Download Diapositiva 1 - Universidad de Guanajuato

Astronomía Extragaláctica
y
Cosmología Observacional
Prof. Dr. César A. Caretta
Depto. de Astronomía (UGto)
Astronomía Extragaláctica y Cosmología Observacional
Lecture 1
Morphological Classification of Galaxies
Brief History
 before the concept of galaxies – the nebulæ
• first observations
• first theoretical-philosophical proposals
• catalogs of nebulæ
• attempts to discover the nature of the nebulæ
• the “Great Debate”
• “The Realm of Nebulæ”
 movie
Classification systems

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

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the Hubble “tuning-fork” diagram
extensions to the Hubble sequence
non-optical bands
new proposals for classification systems
the morphological types of galaxies
Depto. de Astronomía (UGto)
Astronomía Extragaláctica y Cosmología Observacional
 First observations
• 964 d.C. – Abd al-Rahman al-Safi [Persia]:
notes the observation of Al Bakr
(Andromeda)
“Book of Fixed Stars”
• 1519 – Fernão de Magalhães [ocean]: notes
observation of Magellanic Clouds
M31 (NOAO, EUA)
Milky-Way (G. Garradd, Australia)
Magellanic Clouds (MSO, Australia)
 First observations
• 1576 – Thomas Digges [England]: “breaks” the
fixed sphere of stars
“A Perfit Description of the Caelestial Orbes”
• 1610 – Galileo Galilei [Italy]: resolves the MW
(Milky Way) into stars with his telescope
“Sidereus Nuncius” and “The Sideral Messenger”
Milky-Way (C. Cook)
 First theoretical-philosophical proposals
• 1750 – Thomas Wright [England]: stars distributed in
shells, MW is one of these shells
“An Original Theory or New Hypothesis of the Universe”
• 1755 – Immanuel Kant [Germany]: diffuse (nebulous)
celestial objects are “island universes”,
similar to the MW
“Allgemeine Naturgeschichte und Theorie Des Himmels”
 Catalogs of nebulæ
• 1654 – G. B. Hodierna
“De admirandis coeli characteribus” (41 nebulae)
• 1755 – A. N. L. de La Caille
(42 nebulae in the Southern Celestial Hemisphere – South Africa)
M1
• 1784 – Charles Messier
“Catalogue de nébuleuses et des amas d’etoiles que l’on découvre parmi les étoiles fixes, sur
l’horizon de Paris” (103 nebulae) – M1 to M110 now
http://www.seds.org/messier/
http://www.ipac.caltech.edu/2mass/gallery/messiercat.html
• 1864 – John Herschel (results of Herschel family work)
“The General Catalogue of Nebulæ” (5079 nebulae)
• 1888-1908 – John L.E. Dreyer
“New General Catalogue of Nebulæ” (NGC)
“Index Catalogues” (IC)
15000
http://ngcic.org/dss/dss_ngc.htm
M110
 Attempts to discover the nature of nebulæ (the Herschel family)
 F. Wilhelm Herschel
Largest telescopes of XVIII century (1,3m)
Discovery of Netuno (1781)
Planetary Nebulæ (1784)
 Karoline Lucretia Herschel
 John F. W. Herschel
• 1787 – first observational model for MW (William)
• 1791 – two types of nebulæ: (i) luminous fluid
(ii) star system
• 1864 – spiral nebulæ avoid the MW (John)
 Attempts to discover the nature of nebulæ (the Herschel family)
Distribution of 14650 galaxies of the catalogs UGC, ESO and MCG
http://www.eso.org/~mhilker/Gallery/gallery_lect.html
