MICROLENSING-BASED ESTIMATE OF THE MASS FRACTION IN COMPACT OBJECTS IN LENS GALAXIES
- Instituto de Astrofisica de Canarias, VIa Lactea S/N, 38200-La Laguna, Tenerife (Spain)
- Departamento de AstronomIa y Astrofisica, Universidad de Valencia, 46100-Burjassot, Valencia (Spain)
- Smithsonian Astrophysical Observatory, FLWO, P.O. Box, 97, Amado, AZ 85645 (United States)
- Departamento de fisica y Astronomia, Facultad de Ciencias, Universidad de Valparaiso, Avda. Gran Bretana 1111, Valparaiso (Chile)
- Departamento de Astrofisica, Universidad de La Laguna, E-38205 La Laguna, Tenerife (Spain)
We estimate the fraction of mass that is composed of compact objects in gravitational lens galaxies. This study is based on microlensing measurements (obtained from the literature) of a sample of 29 quasar image pairs seen through 20 lens galaxies. We determine the baseline for no microlensing magnification between two images from the ratios of emission line fluxes. Relative to this baseline, the ratio between the continua of the two images gives the difference in microlensing magnification. The histogram of observed microlensing events peaks close to no magnification and is concentrated below 0.6 mag, although two events of high magnification, DELTAm approx 1.5, are also present. We study the likelihood of the microlensing measurements using frequency distributions obtained from simulated microlensing magnification maps for different values of the fraction of mass in compact objects, alpha. The concentration of microlensing measurements close to DELTAm approx 0 can be explained only by simulations corresponding to very low values of alpha (10% or less). A maximum likelihood test yields alpha = 0.05{sup +0.09}{sub -0.03} (90% confidence interval) for a quasar continuum source of intrinsic size r{sub s{sub 0}}approx2.6x10{sup 15} cm. This estimate is valid in the 0.1-10 M {sub sun} range of microlens masses. We study the dependence of the estimate of alpha with r{sub s{sub 0}}, and find that alpha approx< 0.1 for r{sub s{sub 0}}approx<1.3x10{sup 16} cm. High values of alpha are possible only for source sizes much larger than commonly expected (r{sub s{sub 0}}>>2.6x10{sup 16} cm). Regarding the current controversy about Milky Way/LMC and M31 microlensing studies, our work supports the hypothesis of a very low content in MACHOS (Massive Compact Halo Objects). In fact, according to our study, quasar microlensing probably arises from the normal star populations of lens galaxies and there is no statistical evidence for MACHOS in the dark halos.
- OSTI ID:
- 21378096
- Journal Information:
- Astrophysical Journal, Vol. 706, Issue 2; Other Information: DOI: 10.1088/0004-637X/706/2/1451; ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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