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Overview of galaxy properties

Enrico Maria Corsini

Dipartimento di Astronomia

Università di Padova

Lectures of Astrophysics of Galaxies

Astromundus/Laurea Magistrale Astronomia

A.A. 2010-2011

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Outline

Morphology

Photometry

Kinematics

Scaling laws

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Morphology

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It is the most widely-used classification

It gives the basic terminology

Hubble recognizes four galaxy families:

- ellipticals (E)

- normal (S0) and barred (SB0) lenticulars

- normal (S) and barred (SB) spirals

- irregulars (Irr)

and puts them along the tuning-fork diagram

Hubble: morphological types

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Irr I

Irr II

Ellipticals Lenticulars Spirals Irregulars

Hubble: tuning-fork diagram

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Round or elliptical (apparent) shape

Smooth and structureless

Classes are defined according to the apparent

flattening (ellipticity)

En, n=0,1,…7 with n = 10 e = 10 (1-b/a)

Hubble: ellipticals

b

a

e = 1 – b/a

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b/a 1 0.7 0.5 0.3

1-b/a 0 0.3 0.5 0.7

type E0 E3 E5 E7

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Lens shaped

Two components: central bulge and disk with no

evidence of spiral arms

Two types: normal (S0) and barred (SB0) lenticulars

Classes S01, S02, S03 are defined by:

- the strength of dust absorption in the disk

Classes SB01, SB02, SB03 are defined by:

- the prominence of the bar

Hubble: lenticulars

9NGC 5866 S03

NGC 3245 S01 NGC 4111 S02

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Spiral shaped

Two components: central bulge and disk with evidence

of spiral arms

Types: normal (S) e barred (SB) spirals

Classes Sa, Sb, Sc are defined according to the:

- prominence of the bulge with respect to the disk

- tightness of the spiral arms

- resolution of the spiral arms into stars, dust

knots, and nebulae

Hubble: spirals

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Sa

• Prominent bulge

• Tightly wound arms

• Not highly-resolved arms

Sc

• Small bulge

• Loosely wound arms

• Highly-resolved arms

edge-on face-on

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NGC 1302 Sa NGC 2841 Sb NGC 628 Sc

NGC 175 SBa NGC 1300 SBb NGC 7741 SBc

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No symmetric shape

Classes: Type I (Irr I) and Type II (Irr II)

- Irr I: highly-resolved in stars (e.g. LMC)

- Irr II: highly-disturbed (e.g. M82)

Hubble: irregulars

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LMC Irr I M82 (NGC 3034) Irr II

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Not-classified galaxies

2% of nearby galaxies are not E, S0, S, Irr

Most of them are interacting systems

NGC 5128 S0+S pec NGC 4038/39 Sc (tides)

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De Vaucouleurs classifies galaxies according to:

- the main morphological sequence (Hubble stage)

E-E+-S0--S0-S0+-Sa-Sb-Sc-Sd-Sm-Im

- the bar presence

SA = no bar, SAB = weak bar, SB = strong bar

- three varieties

(r) = ring shape, (s) = s shape (spiral arms),

(rs) = mixed shape

and adopts the spindle diagram

de Vaucouleurs: morphological types

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de Vaucouleurs: spindle diagram

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van den Bergh classifies galaxies according to:

- the presence of the disk

ellipticals (E) – disk galaxies (S0,A,S)

- the gas abundance

S0 = no gas, A = gas poor, S = gas rich

and puts them along the trident diagram

Classes a,b,c for S0,A,S are defined according to the

bulge-to-disk ratio

van den Bergh: morphological types

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van den Bergh: trident diagram

Ellipticals Disks

Lenticulars

Anemics

Spirals

D/B

1-3 3-10 >10

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The Milky Way is a SBbc spiral

Most of LG members are dwarf and irregular galaxies

Mophology of Local Group galaxies

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Hubble: history

Irr I

Irr II

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Photometry

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For any point of an extended luminous suorce

surface brightness =

I = F/

is the SB in linear units (e.g. L

pc-2)

= -2.5 log I + costant

is the SB in magnitude units (e.g. mag arcsec-2)

[ B =25 means SB = 25 mag arcsec-2 in B band]

flux

unit solid angle

Surface photometry

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F L / 4 D2 L

A / D2 4 A

SB does not depend

on distance (in nearby

universe):

A,L

D

I = = =

F = measured flux

L = source luminosity

A = source area

D = distance

= source solid angle as seen by the observer

F

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An isophote connects points at the same SB level

