1,720,988 research outputs found
An extended ultraviolet ring around the SB0 galaxy NGC 4262
No full textWe present Galaxy Ultraviolet Explorer (GALEX) satellite observations of the SB0 galaxy NGC 4262 where we detect an extended, outer ring studded with UV-bright knots surrounding the galaxy body. Such a structure, not visible at optical wavelengths, is coupled with a ring of atomic (HI) gas. We will show that both star-forming and HI rings surrounding this SB0 galaxy share the same radial distance from the galaxy center and spatial orientation. We also model the kinematics of the ring(s) and of the galaxy body. Their kinematics is not coupled with that of the galaxy stars. We suggest that NGC 4262 has undergone a major gas stripping event in the past that was the origin of the present "necklace" of UV-bright knots
NGC 7679: an anomalous, composite Seyfert 1 galaxy whose X-ray luminous AGN vanishes at optical wavelengths
Full text linkMorphological disturbances and gas kinematics of the SB0 galaxy NGC 7679 = Arp 216 are investigated to understand the history of this highly composite object, where AGN and starburst signatures dominate in the X-ray and optical/IR regime, respectively. Perturbations of the ionized gas velocity field appear quite mild within 15'' (~5 kpc) of the center, so it can be straightforwardly modeled as a circularly rotating disk. Outside that radius, significant disturbances are seen. In particular, the eastern distorted arm as well as the huge neutral hydrogen bridge connecting NGC 7679 to the nearby Seyfert spiral NGC 7682 unambiguously represent the vestige of a close encounter of the two objects ~500 Myr ago. The relationship of such a past event with the much more recent, centrally located starburst (not older than 20 Myr) cannot be easily established. Together, the classification of NGC 7679 is less extreme than that proposed in the past, being simply a (disturbed) galaxy where starburst and AGN activity coexist with a starburst dominating the bolometric luminosity
The GALEX UV emission in shell galaxies
No full textShell galaxies are widely considered the debris of recent accretion/merging episodes. Their high frequency in low density environment suggests that such episodes could be among the driver of the early-type galaxy secular evolution. We present far and near UV GALEX photometric properties of a sample of shell galaxies
Disentangling the kinematics and stellar populations of counter-rotating stellar discs in galaxies
No full textSpectroscopic VIMOS/IFU observations are presented for three galaxies known to host two stellar counter-rotating discs of comparable sizes. For the first time both the kinematics and stellar population properties of the two counter-rotating discs in the observed galaxies were separated and measured. The secondary, less massive, stellar component rotates in the same direction as the ionised gas and is on average younger and less metal-rich than the main galaxy disc. These results support the scenario of gas accretion followed by star formation as the origin for large counter-rotating stellar discs in galaxies, and set an upper limit of 44% to those formed by binary galaxy mergers
UGC 7639: A Dwarf Galaxy in the Canes Venatici I Cloud
Full text linkWe want to get insight into the formation mechanism and the evolution of UGC 7639, a dwarf galaxy in the Canes Venatici I Cloud (CVnIC). We used archival multiwavelength data to constrain its global properties. Ultraviolet images show that UGC 7639 inner regions are composed mostly by young stellar populations. In addition, we used smoothed particle hydrodynamics simulations with chemophotometric implementation to account for its formation and evolution. UGC 7639 is an example of blue dwarf galaxy whose global properties are well matched by our multiwavelength approach, that is, a suitable approach to highlight the evolution also of these galaxies as a class. We found that the global properties of UGC 7639, namely, its total absolute B-band magnitude, its whole spectral energy distribution, and morphology, are well matched by an encounter with a system four times more massive than our target. Moreover, the current star formation rate of the simulated dwarf, ≈0.03 M⊙ yr−1, is in good agreement with our UV-based estimate. We derived a galaxy age of 8.6 Gyr. Following our simulation, the ongoing star formation will extinguish within 1.6 Gyr, thus leaving a red dwarf galaxy
Is the giant elliptical galaxy NGC 5018 a post-merger remnant?
Full text linkNGC 5018, one of the weakest UV emitters among giant ellipticals (gE) observed with IUE, appears to consist of an optical stellar population very similar to that of the compact, dwarf elliptical M 32, which is several magnitudes fainter in luminosity than NGC 5018 and whose stellar population is known to be similar to3 Gyr old. Here we show that the mid-UV spectra of these two galaxies are also very similar down to an angular scale hundreds times smaller than the WE large aperture (as probed by HST/FOS UV spectra obtained through 0.86" apertures). This implies a reasonably close match of the populations dominating their mid-UV light (namely, their main-sequence turnoff stars). These data indicate that NGC 5018 has, in its inner regions, a rather uniform dominance of a similar to3 Gyr-old stellar population, probably a bit different in metallicity from M 32. Combined with the various structures that indicate that NGC 5018 is the result of a recent major merger, it appears that almost all of stars we see in its center regions were formed about 3 Gyr ago, in that merger event. NGC 5018 is likely the older brother of NGC 7252, the canonical gE-in-formation merger. As such, NGC 5018 is perhaps the best galaxy which can tell us how a merger works, after the fireworks subside, to form a gE galaxy today. For this reason alone, the stellar populations in NGC 5018 at all radii are worth studying in detail
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
Dissecting kinematics and stellar populations of counter-rotating galaxies with 2-dimensional spectroscopy
No full textWe present a spectral decomposition technique and its applications to a sample of galaxies hosting large-scale counter-rotating stellar disks. Our spectral decomposition technique allows to separate and measure the kinematics and the properties of the stellar populations of both the two counter-rotating disks in the observed galaxies at the same time. Our results provide new insights on the epoch and mechanism of formation of these galaxies
Ultraviolet variability in the nucleus of the giant elliptical NGC 4278
No full textThe variability of the UV luminosity and mass of the supermassive black hole (SBH) in the nucleus of the giant elliptical NGC 4278 were derived by analyzing the UV images and Hα spectrum available in the Hubble Space Telescope Science Archive. The UV nuclear source in NGC 4278 is almost certainly associated to the low-luminosity AGN responsible for its known radio emission. The properties of this UV flare and SBH are remarkably similar to the UV-bright nuclear transients and SBHs discovered earlier in other low-luminosity AGNs. This supports the idea that UV flaring near the center of galaxies may be a common event and offers a way to search for SBH-related activities in otherwise quiescent galaxies
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