Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userMulti-epoch properties of the warm absorber in the Seyfert 1 galaxy NGC 985
300
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
(Abridged) NGC 985 was observed by XMM-Newton twice in 2015, revealing that the source was coming out from a soft X-ray obscuration event that took place in 2013. These kinds of events are possibly recurrent since a previous XMM-Newton archival observation in 2003 also showed signatures of partial obscuration. We have analyzed the high-resolution X-ray spectra of NGC 985 obtained by the RGS in 2003, 2013, and 2015 in order to characterize the ionized absorbers superimposed to the continuum and to study their response as the ionizing flux varies. We found that up to four warm absorber (WA) components were present in the grating spectra of NGC 985, plus a mildy ionized (log xi ranging between 0.2 and 0.5) obscuring (log N(H) of about 22.3) wind outflowing at about 6000 km/s. The absorbers have a log N(H) ranging from 21 to about 22.5, and ionization parameters ranging from 1.6 to 2.9. The most ionized component is also the fastest, moving away at 5100 km/s, while the others outflow in two kinematic regimes, at about 600 and 350 km/s. These components showed variability at different time scales in response to changes in the ionizing continuum. Assuming that these changes are due to photoionization we have obtained upper and lower limits on the density of the gas and therefore on its distance, finding that the closest two components are at pc-scale distances, while the rest may extend up to tens of pc from the central source. The fastest, most ionized WA component accounts for the bulk of the kinetic luminosity injected back into the ISM of the host galaxy, which is on the order of 0.8% of the bolometric luminosity of NGC 985. According to the models, this amount of kinetic energy per unit time would be sufficient to account for cosmic feedback.
rate research
Read More
The Seyfert galaxy NGC 985 is known to show a high-frequency excess in its radio continuum spectrum in a milli-Jansky level on the basis of previous observations at 1.4--15 GHz; a steep spectrum at low frequencies (a spectral index of $alpha=-1.10 pm 0.03$) changes at ~10 GHz into an inverted spectrum at higher frequencies ($alpha=+0.86 pm 0.09$). We conduct new observations at 15--43 GHz using the Very Large Array and at 100 GHz using the Nobeyama Millimeter Array. As a result, the high-frequency excess continuing at even higher radio frequencies up to 43 GHz has been confirmed. The non-detection at 100 GHz was not so strong constraint, and therefore the spectral behavior above 43 GHz remains unclear. The astrometric position of the high-frequency excess component coincides with the optical position of the Seyfert nucleus and the low-frequency radio position to an accuracy of 0.1 arcsec, corresponding to ~80 pc; the radio source size is constrained to be <0.02 arcsec, corresponding to <16 pc. We discuss the physical origin of the observed high-frequency excess component. Dust emission at the Rayleigh-Jeans regime, free--free emission from X-ray radiating high-temperature plasma, free--free emission from the ensemble of broad-line region clouds, or thermal synchrotron from hot accretion flow cannot be responsible for the observed radio flux. Compact jets under synchrotron self-absorption may be unlikely in terms of observed time scales. Alternatively, we cannot rule out the hypotheses of synchrotron jets free--free absorbed by a circumnuclear photo-ionized region, and self-absorbed nonthermal synchrotron from disk corona, as the origin of the high-frequency excess component.
We present an analysis of an XMM-Newton observation of the Seyfert 1 Galaxy NGC 985. The EPIC spectra present strong residuals to a single power-law model, indicating the presence of ionized absorbing gas and a soft excess. A broad-band fit to the EPIC and RGS spectra shows that the continuum can be well fit with a power-law and a blackbody component. The RGS can be modeled either with two or three absorption components. In the two absorber model the low-ionization one, accounts for the presence of the Fe M-shell unresolved transition array (Fe VII-XIII), and the high ionization component is required by the presence of several Fe L-shell transitions. The data suggest the presence of a third ionized component with higher ionization, so that the Fe L-shell absorption features are produced by two different components (one producing absorption by Fe XVII-XX, and the other absorption by Fe XX-XXII). However, the presence of the third absorbing component cannot be detected by means of an isolated absorption line in a significant way, so we consider this detection only as tentative. Interestingly, all ionization components have similar kinematics. In addition, whether two or three absorbers are considered, the components appear to be in pressure balance. These results give further support to the idea that warm absorbers in AGN consist of a two or three-phase medium. We note that, while in the model with only two absorbers one of them (the high ionization component) lies on an unstable branch of the thermal equilibrium curve, in the model with three absorbers all of the components lie on stable branches of the curve. This gives further plausibility to a multi-phase absorber.
