No abstract

We present new constraints on the system parameters of the SW Sextantis star DW Ursae Majoris, based on ultraviolet (UV ) eclipse observations with the Hubble Space Telescope. Our data were obtained during a low state of the system, in which the UV light was dominated by the hot white dwarf (WD) primary. The duration of the WD eclipse allows us to set a firm lower limit on the mass ratio, q = M 2 /M 1 > 0.24; if q < 1.5 (as expected on theoretical grounds) the inclination must satisfy i > 71 • . We have also been able to determine the duration of WD ingress and egress from our data. This allows us to constrain the

Recent studies have shown that K-luminous galaxies at have high Ha line widths and high 2 ! z ! 2.5 [N ii] l6583/Ha ratios. If these lines arise from photoionization by massive stars in H ii regions, these results imply that massive, metal-rich galaxies exist at high redshift. Here we investigate the ionization mechanism in a galaxy with and in the Chandra Deep Field-South, using the new Gemini Near-Infrared Spectrograph K p 19.1 z p 2.225 s (GNIRS). GNIRS's cross-dispersed mode gives simultaneous access to the entire 1-2.5 mm wavelength range, allowing accurate measurements of line ratios of distant galaxies. From the ratio of Ha/Hb, we infer that the lineemitting gas is heavily obscured, with . The reddening is higher than that inferred previously2 from the UV-optical continuum emission, consistent with findings for nearby starburst galaxies. We find that the galaxy has Seyfert-like line ratios, and , which can be caused by photoionization [N ii]/Ha ≈ 0.6[O iii] l5007/Hb ≈ 6 by an active galactic nucleus (AGN) or shock ionization due to a strong galactic wind. Although we cannot exclude the presence of an AGN, the lack of AGN spectral features in the rest-frame ultraviolet, the consistency of radio, X-ray, and rest-frame UV star formation indicators, the fact that the [O iii]/Hb ratio remains high out to ∼10 kpc from the nucleus, and the observed gas kinematics all argue for the wind hypothesis. Similar shock-induced ionization is seen in nearby starburst galaxies with strong winds, such as NGC 1482 and NGC 3079. The evidence for shock ionization implies that measurements of metallicities and dynamical masses of star-forming galaxies should z 1 2 be regarded with caution, especially since the existence of strong galactic winds in these objects is well established. Based on Sloan Digital Sky Survey data for nearby galaxies and the limited data available at high redshift, we speculate that the effects of shocks may correlate with dust content. The results presented here demonstrate the importance of measuring the full rest-frame optical spectra of high-redshift galaxies and showcase the potential of GNIRS for such studies.

No abstract