Molecules and atoms at high resolution

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1 Molecules and atoms at high resolution Anita Richards UK ALMA Regional Centre Jodrell Bank Centre for Astrophysics University of Manchester Many thanks to Rob Beswick and other ALMA/JBCA/e-MERLIN colleagues

2 Spectral line science Kinematics Conditions Composition, evolution Fundamental physics Morphology, excitation conditions e.g. shocks Chemistry Temperature, pressure, number density, radiation Gas distribution Doppler velocities; + proper motions 3D dynamics Magnetic field, Maser physics... Single dish domain opens up to high-res interferometry NB formulae used here are in standard text-books

3 Origins of spectral lines EU Upper E EL Lower Absorption BLU Stimulated emission BUL Einstein coefficients Transition emits or absorbs photon at = E/h Spontaneous emission rate depends on temperature Spontaneous emission AUL i.e. Boltzmann distribution of molecule energies Absorption rate also depends on radiation field Energy density U

4 Origins of spectral lines EU Upper E EL Lower e.g. Boltzmann distribution of molecular energies Absorption rate also depends on radiation field Absorption BLU Stimulated emission BUL Spontaneous emission rate depends on temperature Spontaneous emission AUL Energy density U Stimulated emission needed to balance eq. dimensions NUAUL + NUBULU = NLBLUU NU / NL = gu /gl exp(-h /kbt) in LTE = ratio of statistical weights x Boltzmann distribution

5 Coefficients' relationships [ BUL g L B LU AUL gu BUL e h / k B T ] 1 = c 3 8 h 3 e h / k B T 1 Derived using thermal equillibrium But T- and U -dependent terms cancel BLU / BUL = gu / gl BUL/AUL = 3/8 h Probability of stimulated emission 3 Masers are commoner at radio wavelengths

6 Dark, cool clouds Rule of thumb for 'spontaneous' emission, wavelength kbt h so T 0.014/ Weak radiation field in dark clouds Need collisional excitation of upper state of transition Also must exceed critical density: collision rate = AUL High emission-coefficient transitions need high n e.g. CO J 6-5, =0.43 mm, T 33 K e.g. CO needs n > m-3 For high optical depth emission, Tb ~ Tk LTE line opacity coefficient, line profile ( ) = c2 8 2 [ h / k B T N L AUL 1 e ]

Optical depth Optical depth = ds Optically thin

e- Intensity reduction (I0 I a)/i0 = 1 e - If <<1,

7 Optical depth Optical depth = ds Optically thin emission, source func S Integrated absorptivity x path length at Through medium of depth s Ie = S(1 e ) ~ S (for 0 < <<1) - s << 1 Ie Absorption Ia =I0 e- Intensity reduction (I0 I a)/i0 = 1 e - If <<1, (I0 I a)/i0 ~ (I0 I a)/i0 approaches 1 for large Ia I0 >> 1

8 Line profiles Uncertainty principle: E t ℏ Excited lifetime t finite E = h is broadened Lorentzian line profile Atmospheric ozone (APEX) Seen in pressure-broadening Thermal Boltzmann distribution Doppler = 0/c x (2kBT/m) Molecule mass m, rest freq 0 Gaussian line profile ( ) exp[ ( v/ D)2] Complicated by bulk motions HI (Lehtinen+2011)

9 Line shapes Zuckerman 1987

Thermal emission Radio emission from transitions with small E

quantized C O Linear spacing of low-energy transitions for rigid

Isotopomer shifts Ions (splits) C O 13 16 C O 12 16 + C O 12 16

10 Thermal emission Radio emission from transitions with small E Molecular rotation Asymmetric, polar species Angular momentum is quantized C O Linear spacing of low-energy transitions for rigid rotators Rotational transitions within a given vibrational state Isotopomer shifts Ions (splits) C O C O C O J GHz 441

11 Radio transitions Complex molecules have more, close transitions NH3 'symmetric top' Spin states split lines Many transitions around 24 GHz Useful thermometer Energy subdivided between states Weaker individual transitions Wilson+1993

12 Molecules in space >150 molecules identified Largest include HCnN, where n 11 and C60 fullerenes EVLA comissioning Circumstellar envelope

13 Chemistry reveals CepA E double YSO with barely-resolved wind and disc? Contours SMA 875 m, VLA 3cm, resolution ~ 750 AU Spectra show two groups of different lines Multiple protostars at different evolutionary stages? Brogan et al. (2007)

14 Differentiate jet layers High-density, central condensation (Disc?) Shock head Multi-species, multiple lines disenstangles abundance/ excitation effects Shock wings turbulent entrainment L1157 Class 0 protostellar jet (Bachiller+ 2001)

15 Chemical pathways Formation of methyl formate HCOOCH3 Why >25x abundance of isomers acetic acid, glycoaldehyde? Gas phase formation? (Horn+2004) Formaldehyde or CO+ protonated methanol? Formaldehyde + protonated formaldehyde? Methyl ion + formic acid? etc. then HCO(H)OCH3]+ + e- HCOOCH3 + H Lab experiments, model calculations Predict abundances of precursors and sideproducts Compare with observations

16 Chemical pathways Formation of methyl formate HCOOCH3 Why >25x abundance of isomers acetic acid, glycoaldehyde? Gas phase formation? (Horn+2004) Formaldehyde or CO+ protonated methanol? Formaldehyde + protonated formaldehyde? Methyl ion + formic acid? etc. Lab experiments, model calculations Predict abundances of precursors and sideproducts Hatchell+1998 Compare with observations then HCO(H)OCH3]+ + e- HCOOCH3 + H Insufficient precursors/byproducts for proposed pathways Grain surface reactions (Occhiogrosso+2011)? Model OK for dark clouds but not hot cores/corinos...

