Astron. Astrophys. 323, 317-322 (1997)

Astron. Astrophys. 323, 317-322 (1997)

1. Introduction

The origin of the angular momentum of galaxies is one of the questions that any theory on galaxy and cluster formation must answer. No present theories can explain perfectly how galaxies obtained their angular momenta. If the angular momenta of the galaxies have not been altered too much since their formation (Thompson 1976; Farouki & Shapiro 1981), the present orientation of the spin vectors (hereafter SVs) of the disk galaxies can be an indicator of the initial conditions when galaxy and cluster formed. An analysis of the orientation of SVs can teach us something about this formation process.

Many investigators have studied the orientation effects of galaxies and clusters (e.g. Djorgovski 1987, and the references therein), but the results are diverse, maybe due to various methods and sample criteria (Kashikawa & Okamura 1992, hereafter KO; Hu et al. 1995, hereafter HWSL). However, the evidence for alignments is accumulating.

In a previous paper (HWSL), we confirmed the alignment of SVs of disk galaxies in the Virgo cluster, and we concluded that this alignment of SVs may be morphologically dependent. The Virgo cluster is an irregular cluster, its dynamical relaxation on a large scale has just begun. One may ask what is the situation in a more regular cluster, like the Coma cluster. Hawley and Peebles (1975) did not find any anisotropy in the distribution of position angles (hereafter PAs); however, they found a possible indication that PAs are preferentially aligned towards the center of the cluster. Thompson (1976) found no significant preference in the PAs distribution for the Coma cluster, but he also found a tendency for PAs to point toward the cluster center. Djorgovski (1983) reported a prominent effect of galaxies alignment with the Coma cluster itself. These three studies are all based on the examination of the distribution of PAs, as pointed out in KO and HWSL, the approach considering both the PA and axial ratio (Flin & Godlowski 1986, hereafter FG) is more appropriate to study this question. In the present paper, we use the same method as HWSL to examine the orientation effect of disk galaxies in the Coma cluster.

The sample and method are described in Sect. 2, the results are presented in Sect. 3, some discussions are made in Sect. 4.

Online publication: June 5, 1998

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