MMT (and Magellan) Spectroscopic Survey of the Environments of Strong Gravitational Lenses Ivelina Momcheva In collaboration with: Ann Zabludoff Kurtis Williams Chuck Keeton

What are strong gravitational lenses? ● Time delays and H 0 ● Lens statistics and   ● Masses and shapes of DM halos ● Substructure and the nature of DM ● Properties of quasars and quasar host galaxies S L O  z ~ 1-5 z ~ I1I1 I2I2 ''... I made some calculations which show that extragalactic nebulae offer a much better chance than stars for the observation of gravitational lens effects.'' F. Zwicky, 1937, in ''Nebulae as Gravitational Lenses''

Motivation What are the environments in which lens galaxies reside? Lenses are not isolated – at least 25% in dense environments Massive line-of-sight structures also contribute to the potential Both create biases and uncertainties S L O  z ~ 1-5 z ~ I1I1 I2I2

Motivation S L O Lensing is sensitive to all mass! z ~ 1-5 Lens, z ~ I1I1 I2I2 What are the environments in which lens galaxies reside? Lenses are not isolated – at least 25% in dense environments Massive line-of-sight structures also contribute to the potential Both create biases and uncertainties

Motivation What are the environments in which lens galaxies reside? Lenses are not isolated – at least 25% in dense environments Massive line-of-sight structures also contribute to the potential Both create biases and uncertainties What are the properties of intermediate redshift groups? Most common environments for galaxies Difficult to find above z~0.1

Survey 92 lenses in CASTLES (Kochanek, Falco, Impey, Lehar, McLeod, Rix) Deep two-band MOSAIC imaging at KPNO and CTIO of 74 lenses. Obtained photometry (Willams et al. 2006). Selected spectroscopy targets based on a color-projected distance priority scheme. Multi-object spectroscopy at Magellan (LDSS2,LDSS3, IMACS) and MMT (Hectospec) of 28 lenses. Goal: ~90% complete at the magnitude limit I=20.5 for lenses at z < 0.5

Sample ● Doubles ● Quads ● Others FBQ0951 z=0.24 BRI0952 z=0.41 SBS1520 z=0.72 B1600 z=0.41 HE2149 z=0.5 B1152 z=0.44 B0712 z=0.41 PG1115 z=0.31 H1413 z=0.? B1422 z=0.34 B1608 z=0.63 HST14113 z=0.46 B0751 z=0.35 2R MG1131 z=0.8 2R MG1654 z=0.25 R PMN2004 z=? 2R B2114 z= MG1549 z=0.11 R 8 southern lenses, z~ northern lenses, z~

Sample ● Doubles ● Quads ● Others FBQ0951 z=0.24 BRI0952 z=0.41 SBS1520 z=0.72 B1600 z=0.41 HE2149 z=0.5 B1152 z=0.44 B0712 z=0.41 PG1115 z=0.31 H1413 z=0.? B1422 z=0.34 B1608 z=0.63 HST14113 z=0.46 B0751 z=0.35 2R MG1131 z=0.8 2R MG1654 z=0.25 R PMN2004 z=? 2R B2114 z= MG1549 z=0.11 R 12 of the 18 lenses (67%) either lie in a dense environment or have a significant line-of- sight structure Wide range of environment properties All quads are problematic

Lens Environments - PG1115 ● Quad, time delay, zl=0.31 ● Group at lens, 13 members, 440 km/s ● Group contributes ~10% bias ● Background group has ~1% effect

Lens Environments - PG1115 ● Quad, time delay, zl=0.31 ● Group at lens, 13 members, 440 km/s ● Group contributes ~10% bias ● Background group has ~1% effect

Lens Environments – HST14113 ● Quad, zl=0.46, known cluster ● Cluster at lens, ~100 members, >1000 km/s ● Cluster is a major mass component

Lens Environments – HST14113 ● Quad, zl=0.46, known cluster ● Cluster at lens, ~100 members, >1000 km/s ● Cluster is a major mass component

Lens Environments – FBQ0951 ● Double, zl~0.24 ● No group “at” lens ● 3 line-of-sight structures with major effect

Lens Environments – FBQ0951 ● Double, zl~0.24 ● No group “at” lens ● 3 line-of-sight structures with major effect

Summary ● ~50% of strong lenses lie in dense environments, ~10% have a significant line-of-sight structure ● Quads have problems more often ● Groups can be significantly offset from the lens, the lens is not always the brightest galaxy ● A sample of groups with a wide range of properties, selected independent of mass ● “A Spectroscopic Study of the Environments of Gravitational Lens Galaxies “, Momcheva et al., astro-ph/ , in press ● “First Results from a Photometric Survey of Strong Gravitational Lens Environments”, Williams et al., astro-ph/ , in press

Thanks! ● Thanks to the MMT staff. ● Thanks to Dan Fabricant, Nelson Caldwell and the rest of the Hectospec team. ● Thanks to the TAC for awarding us the observing time. ● Thanks to Richard Cool for his reduction pipeline. ● Thank you!