The Distance Scale in the Gaia Era

The Distance Scale in the Gaia Era G. Clementini INAF - Osservatorio Astronomico, Bologna Acknowledgements: A. Brown, C. Cacciari, M. Marconi, V. Ripepi, DPAC, ESA, EADS Astrium G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 1

Layout of the lecture - The astronomical distance scale: - basic concepts - typical distances - Direct measure: trigonometric parallax - Indirect measure: Distance Indicators - Primary indicators - Secondary indicators - Tertiary indicators - Primary Indicators - The distance to the Large Magellanic Cloud - Gaia G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 2

The Hubble Law In standard big bang cosmology the universe expands uniformly; and locally, according to the Hubble law, v = Ho x d where v is the recession velocity of a galaxy at a distance d, and Ho is the Hubble constant, the expansion rate at the current epoch. Freedman et al. 2001, Ap.J. 533, 47 G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010

Typical astronomical distances in time Earth - Sun ~ 8 m ~ 1 A.U. Earth - Pluto ~ 660 m ~ 39.4 A.U. Sun - Alpha Centauri ~ 4.2 l.y. ~ 1.3 pc Sun - Iades ~ 150 l.y. ~ 50 pc Sun - Galactic Center ~ 25.000 l.y. ~ 8 kpc p Sun -LMC ~ 50 kpc Sun - Andromeda ~ 2.5 x 10 6 l.y. ~ 770 kpc Sun - Locale Group ~ 3.3 x 10 6 l.y. ~ 1 Mpc Sun - M81 and Sculptor clusters ~ 6-10 x 10 6 l.y. ~ 2.5 Mpc Sun - M101 cluster ~ 15-20 x 10 6 l.y. ~ 5.4 Mpc Sun - Virgo cluster ~ 40 x 10 6 l.y. ~ 12 Mpc Sun - Coma cluster ~ 300 x 10 6 l.y. ~ 92 Mpc I m - M = - 5 + 5logd pc distance modulus 3 G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010

Distance Ladder Given the range spanned by the astronomical distances, the astronomical distance ladder is made by overlapping techniques and distance indicators, starting from the most closeby that we can calibrate directly." Gaia TRGB 4

Milky Way Direct methods: trigonometric parallax 0<d<100 pc Indirect methods:: - Proper motions + statistical parallax 0-500 pc - Main Sequence Fitting open clusters 40-7000 pc globular clusters 3000-10000 pc Beyond the Milky Way Spectroscopic and photometric parallax > 10000 pc Distance indicators primary secondary tertiary 500-3 10 7 pc 2 10 5-10 9 pc and beyond 5

Trigonometric Parallax Gaia Hipparcos 7 G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010

Direct method: trigonometric parallax p = tang U.A./d ~ U.A./d p = 1" d = 1 pc d pc = 1/p" p «1" p α Cen = 0.76" 0 < d < 100 pc 8

HIPPARCOS Satellite astrometrico lanciato dall'esa nel 1989 e operativo fino al 1993. Ha misurato la parallasse di 118.000 stelle con magnitudine apparente V fino alla 9 e precisione di 0.001 Catalogo finale nel 1997. "Come vedere un astronauta in piedi sulla Luna" 9

GAIA Satellite astrometrico che verra' lanciato dall'esa nel 2012. Misurera' le parallassi di 1000 milioni di stelle della nostra Galassia con magnitudine apparente V fino alla 20-22 e precisione di 0.000001" a V=15. "Come vedere l'unghia di un astronauta sulla Luna http://www.rssd.esa.int/gaia http://yoda.bo.astro.it 10

Gaia in a nutshell ESA mission for launch in mid 2012, expected 5 (+1?) yr lifetime all sky (i.e. ~ 40,000 deg 2 ) survey complete to V lim = 20-22 ~ one billion sources high accuracy astrometry (parallaxes, positions, proper motions) optical spectrophotometry (luminosities, astrophysical parameters) spectroscopy (radial velocities, rotation, chemistry) to V = 16-17 5D (some 6D up to 9D) phase space survey over a large fraction of the Galaxy volume Data distribution policy: final catalogue ~ 2019 20 intermediate data release (TBD) science alerts data released immediately no proprietary data rights 11 G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010

