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We present a catalog of 520 most isolated nearby galaxies with angular velocities V
LG
< 3500 km/s, covering the entire sky. This population of “space orphans” makes up 4.8% among 10 900 galaxies with measured radial velocities. We describe the isolation criterion used to select our sample, called the “Local Orphan Galaxies”(LOG), and discuss their...
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... Evidences are accumulating that over at least a few billion years the evolution of isolated galaxies has not been driven by interactions with physically associated companions (see e.g. Verdes-Montenegro et al. 2005 ;Karachentse v a et al. 2010 ;Karachentse v et al. 2011 ;Rampazzo et al. 2020 , and references therein). In this sense, isolated galaxies are the ideal reference sample to study Downloaded from https://academic.oup.com/mnras/article/528/2/2145/7513192 by guest on 01 February 2024 internal galactic forces and galaxy morphological, dynamical, and photometric evolution minimizing possible environmental effects. ...
Isolated galaxies are the ideal reference sample to study the galaxy structure minimizing potential environmental effects. We selected a complete sample of 14 nearby, late-type, highly inclined (i ≥ 80°), isolated galaxies from the Catalogue of Isolated Galaxies (CIG) which offers a vertical view of their disc structure. We aim to study extraplanar Diffuse Ionized Gas (eDIG) by comparing the old and young disc components traced by near-infrared (NIR) and ultraviolet (UV) imaging with the Hα emission structure. We obtained Hα monochromatic maps from the Fabry–Perot (FP) interferometry, while the old and young discs structures are obtained from the photometric analysis of the 2MASS Ks band, and GALEX NUV and FUV images, thereby identifying the stellar disc and whether the eDIG is present. The Hα morphology is peculiar in CIG 71, CIG 183, and CIG 593 showing clear asymmetries. In general, geometric parameters (isophotal position angle, peak light distribution, and inclination) measured from Hα, UV, and NIR show minimal differences (e.g. Δi ≤ ±10°), suggesting that interaction does not play a significant role in shaping the morphology, as expected in isolated galaxies. From Hα maps, the eDIG was detected vertically in 11 out of 14 galaxies. Although the fraction of eDIG is high, the comparison between our sample and a generic sample of inclined spirals suggests that the phenomenon is uncorrelated to the galaxy environment. As suggested by the extraplanar UV emission found in 13 out of 14 galaxies the star formation extends well beyond the disc defined by the Hα map.
... The isolation index ( ) they calculated shows how many times it is necessary to increase the -based estimated mass of galaxies in a given pair in order this pair to be gravitationally bound (see f.e. Karachentsev et al. (2011)). For example, log( ) ≈ 0 means that a given galaxy is most probably a member of gravitationally bound pair or a group. ...
Spiral structure (both flocculent and Grand Design types) is very rarely observed in dwarf galaxies because the formation of spiral arms requires special conditions. In this work we analyze the sample of about 40 dS-galaxies found by scanning by eye the images of late-type galaxies with $m_B<15^m$ and $M_B>-18^m$ and photometric diameter $D_{25}<12$~kpc. We found that apart from the lower average gas (HI) fraction the other properties of dS-galaxies including the presence of a bar and the isolation index do not differ much from those for dwarf Irr or Sm-types of similar luminosity and rotation velocity (or specific angular momentum).There are practically no dS-galaxies with rotation velocity below 50\,--\,60~km\,sec$^{-1}$.
To check the conditions of formation of spiral structure in dwarf galaxies we carried out a series of N-body/hydrodynamic simulations of low-mass stellar-gaseous discy galaxies by varying the model kinematic parameters of discs, their initial thickness, relative masses and scale lengths of stellar and gaseous disc components, and stellar-to-dark halo masses.
We came to conclusion that the gravitational mechanism of spiral structure formation is effective only for thin stellar discs, which are non-typical for dwarf galaxies, and for not too slowly rotating galaxies. Therefore, only a small fraction of dwarf galaxies with stellar/gaseous discs have spiral or ring structures. The thicker stellar disc, the more gas is required for the spiral structure to form. The reduced gas content in many dS-galaxies compared to non-spiral ones may be a result of more efficient star formation due to a higher volume gas density thank to the thinner stellar/gaseous discs.
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... The isolation index ( ) they calculated shows how many times it is necessary to increase the -based estimated mass of galaxies in a given pair in order this pair to be gravitationally bound (see f.e. Karachentsev et al. (2011)). For example, log( ) ≈ 0 means that a given galaxy is most probably a member of gravitationally bound pair or a group. ...
