arXiv subjects

L. van Zee

Publications and source records attributed to L. van Zee.

21 records · Page 2Linked to original sources

arXiv1998

Neutral Gas Distributions and Kinematics of Five Blue Compact Dwarf Galaxies

We present the results of high spatial resolution HI observations of five intrinsically compact dwarf galaxies which are currently experiencing a strong burst of star formation. The HI maps indicate that these systems have a complex and clumpy interstellar medium. Unlike typical dwarf irregular galaxies, these Blue Compact Dwarf (BCD) galaxies exhibit strong central concentrations in their neutral gas distributions which may provide a clue to the origin of their strong star-burst activity. Furthermore, while all of the systems do appear to be rotating, based on observed velocity gradients, the kinematics are complex. All systems have non-ordered kinematic structure at some level; some of the extended gas is not necessarily kinematically connected to the main system. The observed gas distributions and kinematics place constraints on evolutionary scenarios for BCDs. Evolutionary links between BCDs, dwarf irregulars, and dwarf ellipticals have been postulated to explain their high star formation rates and low luminosity, low metallicity nature. The BCDs appear to have higher central mass concentrations in both gas and stellar content than the dwarf irregulars, indicating that evolutionary scenarios connecting these two classes will require mass redistribution. In addition, the fact that BCDs are rotationally supported systems indicates that BCDs are unlikely to evolve into dwarf ellipticals without substantial loss of angular momentum. Thus, while such evolutionary scenarios may still be possible with the aid of mergers or tidal interactions, the isolated nature of BCDs suggests that the majority of BCDs will not fade to become objects similar to the present day dwarf ellipticals.

astro-ph↗

arXiv1998

Abundances in Spiral Galaxies: Evidence for Primary Nitrogen Production

We present the results of nitrogen and oxygen abundance measurements for 185 HII regions spanning a range of radius in 13 spiral galaxies. As expected, the nitrogen-to-oxygen ratio increases linearly with the oxygen abundance for high metallicity HII regions, indicating that nitrogen is predominately a secondary element. However, the nitrogen-to-oxygen ratio plateaus for oxygen abundances less than 1/3 solar (12+log(O/H) < 8.45), as is also seen in low metallicity dwarf galaxies. This result suggests that the observed trend in dwarf galaxies is not due to outflow of enriched material in a shallow gravitational potential. While the effects of infall of pristine material and delayed nitrogen delivery are still unconstrained, nitrogen does appear to have both a primary and secondary component at low metallicities in all types of galaxies.

astro-ph↗

arXiv1997

The Complex Kinematics of the Neutral Hydrogen Associated with IZw18

We present the results of high velocity and high spatial resolution HI synthesis observations of the blue compact dwarf galaxy IZw18 to investigate the link between its unique evolutionary history and the neutral gas distribution and kinematics. The HI distribution is extensive, with diffuse neutral gas extending to the northwest and south of the main component. This diffuse gas may be a remnant of the nascent HI cloud. The kinematics of the IZw18 system are complex, with 4 components identified: HI-A, HI-C, HI-I, and HI-SX. The gas associated with the main body, HI-A, has a steep velocity gradient; although our analysis is hindered by poor spatial resolution relative to the extent of the system, the main body appears to be undergoing solid body rotation. The optical condensation to the northwest of IZw18 is embedded in the common HI envelope, and is found to be kinematically separate from the main body (HI-C). The interbody gas, HI-I, connects HI-A and HI-C. Finally, a large diffuse, kinematically distinct, gas component extends at least 1 arcmin to the south of the main body (HI-SX), with no known optical counterpart. The peak of the gas column density coincides with the SE HII region in the main body; two other HI peaks are associated with the NW HII region and an HII region in the optical condensation to the northwest. In many respects, the HI properties of the main body of IZw18 (HI-A) are not unusual for dwarf galaxies; the peak column density, gas dispersion, M_H/L_B, and M_H/M_T are remarkably similar to other low mass systems. The neutral gas associated with IZw18 is best described as a fragmenting HI cloud in the early stages of galaxy evolution.

astro-ph↗