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 H0

● 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 ~ 0.1-0.8

I1

I2

''... 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 ~ 0.1-0.8

I1

I2

Motivation

S

L O

Lensing is sensitive to all mass!z ~ 1-5

Lens, z ~ 0.1-0.8

I1

I2

•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

FBQ0951z=0.24

BRI0952z=0.41

SBS1520z=0.72

B1600z=0.41

HE2149z=0.5

B1152z=0.44

B0712z=0.41

PG1115z=0.31

H1413z=0.?

B1422z=0.34

B1608z=0.63

HST14113z=0.46

B0751z=0.35

2R

MG1131z=0.8

2R

MG1654z=0.25

R

PMN2004z=?2R

B2114z=0.34

2+2

MG1549z=0.11

R

•8 southern lenses, z~0.25-0.5

•10 northern lenses, z~0.1-0.8

Sample

● Doubles

● Quads

● Others

FBQ0951z=0.24

BRI0952z=0.41

SBS1520z=0.72

B1600z=0.41

HE2149z=0.5

B1152z=0.44

B0712z=0.41

PG1115z=0.31

H1413z=0.?

B1422z=0.34

B1608z=0.63

HST14113z=0.46

B0751z=0.35

2R

MG1131z=0.8

2R

MG1654z=0.25

R

PMN2004z=?2R

B2114z=0.34

2+2

MG1549z=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/0511594, in press

● “First Results from a Photometric Survey of Strong Gravitational Lens Environments”, Williams et al.,

astro-ph/0511593, 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!