Blueshifted galaxies in the Virgo Cluster

We examine a sample of 65 galaxies in the Virgo cluster with negative radial velocities relative to the Local Group. Some features of this sample are pointed out. All of these objects are positioned compactly within a virial zone of radius 6{\deg} in the cluster, but their centroid is displaced relative to the dynamic center of the cluster, M87, by 1.1{\deg} to the northwest. The dwarf galaxies in this sample are clumped on a scale of ~10' (50 kpc). The observed asymmetry in the distribution of the blueshifted galaxies may be caused by infall of a group of galaxies around M86 onto the main body of the cluster. We offer another attempt to explain this phenomenon, assuming a mutual tangential velocity of ~300 km/s between the Local Group and the Virgo cluster owing to their being repelled from the local cosmological void.Comment: 10 pages, 4 figures, 1 table. Published in Astrophysics, Vol. 53, No. 1, pp. 32-41, 201

Searches for Ultra-Compact Dwarf Galaxies in Galaxy Groups

We present the results of a search for ultra-compact dwarf galaxies (UCDs) in six different galaxy groups: Dorado, NGC1400, NGC0681, NGC4038, NGC4697 and NGC5084. We searched in the apparent magnitude range 17.5 < b_j < 20.5 (except NGC5084: 19.2 < b_j < 21.0). We found 1 definite plus 2 possible UCD candidates in the Dorado group and 2 possible UCD candidates in the NGC1400 group. No UCDs were found in the other groups. We compared these results with predicted luminosities of UCDs in the groups according to the hypothesis that UCDs are globular clusters formed in galaxies. The theoretical predictions broadly agree with the observational results, but deeper surveys are needed to fully test the predictions.Comment: 8 pages, 2 figures, accepted for publication in MNRA

Merging of Low-Mass Systems and the Origin of the Fundamental Plane

We present a new set of dissipationless N-body simulations to examine the feasibility of creating bright ellipticals (following the Kormendy relation) by hierarchically merging present-day early-type dwarf galaxies, and to study how the encounter parameters affect the location of the end-product in the $- R_{e}$ plane. We investigate the merging of one-component galaxies of both equal and different masses, the merging of two-component galaxy models to explore the effect of dark halos on the final galaxy characteristics, and the merging of ultracompact dwarf galaxies. We find that the increase of $$ with $R_e$ is attributable to an increase in the initial orbital energy. The merger remnants shift down in the $- R_{e}$ plane and fail to reach the KR. Thus, the KR is not reproducable by mergers of dwarf early-type systems, rendering untenable the theory that present-day dwarfs are responsible for even a small fraction of the present-day ellipticals, unless a considerable amount of dissipation is invoked. However, we do find that present-day dwarfs can be formed by the merger of ultra-compact dwarfs.Comment: 10 pages, 8 figures. Accepted for publication in MNRA

Structural properties of ultra-compact dwarf galaxies in the Fornax and Virgo Clusters

We present a detailed analysis of high-resolution two-band Hubble Space Telescope Advanced Camera for Surveys imaging of 21 ultra-compact dwarf (UCD) galaxies in the Virgo and Fornax Clusters. The aim of this work is to test two formation hypotheses for UCDs—whether they are bright globular clusters (GCs) or stripped ("threshed") early-type dwarf galaxies—by direct comparison of UCD structural parameters and colors with GCs and galaxy nuclei. We find that the UCD surface brightness profiles can be described by a range of models and that the luminous UCDs in particular cannot be described by standard King models with tidal cutoffs as they have extended outer halos. This is not expected from traditional King models of GCs, but is consistent with recent results for massive GCs. The total luminosities, colors, and sizes of the UCDs (their position in the color-magnitude and luminosity-size diagrams) are consistent with them being either luminous GCs or threshed nuclei of both early-type and late-type galaxies (not just early-type dwarfs). For the most luminous UCDs we estimate color gradients over a limited range of radius. These are systematically positive in the sense of getting redder outward: mean Δ(F606W – F814W) = 0.14 mag per 100 pc with rms = 0.06 mag per 100 pc. The positive gradients found in the bright UCDs are consistent with them being either bright GCs or threshed early-type dwarf galaxies (except VUCD3). In contrast to the above results we find a very significant (>99.9% significance) difference in the sizes of UCDs and early-type galaxy nuclei: the effective radii of UCDs are 2.2+0.2 –0.1 times larger than those of early-type galaxy nuclei at the same luminosity. This result suggests that an important test can be made of the threshing hypothesis by simulating the process and predicting what size increase is expected

Testing Newtonian Gravity with AAOmega: Mass-to-Light Profiles of Four Globular Clusters

