Spectral Line Interferometry science & principles Marc Verheijen ERIS 2013, 9-13 Sept 2013 - Dwingeloo overview ‣ Focus on science with spectral lines in radio domain • for the mm-domain, see lecture by Bremer ‣ The 21cm line of atomic hydrogen • emission / absorption • selected science topics ‣ Astrophysical (Mega)MASERs • OH, H2O, SiO, methanol • selected science examples ‣ Radio Recombination Lines • science and a few examples ERIS 2013, 9-13 Sept 2013 - Dwingeloo the HI 21-cm line of Hydrogen Predicted to be observable by Van de Hulst (1944) First detected by Ewen & Percell (1951) magnetic dipole transition ν 8 α2 1!0 = −3 gp (me/mp) RMc = 1420.40575177 [ MHz ] where gp = g-factor of proton α = fine-structure constant RMc = Rydberg constant ERIS 2013, 9-13 Sept 2013 - Dwingeloo the HI 21-cm line of Hydrogen 4 64π 3 * 2 Coefficient of emission : A10 = ν10 |μ 10| ‣ 3hc3 = 2.85 x 10−15 [s−1] * where |μ 10| = Bohr magneton 14 ‣ Thus, the radiative half-life t½ = 1/A10 = 3.51x10 [s] ≈ 11 million years This implies that even the low-density ISM can excite this transition by means of collisions. ERIS 2013, 9-13 Sept 2013 - Dwingeloo the HI 21-cm line of Hydrogen ‣ Spin temperature Tspin is defined as η1 ≡ g 1 exp ⎛ − hv 10 ⎞ = 3 exp ⎛ − 0.0682⎞ η0 g0 ⎝ kTspin ⎠ ⎝ Tspin ⎠ where g1 and g0 are the statistical weights of the two levels (3:1 for HI) For Tspin = 100 [K], η1=3η0 and ηHI = 4η0 ‣ The line opacity coefficient is given by: hν10 ⎡ ⎛ hν10 ⎞⎤ κν = η0 B01 1− exp − c ⎣ ⎝ kTspin⎠⎦ 2 c g1 ηHI ⎡ ⎛ hν10 ⎞⎤ = 2 A10 1− exp − 8πν10 g0 4 ⎣ ⎝ kTspin⎠⎦ ERIS 2013, 9-13 Sept 2013 - Dwingeloo the HI 21-cm line of Hydrogen 3hcλA10 ηHI or κν ≈ 32πk Tspin The optical depth τν follows from integration along the line-of-sight and multiplying with the line shape φ(ν) given ηHI(s) ds = NHI and φ(ν)dν = 1 los line it follows 3hcλA10 NHI τν = φ(ν) 32πk Tspin For a Gaussian line, the optical depth at line center is -2 NHI [cm ] τ0 = 17 3/2 4.19x10 Tspin [K] ERIS 2013, 9-13 Sept 2013 - Dwingeloo the HI 21-cm line of Hydrogen 20 −2 For NHI = 2x10 [cm ] : CNM : T spin ≈ 100 K → τ0 ≈1 optically thick WNM : Tspin ≈10.000 K → τ0 ≪1 optically thin ‣ Writing τν and φ(ν) in terms of velocity, and integrating over the line profile yields: NHI / Tspin τν dV = [km/s] line 1.83x1018 [cm−2 K−1] or −2 18 NHI [cm ] = 1.83x10 Tspin[K] τν dV[km/s] line ERIS 2013, 9-13 Sept 2013 - Dwingeloo the HI 21-cm line of Hydrogen The observed brightness temperature of an HI cloud can be defined and written as: −τ(ν) Tb = (Tspin − T BG)(1−e ) with TBG = temperature of background source If (Tspin − T BG) > 0 → emission line (Tspin − T BG) < 0 → absorption line TBG Tspin observer ERIS 2013, 9-13 Sept 2013 - Dwingeloo the HI 21-cm line of Hydrogen • If Tspin≫TBG (e.g. TBG = 2.73 K) : −τ(ν) −τ(ν) Tb = (Tspin − T BG)(1− e ) ≈ Tspin (1− e ) −τ(ν) or Tspin = Tb / (1− e ) −2 18 Tb [K] τν → NHI [cm ] = 1.83x10 dV[km/s] line 1− e−τ(ν) In the optically thin regime (τν≪1) : −2 18 NHI [cm ] = 1.83x10 Tb [K] dV [km/s] line ERIS 2013, 9-13 Sept 2013 - Dwingeloo the HI 21-cm line of Hydrogen ‣ For a Gaussian synthesized beam, the relation between the measured flux density and