ModernModern observationalobservational astronomy:astronomy: fromfrom starsstars toto galaxiesgalaxies Martes Martes Miercoles Jueves Martes Martes Viernes I – Overview on modern telescopes & Observation techniques
II – Some history of galactic astronomy
III – Astronomical measurements
IV – Properties of stars
V – Star clusters & Stellar populations
VI – Milky Way & Local Group
VII – Disk galaxies & Group environment
VIII – Ellipticals & Galaxy Clusters
IX – Galaxy evolution in different environments
X – Large scale galaxy distribution & Observational cosmology
Dr. Michael Hilker (Sternwarte Bonn) ModernModern observationalobservational astronomy:astronomy: fromfrom starsstars toto galaxiesgalaxies Universidad Nacional de Colombia, Bogota, Agosto 2005
I – Overview on modern telescopes and observation techniques Dr. Michael Hilker (Sternwarte Bonn) InIn thethe EinsteinEinstein year:year:
DidDid AlbertAlbert EinsteinEinstein hadhad observingobserving experience?experience?
ProbablyProbably not.not.
ButBut forfor sure,sure, hehe waswas interestedinterested inin anyany observationalobservational resultresult atat thatthat time…time… ...... andand alsoalso visitedvisited observatories!observatories!
Dr. Michael Hilker (Sternwarte Bonn) AlbertAlbert EinsteinEinstein visitingvisiting observatoriesobservatories
on solar tower (Mount Wilson 1930)
At Yerkes Observatory (1930)
Dr. Michael Hilker (Sternwarte Bonn) Galileo’sGalileo’s telescopetelescope (1609)(1609) Newton’sNewton’s telescopetelescope (1671)(1671)
Dr. Michael Hilker (Sternwarte Bonn) TheThe telescopestelescopes ofof Hevelius:Hevelius: smallsmall …… largelarge …… hugehuge …… ca.1673ca.1673 ca.1647ca.1647
Dr. Michael Hilker (Sternwarte Bonn) RefractorRefractor ReflectorReflector
For a given focal length f, the tube of a refracting telescope has to be much longer than that of a reflecting telescope. Today, focal reducers allow even shorter telescope support structures.
Dr. Michael Hilker (Sternwarte Bonn) Observatory 350 years ago …
… and today
Dr. Michael Hilker (Sternwarte Bonn) Chile, Atacama desert: the Very Large Telescope (VLT): 4 single telescopes with mirrors of 8.2m diameter
Dr. Michael Hilker (Sternwarte Bonn) Chile, Atacama desert: the Very Large Telescope (VLT): transportation of mirrors
Dr. Michael Hilker (Sternwarte Bonn) Chile, Atacama desert: the Very Large Telescope (VLT): polished 8.2m mirror
Dr. Michael Hilker (Sternwarte Bonn) One of the Unit Telescopes (UT) at „El Paranal“ (VLT)
Dr. Michael Hilker (Sternwarte Bonn) Observing at the beginning of the last century (Edwin Hubble) …
… and today
Dr. Michael Hilker (Sternwarte Bonn) „Residencia“ of the Very Large Telescopes
Dr. Michael Hilker (Sternwarte Bonn) Mauna Kea, Hawaii Las Campanas, Chile
telescope control room
Dr. Michael Hilker (Sternwarte Bonn)
Dr. Michael Hilker (Sternwarte Bonn) The Effelsberg 100-meter radio telescope
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Dr. Michael Hilker (Sternwarte Bonn) RecentRecent developmentsdevelopments Always the progress in astronomy has been dictated by the advances in technology. Some of the advanced astronomical instrumentations and techniques and their implications for galactic astronomy are listed here. Detectors: • charge coupled devices (CCDs) allows to study very faint phenomena, like very distant galaxies and outermost part of galaxies • infrared detector arrays study galaxies in the near infrared where the absorbing effects of dust are small • integral field units (IFUs) makes two-dimensional spectroscopy with high resolution possible, i.e. for dynamics in cores of galaxies Telescope technology: • bigger telescopes, 8 -10m in diameter (Keck, VLT) going to fainter limits • interferometry with radio and optical telescopes improving the resolution • active optics - corrects the mirror deformations improving the PSF • adaptive optics - corrects the atmosphere’s distortions in real time reaching the diffraction limit - resolves very small structures Dr. Michael Hilker (Sternwarte Bonn)
Dr. Michael Hilker (Sternwarte Bonn) Astronomical satellites: • HST - largest optical telescope in space dark sky, diffraction limited, probes galaxies at high redshifts and details in nearby galaxies • astrometry (Hipparcos, GAIA, SIM) measures accurate stellar positions structure of our Galaxy, absolute calibration of distance scale • X-ray (Einstein, ROSAT, Chandra, XMM) detects the hot gas in ellipticals and galaxy clusters, active galactic nuclei
• infrared (COBE, Spitzer) looks through dust (near-IR), maps the dust distribution in galaxies (far-IR)
Computer technology: • fast processors automatic data reduction pipelines, support modern observing technology • storage capacity handling of large quantities of data, availability of large database of galactic astronomy (images, parameters) • parallel processors modelling of galaxy formation and evolution with higher and higher resolution (+ GRAPE processors) Prominent surveys: Sloan Digital Sky Survey (SDSS), 2MASS, 2dF Survey, SAURON, Macho Project, etc.
