Atacama Large Millimeter Array

Transcription

1 Atacama Large Millimeter Array Leonardo Testi (ESO/INAF) è Submillimetre astronomy and ALMA in context Ø ALMA science: the cool side of the universe Ø Submm telescopes single dish vs interferometers è ALMA status, science, future evolution Ø ALMA goals and design Ø ALMA construction, Early Science and development è ALMA studies of star and planet formation Ø Star formation: chemistry, low and high mass sf Ø Protoplanetary disks: structure, evolution, chemistry

2 Part I Submillimetre astronomy and ALMA in context Leonardo Testi (ESO/INAF) è ALMA science: the cool side of the universe è Submm telescopes single dish vs interferometers

3 Millimeter wavelengths: thermal continuum è Thermal emission: Ø near-ir & visible: hot matter 1000K K Ø Far-IR & millimeter: cold matter 3K-100K Ø : m=hc/3kt~0.5/t cm Dust: m=hc/(3+ )kt~0.3/t cm T~20-100K Av<1 T~8-15K Av>1 Dust peak ~ 0.3mm CBR peaks at 1.76 mm

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6 Molecular clouds and star formation

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9 From clouds to stars and planets -3 Log Density (cm ) Disco Stella Terra Nucleo Nubi Log Size (pc)

10 Planet Formation SIMULATION: M planet / M star = 1.0 M Jup /.5 M sun Orbital radius: 5AU Distance: 50pc from Sun ALMA Williams et al. HST Wolf + Simulation of nearby PP disk (e.g.. TW Hy) 5AU =

11 Millimeter wavelengths: line emission è Molecular lines: Ø Rotation Ø Vib (Stretching and Bending) Ø Electronic

12 Molecular rotational lines è Molecular lines: Ø Rotational spectra of molecules J=0,1,2... µ=m1*m2/(m1+m2) è Selection rules: Ø Permanent dipole moment (H2, C2, O2, CH4, C2H2 not ok) Ø J=1 (only adjacent levels) Ø Symmetric molecules => quadrupole transitions ( J=2)

13 Molecular rotational lines è Examples of diatomic molecules: CO (µ=7) and H2 (µ=0.5) è CO levels are closely spaced Ø Smaller E => long wavelength transitions, low excitation Ø J=1-0 -> =115GHz, =2.7mm Ø J=2-1 -> =230GHz, =1.3mm Ø J=3-2 -> =345GHz, =0.87mm è H2 levels are further away, only quadrupole transitions allowed Ø MIR, high excitation lines

14 Molecular rotational lines è Molecular lines: symmetric top rotators Ø Molecules with an axis of three-fold or higher symmetry Ø Examples: NH3,CH3CN,CH3CCH Ø Quantum numbers: J and projection on axis K (K<=J) Ø Selection rules: J=1 (only adjacent levels), K=0 Ø K=J levels are metastable Ø Example: ammonia inversion transitions

15 Molecular rotational lines è Molecular lines: asymmetric rotators Ø Quantum numbers: J and projections on two axes K- and K+ Ø Complicated spectra Ø Example: H2O

16 Interstellar molecules H 2 HD H 3 + H 2 D+ CH CH + C 2 CH 2 C 2 H *C 3 CH 3 C 2 H 2 C 3 H(lin) c-c 3 H *CH 4 C 4 c-c 3 H 2 H 2 CCC(lin) C 4 H *C 5 *C 2 H 4 C 5 H H 2 C 4 (lin) *HC 4 H CH 3 C 2 H C 6 H *HC 6 H H 2 C 6 *C 7 H CH 3 C 4 H C 8 H *C 6 H 6 OH CO CO+ H 2 O HCO HCO+ HOC+ C 2 O CO 2 H 3 O+ HOCO+ H 2 CO C 3 O CH 2 CO HCOOH H 2 COH+ CH 3 OH CH 2 CHO CH 2 CHOH CH 2 CHCHO HC 2 CHO C 5 O CH 3 CHO c-c 2 H 4 O CH 3 OCHO CH 2 OHCHO CH 3 COOH CH 3 OCH 3 CH 3 CH 2 OH CH 3 CH 2 CHO (CH 3 ) 2 CO HOCH 2 CH 2 OH C 2 H 5 OCH 3 (CH 2 OH) 2 CO NH CN N 2 NH 2 HCN HNC N 2 H + NH 3 HCNH + H 2 CN HCCN C 3 N CH 2 CN CH 2 NH HC 2 CN HC 2 NC NH 2 CN C 3 NH CH 3 CN CH 3 NC HC 3 NH + *HC 4 N C 5 N CH 3 NH 2 CH 2 CHCN HC 5 N CH 3 C 3 N CH 3 CH 2 CN HC 7 N CH 3 C 5 N? HC 9 N HC 11 N NO HNO N2O HNCO NH2CHO SH CS SO SO+ NS SiH *SiC SiN SiO SiS HCl *NaCl *AlCl *KCl HF *AlF *CP PN H 2 S C 2 S SO 2 OCS HCS+ c-sic 2 *SiCN *SiNC *NaCN *MgCN *MgNC *AlNC H 2 CS HNCS C 3 S c-sic 3 *SiH 4 *SiC 4 CH 3 SH C 5 S FeO