Spiral structure (both flocculent and Grand Design types) is very rarely observed in dwarf galaxies because the formation of spiral arms requires special conditions. In this work we analyze the sample of about 40 dS-galaxies found by scanning by eye the images of late-type galaxies with $m_B<15^m$ and $M_B>-18^m$ and photometric diameter $D_{25}<12$~kpc. We found that apart from the lower average gas (HI) fraction the other properties of dS-galaxies including the presence of a bar and the isolation index do not differ much from those for dwarf Irr or Sm-types of similar luminosity and rotation velocity (or specific angular momentum).There are practically no dS-galaxies with rotation velocity below 50\,--\,60~km\,sec$^{-1}$. To check the conditions of formation of spiral structure in dwarf galaxies we carried out a series of N-body/hydrodynamic simulations of low-mass stellar-gaseous discy galaxies by varying the model kinematic parameters of discs, their initial thickness, relative masses and scale lengths of stellar and gaseous disc components, and stellar-to-dark halo masses. We came to conclusion that the gravitational mechanism of spiral structure formation is effective only for thin stellar discs, which are non-typical for dwarf galaxies, and for not too slowly rotating galaxies. Therefore, only a small fraction of dwarf galaxies with stellar/gaseous discs have spiral or ring structures. The thicker stellar disc, the more gas is required for the spiral structure to form. The reduced gas content in many dS-galaxies compared to non-spiral ones may be a result of more efficient star formation due to a higher volume gas density thank to the thinner stellar/gaseous discs.
... In this paper, we present detailed analysis for the low-mass galaxy Arakelian 18 (Ark 18; Arakelian 1975), while the study of other objects from our sample (Egorova et al. 2019) will be presented in the forthcoming papers. Ark 18 is located in the Eridanus void (Kniazev, Egorova & Pustilnik 2018) at the distance D 24.1 Mpc. 1 It is considered isolated (Karachentsev et al. 2011), and has no known companions. The deep optical images from SDSS Stripe 82 (Abazajian et al. 2009;Fliri & Trujillo 2016;Román & Trujillo 2018) reveal blue low-surface brightness (LSB) flocculent spirals around a bright redder elliptically shaped central part. ...
The low-mass low-surface brightness (LSB) disc galaxy Arakelian 18 (Ark 18) resides in the Eridanus void and because of its isolation represents an ideal case to study the formation and evolution mechanisms of such a galaxy type. Its complex structure consists of an extended blue LSB disc and a bright central elliptically-shaped part hosting a massive off-centered star-forming clump. We present the in-depth study of Ark 18 based on observations with the SCORPIO-2 long-slit spectrograph and a scanning Fabry-Perot interferometer at the Russian 6-m telescope complemented by archival multi-wavelength images and SDSS spectra. Ark 18 appears to be a dark matter dominated gas-rich galaxy without a radial metallicity gradient. The observed velocity field of the ionised gas is well described by two circularly rotating components moderately inclined with respect to each other and a possible warp in the outer disc. We estimated the age of young stellar population in the galaxy centre to be ∼140 Myr, while the brightest star-forming clump appears to be much younger. We conclude that the LSB disc is likely the result of a dwarf–dwarf merger with a stellar mass ratio of the components at least ∼5:1 that occurred earlier than 300 Myr ago. The brightest star forming clump was likely formed later by accretion of a gas cloud.
... Ark 18 is located in the Eridanus void (Kniazev et al. 2018) at the distance 24.1 Mpc 1 . It is considered isolated (Karachentsev et al. 2011), and has no known companions. The deep optical images from SDSS Stripe 82 (Abazajian et al. 2009;Fliri & Trujillo 2016;Román & Trujillo 2018) reveal blue low surface brightness flocculent spirals around a bright redder elliptically-shaped central part. ...
