arXiv subjects

I. D. Karachentsev

Publications and source records attributed to I. D. Karachentsev.

At least 19 recordsLinked to original sources

arXiv2026

Problems of cosmology on small scales of the Universe

Six challenges for the standard cosmological model $Λ$CDM are listed, which arise when comparing theoretical predictions with observational data on scales of ~1 Mpc. Different parameters of luminous and dwarf galaxies in the local sphere with a radius of 12 Mpc are presented. The average densities of stellar matter and dark matter are reproduced depending on a distance in the Local volume. Observational data on distribution of angular momentum of nearby galaxies are considered. A comparison of the dark matter mass estimates for systems of galaxies based on motions of their internal (virialized) members and neighboring galaxies is given. The reasons for the low derived value of the dark matter density, $Ω_m = 0.08\pm0.02$, in the Local Universe with respect to the global value $Ω_m = 0.30\pm0.02$ are discussed

gr-qc↗

arXiv2025

The Local Volume galaxy census and HST SNAP surveys

We examined F814W and F606W images of dwarf galaxies from the Hubble Space Telescope archive, which were obtained under the HST SNAP programs 17159 to 17797. Among 58 observed dwarfs located outside the Local Group, we found only a few objects that were confidently resolved into stars. We determined two new distances for the galaxies: dw1252+2215 ($5.32\pm0.20$ Mpc) and dw1234+3952 ($4.34\pm0.16$ Mpc) via the Tip of the Red Giant Branch. They turned out to be new probable dwarf satellites of the nearby luminous spiral galaxies NGC 4826 and NGC 4736, respectively. We also note that recent SNAP surveys vary in their productivity in measuring new galaxy distances by more than an order of magnitude.

astro-ph.GA↗

arXiv2025

Search for dwarf galaxies in the southwestern sector of the Local cosmic void

We performed a search for new dwarf galaxies in a direction towards the southwestern part of the Local Void using the data on DESI Legacy Imaging Surveys. In a sky area of $\sim1000$ square degrees, we discovered 12 candidates to nearby dwarfs with a high confidence. Four of them are probable new companions to the nearby galaxy M 83 and others are isolated objects. We found also 20 nearby dwarf candidates with a low confidence. Almost all of the detected galaxies are classified as late type dwarfs. A new cluster of bluish stars with an angular diameter of 0.9$^{\prime}$ is revealed by us at a high galactic latitude, $b = -29^{\circ}$. Being at a distance of $\sim70$ kpc, it can be a globular cluster associated with the Milky Way stellar stream Sagittarius dSph or a new ultra-faint satellite of the Milky Way.

astro-ph.GA↗

arXiv2025

More Local Volume dwarf galaxy candidates

We present the results of searching for new dwarf galaxies in the Local Volume. We found 40 satellite candidates in the double-virial-radius regions of 20 Milky Way-like and LMC-like galaxies in the southern sky using DESI Legacy Imaging Surveys, 10 of which were known but not clearly associated with the Local Volume previously. Among the 40 satellite candidates, 8 are supposed members of the NGC6744 group and 13 are located in the vicinity of the Sombrero galaxy. Based on seven companions to the giant spiral galaxy NGC\,6744 with measured radial velocities, we estimate that the total mass of the group is $M_T = (1.88\pm0.71)\times 10^{12} M_{\odot}$ and the total mass-to-K-luminosity ratio $M_T/L_K = (16.1\pm6.0) M_{\odot}/L_{\odot}$. We reproduce a distribution of 68 early- and late-type galaxies in the Local Volume situated around the Sombrero, noting their strong morphological segregation and also the presence of a foreground diffuse association of dwarf galaxies at 8 degrees to SE from the Sombrero.

astro-ph.GA↗

arXiv2024

Kinematic distances of galaxies in the Local Volume

We consider the kinematic distances to nearby galaxies obtained by the Numerical Action Method (NAM) based on the Cosmic-flow-3 survey data. NAM distances are compared with 418 high-precision distances measured by the Tip of the Red Giant Branch (TRGB) method using the Hubble Space Telescope. We estimated the average difference = -0.30 +- 0.08 Mpc and the standard deviation of 1.57 Mpc. Approximately the same difference in the distance scale is obtained in comparison with less accurate distance estimates through the membership of galaxies in known groups or from the Tully-Fisher relation. We conclude that the NAM method provides distance estimates with an accuracy of 20% within the Local Volume, which is valid for ~90% of the sky, except for the regions of the Virgo cluster and the Coma-I group.