Dr. Michael Hilker (Sternwarte Bonn) The “astronomical” window Many wavelength regimes can only be seen from space
Dr. Michael Hilker (Sternwarte Bonn) The electromagnetic spectrum What do we measure in different wavelengths? Radio: atomic, molecular and ionized gas, hydrogen, (stars) Microwave: dense gas, molecules The shorterInfrared: the interstellar wavelength… dust, star formation old, cold stars Visible: stars, blue: young, metal-poor … the hotter the red: material!old, metal-rich … the moreUltraviolet: energetic young, hot the stars process! X-ray: hot gas in and between galaxies, double stars, SN remnants Gamma: highly accelerated particles, accretion onto black holes
Dr. Michael Hilker (Sternwarte Bonn) The Milky Way as seen in different wavelength regimes
Dr. Michael Hilker (Sternwarte Bonn) Astronomical observations at different wavelengths
Spitzer Space Telescope Hubble Space Telescope Chandra X-ray observatory (infrared) (optical) (X-ray)
Keck Telescope (Hawaii) VLT (Chile) Very Large Array (USA) (optical, IR, UV) (optical, IR, UV) (Radio)
Dr. Michael Hilker (Sternwarte Bonn) Observations from Earth versus Observations from Space - Resolving into fainter details
White dwarfs in M4
Dr. Michael Hilker (Sternwarte Bonn) Observation of the famous Hubble Deep Field
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Dr. Michael Hilker (Sternwarte Bonn) Space based observing at various wavelengths
SN 1987A after 15 years (optical with HST)
Jet of elliptical M87 (X-ray/radio/optical)
Trifid nebula (infrared with Spitzer Space Telescope)
Dr. Michael Hilker (Sternwarte Bonn) The nearest elliptical galaxy: Centaurus A
Dr. Michael Hilker (Sternwarte Bonn) Centaurus A at various wavelengths
Dr. Michael Hilker (Sternwarte Bonn) HI in the merger remnant Centaurus A
Dr. Michael Hilker (Sternwarte Bonn) X-ray in Stephan´s Quintet
Dr. Michael Hilker (Sternwarte Bonn) SomeSome modernmodern instruments:instruments: • FOcal Reducer/low dispersion Spectrograph (FORS) optical imaging and low resolution spectroscopy • Wide Field Imager (WFI) optical wide-field imaging • Infrared Spectrometer And Array Camera (ISAAC) infrared imaging and spectroscopy • Ultraviolet and Visual Echelle Spectrograph (UVES) high resolution spectroscopy • Fibre Large Array Multi Element Spectrograph (FLAMES) low and high resolution multi-object spectroscopy + IFUs • 2dF spectrograph (2 degree field) wide-field multi-object spectroscopy • Very Large Telescope Interferometer (VLTI) high spatial resolution imaging
Dr. Michael Hilker (Sternwarte Bonn)
Dr. Michael Hilker (Sternwarte Bonn) FOcal Reducer/low Dispersion Spectrograph (FORS)
FORS1 CCD chip
FORS optical layout
Dr. Michael Hilker (Sternwarte Bonn) Wide Field Imager (WFI) at 2.2m tele- scope at La Silla
8k x 8k CCD array, field-of-view: 34’x33’
blue red
quantum efficiency of CCDs
Dr. Michael Hilker (Sternwarte Bonn) Infrared Spectrometer And Array Camera (ISAAC)
ISAAC optical layout Dr. Michael Hilker (Sternwarte Bonn) Fibre Large Array Multi Element Spectrograph (FLAMES)
MEDUSA fibre setup
The fibre positioner OzPoz and GIRAFFE spectrograph
Dr. Michael Hilker (Sternwarte Bonn) Ultraviolet and Visual Echelle Spectrograph (UVES)
GIRAFFE spectrograph
Dr. Michael Hilker (Sternwarte Bonn) The Anglo-Australian Observatory
Dr. Michael Hilker (Sternwarte Bonn) The AAO 2 Degree Field Spectrograph
