THE HOBBY EBERLY TELESCOPE
DARK ENERGY EXPERIMENT
Steven Finkelstein - The University of Texas at Austin
for the HETDEX team
PI: Gary Hill (UT Austin)
Project Scientist: Karl Gebhardt (UT Austin)
HETDEX WILL MEASURE H(Z) AT Z=2-3
2
⎛ H (z) ⎞
4
3
2
⎜
⎟ = ω r (1+ z) +ω m (1+ z) +ω k (1+ z) +ω Λ (z)
⎝ H100 ⎠
Expansion Rate
Radiation
Matter
Universe Shape
Dark Energy
•
The expansion rate H(z) is the metric of the universe.
•
Dependance on matter and radiation is well understood, but currently the redshift dependance
of the dark energy equation of state is not well constrained.
•
While BOSS results are consistent with a cosmological constant (no redshift evolution), they
are also consistent with many models due to the somewhat large uncertainty.
•
HETDEX will provide a direct detection of the dark energy density at z=2.3 (assuming Λ).
•
HETDEX will provide a measure of the expansion rate between the local (Cepheids), and the
inferred H0 based on the CMB (Planck), which have an interesting tension.
HOW WILL HETDEX WORK
•
We’re creating the largest spectroscopic map of the distant universe through a blind
spectroscopic survey on the 10m Hobby Eberly Telescope (HET), tracing structure via
Lyα emission at 1.9 < z < 3.5.
•
Our instrument VIRUS is 156 spectrographs (R=750 from 350nm – 550nm), covering
th
1/5 of the focal plane with 34,000 fibers, which is currently being assembled on the
upgraded HET (new top-end, upgrading FOV from 4’ to 22’).
•
Our fiducial survey is 450 square degrees over 3 years (taken in ~6000 pointings of 20
2
minutes each) at 1/5 fill, for nearly 100 deg with spectra.
•
Expect ~1 million redshifts from 1.9<z<3.5 via Lyα
•
Similar in scope to the spectroscopic sample from SDSS, only probing the
universe at a time >10 Gyr into the past.
•
•
Will open up the universe around the peak of cosmic star-formation activity in a
similar way as the SDSS has done locally.
>1 million redshifts from 0<z<0.5 via [OII]
H(z)/(1+z) (km/sec/Mpc)
HOW HETDEX STACKS UP
R = combination
of H(z) and DA(z)
3σ
90
80
70
60
50
0
1
of Λ
fΛ
no
ion
ect
ctio
det
HETDEX
MS-DESI
e
det
5σ
DES
BOSS
eBOSS
Lyα
➢ HETDEX: 2017-2020, 1.9<z<3.5
➢ BOSS: 2009-2014, z=0.35,0.6,2.5
➢ eBOSS: 2015-2018, z=2
➢ WIGGLEZ: done, 0.5<z<0.8
➢ DES: 2012-2016, 0.3<z<1.0
➢ MS-DESI: 2020-2025, 0.6<z<2.5
➢ EUCLID: 2019-2025, 0.8<z<2.0
➢ WFIRST: >2020
➢ CHIME: 0.8<z<2.2
2
z
HETDEX FUNDING AND BUDGET
Funding
Private
Budget
13.0
HET upgrade
17.0
15.0
NSF
8.0
VIRUS
Air Force (NESSI)
4.5
Software
4.0
Project Office
6.0
UT
11.0
Munich, AIP
4.0
TAMU
1.0
Oxford
0.5
Total
Total
42.0 M
Schedule
42.0 M
Take down
7/13
First light
10/15
30 spectrographs
6/17
156 specs
Early/
Mid-2018
Survey
2017-2020
HOW WILL THIS WORK? VIRUS
•
VIRUS: Visible Integral-field Replicable Unit Spectrograph
•
Uses idea of industrial replication:
156 copies of a simple spectrograph,
giving huge cost and schedule
savings.
•
We built a prototype, VIRUS-P,
now re-named the Mitchell
Spectrograph, which has been in
service on the 2.7m Harlan J.
Smith telescope for several years.
