arXiv subjects

I. S. Glass

Publications and source records attributed to I. S. Glass.

22 records · Page 2Linked to original sources

arXiv1998

Multiwavelength Observations of a Seyfert 1 Galaxy Detected in ACO 3627

ACO 3627 is a rich, nearby cluster of galaxies at the core of the Great Attractor. At the low galactic latitude of b = -7.2 the galactic extinction is significant. Nevertheless, its proximity makes it a prime target for studies of environmental effects on its cluster members. Here, we report on a multi-wavelength study of a Seyfert 1 galaxy at 30 arcminutes from the centre of ACO 3627. Its Seyfert nature was discovered spectroscopically and confirmed in X-rays. We have obtained B_J and R_C CCD photometry as well as J, H, K and L aperture photometry at the SAAO, low and high resolution spectroscopy (ESO and SAAO), 21 cm line observations (Parkes Observatory) and X-ray ROSAT PSPC data. The Seyfert 1 galaxy is of morphology SBa(r). It has a nearby companion (dS0) but shows no signs of interaction. A consistent value for the galactic extinction of A_B = 1.6 mag could be determined. The nucleus of the Seyfert is very blue with a strong (B_J - R_C) colour gradient in the inner 2.5 arcsec. The extinction-corrected near-infrared colours of WKK 6092 are typical of a Seyfert 1 and the X-ray spectrum conforms to the expectation of a Seyfert as well. The galaxy has a very low HI flux. This could be explained by its morphology, but also -- due to its very central position within the rich Norma cluster -- to ram pressure stripping.

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arXiv1998

CO in blue compact and star burst galaxies

$^{12}CO(J=1 \to 0)$ observations of 34 blue compact and star burst galaxies are presented. Although these galaxies are experiencing vigorous star formation at the current epoch, CO has been detected in only five of them. The five detections reported in this paper are all in galaxies with relatively red colours, (B-V)_0 > 0.4. The new observations, when combined with previously published data on CO in BCGs, indicate that CO luminosity decreases with absolute luminosity of BCGs. Since the absolute luminosity of a galaxy is correlated with its metallicity, these results confirm that low metallicity BCGs have low abundances of CO gas. We also show that the star formation rate determined from the $H_β$ luminosity is lower than that determined from the far infrared luminosity.

astro-ph↗

arXiv1997

BeppoSAX observations of PKS 0528+134

We report on the BeppoSAX observations of the gamma-ray blazar PKS 0528+134 performed in Feb and Mar 1997, during a multiwavelength campaign involving EGRET and ground based telescopes. The source was in a faint and hard state, with energy spectral index alpha=0.48+-0.04 between 0.1 and 10 keV, and [2-10] keV flux of 2.7E-12 erg/cm2/s. No significant variability was observed. The source was detected in the 20-120 keV band by the PDS, with a flux lying slightly above the extrapolation from lower X-ray energies. Comparing this low state with previous higher states of the source, there is an indication that the X-ray spectrum hardens and the gamma-ray spectrum steepens when the source is fainter.

astro-ph↗

arXiv1995

Multi-Frequency Monitoring of the Seyfert 1 Galaxy NGC~4593 II: a Small, Compact Nucleus ?

We discuss the results of a campaign to monitor spectral variations in the low-luminosity Seyfert~1 galaxy NGC~4593, at X-rays, ultraviolet, optical and near IR frequencies. The observations and data analysis have been described in a companion paper (Santos-Lleó et al. 1994; Paper~1). The active nucleus in this galaxy is strongly and rapidly variable in all wavebands, implying that the continuum source is unusually compact. Its energy distribution from 1.2~$μ$m to 1200~Å\/ obeys a power-law whose index is significantly steeper than is usual in Seyfert's or QSO's; the ``big bump'' is either absent or shifted to wavelengths shorter than 1200~Å\/. The variations of the soft-X~ray {\em excess\/} do not correlate with those of the UV or hard X-ray continuum. The far UV and optical fluxes are well correlated, while the correlation between the hard X-rays and 1447 Å continuum is only marginally significant. Moreover, the optical flux cannot lag behind the UV by more than 6 days. These results cannot be accommodated in the framework of the standard geometrically thin accretion disk model. Rather, they suggest that the bulk of the UV and optical flux originates from thermal reprocessing of X-rays irradiating the disk. The soft X-ray excess is probably the only spectral component which originates from viscous dissipation inside the disk and the near infrared is probably emitted by hot dust heated by the UV radiation. Such a model is consistent with NGC~4593 having a relatively small black-hole mass of the order of $2\times10^{6}{\rm M_{\odot}}$ as inferred from the line variability study. The high ionization/excitation emission lines are very broad and strongly variable and their variations correlate with those of the continuum. The low excitation lines are significantly narrower and remain constant within the accuracy of our measurements. These results suggest a stratified BLR, where the degree of ionization and the velocity dispersion of the gas increase toward small radii. The \lya\ line responds to the variations of the continuum with a delay $\leq 4$ days. To a first order approximation, the BLR in NGC~4593 is well modelled with two different zones at distances of $\sim$~15 and 3 lt-ds from the ionizing source respectively.

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