Dr. Michael Hilker (Sternwarte Bonn) 400 Optical Fibres: ‘Byzantine tangles’
1. Configuration software 4. Results: 400 spectra on 2 CCDs
2. Fibre positioning by robot 3. Completed field plate
Dr. Michael Hilker (Sternwarte Bonn) One of the largest redshift surveys
Dr. Michael Hilker (Sternwarte Bonn)
Dr. Michael Hilker (Sternwarte Bonn) The layout of SAURON
field of view: 41” x 33”, resolution: 0.”94 x 0.”94
Dr. Michael Hilker (Sternwarte Bonn) SAURON stellar velocity field showing NGC 4365 a kinematically reconstructed decoupled core surface bright- ness image and slowly varying position and stellar velo- in outer parts city field showing a kinematically decoupled core triaxiality velocity disper- sion map Mg b map
Hβ map
Dr. Michael Hilker (Sternwarte Bonn) Very Large Telescope Interferometer (VLTI) VLT Interferometer principle
separation/resolution ~ λ/D D: distance between mirrors
Interferometric tunnel
Dr. Michael Hilker (Sternwarte Bonn) SelectedSelected futurefuture developments:developments:
• Atacama Large Millimeter Array (ALMA) high spatial resolution submillimeter ‘imaging’ and spectroscopy proto-type telescopes at place (i.e. APEX), full start in 2008 • Gaia (formerly Global Astrometric Interferometer for Astrophysics) high precision astrometry, photometry and spectroscopy of 1.000.000.000 stars, launch planned for 2011 • OverWhelmingly Large telescope (OWL) 100-meter optical and near-infrared telescope for high spatial resolution imaging and spectroscopy science operations planned for 2021 • … and many more
Dr. Michael Hilker (Sternwarte Bonn) Atacama Large Millimeter Array (ALMA) at 5100 meter altitude on the Chajnantor plateau in Chile’s Atacama desert
APEX telescope
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Dr. Michael Hilker (Sternwarte Bonn)
Dr. Michael Hilker (Sternwarte Bonn) OverWhelmingly Large telescope (OWL)
Dr. Michael Hilker (Sternwarte Bonn)
Dr. Michael Hilker (Sternwarte Bonn)
Dr. Michael Hilker (Sternwarte Bonn) ModernModern observationalobservational astronomy:astronomy: fromfrom starsstars toto galaxiesgalaxies Universidad Nacional de Colombia, Bogota, Agosto 2005
II – Some history of galactic astronomy Dr. Michael Hilker (Sternwarte Bonn) GalaxiesGalaxies -- whatwhat areare they?they? The word “galaxía” is Greek and means “Milky Way” This word originally described the stream of diffuse white light streching across the night sky. In the Greek mythology, the “galaxy” was explained by a river of milk flowing from the breast of Hera, wife of Zeus. The Romans called the same “Via Lactea” = “Milky Way” Only when discovering the true nature of our Milky Way, the word “galaxy” was adopted for all other such systems in the universe. Todays definition of a galaxy:
Gravitationally-bound collection of stars and interstellar matter (gas, dust)
Commonly, the Milky Way is simply called “the Galaxy” and everything “belonging to the Milky Way” with the adjective “Galactic”, whereas “galactic” refers to galaxies in general. The abbreviation for Milky Way is ‘MW’.
Dr. Michael Hilker (Sternwarte Bonn) TheThe discoverydiscovery ofof galaxiesgalaxies andand ourour MilkyMilky WayWay -- aa briefbrief historyhistory --
1610 Galileo Galilei discovers (with the first telescopes in hand) that the luminous “celestial fluid” consists of huge numbers of faint stars, showing that the Milky Way primarily is a stellar system.