Astrometric accuracy: the Pleiades π = 7.59 ± 0.14 mas - 132 pc, MS fitting (Pinsonneault et al. 1998) π = 7.69 mas - 130 pc, various methods (Kharchenko et al. 2005 ) π = 7.49 ± 0.07 mas - 133 pc, from 3 HST-FGS parallaxes in inner halo (Soderblom et al. 2005) π = 8.18 ± 0.13 mas - 122 pc, new reduction Hipparcos data (Van Leeuwen 2007) faintest MS stars have V < 15 Gaia individual parallaxes with σ(π)/π < 0.1 % G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 12

Astrometric performance: summer 2009 status Sky-averaged end-of-mission parallax standard error, in units of µas, as function of Johnson V magnitude for 3 reference stellar types Estimates include a 20% margin for unmodelled errors (e.g. radiation damage effect on CCDs not fully taken into account) Nominal max density for GAIA N 20 ~ 0.25 stars arcsec -2 (likely smaller) σ ω 0.3 mas V lim = 20-22 σ pos = 0.74 σ ω σ µ = 0.53 σ ω 2010 updated performance for B1V-G2V M6V Courtesy A. Brown (J. De Bruijne, GAIA-CA-TN-ESA-JDB-055) G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 13

I metodi indiretti: gli indicatori di distanza La distanza degli oggetti al di fuori della nostra Galassia viene stimata attraverso "tecniche indirette" che si basano sulla identificazione di oggetti celesti di luminosita' nota, che costituiscono delle standard candles". Queste standard candles" devono, pero', essere accuratamente "calibrate". 100 Watt Indicatori Primari Indicatori Secondari Indicatori Terziari G. Clementini School of Astorphysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 14

Primary Indicators Variable Stars Cepheids ~ 3 10 7 pc P/L RR Lyrae < 10 6 pc M V ~ const. Novae 10 6-10 7 pc L/t d Eclipsing binaries Miras ~ 10 7 pc P/L Stars and evolutionary phases with constant luminosity RGB Tip ~ 10 7 pc Red Clump HB stars MS Fitting of open and globular clusters 40 < d < 7000 pc 3000 < d < 10000 pc G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 15

Main Secondary Indicators Brightest stars in galaxies Brightest H II regions Globular clusters luminosity function Surface brightness fluctuations Tully-Fischer relation Colour-luminosity relation in ellipticals Supernovae ~ 8 10 6 pc ~ 2 10 7 pc ~ 10-20 10 6 pc ~ 7 10 7 pc ~ 15 10 7 pc ~ 10 8 pc ~ 10 8 pc Main Tertiary Indicators Luminosity class of spiral galaxies Dimensions of galaxies Total luminosity of the brightest galaxies 3 10 8 pc > 10 9 pc 16

Primary Indicators Pulsating variable stars Cepheids ~ 3 10 7 pc P/L RR Lyrae < 10 6 pc M V ~ const. Stars and evolutionary phases at constant luminosity RGB Tip ~ 10 7 pc MS Fitting of open and globular clusters 40 < d < 7000 pc 3000 < d < 10000 pc G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 17

Pulsating Variable Stars G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 17

