Radio and (Sub)millimeter Astronomy During the Next 10 Years or So…

Relevance for a Cherenkov Telescope Array

Karl M. Menten

Max-Planck-Institut für Radioastronomie, Bonn

CTA Meeting, Paris March 1, 2007

10-2

3

Radio Continuum Emission:

• non thermal (= synchrotron radiation)

• general ISM, SNRs

• AGN

• PSRs

• thermal (= Bremsstrahlung)

• HII regions

Thermal emission can also be observed in spectral lines:

Radio: 21 cm line of neutral hydrogen HI (1421 MHz)

(Sub)mm: Rotational emission from CO: 115.5 GHz and multiples thereof

Our milky way across the electromagnetic spectrum

CO

HI

60 – 100 m

2 – 4 m

The 21-cm Neutral Hydrogen Line

All-sky map of emission in the 21-cm line

G a l a c t i c p l a n e

Hartmann & Burton

Columbia/CfA CO survey (Dame/Thaddeus et al.)

1.2 m

Carbon monoxide (CO) emission

[CO/H2] 10-4

[all other molecules/H2] << [CO/H2]

COBE FIRAS 7 resolution Fixsen et al. 1994

Millimeter

Submillimeter

Galactic plane

Interstellar medium cartoon

very hot low density gas

diffuse cloud

Giant Molecular Cloud (GMC)

Dense cloud coresSupernova

new stars(IR

sources)

*

Giant Molecular Clouds

Typical characteristics of GMCs:

– Mass = 104...106 M

– Distance to nearest GMC = 450 pc (Orion)– Typical size = 5...100 pc– Size on the sky of near GMCs = 5...dozens x full moon– Average temperature (in cold parts) = 20...30 K– Typical density = 102...106 molecules/cm3

– Contain ca. 1% dust (by mass)– Typical (estimated) life time = ~107 year– Star formation efficiency = ~1%...10%

Half-power beamwidth

Full width at half maximum (FWHM) 1.22 /D

Response of a radio telescope to radiation

Main beam B

Full width at half maximum FWHM=1.22/D

FWHM

“Error beam”

Error beam can pick up significant part of the signal, up to 50%

B = 22 @ 380 GHz

APEX 12m

B = 22 @ 112 GHz

IRAM 30m

1.22 /D

(Telescopes are not reproduced on same scale)

B = 22 @ 44 GHz

Effelsberg 100m

B = 4’ @ 4.0 GHz

beambeam efBI 1

1f 1f

is called the filling factorf

1f

Our milky way across the electromagnetic spectrum

CO

HI Atomic Gas: H

Molecular Gas: H2

60 – 100 m

2 – 4 m

rays All interstellar matter

2cm

1

1

)1(

N

fTT

fTT

efTT

L

L

L

1f

Empirical CO column density determination:

• HE (~100 MeV – few GeV) -ray emissivity number of nucleons

• CO emissivity WCO(K km s-1) -ray emissivity

N(cm-2) = XWCO or n(cm-3) = X/l WCO CO emission is always optically thick

Moriguchi

The Galactic Center Region as seen by SCUBA at 850 m

Pierce-Price et al. 2000

(Optically thin) (sub)millimeter continuum emission from interstellar dust is an excellent column density probe

Problem: Weakness of emission. Need N > a few 1022 cm-2 to make large-scale mapping practical.

DSingle dish: = /D

B

Interferometer: = /B

Largest structure that can be imaged given by telescope diameter zero spacing problem

desIbVbs

c

i

2

Interferometry

• combine signals from two antennas separated by baseline vector b in a correlator; each sample is one

“visibility”

• each visibility is a value of the spatial coherence function V (b) at

coordinates u and v

• obtain sky brightness distribution by Fourier inversion:

s

b

• Telescopes can be combined all over the world: Very Long Baseline Interferometry (VLBI) (sub)milliarcsecond

resolution

4.9 GHz/instantaneous sampling of a source at = 30 and hour-angle 0 /VLA/A configuration.

More data points are filled in as the Earth rotates

ALMA snapshot

Central hole

The Very Large Array (VLA)

• Built 1970’s, dedicated 1980

• 27 x 25m diameter antennas

• Two-dimensional 3-armed array design

• Four scaled configurations, maximum baselines 35, 10, 3.5, 1.0 Km.

