-
S~j,~ ~ >~!:7 ~~
s~ &u~~ ~a~~~r~~ 0/ 'i;~cE (~);, --~ ..~ ~ ~ ~7~ r a. ~~. ~
tVo~ ~~~ 0"-P(y~ ("t,+~ > .... ) ~~.v.> ~ effW:>'
@] ~~~~~/~~ ~&..~o~ a?.?
~ tM
-
The Hubble classifica.on reading: Binney
and Merrifield Sec 4.1, 4.1.1
-
Ellip.cal galaxies
• Smooth, structureless • Designated En,
where n=10(1-‐b/a); b/a is ra.o
of major to minor axis
• Can be either very luminous
(giant ellip.cals) or much less
so (dwarf ellip.cal or dE)
• NGC 205, M32 (M31 satellites)
are both dEs • Dwarf spheroidal
(dSph) galaxies are very low
surface brightness objects which are
only possible to detect within
a few Mpc
-
Disk galaxies: Spiral and S0
(len.cular)
• Two branches: barred and not
barred, for both spirals and
S0s
• S0: bright central region (bulge)
plus region where brightness drops
less sharply (envelope; this is
the disk)
• Depending on strength of dust
absorp.on, classified S01, 2 or
3
• Barred S0s classified by strength
of bar: SB01, 2 or 3
-
Disk galaxies: spirals
• Unbarred spiral has central bright
region surrounded by disk with
spiral arms
• Barred spiral has bar interior
to spiral arms
-
Spiral subtypes
• Spiral subtypes Sa, Sb, Sc or
SBa SBb and SBc according to
(a) rela.ve importance
of disk and bulge: Sa
galaxies generally have large B/D
ra.os, Sc galaxies are disk
dominated
(b) .ghtness of
winding of spiral arms: Sa
.ghtly wound, Sc loose
(c) how well spiral
arms are resolved into individual
stars and HII regions: Sc is
most ‘resolved’ – due to young
luminous stars and luminous HII
regions
-
Hubble stage T
-
24 Galaxies today [Ch.2
Figure 2.3. The changing appearance of galaxies in different
parts of the electromagnetic spectrum is illustrated by this series
of images, showing the nearby spiral galaxy M81. In X-rays, only
the active nucleus and accreting compact objects in binary systems
(white dwarfs, neutron stars, and black holes) appear, with no hint
of the rich stellar structure. In the ultraviolet, only the hottest
(unobscured) stars are bright, so that the spiral pattern can be
traced via star-forming regions, but the central bulge of old stars
has almost vanished. This appearance resembles some spiral galaxies
seen at large distances, where the redder bulge light has shifted
out of the optical bands. The familiar visible-light image shows
both the spiral pattern and the old bulge population, while in the
near-infrared, the spiral pattern and starforming regions are much
more subdued. This change in apparent structure with wavelength has
been dubbed the "morphological K-correction". X-ray data are from
ROSAT, extracted from the HEASARC archive at NASA's Goddard Space
Flight center. The UV image is a combination of observations
obtained by the GALEX satellite at wavelengths 1,500 and 2,300 A.,
used courtesy of NASA. The optical images are reproduced courtesy
of Greg Bothun. (The infrared data are from the 2-Micron All Sky
Survey (2MASS), a joint project of the University of Massachusetts
and the Infrared Processing and Analysis Center/California
Institute of Technology, funded by NASA and the NSF.)
-
2)t.Ua¥ tJo.ku UJ ~ vr~)~r~ cue ~
~S
~ y~ : S~ S~) /fY' ;?7V~c~ ~~~~ O
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~1.ot.V - ~c>"V ~ ~ 'P~
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IU~~ ~ ~
F~.
-
The Spectrum of the Night Sky
16
19
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. o!uJbJ
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~7 J
-
o
---++- +'1-+-+....
N
+ - - +++ ---+ +
+ - - .. -+-+ 50
RADIUS (areSLC. )
FIG. 3. Vband luminosity profile. The solid line indicates the
llC:Stfitting r l/4 component while the dashed line corresponds to
the exponential disk. The fits are schematic only, as the total
luminosity profile does not readily deconvolve into distinct
components. Radius is in arcsec.
Itkkv / Ian nL~ 1
-
/f} /0/
30StLC ~~
52" a ~
. 11:5"£ sr ~(/U-AVY) ~~
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4Vt:U(.
- ,w-.Jrut-~~ ~ --
-
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(/IJ"Y ~ oU. 30 ~
-
. .
~ Ilu.MIe.. c/a..sS~4 Zo~ IJerv(!S as ~e. ~~V
~7 cY ~ ,ft~ol.
7k "'O#~/~a.t ~t«A.~ ~oti ~J..1: ~fy~~~ ~ 3~ &.
Q.VOkJ;:o~.