astro-ph.GA↗

arXiv2024

Large diffuse dwarfs in the dynamically cold triple system

We report on the discovery of three large diffuse dwarf (LDD) galaxies located in isolated triple systems. They have effective diameters of (3.6-10.0) kpc and effective surface brightness of (26.2--27.3)$^m/$sq.arcsec. We note that the LDD galaxies tend to occur in small groups with a very low dispersion of radial velocities. The total (orbital) mass of the triplets approximately equals to their integral stellar mass within velocity measurement errors. The presence of LDD galaxies in cold multiple systems seems mysterious.

astro-ph.GA↗

arXiv2024

Average Star Formation Parameters in the Local Volume of the Universe

Based on the fluxes of 1400 nearby galaxies observed in far ultraviolet (${\rm FUV}$) and in the H$α$ line, we determined the global star formation rate per unit Universe volume, $j_{\rm SFR}=(1.34\pm0.16) 10^{-2}\,M_{\odot}$ yr$^{-1}$ Mpc$^{-3}$. With the current star formation rate (SFR), ($65\pm4)$% of the observed stellar mass is reproduced in the cosmological time of 13.8 billion years. The neutral gas reserves in the Local Volume with a radius of 11 Mpc will facilitate the current SFR on a scale of approximately another 5 billion years.

astro-ph.GA↗

arXiv2023

A search for new dwarf galaxies outside the nearby groups

We undertook a search for new nearby dwarf galaxies outside the known groups in the Local Volume using the data on DESI Legacy Imaging Surveys. In a wide sky area of $\sim$5000 square degrees directed toward the Local Void, we found only 12 candidates to nearby low mass galaxies. Almost all of them are classified as irregular or transition type dwarfs. Additionally, we examined areas of the sky exposed with the Hyper Suprime Camera of the Subaru telescope ($\sim$700 square degrees) and found nine more candidates to nearby dwarfs. Finally, nine candidates to the Local Volume were selected by us from the Zaritsky's SMUDG catalog that contains 7070 ultra-diffuse objects automatically detected in the whole area of the DESI surveys. We estimated a fraction of quiescent dSph galaxies in the general cosmic field to be less than 10 percent.

astro-ph.GA↗

arXiv2023

Satellites around Edge-on Galaxies. I. Dynamical Masses

We have undertaken a search for satellites around edge-on galaxies in the EGIPS catalog, which contains 16551 objects with declinations above -30 deg. We searched for systems with a central galaxy dominating in brightness by at least 1 mag compared to its companions. As a result, we discovered 1097 candidate satellites around 764 EGIPS galaxies with projected distances less than 500 kpc and a radial velocity difference less than 300 km/s. Of these, 757 satellites around 547 central galaxies have radial velocity accuracies higher than 20 km/s and satisfy the gravitationally bound condition. The ensemble of satellites is characterized by an average projected distance of 84 kpc and an average radial velocity dispersion of 103 km/s. Treating small satellites as test particles moving on isotropic orbits around central EGIPS galaxies, we determined the projected (orbital) masses of the edge-on galaxies. Within the luminosity range of 1.3*10^10 to 42*10^{10} Lsun, the total mass of the systems is well described by a linear dependence log(Mp)~0.88*log( g) with an average total mass-to-$K$-band luminosity equal to 17.5+-0.8 Msun/Lsun, which is typical for nearby spiral galaxies such as the Milky Way, M 31 and M 81.

astro-ph.GA↗

arXiv2023

Surface photometry of 50 dwarf galaxies in the Local Volume

Results of surface photometry of 50 galaxies in the Local Volume based on archived images obtained with the Hubble Space Telescope are presented. Integrated magnitudes in the V and I bands are introduced for the sample galaxies, along with brightness and color profiles. The obtained photometric parameters are compared with the measurements of other authors.

astro-ph.GA↗

arXiv2023

Orientation of the spins of galaxies in the Local volume

We estimated the angular momentum, $J$, of $720$ galaxies in the Local Volume with distances $r < 12$ Mpc. The distribution of the average angular momentum along the Hubble sequence has a maximum at the morphological type $T= 4$ (Sbc), while the dispersion of the $J$-values for galaxies is minimal. Among the Local Volume population, 27 elite spiral galaxies stand out, with an angular momentum greater than 0.15 of the Milky Way, $J > 0.15 J_{MW}$, making the main contribution ($ > 90\%$) to the total angular momentum of galaxies in the considered volume. Using observational data on the kinematics and structure of these galaxies, we determined the direction of their spins. We present the first map of the distribution of the spins of 27 nearby massive spiral galaxies in the sky and note that their pattern does not exhibit significant alignment with respect to the Local Sheet plane. The relationship between the magnitude of the angular momentum and stellar mass of the local galaxies is well represented by a power law with an exponent of ($5/3$) over an interval of $6$ orders of magnitude of the mass of galaxies.