We present both phenomenological and more physical photoionization models of the Chandra HETG spectra of the Seyfert-1 AGN NGC 4051. We detect 40 absorption and emission lines, encompassing highly ionized charge states from O, Ne, Mg, Si, S and the Fe L-shell and K-shell. Two independent photoionization packages, XSTAR and Cloudy, were both used to self-consistently model the continuum and line spectra. These fits detected three absorbing regions in this system with densities ranging from 10^{10} to 10^{11} cm^{-3}. In particular, our XSTAR models require three components that have ionization parameters of log xi = 4.5, 3.3, & 1.0, and are located within the BLR at 70, 300, and 13,000 R_g, respectively, assuming a constant wind density. Larger radii are inferred for density profiles which decline with radius. The Cloudy models give a similar set of parameters with ionization parameters of log xi = 5.0, 3.6, & 2.2 located at 40, 200, and 3,300 R_g. We demonstrate that these regions are out-flowing from the system, and carry a small fraction of material out of the system relative to the implied mass accretion rate. The data suggest that magnetic fields may be an important driving mechanism.
In about half of Seyfert galaxies, the X-ray emission is absorbed by an optically thin, ionized medium, the so-called Warm Absorber, whose origin and location is still a matter of debate. The aims of this paper is to put more constraints on the warm absorber by studying its variability. We analyzed the X-ray spectra of a Seyfert 1 galaxy, Mrk 704, which was observed twice, three years apart, by XMM-Newton. The spectra were well fitted with a two zones absorber, possibly covering only partially the source. The parameters of the absorbing matter - column density, ionization state, covering factor - changed significantly between the two observations. Possible explanations for the more ionized absorber are a torus wind (the source is a polar scattering one) or, in the partial covering scenario, an accretion disk wind. The less ionized absorber may be composed of orbiting clouds in the surroundings of the nucleus, similarly to what already found in other sources, most notably NGC 1365.
The nearby Sy 1 galaxy NGC 1097 represents an ideal laboratory to explore the molecular chemistry in the presence and surroundings of an active galactic nucleus. Exploring the distribution of different molecular species allows us to understand the physical processes affecting the ISM both in the AGN vicinity as well as in the outer star forming molecular ring. We carried out 3 mm ALMA observations of HCN, HCO+, CCH, CS, HNCO, SiO, HC3N, and SO as well as the 13C isotopologues. All species were imaged over the central 2 kpc (~30) of the galaxy at a resolution of ~2.2x1.5 (150 pc x 100 pc). HCO+ and CS appear to be slightly enhanced in the star forming ring. CCH, showing the largest variations across NGC 1097, is suggested to be a good tracer of both obscured and early stage star formation. HNCO, SiO and HC3N are significantly enhanced in the inner circumnuclear disk surrounding the AGN. Differences in the molecular abundances are observed between the star forming ring and the inner circumnuclear disk. We conclude that the HCN/HCO+ and HCN/CS differences observed between AGN dominated and starburst galaxies are not due to a HCN enhancement due to X-rays, but rather this enhancement is produced by shocked material at distances of 200 pc from the AGN. Additionally we claim the lower HCN/CS to be a combination of a small under-abundance of CS in AGNs together with excitation effects, where a high dense gas component (~10^6 cm^-3) may be more prominent in SB galaxies. However the most promising are the differences found among the dense gas tracers which, at our modest spatial resolution, seem to outline the physical structure of the molecular disk around the AGN. In this picture, HNCO probes the well shielded gas in the disk, surrounding the dense material moderately exposed to X-ray radiation traced by HC3N. Finally SiO might be the innermost molecule in the disk structure.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
