J/ApJ/845/157 IMF in 3 low-redshift strong lenses from SNELLS (Newman+, 2017)
The initial mass function in the nearest strong lenses from SNELLS: assessing
the consistency of lensing, dynamical, and spectroscopic constraints.
Newman A.B., Smith R.J., Conroy C., Villaume A., van Dokkum P.
<Astrophys. J., 845, 157 (2017)>
=2017ApJ...845..157N 2017ApJ...845..157N
ADC_Keywords: Gravitational lensing ; Galaxies, optical ; Spectra, infrared ;
Stars, masses ; Redshifts
Keywords: galaxies: elliptical and lenticular, cD; galaxies: stellar content;
gravitational lensing: strong
Abstract:
We present new observations of the three nearest early-type galaxy
(ETG) strong lenses discovered in the SINFONI Nearby Elliptical Lens
Locator Survey (SNELLS). Based on their lensing masses, these ETGs
were inferred to have a stellar initial mass function (IMF) consistent
with that of the Milky Way, not the bottom-heavy IMF that has been
reported as typical for high-σ ETGs based on lensing, dynamical,
and stellar population synthesis techniques. We use these unique
systems to test the consistency of IMF estimates derived from
different methods. We first estimate the stellar M*/L using lensing
and stellar dynamics. We then fit high-quality optical spectra of the
lenses using an updated version of the stellar population synthesis
models developed by Conroy & van Dokkum. When examined individually,
we find good agreement among these methods for one galaxy. The other
two galaxies show 2-3σ tension with lensing estimates, depending
on the dark matter contribution, when considering IMFs that extend to
0.08M☉. Allowing a variable low-mass cutoff or a nonparametric
form of the IMF reduces the tension among the IMF estimates to
<2σ. There is moderate evidence for a reduced number of low-mass
stars in the SNELLS spectra, but no such evidence in a composite
spectrum of matched-σ ETGs drawn from the SDSS. Such variation
in the form of the IMF at low stellar masses (m≲0.3M☉), if
present, could reconcile lensing/dynamical and spectroscopic IMF
estimates for the SNELLS lenses and account for their lighter M*/L
relative to the mean matched-σ ETG. We provide the spectra used
in this study to facilitate future comparisons.
Description:
The SINFONI Nearby Elliptical Lens Locator Survey (SNELLS) lenses
(Smith+ 2015MNRAS.449.3441S 2015MNRAS.449.3441S) were observed using the IMACS
spectrograph at the 6.5m Magellan Baade telescope during 2015 April
9-10 and 2015 September 25. Spectroscopic observations cover the
wavelength range 3565-9415Å continuously with a uniform resolution
of 2.8Å. Total exposure times ranged from 60 minutes to 100 minutes
per grating. See section 2.1.
All SNELLS lenses were also observed using FIRE, a near-infrared
echellete spectrograph at the Magellan Baade telescope, during the
nights of 2015 April 8, May 3, and September 25. The FIRE spectra
cover 0.82-2.51um, but in this paper we use only the region around the
Wing-Ford band of FeH near 9916Å for SNL-0 and SNL-1. On-target
exposure times for SNL-0 and SNL-1 were 32 minutes and 54 minutes,
respectively. The 1" wide slit provided a resolution of R∼4000.
See section 2.2.
We acquired optical and near-infrared spectra for all the SNELLS
lenses with X-shooter at the 8.2m UT2 of the ESO Very Large Telescope
(VLT). See section 2.3.
We obtained r-band images of SNL-1 and SNL-2 using the LDSS-3 imaging
spectrograph at the Magellan 2 telescope. Photometric calibration was
tied to the SDSS DR9. For SNL-0, we used Hubble Heritage observations
taken with the Advanced Camera for Surveys and the F625W filter
(Proposal 10710). When constructing our dynamical model of SNL-2, we
also use an R-band image obtained in excellent seeing with FORS2 at
the VLT. See section 2.4.
File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 254 3 *Measured quantities for SNELLS lenses
table2.dat 40 8117 Spectra of SNELLS lenses used in SPS analysis
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Note on table1.dat: Proceeding from the total M/L to the stellar M*/L requires
an estimate of the dark matter contribution within θEin. This cannot
be estimated from the lensing constraints alone. One route is to appeal to
simulations of galaxy formation. Here we follow S15
(Smith+, 2015MNRAS.449.3441S 2015MNRAS.449.3441S), who used the EAGLE simulations
(Schaller+ 2015MNRAS.451.1247S 2015MNRAS.451.1247S ; Schaye+ 2015MNRAS.446..521S 2015MNRAS.446..521S) to estimate
dark matter contributions that range from 16% and 25% of MEin. Table 1
lists the stellar (M*/Lr)L+EAGLE derived from lensing and the EAGLE
simulations.
