arXiv subjects

Aleksandrina Smirnova

Publications and source records attributed to Aleksandrina Smirnova.

5 recordsLinked to original sources

arXiv2026

Here Be SDRAGNs - Spiral Galaxies Hosting Large Double Radio Sources

We present a sample of large double radio sources hosted by spiral galaxies (Spiral Double Radio Active Galactic Nuclei, SDRAGNs). Candidates were selected during Radio Galaxy Zoo, and refined using Sloan Digital Sky Survey images. The most promising were targeted in the Zoo Gems Hubble Space Telescope program, yielding images for 36 candidates. We assess the likelihood of each spiral galaxy being the genuine host of the radio emission finding 15 new high-probability SDRAGNs. SDRAGN hosts are seen preferentially close to edge-on. SDRAGNs predominantly show FR II radio structures and optical pseudobulges. Accounting for sample selection effects, the radio-jet axes lie preferentially near the poles of the galaxy disks; we find a constant probability distribution for intrinsic pole-jet angles < 30 degrees, ramping to zero at 60 degrees. We have obtained optical spectra for all these new SDRAGNs. Among both previous and new SDRAGN samples, 8/25 show Seyfert 2 signatures, 6/25 show central star formation, and 5/25 show LINER emission strong enough to indicate AGN or shock ionization, broadly similar to radio galaxies in elliptical hosts with the addition of star formation (diluting or masking weak AGN signatures). SDRAGNs include FR II sources seen at unusually low radio power, and preferentially occur in significant galaxy overdensities on 1-Mpc scales. Our "false alarms" - systems where HST data show the spiral to not be the actual host galaxy - include radio sources seen through large parts of foreground spiral disks, potentially useful for Faraday-rotation studies of disk magnetic fields.

astro-ph.GA↗

arXiv2024

The TELPERION survey for extended emission regions around AGN: a strongly-interacting and merging galaxy sample

We present the results of a search for Extended Emission-Line Regions (EELRs) ionized by extant or recently-faded active galactic nuclei (AGN), using [O III] narrowband imaging and spectroscopic followup. The sample includes 198 galaxies in 92 strongly interacting or merging galaxy systems in the range z=0.009-0.0285. Among these, three have EELRs extended beyond 10 kpc in projection from the nucleus detected in previous studies. We identify a single new distant emission region, projected 35 kpc from UGC 5941. Our optical spectrum does not detect He II, but its strong-line ratios put this in the same class as securely characterized EELR clouds. The nucleus of UGC 5941 is dominated by recent star formation, preventing detection of any weak ongoing AGN. Overall counts of distant EELRs in this and the previous TELPERION samples give incidence 2-5% depending on galaxy and AGN selection, 20-50 times higher than the Galaxy Zoo EELR survey with its higher surface-brightness threshold and much larger input sample. AGN in interacting and merging systems have an increased detection rate $12+/-6$%, while none are detected around noninteracting AGN. Some of these AGN are at luminosity low enough to require additional X-ray or far-infrared information to tell whether the EELR ionization level suggests long-term fading.

astro-ph.GA↗

arXiv2016

Fading AGN Candidates: AGN Histories and Outflow Signatures

We consider energy budgets and radiative history of 8 fading AGN, identified from mismatch between the ionizion of very extended (>10 kpc) ionized clouds and the luminosity of the nucleus viewed directly. All show significant fading on ~50,000-year timescales. We explore the use of minimum ionizing luminosity Q derived from photoionization balance in the brightest pixels in H-alpha at each projected radius. Tests using PG QSOs, and one target with detailed photoionization modeling, suggest that we can derive useful histories of individual AGN; the minimum ionizing luminosity is always an underestimate and subject to fine structure in the ionized material. These tests suggest that the underestimation from the upper envelope of Q values is roughly constant for a given object. These AGN show rapid drops and standstills; the common feature is a rapid drop in the last 20,000 years before our view of the nucleus. E-folding timescales are mostly thousands of years, with a few episodes as short as 400. In the limit of largely obscured AGN, we find additional evidence for fading, comparing lower limits from recombination balance and the maximum luminosities derived from from infrared fluxes. We compare these long-term light curves to simulations of AGN accretion; the strongest variations on these timespans are seen in models with strong and local feedback. Gemini integral-field optical spectroscopy shows a very limited role for outflows in these structures. While rings and loops of emission are common, their kinematic structure shows some to be in regular rotation. UGC 7342 exhibits local signatures of outflows <300 km/s, largely associated with very diffuse emission. Only in the Teacup AGN do we see outflow signatures of order 1000 km/s. Clouds around these fading AGN consist largely of tidal debris being externally illuminated but not displaced by AGN outflows. (Abridged)

