214 research outputs found
Emission line gas in early-type galaxies: Kinematics and physical conditions
Recent studies have found line emission gas in nearby early-type galaxies, but the properties of the emission-line gas in these 'normal' galaxies remain enigmatic. In terms of activity in the nucleus, these LINER-like galaxies form an important link between giant H 2 region galaxies and low-luminosity Seyferts. Despite their large numbers and evolutionary significance, we do not know whether these galaxies form a homogeneous class of objects; nor do we know how the distribution and kinematics of the line emission gas are affected by the host galaxy's environment or by the properties of the central engine, if present. To address these issues we are conducting a magnitude and volume limited survey of nearby early-type galaxies at Lick Observatory and the Michigan-Dartmouth-MIT Observatory. We have selected approximately 100 galaxies from radio catalogs. A large sample is necessary because while studies of individual 'LINERS' have led to a certain understanding of the phenomenon, these studies have not provided a global framework. Here we present results from our first run of medium resolution (approximately 5 A FWHM) spectroscopy. Kinematic data and line ratios determined along the major and minor axes of 6 galaxies are discussed. The information gleaned from spectroscopic data, when combined with data at other wavelengths, will enable a thorough investigation into the nature of low luminosity nuclear activity
BeppoSAX observations of the Seyfert 1 Galaxy NGC 3516
We present the results of two observations of the bright Seyfert 1 galaxy NGC
3516, obtained with BeppoSAX in 1996 November and 1997 March. Useful signal is
detected between 0.2 and 60 keV, allowing for the first time the simultaneous
observation of all main spectral features. The source was brighter by a factor
2 at the second epoch of observation. Both spectra present a strong Fe Kalpha
line, and a reflection hump at high energy. An absorption edge at 0.8 keV is
visible in the later spectrum, but not in the earlier one, indicating that this
feature is strongly variable.Comment: to appear in : The Active X-ray Sky: Results from BeppoSAX and
Rossi-XTE, Nuclear Physics B Proceedings Supplements, L. Scarsi, H. Bradt, P.
Giommi and F. Fiore (eds.), Elsevier Science B.V. 4 pages LateX and 6 ps
figures, using espcrc2 and epsfi
ANTIOXIDANT ACTIVITY AND ANTIPROLIFERATIVE ACTION OF METHANOLIC EXTRACT OF LIQUORICE (GLYCYRRHIZA GLABRA) IN HEPG2 CELL LINE
Objective: To evaluate the in vitro antioxidant activity of liquorice (Glycyrrhiza glabra) against H2O2 induced oxidative stress in HepG2 cell line.Methods: Antioxidant activity of methanolic extracts of Glycyrrhiza glabra was investigated by measuring total phenolic content using folin-ciocalteu reagent (FCR), free radical scavenging activity by DPPH and ferric reducing antioxidant power (FRAP). The presence of phenolic compounds and flavonoids in the extract was confirmed by Liquid Chromatography-Mass Spectrometry (LC-MS) analysis. Furthermore, the protective effect of methanolic extract of Glycyrrhiza glabra against oxidative stress induced by H2O2 in HepG2 cells was investigated by MTT assay. HepG2 cells were exposed with five different treatments viz. liquorice, H2O2, ascorbic acid, H2O2+liquorice and H2O2+ascorbic acid, to explore the effect of the extract on malondialdehyde (MDA) production, catalase activity, and glutathione reductase levels.Results: The total phenolic content estimated in Glycyrrhiza glabra extract was found to be 241.47 µg per 1000 µg/ml of methanolic extract. It was found that as the concentration of the extract was increased both the free radical scavenging activity and ferric ion reducing power was also found to increase. LC-MS analysis confirmed the presence of eight different phenolic compounds in the methanolic extract which are possibly contributing to the antioxidant activity exhibited by the extract. It was also observed that liquorice treated HepG2 cells showed lower MDA and higher glutathione and catalase levels as compared to only H2O2 treated HepG2 cells where increased MDA production, decreased glutathione reductase and catalase production was observed.Conclusion: Our results thus conclude that, the methanolic extract of Glycyrrhiza glabra can be used as natural supplements in various disease conditions where oxidative stress has been reported. Â
