Properties and environment of the molecular complex near Holmberg IX

Abstract

Abstract. This paper is aimed at providing new insight into the nature and origin of the molecular complex situated near the line of sight toward Holmberg IX in the M 81 group of galaxies. The first high resolution CO maps of the complex as well as single dish 13 CO(1-0), 12 CO(3-2) and millimeter continuum observations and the results of a survey of 12 CO in the region are presented. These data together with the available HI, optical and X-ray observations are analyzed to study the properties and environment of the complex. We confirm there is no unobscured massive star formation inside the complex, and from the millimeter constraint on the extinction it must have a low star formation rate or be forming only low mass stars. According to the CO line ratios the abundances and physical conditions could be similar to that of cold gas in spirals. We find from its dynamics (no rotation) and its mass (2-6 million solar masses) that it resembles a massive GMC. Also, re-inspecting N-body simulations of the M 81 group and the H  data we find that it might be located inside the extreme outer disk of M 81 and be cospatial with the H  feature known as Concentration . The negative result of the CO survey suggests that the complex is unique in this region and calls for a peculiar local formation process. We find that the distribution of the CO emission in the data cube is asymmetrical in a way similar to a cometary object. The optical observations of the nearby supershell MH9/10 suggest the existence of an outflow toward the complex. We consider the possibility that the molecular complex is related to this hypothetical outflow.

A panoramic view of M81: new stellar systems in the debris field

“…This suggests that these stellar systems have been assembled from pre-enriched material. This is consistent with the conclusions of Boone et al (2005) towards Holmberg IX are similar to those found in the discs of spiral galaxies. The distribution of the stellar clumps along an H I tail, tracing the densest clouds within the gaseous arm, indicates that these systems may have been assembled out of gas pulled from one of the large interacting galaxies in the group.…”

Optical observations of M81 galaxy group in narrow band [SII] and Hα filters: Holmberg IX

“…4; additional dark features are stars not subtracted well). Eleven sources (1-11) were previously identified by Miller & Hodge (1994) and one by Boone et al (2005) (source 12). 2 Thus, we found nine new sources (13-21).…”

“…Nevertheless, we identified 21 objects with significant Hα emission. Eleven sources (1-11) were previously identified by Miller and Hodge (1994) and one by Boone et al (2005) (source 12). Thus, we found nine new sources (13-21) -not catalogued HII regions.…”