Extra-galactic spectral lines–SWG SKA Town Hall2017 · PDF file–Success of instruments like ALMA underline the crucial ... ‘Receiver bands 2, ... – For this SWG it remains

Extra-galactic spectral lines – SWGSKA Town Hall2017

Rob Beswick &Francoise Combes

On behalf of the ex-gal spectral line SWG

SWG update

New SWG co-chair – Francoise Combes (Obs. Paris)– John Conway stepped down as SWG co-chair effective Mar.

2017. – John has made numerous contributions to the founding

and development of this SWG, and continues to play a major role.

Continued activity and growth of SWG membership. – Strong recognition of science area in the community and

the potential SKA capabilities

Background to SWG science areas

This SWG: – Many important astrophysical line tracers beyond HI (21-cm)

• Uniquely trace different material/environment = different science• From high-redshifted lines to local universe probe of physics

– Success of instruments like ALMA underline the crucial nature of such traces

– SKA-MID Bands 2 & 5 provide critical science capabilities in this area.. This SWG is a strong advocate of increased frequency range/capability

– Strongly supports the band priority order assigned in 2015 Re-baseline process:

‘Receiver bands 2, 5 and 1 should be constructed for all SKA1-Mid dishes with their priority order as written.’

Science areas

Our aims to facilitate the science development:• focus on ‘key science concepts (KSCs)’ rather than projects -• Commensal/complementary science goal synergies with other

SWG areas

Broad range of science areas/drivers…• Galactic-type masers in local universe• Local galaxies

– Dense molecular gas traces [thermal & masers lines]– RRLs

• Wide-area line Maser searches (OH/H20 etc)• High-z dense gas tracers

– CO/CS/HCN etc, lensed lines [follow-up]

Combination of commensal observing as well as specific programmes

5

Frequency coverage of main lines*

19.2 [GHz]9.64.82.41.20.60.3

SKA

1-M

ID

Band 54.6-13.8 GHz

ALM

A

38.419.29.64.82.41.20.60.3 76.8 [GHz]

1 2 3

Band 10.4-1.1 GHz

Band 20.9-1.75 GHz

OH

mas

ers

H2O

mas

er

form

alde

hyde

mas

er

OH

* m

aser

s

OH

* m

aser

sm

etha

nol m

aser

met

hano

l* m

aser

*NOTE: the SKA rebaselineprocess Band 5 (4.6-13.7 GHz) or now band 5a/b/[c]) was prioritized to second highest science priority.Science priority order Band 2, 5, 1

View supported by this SWG.

6

19.2 [GHz]9.64.82.41.20.60.3

SKA

1-M

ID

Band 54.6-13.8 GHz

ALM

A

38.419.29.64.82.41.20.60.3 76.8 [GHz]

1 2 3

Radio recombinationlines

Band 10.4-1.1 GHz

Band 20.9-1.75 GHz

Radio recombinationlines

Frequency coverage of main lines

Local dense gas tracers – HCN, HCO+, HNC etc

7

19.2 [GHz]9.64.82.41.20.60.3

SKA

1-M

ID

Band 54.6-13.8 GHz

ALM

A

38.419.29.64.82.41.20.60.3 76.8 [GHz]

1 2 3

Band 10.4-1.1 GHz

Band 20.9-1.75 GHz

HCN[1-0]

HCO+[1-0]

CS[1-0]

CO[1-0]

HCN

[1-0

]H

CO+[

1-0]

CS[1

-0]

CO[1

-0]

redshift

Frequency coverage of main lines

Cost Control project

This SWG: On-going assessment of implications. Time constraints mean this review is not complete yet.

Short preliminary assessments presented here


Preliminary headline science conclusions:1. [MID] Band 5 capabilities critically important to SWG.

– Band 5 to 2.5GHz B/w [5.13.2] – if frequency-slicing/zoom modes can be spread over full tuneable range for lines – OKAY, but still effects line search parameter space.

– Reduce MID band 5: 2.5 to 1.4GHz à Effect on simultaneous line observations, and line searches. -> loss of commensality, efficiency and loss of science

– Cuts half (130à67) RXs elements deployed detrimental to capabilities [5.5.2] – loss in sensitivity & capability

– Full loss of Band 5 – Devastating science implications/losses

(SWG’s view is that there is a disproportionate number of cuts to band 5, cf. ‘lower priority’ band 1)

2. [MID] Baseline length reductions [5.24.] – ‘initially incremental downgrade’ SWG consensus opinion prefers removal core dishes over further erosion of resolution. – Longer integrations can re-gain sensitivity on already well sampled short

spacings. But reducing baseline lengths cannot be mitigated for by operational/observational adaptations – should be guarded against.

