Low Surface Brightness Dwarf Galaxies

in the Local Supercluster General Field

V.E.Karachentseva (MAO NASU, Kiev),M.E.Sharina (SAO RAS, N.Arkhyz), K.V.Shipova (Kazan State University)

The international conference "Nearby Dwarf Galaxies”

SAO RAS, N. Arkhyz, September, 2009

Well-known general properties of the LSB dwarfs:

Mean B surface brightness: 1 - 10 % of the night sky surface brightness;

Morphology: dSph, dIr, dIm, dSm and transient types. Localization: dSphs dominate by number in the Virgo and Fornax

clusters as well as locate in groups while the late-type dwarfs populate the groups and field. Inside clusters and groups there is a similar morphological segregation with distance of the center.

General characteristics of dwarfs of the same morphological type are practically similar in the regions of high and low galaxy density.

There is a real problem with detection and confirmation of such a dwarf

galaxies. Another problem is a sharp decreasing of the number of detected dwarfs with a distance. There is specificity in the searching of dwarfs in an individual cluster(group) and in the field.

Goal of our work:

to select the isolated LSB dwarfs (and the associations of dwarfs) in the general field of the Lscl, to compile the available observational data, for studying their properties in comparison with dwarfs located in the galaxy systems. It is important for investigation of the LSB dwarfs formation and evolution in the low-density galaxy regions; for study their star formation histories, ages, dark matter problem.

Material:

* The Catalogue of Low Surface brightness dwarf galaxies, (Karachentseva, Sharina, 1988): an all-sky reference catalogue of 1500 LSB dwarfs taken from different catalogs and lists and revisited on the POSS-1 and ESO-SERC surveys ** "the 5 lists" sample- kk, kkr, kks, kkh, kksg (1998-2001): new all-sky searching for nearby dwarf galaxies on the POSS-2, ESO-SERC, SERCJ sky surveys

- HI observations by W.K. Huchtmeier (1997-2001)

- HIPASS and HIJASS HI surveys

- LEDA, NED databases

- DSS-1,2 and SDSS sky surveys

Selection of objects: - we omitted the objects in the regions of the Virgo, Fornax clusters, as well as the well-known groups;

Altogether in * + ** samples N~700 objects, ~300 of them have V_h. The mean radial velocities for * and ** samples: * <V_h> = 1460 km/s, N=186, ** <V_h> = 1489km/s, N=128, so we work in the same volume;

- we omitted the objects with A_B> 1 mag; non-galaxy objects; with V_LG <500km/s (Local Volume) and V_LG>3500 km/s; common for 2 our samples; we omitted also the dwarfs having neighbors (at the distance ~300 - 500 kpc) with close radial velocities.

Number of remaining isolated dwarfs N=209. <V_LG>=1325 km/s, SD=679 km/s

A large part of 380 dwarfs was observed but not detected in HI. The reasons of non-detection are due to: - the low amount of HI gas in the observed dwarfs; - the dwarfs locate behind the velocity range used in the HI observations; - in several cases there is a confusion from nearby galaxy;

The distribution of 380 dwarf without measured V in equatorial coordinates

For 209 dwarfs:

- we used NED to check the coordinates, identifications as well as to inspect wide environments of targets (to search the neighbors with close velocities);

- we extract from LEDA the main parameters: mags, angular diameters, velocities etc;

This work is not yet finished: it is necessary to add HI parameters and other ones as possible;

- on DSS-1,2 we performed the inspection of environments;

- on DSS-1,2 and SDSS we made the morphological classification.

This work is also not yet finished: it is necessary to do more fine classification.

The distribution of 209 LSB dwarf galaxies with measured velocities in equatorial coordinates

<V_LG>=1325km/s, SD=679 km/s

KDG 32V_LG=1898 km/sM=-15.3,A=11.8 kpc,Sph/Ir; SB0-:

BTS 93= KK 122 V_LG=936 km/sM=-14, A=3.6 kpc Ir/Im

ESO 146- GA02= KK 255 V_LG=1593 km/sM=-17.1, A=9.3 kpcIr/Im, loop

AM 1014-331 V_LG=2472 km/sM=-15.9, A=12.5 kpcIm/Sm, loop

ESO 305-9

M=-17.3SB(s)dm

UGC 7913

M=-16.9SAB(s)m

UGC 2259

M=-16.6SB(s)dm

DDO 149

M=-16.8IB(s)m

For isolated dwarf galaxies we found the expected relations between morphological type and absolute magnitude/mean surface brightness.

Type <M> M.er. of m. <SB> M.er. of m. NSm -15.34 0.27 23.50 0.54 40Im -15.00 0.18 24.52 0.36 60Ir -14.74 0.15 25.76 0.24 58

Sph/Ir -14.06 0.27 25.88 0.44 5

(Magnitudes and diameters are in the LEDA system)

A special interest is the finding of pairs and triplets consisting of dwarf galaxies. Inspecting the surroundings we found that 15 dwarfs from our list have one companion, 5 ones have two companions, and 3 dwarfs enter in galaxy groups.

ESO 249-36ESO 249-35

M=18.4*10^10M/L= 830 (in solar units)

Examples:

ESO 438-7ESO 438-6

M=8.3*10^10M/L=57 (in solar units)

KDG 81,V_LG=762

SDSS 11 55 06 +44 06 12 V_LG=664

SDSS 11 55 13 +44 13 08,V_LG=653

KDG 81SDSS 11 55 13 +44 13 08SDSS 11 55 06 +44 06 12

M=1.9*10^10M/L= 282 (in solar units)

These selected isolated dwarfs as well as isolated associations of dwarfs may be used in different observational programs.

Thank you!