Abstract.A sample of 40 bright spiral galaxies (BT < 12) with low inclination and without bar was observed with JHK filters. For this purpose the MAGIC NICMOS3 camera at the 2.2 m telescope of the Calar Alto observatory, Spain was used. With a newly developed 2-dimensional algorithm the distribution of the surface brightness was fitted simultaneously by corresponding functions for the disk-and bulge-structure. While the disk was fitted with an exponential function, the bulge profile was fitted with a generalized de Vaucouleurs R β law, with the concentration parameter β = 1/n as a further fit variable. The correlation of the resulting structural parameters of disks and bulges lead to some interesting relations: 1. The use of a variable exponent β is necessary for a realistic description of the bulge structure; 2. Disks and bulges show similar correlations between effective radius, effective surface brightness and luminosity; 3. They populate a common strip in the fundamental plane; 4. From the correlations between β and Hubble type some conclusions about the formation and evolution of spiral galaxies can be drawn.
We present the B-band Tully-Fisher relation (TFR) of 60 late-type galaxies with redshifts 0.1 − 1. The galaxies were selected from the FORS Deep Field with a limiting magnitude of R = 23. Spatially resolved rotation curves were derived from spectra obtained with FORS2 at the VLT. High-mass galaxies with v max 150 km/s show little evolution, whereas the least massive systems in our sample are brighter by ∼ 1 − 2 mag compared to their local counterparts. For the entire distant sample, the TFR slope is flatter than for local field galaxies (−5.77 ± 0.45 versus −7.92 ± 0.18). Thus, we find evidence for evolution of the slope of the TFR with redshift on the 3 σ level. This is still true when we subdivide the sample into three redshift bins. We speculate that the flatter tilt of our sample is caused by the evolution of luminosities and an additional population of blue galaxies at z 0.2. The mass dependence of the TFR evolution also leads to variations for different galaxy types in magnitude-limited samples, suggesting that selection effects can account for the discrepant results of previous TFR studies on the luminosity evolution of late-type galaxies.
We present corrections for the change in the apparent scalelengths, central surface brightnesses and axis ratios due to the presence of dust in pure disk galaxies, as a function of inclination, central face-on opacity in the B-band (τ f B ) and wavelength. The correction factors were derived from simulated images of disk galaxies created using geometries for stars and dust which can reproduce the entire spectral energy distribution from the ultraviolet (UV) to the Far-infrared (FIR)/submillimeter (submm) and can also account for the observed surface-brightness distributions in both the optical/Near-infrared and FIR/submm. We found that dust can significantly affect both the scalelength and central surface brightness, inducing variations in the apparent to intrinsic quantities of up to 50% in scalelength and up to 1.5 mag in central surface brightness. We also identified some astrophysical effects for which, although the absolute effect of dust is non-negligible, the predicted variation over a likely range in opacity is relatively small, such that an exact knowledge of opacity is not needed. Thus, for a galaxy at a typical inclination of 37• and having any τ f B > 2, the effect of dust is to increase the scalelength in B relative to that in I by a factor of 1.12 ± 0.02 and to change the B − I central colour by 0.36 ± 0.05 mag. Finally we use the model to analyse the observed scalelength ratios between B and I for a sample of disk-dominated spiral galaxies, finding that the tendency for apparent scalelength to increase with decreasing wavelength is primarily due to the effects of dust.
Abstract.A sample of 26 bright spiral galaxies (B tot < 12.7) with low to medium inclination and without a bar was observed with UBVRI filters. The CAFOS focal reducer camera at the Calar Alto 2.2 m telescope was used. The surface-brightness distributions were fitted using a 2-dimensional algorithm with corresponding functions for the disk-and bulge-structure. For the disks an exponential function was used, for the bulges a Sérsic R β law, was applied with the concentration parameter β = 1/n as another fit variable. Correlations of the resulting structural parameters of disks and bulges in UBVRI are investigated, giving clues to the formation history of the bulges. We confirm that the large and bright bulges of early-type spirals are similar to elliptical galaxies. They were probably formed prior to the disks in a monolithic collapse or via early mergers. Late-type spirals have tiny and faint bulges with disk-like profiles. These bulges were probably formed after the disk in secular evolution processes, e.g. from a disk instability. The comparison of the color indices of corresponding spirals and bulges with population synthesis computations support above formation scenarios.
Abstract. Using a sample of 57 VLT FORS spectra in the redshift range 1.37 < z < 3.40 (selected mainly from the FORS Deep Field survey) and a comparison sample with 36 IUE spectra of local (z ≈ 0) starburst galaxies we derive C and Si equivalent width values and estimate metallicities of starburst galaxies as a function of redshift. Assuming that a calibration of the C equivalent widths in terms of the metallicity based on the local sample of starburst galaxies is applicable to high-z objects, we find a significant increase of the average metallicities from about 0.16 Z at the cosmic epoch corresponding to z ≈ 3.2 to about 0.42 Z at z ≈ 2.3. A significant further increase in metallicity during later epochs cannot be detected in our data. Compared to the local starburst galaxies our high-redshift objects tend to be overluminous for a fixed metallicity. Our observational results are in good agreement with published observational data by other authors and with theoretical predictions of the cosmic chemical evolution.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.