astro-ph.GA↗

arXiv2023

Distances to 10 nearby galaxies observed with the Hubble space telescope

Images of 10 galaxies in F814W and F606W filters obtained on the Hubble Space Telescope (HST) are used to construct color-magnitude diagrams for the star population of these galaxies. The distances to the galaxies are estimated from the luminosity of the tip of the red giant branch. The galaxies examined here have radial velocities from 250 to 760 km/s relative to the centroid of the Local Group and distances ranging from 3.7 to 13.0 Mpc. Several other observed galaxies with low radial velocities are noted at distances beyond the limit of 13 Mpc.

astro-ph.GA↗

arXiv2023

The pride of lions around Messier 105

We undertook a search for new dwarf galaxies in the Leo-I group using the data from the DECaLS digital sky survey. Five new presumed members of this group have been found in a wide vicinity of ${\rm M}\,105 ({\rm NGC}\,3379$). Currently, the group has a population of $83$ galaxies, $33$ of which have measured radial velocities. More than half of the group members belong to early types with no signs of ongoing star formation. About a quarter of the galaxies are outside the group's virial radius, $R_v = 385$~kpc. The presence of multiple systems with a size of about 15~kpc is evident in the group, but there are no noticeable global flat or filamentary substructures. The luminosity function of the group looks to be deficient in galaxies with absolute magnitudes in the interval $M_B = [-18, -15]$ mag. The ${\rm M}\,105$ group is characterized by a radial velocity dispersion of $136$~km~s$^{-1}$, orbital mass estimate $(5.76\pm1.32)\times 10^{12}~M_{\odot}$, and the total mass-to-K-band-luminosity ratio $(17.8\pm4.1) M_\odot/L_\odot$. The neighboring group of galaxies around ${\rm M}\,66 ({\rm NGC}\,3627$) has a similar virial radius, $390$~kpc, velocity dispersion, $135$~km~s$^{-1}$, and total mass-to-luminosity ratio, $(15.6\pm3.9) M_\odot/L_\odot$. Both groups in the Leo constellation are approaching the Local Group with a velocity of about 100~km~s$^{-1}$. In the background of the ${\rm M}\,105$ group, we noted a group of 6 galaxies with an unusually low virial mass-to-luminosity ratio, $M_T/L_K = (4.1\pm2.2) M_\odot/L_\odot$.

astro-ph.GA↗

arXiv2022

Peekaboo: the extremely metal poor dwarf galaxy HIPASS J1131-31

The dwarf irregular galaxy HIPASS J1131-31 was discovered as a source of HI emission at low redshift in such close proximity of a bright star that we call it Peekaboo. The galaxy resolves into stars in images with Hubble Space Telescope, leading to a distance estimate of 6.8+-0.7 Mpc. Spectral optical observations with the Southern African Large Telescope reveal HIPASS J1131-31 to be one of the most extremely metal-poor galaxies known with the gas-phase oxygen abundance 12+log(O/H) = 6.99+-0.16 dex via the direct [OIII] 4363 line method and 6.87+-0.07 dex from the two strong line empirical methods. The red giant branch of the system is tenuous compared with the prominence of the features of young populations in the color-magnitude diagram, inviting speculation that star formation in the galaxy only began in the last few Gyr.

astro-ph.GA↗

arXiv2022

New Local Volume Dwarf Galaxy Candidates from the DESI Legacy Imaging Surveys

We undertook a search for new dwarf galaxies in the vicinity of relatively isolated nearby galaxies with distances $D < 12$ Mpc and stellar masses in the $2\times10^{11}-3\times10^8~M_{\odot}$ interval, using the data from the DESI Legacy Imaging Surveys. Around the 46 considered Local Volume galaxies, $67$ new candidates for satellites of these galaxies were found. About half of them are classified as spheroidal dwarfs of low surface brightness. The new galaxies are included in the Local Volume database (LVGDB), which now contains 1421 objects, being 63% more than the Updated Nearby Galaxy Catalog.

