oa-romaaf.it/a.antonelli/lectures/

1. Extragalactic Astrophysics 1 A.A. 2011-2012Prof. L. A. Antonelliangelo.antonelli@oa-roma.inaf.it http://www.oa-roma.inaf.it/a.antonelli/lectures/

2. chapters 1,2 galaxies Milky Way, Local Group, disk and elliptical galaxies, irregular and starburst galaxies, etc chapters 3,4,5 active galactic nuclei BH paradygm, line and continuum spectrum, BLR and NLR, unified models, host galaxies and environment, cosmological framework, surveys, luminosity function, etc Peterson An Introduction to Active Galactic Nuclei Cambridge University Press Sparke & Gallagher Galaxies in the Universe Cambridge University Press chapter 7 high redshift Universe Ly-alpha forest, high-z galaxies, passive and active evolution, downsizing, etc

3. Ch.1

4. Milky Way 1000-1500 pc 15 kpc 300-400 pc 2 kpc 8.5 kpc main data radius RG~15 kpc (stars), ~18-20 kpc (HI); Sun distance from galactic center 8.5 kpc luminosity mass 75-80% DM, 15-20% disk, <5% bulge+halo central BH rotation periods: Solar neibourhood ~240 Myr (galactic year), bulge ~10 Myr

5. catalogue: of the order of 1 billion stars • accuracies: median parallaxes of 4 µas at V=10 mag, 11 µas at V=15 mag, 160 µas at V=20 mag • distance accuracies: 21 million better than 1 per cent, 46 million better than 2 per cent, 116 million better than 5 per cent, 220 million better than 10 per cent GAIA (~2012) distances and velocities within the Milky Way for nearby stars it is used the trigonometric parallax, based on Earth orbit proxima centauri: p=0.8”, d=1.3 pc Hipparcos, 1989-93: 12000 stars up to ~500 pc, precision ~10-3 arcsec http://www.atlasoftheuniverse.com/

6. mobile cluster method Hiades Cluster is very nearby, and it is possible to measure a decreasing of its apparent diameter due to its outwards motion receding velocity is measured by Doppler shift

7. masers in the Galactic Center Doppler shift proper motion if it is known (or if it can be assumed) how Vt and Vr are related for a particular object, then distance can be determined by the combined measures example: Sagittarius B2 (North), star cluster in the Galactic Center. radiation by massive stars excites H2O maser sources within circumstar gas, very strong in spectral line at 22.2 GHz. VLBI observations allow to measure relative positions with precision 10-5 arcsec the observed motion is mainly radially directed with respect to the cluster center assume i.e. average of all the maser sources it is found the uncertainty is due to the relative low number of bright maser sources

8. light echo from Supernova 1987A in LMC ~ 85 days after SN observation narrow emission lines of ionized C and N have been detected from a ring, probably circular but inclined from the delay we can measure ring radius, and then distance inclination is deduced from apparent axial ratio: measured delays are t-=86 d and t+=413 d and corresponding path differences are: it is found: LMC distance 0.83”

9. spectroscopic parallaxes if a star’s spectral type is known, we can derive its luminosity from HR diagram, once calibrated with parallax measurements of nearer stars, so we can measure distance, if we can estimate interstellar absorption for MS stars it works well: uncertainties ~ 10% luminosity, ~5% distance for giants HR diagram is ~vertical: uncertainty ~50% luminosity, ~25% distance luminosity spectral type photometric variant, estimate spectral type from color example: looking orthogonally to galactic plane, red stars fainter than mV~14 are almost all K ed M dwarfs (for giants instead MV~0 and mv~MV+5logd-5~10, with d~1 kpc) from color, we get MS luminosity. there is little dust normal to galactic disc, then distance measurements are reliable enough scale length scale height spectral type we can measure the spatial distribution of stars: z R thin disk thick disk

