arXiv subjects

I. D. Karachentsev

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

136 records · Page 8Linked to original sources

arXiv2000

The Stellar Content and Distance of UGC 4483

We present HST/WFPC2 observations of UGC 4483, an irregular galaxy in the M81/NGC 2403 complex. Stellar photometry was carried out with HSTphot, and is complete to V ~ 26.0 and I ~ 24.7. We measure the red giant branch tip at I = 23.56 +/- 0.10 and calculated a distance modulus of (m-M)o = 27.53 +/- 0.12 (corresponding to a distance of 3.2 +/- 0.2 Mpc), placing UGC 4483 within the NGC 2403 subgroup. We were able to measure properties of a previously-known young star cluster in UGC 4483, finding integrated magnitudes of V = 18.66 +/- 0.21 and I = 18.54 +/- 0.10 for the stellar contribution (integrated light minus Halpha and [OIII] contribution), corresponding to an age of ~10-15 Myr and initial mass of ~10^4 Msun. This is consistent with the properties of the cluster's brightest stars, which were resolved in the data for the first time. Finally, a numerical analysis of the galaxy's stellar content yields a roughly constant star formation rate of 1.3x10^-3 Msun/yr and mean metallicity of [Fe/H] = -1.3 dex from 15 Gyr ago to the present.

astro-ph↗

arXiv2000

Dwarf Spheroidal Galaxies in the M81 Group Imaged with WFPC2

We obtained HST/WFPC2 images of the dwarf spheroidal (dSph) galaxies K61, K63, K64, DDO78, BK6N, and kk77 in the M81 group. Our color-magnitude diagrams show red giant branches with tips (TRGB) falling within the range of I = [23.8 -24.0] mag. The derived true distance moduli (DM) of the 6 dSphs ranging from 27.71 to 27.93 mag are consistent with their membership in the group. Given accurate distances of 5 other group members, which have been derived via TRGB or cepheids, the mean DM of the M81 group is (27.84+-0.05) mag. We find the difference of the mean distances to the M81 and NGC2403 groups to be D_M81 - D_NGC2403 =(0.5+-0.2) Mpc, which yields a deprojected separation of 0.9 Mpc. With respect to the Local group, M81 and NGC2403 have radial velocities of 106 and 267 km/s respectively, while the velocities of the group centroids are 142 and 281 km/s. The higher velocity of the closer system may indicate that these groups are moving towards each other, similar to the Milky Way and M31 in the Local group. Several globular cluster candidates have been identified in the galaxies.

astro-ph↗

arXiv2000

A group of galaxies around the giant spiral NGC 6946

We present large-scale CCD images of a dozen low surface brightness objects in the vicinity of giant Sc galaxy NGC 6946, which have been found recently on POSS-II copies. Six of them: UGC 11583, kk251, kk252, kkr55, kkr56, and kkr59 are dwarf irregular galaxies resolved into stars. We determined their distances from the luminosity of the brightest blue stars. The mean estimated distance to the NGC 6946 group is 5.9 +- 0.4 Mpc. Together with Cepheus 1, discovered before, the group consist of 8 late type galaxies. Almost all of them are detected or marginally detected in the HI line. The group is characterized by a linear projected diameter of 420 kpc, a radial velocity dispersion of 95 km/s, and a virial mass-to-luminosity ratio about 56 M_sun/L_sun.

astro-ph↗

arXiv2000

A Dwarf Galaxy Survey in the Local Volume

We are carrying out a comprehensive multi-wavelength study of dwarf galaxies in the Local Volume (< 5 Mpc). After our all-sky survey more than doubled the dwarf census we are now measuring structural parameters, integrated properties, and velocities. Our 200-orbit HST snapshot program yields stellar content, star formation history, and TRGB distances. We can thus study the morphology-density relation in galaxy groups in three dimensions, the influence of environment on galaxy evolution, and the universality of the metallicity-surface brightness-luminosity relation.