 Attempts to discover the nature of nebulæ (new techniques and tools)
• 1797 – Pierre S. de Laplace [France]: nebular hypothesis
for the formation of solar system
“Exposition du Système du Monde”
• 1826 – Photography
N. Nièpce (1826)
J. M. Daguérre (1839)
J. Herschel (1839)
H. Draper (1880) – photographic plates (Orion)
• 1832 – Thomas Henderson [Cape Obs., South Africa]:
measures the parallax of αCent
• 1838 – Friedrich W. Bessel [Germany]: announces the first
measurement of a stellar parallax (61 Cygni)
 Attempts to discover the nature of nebulæ (new techniques and tools)
Leviathan:
1.8 m (72”)
M51
• 1845-1850 – William Parsons, the Lord Rosse [Ireland]: spiral nebulæ
(M51, M99, M33, M74, M101)
• 1864 – William Huggins [England]: first spectroscopic observations of
diffuse nebulæ (NGC6543: 3 lines: H, N and “nebulium” = OIII)
~1868
70 nebulae:
1/3 emission line spectra
(like M42)
2/3 stelar spectra (“white”)
(like M31)
N6543
 The “Great Debate”
• 1906-1922 – Jacobus C. Kapteyn [Netherlands]: counts
of stars in 206 zones (Kapteyn Model)
“First Attempt at a theory of the arrangement and motion of the sideral system”
• 1912-1917 – Vesto M. Slipher [Lowell Obs., USA]:
measured radial velocities of spirals
1913 – 4 ( 3 redshifts, M31 blueshift)
1914 – 12 (11 redshifts, M31 blueshift)
1925 – 43 (41 redshifts, 2 blueshifts)
• 1918 – Harlow Shapley [1.5m (60”), Mt. Wilson
Obs. USA]: distr. of Globular Clusters
(Shapley Model)
• 1916-1923 – Adriaan van Maanen
[Mt. Wilson Obs, USA]:
reported detection of “high
speed” rotation (T  105 yrs)
on M33 and M101
(not confirmed later)
 15 kpc
 100 kpc
 The “Great Debate”
• 1920 – the Great Debate [Nac. Academy of Science, USA]
Opposing views in
2 fundamental issues
▪ the size of the MW
▪ existence of external galaxies
Harlow Shapley lecture and paper (1921)
Spiral nebulae are members of the Great Galaxy
 globular clusters are major structure elements of MW
 MW has lower surface brightness than spiral nebulæ
absorption
 MW stars are redder, on mean, than spirals
 1885 (super)nova on M31, much brighter to be extragalactic
 rotation of spirals (van Maanen), would have supraluminal
velocities if extragalactic
Herbert Curtis lecture and paper (1921)
Spiral nebulae are “island universes”, like the MW
absorption
 Kapteyn model – Shapley distances are overestimated
 all other novæ on spirals are fainter than in MW (M31 ~100 kpc)
 spiral nebulæ avoid the MW plane (J. Herschel)
 spiral diameters have a large angular range (large dist. range)
 spirals have large radial velocities (Slipher), would escape from MW
 edge-on spirals present a dark band, like MW plane
N891
 “The Realm of Nebulæ”
• 1912 – Henrietta S. Leavitt [Harvard College
Obs, USA]: discovered the
period-luminosity relation for Cepheid
variables
• 1925-1929 – Edwin Hubble [2.5m (100”),
Mt. Wilson Obs., USA]:
measured distances for N6822,
M33 and M31 (300 kpc) using Cepheids
• 1929 – E. Hubble: Hubbles’s Law (expansion of the
Universe): v = H0 D
• 1936 – E. Hubble: “The Realm of Nebulæ”
(Hubble sequence...)