10. thin disk and thick disk older stars have larger velocity dispersions and scale heights, because they suffer for a longer time the gravitational potential irregularities (giant clouds, star clusters) which tend to make their motion disordered F main sequence stars in the Solar neiborhood (< ~40 pc) the average velocity of stars with respect to Sun is negative because Sun has positive velocity (+7 km/s) with respect to LSR metal-poor stars ( ) thick disk stars are usually metal-poor ( ) thick disk could be the result of a “gas-rich merger” with a satellite galaxy, where most thick disk stars were born in situ

12. for open and globular clusters more precise distance determinations are possible, because all the stars of the same cluster have about the same age, chemical composition, and distance. optimal agreement of isochrones with HR diagram can be found open clusters pleiades isochrone binary sist open clusters are absorbed by dust within galactic disk, we can see them only up to ~5 kpc. we know ~1200 of them

13. globular clusters for globular clusters there is no absorption problem. ~130 are known globular clusters are old up to ~12-15 Gyr. taking account of uncertainties in stellar evolution theory, age might go down to 11-12 Gyr. problems with the age of the Universe: to=2/3 Ho-1~9 Gyr (Einstein-deSitter, Ho=75); concordance model ok: Ho=70, Ωm=0.3 ΩΛ=0.7: to~13 Gyr metal-rich globular clusters Z=1/3-1/10 of solar value flattened distribution, may be part of thick disk metal-poor globular clusters Z~1/300 of solar value nearly spherical distribution

14. RR Lyrae variables another method to estimate distance of globular clusters is to use RR Lyrae stars, which have periods ~ 0.5 days and mean luminosity about uniform from measurement of apparent magnitude, distance can be determined similarly, for external galaxies, cepheid variables are used, which have a P-L relation they cannot be used in the Milky Way because they are in the disk and are absorbed by dust

15. infrared in the galactic plane, visible light is absorbed by dust. it is convenient to observe in the IR, which is less absorbed. it is found, both for thick and thin disk, scale length 2 kpc < hR < 4 kpc it is observed a flattened bulge, larger on one side, probably due to a bar, with semilength ~2-3 kpc from center probably Milky Way type is between Sbc e Sc, not clearly barred as in SB types, it sometimes classified SBA, intermediate type between S and SB

16. central cluster Sagittarius B2, ~150 pc galactic center central density , halves at ~ 2-3 pc from center resembles a globular cluster, ma still forms stars there is gas inflow total mass central black hole BH model of distribution of mass in the central region, to account for observed rotational velocities: central cluster DM

17. stellar orbits around Milky Way central BH S2 Gillessen et al 2008 MBH=(4.31±0.06±0.36) x106 28 well determined orbits S2 completed orbit stat astrom Unprecedented 16-Year Long Study Tracks Stars Orbiting Milky Way Black Hole http://www.eso.org/public/outreach/press-rel/pr-2008/phot-46-08.html

18. differential rotation stars and gas rotate in the galactic plane with nearly circular orbits, but with angular velocity increasing toward galactic center differential rotation affects transverse and radial velocities with respect to Sun, and was indeed discovered from proper motions of nearby stars towards galactic center, we see stars going ahead and in the opposite direction stars remain behind, with respect to Sun. stars in the same galactocentric orbit as Sun have same velocity in absolute value, but relative velocity has a transverse component as in figure this configuration of proper motions was already noted around 1900 and explained by Oort in 1927 with the differential rotation

19. radial velocities + - S + - - + this is valid not only for stars, but also for the gas, which is best observed in the radio band, e.g. HI 21 cm, CO 2.6 mm

20. Oort constants for d<<R we can approximate: proper motions:

21. rotation curve if we can measure Vr at various distances: for the stars there is a problem: absorption by dust for HI at 21 cm we miss information on distance, use the tangent-point method: orbit of cloud No. 4 is tangent to line of sight, we get . and Vr is maximum Ro R contributions of various clouds along the line of sight Oort 1952 but method doesn’t apply for R>Ro, in such case we must use associations of young stars, measure distance with spectroscopic parallaxes and measure Vr through emission lines from circumstellar gas it is found that V(R) doesn’t decrease either in the external parts of Milky Way

