Packed Ultra-wideband Mapping Array (PUMA) is a proposed radio telescope operating at 200MHz-1100MHz, optimized for the 21 cm intensity mapping in the post-reionization era but also addressing other science goals amenable to such observations, primarily Fast Radio Bursts (FRBs), pulsar monitoring and transients as a part of multi-messenger observations.
This idea grew up from deliberations of the Cosmic Visions Dark Energy Committee, a panel tasked with investigating possible future directions for Dark Energy program within the Office of Science of the US Department of Energy. A working group has been established that led to the development of a Stage II 21cm experiment that eventually morphed into PUMA.
For inquiries about PUMA or to get onto mailing list, please contact: Anže Slosar (anze AT bnl.gov).
In the next decade, three flagship US-led dark energy projects will be nearing completion: (i) DESI, a highly multiplexed optical spectrograph on the 4m Mayall telescope capable of measuring spectra of 5000 objects simultaneously; (ii) LSST, a 3 gigapixel camera on a new 8m-class telescope in Chile, enabling an extreme wide-field imaging survey to 27th magnitude in six filters; and (iii) WFIRST, a space mission with a significant dark energy component, measuring both spectra and images of galaxies over very small, but very deep fields. These experiments will characterize dark energy at lower redshift with exquisite precision. Together with the continued exploration of the Cosmic Microwave Background (CMB), they will keep the US at the forefront of cosmological observations. Having said that, they will leave a majority of the post-reionization Universe, i.e. within z < 6, uncovered - this range can be fully surveyed via 21cm intensity mapping.
With PUMA, we propose a revolutionary post-DESI, post-LSST program for dark energy, and more, based on intensity mapping of the redshifted 21cm emission line from neutral hydrogen; the field of observation will stretch from our local cosmological neighborhood, at z ~ 0.3, out to z ~ 6, just after reionization. Unlike optical and CMB surveys, which are mature and now planning 3rd and 4th generation experiments, hydrogen intensity mapping is a relatively new technique, but one that offers important complementary science to these planned probes. The PUMA experiment has the unique capability to quadruple the volume of the Universe surveyed by optical programs, providing a percent-level measurement of the cosmic expansion history and growth to z ~ 6. This measurement will significantly improve the precision on standard cosmological parameters, while also opening a window for new physics beyond the concordance LCDM model.
In its full configuration, the total noise will be equivalent to the sampling (Poisson) noise from a spectroscopic galaxy survey of 2.9 billion galaxies (or 600 million galaxies in the more modest, "petite" configuration) on large, linear scales. In addition, multiple cross-correlations with optical surveys and the CMB will dramatically improve the characterization of dark energy and new physics. The rich dataset produced by PUMA will simultaneously be useful in exploring the time-domain physics of fast radio transients and pulsars, potentially in live "multi-messenger" coincidence with other observatories.
PUMA is proposed with six basic science drivers in mind: two relate to fundamental advances in dark energy and modified gravity; two probe the inflationary period; and two touch on astrophysical goals, namely the detection and characterization of FRBs and pulsars. These six agendas can all be fulfilled by the same specialized instrument, as outlined in table below . While these goals inform and primarily determine the design of the instrument, as with any synoptic project, PUMA will open doors to numerous other science goals.
The design of an instrument to map large swaths of the sky at modest angular resolution, but high sensitivity, is fundamentally different from that of radio telescopes specializing in imaging of individual radio sources. This experiment is therefore not in competition with the ngVLA or SKA. Instead, PUMA is an evolution of a different lineage of experiments, including CHIME, HIRAX, which we refer to as Stage I experiments. Compared to high-resolution imaging arrays, PUMA will be fundamentally different in three aspects:
In Figure 1 below , we compare a few relevant experiments in terms of an intensity mapping Figure of Merit (FOM), which is the total number of baselines probing linear scales multiplied by a single element's collecting area.
