Äîêóìåíò âçÿò èç êýøà ïîèñêîâîé ìàøèíû. Àäðåñ îðèãèíàëüíîãî äîêóìåíòà : http://www.atnf.csiro.au/people/Angel.Lopez-Sanchez/proceedings/mrk1087.pdf Äàòà èçìåíåíèÿ: Sun Feb 3 03:57:46 2008 Äàòà èíäåêñèðîâàíèÿ: Mon Apr 14 02:39:15 2008 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: arp 220

A Massive Star Odyssey, from Main Sequence to Supernova Proceedings IAU Symposium No. 212, c 2002 IAU K.A. van der Hucht, A. Herrero & C. Esteban, eds.

MRK 1087: a puzzling susp ected Wolf-Rayet galaxy
´ C´sar Esteban, Angel R. L´pez-S´nchez e o a Instituto de Astrof´ ica de Canarias, 38200 - La Laguna, Tenerife, Spain is M´nica Rodr´ uez o ig Instituto Nacional de Astronom´ , Optica y Electronica, Apdo. Postal ia ´ ´ 51 y 216, 72000 Puebla, Pue., Mexico
Abstract. We present new observations of Mrk 1087 that indicate this galaxy is experiencing a strong star formation event due to the interaction with -at least- two nearby galaxies, one of them is a star-forming dwarf. We also discover that some of the surrounding non-stellar ob jects are tidal dwarves hosting weak starbursts.

Mrk 1087 (distance = 111 Mpc) is a suspected Wolf-Rayet galaxy (Schaerer et al. 1999). It has a companion galaxy (K72 103a) at 81 kpc to the southwest and at the same distance. Keel (1988) proposes that the ob ject is a galaxy in formation surrounded by filaments of infalling ionized gas. We have obtained long-slit intermediate-resolution spectroscopy covering most of the ob jects surrounding the galaxy reported by M´ndez & Esteban (2000) and a deep V-band CCD image e of the whole group (Figure 1). Our new image shows a new faint companion galaxy (MV -18.2) just to the north of Mrk 1087 (labeled as companion in Figure 1). It has an elliptical shape and shows nebular emission. It shows a radial velocity of +117 km s-1 with respect to the main body of Mrk 1087. Therefore, both galaxies may be physically associated and at a relative distance of about 60 kpc. We have detected faint nebular emission in ob jects #1, #3, and #7, but not in #12. Ob jects #2 and #11 were not observed. Ob jects #1 and #3 show radial velocities close to the systemic velocity of Mrk 1087. Keel (1988) interpreted #7 as a companion external ob ject interacting with the main galaxy however, we do not confirm his result, in fact #7 seems to follow closely the general rotation pattern of the ionized gas of the main galaxy. We do not detect the [OIII] 4363 ° line in any of the spectra and therefore we have estimated A the ionic abundances from the so-called empirical calibrations, making use of the R23 parameter and/or the [NII]/H ratio. The absolute magnitudes of the ob jects indicate that all the ob jects except the main body of Mrk 1087 can be considered as dwarf galaxies. The O/H ratio estimated for ob jects #1, #3 is similar to that of the main galaxy (12+log O/H = 8.7) and larger than the abundance expected for the metallicity-luminosity relation for classical dwarves. This result indicates that ob jects #1 and #3 can be considered as tidal dwarves originated from material stripped from Mrk 1087. Ob ject #7 shows O/H and 1


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Esteban, L´pez-S´nchez & Rodr´ uez o a ig

Figure 1.

Deep CCD image in the V filter of Mrk 1087 and its surroundings.

N+ /O+ ratios lower but not so different to that of the main galaxy. The O/H abundance is larger than that expected for a dwarf galaxy and therefore we interpret #7 as an intense star-forming zone off-center of Mrk 1087. The O/H ratio obtained for the companion ob ject (12+log O/H = 8.3) is lower than that of the main galaxy and consistent with the metallicity-luminosity relation for dwarves. Moreover, the N+ /O+ is also lower than that of Mrk 1087 and of the order of the typical value for dwarf galaxies (-1.55, for the main galaxy is -0.99). Therefore, the north companion should be interpreted as an independent nearby dwarf galaxy that is probably interacting with Mrk 1087. This could explain the presence -at least- of the tidal dwarf #1 and its associated bridge, which is almost aligned with the companion galaxy (see Figure 1). As a conclusion, we consider that Mrk 1087 and its surroundings can be considered as a compact group of galaxies. This result is a further indication of the importance of the interactions with difficult-to-detect dwarf galaxies in the triggering of strong starburst and specially in Wolf-Rayet galaxies. References
Keel, W.C. 1988, A&A 202, 41 M´ endez, D.I., Esteban, C. 2000, A&A 359, 493 Schaerer, D., Contini, T., Pindao, M. 1999, A&AS 335, 85