1’

N

E

B=16.78 B=21.28

10”

NGC 1291 has two bars

Isophotes

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If I(r, ) is SB in P(r, ) then the total luminosity LT is:

For circular isophotes LT:

Total magnitudine mT:

Luminosity and total magnitude

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The equivalent radius r* of an isophote with area A is:

The integrated luminosity L(r*) within r*:

The relative integrated luminosity k(r*) within r* is:

The effective radius re corresponds to:

k(re)=1/2

Equivalent and effective radius

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Surface-brightness radial profile

The SB radial

profile (as a function

of r*) is a global

description of the SB

distribution of the

galaxy

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de Vaucouleurs’ (or r1/4) law

It is a description of the SB radial profile of

ellipticals and bulges

It is a straight line in the r1/4- plane

Ie (or e) = effective SB

re = effetctive radius

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1”

r 103

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I 106

e=22.25

effective radius: re=56.6”

sky=22.7

effective SB:

22’

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In the outskirts, SB is

brighter than the

extrapolation of the r1/4 law

( bright halo contributes

8% of the total luminosity).

M87 shows departures

from the r1/4 law at large

radii from the center

Departures from r1/4 at large radii

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The seeing blurs the

inner SB (=“core”)

Typical angular

resolution of ground-

based observations 1”.

V

1”

Departures from r1/4 at small radii

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HST images are diffraction-limited but not blurred by

seeing. Its typical angular resolution is 0.1”.

This SB

flattening is

real and not

due to seeing

or PSF effects 0.05”1”

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Nuker’s law

• rb = break radius (slope change)

• Ib = SB at rb

• for r rb slope -

• for r rb slope -

• = maximal curvature

It is adopted for the SB profile in the inner regions

of elliptical galaxies

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core profiles

power-law profiles

rb = break radius

Ib

r-r-

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K = scale SB

rc = core radius

rt = tidal radius

It is used for the SB of ellipticals (dwarfs and nuclei) and

globular clusters

Parametric law with a teorethical basis (spherical

systems with isotropic velocities)

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King’s law

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C = log (rt/rc) = concentration parameter

c

42 Comparison between King’s and r1/4 laws

King

de Vaucouleurs

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The SB profile of E1 NGC 3379 fitted by the King’s law

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It is used for the SB profile of disks

It is a straight line in the r- plane

I0 (or 0) = central SB

h = scale length

Freeman’s (or exponential) law

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central SB:

0=21.9

scale length: h =43.0”

sky

(h)= 0+1.086

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exponential disk

r1/4 bulge

bulge+disk

data

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Sometimes r1/4 bulge+exponential disk gives a “good”

model of the data

B/D=0.28 B/T=0.22 B/D=1.51 B/T=0.60

B = bulge, D = disk, B+D = T = total

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NGC 7013

bulge+disk+ring+lens

exponential disk

r1/n bulge

data

ring

lens

Sometimes r1/4

bulge+exponential disk is

not “sufficient” to account

for the data

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Usually (in

ellipticals) isophotes

have an elliptical

shape

isophote

fitted ellipse

Shape of the isophotes

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19/03/2003 R.P. Saglia 15

NGC 4278

N

E

PA

b

a

(x0,y0)E

19/03/2003 R.P. Saglia 15

NGC 4278

N

E

PA

b

a

Each isophote is defined by:

SB level:

center coordinates: x0,y0

length of the semiaxes: a,b

PA of the major semiaxis: PA

PA

N

NGC 4278

PA twist

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x0 y0

e=1-b/a

PA

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R

P(x,y) P(R, )

a

b

x

y

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isophote Riso( )

fitted ellipse Rell( )

Sometimes isophotes

are not perfect ellipses

An and Bn describe the

deviations of the shape of

the isophote from perfect

ellipse

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X0Y0

PAe

symmetric dev.

X axis

boxy/disky

symmetric dev.

Y axis

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disky a4>0

boxy a4<0 NGC 5322

NGC 4660

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NGC 4660

disky a4>0

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NGC 4365

boxy a4<0

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Kinematics

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The observed spectrum of a galaxy is the sum of the

spectra of the stars along l.o.s shifted according to the their

radial velocities. If S(λ) is the stellar (i.e. template)

spectrum, then the measured galaxy spectrum G(λ) is the

weighted integral of S(λ) with the (Gaussian) distribution

function of the radial velocities along the l.o.s. B(V,σ,…).