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See also:
V/139 : The SDSS Photometric Catalog, Release 9 (Adelman-McCarthy+, 2012)
J/MNRAS/276/1341 : Spectroscopy of E and S0 galaxies (Jorgensen+, 1995)
J/MNRAS/313/469 : Streaming motions of galaxy clusters. I. (Smith+, 2000)
J/MNRAS/371/703 : MILES library of empirical spectra (Sanchez-Blazquez+, 2006)
J/ApJ/682/964 : Sloan lens ACS survey. V. (Bolton+, 2008)
J/ApJ/705/1099 : The Sloan Lens ACS (SLACS) Survey. IX. (Auger+, 2009)
J/ApJ/690/670 : The Sloan lens ACS Survey. VIII. (Treu+, 2009)
J/MNRAS/443/1231 : 6dF Galaxy Survey: Fundamental Plane data (Campbell+, 2014)
J/A+A/568/A9 : 300-2500nm flux calibration ref. spectra (Moehler+, 2014)
J/A+A/582/A97 : SSP in NIR. II. Synthesis models (Meneses-Goytia+, 2015)
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Name Lens system identifier
(<[SLC2015] SNL-N> in Simbad)
7- 11 F5.3 --- z [0.03/0.06] Redshift
13- 15 F3.1 arcsec Re Effective radius in J-band
17- 20 F4.2 arcsec theta [2.2/2.9] Einstein radius θEin
22- 25 F4.2 10+10Lsun Lr [1.6/3] Luminosity within θEin in
the SDSS r-band Lr,Ein (1)
27- 30 F4.2 10+10Lsun e_Lr [0.05/0.07] Lr uncertainty
32- 34 I3 km/s sig [274/335] Velocity dispersion σraw
measured in 4"x1.8" X-shooter IFU aperture
36- 37 I2 km/s e_sig sig uncertainty
39- 41 I3 km/s Sige [263/312] Aperture velocity dispersion
σe/2; see section 4.4
43- 44 I2 km/s e_Sige Sige uncertainty
46- 49 F4.2 Msun/Lsun (M/Lr)L [4.7/5.5] Total MEin/Lr,Ein (2)
51- 54 F4.2 Msun/Lsun e_(M/Lr)L (M/Lr)L uncertainty
56- 59 F4.2 Msun/Lsun (M/Lr)D ? Total projected M/L within θEin
from stellar dynamical modeling only
61- 64 F4.2 Msun/Lsun e_(M/Lr)D ? (M/Lr)D uncertainty
66- 69 F4.2 Msun/Lsun (M/Lr)L+E [3.5/4.7] Stellar M*/L based on dark
matter fractions from EAGLE
71- 74 F4.2 Msun/Lsun e_(M/Lr)L+E (M/Lr)L+E uncertainty
76- 79 F4.2 Msun/Lsun (M/Lr)L+D ? Stellar M*/L from joint lensing and
dynamics model
81- 84 F4.2 Msun/Lsun e_(M/Lr)L+D ? (M/Lr)L+D uncertainty
86- 89 F4.2 Msun/Lsun (M/Lr)MW [3.6/4.1] Spectroscopic M*/L from Kroupa
IMF
91- 94 F4.2 Msun/Lsun e_(M/Lr)MW (M/Lr)MW uncertainty
96- 99 F4.2 Msun/Lsun (M/Lr)1PL Spectroscopic M*/L from single power-law
IMF at m<1M☉
101-104 F4.2 Msun/Lsun e_(M/Lr)1PL (M/Lr)1PL negative uncertainty
106-109 F4.2 Msun/Lsun E_(M/Lr)1PL (M/Lr)1PL positive uncertainty
111-114 F4.2 Msun/Lsun (M/Lr)2PL Spectroscopic M*/L from double power-law
IMF at m<1M☉
116-119 F4.2 Msun/Lsun e_(M/Lr)2PL (M/Lr)2PL negative uncertainty
121-124 F4.2 Msun/Lsun E_(M/Lr)2PL (M/Lr)2PL positive uncertainty
126-129 F4.2 Msun/Lsun (M/Lr)2PLc Spectroscopic M*/L from double power-law
with low-mass cutoff
131-134 F4.2 Msun/Lsun e_(M/Lr)2PLc (M/Lr)2PLc negative uncertainty
136-139 F4.2 Msun/Lsun E_(M/Lr)2PLc (M/Lr)2PLc positive uncertainty
141-144 F4.2 Msun/Lsun (M/Lr)np [3.8/6.3] Spectroscopic M*/L,
nonparametric IMF
146-149 F4.2 Msun/Lsun e_(M/Lr)np (M/Lr)np negative uncertainty
151-154 F4.2 Msun/Lsun E_(M/Lr)np (M/Lr)np positive uncertainty