• Eight bands centered at .074, .327, 1.4, 4.6, 8.4, 15, 23, 45 GHz

• 100 MHz total IF bandwidth per polarization

• Full polarization in continuum modes.

• Digital correlator provides up to 512 total channels – but only 16 at maximum bandwidth.

VLA in D-configuration(1 km maximum baseline)

Angular Resolution

DSingle dish: = /D

B

Interferometer: = /B

Largest structure that can be imaged given by telescope diameter zero spacing problem

Largest Angular Scale

The Australia Telescope Compact Array

Six 22m diameter antennas movable in E-W direction

Most interesting for CTA: L- and S-band (1350 and 2700 MHz)

Radio void HESS peak

SNR RXJ713.7-3946 a.k.a. G347.3-0.5

ROSAT

ATCA 40” beam

Lazendic et al. 2004

Interferometer field of view = FWZP of unit telescope

“Mosaicing”

1357 MHz 2495 MHz

NVSS “offi

cial

ly” s

tops

here

ATCA NRAO VLA Sky Survey

Aharonian et al. 2005

Brogan et al. 2005

March 2007

Aharonian et al. 2006 Funk et al. et al. 2007

MOST 843 MHz B = ca. 2 arcmin

Whiteoak & Green 1996

ASCA Source

J1640-465

Chandra

ALMA Science Requirements• High Fidelity Imaging • Precise Imaging at 0.1” Resolution• Routine Sub-mJy Continuum Sensitivity• Routine mK Spectral Sensitivity• Wideband Frequency Coverage• Wide Field Imaging Mosaics• Submillimeter Receiver System• Full Polarization Capability• System Flexibility (Total Power capability on

ALL antennas)

Chajnantor

SW from Cerro Chajnantor, 1994 May AUI/NRAO S. Radford

Complete Frequency Access

Note: Band 1 (31.3-45 GHz) not shown

ALMA Specifications• 50 12-m antennas, at 5000 m altitude site• Surface accuracy 25 m, 0.6” reference pointing

in 9m/s wind, 2” absolute pointing all-sky• Array configurations between 150m to ~15km• 10 bands in 31-950 GHz + 183 GHz WVR. Initially:

• 86-119 GHz “3”• 125-163 GHz “4”• 211-275 GHz “6”• 275-370 GHz “7”• 385-500 GHz “8”• 602-720 GHz “9”

• 8 GHz BW, dual polarization• Interferometry, mosaics, & total-power observing• Correlator: 4096 channels/IF (multi-IF), full Stokes• Data rate: 6Mb/s average; peak 60Mb/s

150 m

Very small field of view: 20” FWHM at 300 GHz

ALMA – Extreme Configurations

Most compact:

10,000m

Most extended:

The CTA will have an angular resolution of ca. 2 arcmin.

Most HESS sources are extended on 10’s of arcmin to ~1 degree scale

In radio and (sub)mm, want imaging capability that allows good fidelity multi-wavelength imaging that recovers these structures.

• Radio: Interferometer multi- (at least 2-), long wavelengths

• (Sub)mm: Single dish telescopes with spectral line receiver arrays

The APEX telescopeBuilt and operated by• Max-Planck-Institut fur Radioastronomie• Onsala Space Observatory• European Southern ObservatoryonLlano de Chajnantor (Chile)Longitude: 67° 45’ 33.2” WLatitude: 23° 00’ 20.7” SAltitude: 5098.0 m

• 12 m• = 200 m – 2 mm• 15 m rms surface accuracy• In opertaion since September 2005• First facility instruments:

• 345 GHz heterodyne RX• 295 element 870 m Large Apex Bolo-

meter Camera (LABOCA) http://www.mpifr-bonn.mpg.de/div/mm/apex/

MPG45%

ESO24%

OSO21%

Chile10%

To study larger-scale molecular cloud environments, degree-scale areas have to mapped.

CO lines are relatively strong.