The low-mass low-surface brightness (LSB) disc galaxy Arakelian 18 (Ark 18) resides in the Eridanus void and because of its isolation represents an ideal case to study the formation and evolution mechanisms of such a galaxy type. Its complex structure consists of an extended blue LSB disc and a bright central elliptically-shaped part hosting a massive off-centered star-forming clump. We present the in-depth study of Ark 18 based on observations with the SCORPIO-2 long-slit spectrograph and a scanning Fabry-Perot interferometer at the Russian 6-m telescope complemented by archival multi-wavelength images and SDSS spectra. Ark 18 appears to be a dark matter dominated gas-rich galaxy without a radial metallicity gradient. The observed velocity field of the ionised gas is well described by two circularly rotating components moderately inclined with respect to each other and a possible warp in the outer disc. We estimated the age of young stellar population in the galaxy centre to be ~140 Myr, while the brightest star-forming clump appears to be much younger. We conclude that the LSB disc is likely the result of a dwarf-dwarf merger with a stellar mass ratio of the components at least ~5:1 that occurred earlier than 300 Myr ago. The brightest star forming clump was likely formed later by accretion of a gas cloud.
... • Karachentsev et al. (2011). c From . ...
... In total, we selected 18 galaxies with absolute magnitudes M B ranging from −19.1 m to −14.5 m . Ten objects were included in the samples of nearby isolated galaxies by Karachentseva, Karachentsev & Sharina (2010), Karachentsev et al. (2011), andKaisina (2013), while others are mainly part of systems with different stages of interaction. Almost all our sample galaxies exhibit a peculiar morphology, although more than half of them are considered to be isolated with no known companions. ...
We present the first results of a project aimed at searching for gas accretion events and interactions between late-type galaxies in the void environment. The project is based on long-slit spectroscopic and scanning Fabry–Perot interferometer observations performed with the SCORPIO and SCORPIO-2 multimode instruments at the Russian 6-m telescope, as well as archival multiwavelength photometric data. In the first paper of the series we describe the project and present a sample of 18 void galaxies with oxygen abundances that fall below the reference ‘metallicity-luminosity’ relation, or with possible signs of recent external accretion in their optical morphology. To demonstrate our approach, we considered the brightest sample galaxy NGC 428, a late-type barred spiral with several morphological peculiarities. We analysed the radial metallicity distribution, the ionized gas line-of-sight velocity, and velocity dispersion maps together with Wide-field Infrared Survey Explorer and SDSS images. Despite its very perturbed morphology, the velocity field of ionized gas in NGC 428 is well described by pure circular rotation in a thin flat disc with streaming motions in the central bar. We also found some local non-circular gas motions clearly related to stellar feedback processes. At the same time, we revealed a circumnuclear inclined disc in NGC 428 and a region with significant residual velocities that could be considered as a result of a recent (<0.5 Gyr) accretion event. The observed oxygen abundance gradient does not contradict this conclusion.
... In total, we selected 18 galaxies with absolute magnitudes MB ranging from −19.1 m to −14.5 m . Ten objects were included in the samples of nearby isolated galaxies by Karachentseva et al. (2010); Karachentsev et al. (2011Karachentsev et al. ( , 2013, while others are mainly part of systems with different stages of interaction. Almost all our sample galaxies exhibit a peculiar morphology, although more than half of them are considered to be isolated with no known companions. ...
... The data were reduced in a standard way using the idl-based pipeline developed for the SCORPIO data. The main steps of the data reduction process include bias sub- (2016) 1 included in the "Local Orphan Galaxies" sample by Karachentsev et al. (2011); 2 according to Karachentsev et al. (2013); 3 according to Karachentseva et al. (2010). traction, line curvature and flat-field corrections, wavelength calibration, and air-glow line subtraction. ...
We present the first results of a project aimed at searching for gas accretion events and interactions between late-type galaxies in the void environment. The project is based on long-slit spectroscopic and scanning Fabry-Perot interferometer observations performed with the SCORPIO and SCORPIO-2 multimode instruments at the Russian 6-m telescope, as well as archival multiwavelength photometric data. In the first paper of the series we describe the project and present a sample of 18 void galaxies with oxygen abundances that fall below the reference `metallicity-luminosity' relation, or with possible signs of recent external accretion in their optical morphology. To demonstrate our approach, we considered the brightest sample galaxy NGC 428, a late-type barred spiral with several morphological peculiarities. We analysed the radial metallicity distribution, the ionized gas line-of-sight velocity and velocity dispersion maps together with WISE and SDSS images. Despite its very perturbed morphology, the velocity field of ionized gas in NGC 428 is well described by pure circular rotation in a thin flat disc with streaming motions in the central bar. We also found some local non-circular gas motions clearly related to stellar feedback processes. At the same time, we revealed a circumnuclear inclined disc in NGC 428 and a region with significant residual velocities that could be considered as a result of a recent (<0.5 Gyr) accretion event. The observed oxygen abundance gradient does not contradict this conclusion.