156-159 F4.2 Msun/Lsun aL+E [0.9/1.2] Mass factor α using the
lensing mass and EAGLE dark matter
contribution (3)
161-164 F4.2 Msun/Lsun e_aL+E aL+E uncertainty
166-169 F4.2 Msun/Lsun aL+D ? Mass factor α from joint lensing
and dynamical modeling (3)
171-174 F4.2 Msun/Lsun e_aL+D ? aL+D uncertainty
176-179 F4.2 Msun/Lsun aL+noD Total lensing mass; assumes no dark
matter αL+noDM (3)
181-184 F4.2 Msun/Lsun e_aL+noD aL+noD uncertainty
186-189 F4.2 Msun/Lsun aD+noD ? Total dynamical mass; assumes no dark
matter αD+noDM (3)
191-194 F4.2 Msun/Lsun e_aD+noD ? aD+noD uncertainty
196-199 F4.2 Msun/Lsun a1PL single power-law IMF at m<1M☉ (3)
201-204 F4.2 Msun/Lsun e_a1PL a1PL negative uncertainty
206-209 F4.2 Msun/Lsun E_a1PL a1PL positive uncertainty
211-214 F4.2 Msun/Lsun a2PL double power-law IMF at m<1M☉ (3)
216-219 F4.2 Msun/Lsun e_a2PL a2PL negative uncertainty
221-224 F4.2 Msun/Lsun E_a2PL a2PL positive uncertainty
226-229 F4.2 Msun/Lsun a2PLc double power-law with low-mass cutoff
α2PL+cut (3)
231-234 F4.2 Msun/Lsun e_a2PLc a2PLc negative uncertainty
236-239 F4.2 Msun/Lsun E_a2PLc a2PLc positive uncertainty
241-244 F4.2 Msun/Lsun anp [1/1.6] nonparametric IMF
αnon-p (3)
246-249 F4.2 Msun/Lsun e_anp anp negative uncertainty
251-254 F4.2 Msun/Lsun E_anp anp positive uncertainty
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Note (1): Mr,☉=4.64 AB; distance error not included.
Note (2): Total MEin/Lr,Ein with MEin from S15
(Smith+, 2015MNRAS.449.3441S 2015MNRAS.449.3441S)
Note (3): The lensing and dynamical data place integral constraints on the IMF
via the mass factor α, also referred to as the "IMF mismatch"
factor; see Equation (1):
α = (M*/Lr)/(M*/Lr)MW
where (M*/Lr)MW is inferred from SPS modeling assuming a fiducial
Kroupa (2001MNRAS.322..231K 2001MNRAS.322..231K) IMF. See section 5.2.
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 5 A5 --- Name Galaxy name (1)
7- 15 F9.3 0.1nm lambda [3918.4/10543] Observed-frame wavelength
in vacuum units (2)
17- 25 F9.5 --- Flux [0/211] Flux density in arbitrary units
27- 33 F7.5 --- e_Flux [0/3.1] The 1σ uncertainty in Flux
35- 35 I1 --- Flag [0/1] Mask pixel from fit when Flag=0
37- 40 F4.1 km/s Res [32/89.3] Instrumental resolution;
σ of gaussian
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Note (1): SNL-0 and SNL-1 include data from IMACS and from FIRE; SNL-2
includes only IMACS. The FIRE data begin at wavelengths > 9900 A.
Note that there is a discontinuity in the (arbitrary) scaling of
Flam between the IMACS and FIRE spectra. As described in
Section 2.3, for each lens, a small gap around the Ca4227 feature
has been filled in using the X-Shooter spectrum.
Note (2): Only the six wavelength ranges described in Section 6 were used
to constrain models, regardless of the value of the Flag field.
This table contains slightly more wavelength coverage for
completeness.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Emmanuelle Perret [CDS] 06-Apr-2018