THE DARK-MATTER FRACTION IN THE ELLIPTICAL GALAXY LENSING THE QUASAR PG 1115+080

We determine the most likely dark-matter fraction in the elliptical galaxy quadruply lensing the quasar PG 1115+080 based on analyses of the X-ray fluxes of the individual images in 2000 and 2008. Between the two epochs, the A2 image of PG 1115+080 brightened relative to the other images by a factor of 6 in X-rays. We argue that the A2 image had been highly demagnified in 2000 by stellar microlensing in the intervening galaxy and has recently crossed a caustic, thereby creating a new pair of microimages and brightening in the process. Over the same period, the A2 image has brightened by a factor of only 1.2 in the optical. The most likely ratio of smooth material (dark matter) to clumpy material (stars) in the lensing galaxy to explain the observations is ∼90% of the matter in a smooth dark-matter component and ∼10% in stars.

[1]  A. Bolton,et al.  Accepted for publication in The Astrophysical Journal Preprint typeset using L ATEX style emulateapj v. 10/09/06 THE SLOAN LENS ACS SURVEY. VII. ELLIPTICAL GALAXY SCALING LAWS FROM DIRECT OBSERVATIONAL MASS MEASUREMENTS 1 , 2022 .

[2]  T. O. S. University,et al.  X-Ray and Optical Microlensing in the Lensed Quasar PG 1115+080 , 2008, 0802.1210.

[3]  D. Long,et al.  The multiple quasar Q2237+0305 under a microlensing caustic , 2007, 0711.4265.

[4]  Christopher S. Kochanek,et al.  The Spatial Structure of an Accretion Disk , 2007, 0707.0003.

[5]  P. Schechter,et al.  X-Ray and Optical Flux Ratio Anomalies in Quadruply Lensed Quasars. I. Zooming in on Quasar Emission Regions , 2006, astro-ph/0607655.

[6]  P. Schechter,et al.  A Strong X-Ray Flux Ratio Anomaly in the Quadruply Lensed Quasar PG 1115+080 , 2006, astro-ph/0604152.

[7]  T. O. S. University,et al.  Microlensing of the Lensed Quasar SDSS 0924+0219* , 2006, astro-ph/0601523.

[8]  D. Pooley,et al.  X-Ray and Optical Flux Anomalies in the Quadruply Lensed QSO 1RXS J1131–1231 , 2005, astro-ph/0509027.

[9]  Paul L. Schechter,et al.  ACCEPTED IN APJ Preprint typeset using LATEX style emulateapj v. 11/26/03 DIFFERENTIAL MICROLENSING OF THE CONTINUUM AND BROAD EMISSION LINES IN SDSS J0924+0219, THE MOST ANOMALOUS LENSED QUASAR ∗ , 2005 .

[10]  Christopher S. Kochanek,et al.  Strong Gravitational Lensing , 2006 .

[11]  Jaxa,et al.  Subaru Mid-Infrared Imaging of the Quadruple Lenses PG 1115+080 and B1422+231: Limits on Substructure Lensing , 2005, astro-ph/0503487.

[12]  C. Kochanek.  Quantitative Interpretation of Quasar Microlensing Light Curves , 2003, astro-ph/0307422.

[13]  B. Gaudi,et al.  Identifying Lenses with Small-Scale Structure. I. Cusp Lenses , 2002, astro-ph/0210318.

[14]  Institute for Advanced Study,et al.  Tests for Substructure in Gravitational Lenses , 2003, astro-ph/0302036.

[15]  P. Schechter,et al.  Quasar Microlensing at High Magnification and the Role of Dark Matter: Enhanced Fluctuations and Suppressed Saddle Points , 2002, astro-ph/0204425.

[16]  R. Benton Metcalf,et al.  Flux Ratios as a Probe of Dark Substructures in Quadruple-Image Gravitational Lenses , 2001, astro-ph/0111427.

[17]  M. Chiba.  Probing Dark Matter Substructure in Lens Galaxies , 2001, astro-ph/0109499.

[18]  Ucsd,et al.  Direct Detection of Cold Dark Matter Substructure , 2001, astro-ph/0111456.

[19]  P. Madau,et al.  Compound Gravitational Lensing as a Probe of Dark Matter Substructure within Galaxy Halos , 2001, astro-ph/0108224.

[20]  Joachim Wambsganss,et al.  Gravitational lensing: numerical simulations with a hierarchical tree code , 1999 .

[21]  A. Dekel,et al.  Formation of Structure in the Universe , 1999 .

[22]  P. Jetzer.  Gravitational Microlensing , 1999, Naturwissenschaften.

[23]  J. Tonry.  Redshifts of the Gravitational Lenses B1422+231 and PG 1115+080 , 1997, astro-ph/9706199.

[24]  P. Schneider,et al.  Evidence for substructure in lens galaxies , 1997, astro-ph/9707187.

[25]  K. Gebhardt,et al.  The Quadruple Gravitational Lens PG 1115+080: Time Delays and Models , 1996, astro-ph/9611051.

[26]  P. Schechter,et al.  On the universality of microlensing in quadruple gravitational lenses , 1995 .

[27]  R. Brandenberger.  Formation of structure in the universe , 1995, astro-ph/9508159.

[28]  T. Kundić,et al.  Gravitational Microlensing by Random Motion of Stars: Analysis of Light Curves , 1995, astro-ph/9503035.

[29]  D. Schneider,et al.  Imaging of the gravitational lens system PG 1115+080 with the Hubble Space Telescope , 1993 .

[30]  G. Gilmore,et al.  The distribution of low-mass stars in the Galactic disc , 1993 .

[31]  T. Kundić,et al.  Gravitational microlensing - The effect of random motion of individual stars in the lensing galaxy , 1993 .

[32]  J. Wambsganss,et al.  A direct gravitational lensing test for 10 exp 6 solar masses black holes in halos of galaxies , 1992 .

[33]  P. Waddell,et al.  Detection of the Lensing Galaxy in PG 1115+080 , 1987 .

[34]  J. Angel,et al.  The triple QSO PG1115 + 08: another probable gravitational lens , 1980, Nature.

[35]  W. Cash,et al.  Parameter estimation in astronomy through application of the likelihood ratio. [satellite data analysis techniques , 1979 .

[36]  L. Lucy.  An iterative technique for the rectification of observed distributions , 1974 .

[37]  William H. Richardson,et al.  Bayesian-Based Iterative Method of Image Restoration , 1972 .

[38]  Journal of the Optical Society of America , 1950, Nature.