Far-UV Observations of NGC 4151 during the ORFEUS-SPAS II Mission

We observed the Seyfert 1 galaxy NGC 4151 on eleven occasions at 1-2 day intervals using the Berkeley spectrometer during the ORFEUS-SPAS II mission in 1996 November. The mean spectrum covers 912-1220 A at ~0.3 A resolution with a total exposure of 15,658 seconds. The mean flux at 1000 A was 4.7e-13 erg/cm^2/s/A. We identify the neutral hydrogen absorption with a number of components that correspond to the velocity distribution of \ion{H}{1} seen in our own Galaxy as well as features identified in the CIV 1549 absorption profile by Weymann et al. The main component of neutral hydrogen in NGC 4151 has a total column density of log N_HI = 18.7 +/- 1.5 cm^{-2} for a Doppler parameter b=250 +/- 50 km/s, and it covers 84 +/- 6% of the source. This is consistent with previous results obtained with the Hopkins Ultraviolet Telescope. Other intrinsic far-UV absorption features are not resolved, but the CIII* 1176 absorption line has a significantly higher blueshift relative to NGC 4151 than the CIII 977 resonance line. This implies that the highest velocity region of the outflowing gas has the highest density. Variations in the equivalent width of the CIII* 1176 absorption line anticorrelate with continuum variations on timescales of days. For an ionization timescale <1 day, we set an upper limit of 25 pc on the distance of the absorbing gas from the central source. The OVI 1034 and HeII 1085 emission lines also vary on timescales of 1-2 days, but their response to the continuum variations is complex. For some continuum variations they show no response, while for others the response is instantaneous to the limit of our sampling interval.Comment: 4 pages, 2 PostScript figures, uses emulateapj.sty, apjfonts.sty. To appear in the Astrophysical Journal (Letters) special issue for ORFEU

Quasars as Cosmological Probes: The Ionizing Continuum, Gas Metallicity and the EW-L Relation

Using a realistic model for line emission from the broad emission line regions of quasars, we are able to reproduce the previously observed correlations of emission-line ratios with the shape of the spectral energy distribution (SED). In agreement with previous studies, we find that the primary driving force behind the Baldwin Effect (EW ~ L^beta, beta < 0) is a global change in the SED with quasar luminosity, in that more luminous quasars must have characteristically softer ionizing continua. This is completely consistent with observations that show correlations between L_uv, alpha_ox, alpha_uvx, line ratios and EWs. However, to explain the complete lack of a correlation in the EW(NV)--L_uv diagram we propose that the more luminous quasars have characteristically larger gas metallicities (Z). As a secondary element, nitrogen's rapidly increasing abundance with increasing Z compensates for the losses in EW(NV) emitted by gas illuminated by softer continua in higher luminosity quasars. A characteristic relationship between Z and L has an impact on the EW--L_uv relations for other lines as well. For a fixed SED, an increasing gas metallicity reduces the EW of the stronger metal lines (the gas cools) and that of Ly_alpha and especially HeII (because of the increasing metal opacity), while the weaker lines (e.g., CIII] 1909) generally respond positively. The interplay between the effects of a changing SED and Z with L results in the observed luminosity dependent spectral variations. All of the resulting dependences on L_uv are within the range of the observed slopes.Comment: 11 pages, 3 figures, AASTeX aas2pp4.sty, accepted for publication in Ap

Intergalactic UV Background Radiation Field

We have performed proximity effect analysis of low and high resolution data, considering detailed frequency and redshift dependence of the AGN spectra processed through galactic and intergalactic material. We show that such a background flux, calculated using the observed distribution of AGNs, falls short of the value required by the proximity effect analysis by a factor of $\ge$ 2.7. We have studied the uncertainty in the value of the required flux due to its dependence on the resolution, description of column density distribution, systemic redshifts of QSOs etc. We conclude that in view of these uncertainties the proximity effect is consistent with the background contributed by the observed AGNs and that the hypothesized presence of an additional, dust extinct, population of AGNs may not be necessary.Comment: To be published in the Journal of Astronomy and Astrophysics aasms, 2 figures, 2 tables. Paper replaced to include the figure

Identification of new participants in the rainbow trout (Oncorhynchus mykiss) oocyte maturation and ovulation processes using cDNA microarrays

BACKGROUND: The hormonal control of oocyte maturation and ovulation as well as the molecular mechanisms of nuclear maturation have been thoroughly studied in fish. In contrast, the other molecular events occurring in the ovary during post-vitellogenesis have received far less attention. METHODS: Nylon microarrays displaying 9152 rainbow trout cDNAs were hybridized using RNA samples originating from ovarian tissue collected during late vitellogenesis, post-vitellogenesis and oocyte maturation. Differentially expressed genes were identified using a statistical analysis. A supervised clustering analysis was performed using only differentially expressed genes in order to identify gene clusters exhibiting similar expression profiles. In addition, specific genes were selected and their preovulatory ovarian expression was analyzed using real-time PCR. RESULTS: From the statistical analysis, 310 differentially expressed genes were identified. Among those genes, 90 were up-regulated at the time of oocyte maturation while 220 exhibited an opposite pattern. After clustering analysis, 90 clones belonging to 3 gene clusters exhibiting the most remarkable expression patterns were kept for further analysis. Using real-time PCR analysis, we observed a strong up-regulation of ion and water transport genes such as aquaporin 4 (aqp4) and pendrin (slc26). In addition, a dramatic up-regulation of vasotocin (avt) gene was observed. Furthermore, angiotensin-converting-enzyme 2 (ace2), coagulation factor V (cf5), adam 22, and the chemokine cxcl14 genes exhibited a sharp up-regulation at the time of oocyte maturation. Finally, ovarian aromatase (cyp19a1) exhibited a dramatic down-regulation over the post-vitellogenic period while a down-regulation of Cytidine monophosphate-N-acetylneuraminic acid hydroxylase (cmah) was observed at the time of oocyte maturation. CONCLUSION: We showed the over or under expression of more that 300 genes, most of them being previously unstudied or unknown in the fish preovulatory ovary. Our data confirmed the down-regulation of estrogen synthesis genes during the preovulatory period. In addition, the strong up-regulation of aqp4 and slc26 genes prior to ovulation suggests their participation in the oocyte hydration process occurring at that time. Furthermore, among the most up-regulated clones, several genes such as cxcl14, ace2, adam22, cf5 have pro-inflammatory, vasodilatory, proteolytics and coagulatory functions. The identity and expression patterns of those genes support the theory comparing ovulation to an inflammatory-like reaction