17 Interstellar molecules

18 Complex Organic Molecules Detected Not (yet) detected Acetic acid Di-methyl ether Glycine Purine Ethanol Sugar Methyl cyanide Methyl formate Pyrimidine Caffeine How far does chemical complexity go? Can we find pre-biotic molecules in Disks? Benzene Ethyl cyanide Based on Ehrenfreund 2003

19 No. 2, 2000 ANRV320-AA45-13 TESTING YSO ENVELOPE MOD ARI 26 July :49 Galactic latitude ANRV320-AA ARI 24 July : log Tmbdv (K km s 1) Galactic longitude Figure b Declination offset (arcsec) Map of the molecular gas in the Orion-Monoceros region. Color scale and contours show the 106 velocity-integrated intensity of the J = 1 0 CO line (Wilson et al. 2005). Orion 50 A (lower region), Orion B (middle right), and Mon R2 (slightly left of center) each contain a total gas mass 105 M#. The angular size of 10 corresponds to 80 pc at the mean distance of the 0 Orion complex. The Mon R2 region appears to be several hundred parsecs farther away than the Orion clouds. Annu. Rev. Astro. Astrophys : Downloaded from arjournals.annualreviews.org by University of Leiden - Waleus Library on 02/24/10. For personal use only. Annu. Rev. Astro. Astrophys : Downloaded from arjournals.annualreviews.org by University of Leiden - Waleus Library on 02/22/10. For personal use only. 5 ENOCH E of (half Declination offset (arcsec) Declination offset (arcsec) For a log-normal distribution, the mass-weighted median density the mass 850 µm is at densities above and below this value) is ρmed = ρ exp(µx ), whereas the mass weighted mean density is &ρ' M = ρ exp(2µx ). Based on 3D unmagnetized simulations, Padoan, Jones & Nordlund (1997) propose that µx 0.5 ln( M2Right ). Other ascension offset (arcsec) 3D simulations with magnetic fields (β = ) have found µx for M 5 10 (Ostriker et al. 2001). These models confirm that the mean density 100 one-to-one 100 contrast generally grows as the turbulence level increases, but find no c d relationship between µx and M [or the fast magnetosonic Mach number, M F large scatter at large M is because the flow is dominated σv /(c s2 + va2 )1/2 ]. The by(a) a small number of large-amplitude modes (i.e., large cosmic variance), some of which Theory of Star Formation Figure 3. CARMA 230 GHz maps of Serpens FIRS 1 for short baseline data only 100 (B, C configurations; panel (c)). Contours in panel (b) are (2,4...10,15,20, ) tim N24σ H+ Jand = 1 6σ 0, respect C18O J = 1 in0 panels (a) and (c) are similar but start at lower right). Contours in scale in each panel. The direction of the 3.6 cm jet (Rodrı guez et al. 1989; Curiel Right ascension offset (arcsec) Figure 7 (a) A deep optical image of the dark globule Barnard 68 (Alves, Lada & Lada 2001) along with contour maps (b d ) of integrated intensity from molecular emission lines of N2 H+ (contour levels: by 0.3 K km s 1 ), C18 O ( by 0.1 K km s 1 ), and 850-µm dust continuum emission (10 70 by 10 mjy beam 1 ). Molecular data, with an angular resolution of 25 arcsec, are from Bergin et al. (2002) and dust emission (angular resolution of 14.5 arcsec) from Bianchi et al. (2003). also Caselli et al. 1999). From the abundance profile it is estimated that the CO and CS abundance traces a large dynamical range with declines of at least 1 2 orders of magnitude in the core centers relative to the lower density core edge, while the abundances of nitrogen molecules either stay constant or decay more slowly. The interpretation of selective freeze-out, where molecules exhibit different behavior in Right ascension offset (arcsec) Cold Dark Clouds 371

20 NGC 7331 (Regan et al. 2004) 20

21 Starburst galaxy

22 The Early Universe Hubble Deep Field North

23 History of Galaxies è Measuring redshift (and more) using CO, [CII] or [OI]

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25 Radio telescopes è The reflector concentrates the plane parallel waves in the focal position where they will be received è To work effectively a reflector need to be in the far field Aperture Pattern of transmitted emission Eff Power pattern P= Eff 2 Circular aperture => P~Airy disk

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31 mm radio telescopes è Large collective area for sensitivity è Large diameter also important for angular resolution è High precision reflective surface è High altitude to reduce atmospheric absorption è Heterodyne receivers offer high spectral resolution

