Low-Mass X-Ray Binaries Indicate a Top-Heavy Stellar Initial Mass Function in Ultracompact Dwarf Galaxies

Dabringhausen, J.; Kroupa, Pavel; Pflamm-Altenburg, Jan; Mieske, S.

doi:10.1088/0004-637x/747/1/72

Cited by 106 publications

(152 citation statements)

References 61 publications

Supporting

Mentioning

141

Contrasting

Unclassified

Order By: Relevance

“…Other scenarios include a globally different IMF (Mieske & Kroupa 2008;Dabringhausen et al 2012), or highly concentrated dark matter (Haşegan et al 2005;Goerdt et al 2008;Baumgardt & Mieske 2008).…”

Section: Discussionmentioning

confidence: 99%

“…The elevated dynamical M/L in the regime of UCDs have received significant attention in the literature (Haşegan et al 2005;Dabringhausen et al 2009Dabringhausen et al , 2010Dabringhausen et al , 2012Baumgardt & Mieske 2008;Mieske & Kroupa 2008;Taylor et al 2010;Frank et al 2011;Strader et al 2013). One possible explanation for this rise is a change of the initial stellar mass function (IMF) in these extreme environments.…”

Section: The Elevated Dynamical M/l Of Ucdsmentioning

confidence: 99%

See 1 more Smart Citation

On central black holes in ultra-compact dwarf galaxies

Mieske

Frank

Baumgardt

et al. 2013

A&A

200

View full text Add to dashboard Cite

Context. The dynamical mass-to-light (M/L) ratios of massive ultra-compact dwarf galaxies (UCDs) are about 50% higher than predicted by stellar population models. Aims. Here we investigate the possibility that these apparently elevated M/L ratios of UCDs are caused by a central black hole (BH) that heats up the internal motion of stars. We focus on a sample of ∼50 extragalactic UCDs from the literature for which velocity dispersions and structural parameters have been measured. Methods. To be self-consistent in our BH mass estimates, we first redetermine the dynamical masses and M/L ratios of our sample UCDs, using up-to-date distance moduli and a consistent treatment of aperture and seeing effects. On average, the homogeneously redetermined dynamical mass and M/L ratios agree to within 5% with previous literature results. We calculate the ra-pop between the dynamical and the stellar population M/L for an assumed age of 13 Gyr. Ψ > 1 indicates an elevated dynamical M/L ratio, suggesting dark mass on top of a canonical stellar population of old age. For all UCDs with Ψ > 1 we estimate the mass of a hypothetical central black hole needed to reproduce the observed integrated velocity dispersion Results. Massive UCDs (M > 10 7 M ) have an average Ψ = 1.7 ± 0.2, implying notable amounts of dark mass in them. We find that, on average, central BH masses of 10-15% of the UCD mass can explain these elevated dynamical M/L ratios. The implied BH masses in UCDs range from several 10 5 M to several 10 7 M . In the M BH -luminosity plane, UCDs are offset by about two orders of magnitude in luminosity from the relation derived for galaxies. Our findings can be interpreted such that massive UCDs originate from progenitor galaxies with masses around ∼10 9 M , and that those progenitors have SMBH occupation fractions of ∼60-100%. The suggested UCD progenitor masses agree with predictions from the tidal stripping scenario. Also, the typical BH mass fractions of nuclear clusters in such ∼10 9 M galaxy bulges agree with the 10-15% BH fraction estimated for UCDs. Lower-mass UCDs (M < 10 7 M ) exhibit a bimodal distribution in Ψ, suggestive of a coexistence of massive globular clusters and tidally stripped galaxies in this mass regime. Conclusions. Central BHs as relict tracers of tidally stripped progenitor galaxies are a plausible explanation for the elevated dynamical M/L ratios of UCDs. Direct observational tests of this scenario are suggested.