astro-ph.GA↗

arXiv2022

Around the Spindle galaxy: the dark halo mass of NGC3115

We report observations of five dwarf galaxies in the vicinity of the luminous S0 galaxy NGC 3115 performed with the Advanced Camera for Surveys on the Hubble Space Telescope. Their distances determined via the Tip of the Red Giant Branch are: 10.05 Mpc (UGCA 193), 9.95 Mpc (KKSG 17), 10.13 Mpc (2MASX-J0957-0915), 10.42 Mpc (2dFGRS-TGN218Z179) and 11.01 Mpc (KKSG 19). With their typical distance error of about 0.75 Mpc all the five dwarfs are consistent to be true satellites of the host galaxy NGC 3115 (10.2$\pm$0.2 Mpc). Using the DESI Legacy Imaging Surveys we also found 5 new probable dwarf satellites of NGC3115, as well as 4 new probable members of the neighboring group around NGC 3521 situated 3 Mpc away from the NGC 3115 group. Based on the radial velocities and projected separations of 10 dwarf companions, we derived the total (orbital) mass of NGC 3115 to be (4.89$\pm$1.48) $10^{12}$ $M_{\odot}$. The ratio of the total mass-to-K-luminosity of NGC 3115 is (50$\pm$15) $M_\odot/L_\odot$, which is typical for the early-type luminous galaxies.

astro-ph.GA↗

arXiv2021

Local Volume Late-Type Galaxies with an Extreme Ratio of $Hα$-to-$FUV$ Star-Formation Rates

Using a currently most representative sample of 477 late-type galaxies within 11 Mpc of the Milky Way with measured star-formation rates ($SFR$s) from the far ultraviolet ($FUV$) and H$α$ emission line fluxes, we select galaxies with the extreme ratios: $SFR(Hα)/SFR(FUV) > 2$ and $SFR(Hα)/SFR(FUV) < 1/20$. Each subsample amounts to $\sim5$\% of the total number and consists of dwarf galaxies with the stellar masses $M^*/M_{\odot} = (5.5 - 9.5)$~dex. In spite of a huge difference in their $SFR(Hα)$ activity on a scale of $\sim10$~ Myr, the temporarily "excited" and temporarily "quiescent" galaxies follow one and the same relation between $SFR(FUV)$ and $M^*$ on a scale of $\sim100$~Myr. Their average specific star-formation rate $\log[SFR(FUV)/M^*] = -10.1\pm0.1$ (yr$^{-1}$) coinsides with the Hubble parameter $\log(H_0)= -10.14$ (yr$^{-1}$). On a scale of $t \sim10$~Myr, variations of $SFR$ have a moderate flash amplitude of less than 1 order above the main-sequence and a fading amplitude to 2 orders below the average level. In general, both temporarily excited and temporarily quiescent galaxies have almost similar gas fractions as normal main-sequence galaxies, being able to maintain the current rate of star-formation on another Hubble time scale. Ranging the galaxies according to the density contrast produced by the nearest massive neighbor exhibits only a low average excess of $SFR$ caused by tidal interactions.

astro-ph.GA↗

arXiv2021

Early-Type (E, S0) Galaxies in the Catalog of Isolated Galaxies (KIG)

We use the data of modern digital sky surveys (PanSTARRS-1, SDSS) combined with HI-line and far ultraviolet (GALEX) surveys to reclassify 165 early-type galaxies from the Catalog of Isolated Galaxies (KIG). As a result, the number of E- and S0-type galaxies reduced to 91. Our search for companions of early-type KIG galaxies revealed 90 companions around 45 host galaxies with line-of-sight velocity differences $|dV| < 500$ km s$^{-1}$ and linear projected separations $R_{p} < 750$ kpc. We found no appreciable differences in either integrated luminosity or color of galaxies associated with the presence or absence of close neighbors. We found a characteristic orbital mass-to-luminosity ratio for 26 systems "KIG galaxy--companion" to be $M_{\odot}/L_{K} = (74\pm26) M_{\odot}/L_{\odot}$, which is consistent with the $M_{\rm orb}/L_{K}$ estimates for early-type isolated galaxies in the 2MIG catalog ($63 M_{\odot}/L_{\odot}$), and also with the $M_{\rm orb}/L_{K}$ estimates for E- and S0-type galaxies in the Local Volume: $38\pm22$ (NGC 3115), $82\pm26$ (NGC 5128), $65\pm20$ (NGC 4594). The high halo-to-stellar mass ratio for E- and S0-type galaxies compared to the average $(20\pm3) M_{\odot}/L_{\odot}$ ratio for bulgeless spiral galaxies is indicative of a significant difference between the dynamic evolution of early- and late-type galaxies.

astro-ph.GA↗