astro-ph.GA↗

arXiv2015

HST Imaging of Fading AGN Candidates I: Host-Galaxy Properties and Origin of the Extended Gas

We present narrow- and medium-band HST imaging, with additional supporting ground-based data, for 8 galaxies identified as hosting fading AGN. These have AGN-ionized gas projected >10 kpc from the nucleus, and significant shortfall of ionizing radiation between the distant gas and the AGN, indicating fading AGN on ~50,000-year timescales. Every system shows evidence of ongoing or past interactions; a similar sample of obscured AGN with extended ionized clouds shares this incidence of disturbances. Several systems show multiple dust lanes in different orientations, broadly fit by differentially precessing disks of accreted material ~1.5 Gyr after initial arrival. The gas has lower metallicity than the nuclei; three systems have abundances uniformly well below solar, consistent with an origin in tidally disrupted low-luminosity galaxies, while some systems have more nearly solar abundances (accompanied by such signatures as multiple Doppler components), which may suggest redistribution of gas by outflows within the host galaxies themselves. These aspects are consistent with a tidal origin for the extended gas in most systems, although the ionized gas and stellar tidal features do not always match closely. In contrast to clouds near radio-loud AGN, these are dominated by rotation, in some cases in warped disks. Outflows are important only in localized regions near some of the AGN. In UGC 7342 and UGC 11185, luminous star clusters are seen within projected ionization cones, potentially triggered by outflows. As in the discovery example Hanny's Voorwerp/IC 2497, some clouds lack a strong correlation between H-alpha surface brightness and ionization parameter, indicating unresolved fine structure. Together with thin coherent filaments spanning several kpc, persistence of these structures over their orbital lifetimes may require a role for magnetic confinement. (Abridged)

astro-ph.GA↗

arXiv2011

A new catalogue of polar-ring galaxies selected from the SDSS

(Abridged) Galaxies with polar rings (PRGs) are a unique class of extragalactic objects allowing to investigate a wide range of problems, linked with the formation and evolution of galaxies, and to study the properties of their dark haloes. The progress in the study of PRGs is constrained by a small number of known objects of this type. Up to date, we can only attribute about two dozens of kinematically-confirmed galaxies to this class, mostly from Whitmore et al. (1990) catalogue. We present a new catalogue of PRGs based on the results of the original Galaxy Zoo project. Based on the preliminary classification of the Galaxy Zoo, we viewed more than 40000 images of the Sloan Digital Sky Survey (SDSS) and selected 275 galaxies, included in our catalogue. Our Sloan-based Polar Ring Catalog (SPRC) contains 70 galaxies that we classified as "the best candidates", among which we expect to have a very high proportion of true PRGs, and 115 good PRG candidates. 53 galaxies are classified as PRG related objects.We identified 37 galaxies that have their presumed polar rings seen almost face-on. The SPRC objects are on the average fainter and located further away than the galaxies from the catalog by Whitmore et al., although our catalogue does include dozens of new nearby candidate PRGs. The new catalogue significantly increases the number of genuine PRG candidates, and may serve as a good basis both for the further detailed study of individual galaxies, and for the statistical analysis of PRGs as a separate class of objects. We performed spectroscopic observations of six galaxies from the SPRC at the 6-m telescope. The existence of polar rings was confirmed in five galaxies, and one object appeared to be a projection of a pair of galaxies. Adding the literature data, we can already classify 10 galaxies from our catalogue to the kinematically-confirmed PRGs.

astro-ph.CO↗