Properties of moderate luminosity mergers

Manthey, E.; Hüttemeister, Susanne; Haberzettl, Luz

doi:10.22323/1.014.0040

Cited by 2 publications

(5 citation statements)

References 3 publications

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“…Using optical spectra, Bergvall (1981) found indications of a period of enhanced star formation in the past, since the stellar population is younger than that of a normal elliptical galaxy. Our own optical spectra confirm this and we estimate that a moderate starburst occurred ∼1 Gyr ago (Manthey et al 2005).…”

Section: Introductionsupporting

confidence: 88%

“…In NGC 4441, the total H i mass is 1.5 × 10 9 L (Manthey et al 2008a). The ongoing star formation rate is rather low (1−2 M yr −1 ), because the merger is in such an advanced phase that most of the gas has been already used for star formation (Manthey et al 2005(Manthey et al , 2008a. Using optical spectra, Bergvall (1981) found indications of a period of enhanced star formation in the past, since the stellar population is younger than that of a normal elliptical galaxy.…”

Section: Introductionmentioning

confidence: 99%

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The molecular gas content of the advanced S+E merger NGC 4441

Juette

Aalto

Huettemeister³

2010

A&A

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Context. Despite their importance to galaxy evolution, mergers between a spiral and an elliptical (S+E mergers) have been poorly studied so far. NGC 4441 is a nearby candidate of an advanced remnant of such a merger, showing typical tidal structures such as an optical tail and two shells as well as two H i tails.Aims. Studying the molecular gas content provides clues about the impact of a recent merger event on the star formation. Simulations of S+E mergers yield conflicting predictions about both the strength and the extent of an induced starburst. Thus, observations of the amount and the distribution of the molecular gas, the raw material of star formation, are needed to understand the influence of the merger on the star formation history. Methods. 12 CO and 13 CO (1−0) and (2−1) observations were obtained using the Onsala Space Observatory 20 m and IRAM 30 m telescope as well as the Plateau de Bure interferometer. These data allow us to carry out a basic analysis of the molecular gas properties, such as estimates of the molecular gas mass, temperature, and density and the star formation efficiency. Results. The CO observations detect an extended molecular gas reservoir out to ∼4 kpc, with a total molecular gas mass of ∼5 × 10 8 M . Furthermore, high resolution imaging shows a central molecular gas feature, which is probably a rotating disc hosting most of the molecular gas (∼4 × 10 8 M ). This nuclear disc has a different sense of rotation to the large-scale H i structure, indicating a kinematically decoupled core. We modeled the state of the interstellar medium with the radiative transfer code RADEX, using the ratios of the 12 CO to 13 CO line strenghts. The results are consistent with a diffuse (n ≤ 10 3 cm −3 ) molecular medium with no significant indications of cold, dense cores of ongoing star formation. This is in agreement with the moderate star formation rate of 1−2 M yr −1 measured for NGC 4441. Assuming a constant star formation rate, the gas depletion time is τ = 4.8 × 10 8 yr. NGC 4441 might be a nearby candidate early-type galaxy with a dominant A-star population, a so-called E+A galaxy, which is in a post-starburst phase several 10 8 yr after a merger event.

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Section: Introductionsupporting

confidence: 88%

Section: Introductionmentioning

confidence: 99%

The molecular gas content of the advanced S+E merger NGC 4441

Juette

Aalto

Huettemeister³

2010

A&A

View full text Add to dashboard Cite

show abstract

“…However, there must have been a period of enhanced star formation, since the stellar population is younger than that of a normal elliptical galaxy (Bergvall 1981). Our own optical spectra confirm this and we estimate that a moderate starburst occured ∼1 Gyr ago (Manthey et al 2005). …”

Section: Introductionsupporting

confidence: 87%

“…By looking at the FIR luminosity, the 20 cm continuum emission and the optical spectra (Manthey et al 2005), however we do not find any indication for a strong starburst, neither ongoing nor in the recent history, in NGC 4441. Therefore, less gas is probably involved in this merger event, which is naturally the case when one progenitor is an elliptical.…”

Section: Spiral+elliptical Merger?contrasting

confidence: 56%

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The H I content of the advanced merger NGC 4441

Manthey

Aalto

Hüttemeister

et al. 2008

A&A

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Context. NGC 4441 is a candidate for a merger between a spiral and an elliptical galaxy (S+E merger), because it shows typical tidal structures such as an optical tail and two shells. With a far-infrared luminosity of ∼5 × 10 9 L this galaxy belongs to the class of moderate luminosity mergers, in which the merging process induces (if at all) only a moderate starburst. Aims. The study of the atomic gas content allows us to investigate the merger history and the impact on the star formation. In particular, it is not clear from simulations whether an S+E merger leads to a gas concentration in the nucleus, resulting in a starburst, or whether the gas is spread out and therefore too diffuse for new star forming regions.Methods. We used the Westerbork Radio Synthesis Telescope to observe the properties of the H i. By using this interferometer, we are able to study the large-scale H i distribution and kinematics with high spatial and velocity resolution. Results. We found two H i tails extending out to more than 40 kpc. In a central disc, the gas shows a fairly regular rotation pattern indicating that the gas started to settle after the merger. The total H i mass adds up to 1.5 × 10 9 M . By comparing the high resolution H i maps with deep optical images, differences between the stellar and gaseous tidal features are apparent, which indicates an S+E merger origin.

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Properties of moderate luminosity mergers

Cited by 2 publications

References 3 publications

The molecular gas content of the advanced S+E merger NGC 4441

The molecular gas content of the advanced S+E merger NGC 4441

The H I content of the advanced merger NGC 4441

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