A Cutoff in the X-ray Fluctuation Power Density Spectrum of the Seyfert 1 Galaxy NGC 3516
During 1997 March-July, XTE observed the bright, strongly variable Seyfert 1
galaxy NGC 3516 once every ~12.8 hr for 4.5 months and nearly continuously
(with interruptions due to SAA passage but not Earth occultation) for a 4.2 day
period in the middle. These were followed by ongoing monitoring once every ~4.3
days. These data are used to construct the first well-determined X-ray
fluctuation power density spectrum (PDS) of an active galaxy to span more than
4 decades of usable temporal frequency. The PDS shows no signs of any strict or
quasi-periodicity, but does show a progressive flattening of the power-law
slope from -1.74 at short time scales to -0.73 at longer time scales. This is
the clearest observation to date of the long-predicted cutoff in the PDS. The
characteristic variability time scale corresponding to this cutoff temporal
frequency is 1 month. Although it is unclear how this time scale may be
interpreted in terms of a physical size or process, there are several promising
candidate models. The PDS appears similar to those seen for Galactic black hole
candidates such as Cyg X-1, suggesting that these two classes of objects with
very different luminosities and putative black hole masses (differing by more
than a factor of 10^5) may have similar X-ray generation processes and
structures.Comment: 21 pages, incl. 5 figures, AASTe
BL Lac X-ray Spectra: simpler than we thought
We report results from {\it XMM-Newton} observations of thirteen X-ray bright
BL Lacertae objects, selected from the {\it Einstein} Slew Survey sample. The
spectra are generally well fit by power-law models, with four objects having
hard () spectra that indicates
synchrotron peaks at keV. None of our spectra show line features,
indicating that soft X-ray absorption ``notches'' must be rare amongst BL Lacs,
rather than common or ubiquitous as had previously been asserted. We find
significant curvature in most of the spectra. This curvature is almost
certainly intrinsic, as it appears nearly constant from 0.5 to 6 keV, an
observation which is inconsistent with the small columns seen in these sources.Comment: 4 pages, 1 figure; to be published in proceedings of the Cozumel
meeting on "Multiwavelength Surveys for AGN", Cozumel 200
Below the Lyman Edge: UV Polarimetry of Quasars
The Lyman edge at 912 \AA is an important diagnostic region for studying
quasi-stellar objects (QSOs). In particular, it reveals a great deal about the
physical conditions within the atmospheres of accretion disks, a ubiquitous
component of QSO theories. A robust prediction of accretion disk models is a
significant polarization due to electron scattering just longward (in
wavelength) of the Lyman edge because of the wavelength dependence of the
Hydrogen absorption opacity. Observations of the Lyman edge regions of QSOs
have shown scant evidence for the predicted features-few QSOs show the broad,
partial Lyman edges expected to be common according to most theories, and none
show the high polarizations expected longward of the Lyman edge. Still,
polarization spectra of a small number of QSOs have shown a rising polarization
(up to 20%) at wavelengths shortward of the Lyman edge. We have now doubled our
sample of intermediate-redshift QSOs observed with the HST/FOS
spectropolarimeter to determine the amount of polarization on both sides of the
Lyman limit. For this new sample of six objects, polarizations are low and
mostly consistent with zero below the Lyman edge.
Another important result of the new data is that it strengthens the
conclusion that quasars are generally not polarized significantly just longward
of the Lyman edge at $\sim 1000 \AA. There is no significant statistical
wavelength dependence to the polarization longward of the Lyman edge indicating
that simple plane-parallel atmospheres with scattering-dominated opacity are
not significant sources of UV flux in quasars.Comment: Accepted to Ap.J., 30 pages, 8 figure
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