Environment status of blue compact galaxies and trigger of star formation

A&A 373, 24-37 (2001)
DOI: 10.1051/0004-6361:20010555

Environment status of blue compact galaxies and trigger of star formation

S. A. Pustilnik^{1, 2}, A. Y. Kniazev^{1, 2}, V. A. Lipovetsky¹ and A. V. Ugryumov^{1, 2}

¹ Special Astrophysical Observatory RAS, Nizhnij Arkhyz, 369167, Karachai-Circassia, Russia
² Isaac Newton Institute of Chile, SAO Branch

(Received 26 December 2000 / Accepted 26 March 2001)

Abstract
The work studies of the environment of low-mass galaxies with active star formation (SF) and a possible trigger of SF bursts due to gravitational interaction. Following the study by Taylor et al. (1995), we extend the search for possible disturbing galaxies of various masses to a much larger sample of 86 BCGs from the sky region of the Second Byurakan survey (SBS). The BCG magnitudes and radial velocities are revised and up-dated. The sample under study is separated by the criteria: EW([OIII] $_{\lambda5007}) > 45$ Åand $V_{\rm h} < 6 000$ km s-1and should be representative of all low-mass galaxies which experience SF bursts. We argue that the moderate tidal disturbers should be taken into account, and incorporate the respective range of distances in the search for disturbing neighbours. The majority of the neighbours in the vicinity of the studied BCGs are found through the study of their environment among UZC (Falco et al. 1999) galaxies, and the follow-up careful search of the fainter galaxies in the NED database. For the remaining BCGs, the neighbouring galaxies are found based on the results of the SAO 6 m telescope spectroscopy. By studing the data on the radial velocities of galaxies in the vicinity of BCGs we found: 1) 33 of the studied BCGs ( ${\sim}38.5\%$ ) are associated with significantly brighter galaxies ( $\Delta B \geq$ 1.5m); 2) 23 BCGs ( ${\sim}26.5\%$ ) have neighbours either of comparable or significantly lower brightness; 3) 14 of the studied BCGs (16% ) with no evident associated galaxy are either certain, or probable, mergers. Summarizing, we conclude that in ${\sim}80\%$ (or more) BCGs from the studied sample, the SF bursts are triggered either by tidal action of various strengths from other galaxies, or due to mergers of low-mass galaxies. We briefly discuss the implications of our main conclusion for evolutionary links of BCGs to other types of low-mass galaxies. Part of our sample falls into the volume belonging to the Local Supercluster. Therefore we formulate the results separately on the "Local Supercluster volume" and "general field region" . The total fractions of BCGs likely triggered by interaction with other galaxy are respectively, ${\sim}84.5\%$ and 80% for the nearby volume and for the general field. The fractions of BCGs with significantly brighter disturbers in these two groups are seemingly different ( ${\sim}54\pm14\%$ vs. ${\sim}31.5\pm7\%$ , respectively). Among the so called "isolated" BCGs (that is, without a bright neighbouring galaxy) in both the Local Supercluster volume and in general field, ${\sim}43\pm10\%$ are probably disturbed by dwarf galaxies and ${\sim}26\pm8\%$ have a merger morphology. In the Appendix we present the results of the spectroscopy with the SAO 6 m telescope of 27 galaxies in an attempt to find possible disturbing galaxies in the vicinity of some of the sample BCGs.

Key words: galaxies: dwarf -- galaxies: interaction -- galaxies: evolution -- galaxies: starburst

Offprint request: S. Pustilnik, sap@sao.ru

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