spectroscopic follow-up from within a carefully chosen colour-magnitude selection window, optimised for efficient detection of bulge K giants. Some 1500 stellar spect...