Wide Field Corrector
Focal Plane
Tracker
Optical Fibers
Spectrographs (VIRUS)
Primary Mirror
Integral Field Unit production
• Each IFU is a bundle of 448 fibers split into
two slits to feed a VIRUS pair
IFU input heads
– Simple design maximizes throughput and
minimizes cost
• Development in collaboration with AIP
– nine already delivered
IFU input
IFU output
Focal Plane of HET
➢ 78 IFUs feed 156
spectrographs
100”
➢ Focal plane is shared with
other instruments, allowing
parallel mode
➢ 1/5th fill over the full 22’
diameter field
IFU 448 fibers
50 x 50 sq. arcsec
15.6’
Example data frame (2.9 million of these in total)
We are in commissioning mode, with 16
IFUs on the telescope (2nd to MUSE in
terms of sky coverage with spectra, soon
to be first). Data is coming in weekly. Full
survey to start in 2017.
Example spectra and imaging for OII
galaxy (top) and two potential Lymanalpha emitters.
N
FIRST CONFIRMED LAE
Detect_Visualization_all_emis
RA
Dec
Source_Info
2D Plots
Spec Plots
S/N: 9.02
chi2: 1.42
flux: 817.8
eqw: -78.3
80 214.71619 52.79753
RA: 14:18:51.88
Dec: 52:47:51.09
X: 12.58, Y: 16.37
black=VIRUS
Red/Green/Blue=
20 min LRS2 followup
Cutouts
Data from last week!
THE SURVEY FIELDS
Spring field:
300 deg2 in
the North (in
Ursa Major)
Fall field:
150 deg2
in Stripe 82
Figure 2: The layout of the HETDEX spring field (top) and fall field (bottom) in red, overlaid on a
combined image of the surrounding region using the WISE, SDSS and WFCAM LAS survey data.
The other colored regions denote ancillary imaging, notably the yellow, which denotes the imaging
surveys we will use to ensure a minimal contamination by lower-redshift objects, and the blue,
which denotes
Spitzer programimaging
which willdata
allow needed
us to calculate
robust stellar
masses.
NB:the
AtSHELA
least single-band
to constrain
EWs
to distinguish
LAEs
(line
will not
be resolved).
nstalled by March 2014, between
at which point
we at
will[OII]
beginemitters
our primary
survey.
We expect
very little
chedule slippage as the majority of our risks have been retired, including the tracker hardware and
THE SURVEY FIELDS
Spring field:
300 deg2 in
the North (in
Ursa Major)
Current status:
13 working IFUs on the telescope.
Expect 50 by August, and start our
survey this fall.
Presently updating/shaking down
software pipeline, from reduction,
through emission line detection and
identification.
Fall field:
150 deg2
in Stripe 82
Figure 2: The layout of the HETDEX spring field (top) and fall field (bottom) in red, overlaid on a
combined image of the surrounding region using the WISE, SDSS and WFCAM LAS survey data.
The other colored regions denote ancillary imaging, notably the yellow, which denotes the imaging
surveys we will use to ensure a minimal contamination by lower-redshift objects, and the blue,
which denotes
Spitzer programimaging
which willdata
allow needed
us to calculate
robust stellar
masses.
NB:the
AtSHELA
least single-band
to constrain
EWs
to distinguish
LAEs
(line
will not
be resolved).
nstalled by March 2014, between
at which point
we at
will[OII]
beginemitters
our primary
survey.
We expect
very little
chedule slippage as the majority of our risks have been retired, including the tracker hardware and
IS THIS A COSMOLOGY MEETING?!?
Hint: No
•
HETDEX will be great for cosmology, but thats not what I (or most of
you!) do.
•
•
Its going to be a Lyα machine, finding LAEs over an incredible 8.5
Gpc3 volume.
Will enable a wide variety of Lyα-based studies, I’ll spend my last few
minutes on a few:
•
1) Global evolution of Lyα escape fraction and fraction. of SFR
density contributed by LAEs.
•
2) Evolution of faint-end slope of AGN luminosity function.
•
3) Identification of physical properties which regulate Lyα emission.
INSIGHTS FROM THE Lyα LUMINOSITY FUNCTION
•
By robustly quantifying
the Lyα luminosity
function,
measure both:
The Astrophysical
Journal, 736:31
(21pp), we
2011can
July 20
•
•
we can integrate the Lyα luminosity function measured in the
The evolution ofprevious
the Lyαsection
photon
escape the
fraction
to estimate
Lyα luminosity density (ρLyα )
at these redshifts. Comparing this observed luminosity density
• Requires measurement
of total
intrinsic
Lyα
luminosity,
possible
with that predicted
from
the global
SFR
density (ρSFR
) for the
entire
galaxy SFR
population
provides
an estimate
via measures
of cosmic
density
at a given
epoch. of the global
escape fraction of Lyα photons and its evolution with redshift.
