Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userFar UV and X-ray observation: a hot view of shell galaxies
107
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Shell galaxies are considered the debris of recent accretion/merging episodes. Their high frequency in low density environments suggest that such episodes could drive the secular evolution for at least some fraction of the early-type galaxy population. We present here the preliminary results of ultraviolet and X-ray data for a sample of three shell galaxies, namely NGC 474, NGC 7070A and ESO 2400100. The Far UV morphology and photometry are derived using the observations obtained with the Galaxy Evolution Explorer and the XMM- Newton Optical Monitor. We aim at investigating the rejuvenation processes in the stellar population using the UV information as well as at gaining information about the possible evolution with time of the X-ray emission due interaction/merging processes.
rate research
Read More
We present XMM-Newton X-ray observations of two shell galaxies, NGC 7070A and ESO 2400100, and far UV observations obtained with the Optical Monitor for these and for an additional shell galaxy, NGC 474, for which we also have near and far UV data from GALEX. We aim at gaining insight on the overall evolution traced by their star formation history and by their hot gas content. The X-ray and the far UV data are used to derive their X-ray spatial and spectral characteristics and their UV luminosity profiles. We use models developed ad hoc to investigate the age of the last episode of star formation from the (UV - optical) colors and line strength indices. The X-ray spatial and spectral analysis show significant differences in the two objects. A low luminosity nuclear source is the dominant component in NGC 7070A log L_X=41.7 erg s^{-1} in the 2-10 keV band. In ESO 2400100, the X-ray emission is due to a low temperature plasma with a contribution from the collective emission of individual sources. In the Optical Monitor image ESO 2400100 shows a double nucleus, one bluer than the other. This probably results from a very recent star formation event in the northern nuclear region. The extension of the UV emission is consistent with the optical extent for all galaxies, at different degrees of significance in different filters. The presence of the double nucleus, corroborated by the (UV - optical) colors and line strength indices analysis, suggests that ESO 2400100 is accreting a faint companion. We explore the evolution of the X-ray luminosity during accretion processes with time. We discuss the link between the presence of gas and age, since gas is detected either before coalescence or several Gyr (>3) after (Abridged).
From the disk of normal galaxies to the nucleus of prototype active sources, we review the wealth of results and new understanding provided by recent infrared probes and, in particular, the four instruments on-board of ISO.
The hot circum-galactic medium (CGM) represents the hot gas distributed beyond the stellar content of the galaxies while typically within their dark matter halos. It serves as a depository of energy and metal-enriched materials from galactic feedback and a reservoir from which the galaxy acquires fuels to form stars. It thus plays a critical role in the coevolution of galaxies and their environments. X-rays are one of the best ways to trace the hot CGM. I will briefly review what we have learned about the hot CGM based on X-ray observations over the past two decades, and what we still do not know. I will also briefly prospect what may be the foreseeable breakthrough in the next one or two decades with future X-ray missions.
The excess of far-ultraviolet (far-UV) radiation in elliptical galaxies has remained one of their most enduring puzzles. In contrast, the origin of old blue stars in the Milky Way, hot subdwarfs, is now reasonably well understood: they are hot stars that have lost their hydrogen envelopes by various binary interactions. Here, we review the main evolutionary channels that produce hot subdwarfs in the Galaxy and present the results of binary population synthesis simulations that reproduce the main properties of the Galactic hot-subdwarf population. Applying the same model to elliptical galaxies, we show how this model can explain the main observational properties of the far-UV excess, including the far-UV spectrum, without the need to invoke ad hoc physical processes. The model implies that the UV excess is not a sign of age, as has been postulated previously, and predicts that it should not be strongly dependent on the metallicity of the population.
The power mechanism and accretion geometry for low-power FR1 radio galaxies is poorly understood in comparison to Seyfert galaxies and QSOs. In this paper we use the diagnostic power of the Lya recombination line observed using the Cosmic Origins Spectrograph (COS) aboard the Hubble Space Telescope (HST) to investigate the accretion flows in three well-known, nearby FR1s: M87, NGC4696, and HydraA. The Ly$alpha$ emission lines luminosity, velocity structure and the limited knowledge of its spatial extent provided by COS are used to assess conditions within a few parsecs of the super-massive black hole (SMBH) in these radio-mode AGN. We observe strong Ly$alpha$ emission in all three objects with similar total luminosity to that seen in BL Lacertae objects. M87 shows a complicated emission line profile in Lya which varies spatially across the COS aperture and possibly temporally over several epochs of observation. In both NGC 4696 and M87, the Ly$alpha$ luminosities $sim 10^{40}$ ergs/s are closely consistent with the observed strength of the ionizing continuum in Case B recombination theory and with the assumption of near unity covering factor. It is possible that the Ly$alpha$ emitting clouds are ionized largely by beamed radiation associated with the jets. Long-slit UV spectroscopy can be used to test this hypothesis. Hydra A and the several BL Lac objects studied in this and previous papers have Lya luminosities larger than M87 but their extrapolated, non-thermal continua are so luminous that they over-predict the observed strength of Ly$alpha$, a clear indicator of relativistic beaming in our direction. Given their substantial space density ($sim 4times10^{-3} Mpc^{-3}$) the unbeamed Lyman continuum radiation of FR1s may make a substantial minority contribution (~10%) to the local UV background if all FR1s are similar to M87 in ionizing flux level.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