Stellar kinematics

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Elliptical galaxies

KIII star

(nm)

(nm)

Flu

x

Flu

xG( )= S[ (1+v/c)]B(v|V, ,h3,h4)dv

-

+

G = S B (Direct Fitting Method)

G = S • B (Fourier Quotient Method)~ ~ ~

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Line of sight velocity distribution (LOSVD)

B(v) = I0exp(-y2/2)[1+h3H3(y)+h4H4(y)]

where

y = (v-vfit)/ fit

and

H3(y) = (2 2y3-3 2y)/ 6

H4(y) = (4y4-12y2+3)/ 24

are the Gauss-Hermite function.

Gerhard (2003)

van der Marel & Franx (2003)

_ _ _

__

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Stellar kinematics: LOSVD

ln ln

F/F

continuum

-1

HR6018 (K1III) NGC4807 (S0) r=0”

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F/F

continuum

-1

ln ln

star & galaxy star (v=6993 km/s) & galaxy

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F/F

continuum

-1

LOSVD & fit

ln

v = 6993 km/s

= 228 km/s

h3 = -0.001

h4 = 0.002

v (km/s)

star & galaxy

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NGC 4889 cD

major axis minor axis

NGC 4931 S0

major axis minor axis

Kinematics profiles

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70Bender et al. (1990)

V>0 (receding) h3<0

V<0 (approaching) h3>0

1

2

2

LOSVD: h3

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tangential anisotropy h4<0

radial anisotropy h4>0

(R. Saglia)

LOSVD: h4

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Scaling laws

73spheroid disk

no bar

bar

Extension of Hubble including disky/boxy galaxies

boxy disky

disk

Kormendy & Bender: morphological types

74boxy disky boxy disky

rotation

pressure

strong grad.

weak grad.

bright

faint

ellipticity

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CORES

SLOW ROT

log rb

(pc)

POWER-LAW remaining

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CORES

BOXY

log rb

(pc)

POWER-LAW remaining

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E with power-law profiles:

smaller

fainter

disky

rotation supported

E with core profiles:

larger

brighter

boxy

pressure supported

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Brighter ellipticals have larger velocity dispersions. This

relation by Faber & Jackson (1976) is given by

log LT = a log + b

LT4

FJ links distance-dipendent LT with distance-independent .

By measuring apparent magnitude and calculating absolute

magnitude by with FJ, we measure galaxy distance.

Faber-Jackson relation

79R = 0”

0

Stellar kinematics of M87

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Larger ellipticals have fainter effective SB. This relation by

Kormendy (1977) is given by

e = a log Re + b

with a = 3.02, b = 19.74 (con H0 = 50 km s-1 Mpc-1 in V band) or

alternatively

e = a’ log Re + b’

Re I e-0.90

Since Le = I e Re2 it is

I e Le–3/2

which menas that brighter ellipticals have fainter effective SB

Kormendy relation

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Ellipticals are not randomly distributed in the (log Re, e, log

) space but are lying on the fundamental plane (FP, Djorgovski

& Davis 1987, Dressler et al. 1987) defined as

log Re = a log + b e + c

with a = 1.39, b = 0.36, c = -6.71 (with H0 = 50 km s-1 Mpc-1 in rG

band) and a = 1.25, b = 0.32, c=cost (with H0 = 50 km s-1 Mpc-1

in r band). For log I e it is b=-0.82.

FP links distance-dipendent Re with distance-indipendent

e and . By measuring Re in arcsec and calculating its value

in kpc with FP, we measure galaxy distanza (with 20% error)

Fundamental plane

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Fundamental plane

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a) Face-one view

b) Long-edge view

c) Short-edge view

Jorgensen et al. (1996)

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Brighter spirals spin faster. This relation found

by Tully & Fisher (1977) is given by

LT V4

log LT = 4 log V + cost

Brighter galaxies are more massive

Tully-Fisher relation

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gas (= Vc)

V = v/sini

kinematics:

v

imaging:

mT ,i

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NGC 3198

Optical

isophotes

Radio

HI map

Rotation

curve

on the

major axis

HI line

profile

W20

20%

v

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LT V4

90

Found in radio (HI) it works in optical too (HII)

Different definition of V: W20, WR, 2Vmax, 2Vflat

TF calibrated with galaxies of known distance

with B=0.25 e V=0.06 empirical arbitrary corrections to

correct for color differences between field and cluster galaxies.