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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!