22. dark matter for a spherically simmetric configuration, centripetal acceleration of a star in circular orbit at galactocentric radius R is determined by mass internal to radius R, M(<R): thus, measurement of V(R) provides a mass determination: [ ] for a flattened configuration like a disk F≠GM/R2 and formula gives M(<R) with error ~10-15% because V(R) doesn’t decrease, M must increase at least as R if M is confined to a given radius Ro , M(<R)=const for R>Ro so V~R-1/2 (keplerian case) Ro there must be other matter, other than that visible in stars, the Dark Matter, which is believed to be distributed within a dark halo

23. dark matter DM can account for 80% of the total mass: what is it done of? weakly interacting massive particles (neutrinos, neutralinos, gravitinos ...) difficult to detect directly [non-barionic dark matter] WIMPs: and/or massive compact halo objects (black holes, planets, brown dwarfs, white dwarfs ...) detectable by their effects of gravitational microlensing [barionic dark matter] MACHOs: in the Universe: (from Big Bang nucleosynthesis) most matter is DM most DM is non-barionic also some is barionic

24. Local Group 1Mpc M31 M33

25. Local Group galaxies the 3 dominant galaxies ~90% of the LG Luminosity the only elliptical distances measured through Cepheids P=L relation known within ~10% for brightest galaxies nearest one (low surface brightness, discovered 1994) boldface: Milky Way satellites italics:M31 satellites most are dwarfs: dSph, dIrr, dE

26. Milky Way satellites most lie close to a plane umi dSph draco dSph sextans dSph carina dSph LMC SMC fornax dSph sculptor dSph sagittarius dSph

27. NGC 147 IC 10 Local Group M31 (Sb) NGC 185 M32 (E2) (dE) (dE) (Irr) NGC 3109 (Irr) (dE) NGC 205 M31 M33 M33 (Sc)

28. velocities [ ] transverse velocities we can measure them only for nearest satellites: at d~100 kpc, with Vt~100 km/s, need to select distant quasars and galaxies in order to define a non-moving reference frame radial velocities easily measurable subtracting solar motion, it is found that Milky Way and M31 approach each other at V~120 km/s most other galaxies have velocities within ~60 km/s from MilkyWay+M31 center of mass, not enough to escape from LG: Local Group represents a typical galactic environment: less dense than a galaxy cluster like Virgo or Coma, but contains enough mass to bind the galaxies together Local Group constitutes a great opportunity to study stellar systems close-up: we can resolve stars, analyse their HR diagrams, and determine their ages and chemical compositions

29. Magellanic Clouds they are the most prominent Milky Way companions, clearly visible with naked eye in the southern sky, they form stars and star clusters in abundance LMC measures 15o x 13o on the sky and is ~14 kpc long it is a disc, tilted ~45o from plane of the sky, with a strong bar. rotation velocity reaches ~80 km/s. very gas-rich: M(HI)/LB~0.3 (compare MW, M(HI)/LB~0.1) SMC measures 7o x 4o on the sky and is ~8 kpc long it is an elongated structure seen roughly end-on, with depth ~15 kpc no rotation motion. M(HI)/LB~1 Magellanic Bridge: bridge of gas connecting the two clouds Magellanic Stream: long tail of gas behind SMC, contains ~ Leading Arm: stream of gas between LMC and MW

30. Magellanic Clouds LMC and SMC orbit around their common center of mass, and also orbit the Milky Way. orbit of the Clouds is slowly decaying as energy is transferred to random motions of MW stars. position and motion of the Clouds suggest that their orbit is strongly eccentric, with a period ~2Gyr, and that ~200-400 Myr have elapsed from their closest approach to MW. distance between LMC and SMC ~ 20 kpc, but could have been shorter (~10 kpc) at epoch of closest approach, and gravitational attraction by LMC has likely extracted some gas from SMC, so forming the Magellanic Stream