The PUMA requirements are based on achieving 6 main science drivers from three thematic areas:
Probing the Physics of Dark Energy:
Probing the Physics of Inflation:
Probing the Physics of the Transient Radio Sky:
Main Science Goals determine the parameters of the instrument outlined in Key Parameters:
Scientific Measurement Requirement
expansion history in the pre-acceleration
Measure Baryonic Acoustic Oscillations to volume limited
Measure 21 cm intensity
– over 2 < z < 6
– to k ∼ 0.4hMpc-1
– with SNR per mode ∼ 1 at k ∼ 0.2hMpc-1
Bandwidth must include 200-475MHz
Maximum baseline Lmax ≳ 600 m
ND > 25km at Lmax = 600m
structure growth in the pre-acceleration era
Measure growth through 21 cm power spectrum on weakly
non-linear scales to volume limited accuracy
Measure 21 cm intensity:
– over 2 < z < 6
– to k ∼ 1:0hMpc-1
– with SNR per mode ∼ 1 at k ∼ 0.6hMpc-1
Bandwidth must include 200-475MHz
Maximum baseline Lmax ≳ 1500 m
ND > 200km at Lmax = 1500m
detect primordial inflationary non-Gaussianity
Measure 21 cm bispectrum to achieve non-Gaussianity
– orthogonal: σ [fNLortho] < 10
– equiliateral: σ [fNLequil] < 10
Measure ≳ 109 linear modes with SNR per
mode ∼ 1
Same as above plus:
bandwidth 200 — 1100MHz (z ∼ 0.3 — 6) assuming fsky ∼ 0.5
D. Constrain or
detect features in primordial power spectrum
Constrain features in the matter power spectrum over
available scales to
– sensitivity σ[Alin] < 10-3
Same as above.
Same as above.
E. Fast Radio
Volume limited measurement of electron power spectrum,
stellar mass census
– 1 million FRBs
– covering two frequency octaves
– 3” localization precision
Fluence sensitivity threshold ≲ 2.5
fsky Jy ms
Provide real-time FRB back-end
Provide baseband buffer with triggered readout
Monitor all pulsars discovered by SKA
Detect all pulsars in current Field of View
brighter than 10μJy
10 σ point source sensitivity >10μJy / transit
Provide real-time pulsar back-end
The total science reach of this experiment is considerably wider than the six main goals. In the following, we provide a brief overview of some of the other exciting science capabilities of PUMA:
|Antenna Array||Hexagonal close-packed transit array|
|Petite||Full||Petite array: Achieve science
goals A. & F. and
∼ 30% of B.-E.
|fill factor||50%||50%||Full array: Achieve all science goals|
|number of elements||5,000||32,000|
|10 σ single transit sens.||8.7μJy||1.3μJy|
|Array element||Parabolic on-axis with N-S pointing||transit observations, campaign repointing|
|dish diameter||6m||shortest possible baselines with, D ≫ λmin|
|construction||on-site fiber glass production, mm surface accuracy||Better beam control than Stage I for systematics|
|frequency coverage||200 - 1100 MHz|
|OMT||ultra-wide band, dual-pol|
|front-end||amplifiers and digitizers integrated with OMT||alternative arrangement to be explored|
|channelizer||one per 10-100 dishes||helps with corner-turning, alternatives possible|
|Correlator||FFT correlator with partial N2 correlations||Individual baseline correlation mode for calibration.|
|FRB capability||real-time FRB search engine|
|real-time beam-forming||104 concurrent tracking beams||pulsar, transients, multi-messenger|
|Area||50% of sky|
|Observing time||5 years on sky, wall-time 7-10 years|
|Equivalent source density|
|at z=2, k=0.2 h Mpc-1||7.4 / 2.0 × 10-3 h3 Mpc-3 (full / petite)|
|Total equivalent sources|
|at k=0.2 h Mpc-1||2.9 / 0.6 billion (full / petite)|
|at k=0.5 h Mpc-1||2.5 / 0.4 billion (full / petite)|
|FRB rates (expected)|
|200 - 400 MHz||1200 / 70 per day (full/petite; uncertain)|
|400 - 700 MHz||1000 / 60 per day (full/petite)|
|700 - 1100 MHz||1300 / 80 per day (full/petite)|
|complex amplitude||sky sources|
|primary beam||per antenna calibration using fixed wing drones|
|clock distribution||100 fs clock distribution for phase stability|
For a python module that calculates the noise parameters see Downloads.