32 Atmospheric transmission

33 Typical high-frequency radio telescope

34 Example: IRAM 30m telescope è 30m diameter è Pico Veleta 2900m, Sierra Nevada near Granada in Spain (latitude +37) è Surface accuracy 50µm (in optimal conditions) è Frequency range GHz (0.8-4mm) è Angular resolution 35-7

35 Example: the APEX telescope è 12m diameter è Atacama Pathfinder EXperiment modified ALMA prototype antenna è Chajnantor plateau 5000m, northern Chile (latitude -22) è Surface accuracy 20µm (in optimal conditions) è Frequency range GHz ( mm) è Angular resolution 30-6

36 Interferometers PdBI VLA ALMA VLTI

37 Young experiment è Angular fringe spacing is given by lambda/d è This is essentially the way optical/ir interferometers work with direct fringe detection

38 Receivers è Optics (warm/cold) Ø Reimaging Ø Waveguides è LO mixing Ø LO input Ø Mixer è IF e Sidebands X filtering

39 Fringe pattern è 2 element interferometer defined by the vector b è Monochromatic plane wave from direction s è Signals from the two antennas are multiplied and integrated by the correlator è The time dependent response r(t) of the system is given by: (assuming to integrate over a time step >1/, by shorter than g (t) variations): r(t)=<v 1 cos(2 (t- g (t)))v 2 cos(2 t)>=v 1 v 2 cos(2 g (t)) r(t) is modulated as a cosine function: Fringe Pattern

40 Response to an extended source è In the case of an extended source one needs to consider: Ø Power pattern of each antenna Ø Different portions of the source correspond to different delays è Assumptions: Ø Far field (point source=plane wave) (NB: not true for some SS applications!) Ø Source is incoherent (sum of plane waves) Ø Identical antennas, i.e. same P(, ) s 0 is the pointing direction of the interferometer with delay b s 0 /c, each point on the source has a different delay b s/c= b (s 0 +â)/c

41 Visibility Insert the delay: Definition of Visibility: The signal from the interferometer can be written as:

42 Visibility and FT What are we measuring? Go back to visibility Standard notation: b=(u,v,w); S=(x,y,z) (in the system of s 0 ) b S/c=ux+vy+wz; b S 0 /c=w; z 2 =1-x 2 -y 2 ; d =dxdy/z then: If (x,y)<<1, then w(z-1)~w(x 2 +y 2 )/2~0 e z~1, then: In this approximations, V(u,v) is the Fourier Transform of P(x,y)I(x,y)

43 Interlude: FTs è Sharp edges need more Fourier components... è A gaussian, is a gausssian, is a gaussian...

44 Interlude: FTs è What is this?

45 Interlude: FTs è What is this?

46 Interlude: FTs è Amplitudes and phases

47 Imaging è Normally you would like to estimate the brightness disctribution on the sky rather than working with visibilities: Visibilities are sampled on an irregular and incomplete grid by the interferometer. This is described by the sampling function S(u,v) (this function normally includes also the weights of each measurement, related to the errors). Imaging is the art of estimating the best I(x,y) from S(u,v) e V(u,v). W(u,v) is an arbitrary weight function. Using the FT properties:

48 Gridding and deconvolution I w (x,y) is the convolution between [P(x,y)I(x,y)] and D(x,y) D(x,y) is the fourier transform of S(u,v)W(u,v), called Dirty Beam (I w is the Dirty Image ). V(u,v) and S(u,v) An appropriate W(u,v) can modify D w (x,y) FT Non linear operation! I w (x,y) and D w (x,y) Deconv I (x,y)

49 mm Interferometers (u,v) coverage OVRO mm Array, 6 Antennas L-configuration single integration L-Configuration few hrs of observations Final coverage: a few hrs in both the L and H configurations N.B. (u,v) coverage is not uniform

50 mm Interferometers (u,v) coverage Very Large Array, 27 Antennas, 1.5h of observing time! N.B. (u,v) coverage is still not uniform. Critical parameters: Long baselines Short baselines Number of (u,v) points (u,v) coverage distribution

51 ALMA è Provide a transformational jump as compared to previous generation instruments è Site: atmospheric transparency and phase stability è Antennas: better telescopes and large collective area è Receivers: close to quantum noise limit, wide bandwidth è Angular resolution & Image fidelity

52 Atacama Large Millimeter Array è At least 50x12m Antennas è Frequency range GHz (0.3-10mm) è 16km max baseline (<10mas) è ALMA Compact Array (4x12m and 12x7m) 1. Detect and map CO and [C II] in a Milky Way galaxy at z=3 in less than 24 hours of observation 2. Map dust emission and gas kinematics in protoplanetary disks 3. Provide high fidelity imaging in the (sub)millimeter at 0.1 arcsec resolution

53 mm Interferometers (u,v) coverage è è Current mm interferometers offer typically ~10 4 visibility measurements in several hours, the VLA delivers ~10 5 visibilities per hour ALMA will improve by almost two orders of magnitude