... Isolated galaxies have various definitions (Haynes & Giovanelli 1984;Karachentsev et al. 2011;Brough et al. 2013;Hirschmann et al. 2013). Geha et al. (2012) find that low-mass galaxies with * < M M log 9.0 located at least 1.5Mpc from a massive galaxy are always star-forming and isolated quenched galaxies with * < < M M 9.0 log 9.5 are extremely rare. ...
We investigate the global neutral hydrogen (H i) content of isolated galaxies selected from the SDSS spectroscopic survey with optical evidence of Active Galactic Nuclei (AGNs). Our sample includes galaxies with unresolved H i observations from the ALFALFA 70% data release combined with deeper H i observations of low-mass galaxies with . We examine the H i masses of this sample using the distance from the star-forming sequence on the [O iii]/Hβ and [N ii]/Hα Baldwin Phillips Terlevich (BPT) diagram as a measurement of AGN activity. In agreement with previous studies, we find that, for galaxies with , AGN activity does not correlate with the global H i content. However, for galaxies with , we identify a set of objects at large distances from the BPT star-forming sequence and lower than expected H i masses. This gas-depleted sample is red in both g - r and NUV - r colors and compact without distinguishable signs of star formation. This is surprising because the vast majority of isolated galaxies in this stellar mass regime are both star-forming and gas-rich. These galaxies are greater than 1.5 Mpc from any massive galaxy, ruling out environmental processes as a source of the gas depletion. We suggest that either black hole feedback or shocks from extremely bursty star formation cause the emission lines and have destroyed or otherwise consumed the cold gas. © 2018. The American Astronomical Society. All rights reserved..
... For the Lynx-Cancer void as a whole, the density of galaxies with MB −14 is estimated to be ∼10% of the mean value (Chengalur & Pustilnik 2013). UGC 3672 is also a member of the Catalog of Nearby Isolated galaxies (Karachentsev et al. 2011). UGC 3672 is clearly located in a highly unusual region. ...
We present HI 21cm and optical observations of UGC 3672 which is located near the centre of the nearby Lynx-Cancer void. We find that UGC 3672 consists of an approximately linearly aligned triplet of gas rich dwarfs with large scale velocity continuity along the triplet axis. The faintest component of the triplet is extremely gas-rich (MHI/LB ~ 17) and also extremely metal deficient (12+log(O/H) ~ 7.0). The metallicity of this dwarf is close to the 'floor' observed in star forming galaxies. Low resolution HI images show that the galaxy triplet is located inside a common HI envelope, with fairly regular, disk like kinematics. At high angular resolution however, the gas is found to be confined to several filamentary tidal tails and bridges. The linear alignment of the galaxies, along with the velocity continuity that we observe, is consistent with the galaxies lying along a filament. We argue that the location of this highly unusual system in an extremely low density environment is not a coincidence, but is a consequence of structure formation proceeding more slowly and also probing smaller scales than in regions with average density. Our observations also indicate that wet mergers of galaxies flowing along filaments is a possible pathway for the formation of gas rich disks. The UGC 3672 system provides an interesting opportunity to study the kind of interactions typical between high redshift extremely gas rich unevolved small systems that lie at base of the hierarchical galaxy formation model.
... NGC 3499. It is isolated (Karachentsev et al. 2011), small, close to face-on S0/a galaxy. Its HI content is rather modest but detectable: 7 × 10 7 solar masses according to the Green Bank Tele-scope integrated data (Wei et al. 2010). ...
I analyze statistics of the stellar population properties for stellar nuclei and bulges of nearby lenticular galaxies in different environments by using panoramic spectral data of the integral-field spectrograph SAURON retrieved from the open archive of Isaac Newton Group. I estimate also the fraction of nearby lenticular galaxies having inner polar gaseous disks by exploring the volume-limited sample of early-type galaxies of the ATLAS-3D survey. By inspecting the two-dimensional velocity fields of the stellar and gaseous components with running tilted-ring technique, I have found 7 new cases of the inner polar disks. Together with those, the frequency of inner polar disks in nearby S0 galaxies reaches 10% that is much higher than the frequency of large-scale polar rings. Interestingly, the properties of the nuclear stellar populations in the inner polar ring hosts are statistically the same as those in the whole S0 sample implying similar histories of multiple gas accretion events from various directions.