Testing Newtonian gravity in the weak-acceleration regime is vital to our understanding of the nature of the gravitational interaction. It has recently been claimed that the velocity dispersion profiles of several globular clusters flatten out at large radii, reminiscent of galaxy rotation curves, even though globular clusters are thought to contain little or no dark matter. We investigate this claim, using AAOmega observations of four globular clusters, namely M22, M30, M53 and M68. M30, one such cluster that has had this claim made for its velocity dispersion, was included for comparison with previous studies. We find no statistically significant flattening of the velocity dispersion at large radii for any of our target clusters and therefore we infer the observed dynamics do not require that globular clusters are dark matter dominated, or a modification of gravity. Furthermore, by applying a simple dynamical model we determine the radial mass-to-light profiles for each cluster. The isothermal rotations of each cluster are also measured, with M22 exhibiting clear rotation, M68 possible rotation and M30 and M53 lacking any rotation, within the uncertainties.Comment: 7 pages, 4 figures and two tables. Accepted by MNRA

Bridging the gap between low and high mass dwarf galaxies

While the dark matter content within the most massive giant and smallest dwarf galaxies has been probed -- spanning a range of over one million in mass -- an important observational gap remains for galaxies of intermediate mass. This gap covers K band magnitudes of approximately -16 > M_K > -18 (for which dwarf galaxies have B--K ~ 2). On the high mass side of the gap are dwarf elliptical (dE) galaxies, that are dominated by stars in their inner regions. While the low mass side includes dwarf spheroidal (dSph) galaxies that are dark matter-dominated and ultra compact dwarf (UCD) objects that are star-dominated. Evolutionary pathways across the gap have been suggested but remain largely untested because the `gap' galaxies are faint, making dynamical measurements very challenging. With long exposures on the Keck telescope using the ESI instrument we have succeeded in bridging this gap by measuring the dynamical mass for five dwarf galaxies with M_K ~ -17.5 (M_B ~ --15.5). With the exception of our brightest dwarf galaxy, they possess relatively flat velocity dispersion profiles of around 20 km/s. By examining their 2D scaling relations and 3D fundamental manifold, we found that the sizes and velocity dispersions of these gap galaxies reveal continuous trends from dE to dSph galaxies. We conclude that low-luminosity dwarf elliptical galaxies are dominated by stars, not by dark matter, within their half light radii. This finding can be understood if internal feedback processes are operating most efficiently in gap galaxies, gravitationally heating the centrally-located dark matter to larger radii. Whereas external environmental processes, which can strip away stars, have a greater influence on dSph galaxies resulting in their higher dark matter fractions. Abridged.Comment: 20 pages, includes 12 figures, accepted for publication in MNRA

Internal properties of ultracompact dwarf galaxies in the Virgo cluster

We present new imaging and spectroscopic observations of six ultracompact dwarf (UCD) galaxies in the Virgo Cluster, along with reanalyzed data for five Fornax Cluster UCDs. These are the most luminous UCDs: -14 mag < M-V < -12 mag. Our Hubble Space Telescope imaging shows that most of the UCDs have shallow or steep cusps in their cores; only one UCD has a flat "King'' core. None of the UCDs show tidal cutoffs down to our limiting surface brightness. Spectroscopic analysis shows that Virgo UCDs are old ( older than 8 Gyr) and have metallicities in the range from [Z/H] = -1.35 to +0.35 dex. Five Virgo UCDs have supersolar [alpha/Fe] abundance ratios, and one Virgo UCD has a solar abundance ratio. The supersolar [alpha/Fe] abundances are typical of old stellar populations found in globular clusters and elliptical galaxies. We find that Virgo UCDs have structural and dynamical properties similar to Fornax UCDs. The Virgo and Fornax UCDs all have masses approximate to(2-9) x 10(7) M-circle dot and mass-to-light ratios approximate to(3-5) M-circle dot/L-circle dot,(V). The dynamical mass-to-light ratios for Virgo UCDs are consistent with simple stellar population model predictions: the Virgo UCDs do not require dark matter to explain their mass-to-light ratios. We conclude that the internal properties of Virgo UCDs are consistent with them being the high-mass/high-luminosity extreme of known globular cluster populations. We refrain from any firm conclusions on Fornax UCD origins until accurate age, metallicity, and alpha-abundance estimates are obtained for them. Some of our results, notably the fundamental plane projections, are consistent with the formation of UCDs by the simple removal of the halo from the nuclei of nucleated dwarf galaxies. However, the ages, metallicities, and abundances for Virgo UCDs are not consistent with this simple stripping model. It might be consistent with more sophisticated models of the stripping process that include the effects of gas removal on the chemical evolution of the nuclei

The charge state of pt in binary compounds and synthetic minerals determined by x-ray absorption spectroscopy and quantum chemical calculations

