1,721,047 research outputs found
THE COMPLEX NATURE OF THE INTERACTING SYSTEM NGC 7592
No full textA detailed analysis of the physical conditions and of the kinematical and dynamical properties of the system of interacting galaxies NGC 7592, the western component of which shows signs of Seyfert activity, is presented. The aspect and kinematics of the galaxies suggest that a prograde encounter between the eastern and the western component of the system is occurring. The large Hα luminosity indicates that all galaxies are undergoing a strong burst of star formation, with a very large global star formation rate (about 20 solar masses/yr). In the spectra of the nuclear and circumnuclear regions of the western component, the high ionization lines are redshifted by about 50 km/s with respect to the low ionization lines, and their ratios indicate the simultaneous presence of thermally and nonthermally ionized gas. This is interpreted in terms of the coexistence in the nucleus of the western component of Seyfert and Starburst activity, the latter being responsible for about 75 percent of the Hα line luminosity
On core-collapse supernovae in normal and in Seyfert galaxies
No full textThis paper estimates the relative frequency of different types of core-collapse supernovae, in terms of the ratio S between the number of Type Ib-Ic and of Type H supernovae. We estimate S independently for all normal and Seyfert galaxies whose radial velocity is less than or equal to 14 000 km s(-1), and which had at least one supernova event recorded in the Asiago catalogue from 1986 January to 2000 August. We find that the ratio S is approximate to 0.23 +/- 0.05 in normal galaxies. This value is consistent with constant star formation rate and with a Salpeter initial mass function and an average binary rate approximate to50 per cent. On the contrary, Seyfert galaxies exceed the ratio S in normal galaxies by a factor approximate to4 at a confidence level; greater than or similar to20sigma. A caveat is that the numbers for Seyferts are still small (six of Type lb-Ic and six of Type H supernovae discovered as yet). Assumed to be real, this excess of Type We supernovae may indicate a burst of low-age star formation (tau less than or similar to 20 Myr), a high incidence of binary systems in the inner regions (r less than or similar to 0.4R(25)) of Seyfert galaxies, or a top-loaded mass function
The close environment of Seyfert galaxies and its implication for unification models
No full textIn this Letter, we present a statistical analysis of the circumgalactic environment of nearby Seyfert galaxies based on a computer-aided search of companion galaxies on the Digitized Sky Survey. We defined a sample of 72 nearby Seyfert 1 galaxies (redshift 0.007 ≤ z ≤ 0.034) and a sample of 60 Seyfert 2 galaxies (0.007 ≤ z ≤ 0.020), which include only high galactic latitude objects. In addition, we built two control samples of nonactive galaxies that match the number of sample members, the redshift, morphological type, and diameter distribution of the Seyfert 1 and Seyfert 2 galaxy samples separately. We stress how our sample selection introduces important methodological improvements that avoid several sources of strong bias. An intrinsic difference between the environment of Seyfert 1 galaxies and that of Seyfert 2 galaxies, suggested by previous work, is confirmed as statistically significant. For Seyfert 2 galaxies, we find a significant excess of large companions (DC ≳ 10 kpc) within a search radius ≲100 kpc of projected linear distance as well as within a search radius equal to 3 times the diameter DS of each Seyfert galaxy. For Seyfert 1 galaxies, there is no clear evidence of any excess of companion galaxies either within 100 kpc or within 3DS. For all samples, the number of companions that are actually counted within a search radius of 3DS is a factor of ≈2 above the expectation values derived from the number density of galaxies over the 1 deg2 fields that are centered on the sample galaxies, suggesting a markedly non-Poissonian distribution for galaxies on scales ≲100 kpc. This difference in environment is not compatible with the simplest formulation of the unification model for Seyfert galaxies: both type 1 and type 2 should be intrinsically alike, the only difference being the result of the orientation of an obscuring torus. We propose an alternative formulation.</p
The Merging Seyfert Galaxies MARKARIAN:423 and MARKARIAN:739
No full textIn this paper long slit spectroscopy and broad band imaging of the intermediate Seyfert galaxies Mkn 423 and Mkn 739 are presented. The analysis of the extranuclear emissions reveals that Mkn 423 and Mkn 739 are undergoing a strong burst of star formation spread over a kpc-sized scale. Although the morphological appearance of Mkn 423 is suggestive of a galaxy of type Sa/SBa with a giant HII region (component B), the peculiar kinematics of Mkn 423 and the very large Hα luminosity of component B suggest that this system could be the result of an ongoing merging of two galaxies. The resolution ~2 A FWHM of the spectra taken in the range 4000-5500 A allowed to resolve substructures in the Hβ and [OIII]λλ4959,5007 line profiles, permitting an analysis of the circumnuclear regions of these objects. The narrow line spectrum of Mkn 423 originates in two partially resolved blobs, of high ionization degree, which are likely to be the optical counterpart of two radio emitting sources or which are associated with the NLR and circumnuclear gas ionized by the central source. Mkn 739 shows extended high-ionization gas up to a distance ~4 h^-1^ kpc from the Seyfert nucleus. This gas is photoionized by the active nucleus itself, and it is in a kinematical status (probably in outflow) different from that of the low ionization gas associated with star formation. The high ionization degree observed as far as ~2 h^-1^ kpc from the Seyfert nucleus suggests that the central ionizing source is most probably anisotropic
Arp 194: Evidence of Tidal Stripping of Gas and Cross-Fueling
No full textWe present new imaging and spectroscopic observations of the interacting system Arp 194 (≡UGC 6945≡VV 126). The northern component (A194N) is a distorted spiral or ring galaxy likely disrupted by a collision or close encounter with a southern galaxy (A194S). There is evidence that a third galaxy with similar recession velocity is projected on A194N, but its role is likely secondary. A194S is connected to A194N by a string of emission knots, which motivates our interpretation that the former was the intruder. Three of the knots are easily discernible in B, R, and Hα images and are assumed to trace the path of the intruder following the encounter, which we estimate occurred a few times 108 yr ago. Both A194S and A194N are experiencing strong bursts of star formation: the Hα luminosity indicates a total star formation rate ~10 Msolar yr-1. The lack of detectable J and K emission from the blobs, along with strong Hα emission, indicates that an evolved stellar population is not likely to be present. The brightest knot (closest to A194S) shows a star formation rate of ~1.2 Msolar yr-1, which, if sustained over a time ~7×107 yr, could explain the spectral energy distribution. This suggests that the stripped matter was originally predominantly gaseous. The brightest knot is detected as a FIRST radio source, and this is likely the signature of supernova remnants related to enhanced star formation. Motions in the gas between the brightest knot and A194S, traced by an emission line link of increasing radial velocity, suggests infall toward the center of the intruder. Arp 194 is therefore one of the few galaxies where evidence of ``cross-fueling'' is observed
Past, Present, and Future of the Scaling Relations of Galaxies and Active Galactic Nuclei
Full text linkWe review the properties of the established Scaling Relations (SRs) of galaxies and active galactic nuclei (AGN), focusing on their origin and expected evolution back in time, providing a short history of the most important progresses obtained up to now and discussing the possible future studies. We also try to connect the observed SRs with the physical mechanisms behind them, examining to what extent current models reproduce the observational data. The emerging picture clarifies the complexity intrinsic to the galaxy formation and evolution process as well as the basic uncertainties still affecting our knowledge of the AGN phenomenon. At the same time, however, it suggests that the detailed analysis of the SRs can profitably contribute to our understanding of galaxies and AGN
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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