 The Hubble “tuning-fork” diagram
Ellipticals
Irregulars
(I, II)
EARLY
→
LATE
UNCLASSIFIED
[Hubble 1926, ApJ 64, 321; Hubble 1936 “The Realm of Nebulae”; Sandage 1975, “Galaxies and the Universe”]
SBbc (NGC 1300)
E0 (M89)
E5 (M59)
Sa (M96)
IrrII (SMC)
 The Hubble “tuning-fork” diagram: criteria
Ellipticals – En
ε = (1  b/a)
n = 10ε
ellipticity*
b
a
E6 (M110)
No ellipticals more
flattened than E7
exist, probably
because there is a
stability limit for
non rotating systems
E5 (M59)
E4 (M49)
* Do not confuse
with “eccentricity”
E1 (M87)
Є=
E0 (M89)
E2 (M60)
 1– b2/a2
 The Hubble “tuning-fork” diagram: criteria
Normal (and Barred) Spirals – S(B)a, S(B)b, S(B)c
Sa (M96)
a → spiral arms tightly wound and smooth
(not resolved into stars or HII regions),
and dominant central bulge or bar
b → spiral arms more open and resolved,
smaller bulge or bar
c → spiral arms very open, patchy and resolved
into stars, star clusters and HII regions,
bulge or bar not prominent
Order of importance:
(i) openness of the winding of the spiral arms,
(ii) size of the bulge or central bar relative to the disc (B/D),
(iii) degree of resolution of the arms into stars and HII regions
Sb (M31)
Sc (M74)
SBa (NGC 4643)
SBb (M95)
SBc (NGC 1365)
 The Hubble “tuning-fork” diagram
IrrII (M82)
IrrI (LMC)
IrrII (N5195)
Irregulars – IrrI, IrrII
I → similar to the
Magellanic Clouds
II → abnormal galaxies,
peculiar
IrrI (SMC)
 Extensions to the Hubble sequence
• 1940 – Shapley & Paraskevopoulos [Proc. N. Ac. Sc. 26, 31]:
added the S(B)d type {between S(B)c and Irr I}
• 1951 – Spitzer & Baade [ApJ 113, 413]: first reference to
lenticular galaxies (already observed by Hubble) –
with discs but not spiral arms
• 1954 – Gerárd de Vaucouleurs [AJ 60, 126]: discovered
a weak spiral structure in LMC
• 1959 – G. de Vaucouleurs [Handbuch of Physik 53, 275]:
introduced intermediate types and fine classifications:
SBb(r) (M95)
S0 (NGC 3115)
 transition between Sp types:
a, ab, b, bc, c
 extension of the sequence beyond S(B)c:
cd, d, dm, m, Im and I0
 transition between “Ordinary” and Barred Sp:
SA, SAB and SB
 presence or absence of rings:
R, (r), (rs), (sr) and (s)
 Extensions to the Hubble sequence: de Vaucouleurs criteria
Extensions:
S(B)d → later spirals (weakly chaotic)
S(B)m → transition Sp/Irr (LMC)
Im → very irregular and loose (SMC)
I0 → chaotic, very rich in gas
and SF regions
Rings:
s → spiral arms begin directly
at the nucleus or a bar
rs, sr → intermediate rings
r → spiral arms begin at a ring
R → external ring
Bars:
A → unbarred
AB → weakly barred
B → barred
Obscuring matter:
S0- → free
S0 → intermediate
amount
S0+ → dark band
 Extensions to the Hubble sequence: classification volume
 Extensions to the Hubble sequence: T stage
• 1974 – G. De Vaucouleurs [In The Formation and Evolution of Galaxies,
ed. J.R. Shakeshaft]:
E
S0
Sa
Sb
Sc
IrrI
IrrII
E-
E0
E+ S0- S00 S0+ S0a Sa Sab Sb Sbc Sc Scd Sd Sdm Sm Im
I0
-6
-5
-4
11
-3
-2
-1
0
1
2
3
4
5
6
7
8
9
10
 Morphological Classification
Some comments on Morphological Classification:
 they were defined from the appearance of galaxies in photographic plates (optical)
 they refer primarily to intrinsic luminous galaxies, but there exists a large population of
dwarf galaxies (van den Bergh, 1960)
(as luminosity decreases, first the rings become invisible, then the spiral arms, and finally
the bar and disc – dwarfs are more frequently E and Irr)
 the word “normal” for unbarred spirals and lenticulars do not mean that they are more common
than barred: about 30% of the spirals and S0s are classified as barred, but this includes
only the most extreme examples since this pattern may be unseen on near edge-on galaxies
 although other classification systems were proposed, the Hubble sequence is still the most used
currently since it retains the main features (and thus accommodates the great majority of bright
galaxies), and it correlates well with some astrophysical properties like bulge/disc ratio, gas
content, star-formation strength, spectrum, integrate colors, chemical composition of ISM, etc
 classifying galaxies is not an unambiguous task: since it is subjective in some aspects, distinct
observers may classify the same object differently
 New proposals for classification systems...