The above approach is equivalent to taking the ratio between the
The contributionSFR
of LAEs
the cosmic
density.
densitytoimplied
by theSFR
observed
Lyα luminosity density
using Equation (2) (ρSFR,Lyα ), and the total ρSFR . This method
• Need to measure
theapplied
SFR density
provided
by LAEs
calculate
has been
by Cassata
et al. (2011).
In- this
work we
their analysis
included the Cassata et al. (2011)
the rest-UV extend
luminosity
functionwhich
of LAEs.
data at 2 < z < 6.6, the measurement of Gronwall et al. (2007)
at z = 3.1, and the data of Ouchi et al. (2008) at z = 3.1,
3.7, and 5.7. We add the HETDEX Pilot Survey data points at
1.9 < z < 3.8, as well as the z ∼ 0.3 LAE data from Deharveng
et al. (2008) and Cowie et al. (2010), the z = 2.2 data of Hayes
et al. (2010), the z = 4.5 measurement by Dawson et al. (2007),
the measurement at z = 5.7 of Shimasaku et al. (2006), the
z = 6.5 data from Kashikawa et al. (2006), the data of Ouchi
et al. (2010) at z = 6.6, and the z = 7.7 measurement of Hibon
et al. (2010). A similar data set has been analyzed in this way
in a recent submission by Hayes et al. (2011), although using
a different set of Hα and UV luminosity functions at different
redshifts to estimate the total SFR density.
The top panel in Figure 14 shows ρSFR,Lyα derived from the
observed Lyα luminosity density using Equation (2). We present
our results for the full sample and for the low-z and high-z
bins of the HETDEX Pilot Survey (red, blue, and green filled
circles), as well as the compilation of data points calculated from
the Lyα luminosity functions at 0.3 < z < 7.7 mentioned above
(black filled circles). Vertical error bars are estimated from the
published uncertainties in L∗ and φ ∗ , and horizontal error bars
show the redshift range of the different samples (omitted for
narrowband surveys).
Also presented is the latest estimate of
α
the total SFR density history of the universe from Bouwens
et al. (2010b), which has been derived from the best to date
Blanc et al.
Figure 14. Top panel: SFR density (ρSFR ) as a function of redshift. The solid
and dotted lines show the total BLANC+2011
ρSFR from Bouwens et al. (2010b) and its typical
uncertainty of 0.17 dex. Blue, green, and red filled circles show ρSFR,Lyα derived
HETDEX
SURVEY
from the Lyα luminosity
function in PILOT
the two redshift
bins at 1.9 < z < 2.8 and
2.8 < z < 3.8, as well as for the full sample. Black filled circles show the
INSIGHTS FROM THE Lyα LUMINOSITY FUNCTION
•
By robustly quantifying the Lyα luminosity function, we can measure both:
•
The evolution of the Lyα photon escape fraction
•
•
Requires measurement of total intrinsic Lyα luminosity, possible
via measures of cosmic SFR density at a given epoch.
The contribution of LAEs to the cosmic SFR density.
•
Need to measure the SFR density provided by LAEs - calculate
the rest-UV luminosity function of LAEs.
z~2.2
10000
105
HETDEX 3 Years
HETDEX 3 Years
HETDEX 1 Year
Commissioning
103
HETDEX
Commissioning
101
42
43
44
log Lyα Luminosity
45
2.0
2.5
Ouchi+08
1
Konno+16
102
Ciardullo+12
AGN
Dominated
10
HETDEX 1 Year
Zheng+16
Star
Formation
Dominated
100
HSC
104
Konno+16
Number
Number
1000
3.0
Redshift
3.5
52.0
51.5
24
51.0
50.5
Figure 13. (a) Combined SF and AGN Lyα
50.0LF at z = 0.195-0.44 in deep GALEX grism fields with EW (Lyα) !