• Still: 1 deg2 40000 APEX beam areas

Advantages of array receivers:

• Mapping speed

• Mapping homogeneity (map lage areas with similar weather conditions/elevation) minimize calibration uncertainties.

Important:

• Uniform beams

• Uniform TRX

and

TRX not “much” worse than TRX of state-of-the-art single pixel RX

Common sense requirements:

Schuster et al. 2004

http://iram.fr/IRAMES/telescope/HERA/

Columbia/CfA 1m CO J = 1 0 (115 GHz)

FWHM = 8.7 arcmin FWHMeff= 30 arcmin

IRAM 30m CO J = 2 1 (231 GHz)

HERA 9 x 11”

Factor ~160

in resolution!

Schuster et al. 2004

Ungerechts & Thaddeus 1987

• 2 x 7 pixels

• frequency range 602 – 720 and 790 – 950 simultaneously

• beamsize 9" – 7" and 7" – 6"

• IF band 4 – 8 GHz

CHAMP+Carbon Heterodyne Array of the MPIfR

Philipp et al. 2005

COBE FIRAS 7 resolution Fixsen et al. 1994

Covered now by CHAMP+@APEX 7 450 m/7 350 m array

Will be Covered by APEX 7 870 m/19 600 m array (to arrive in 2008)

The APEX Galactic Plane survey

• Image continuum emission from interstellar dust over -80° < l < +20° ; | b | < 1°• Instrumentation: LABOCA (Large APEX BOlometer CAmera) = 295 bolometers for observing at 870 m

• APEX beam at 870 m:18"= MSX pixels = Herschel at 250 m

Other Submillimeter Facilities in the high Atacama desert:• ASTE – The Atacama Submillimeter Telescope Experiment

• 10m

• NAO Japan, Tokyo U., Osaka Prefecture U., U. Chile

• Nanten-2

• 4m

• Nagoya U., Osaka Prefecture U., Seoul National U., Cologne U., Bonn U., U. Chile

The Expanded Very Large Array

The EVLA Project:– builds on the existing infrastructure - antennas, array,

buildings, people - and, – implements new technologies to produce a new array

whose top-level goal is to provide

Ten Times the Astronomical Capability of the VLA. – Sensitivity, Frequency Access, Image Fidelity, Spectral

Capabilities, Spectral Fidelity, Spatial Resolution, User Access

– With a timescale and cost far less than that required to design, build, and implement a new facility.

Frequency – Resolution Coverage

● A key EVLA requirement is continuous frequency coverage from 1 to 50 GHz.

● This will be met with 8 frequency bands:

– Two existing (K, Q)– Four replaced (L, C, X, U)– Two new (S, A)

● Existing meter-wavelength bands (P, 4) retained with no changes.

● Blue areas show existing coverage.

● Green areas show new coverage.

Current Frequency Coverage

Additional EVLA Coverage

Sensitivity Improvement 1s, 12 hours

Red: Current VLA, Black: EVLA Goals

This talk concentrated on observations of extended objects.

Needless to say, the greatly enhanced point source sensitivity of the EVLA will greatly enhance observing capabilities for compact sources (AGN, pulsars, GRBs)

• LSI+61303 is also a famous radio source!

• All the PKS objects are strong radio sources

Problem: No good VLBI capability in the southern hemisphere

Even greater sensitivity will be provided by the Square Kilometer Array (“A hundred times the VLA”)

One part of the EVLA plan currently not funded is the “E”-configuration, which would give much better response to extended structure

E configuration would allowhigh fidelity imaging of 10’ sized structures up to 5 GHz

Some conclusions:Some conclusions:• Long wavelength radio continuum observations can give interesting complemenary data to the CTA

• Relation of radio continuum emission to VHE ray emission presently unclear (“What makes a VHE ray source radio=loud?”)

• Need targeted radio observations. Survey data not sufficient

• (Sub)millimeter spectral line observations show were the baryons are. Can provide information on the column densities and dynamics of molecular material in the vicinity of VHE ray sources

• Didjn’t talk about high resolution radio observations of pulsarsand extragalactic VHE ray sources

All of the above will greatly be enhanced by capabilities that come available within the next 3 – 4 years

It would be good to have an EVLA in the southern hemisphere