temperature is: 2 (1+z)2 1 [K] = 605.7 ⎛ ν 0 ⎞ = 605.7 [mJy] θx θy ⎝ ν ⎠ θx θy where θx, θy = FWHM in arcsec of a Gaussian beam ν0, ν = rest and observed frequency of HI line Note that the column density sensitivity can be improved by smoothing the data to a larger beam. ERIS 2013, 9-13 Sept 2013 - Dwingeloo the HI 21-cm line of Hydrogen • If TBG < Tspin < Tsrc : HI line is seen in absorption against bright source −τ(ν) Tb = (Tspin − T src)(1− e ) < 0 T T = b + T spin 1− e−τ(ν) src Tspin Tsrc TBG observer Measuring the temperatures both on/off source and on/off line, allows determination of both τν and Tspin and thus NHI . ERIS 2013, 9-13 Sept 2013 - Dwingeloo the HI 21-cm line of Hydrogen Taking cosmological effects into account: −2 18 2 NHI [cm ] = 1.83x10 (1+z) Tb [K] dV [km/s] line 2 5 Dlum [Mpc] MHI [Msun] = 2.36x10 Sv [Jy] dV [km/s] 1+ z line More details on the radiative process of the HI line can be found in many places online. E.g.: http://www.cv.nrao.edu/course/astr534/HILine.html http://astro.berkeley.edu/~ay216/08/NOTES/Lecture10-08.pdf ERIS 2013, 9-13 Sept 2013 - Dwingeloo HI disks reach far into the Dark Matter halos NGC 2403 NGC 6946 Fraternali et al (2001) Boomsma (2007) NGC 5055 Messier 31 Westerbork from HI data Battaglia et al (2005) Braun et al Cosmic Flows, Marseille, June 2013 typical HI data products HI column density map velocity field luminosity profile radial HI distribution position-velocity diagram Begeman (1987) Begeman dark matter ‘conspires’ with baryons to keep outer rotation curve flat Cosmic Flows, Marseille, June 2013 major HI imaging surveys Targeted Surveys of selected samples: • WHISP (350) northern spirals with F>100 mJy • VIVA (53) SFR-selected Virgo spirals • UMa (85) Ursa Major group with MB< -18.5 • THINGS (34) HI follow-up of SINGS sample • LittleTHINGS (42) Local dIm and BCDs • FIGGS (47) Faint Irregular galaxies • ATLAS3D (166) HI follow-up of northern early-types • HALOGAS (22) the deepest HI survey of spirals • VLA-ANGST (36) HI follow-up of HST/ACS survey Blind Surveys of different environments: • Coma (WSRT) • Perseus-Pisces (VLA) • Ursa Major (VLA) • CVn (WSRT) ERIS 2013, 9-13 Sept 2013 - Dwingeloo 21cm spectral-line imaging - Dwarfs Swaters et al (2002) Cosmic Flows, Marseille, June 2013 21cm spectral-line imaging - Ursa Major Verheijen & Sancisi (2001) Cosmic Flows, Marseille, June 2013 21cm spectral-line imaging - Ursa Major Verheijen & Sancisi (2001) Cosmic Flows, Marseille, June 2013 21cm spectral-line imaging - massive spirals 21% decline Noordermeer et al (2005) Cosmic Flows, Marseille, June 2013 21cm spectral-line imaging - THINGS 12% decline de Blok+ (2008) de Cosmic Flows, Marseille, June 2013 21cm spectral-line imaging - THINGS de Blok+ (2008) de Cosmic Flows, Marseille, June 2013 21cm spectral-line imaging - perturbed disks perturbed velocity fields perturbed velocity bars, warps, lopsided kinematics, interactions kinematics, lopsided warps, bars, Cosmic Flows, Marseille, June 2013 HI scaling relations HI to optical diameters (UMa) optical diameter 10 ) ⦿ 9 (M Verheijen & Sancisi ‘01 HI HI diameter Log M Verheijen & Sancisi ‘01 & Sancisi Verheijen 10 8 