data; solid circles–corrected for the effects of incompleteness using the results from our Monte Carlo simulations). The
the best-fit Schechter function + power-law to the combined data assuming a Schechter fixed faint-end slope of α
dashed curve and line indicate the underlying
function and power-law, respectively. We calcul
49.5 best-fit Schechter
obs
obs
luminosity density and find log ρLyα,SF = 38.3 ± 0.1 and log ρLyα,AGN = 38.2 ± 0.2. (b) Same as Figure 13(a), bu
Finkelstein+17, in prep
a Saunders function + power-law. Comparing both results, we find that the computed luminosity densities agree wit
49.0
Figures, we also show the effect of allowing
the power law slope to be a free parameter (grey dashed and solid curv
alteration does not significantly alter our computed
densities.
All results
4 luminosity
6
8
10 are summarized
12
14in Table 2.
4
6
(A color version of this figure is available in the online journal.)
Redshift
7
00
l. 2
2
2015
AGNs contribute ~50%
of ionizing emissivity at
z=6 if galaxy fesc are <5%
.
Total HI Ionizing Emissivity (NHI)
Galaxy HI Ionizing Emissivity
AGN HI Ionizing Emissivity
.
Galaxy NHI (fesc=13%, Mlim=-13)
AGN HeII Ionizing Emissivity
ta
0
Haardt
e
ins
pk
10
HETDEX
Redshift
Range
Madau
&
Ionizing Emissivity
10
25
Ho
AGN Comoving Ionizing Emissivity
THE FAINT-END OF THE AGN LUMINOSITY FUNCTION
Redshift
Konno+16
Wold+17
Figure 14. (a) Evolution of the combined SF and AGN Lyα LFs from z ∼ 0.3 to z = 2.2 with best-fit Schechter f
THE PHYSICS PROMOTING Lyα ESCAPE
•
The Spitzer-HETDEX Exploratory Large Area (SHELA) survey.
2
3
•
Covers 24 deg (~0.45 Gpc ) of the HETDEX fall field to u’=26.5, g’r’i’z'=25.5 (DECam; PI
Papovich), KAB~23 (NEWFIRM; PI Finkelstein) and 3.6,4.5 μm=22.5 (IRAC; PI Papovich).
•
HETDEX will cover this field at full-fill; we expect ~300,000 LAEs (~half or more detected in the
IR).
•
Except a comparable number of photo-z selected, non-Lyα emitters (w/ VIRUS upper limits).
•
An excellent laboratory for disentangling which physical properties best promote Lyα escape!
THE data
PHYSICS
PROMOTING
Lyα inESCAPE
This imaging
exists *now*
(Papovich+2016; Wold+17
prep; Stevans+17 in
prep).
UT Grad student Matt Stevans is currently searching for extremely bright/massive
star-forming and quiescent galaxies at z~3-5.
•
The Spitzer-HETDEX Exploratory Large Area (SHELA) survey.
•
2
3
Covers 24 deg (~0.45 Gpc ) of the HETDEX fall field to u’=26.5, g’r’i’z'=25.5 (DECam; PI
Papovich), KAB~23 (NEWFIRM; PI Finkelstein) and 3.6,4.5 μm=22.5 (IRAC; PI Papovich).
r’=20.7 galaxy at z ~3.7. Previous measures of the
luminosity function predict zero of these in the universe.
•
HETDEX will cover this field at full-fill; we expect ~300,000 LAEs (~half or more detected in the
phot
IR).
•
Except a comparable number of photo-z selected, non-Lyα emitters (w/ VIRUS upper limits).
•
An excellent laboratory for disentangling which physical properties best promote Lyα escape!
SUMMARY
•
HETDEX will, starting this fall, begin a blind spectroscopic survey targeting LAEs at
z=1.9-3.5.
•
Over our full three year survey, we expect ~one million spectroscopically
identified LAEs.
•
This large sample will allowed detailed investigation into the evolution of the Lyα
luminosity function, EW distribution, Lyα escape fraction, AGN faint-end slope
over small (Δz~0.1) redshift intervals with extremely small Poisson uncertainties.
•
Follow-up imaging in the SHELA field will allow an extremely in-depth
investigation into the physical processes regulating Lyα escape.
•
By performing detailed comparisons between LAEs and non-LAEs, we can
identify physical characteristics which best promote Lyα emission. It is these
galaxies we should be targeting at z > 6.5 to study reionization.