17 RNA precursor? Glycoaldehyde 2nd isomer GBT detection in Sgr B2 Hollis Sugar in space! Acetic acid is the 3rd isomer

18 Chemistry of life Biologically interesting molecules Methyl Cyanide Glycine? Caffeine?

19 The first galaxies CO lines at all redshifts CMB hotter Metallicity, T, kinematics Fine structure constant Higher transitions bright CII rest mm Main Milky Way coolant BR z=4.43 CII redshifted to 349 GHz ALMA commissioning data

20 Atomic transitions Electronic Recombination lines at radio freqs E 1/n2 1/( n+ n)2 Closely spaced, low-energy, high-n transitions Can observe simultaneously and stack e.g. H(~90 110) (~8 10 GHz) Close to LTE, minimal collisional broadening Continuum free-free optically thin Line ratios provide a thermometer [ T e GHz v km s 1 1 TC TL ] 0.87

21 Te gradient in Galactic disc 76 Galactic HII regions H91, H92, He91, He GHz free-free continuum Te gradient 287(46) K kpc-1 Decreasing metallicity? Quireza et al. 2006

22 Neutral Hydrogen H spin flip: 21-cm (1420 MHz) line Low probability: t1/2 ~ 11 million yr Spin temperature defined by NU/NL gu/gl exp[-h /kbts] Critical density very low, << 10-6 m-3 h /kbts ~ at Ts =150 K so 1 exp[- h /kbts] ~h /kbts Emission from nh neutral H atoms per m-3 = 3c2/32 AUL nh (h/kbts) ( ) If << 1, integrated H emission brightness Tb ~ Ts But 1/Ts in Rayleigh Jeans limit so Tb independent of Ts Column density integrated over line profile in km s-1 NH ~ Tb dv m-2

23 Galactic rotation curve Clemens et al Kriscunias & Yenne (wikipedia)

24 Kinematic distance VLSR = S [(R/R )VR VR ] at D from R from Gal. centre D = CR ± [R2-R 2( 1 C2)] S = sin(l ) cos(b) C = cos(l ) cos(b) Ambiguity if R < R Peculiar motions Older stars, binary ejections... Rotational velocity VR = 220 km s-1 R = 8.5 kpc l D R VR

25 Sensitivity and resolution Flux density per beam S = 2kB Tb / 2 HI thermal emission at 150 K Most sensitive arrays at 1.4 GHz are GMRT, EVLA (soon MeerKAT, ASCAP) Area on sky = 5x10-29x0.212 / 2x1.38x10-23x150 sr Equivalent to beam size 123x (S(mJy)/T) = 4.7'' Cannot currently observe HI with sub-arcsec resolution Collecting area 0.05 km2 5 ~5 mjy/beam per ~6 km s-1 in ~half to a whole day Need SKA, ~20x area, 50+ km baselines CO J 3-2 with full ALMA, 850 m, T 30 K BJ3-2 = 0.04'' for 1 mjy/beam sensitivity, in <1 hr

26 Absorption Can probe HI/other cm thermal lines at mas resolution Absorption against bright background continuum Non-thermal sources have Tb(radio) > 104 K Gas must be in front of continuum NB absorption only seen where there is background... Blueshifted must be expansion/outflow, redshifted infall Tspin is determined by T21cm, Tkinetic & TLy Dark regions: Ts ~ Tk also in bright regions (near AGN) if n > 109 m-3 Low density, bright regions: Ts > Tk but not by much, as HI,absorption 1/Ts/ V Absorption preferentially reveals cooler clumps

27 HI absorption Radio continuum greyscale HI absorption contours Gallimore+99

28 Absorption measurements Continuum + line IC = ln [( IC IL)/IC) HI column density NHI = Ts (v) dv m-3 Line after subtraction IL Velocity v km s-1 See Gallimore et al. (1999) for more details

29 Moment maps 0 total intensity 1 velocity 2 velocity dispersion Dumas+2010

30 HI emission Mundell '' resolution CO emission Dumas NGC 4151 HI absorption Mundell mas resolution

31 Example: M82 H1 absorption Continuum plus line 14th September 2007 ERIS Bonn 2007 M82 HI (Wills, Pedlar et al) 31

32 M82 H1 Optical depth M82 HI 14th September 2007 Optical Depth ERIS Bonn

33 Spectral surveys Single dish? Interferometers with a large field of view Small dishes Focal plane arrays Large bandwidth Really large (many degree) areas only practical at cm- Simpler, but limited by noise/rfi and confusion WSRT Apertif, MeerKAT, ASCAP... SKA Often 'wedding cake' strategy Small deep field; broader, shallower fields

34 HI survey from here to z 0.25 ASCAP Wallaby 4 km s-1, 30'' resolution 500,000 galaxies in a year Apertif Northern counterpart Verheigen+09 Very time-consuming join a large project! Braun+ 2004

CO at z ~ 7 MeerKAT MESMER Heywood+2011 CO J 1-0 6.95 < z < 9.

