arXiv subjects

Roelof S. de Jong

Publications and source records attributed to Roelof S. de Jong.

76 records · Page 5Linked to original sources

arXiv1996

Near-infrared and optical broadband surface photometry of 86 face-on disk dominated galaxies. IV. Using color profiles to study stellar and dust content of galaxies

The stellar and dust content of spiral galaxies as function of radius has been investigated using near-infrared and optical broadband surface photometry of 86 face-on spiral galaxies. Colors of galaxies correlate with the azimuthally averaged local surface brightness both within and among galaxies, with the lower surface brightness regions being bluer. The colors formed from different passband combinations correlate strongly indicating that they probably arise from the same physical process. A 3D radiative transfer model was developed to calculate the effect of dust absorption and scattering on the luminosity and color profiles of galaxies. Stellar synthesis models were used to investigate the effects of the star formation history and the metallicity on the broadband color profiles. Combining all optical and near-infrared data shows that the color gradients in this sample of face-on galaxies are best explained by a combined stellar age and metallicity gradient across the disk, with the outer regions being on average younger and of lower metallicity. Dust reddening probably plays only a minor role, as the dust models cannot produce reddening profiles that are compatible with the observations. The observed color differences implicate substantial M/L_lambda differences, both within galaxies and among galaxies. The variations are such that the ``missing light'' problem derived from rotation fitting becomes even worse. Late-type galaxies (T>=6) have lower metallicities and are often of younger average age than earlier types and have therefore an entirely different M/L_λin most passbands. The near-infrared passbands are recommended for studies where the M/L_λratios should not vary too much.

astro-ph↗

arXiv1996

Near-infrared and optical broadband surface photometry of 86 face-on disk dominated galaxies. III. The statistics of disk and bulge parameters

The statistics of the fundamental bulge and disk parameters of galaxies and their relation to the Hubble sequence were investigated by an analysis of optical and near-infrared observations of 86 face-on spiral galaxies. The availability of near-infrared K-passband data made it possible for the first time to trace fundamental parameters related to the luminous mass while hardly being hampered by the effects of dust and stellar populations. The observed number frequency of galaxies was corrected for selection effects to calculate volume number densities of galaxies with respect to their fundamental parameters. The main conclusions of this investigation are: 1) Freeman's law has to be redefined. There is no single preferred value for the central surface brightnesses of disks in galaxies. There is only an upper limit to the central surface brightnesses of disks, while for lower central surface brightnesses the number of galaxies per volume element decreases only slowly as function of the central surface brightness. 2) The Hubble sequence type index correlates strongly with the effective surface brightness of the bulge, much better than with the bulge-to-disk ratio. 3) The disk and bulge scalelengths are correlated. 4) These scalelengths are not correlated with Hubble type. Hubble type is a lengthscale-free parameter and each type therefore comes in a range of magnitudes (and presumably a range of total masses). 5) Low surface brightness spiral galaxies are not a separate class of galaxies. In a number of aspects they are a continuation of a trend defined by the high surface brightness galaxies. Low surface brightness galaxies are in general of late Hubble type.

astro-ph↗

arXiv1996

Near-infrared and optical broadband surface photometry of 86 face-on disk dominated galaxies. II. A two-dimensional method to determine bulge and disk parameters

In this paper I present a new two-dimensional decomposition technique, which models the surface photometry of a galaxy with an exponential light profile for both bulge and disk and, when necessary, with a Freeman bar. The new technique was tested for systematic errors on both artificial and real data and compared with widely used one-dimensional decomposition techniques, where the luminosity profile of the galaxy is used. The comparisons indicate that a decomposition of the two-dimensional image of the galaxy with an exponential light profile for both bulge and disk yields the most reproducible and representative bulge and disk parameters. An extensive error analysis was made to determine the reliability of the model parameters. If the model with an exponential bulge profile is a reasonable description of a galaxy, the maximum errors in the derived model parameters are of order 20%. The uncertainties in the model parameters will increase, if the exponential bulge function is replaced by other often used bulge functions as the de Vaucouleurs law. All decomposition methods were applied to the optical and near-infrared data set presented by de Jong & van der Kruit (1994), which comprises 86 galaxies in six passbands.

astro-ph↗

arXiv1995

Colour Gradients in the Optical and Near-IR

For many years broadband colours have been used to obtain insight into the contents of galaxies, in particular to estimate stellar and dust content. Broadband colours are easy to obtain for large samples of objects, making them ideal for statistical studies. In this paper I use the radial distribution of the colours in galaxies, which gives more insight into the local processes driving the global colour differences than integrated colours. Almost all galaxies in my sample of 86 face-on galaxies become systematically bluer with increasing radius. The radial photometry is compared to new dust extinction models and stellar population synthesis models. This comparison shows that the colour gradients in face-on galaxies are best explained by age and metallicity gradients in the stellar populations and that dust reddening plays a minor role. The colour gradients imply $M/L$ gradients, making the `missing light' problem as derived from rotation curve fitting even worse.

astro-ph↗