Morphology-Density Relation. The fraction of the population that is spiral decreases from the field to high density regions. Nature or Nurture?

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Clyde Robinson
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1 Morphology-Density Relation Spirals/Irr The fraction of the population that is spiral decreases from the field to high density regions. S0 Ellipticals Nature or Nurture? Low High [Dressler 1980]

2 The HI Line and Extragalactic Astronomy 0. Predicted 1945 van de Hulst First detected 1951 Ewen & Purcell First extragalactic detection The spectral line of atomic Hydrogen (HI) at a rest wavelength of 21cm is a powerful tool for the measurement of the distances of disk galaxies. 2. The large radial extent at which HI can be found in disk galaxies, makes it the most sensitive instrument to sense the dynamical environment, the distribution of Dark Matter and tidal perturbations due to other neighboring systems.

3 Substructure in the Local Group Giant spirals dsph (+dell) dirr dirr/dsph

4 VLA maps

5 See John Hibbard s Gallery of Rogues at astrores/ HIrogues

6 NGC 3628 Leo Triplet NGC 3627 NGC 3623

7 M96 Ring VLA map Arecibo map Schneider, Salpeter & Terzian 19

8 Optical galaxy HI

9 Clusters of galaxies are the most massive, gravitationally bound objects. Their environments are often referred as evolution accelerators : High velocity encounters, hot intracluster medium make cold gas-rich galaxies vulnerable to severe disruption. The nearest (16 Mpc) such cluster is The Virgo Cluster of Galaxies

10 The Virgo Cluster Virgo Cluster Catalog (BST85) ~2000 gals, based on morphological appearance Largely confirmed by redshift measurements Binggeli, Sandage & Tammann 1985, AJ 90, 1681

11 Substructure in the Virgo Cluster Extended X-ray emission implies hot ICM Redshift distribution implies substructure including main cluster around M87, secondary one around M49, plus infalling spiral groups

12 NGC 4438: A ram-pressure current victim

13 HI deficiency in Virgo Spirals embedded in the hot X-ray intracluster gas are HI deficient relative to isolated galaxies of the same size and morphology, sometimes by >10X Dots: galaxies w/ measured HI Contours: HI deficiency Greyscale: ROSAT kev Solanes et al. 2002

14 The Observational Foundations of Modern Cosmology 1. The Universe expands (Hubble 1929); the expansion appears to be accelerating (SN type Ia, WMAP) and to have started 13.7 Gyr ago 2. A background of microwave cosmic radiation (CMB) exists (1965); it has BB spectrum with T = 2.73 K, a dipole at the 3 mk level (due to the peculiar velocity of the MW) and fluctuations at the mk level of well understood statistical properties ( ) 3. The cosmic abundance of light isotopes ( 2 H, 3 He, 7 Li) determines the baryonic energy density of the Universe(1970s-) 4. The statistical properties of the Large scale structure in the distribution of luminous matter (galaxies) 5. The night sky is dark ( Olbers paradox )

Universal Expansion 1664 Newton s Theory of Gravitation He realizes the Universe must be infinite to prevent collapse and that equilibrium is unstable 1917 Einstein

Einstein declares introduction of his greatest error ever late 1940s Gamow, Alpher and Herman postulate existence of cosmic radiation background with T ~ 5 K early 1960s

15 Universal Expansion 1664 Newton s Theory of Gravitation He realizes the Universe must be infinite to prevent collapse and that equilibrium is unstable 1917 Einstein obtains new set of equations of gravitational field (TGR) unstable Universe, unless a cosmological constant term is introduced Friedman obtains set of expanding solutions of Einstein s equations. They are independently obtained by Lemaitre in Hubble discovers universal expansion: v = H o d He determines H o to be ~500 km/s/mpc universal age ~ 2 Gyr Einstein declares introduction of his greatest error ever late 1940s Gamow, Alpher and Herman postulate existence of cosmic radiation background with T ~ 5 K early 1960s Quasars are shown to be at cosmological distances 1964 Hoyle and Tayler show that He abundance can be explained by primordial nucleosynthesis 1965 Penzias and Wilson detect Cosmic Microwave Background radiation 1992 COBE detects fluctuations in the CMB 2003 WMAP accurately determines main cosmological parameters

16 Integrated Galaxy Spectra MgI MgI H H Ellipticals show absorption line spectra characteristic of older stellar population; spirals show emission lines, characteristic of star-formation regions.

17 A Doppler shift results from the relative motion of the light emitting object and the observer. If the source of light is moving away from you then the wavelength of the light is shifted towards the longer wavelengths. Since early astronomical work was entirely made in the visible part of the spectrum, a shift towards longer wavelengths was referred to as a redshift.

18 Operationally, the redshift is defined as the change in the wavelength of the light divided by the rest wavelength of the light, as z = (Observed wavelength - Rest wavelength)/(rest wavelength) That is z o o o Note that positive values of z correspond to increased wavelengths (redshifts). So long as the relative velocity between source and observer v is much less than the speed of light, z A relativistic Doppler formula is required when velocity is comparable to the speed of light. z v c 1 v / c 1 v / c 1

19 z o o o

20 z o o o E.g. A QSO at redshift z=3 has its H line shifted by x 3 = 1969 nm. That means we observe it at =2625nm. This is way out in the IR.

22 Hubble s Law Recessional Velocity = H o x Distance Hubble constant units: (km/s)/mpc

23 The Cosmological Redshift is caused by the expansion of space : Hubble Flow Light takes time to travel between its point of emission and its point of detection. The wavelength of light increases by the same amount that space has expanded during the crossing time. So the cosmological redshift is both an indication of distance and of look-back time.