The binary synthetic compounds of Pt with chalcogens (O, S, Se, Te), pnictogens (As, Sb, Bi), and intermetallic compounds with Ga, In, and Sn of various stoichiometry were studied via X-ray absorption spectroscopy (XAS). The partial atomic charges of Pt in the compounds were computed using quantum chemical density functional theory (DFT) based methods: the Bader (QTAIM) method, and the density-derived electrostatic and chemical (DDEC6) approach. Strong positive correlations were established between the calculated partial atomic charges of Pt and the electronegativity (χ) of ligands. The partial charge of Pt in PtL2 compounds increases much sharply when the ligand electronegativity increases than the Pt partial charge in PtL compounds. The effect of the ligand-to-Pt atomic ratio on the calculated Pt partial charge depended on ligand electronegativity. The DDEC6 charge of Pt increases sharply with the growth of the number of ligands in PtSn (n = 1, 2; electronegativity χ(S) &gt;&gt; χ(Pt)), weakly depends on the phase composition in PtTen (n = 1, 2; χ(Te) is slightly lower than χ(Pt)), and decreases (becomes more negative) with increase of the ligand-to-Pt ratio in intermetallic compounds with electron donors (χ(L) &lt; χ(Pt), L = Ga, In, Sn). According to XANES spectroscopy, the number of 5d (L2,3 absorption edges) and 6p (L1-edge) electrons at the Pt site decreased when ligand electronegativity increased in chalcogenides and pnictides groups. An increase of the ligand-to-Pt ratio resulted in the increase of the Pt L3-edge white line intensity and area in all studied compounds. In the case of chalcogenides and pnictides, this behavior was consistent with the electronegativity rule as it indicated a loss of Pt 5d electrons caused by the increase of the number of ligands, i.e., acceptors of electrons. However, in the case of ligands–electron donors (Te, Sn, Ga, In) this observation is in apparent contradiction with the electronegativity arguments as it indicates the increase of the number of Pt 5d-shell vacancies (holes) with the increase of the number of the ligands, for which the opposite trend is expected. This behavior can be explained in the framework of the charge compensation model. The loss of the Pt d-electrons in compounds with low ligand electronegativity (χ(Pt) &gt; χ(L)) was overcompensated by the gain of the hybridized s-p electron density, which was confirmed by Pt L1-edge spectra analysis. As a result, the total electron density at the Pt site followed the electronegativity rule, i.e., it increased with the growth of the number of the ligands-electron donors. The empirical correlations between the Pt partial atomic charges and parameters of XANES spectral features were used to identify the state of Pt in pyrite, and can be applied to determine the state of Pt in other ore minerals. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.This study was supported by RFBR grant No. 20-35-70049, the program 211 of the Russian Federation Government, agreement No. 02.A03.21.0006, by the Russian Government Program of Competitive Growth of Kazan Federal University, and by Ministry of Education and Science of the Russian Federation grant No. 075-15-2020-802

NGC 7468: a galaxy with an inner polar disk

We present our spectroscopic observations of the galaxy NGC 7468 performed at the 6-m Special Astrophysical Observatory telescope using the UAGS long-slit spectrograph, the multipupil fiber spectrograph MPFS, and the scanning Fabry-Perot interferometer (IFP). We found no significant deviations from the circular rotation of the galactic disk in the velocity field in the regions of brightness excess along the major axis of the galaxy (the putative polar ring). Thus, these features are either tidal structures or weakly developed spiral arms. However, we detected a gaseous disk at the center of the galaxy whose rotation plane is almost perpendicular to the plane of the galactic disk. The central collision of NGC 7468 with a gas-rich dwarf galaxy and their subsequent merging seem to be responsible for the formation of this disk.Comment: 8 pages, 6 figures, accepted in Astronomy Letters, 2004, vol 30., N 9, p. 58

A Comparison of surface brightness profiles for ultra-compact dwarfs and dwarf elliptical nuclei: implications for the `threshing' scenario

Using imaging from the Hubble Space Telescope, we derive surface brightness profiles for ultra-compact dwarfs in the Fornax cluster and for the nuclei of dwarf elliptical galaxies in the Virgo cluster. Ultra-compact dwarfs are more extended and have higher surface brightnesses than typical dwarf nuclei, while the luminosities, colors, and sizes of the nuclei are closer to those of Galactic globular clusters. This calls into question the production of ultra-compact dwarfs via ``threshing'' whereby the lower surface brightness envelope of a dwarf elliptical is removed by tidal processes, leaving behind a bare nucleus. Threshing may still be a viable model if the relatively bright Fornax ultra compact dwarfs considered here are descended from dwarf ellipticals whose nuclei are at the upper end of their luminosity and size distributions.Comment: 5 pages, 2 figures, 1 table, uses emulateapj.cls (included) ApJ Letters, accepted for publicatio