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## Detection of a dark substructure through gravitational imaging

Vegetti, S., Koopmans, L. V. E., Bolton, A., Treu, T. & Gavazzi, R., 11-Nov-2010, In : Monthly Notices of the Royal Astronomical Society. 408, 4, p. 1969-1981 13 p.Research output: Contribution to journal › Article › Academic › peer-review

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*Monthly Notices of the Royal Astronomical Society*,

*408*(4), 1969-1981. https://doi.org/10.1111/j.1365-2966.2010.16865.x

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*Monthly Notices of the Royal Astronomical Society*, vol. 408, no. 4, pp. 1969-1981. https://doi.org/10.1111/j.1365-2966.2010.16865.x

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**Detection of a dark substructure through gravitational imaging.** / Vegetti, S.; Koopmans, L. V. E.; Bolton, A.; Treu, T.; Gavazzi, R.

Research output: Contribution to journal › Article › Academic › peer-review

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TY - JOUR

T1 - Detection of a dark substructure through gravitational imaging

AU - Vegetti, S.

AU - Koopmans, L. V. E.

AU - Bolton, A.

AU - Treu, T.

AU - Gavazzi, R.

PY - 2010/11/11

Y1 - 2010/11/11

N2 - We report the detection of a dark substructure - undetected in the Hubble Space Telescope HST ACS F814W image -in the gravitational lens galaxy SDSSJ0946+1006 (the 'double Einstein ring'), through direct gravitational imaging. The detection of a small mass concentration in the surface density maps, at 4.3 kpc from the galaxy centre, has a strong statistical significance. We confirm this detection by modelling the substructure with a tidally truncated pseudo-Jaffe density profile; in that case the substructure mass is M(sub) = (3.51 +/- 0.15) x 10(9) M(circle dot), precisely where also the surface density map shows a strong convergence peak (Bayes factor Delta log epsilon = -128.0; equivalent to a similar to 16 sigma detection). The result is robust under substantial changes in the model. We set a lower limit of (M/L)(V,circle dot) greater than or similar to 120 M(circle dot)/L(V,circle dot) (3 sigma) inside a sphere of 0.3 kpc centred on the substructure (r(tidal) = 1.1 kpc). The mass and luminosity limit of this substructure are consistent with Local Group results if the substructure had a virial mass of similar to 10(10) M(circle dot) before accretion and formed at z greater than or similar to 10. Our detection implies a projected dark matter mass fraction in substructure at the radius of the inner Einstein ring of f = 2.15(-1.25)(+2.05) per cent [68 per cent confidence level (CL)] in the mass range 4 x 10(6)-4 x 10(9) M(circle dot), assuming alpha = 1.9 +/- 0.1 (with dN/dm alpha m(-alpha)). Assuming a flat prior on alpha, between 1.0 and 3.0, increases this to f = 2.56(-1.50)(+3.26) per cent (68 per cent CL). The likelihood ratio is similar to 0.5 between these fractions and that from simulations (f(N-body) approximate to 0.003). Hence the inferred dark matter mass fraction in substructure, admittedly based on a single-lens system, is large but still consistent with predictions.

AB - We report the detection of a dark substructure - undetected in the Hubble Space Telescope HST ACS F814W image -in the gravitational lens galaxy SDSSJ0946+1006 (the 'double Einstein ring'), through direct gravitational imaging. The detection of a small mass concentration in the surface density maps, at 4.3 kpc from the galaxy centre, has a strong statistical significance. We confirm this detection by modelling the substructure with a tidally truncated pseudo-Jaffe density profile; in that case the substructure mass is M(sub) = (3.51 +/- 0.15) x 10(9) M(circle dot), precisely where also the surface density map shows a strong convergence peak (Bayes factor Delta log epsilon = -128.0; equivalent to a similar to 16 sigma detection). The result is robust under substantial changes in the model. We set a lower limit of (M/L)(V,circle dot) greater than or similar to 120 M(circle dot)/L(V,circle dot) (3 sigma) inside a sphere of 0.3 kpc centred on the substructure (r(tidal) = 1.1 kpc). The mass and luminosity limit of this substructure are consistent with Local Group results if the substructure had a virial mass of similar to 10(10) M(circle dot) before accretion and formed at z greater than or similar to 10. Our detection implies a projected dark matter mass fraction in substructure at the radius of the inner Einstein ring of f = 2.15(-1.25)(+2.05) per cent [68 per cent confidence level (CL)] in the mass range 4 x 10(6)-4 x 10(9) M(circle dot), assuming alpha = 1.9 +/- 0.1 (with dN/dm alpha m(-alpha)). Assuming a flat prior on alpha, between 1.0 and 3.0, increases this to f = 2.56(-1.50)(+3.26) per cent (68 per cent CL). The likelihood ratio is similar to 0.5 between these fractions and that from simulations (f(N-body) approximate to 0.003). Hence the inferred dark matter mass fraction in substructure, admittedly based on a single-lens system, is large but still consistent with predictions.

KW - gravitational lensing: strong

KW - galaxies: structure

KW - EARLY-TYPE GALAXIES

KW - LENS ACS SURVEY

KW - SMALL-SCALE STRUCTURE

KW - MATTER SUBSTRUCTURE

KW - ELLIPTIC GALAXIES

KW - MASS SUBSTRUCTURE

KW - MILKY-WAY

KW - IDENTIFYING LENSES

KW - COSMOLOGICAL MODEL

KW - EVOLUTION

U2 - 10.1111/j.1365-2966.2010.16865.x

DO - 10.1111/j.1365-2966.2010.16865.x

M3 - Article

VL - 408

SP - 1969

EP - 1981

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 4

ER -

ID: 5198270