show abstract

Section: Discussionmentioning

confidence: 99%

Section: The Elevated Dynamical M/l Of Ucdsmentioning

confidence: 99%

On central black holes in ultra-compact dwarf galaxies

Mieske

Frank

Baumgardt

et al. 2013

A&A

200

View full text Add to dashboard Cite

show abstract

“…A comparison of the X-ray binary count studies of Dabringhausen et al (2012) and Peacock et al (2014) suggests a top-heavy IMF for ultracompact dwarf galaxies. Several spectral studies point at an enhanced fraction of lowmass stars in ETGs with respect to a standard Kroupa IMF.…”

Section: Introductionmentioning

confidence: 95%

Implications of a variable IMF for the interpretation of observations of galaxy populations

Clauwens

Schaye

Franx

2016

Mon. Not. R. Astron. Soc.

View full text Add to dashboard Cite

We investigate the effect of a metallicity-dependent stellar initial mass function (IMF), as deduced observationally by Martín-Navarro et al. (2015c), on the inferred stellar masses and star formation rates (SFRs) of a representative sample of 186,886 SDSS galaxies. Relative to a Chabrier IMF, for which we show the implied masses to be close to minimal, the inferred masses increase in both the low-and high-metallicity regimes due to the addition of stellar remnants and dwarf stars, respectively. The resulting galaxy stellar mass function (GSMF) shifts toward higher masses by 0.5 dex, without affecting the high-mass slope (and thus the need for effective quenching). The implied low-redshift SFR density increases by an order of magnitude. However, these results depend strongly on the assumed IMF parametrisation, which is not directly constrained by the observations. Varying the low-end IMF slope instead of the highend IMF slope, while maintaining the same dwarf-to-giant ratio, results in a much more modest GSMF shift of 0.2 dex and a 10 per cent increase in the SFR density relative to the Chabrier IMF. A bottom-heavy IMF during the late, metal-rich evolutionary stage of a galaxy would help explain the rapid quenching and the bimodality in the galaxy population by on the one hand making galaxies less quenched (due to the continued formation of dwarf stars) and on the other hand reducing the gas consumption timescale. We conclude that the implications of the observational evidence for a variable IMF could vary from absolutely dramatic to mild but significant.

show abstract

“…The M V values are taken from Dunlop et al (1993) and Dunlop et al (2003). ; Dabringhausen et al (2009);Dabringhausen et al (2012)). …”

Section: Statistical Importancementioning

confidence: 99%

The formation of ultra compact dwarf galaxies and massive globular clusters

Jeřabková

Kroupa

Dabringhausen

et al. 2017

A&A

View full text Add to dashboard Cite

The stellar initial mass function (IMF) has been described as being invariant, bottom-heavy, or top-heavy in extremely dense starburst conditions. To provide usable observable diagnostics, we calculate redshift dependent spectral energy distributions of stellar populations in extreme star-burst clusters, which are likely to have been the precursors of present day massive globular clusters (GCs) and of ultra compact dwarf galaxies (UCDs). The retention fraction of stellar remnants is taken into account to assess the mass to light ratios of the ageing star-burst. Their redshift dependent photometric properties are calculated as predictions for James Webb Space Telescope (JWST) observations. While the present day GCs and UCDs are largely degenerate concerning bottom-heavy or top-heavy IMFs, a metallicity-and density-dependent top-heavy IMF implies the most massive UCDs, at ages <100 Myr, to appear as objects with quasar-like luminosities with a 0.1-10% variability on a monthly timescale due to core collapse supernovae.

show abstract

Low-Mass X-Ray Binaries Indicate a Top-Heavy Stellar Initial Mass Function in Ultracompact Dwarf Galaxies

Cited by 106 publications

References 61 publications

On central black holes in ultra-compact dwarf galaxies

On central black holes in ultra-compact dwarf galaxies

Implications of a variable IMF for the interpretation of observations of galaxy populations

The formation of ultra compact dwarf galaxies and massive globular clusters

Contact Info

Product

Resources

About