Morphology-Density Relation

The fraction of the population that is

spiral decreases from the field to high density regions.

[Dressler 1980]

High Low

EllipticalsS0

Spirals/Irr

Nature or Nurture?

The HI Line and Extragalactic Astronomy

0. Predicted 1945 van de HulstFirst detected 1951 Ewen & PurcellFirst extragalactic detection 1953

1. 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.

Substructure in the Local Group

Giant spiralsdSph (+dEll)dIrrdIrr/dSph

VLA maps

SeeJohn Hibbard’sGallery of Roguesat

www.nrao.edu/astrores/HIrogues

NGC 3628

NGC 3623NGC 3627

Leo Triplet

M96 Ring

Schneider, Salpeter & Terzian 19Arecibo map

VLA map

HI 1225+01

Optical galaxy

The Virgo Cluster of Galaxies

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

• Virgo Cluster Catalog (BST85)• ~2000 gals, based on morphological

appearance• Largely confirmed by redshift

measurements Binggeli, Sandage & Tammann 1985, AJ 90, 1681

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

NGC 4438:A ram-pressure current victim

Solanes et al. 2002

Dots: galaxies w/ measured HIContours: HI deficiencyGreyscale: ROSAT 0.4-2.4 keV

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

The Observational Foundations of Modern Cosmology

1. The Universe expands (Hubble 1929); the expansionappears 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 velocityof the MW) and fluctuations at the mK level of wellunderstood statistical properties (1992-2003)

3. The cosmic abundance of light isotopes (2H, 3He, 7Li)determines the baryonic energy density of the Universe(1970s-)

4. The statistical properties of the Large—scale structurein 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 collapseand that equilibrium is unstable

•1917 Einstein obtains new set of equations of gravitational field (TGR) unstable Universe, unless a “cosmological constant ” term is

introduced•1922-23 Friedman obtains set of expanding solutions of Einstein’s

equations. They are independently obtained by Lemaitre in 1927•1929 Hubble discovers universal expansion: v = Ho d

He determines Ho to be ~500 km/s/Mpc universal age ~ 2 GyrEinstein declares introduction of his “greatest error ever”

•late 1940s Gamow, Alpher and Herman postulate existence ofcosmic 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

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.

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.

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

Note that positive values of z correspond to increased wavelengths (redshifts).

oo

oz

So long as the relative velocity between source and observer v is much less than the speed of light,

A relativistic Doppler formula is required when velocity is comparable to the speed of light.

cvz

1/1/1

cvcvz

oo

oz

E.g. A QSO at redshift z=3 has its H line shifted by 656.3 x 3 = 1969 nm.

That means we observe it at 1969+656.3=2625nm. This is way out in the IR.

oo

oz

Recessional Velocity = Ho x Distance

“Hubble constant” units: (km/s)/Mpc

Hubble’s Law

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 ofdistance and of “look-back time”.

The Expansion of the Universeand the “Distance Ladder”

Is there a center of expansion?

Recessional Velocity = Ho x Distance

“Hubble constant” units: (km/s)/Mpc

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/knotsevery 50 ft throw plank to sea andcount nr of knots over a 30sec lapse(e.g. as measured by a sand clock)nr of knots over 30sec = speed in nauticalmiles per hour

1 A.U. = 149 597 870 691+/-6 m

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:

E

V

S

Sizing up the Orbits of Inner Planets

When Venus (V) is at maximum elongation,

angle EVS = 900

and angle SEV=470

The radius of Venus’ orbit (VS) is then

VS=ES x sin (SEV)= 0.7 AU

Analogous calculation can be done for Mercury.

Stellar Distances:parallax

Nearest star: Proxima Cenparallax = 0.76”distance =1/0.76=1.3 pc

Unit of distance parsecThat’s the distance at which the angle of parallax is 1” 1 parsec = 3.26 l.y.

Parallactic distances have been measured out to a few 100 pc, for ~ 106 stars.

Solar Neighborhood

For stars; for radio sources >10 kpc

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?

Light curve ofan RR Lyrae

star

Light Curve ofa Cepheid

star

The Local Group of Galaxies

The Virgo Cluster

• Extended X-ray emission: hot ICM• Detailed optical catalog (VCC)• Well characterized substructure

TF Relation: Data

SCI : cluster Sc sampleI band, 24 clusters, 782 galaxies

A clear correlation exists betweenthe rotational velocity of spiralgalaxies and their luminosity.

Thus, a measure of the amplitude ofthe rotational velocity can be used toinfer the luminosity, and thus the distance of a galaxy.

100 150 250 km/s

Measurement of a velocity Width1. 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 diskinclination, usingisophotal ellipticity

6. You now have a rotation curve.

7. Measure the width

TF Relation: Data

SCI : cluster Sc sampleI band, 24 clusters, 782 galaxies

A clear correlation exists betweenthe rotational velocity of spiralgalaxies and their luminosity.

Thus, a measure of the amplitude ofthe rotational velocity can be used toinfer the luminosity, and thus the distance of a galaxy.

100 150 250 km/s

As for SN type Ia …

•Supernovae of type Ia are “standard candles”, i.e. they alwaysshine to a uniform, predictable maximum brightness. They canthus 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 Masslimit between white dwarfs and neutron stars.

•This is the case because the progenitor is a white dwarf starin a binary system: mass transfer from the companion forcesthe white dwarf to exceed the Chandrasekhar mass limit, andthe star must collapse into a neutron star: the transition producesa SN explosion.

•SN type Ia are very bright, and they can be seen at very largedistances. They can thus be used to monitor the Hubble expansionat earlier epochs in the history of the Universe.

The Accelerating 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

Fate of the Universe

• Accelerating universe:Expansion will accelerate with time

The cosmic matter/energy density budget

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

The Universe expands

The expansion appears to be accelerating

The main dynamical component in theaccelerating Universe is, now:

NOT baryonic matterNOT dark matter

but rather

First Stars FormGalaxy formation starts

Solar System forms

Dinosaurs reign on EarthAdam and eve eat apples

The galaxy with the highest redshiftto 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

oo

oz

The Observational Foundations of Modern Cosmology

1. The Universe expands (Hubble 1929); the expansionappears 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 velocityof the MW) and fluctuations at the mK level of wellunderstood statistical properties (1992-2003)

3. The cosmic abundance of light isotopes (2H, 3He, 7Li)determines the baryonic energy density of the Universe(1970s-)

4. The statistical properties of the Large—scale structurein the distribution of luminous matter (galaxies)

5. The night sky is dark (“Olbers’ paradox”)