G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 18

Pulsating Stars Class Period (days) M V Pop Evo. Phase δ Cephei (CC) 1 100(?) -7(-8) -2 I Blue Loop δ Scuti (δsc) < 0.5 2 3 I MS-PMS β Cephei < 0.3-4.5-3.5 I MS RV Tauri 30 100-2 -1 I, II post-agb Miras > 100-2 1 I, II AGB Semiregulars (SR) > 50-3 1 I, II AGB RR Lyrae (RRL) 0.2 1 ~0.5 0.6 II HB W Virginis (Type2C) 10 50-3 -1 II post-hb BL Herculis (Type2C) < 10-1 0 II post-hb SX Phoenicis (SXPhe) < 0.1 2 3 II MS ACs 0.3-2.5-2 0? HB-turnover SP Cepheids (SPC) < 2 0.0 I Blue Loop LL Cepheids (LLC) 0.55 0.65 0.4?? adapted from Marconi 2001 19

LMC pulsating variables from OGLE III Red Variables CCs ACs Type2C RRL δsc Soszynski et al. 2009 20

OGLE II LMC OGLE III Soszynski et al. 2006 Soszynski et al. 2009 G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 21

Characteristics Classical Cepheids P = 1 100(?) days A v 1.5 mag Sp Type: F6 K2 Pop I Evo. Phase: Blue Loop Young stars, tracing star forming regions, spiral arms 22

Classical Cepheid P/L relation Cepheid PL relation L = αlog P + β Cepheids in the LMC α Trig. Parall. of MW Cepheids B-W of MW Cepheids β universal? metallicity dependent? if yes if yes MCs Cepheid P/L relation at varius wavelengths Madore & Freedman 1991, 1992 (*) but see e.g. Saha et al. (2001), Tamman et al (2008, and references therein) for different conclusions about the value of H 0. HST Key Project 31 galaxies 700 Kpc < d < 20 Mpc H 0 = 72 ± 8 km s -1 Mpc Freedman et al. 2001-0.2 ± 0.2 mag/dex in V, I -1 (*) 23

Classical Cepheid P/L relation Cepheid PL relation L = αlog P + β Cepheids in the LMC α Trig. Parall. of MW Cepheids B-W of MW Cepheids β universal? metallicity dependent? if yes if yes MCs Cepheid P/L relation at varius wavelengths Madore & Freedman 1991, 1992 MCs Cepheid VIW(Ogle2)JHK P/L relations Fouque et al. 2003 HST (*) but Key see Project e.g. Saha -0.2 et ± 0.2 al. mag/dex (2001), 31 Tamman galaxies et al (2008, and in V, references I 700 therein) Kpc < for d < different 20 Mpc conclusions about H 0 = 72 ± 8 km s -1 Mpc -1 (*) the value of H 0. Freedman et al. 2001 23

Cepheid P/L relations in the MCs V 0 (LMC)=-2.760 logp-17.042 σ=0.159 mag (649 FU CCs) V 0 (SMC)=-2.760 logp-17.611 σ=0.258 mag (466 FU CCs) Theoretical P/L: Udalski et al. 1999 Mv=-2.75 logp -1.37 σ= 0.18 mag Caputo, Marconi, Musella 2000 24

Classical Cepheids: open issues 1) Dependence of the Cepheid properties and PL relation on the chemical composition 2) Linearity of the PL over the whole observed period range G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 25

Dependence of the Cepheid PL on chemical composition The Cepheid PL relation is often assumed to be universal: the LMC PL is used to measure the distance to extragalactic Cepheids independently of their chemical composition (see e.g. the HST Key Project). Dependence on chemical composition systematic effects on the extragalactic distance scale (and H 0 )!! A general consensus on the universality of the P-L relations for Cepheids has not been reached yet! G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 26

- Is the Cepheid P/L relation metallicity dependent? Romaniello et al. 2008 G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 27

Non-linear LMC P/L relations: the 10 days break Marconi, Musella & Fiorentino 2005 see also: Fouque et al. 2003 Sandage et al. 2004 Ngeow et al. 2005 28

Ultra Long Period Cepheids Bird et al. 2009 29

Ultra Long Period Cepheids Bird et al. 2009 30

Ultra Long Period Cepheids Bird et al. 2009 31

Characteristics RR Lyrae stars Pop II Evo. Phase: HB (He-core burning) t > 10 Gyr M v (RR) = α[fe/h] +β PLZ in the K band Smith 1995 32

Luminosity metallicity relation of RR Lyrae stars M v (RR) = α [Fe/H] + β 0.13 < α < 0.30 0.5 < β < 1.0 β from : - Trig. Parallax π RRLyr Hipparcos HST π = 4.36 ± 0.59 mas π = 3.82 ± 0.2 mas - Baade-Wesselink - HB (non variable stars) - Statistical Parallaxes Trig. Parallaxes MSF HB models 33 G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010

RR Lyrae stars α from: MW α = 0.20 ± 0.04 LMC α = 0.214 ± 0.047 M31 α = 0.22 ± 0.06 HB Models α 0.23 Pulsation Models α 0.23 34

RR Lyrae stars in the near-ir Smaller amplitudes (A K ~ 0.2-0.3 mag) Tight PLZ K relation (σ~0.05 mag) M K =-2.101 logp+0.231[fe/h] 0.77 (Bono et al. 2003) M K =-2.353 logp+0.175logz 0.597 (Catelan et al. 2004) M K =-2.38 logp+0.08[fe/h] 1.07 (Sollima et al. 2008) Reticulum Dall Ora et al. 2004 Szewczyk et al. 2008 35

RR Lyrae PLK in the Gaia SEP calibra4on field G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 38

RR Lyrae PLK in the Gaia SEP calibra4on field Blue=Bono et al. (2003); Red=Sollima et al. (2006) 37

Stars and evolutionary phases with constant luminosity G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 40

The I luminosity of the RGB Tip is constant with metallicity: -2.2< [Fe/H] <-0.7 and age: 7< t < 17 Gyr RGB Tip The RGB Tip luminosity in the I band is about 4 mag brighter than the HB: d ~ 3 10 6-10 7 pc Calibration: a) via a theoretical model providing the absolute luminosity of the RGB Tip b) from the absolute magnitude of the RGB Tip of a cluster at known distance (e.g. ωcen) G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 41

RGB Tip Calibration: a) from the absolute magnitude of the RGB Tip of a cluster at known distance (e.g. ωcen) G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 42

MS Fitting of open clusters Ammasso Aperto M11 ~ 920 pc G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 43

MS Fitting: Open Clusters G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 44

MS Fitting: Open Clusters ΔV = 3 mag (m-m) Iades = 3.3 mag (m-m) Praesepe = 3.3 + 3 = 6.3 mag d Praesepe = 182 pc G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 45

MS Fitting: Globular Clusters Ammasso globulare M80 ~ 10 kpc G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 46

MS Fitting: Globular Clusters Fitting the Main Sequence of a globular cluster to a reference sequence formed by field subdwarfs of the same metallicity with known distance via trigonometric parallax. (m - M ) 0 = - 5 + 5 log d pc globular cluster MS subdwarf reference sequence globular cluster distance G. Clementini School ofastrphysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 47

MS Fitting: Globular Clusters Carretta et al. 2000, Ap. J. 533, 215 48

MS Fitting: Globular Clusters G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 49

The distance to the LMC: short or long scale? Freedman et al. 2001 Benedict et al. 2002 48

The distance to the LMC: short or long scale? short scale RR Lyrae Red Clump Eclipsing Binaries White Dwarfs statistical parallaxes Baade - Wesselink M v (RR) = 0.70 at [Fe/H] = -1.5 Age(GCs) = 16 x 10 9 yrs μ LMC = 18.25 mag D = 45 kpc Ho = 65-80 km s -1 Mpc long scale Cepheids GCs MSF Miras SN1987A RGB tip double mode RR Lyrae Trig. Parallax Baade Wesselink PL relation MS fitting M v (RR) = 0.50 at [Fe/H] = -1.5 Age(GCs) = 13 x 10 9 yrs μ LMC = 18.50 mag D = 50 kpc Ho = 55-75 km s -1 Mpc G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 51