1750 Thomas Wright - historical model of the Milky Way
Dr. Michael Hilker (Sternwarte Bonn) ~1750 Immanuel Kant publishes his work on “General Natural History and Theory of the Heavens”. Based only on a small amount of observational evidence, Kant presented, using his powers of reasoning, the following line of arguments:
- the rotation of the planets in a plane naturally follows from the attractive force of gravity from the Sun which bounds the Solar System - the stellar system of the Milky Way is similar in arrange- ment to the Solar System, but on a huge scale - if gravity acts between stars as it does between Sun and planets, the Milky Way should show a disk-shaped stellar distribution
Dr. Michael Hilker (Sternwarte Bonn) Kant’s line of arguments (continued): - because of its huge size the motion of the stars on the sky (rotation of the disk) is immeasurable - the small number of stars seen away from the Milky Way do not follow the ordered motion of the main component, but have randomly distributed orbits (like comets) - some of the faint, fuzzy, elliptical patches of light seen in the sky are complete island universes like our Milky Way viewed from large distances and at a variety of angles
~1790 Charles Messier compiled a catalog of 109 of the brightest “nebulae” in the northern hemisphere. Many of the brightest, nearby galaxies still today are commonly called M##, for example M31 = Andromeda Galaxy
Dr. Michael Hilker (Sternwarte Bonn) 110 Messier objects Messier 110 110 Messier objects
only 29 objects are indeed galaxies
Dr. Michael Hilker (Sternwarte Bonn) ~1800 Sir William Herschel and his sister Caroline and his son John compiled a catalog of nearly 5000 nebulae. Also they resolved star clusters into indi- vidual stars, and discovered planetary nebulae. By “star gauging”, the first map of the Milky Way was drawn by Herschel in 1785.
Dr. Michael Hilker (Sternwarte Bonn) ~1850 William Parsons (Third Earl of Rosse) constructed a 72 inch telescope, the largest telescope at that time (only surpassed by the 100-inch Mount Wilson telescope in 1917). He examined Herschel’s nebulae and could resolve them in more details which resulted in the division of two classes of objects:
spiral nebulae and elliptical nebulae also point-like sources in nebulae were found
Dr. Michael Hilker (Sternwarte Bonn) Lord Rosse’s sketch of the Whirlpool Nebula (M51)
~1850
Observatorium Hoher List (M. Altmann, 1998) Dr. Michael Hilker (Sternwarte Bonn) 1888 John Luis Emil Dreyer publishes the New General Catalog (NGC) with 7840 objects (3200 galaxies), 1895 follows the extension, the Index Catalog (IC) with a further 5836 objects (2400 galaxies), then 1908 the Second IC. Still today the use of galaxy names according to these catalogs is very common, for example NGC 1399 (a galaxy in the Fornax Cluster) since 1890 The application of photography to astronomy revolutionized the subject. A new age of quantitative analyses was born.
today CCD-technology took the place of photography. Bigger and bigger telescopes as well as various satellites allow the detection of fainter and fainter galaxies and the resolution in more and more details.
Dr. Michael Hilker (Sternwarte Bonn) Map showing the distribution of NGC and IC objects
“zone of avoidance”
Dr. Michael Hilker (Sternwarte Bonn) TheThe modelmodel ofof ourour MilkyMilky Way:Way: situationsituation inin 17901790
“star gauging”: counting all stars in 683 different regions of the sky assumptions: • all stars have about the same intrinsic brightness • they are distributed uniformly through the Galaxy • one can see stars all the way to the edge of the system
ImprovementImprovement byby KapteynKapteyn 19101910
Kapteyn Universe: photographic plates of 200 selected areas improvements: proper motions, radial velocities average distances for stars at various brighness levels three-
dimensional distribution of stars
Dr. Michael Hilker (Sternwarte Bonn) Kapteyn’s results: • Sun is located close to the center heliocentric Universe • density of stars drops uniformly with distance from the center • absolute size: thickness: 50% density at 150 pc diameter: 10% density at 5.600 pc, 1% at 17.000 pc alternative explanation: • significant obscuration of distant stars by interstellar medium • some absorbing clouds where no star is seen rejected by the following line of arguments (Kapteyn): • the light of stars travels through a homogeneous interstellar gas • Rayleigh scattering of the star’s photons is more efficient for blue light • thus distant stars should be systematically redder • comparison of photographic and visual magnitudes shows hardly reddening obscuration is unimportant!! Dust: Aλ ~ 1/λ What’s wrong? What didn’t Kapteyn know? Gas : Aλ ~ 1/λ4 The dominant source of obscuration is dust!!! Dust absorption is less wavelength dependent which results in large obscuration but low reddening. Trumpler (1930) first determined the amount of dust by analysing the apparent brightnesses of open clusters as a function of their distances.