35 CO at z ~ 7 MeerKAT MESMER Heywood+2011 CO J < z < GHz Resolution <1'' 100 km s-1 Square degree in 340x4.7 hr

36 Microwave Amplification of Stimulated Emitted Radiation Tx = (h /kb) ln (NL/NU gu/gl ) If NU/NL > 1 Excitation temperature Tx < 0 Opacity k is negative Incoming/ambient radiation amplified exponentially I S0exp-k 2r Pump collisional (H2O) or radiative (OH, MIR) e.g. OH 2 3/2 J 3/2 overpop'ed Quenched when CR > BUL n >5x1015 m-3 for H2O, 1000 K

High-precision cosmology: NGC 4258 22-GHz continuum jet Water masers in warped Keplerian disc (Miyoshi, Diamond, Herrnstein.

37 High-precision cosmology: NGC GHz continuum jet Water masers in warped Keplerian disc (Miyoshi, Diamond, Herrnstein...) H2O clumps in hostile environment VLBI resolution <1 mas / 0.03 pc Proper motions 3D kinematics Best evidence for AGN black hole: compact object of M Precise distance: 7.2 Mpc

38 Multiple transitions in W3(OH) Star-forming region at ~2 kpc Blue: OH 6.0 GHz Red/orange: 1.6 GHz OH Wright+ 04 Alignment accuracy of 2-20 mas 3100 AU filament OH 4.7 GHz Methanol 6.7 GHz Etoka+05 Harvey-Smith+06 dvlsr 120 km/s/pc Disc? Shock?

Methanol, OH co-propagation models Based on Green+07 Cragg+02, 05 W3(OH): diagnostics for different regions 1.6, 1.6 6 GHz OH mainlines associated: T 50-75 K 4.7, 1.

39 Methanol, OH co-propagation models Based on Green+07 Cragg+02, 05 W3(OH): diagnostics for different regions 1.6, GHz OH mainlines associated: T K 4.7, 1.7 sattelite line association: T>100 K, higher noh OH CH3OH separation 15 mas but similar V (T)- why? 1.6 GHz OH quenched at lower nt than CH OH Szymczak CH3OH evaporates before OH? needs deeper N

40 Masers in circumstellar envelopes VX Sgr Locations consistent with excitation temperatures? OH 1612 MHz (TE few K), at >50 R H2O (TE~650 K), at 5-30 R SiO (TE>2000 K) within 4 R OH mainlines ( MHz) can overlap H2O and 1612 MHz masers

41 Ex pa ns ion ve l oc i ty i nc re as es wi th ra d iu s Concentric shells V

42 Water masers measurements Spatial 2-D Gaussian component fitting Position accuracy ( B/s.n.r.) e.g. B = 10 mas I = 1 Jy, rms = 20 mjy pos = 10/50 = 0.2 mas Deconvolved spot size s s = 2 pos Area =( /4 ln2)s2 Tb = S 2/ (2kB ) ~ 1011 K S Per 16x0.1 km s-1 channels averaged

43 Components trace steam clouds E d u o cl r e t e m dia RcloudRSG AU Brighter spots are smaller

component size per channel Brighter maser

44 Beaming from spherical clouds L Amplification-bounded beaming s L = Measured size of multi-chan clouds Observed (beamed) size s Measured component size per channel Brighter maser (peak Iv), tighter beam s 1/sqrt [ln(iv)] log(s) v. log [ln(iv)] S Per

45 Beaming from shocked slabs Shock 'into page' Maser propagates perpendicular to shock Pump photons escape orthogonally Entire surface emission is amplified Matter bounded beaming apparent size ~ actual size (s ~ L) log(s) v. log [ln(iv)] U Ori

46 Light curves (AAVSO) U Ori U Her, U Ori also OH and Ha flares (Etoka, Rudnitskj et al.) U Her IK Tau RT Vir S Per

Maser properties reveal wind disturbances Brighter spots smaller ~spherical clouds Smoother outflow No clear shrinking Shocked regions Pulsations?

47 Maser properties reveal wind disturbances Brighter spots smaller ~spherical clouds Smoother outflow No clear shrinking Shocked regions Pulsations? Flares? Based on Richards Elitzur & Yates 2010 Elitzur Hollenbach & McKee 1992 Also see books: Elitzur 1992, Gray 2011 for topics not covered e.g. saturation

Masers around evolved stars from kinematics to physics

Masers around evolved stars from kinematics to physics Anita Richards UK ARC, JBCA, Manchester with thanks to Al-Muntafki, Bains, Bartkiewicz, Diamond, Elitzur, Etoka, Gray, Humphreys, Murakawa, Rosa-Gonzalez,