Although <NHI> within D25 varies significantly, it is nearly -2 invariant within DHI (1 M⦿pc ). diameter (kpc) ERIS 2013, 9-13 Sept 2013 - Dwingeloo HI science topics • Galactic and galaxy structure & kinematics. - the ISM, warps, lopsidedness, rotation curves, angular momentum, non-circular motions... • Accretion and depletion of gas onto galaxies. - minor mergers, cold accretion, ram-pressure stripping, outflows and feedback... • Formation of galaxies and large scale structure. - HIMF, major mergers, spin alignments, void population, cosmic web, TF distances... • Cosmic evolution of gas in galaxies. - ΩHI(z), gas fractions vs mass, role of gas in downsizing... ERIS 2013, 9-13 Sept 2013 - Dwingeloo slopes of outer rotation curves slope between 2 hdisk and the last measured point Log( V2h / Vlmp ) S2h,lmp = Log( R2h / Rlmp ) S>0 : rising S=0 : flat S<0 : declining Begeman et al (1991) Cosmic Flows, Marseille, June 2013 slopes of outer rotation curves Casertano & van Gorkom Verheijen & Sancisi Noordermeer et al Swaters et al Spekkens & Giovanelli Cosmic Flows, Marseille, June 2013 Rotation curves and the Tully-Fisher relation rising flat declining Rotation curves beyond the optical radius (R25) provide the relevant kinematic measure. Extent of Hα rotation curves is insufficient N = 31 N = 31 N = 22 to measure Vflat α = −3.4 α = −3.4 α = −4.3 consistently. σ = 0.56 σ = 0.71 σ = 0.32 MV01 Verheijen ‘01 W20 Vmax Vflat ERIS 2013, 9-13 Sept 2013 - Dwingeloo Oosterloo et al 2007 role and fate of gas in galaxy (trans)formation Fraternali et al 2002 Fraternali et al Baldry et al 2004 Oosterloo & van Gorkom 2005 Gorkom & van Oosterloo ERIS 2013, 9-13 Sept 2013 - Dwingeloo Fueling the Blue Cloud 25% of galaxies undergo minor mergers sustaining star formation - building up stellar mass Evidence for cold accretion or Galactic Fountain / Fallback? Sancisi+ A&A Rev. 2008 Rev. A&A Sancisi+ M 101 Oosterloo+ 2007 ERIS 2013, 9-13 Sept 2013 - Dwingeloo Warps and stellar streams Is there a link? NGC 5055 NGC 5907 Battaglia+ 05 R. Jay GaBany R. R. Jay GaBany R. NGC 4013 Shang+98 Bottema 95 R. Jay GaBany R. ERIS 2013, 9-13 Sept 2013 - Dwingeloo Crossing the Green Valley gas-stripping in the Virgo cluster NGC 4522 VLA NGC 4388 WSRT Oosterloo & van Gorkom, 2005 Gorkom, & van Oosterloo Kenney et al, 2004 et al, Kenney Ram-pressure induced (and truncated?) star formation NRF/NWO workshop, 18-19 Oct 2012 - Cape Town Passive galaxies on the Red Sequence ? Atlas3D : HI imaging of 166 early-types 1/3 detected Lower density regions : extended and regular HI disk 40% of E’s in field Higher density regions : clumpy and unstructured Serra et al. 2011 al. et Serra NRF/NWO workshop, 18-19 Oct 2012 - Cape Town Environmental dependence of gas content Virgo Ursa Major Chung et al 2009 Very Large Array Verheijen & Sancisi 2001 Westerbork VIVA : VLA Imaging of Virgo galaxies in Atomic gas ERIS 2013, 9-13 Sept 2013 - Dwingeloo HI, ICM, SFR, SP interrelations Coma Abell 2670 Poggianti & van Gorkom, 01 van Gorkom, & Poggianti Bravo-Alfaro+ 01 Bravo-Alfaro+ ERIS 2013, 9-13 Sept 2013 - Dwingeloo Void Galaxy Survey Kreckel+ 11 A pilot study of 15 void galaxies.