Dr. Michael Hilker (Sternwarte Bonn) The Milky Way seen through a 50cm telescope
Dr. Michael Hilker (Sternwarte Bonn) 19201920
New discovery by Shapley: • detailed study of globular clusters shows a concentration of their distribution towards Sagittarius as major element of the Galaxy they should be symmetrically distributed around its center the Sun is not in the center of the Milky Way (~ 15 kpc away) the globular cluster system has a size of ~ 100 kpc in diameter (using Cepheids as distance indicators)
Also Shapley didn’t know about dust absorption, and concluded: • absence of globular clusters in the Galactic plane can be explained by rapid destruction due to strong tidal forces in the plane • there exists a local concentration of stars around the Sun (indeed the so called Gould’s Belt is a local loose cluster centered around the Sun)
Dr. Michael Hilker (Sternwarte Bonn) Curtis: • the Milky Way is small • the nebulae are similar large remote universe islands
AprilApril 19201920 thethe GreatGreat DebateDebate (National Acadamy of Science, Washington) Result: no winner in this “debate”, ? but Curtis was the better, Shapley: more convincing speaker • the Milky Way is large (better discussion fol- • nebulae are small and within the Milky Way lowed in publications)
Dr. Michael Hilker (Sternwarte Bonn) Curtis’ arguments in favor of nebulae being remote stellar systems: • different angular sizes of similar nebulae (arcseconds to degrees) • “novae” in M31 point to remote system at ~ 100 kpc (with diameter of 3 kpc) • spectra of nebulae similar to integrated MW spectrum • Doppler-shift of lines in nebulae spectra are larger than for stars in MW • nebulae have no notable transverse motion, so must be far away • edge-on spirals contain dark bands through there centers ring of dust can explain the absence of nebulae in the zone of avoidance
Shapley’s arguments in contra: • since the MW is very large, nebulae would be at tremendous distances • MW has lower surface brightness than spiral nebulae • many spiral nebulae are significantly bluer than the MW • observation by van Maanen: spiral nebulae are rotating with a period of ~ 10 years must be small in order to not exceed speed of light
Both, Curtis and Shapley, were right in some points, but didn’t know about dust absorption and were confused by the results of others (Kapteyn’s model, van Maanen’s spurious detections)
Dr. Michael Hilker (Sternwarte Bonn)
5 1923 Edwin Hubble puts an end to the de- bate when resolving with the 100-inch telescope at Mount Wilson the outer parts of nearby spirals into stars. In Andromeda (M31) he found Cepheid variable star, putting its distance to ~ 300 kpc (today: ~ 760 kpc)
1927 Lindblad Detailed kinematical model of the Milky Way 1928 Oort Theory of Galactic stellar kinematics 1930 Trumpler Study of open clusters and dust absorption 1932 Jansky Detection of radio emission of the Galaxy 1944 Baade Study of resolved stellar populations in galaxies 1958 Oort, Kerr & Westerhout First complete HI map (21 cm) 1970s Dynamical and observable mass differ dark matter
Dr. Michael Hilker (Sternwarte Bonn) The Hubble “Tuning” Forke
early-types late-types Hubbles idea: ellipticals evolve to spirals
1926: simple tuning fork 1936: S0 & SB0s added
Dr. Michael Hilker (Sternwarte Bonn) Distribution of atomic hydrogen in the plane of the Milky Way (Oort, Kerr & Westerhout 1958)
Dr. Michael Hilker (Sternwarte Bonn)
Dr. Michael Hilker (Sternwarte Bonn) Optical image of the Milky Way (Lund Observatory)
Some properties of the Milky Way (a typical spiral galaxy): mass: ~ 10 M = 2x10 kg (1 M = 2x10 kg) diameter of disk: ~ 30 kpc
Dr. Michael Hilker (Sternwarte Bonn)
average density: ~ 0.1 star per pc thickness of disk: ~ 1 kpc
11 41 30
3 Infrared image of the Milky Way by the COBE satellite
Dr. Michael Hilker (Sternwarte Bonn) A more generalised classification scheme including dwarfs
mass
star formation activity
Dr. Michael Hilker (Sternwarte Bonn)
Dr. Michael Hilker (Sternwarte Bonn)
Dr. Michael Hilker (Sternwarte Bonn) foreseen launch in June 2008
Dr. Michael Hilker (Sternwarte Bonn) KEPLER: detection of telluric planets
mission goals: ~50 planets with R ~ 1 Re ~185 planets with R ~ 1.3 Re ~640 planets with R ~ 2.2 Re ~870 giant inner planets with P < 1 week
Dr. Michael Hilker (Sternwarte Bonn) KEPLER: field-of-view and neighbourhood
Dr. Michael Hilker (Sternwarte Bonn)
Dr. Michael Hilker (Sternwarte Bonn)
Dr. Michael Hilker (Sternwarte Bonn)