31. Magellanic Clouds they are rich in star clusters. can use HR diagrams to determine age, chemical composition, and distance LMC: it is found dLMC ~ 50 kpc, in agreement with measurement obtained through SN1987A. from HI rotation curve it is found SMC: from globular clusters and from variable stars, it is found dSMC ~ 60 kpc HI map globular clusters (LMC), bimodal age dist: many old (>~10 Gyr) and metal-poor ( ), do not form a halo, instead lie in a thick disk, with larger velocities than the gas: few clusters between 4 and 10 Gyr, many young clusters and associations, some very populous (~100 times MW open clusters), may be young version of LMC GCs ages of SMC clusters are continuously distributed between few and ~12 Gyr, with no gap

32. LMC 30 Doradus (Tarantula) SN1987A

33. LMC radio image in HI

34. SMC NGC 362 (Milky Way) 47 Tucanae (Milky Way)

35. search for isolated galaxies with luminosity similar to MW + satellites 2-4 mag fainter

36. Cepheid variables Cepheids are massive, Helium-burning, pulsating stars, with luminosities up to and periods between 1 and 50 days Henrietta Leavitt found in 1912 that brighter Cepheids in LMC had longer periods: as distance is the same for all, brighter Cepheids have also higher Luminosity, and a period-luminosity relation is found: from measurement of period it is determined the luminosity (standard candle), and then from apparent magnitude the distance is found also RR Lyrae can be used:

37. Cepheid variables factor due in part to the different distance of LMC and SMC, and also to the different chemical composition and interstellar absorption with Hubble Space Telescope we can use RR Lyrae up to ~2-3 Mpc and Cepheids up to ~30 Mpc

38. cosmic distance ladder Cepheids constitute an important step in the cosmic distance ladder. each measurement method must be calibrated through the previous one HST trigonometric parallax

39. dwarf spheroidals Milky Way subsystem includes also 9 dwarf spheroidals with low surface brightness, ~1/100 than Magellanic Clouds they are gas-free systems, with no stars younger than 1-2 Gyr many of them contain RR Lyrae variables, with ages at least ~8 Gyr some have luminosities similar to Milky Way GCs, but with much larger sizes (~102pc vs ~pc or less) however they are true galaxies: fornax and sagittarius possess GC systems. spheroidals did not form stars at same epoch like in GCs, but distributed on many Gyr, from gas with different metallicities, e.g. Carina -> from radial velocities and sizes Virial Theorem gives estimates of mass, and M/L, which in some cases is much higher than for MW e.g. Carina M/L~75 => large abundance of DM Carina 3 Gyr 7 Gyr 15 Gyr chemical abundances are relatively low <~1/30 than Solar. metal rich gas could have been lost and transferred to Intra Group Medium

40. spirals • M 31, Andromeda • larger than Milky Way: • 50% more luminous • larger disk, scale length hR~6-7 kpc, twice MW • higher rotation velocity, V(R)~260 km/s, ~20% more than MW • more numerous globular clusters, 300 (vs 130) M31 (Sb) M32 (E2) (dE) NGC 205 satellites: M32 (E2) + 3 dE + at least 6 dSph two central concentrations, ~ 0.5 arcsec apart (2pc): BH with + star cluster luminous star forming ring around the bulge at R~10 kpc no clear large scale spiral pattern radio observations of HI show S-shaped disk in the outer parts, similar to MW

41. optical IR: Spitzer star-forming ring IR: IRAS

42. spirals in shows loops, filaments and shells due to SNe and stellar winds, which heat the gas and stop star formation (feedback) M 33, Triangulum tiny bulge: Sc or Scd smaller than MW: hR~1.7 kpc V(R)~120 km/s HI disk very extended, ~3 Holmberg radii, i.e. ~30 kpc, appreciable fraction of the distance M33-M31 (200 kpc) very luminous nuclear cluster with old, intermediate, and young stars (differently than for GCs) no evidence of a central BH strong central X-ray source + many weaker sources optical spectrum: strong emission line by NII