Cost Control project –details #1 specific SWG comments

Essential that Zoom modes be preserved


Reduced resolution: Prefer to see dishes removed from core rather than arms. But cost implications noted.

Significant effect on band 5 continuum science –but less critical for this SWGs specific work1. Targeted line work – Okay as long and B/W

can be split to accommodate multiple simultaneous lines separated by >2.5GHz

2. Line searches – e.g. redshifted CO etc. loss of search parameter space.

Implications for this SWG. Reduction in availability of highest data rate projects reduced may commensality with other programmes


Significant effect on band 5 science – multiple SWGs.1. Major reduction in sensitivity – inc high res capabilities

(re-weighting withstanding)2. Core baselines required for VLBI (inc work in this SWG).Significant reduction in competiveness c.f jVLA (sensitivity) or e-MERLIN (resolution). Compounded for continuum science when bandwidth reductions are included

Aside: Band 5 deployment locations

• Locations of Band 5 systems only to be deployed on half RXs– [option a] ‘core+arms’– [option b] ‘deploy on arms only’– [option c] ‘deploy core only’

SWG preference for options b/a- As standalone instrument option b is preferable. - But – Major loss and compromise to ability to phase-core

up in VLBI-mode. – large science potential loss for this SWG (e.g. maser follow-ups).

- Logical compromise is a blend of options b and a.- If option B, needs enough feeds (~20++) deployed on inner part

b~<10km for phasing-up for VLBI

- Option c strongly disfavoured


Further reductions on band 5 B/W – multiple SWGs.1. Major reduction in sensitivity for continuum 2. Simultaneous line capabilities removed – detriment to

this SWG


Implications for this SWG less clear. Reduction in availability of highest data rate projects/reduced commensality of programmes


Transformational(?) and comments/ordering

The two highest priority bands for this SWG are MID bands 2 & 5Band 5:• Cuts even above the line and especially to Band 5 risks the science in a

number of areas (inc. this SWG). – Combined 50% cut in feeds deployed, B/w limitations have a large cumulative

effect– Biggest effect is on continuum science objectives but line work also hit hard. – Ratio of cuts between band 5 and band 1 is disproportionate – no direct cuts

proposed to band 1 until the worst-case scenario below the cost cap. This is at complete odds to the re-baseline priority order.

Competitive edge compared to jVLA & e-MERLIN is eroded in this band, albeit less of an erosion for line work than for continuum science

Other SWGs will have different opinions of science priorities, ability to reinstate elements is important to remember – ‘and should be some comfort’.

Band 2:• Minimal cuts specific to band 2.

– For this SWG it remains essential that the Band 2 top frequency remains at 1750MHz or greater so that OH lines at low redshift can be accesses.

Band 1: Not a top priority for this group (compared other bands at least)


Preliminary headline science conclusions:1. [MID] Band 5 capabilities critically important to SWG.

– Band 5 to 2.5GHz B/w [5.13.2] – if frequency-slicing/zoom modes can be spread over full tuneable range for lines – OKAY, but still effects line search parameter space.

– Reduce MID band 5: 2.5 to 1.4GHz à Effect on simultaneous line observations, and line searches. -> loss of commensality, efficiency and loss of science

– Cuts half (130à67) RXs elements deployed detrimental to capabilities [5.5.2] – loss in sensitivity & capability

– Full loss of Band 5 – Devastating science implications/losses

(SWG’s view is that there is a disproportionate number of cuts to band 5, cf. ‘lower priority’ band 1)

2. [MID] Baseline length reductions [5.24.] – ‘initially incremental downgrade’ SWG consensus opinion prefers removal core dishes over further erosion of resolution. – Longer integrations can re-gain sensitivity on already well sampled short

spacings. But reducing baseline lengths cannot be mitigated for by operational/observational adaptations – should be guarded against.

Band 5 sensitivities

133 à130Loose 3 out antennas[5.24]

133 à 64loose out 3 antennas + core [5.52]

Continuum sensitivity of band 5, uniform weight & Gaussian taper.Sensitivity degradation across all spatial scales

Documents

Extra-galactic spectral lines–SWG SKA Town Hall2017 · PDF file–Success of instruments like ALMA underline the crucial ... ‘Receiver bands 2, ... – For this SWG it remains