Transcript SHADES paper VII (b)

eMerlin lenses and starbursts
from the widest-area Herschel
and SCUBA-2 surveys
Stephen Serjeant, July 17th 2007
The SCUBA-2 All-Sky Survey
5 150mJy at 850m over 4000 deg2 (2 years) then the
whole JCMT-accessible sky (5 years)
• Find galaxies in the top 2-3 most luminous in the Hubble volume;
the complete range of submm galaxy properties
• Determine the bright submm number counts
• Determine the gravitational lensing fraction of submm galaxies
• Mapping the peaks in the star formation density field (SCUBA-2
follow-up of SASSy sources)
• Provide high-resolution foregrounds for Planck
• Identify new populations of local cold ultraluminous galaxies
• Provide new submm pointing and flux calibrators
The Herschel Kilo-Degree open
time survey*
• Approximately 1200 hours open time key project
proposal - a SLOAN for Herschel
• 1000 deg2 SPIRE and PACS survey (110-500m):
300 deg2 in SDSS / UKIDSS-LAS NGP
(LOFAR, eMerlin, Hawaii, La Palma)
300 deg2 in KIDS-N
(SKA pathfinders for HI and radio continuum; shallower LOFAR;
visible from Atacama, ESO, La Palma)
400 deg2 in KIDS-S
(SKA pathfinders for HI and radio continuum; SPT/SZ surveys;
ALMA; GAMA; DES over part)
* = obligatory contrived acronyms under discussion
The Herschel Kilo-Degree open
time survey*
• Local galaxies to 104-5 M of dust
• ~150,000 galaxies at z<0.3; half a million galaxies in
total
• Around 1000 strong gravitational lenses; other rare
objects
• Fluctuations in the far-IR background
• High-resolution imaging of Planck HFI galaxies,
radiogalaxies, and S-Z clusters
• Large-scale structure of the submm sky
* = obligatory contrived acronyms under discussion
Strong lensing predictions
 UNLENSED proto-spheroids
(black solid line; Granato et al. 2004)
 IRAS galaxies
(starbursts & spirals galaxies
Silva et al. 2004, 2005)
 radio sources
(blazars; De Zotti et al. 2005)
 STRONGLY LENSED proto-spheroids
(black dashed line;
Negrello et al. 2007)
Mattia Negrello, priv. comm.
Strong lensing predictions
• Counts of unlensed proto-spheroids
– shape of bright (S>100mJy) source counts unknown
• however for the magnifications considered (~10) the sources being
magnified are in the constrained region of the counts
– extrapolation of 850m counts to shorter wavelengths
• uncertainties mainly at 250-350m, but Granato model reproduces
160m counts
• Modelling of strong lensing
– dark matter halo profile
• SIS and NFW have similar integrated magnification distributions  less
than x2 uncertainty in magnification bias
– presence of satellites and structures not considered
• would enhance the lensing probability
Mattia Negrello, priv. comm.
Strong lensing predictions
5 sensitivities
(mJy)
250 m
350 m
500 m
T1000
(hours)
PMode
45
62
53
1168
A = 1000
deg2
250 m
350 m
500 m
Time
(hours)
PMode
2984 (1%)
1570 (4%)
741 (35%)
1168
Mattia Negrello, priv. comm.
Cosmological constraints
Relative probability that zs=3 galaxy is lensed
• Observed lens n(zL) is a
convolution of intrinsic n(z)
and the probability that a
galaxy at z will act as a
lens
• Differences due to
cosmology are much
bigger than differences
due to lens model
uncertainty
• Plot shows normalized
p(zL) but in principle the
absolutes give even
stronger constraints on
cosmology
Simon Dye, priv. comm.
Cosmological constraints
Method:
1. Create 1000 realisations of n(zL) for a given cosmology
(m=0.3, =0.7 in this case)
2. Fit n(zL) for a range of cosmologies
3. Vary the redshifts and repeat 1.
Current limitations:
1. Fitting ignores absolute probabilities (e.g. larger  makes
lensing more likely)  can do better
2. Only fixed source redshifts
3. Selection effects ignored  uncertainties will really be higher
Simon Dye, priv. comm.
Cosmological constraints
560 lenses, zs=6
0
0.5
0.5

0

1
1
560 lenses, zs=3
0
0.5
m
1
0
0.5
1
m
Degeneracy different to CMB; m better constrained than 
Simon Dye, priv. comm.
eMerlin imaging
• Confirmation of lensing: the
most efficient lensing survey
• Multiple image statistics; lens
matter distribution of
0.3<z<1.5 galaxies
• Starburst morphologies
• Identifications of ≤ 250m
drop-outs
Confusing sources for eMerlin 1.4GHz snapshots:
~2 sources at ~10mJy per eMerlin primary beam