The low-luminosity galaxy population in the NGC 5044 Group

Abstract

We present multicolour imaging for 33 dwarf and intermediate-luminosity galaxies in the field of the NGC 5044 Group, complemented with mid-resolution spectroscopy for a subsample of 13 objects. With these data, a revised membership and morphological classification is made for the galaxies in the sample. We were able to confirm all but one of the "definite members" included in the spectroscopic subsample, which were originally classified based on morphological criteria; however, an important fraction of background galaxies is probably present among "likely" and "possible" members. The presence of a nucleus could be detected in just five out of the nine galaxies originally classified as dE,N, thus confirming the intrisic difficulty of photographic-plate morphological classification for this kind of object. Our deep surface photometry provided clear evidences for disc structure in at least three galaxies previously catalogued as dE or dS0. Their transition-type properties are also evident from the colour-magnitude diagram, where they lie near the late-type galaxies locus, suggesting an evolutionary connection between a parent disc-galaxy population and at least part of present-day dEs. Six new dSph candidates were also found, most of them at small projected distances from NGC 5044, the central galaxy of the Group. The NGC 5044 Group appears clearly defined in redshift space, with a mean heliocentric radial velocity, <v_r>=2461 +/- 84 km/s (z=0.0082), and a moderate dispersion, \sigma_{v_r}=431 km/s. Our data show no luminosity segregation for early-type galaxies: both dwarf and bright E/S0 systems show very similar velocity distributions (\sigma_{v_r} ~ 290 km/s), in contrast to late-type galaxies that seem to display a broader distribution (\sigma_{v_r} ~ 680 km/s).Comment: 12 pages, 6 figures, uses mn2e.cls. To be published in MNRAS. For more info, full-resolution paper and colour figures see http://www.bo.astro.it/~eps/home.htm

Redshift determination of the BL Lac object 3C 66A by the detection of its host galaxy cluster at z = 0.340 ★

“…3). Shifts in g − i colour and g magnitude were established using Kand evolutionary corrections computed through the stellar population synthesis template galaxy models of Buzzoni (2005). We obtain for the Virgo red-sequence at z = 0.34: ∆(g − i ) = 0.894 mag and ∆g = 10.33 mag.…”

“…Given the adopted Cosmology, M * R = −21.10 mag. This magnitude was transformed into the Gunn-Sloan photometric system through the colours given by Buzzoni (2005) for galaxies of different ages, resulting in M * g = −20.26 mag. Therefore, an appropriate magnitude cut can be set at M g = −18.26 mag, corresponding to g = 23.88 mag for this cluster (z = 0.34).…”

“…The other candidates (including objects #5 and #11, for which we could obtain no spectroscopic redshift, due to their very low surface brightnesses), however, show clear dE (dwarf elliptical) morphologies; this has been shown to be an excellent membership indicator for low-redshift clusters (e.g. Cellone & Buzzoni 2005, and references therein), so we retain them as probable members of the z = 0.02 group. Note that no CRS for z ∼ 0.0677 is evident in Fig.…”

Small-scale systems of galaxies

“…Group membership may also be defined in terms of the group velocity dispersion, σ group , leading to a selection that is more capable of being adapted to the true group's properties. In this case, a limit of |(v galaxy − v group )| ≤ 3σ group has been used, reflecting the approximate dynamical boundaries of the group (see e.g., Mulchaey 2000;Cellone & Buzzoni 2005;Firth et al 2006). Different membership criteria applied to our sample yield the same result: there are no galaxies close to the velocity limits set by the above criteria (the group velocity dispersions used in the flexible group membership criterion are listed in Table 5).…”

The Low-luminosity Galaxy Population in the NGC 5044 Group

“…Note the striking spatial segregation of dwarf spheroidals, preferentially located around bright group members. galaxy class is characterized by a shallow SBP, clearly distinct from the dE one (but see [7] for possible selection effects). Among the latter, N139 (the most compact object labelled on Fig.…”