Distanza della Grande Nube di Magellano 52

The promise of Gaia Gaia is planned for launch in mid 2012. During its lifetime of nominally 5(+1?) years, Gaia will scan the entire sky (i.e. ~ 40,000 deg 2 ) repeatedly, observing all the sources brighter than V lim = 20-22 mag (10 9 stars), with 80 measurements/ object on average over the 5 year span. According to current estimates, from 2000 to 8000 Classical Cepheids and about 70000 RR Lyrae stars will be observed by Gaia. Also, about 2000 Population II Cepheids are likely to be observed by the satellite. Complete census of the MW Classical Cepheids. ~2000/1000 Classical Cepheids are know in the Magellanic Clouds and observable by Gaia G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010

The distance scale: local standard candles RR Lyrae Mv= 0.5-0.6: Presently, 126 RR Lyraes with < V > = 10 to 12.5 (750-2500 pc) σ π /π 30 % (Hipparcos) (Fernley et al. 1998) RR Lyr (<V>=7.8): only RRL star with good parallax estimate π = 3.46 ± 0.64 mas mod = 7.30 mag (new Hipparcos, van Leeuwen 2007) π = 3.82 ± 0.20 mas mod = 7.09 mag (HST, Benedict et al. 2002) ΔMv ~ 0.2 mag distance to 10%! Gaia: within 1.5 kpc to σπ/π < 1% ( 2.5% within 3 kpc, 25-30% at 10 kpc) RR Lyraes in globular clusters with mean σπ/π < 1% G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 54

The distance scale: local standard candles Metal-poor subdwarfs Mv= 5.0 to 7.5: Presently, ~ 30 subdwarfs available (Hipparcos) within 100 pc Gaia: within 1 kpc distance to σπ/π < 2 6 % a factor 10 (1000) in distance (volume) several thousands expected G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 55

The distance scale: MW Cepheids Only ~ 800 Galactic Cepheids are known most are located in the Solar neighbourhood 400 Galactic Cepheids from David Dunlap DB distance and magnitude Gaia predicted accuracy for parallax 15 @ d < 0.5 kpc 65 @ d < 1 kpc 165 @ d < 2 kpc Presently, ~ 250 Cepheids with parallax & photometry (10 with HST parallax) only ~ 100 with σ π 1 mas (Hipparcos) Figure courtesy A. Brown Most (~ 3/4) Galactic Cepheids will have Gaia individual parallaxes to < 3% 56 G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010

The distance scale: MC Cepheids ~ 2000/1000 Cepheids are known (and observable by Gaia) in the LMC/SMC The bulk of the distribution for fundamental LMC pulsators lies at Period = 3 5 days Mv ~ -3 V ~ 15.8 16 individual distances to ~ 150% mean of 400 to ~ 7-8 % Cepheids with P 10 d Mv ~ - 4.2 V ~ 14.5 individual distances to ~ 80% Ultra-long period (> 100 d) Cepheids Mv ~ - 7 V ~ 12 4 in LMC, 3 in SMC (Bird et al. 2009) individual distances to ~ 45% (LMC) - 55% (SMC) 600 Cepheids in the LMC (OGLE, Udalski et al. 1999) direct (trigonometric) calibration of the cosmological distance scale 57 G. Clementini School ofastrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010

GAIA Concept and Technology Study Report, 2000, ESA-SCI(2000)4 The Three-Dimensional Universe with GAIA, 2005, ESA-SP 576 more information on http://www.rssd.esa.int/gaia 58 G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010

The Fundamental Cosmic Distance Scale: State of the Art and the Gaia Perspective Naples, May 3-6, 2011 more information on: http://www.oacn.inaf.it/esfdistance see also: WGA8 Distance scale, at: http://camd08.ast.cam.ac.uk/greatwiki/wga8distancescales Thank you! G. Clementini School of Astrophysics F. Lucchin II Cycle 2010, Asiago, 24-30 October 2010 59