• 1958 – Morgan (Yerkes) system [PASP 70, 364]: based strictly on the
prominence of disc and bulge (E, S, B, I, D, N, L, db), on inclination
(classes 1-7) and on a spectroscopic type corresponding to the nearest
stellar equivalent (a, f, g, k)
{only the N (light dominated by an unresolved nucleus) , D/cD [(supergiant)
spherical galaxies with extended envelopes] and db (dumbbell) are still used
from this system}
• 1960 – Sidney van den Bergh [ApJ 131, 215]: proposed a parallel sequence
of “anemic” spirals (A), putting the tuning-fork as a trident {anemic
spirals are only common on rich clusters...}, and a lum.
class (I-V) based on the degree of order of the spiral
pattern {luminosity correlates with definition of structures!}
• 1982 – Elmegreen & Elmegreen [MNRAS 201, 1021]:
proposed 12 arm classes: from chaotic/fragmented
(1, called “flocculent”) to well-defined (12, called
“grand design”) {classes correlate with luminosity}
• 1996 – Kormendy & Bender [ApJL 464, L119]  :
disky/boxy shaped ellipticals and bulges...
 New proposals for classification systems...
• 1997 – S. van den Bergh
[AJ 113, 2054]  :
proposed another
“volume”
classification system
to include the dwarf
galaxies (discovered
by Shapley in 1939
[Proc. N. Ac. Sc.
USA 25, 565]) and
the cDs (discovered
by Matthews et al.
in 1964
[ApJ 140, 35])
 Non-optical bands
 classification in photographic plates (usually in blue light) loose certain components of galaxies
that are not bright in this band
 galaxies at a substantial redshift have their UV light seen in the blue band!
observing in the band
you see the B band at z
B
0.0
V
0.24
R
0.48
I
0.81
J
1.74
H
2.66
K
3.92
L
6.75
M
9.67
 in other bands, other physical properties dominate the galaxy emission
X-rays
UV
Opt
ROSAT satellite
UIT (Columbia shuttle)
1.3m tel. (KPNO)
young star clusters (obscured
by dust) and weak AGN
yellow bulge (old stars)
+ blue SF regions (spiral
arms defined by dust)
only high energy sources:
AGN and close binaries
near IR
2MASS
old stars of bulge
dominate, arms less
define (less absorption)
far IR
IRAS (60μm)
warm dust (normaly
associated to SF
regions – hot stars)
• Bill Keel’s homepage:
http://www.astr.ua.edu/gifimages/m81series2.html
radio
VLA
SF sites with no dust
absorption [ionized gas +
nonthermal (magn. field)]
 The morphological types
Ellipticals:
 have an elliptical appearance (look as spheroids or ellipsoids)
 have no particular structural features
 have no or little gas, but a population of relatively old stars and
globular clusters
 their luminosity decreases very regularly from center to edge
 their absolute magnitudes range from among the most luminous
galaxies known (MB  -24), to dwarf ellipticals (dE)
 they include the most massive galaxies known
E1 (M87, VirgoA)
Lenticulars (or S0):
 normally they have a ‘lens-like’ shape
 have two main components: bulge and disc,
but without spiral arms
 have large bulges, with smooth light distribution like
the elliptical galaxies, and axial ratios b/a < 0.3
 the disc is very thin and sometimes may contain
some dust (obscuring material)
S0 (M102, N5866)
SBbc (NGC 1300)
 The morphological types
Spirals:
 have a disc-like appearance, with more or less conspicuous
spiral arms of enhanced luminosity, emanating from their
central regions
 central bulge, or spheroidal component, resembles ellipticals