24 The Expansion of the Universe and the Distance Ladder

25 Is there a center of expansion?

26 Recessional Velocity = H o x Distance Hubble constant units: (km/s)/mpc

into the water and observe how fast it moves away from the ship ship speed - multiply by time distance travelled -What s a knot?

27 How do we measure distances on Earth? Use your two eyes (parallax) Use measuring tape or rod Count steps Record your speed and measure time of trip At Sea: -Throw a wood log into the water and observe how fast it moves away from the ship ship speed - multiply by time distance travelled -What s a knot? measure of sea speed 1 knot 1 nautical mile/hour Wood plank attached to rope w/knots every 50 ft throw plank to sea and count nr of knots over a 30sec lapse (e.g. as measured by a sand clock) nr of knots over 30sec = speed in nautical miles per hour

29 The Astronomical Unit (A.U.) the mean distance between Earth and the Sun - can now be measured by radar techniques - e.g. recording the round trip travel time of a signal bounced off the surface of a planet - or from telemetry of space probes. Its value is: 1 A.U. = /-6 m

30 Sizing up the Orbits of Inner Planets V When Venus (V) is at maximum elongation, E S angle EVS = 90 0 and angle SEV=47 0 The radius of Venus orbit (VS) is then VS=ES x sin (SEV) = 0.7 AU Analogous calculation can be done for Mercury.

32 Stellar Distances: parallax Unit of distance parsec That s the distance at which the angle of parallax is 1 1 parsec = 3.26 l.y. Nearest star: Proxima Cen parallax = 0.76 distance =1/0.76=1.3 pc Parallactic distances have been measured out to a few 100 pc, for ~ 10 6 stars.

33 Solar Neighborhood

34 For stars; for radio sources >10 kpc

35 Suppose we measure the color or spectral type of a star As marked, it could be: -A white dwarf -A MS -A giant Correspondingly, the star will have widely different luminosities. How can we distinguish among them?

37 Light curve of an RR Lyrae star Light Curve of a Cepheid star

38 The Local Group of Galaxies

39 The Virgo Cluster Extended X-ray emission: hot ICM Detailed optical catalog (VCC) Well characterized substructure

41 TF Relation: Data km/s SCI : cluster Sc sample I band, 24 clusters, 782 galaxies A clear correlation exists between the rotational velocity of spiral galaxies and their luminosity. Thus, a measure of the amplitude of the rotational velocity can be used to infer the luminosity, and thus the distance of a galaxy.

42 Measurement of a velocity Width 1. Get good image of galaxy, measure PA, position slit 2. Pick spectral line, measure peak along slit 3. Center kinematically 4. Fold about kinematical center 5. Correct for disk inclination, using isophotal ellipticity 6. You now have a rotation curve. 7. Measure the width

43 TF Relation: Data km/s SCI : cluster Sc sample I band, 24 clusters, 782 galaxies A clear correlation exists between the rotational velocity of spiral galaxies and their luminosity. Thus, a measure of the amplitude of the rotational velocity can be used to infer the luminosity, and thus the distance of a galaxy.

46 As for SN type Ia Supernovae of type Ia are standard candles, i.e. they always shine to a uniform, predictable maximum brightness. They can thus be used as distance indicators. They are standard candles because the progenitors of SN Ia are all stars of exactly the same mass: the Chandrasekhar Mass limit between white dwarfs and neutron stars. This is the case because the progenitor is a white dwarf star in a binary system: mass transfer from the companion forces the white dwarf to exceed the Chandrasekhar mass limit, and the star must collapse into a neutron star: the transition produces a SN explosion. SN type Ia are very bright, and they can be seen at very large distances. They can thus be used to monitor the Hubble expansion at earlier epochs in the history of the Universe.

47 The Accelerating Universe

48 Fate of the Universe Recollapsing Universe: the expansion will someday halt and reverse Critical Universe: will not collapse, but will expand more slowly with time Coasting Universe: will expand forever with little slowdown Accelerating universe: Expansion will accelerate with time

50 The cosmic matter/energy density budget

51 What s in store for the future?... Expansion rate accelerating Clustering increasing Intergalactic space density decreasing SFR decreasing Stars running out of fuel it ll be cold and miserable out there

52 The Universe expands The expansion appears to be accelerating The main dynamical component in the accelerating Universe is, now: NOT baryonic matter NOT dark matter but rather

53 Adam and eve eat apples Dinosaurs reign on Earth Solar System forms Galaxy formation starts First Stars Form

54 z o o o The galaxy with the highest redshift to date has z ~ 8.5 That corresponds to a lookback time of ~13.1 Gyr a recessional velocity of ~ 0.97 c an age of the Universe of ~ 700 Myr a present distance of ~ 30 Gyr

55 The Observational Foundations of Modern Cosmology 1. The Universe expands (Hubble 1929); the expansion appears to be accelerating (SN type Ia, WMAP) and to have started 13.7 Gyr ago 2. A background of microwave cosmic radiation (CMB) exists (1965); it has BB spectrum with T = 2.73 K, a dipole at the 3 mk level (due to the peculiar velocity of the MW) and fluctuations at the mk level of well understood statistical properties ( ) 3. The cosmic abundance of light isotopes ( 2 H, 3 He, 7 Li) determines the baryonic energy density of the Universe(1970s-) 4. The statistical properties of the Large scale structure in the distribution of luminous matter (galaxies) 5. The night sky is dark ( Olbers paradox )

1924: Hubble classification scheme 1925: Hubble measures Cepheids (Period-Luminosity) in Andromeda case closed

1924: Hubble classification scheme 1925: Hubble measures Cepheids (Period-Luminosity) in Andromeda case closed Galaxies 1920 - Curtis-Shapley debate on nature of spiral nebulae - distribution in the sky: zone of avoidance Curtis: extinction Shapley:? - apparent brightness of stars(?) observed in some nebulae Shapley: