Galaxies Astro 530 Fall 2015

Transcription

1 Galaxies Astro 530 Fall 2015 Prof. Jeff Kenney CLASS 12 October 12, 2015 EllipDcal Galaxies: Structure, KinemaDcs, Orbits 1

2 Midterm exam next Monday Oct 19 Covers up thru lecture of Oct 5 and HW5 (thru disk phenomena, no EllipDcals) Next HW (#6, on E s) will be due Wed, Oct 28 Galaxy lunch talks I will circulate more specific guidelines in next few days & assign people stardng Wed Oct 28. 2

3 IntroducDon to kinemadcs for EllipDcals Ordered mo(ons: v: mean velocity v = v rot + v noncirc measured by peak or mean of line Disordered mo(ons: σ: velocity dispersion, measured by linewidth The rado v/σ is used to compare the reladve importance of ordered and random modons 3

4 Line of sight velocity distribudon (LOSVD) for spiral disk km/s 0 km/s +200 km/s V los Small area of outer spiral disk Simple case Fast rotadon modon Small random modons V los /σ los >>1 FWHM V los V los = mean los velocity σ los = los velocity dispersion = FWHM/2.35 (if gaussian) 4

5 Line- of- sight Velocity DistribuDon (LOSVD) Observed spectrum Spectrum of 1 star LOSVD 5

6 Line of sight velocity distribudon (LOSVD) The observed profile of a stellar absorpdon line from a galaxy is generally complex because a. the distribudon of stellar velocides at any point in a stellar system may be complex (stars in galaxies are ~collisionless, so stars which pass thru any point in a galaxy can have very different orbits) b. The observed stellar absorpdon lines from a galaxy are a weighted sum of stars within a 3D volume: all the stars along the LOS (z direcdon) and within the spadal resoludon element (x,y direcdons) 6

7 Within each resoludon element extended in x & y direcdons and at each depth z there are y stars on various orbits x Slice at depth z only the LOS (z) component of velocity is observed via doppler shik z direcdon = Line of sight (LOS) GALAXY 7

8 IntroducDon to kinemadcs for EllipDcals Ideally would like to measure v, σ at every point in 3D space v/σ ordered/disordered ObservaDonally v los and σ los are luminosity- weighted averages over finite volumes and along line- of- sight v los /σ los ordered/disordered+ordered (since averaging over large volume includes some ordered component which varies within volume) 8

9 Line of sight velocity distribudon (LOSVD) for spiral disk km/s 0 km/s +200 km/s V los Small area of outer spiral disk Simple case Fast rotadon modon V los = 200 km/s Small random modons σ los = 20 km/s V los /σ los >>1 FWHM V los V los = mean los velocity σ los = los velocity dispersion = FWHM/2.35 (if gaussian) 9

10 LOSVD for ellipdcal km/s 20 km/s 0 km/s +200 km/s V los FWHM Small area of ellipdcal V Simple case los slow rotadon modon V los ~ 20 km/s large random modons σ los ~ 200 km/s V los /σ los <<1 V los = mean los velocity σ los = los velocity dispersion = FWHM/2.35 (if gaussian) 10

11 Complex case of LOSVD km/s 30 km/s 0 km/s +200 km/s V los FWHM Few stars with large counter- rotadonal modons and small random modons (accreted small galaxy?) V los Few stars with large Main component of line profile rotadonal modons not symmetric and small random modons not gaussian (disk component?) but V los < σ los For most stars random modons dominate 11

12 Stellar velocity dispersion in general is anisotropic σ R, σ φ, σ z need not be equal σ los depends on σ R : σ φ : σ (rados) and which z components happen to be along l- o- s Simplest case: isotropic velocity dispersion σ R = σ φ = σ z = σ los (σ los doesn t depend on viewing angle) 12

13 E galaxy rotadon vs. dispersion v<<σ NGC 1399 cd ellipdcal Center of Formax Cluster V rot ~30 km/s σ~250 km/s à v/σ ~0.1 is low!! Most modon in random direcdons! σ ~ constant over much of galaxy, although is ~50% higher in center - > oken reasonable to characterize E galaxy with single value of σ 13

14 Cool + red spectra of main sequence stars Warm + yellow Hot + blue spectrum of ellipdcal 14

15 Are EllipDcals Oblate Spheroids whose shape is governed by rotadon? Open circles: mid- sized E s (lower luminosity, M B >19.5) Filled circles: luminous (M B <19.5) E s Dosed line: oblate spheroid flasened by rotadon (O.S.F.B.R.) ProjecDon effects: both V los and ε vary by appx sin(i) for inclined system Most mid- sized E s (& bulges) consistent with O.S.F.B.R. Many luminous E s NOT O.S.F.B.R. but must instead be triaxial bodies flasened due to anisotropic distribudon of random velocides. Systems not fully relaxed by violent relaxadon process, since fully relaxed system WOULD BE O.S.F.B.R. Orbits sdll contain informadon from Dme of formadon. 15

16 System flasened by anisotropic velocity distribudon 16

17 V/σ vs. Luminosity and Disky- Boxy Open circles: mid- sized E s (lower lum., M B >19.5) Filled circles: luminous (M B <19.5) E s (v/σ * ) = (v max /σ) / (v/σ iso ) SG Fig 6.15 (Bender) Many high luminosity E s are triaxial bodies with low v/σ and boxy isophotes - > Could form through mergers of gas- poor galaxies (less dissipadon during formadon) Many low luminosity E s are oblate spheroids with high v/σ and disky isophotes à Could form through mergers of gas- rich galaxies (since gas sesles to a rotadng disk before it forms many stars)(more dissipadon during formadon) Disky E s contain embedded stellar disks, may be part of condnuous sequence with S0 s. 17

18 80% of E s show deviadons from purely ellipdcal isophotes φ a a 4 DeviaDons from ellipses can be described by a fourier series expansion in azimuth = a 3 cos(3φ)+a 4 cos(4φ)+a 5 cos(5φ)+ cos(4φ) term generally dominates a 1 term offset center a 2 term ellipse of different shape 18

19 Disky & boxy isophotes in EllipDcals SchemaDc diagrams of disky isophotes with a 4 /a=0.1 and boxy isophotes with a 4 /a=- 0.1 a a 4 Bender etal

20 Disky vs. Boxy EllipDcals Disky galaxies: pointed isophotes indicate presence of weak, highly inclined stellar disks which lie within larger bulge- like component (mostly oblate spheroids) Boxy galaxies: triaxial galaxies have many stars on box orbits which have no fixed sense of rotadon around center, and which fill a roughly boxed- shape region (mostly triaxial galaxies)(more likely to have isophote twists) 20

21 Disky ellipdcals Similar to Sa galaxy M104, but without gas & dust. Large bulge with embedded stellar disk. 21

22 Orbits in triaxial potendal (non- rotadng) a.) b.) a.) Loop orbit: Rotates around center, angular momentum not constant, but falls within some narrow range c.) b.) Box orbit: no fixed sense of rotadon around center & angular momentum varies greatly, somedmes 0 à Can pass through center! c.) ChaoDc orbit 22

23 Box orbits in ellipdcal galaxies Box- like orbits in triaxial galaxies with figure rotadon Deibel

24 Galaxy ClassificaDon: Kormendy & Bender (2012) ApJS, 198, 2 Modified version of van den Bergh (1976) classificadon scheme Normalized SFR DirecDon of evoludon Stellar Bulge/disk rado 24

25 V/σ vs. Luminosity and Disky- Boxy Open circles: mid- sized E s (lower lum., M B >19.5) Filled circles: luminous (M B <19.5) E s (v/σ * ) = (v max /σ) / (v/σ iso ) SG Fig 6.15 (Bender) Many high luminosity E s are triaxial bodies with low v/σ and boxy isophotes - > Could form through mergers of gas- poor galaxies (less dissipadon during formadon) Many low luminosity E s are oblate spheroids with high v/σ and disky isophotes à Could form through mergers of gas- rich galaxies (since gas sesles to a rotadng disk before it forms many stars)(more dissipadon during formadon) Disky E s contain embedded stellar disks, may be part of condnuous sequence with S0 s. 25

26 Disky- Boxy vs. Radio & X- Ray luminosity Open circles: mid- sized (lower luminosity, M B >19.5) E s Filled circles: luminous (M B <19.5) E s Boxy E s generally have the strongest radio AGN sources and the most luminous X- Ray emission (the most hot ISM) 26

27 Faber- Jackson RelaDon for EllipDcals L ~ σ 4 log σ velocity dispersion (km/s) Original Faber & Jackson (1976) reladon 1. Distance indicator 2. InformaDon about galaxy structure Similar to Tully- Fisher reladon for spirals BUT: a. More scaser (~35% vs ~15%) b. Scaser is correlated with some third parameter à Find a reladon with less scaser if we use 3 parameter reladon (fundamental plane) 27

28 Which EllipDcal has odd core kinemadcs? Franx, Illingworth & Heckman 1989

29 Which EllipDcal has odd core kinemadcs? In M86 (NGC 4406), the inner and outer galaxy rotate about different axes. They differ by 90 deg. Stellar velocity Map of central +/- 30 in M86 Franx, Illingworth & Heckman 1989 ATLAS 3D Krajnovic+2011

30 KinemaDcally decoupled core in ellipdcal NGC 4365 Davies etal 2001 Inner 7 rotates orthogonally to main body of galaxy Inner 4 disky, outer part boxy Inner part v/σ =1.3 (disklike) 2% of total mass in central decoupled disk Shallow central cusp Overall galaxy is triaxial No shells or other morphological peculiarides No sign of dust Age of stellar populadon is ~14 Gyr in both decoupled disk and main body Formed through old merger(s) NGC 4365 SDSS image

31 Decoupled core in NGC 4365 Surma & Bender 1995

32 KinemaDcally disdnct core in NGC 2865 Evidence for very recent star formadon in kinemadcally decoupled core Core (central 500 pc), co- rotates with main body but has much lower dispersion, younger stellar populadon Disturbed morphology also suggests recent merger Hua, Carter & Balcells 1999