astro-ph↗

arXiv2000

Survey of rotation curves for northern spiral edge-on galaxies

Rotational curves are measured for almost complete sample of 308 northern spiral galaxies using the 6-m telescope. For observations we selected edge-on galaxies from RFGC catalog with apparent axial ratio a/b>8, angular diameter a<2', and declinations delta>+38deg above the Arecibo belt. About 97% of the galaxies are detected in the H-alpha line. For them a typical rotation curve extends till 87% of the standard galaxy radius. The rotation curve amplitude shows close correlation with a width of the HI line. The median radial velocity for the galaxies is 7800 km/sec, and the median maximum of the rotation curves is 137 km/s. These new observational data will be used to study cosmic streamings of galaxies seen on a scale of 200 Mpc.

astro-ph↗

arXiv1999

HI observations of nearby galaxies I. The first list of the Karachentsev catalog

We present HI observations of the galaxies in the first list of the Karachentsev catalog of previously unknown nearby dwarf galaxies (Karachentseva & Karachentsev 1998). This survey covers all known nearby galaxy groups within the Local Volume (i.e. within 10 Mpc) and their environment, that is about 25% of the total sky. A total of 257 galaxies have been observed with a detection rate of 60%. We searched a frequency band corresponding to heliocentric radial velocities from -470 km/s to about +4000 km/s. Non-detections are either due to limited coverage in radial velocity, confusion with Local HI (mainly in the velocity range -140 km/s to +20 km/s, or lack of sensitivity for very weak emission. 25% of the detected galaxies are located within the Local Volume. Those galaxies are dwarf galaxies judged by their optical linear diameter (1.4 +/- 0.2 kpc on the average), their mean total HI mass (4.6 E7 solar masses), and their observed linewidths (39 km/s).

astro-ph↗

arXiv1999

The dwarf spheroidal galaxy DDO 44: stellar populations and distance

We present ground-based and HST WFPC2 imaging of the nearby low surface brightness dwarf spheroidal galaxy DDO 44. For the first time DDO 44 was resolved into stars. The resulting color-magnitude diagram for about 1290 stars shows the red giant branch with a tip at I=(23.55+-0.15) mag, which yields a distance of (3.2+-0.2) Mpc consistent with membership of DDO 44 in the NGC 2403 group. The linear separation of DDO 44 from NGC 2403 is 75 kpc on the sky and (30+-450) kpc along the line of sight. The relationship between the dwarf galaxy's absolute R magnitude of -13.1 mag, its central surface brightness of 24.1 mag/square arcsec, and its mean metallicity of -1.7 dex follow the trend for other nearby dwarf spheroidal galaxies. One globular cluster candidate has also been identified in DDO 44.

astro-ph↗

arXiv1999

A new catalogue of multiple galaxies in the Local Supercluster

To reveal small galaxy groups in the Local Supercluster, a new approach is suggested which allows for individual properties of galaxies. The criterion is based on the assumption of closed motions of companions around the dominating group member within a zero velocity sphere. The criterion is applied to a sample of 6321 nearby galaxies with radial velocities $V_0\le3000$ km/s. The 3472 galaxies have been assigned to 839 groups that include 55% of the considered sample. For the groups revealed by the new algorithm (with $k \geq 5$ members) the median velocity dispersion is 86 km/s, the median harmonic radius is 247 kpc, the median crossing time is 0.08(1/H), and the median virial-mass-to-light ratio is $56 M_\odot/L_\odot$.

astro-ph↗

arXiv1999

HI properties of nearby galaxies from a volume-limited sample

We consider global HI and optical properties of about three hundred nearby galaxies with V$_0 < 500$ km/s. The majority of them have individual photometric distance estimates. The galaxy sample parameters, e.g. their linear diameters, their HI mass-to-luminosity ratio, their total mass-to-luminosity ratio, their mean optical surface brightness show some known and some new correlations implying a meaningful dynamic explanation. For the LV galaxies their HI mass and angular momentum follow a nearly linear relation expected for rotating gaseous disks being near the threashold of gravitational instability, favourable for active star formation.

astro-ph↗

arXiv1999

New Dwarf Galaxies in the IC342/Maffei Group

We report detection of HI-emission from three 'new' dwarf galaxies Perseus A, Perseus B, and Camelopardalis D in the IC342/Maffei group of galaxies and of Draco A. The actual number of (probable) members of this group increases to 19 galaxies. Its velocity dispersion is 87 km/s. With a distance of 2.2+-0.5 Mpc this group is the nearest to the Local Group and might have considerable dynamical influence on the Local Group.

astro-ph↗