(tN' rIDes t/; .'?) /J') t ~)(fe ~ k~ :i4~ ~ ~~
~~.
1l'Ju.L&;.,;~cJi: ~81S ~.!«e.S 84:.CU .e. ~Yo.L e
-
~-~ ~~~~~ ~ .A, "'- oaL* ~. ~ .kStd.
-
1.5
1\ 5 t~ t t t +~ t; t! 't t t t ~
-V 1 tID Itt t I Itt t t~.2
( a ) 15
11 -
1\.. ...J T , t~ t 'f 'f 't 't T t
V 10 0 tID .2
r f r r f 'Ij 1T 9 (b) II
r~--r---I I I I I o
r -I
11 1\ L10 '1 'f T~ 'T fo !
...t" < V r iTT !! 1) tID I f, ..,..2 10
(c) 1f
J
E so SOn Sa Sab Sb @ Se Sed Sd Sm 1m FiKure 2 Global galaxy
lJarameters vs morphological type. Circles represent the RC3-UGC
sample; squares the RC3-LSc sample. Filled symbols are medians;
open ones are mean values. The lower bar is the 25th percentile;
the upper the 75th percentile. Their range measures half the
sample. The sample size is given in Table I. (a) log linear radius
Rlin(kpc) to an isophote of 25 B mag/arcsec2 , (b) log blue
luminosity Lo in solar units. (c) log total mac;s MT in solar
units. (d) log total mass-to-Iuminosity ratio MT/Lo.
-
,yet co~
~ .sh.vS a.
-
~ ':/ ~~ /I 3~uoc::! ,.,tUSwe, "tvs C /I cC,,/~ !Y ~.fro""- ~.s)
)Z.;,. , hi "-:J r ~ ~ sta,.. ~~ ~~ £) so) SGl. lI$r CIa:;!)
N~& ~ ~~
100 ~------r----.-------r-~
~e..
10
(!) ....J o... o ~
a: w a.
-l -ZII
0.1
0.01 L-- ---l.. ...I-_-.J._--'_---' 37
Fif.:ure 6 The cumulative HII region lumino!iity function for
different galaxy type!i from Kennicutt et al (1989).
38 39 40
log L ( Hex) erg I sec
-
/I~~~~~~" . .
d40~~ (UIl ~st-) ~~
1Jteu.5~ " .. . . a... ~ ~.
G&J,.. ~;oz:.:; ~ ~U~~ "t:w.-S ~ ~
tY~ ~c,YJlf~ ,~s eve- ~) ~
~ ~-r ~ ~ ~ ~e. H!.~
~ a.k dd~ ~ eve 'C:/ ~ - eo-- ~~v~ .=l
-
Figure 2.7. The color of galaxies along the Hubble sequence. The
star-forming history of galaxies is traced by their broad-band
colors. This is illustrated in these mean colors from a sample of
456 bright galaxies in the Sloan Digital Sky Survey, with the bands
approximately at 3,500 A(u), 4,800 A(g), 6,250 A(r), 7,700 A(i),
and 9,100 A(z). Smaller differences among these magnitudes (color
indices) denote a bluer spectral shape. The difference is most
conspicuous at shorter wavelengths (as in u - g color), since
stellar evolution is most rapid for the more massive bluer stars.
(Data from Shimasaku et al., Astronomical Journal, 122,
1238,2001.)
8 10
r-i .....
g-r
u-g
024 6 Morphological type T
:
1G..eL: Galaxy components and quantitative classification 31
: :
1.5
2.0
0.5
CIl Q) C).'0
.5 1.0 J,., o '0 u
has seen use in asking how local galaxy samples populate the CAS
space, and in comparing this with samples at high redshift.
Such a pattern of grouping and quantifying galaxies through some
small set of observable quantities, such as color, image
concentration, and an index of image symmetry, takes us into the
more abstract field of quantitative classification. For many years,
a need has been expressed for fully quantitative and numeric ways
to classify galaxies, not necessarily to supplant but more
completely to supplement the classical morphological schemes such
as the Hubble and de Vaucouleurs systems. Such parameters could, if
we are fortunate, be linked directly to the dynamical components of
galaxies, and be defined in ways that make them more robust to data
quality and resolution than the usual visual classifications. As
candidate systems have been proposed and evaluated, it is one
measure of the lasting influence of the Hubble system that most of
the quantities they derive have been shown plotted as functions of
... Hubble class. We may consider such interesting additional
quantities as color of the stellar population, gas content per unit
optical luminosity, normalized starformation rate from Ha or
far-infrared indicators, or mean rotational velocity, and in each
case we see a clear correlation with galaxy type (as seen in sample
quantities in Figure 2.7). The color dependence can be so strong
that color is often used as the independent variable in studies of
galaxy populations, as a proxy for the star-forming history of a
system (Chapter 4).
Sec. 2.2)
aug25aug25Pages from 16-jan.pdf
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