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

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: GHz and multiples thereof

Our milky way across the electromagnetic spectrum COHI 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/H 2 ]  [all other molecules/H 2 ] << [CO/H 2 ]

COBE FIRAS 7  resolution Fixsen et al Millimeter Submillimeter

Galactic plane Interstellar medium cartoon very hot low density gas diffuse cloud Giant Molecular Cloud (GMC) Dense cloud cores Supernova new stars (IR sources) *

Giant Molecular Clouds Typical characteristics of GMCs: – Mass= M  – Distance to nearest GMC= 450 pc (Orion) – Typical size= pc – Size on the sky of near GMCs= 5...dozens x full moon – Average temperature(in cold parts) = K – Typical density= molecules/cm 3 – Contain ca. 1% dust (by mass) – Typical (estimated) life time= ~10 7 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 = GHz APEX 12m  B = GHz IRAM 30m 1.22 /D (Telescopes are not reproduced on same scale)  B = GHz Effelsberg 100m  B = 4.0 GHz

is called the filling factor

Our milky way across the electromagnetic spectrum COHI Atomic Gas: H Molecular Gas: H 2 60 – 100  m 2 – 4  m  rays All interstellar matter

Empirical CO column density determination: HE (~100 MeV – few GeV)  -ray emissivity  number of nucleons CO emissivity W CO (K km s -1 )   -ray emissivity  N(cm -2 ) = X  W CO or n(cm -3 ) = X/l  W CO CO emission is always optically thick

Moriguchi

The Galactic Center Region as seen by SCUBA at 850  m Pierce-Price et al (Optically thin) (sub)millimeter continuum emission from interstellar dust is an excellent column density probe Problem: Weakness of emission. Need N > a few cm -2 to make large-scale mapping practical.

D Single dish:  = /D B Interferometer:  = /B Largest structure that can be imaged given by telescope diameter  zero spacing problem

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: 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 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

D Single 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 RXJ a.k.a. G

ROSAT ATCA 40” beam Lazendic et al. 2004

Interferometer field of view = FWZP of unit telescope “Mosaicing”

1357 MHz2495 MHz

NVSS “officially” stops here ATCA NRAO VLA Sky Survey

Aharonian et al Brogan et al. 2005

March 2007 Aharonian et al Funk et al. et al MOST 843 MHz  B = ca. 2 arcmin Whiteoak & Green 1996 ASCA Source J

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 ( GHz) not shown

ALMA Specifications 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 GHz GHz WVR. Initially: GHz “3” GHz “4” GHz “6” GHz “7” GHz “8” 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 telescope Built and operated by Max-Planck-Institut fur Radioastronomie Onsala Space Observatory European Southern Observatory on Llano de Chajnantor (Chile) Longitude: 67° 45’ 33.2” W Latitude: 23° 00’ 20.7” S Altitude: 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)

To study larger-scale molecular cloud environments, degree-scale areas have to mapped. CO lines are relatively strong. Still: 1 deg 2  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 T RX and T RX not “much” worse than T RX of state-of-the-art single pixel RX Common sense requirements: Schuster et al

Columbia/CfA 1m CO J = 1  0 (115 GHz) FWHM = 8.7 arcmin FWHM eff = 30 arcmin IRAM 30m CO J = 2  1 (231 GHz) HERA 9 x 11” Factor ~160 in resolution! Schuster et al 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 Covered now by 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

An Obsolescent VLA ● The VLA was built with 1970s technology, with 1970s science goals in mind. ● There has been no significant technical upgrades since. ● Modern astronomy needs: – Full spectrum access (‘DC to Daylight’) – High resolution in time, space, frequency – Much higher sensitivity (both continuum and line) – Extensive survey capabilities (‘all things at all times in all directions’) – Much more extensive and flexible correlator capabilities ● The VLA, despite its mighty power, is not well matched to address the key science questions of the current, or next, generation.

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 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”)

EVLA-I Performance Goals ParameterVLAEVLA-IFactor Point Source Sensitivity (1- , 12 hours)10  Jy1  Jy 10 Maximum BW in each polarization0.1 GHz 8 GHz80 # of frequency channels at max. bandwidth1616, Maximum number of frequency channels5124,194, Coarsest frequency resolution50 MHz2 MHz25 Finest frequency resolution381 Hz0.12 Hz3180 (Log) Frequency Coverage (1 – 50 GHz)22%100%5 The EVLA’s performance is vastly better than the VLA’s: These fantastic improvements come at a cost less than ¼ the VLA capital investment, with no increase in basic operations cost!

What is the EVLA Not Doing? ● Expanding to provide 10 times the current best resolution (the New Mexico Array). – The ~few Kelvin brightness sensitivity at milliarcsecond resolution capability provided by the full EVLA did not pass muster at the NSF. ● Contracting to a super-compact configuration, for low surface brightness imaging (the ‘E’ configuration). – This ~$6M component could easily and quickly be done as a standalone project. ● A sub-1 GHz facility. The VLA’s optics system makes it very difficult to implement an efficient wide-band low-frequency capability. – All proposed methods to do this require extensive design and development – for which we have no budget.

The Eight Frequency Bands Band (GHz) System Temp (K) Aperture Effic. (%) IF BW (GHz) Digitization x1 2 x 2GS/s x 8bits x24 x 2 x x44 x 4 x x44 x 4 x x66 x 4 x x88 x 4 x x88 x 4 x x88 x 4 x 3 Blue = System tested and in place, or under installation. Green = Prototypes to be tested in 2007 Red = Deferred to end of project

Summary ● The EVLA is a fully funded project which will improve cm- wavelength astronomy capabilities more than tenfold. ● The project is progressing well, and is on-track for completion in 2010 (antennas and correlator), and 2012 (for all bands). ● We expect no descoping of any aspect of the hardware goals. ● Powerful new capabilities will begin to be available in 2008 – less than two years from now! ● We need new staff! Two new positions – one on staff, the other a post-doc, about to be advertised: ● With the correlator arriving soon, and with new wide-band antennas available, it’s a good time to get on board!

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 allow high fidelity imaging of 10’ sized structures up to 5 GHz

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 pulsars and 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