but is small
 sometimes present a bar crossing the bulge, from the end of which the spiral arms originate
(normally less tightly wound)
 their discs are very flattened and with less steeply declining brightness
 contain much gas, young stars and active regions of star formation (HII regions)
 double spiral pattern is common, also a remarkable degree of symmetry with respect to the centre,
but many more complicated configuration of spiral structure are known
Irregulars:
 have amorphous shapes (with no nucleus, no disc,
no spiral arms, and so on)
 are very rich in interestellar matter and young stars,
and are often the location of major outbursts of
star formation
I0 (M82)
 The morphological types
Peculiar (and interacting galaxies):
 have a strange appearance (with tails, jets, ring-like structures,
distortions, etc), normally due to gravitational interactions or collision
between galaxies
 they are amongst the most luminous extragalactic sources in the
far IR due to enhanced SF
 there is only a small % of peculiar systems currently, but this
increases dramatically as we look further and further back in time!
 they are usually classified as having some Hubble type plus a
“p”, indicating the peculiarity
M87
NGC 6872 + IC 4970
Cartwheel
Antennae
 The morphological types
Dwarfs:
 are much less luminous (and massive) than “normal” galaxies
 are hardly seen at distances far beyond the LG
 are the most abundant galaxies in the Universe, and “building blocks”
 frequently they orbit around larger galaxies as satellites
 most have low surface brightness
 may be of several types:
▫ dE – less luminous E (no current SF)
▫ dSph – very low surface brightness spheroids (more massive, but
less centrally concentrated than GC), similar to dIrr in struct.
▫ dS0 – less luminous lenticulars
▫ dS – the last to be discovered [Schombert et al. 1995]
▫ dIrr or dIm – less luminous irregulars (show active SF)
▫ BCD – blue compact dwarves (with centrally concentrated SF, or HII
galaxies, if spread), the only ones with high surf. brightness
dS (N5474)
dS0 (N4431)
BCD (N1705)
dE (M32)
dSph (Cass. Dwarf)
dIrr (IC 10)
 The morphological types
Low Surface Brightness Galaxies (LSB):
 most are dwarves, but there are many “normal” LSB
 their abundance (frequency) and properties are very badly known
since they are very hard to detect
LSB (UGC 285)
LSB (IC 342)
LSB (UGC 7332)
LSB (UGC 7698)
 Further readings:
Papers:
 V. Trimble, 1995. PASP 107, 1133 – 1920 Shapley-Curtis Debate
 A. Sandage, 1975. In “Galaxies and the Universe”, eds. A. Sandage, M. Sandage &
J. Kristian, Univ. Chicago Press – Morphological classification of galaxies from
before Hubble to 1975
 A. Naim et al. 1995. MNRAS 274, 1107 – Expert astronomers  machines in
classifying galaxies
Books:
 F. Combes, P. Boisse, A. Mazure & A. Blanchard 1995. “Galaxies and Cosmology”
(A&A Library), Springer-Verlag – chapter 1
 J. Binney & M. Merrifield 1998. “Galactic Astronomy” (Princeton Series in
Astrophysics), Princeton Univ. Press – chapter 4
 M.S. Longair 1998. “Galaxy Formation” (A&A Library), Springer-Verlag
– chapter 3
 M.H. Jones & R.J.A. Lambourne 2003. “An Introduction to Galaxies and
Cosmology”, Cambridge Univ. Press – chapter 2
Internet:
 http://www.astr.ua.edu/keel/galaxies/ – Bill Keel’s homepage
 http://nedwww.ipac.caltech.edu/level5/basic_data.html