43. radio map of M33 false colors indicate radial velocity and show rotation

44. NGC 604 giant gaseous nebula with strong star formation

45. it is one of the best studied galaxies in X-rays. there is diffuse emission + many tens of point-like sources, among which most conspicuous are X-8 Ultra Luminous X-ray source (ULX) with LX~1039 erg/s, and X-7 with a BH of ~15 solar masses. normal galaxies have total LX(0.5-10 keV) ~1038-1041 erg/s M33 in X-rays X-8 X-7

46. formation of Local Group galaxies recombination epoch: T~3000 K, z~1100, t~300,000 yr from this epoch: - H atoms are neutral, not ionized - photons do not interact with matter any more - Universe is transparent to radiation - matter is not supported by photon pressure, and can collapse to form condensations condensations which will later form galaxies (protogalaxies) begin to grow in regions of higher density protogalaxies form close to each other (Universe was smaller than now) and gain angular momentum through tidal torques

47. formation of Local Group galaxies first stars must have been born at z~6, when cosmic background radiation cooled to ~20 K, so that protostars could be able to radiate heat away and collapse born from clouds with masses , they had primordial chemical composition, then at their death they polluted the residual gas with heavy elements, raising it to abundance ~10-3-10-2 solar during protogalaxy collapse, many gas clouds gave rise to globular clusters, forming stars inside them. other less dense clouds continued collapse, and collided, increasing gas density and forming a disk, rotating due to conservation of angular momentum previously gained, locating themselves in nearly circular orbits, those with minimum energy for a given angular momentum on the contrary, stars and globular clusters born during collapse do not lose a significant amount of energy in collisions and move on elongated orbits with random orientations, and with negligible total angular momentum Bulge stars are younger than globular clusters (age < ~8-10 Gyr). they could have been formed in the densest region of the protogalactic gas, or in a dense region of the disk, or they could be remnants of globular clusters fallen in the center because of dynamical friction. Once formed the Bulge, the galactic gravitational field helps confining the gas enriched by SNe and enables the birth of metal-rich stars dark matter is located mainly in external regions. in fact, DM is supposed to be very weakly interacting matter, so it doesn’t lose energy and remains in elongated orbits

48. chemical evolution simplified scheme: 1 zone model: well mixed gas, with homogeneous chemical composition instantaneous recycle: enriched gas poured rapidly into ISM, before forming stars closed box: gas doesn’t enter or escape from galaxy gas mass at time t mass in low mass stars and remnants of high mass stars, at time t mass in heavy elements at time t metallicity yield (fraction of heavy elements in the gas returned from stars) a given amount of stars dMs produces a mass of heavy elements dMh, which partly goes back to the gas, with a mass pdMs, while a mass ZdMs is subtracted to form new stars (closed box) morever, it is supposed p indipendent of Z (primary elements: their production doesn’t depend on the presence of other elements)

49. chemical evolution metallicity increases as gas is consumed mass in stars born up to time t, with Z<Z(t): mass in stars between Z and Z+dZ: in agreement with the observations of the Galactic Bulge, with Z(0)=0 e

50. dwarf ellipticals and dwarf spheroidals dSph are slightly more luminous than GCs but much more diffuse dE are more luminous versions of dSph, or e.g. M31 satellites: NGC 147, NGC 185, NGC 205 they are vulnerable to tidal stripping no evidence of rotation, probably triaxial shape relatively old stars > ~5 Gyr, but also young (100-500 Myr) in the central parts M32 elliptical with very high central surface brightness no stars younger than some Gyr central BH dE dSph called dE in the original paper (Binggeli 1994), now called dSph M32 might be small version of a giant elliptical, or a central remnant, deprived of the envelope and of GCs warm system: in M32, compare MW ~7 (cold), dSph<<1 (hot)