bullbull

srnll ivJ5 ~

~e9rotp ~+

00 ~MI- ~iJ ~Otf 3pound ~ ~ zta s~ joNIA~ ~~ tAshy

o u ~

~ a1wy I c~

~IOJI~ ~ lHJJ4c~

s~ MOc64 ( cu JootL 4S

~s tUe

bull tJof -~ s7ttAO

-~ 1t~ MASS

- ampts Y MQSS hss

+ ViJool4S s~~V -s6-07c1~

168 4 Our backyard the Local Group

E gt

Q)

U J C CJl 0

E gt c Q) I

0 0 0 0

20

22

24

26

10000

1000

100

012

V-I (magnitudes)

-1 3

Figure 420 Color-magnitude diagram for the dwarf irregular galaxy Sextans A its lumishy

nosity Lv 4 x 107 Lo at a distance d = 1400 kpc The bluest near-vertical plume

of stars rising from V - I mv (-0325) is the main sequence Stars in the

slightly redder plume beside it at V - I 0 are blue supergiants massive stars with

M 2 2Mo burning helium in their cores The red giant branch rises from the red clump

at V - I mv (0826) the stars with L 2 1000Lo and V - I 1 are red supergiantsshy

R Dohm-Palmer et al

supergiants on the parallel plume at V - I ~ O The mass of stars at V - I ~ 08 at the base of the figure is the red clump the red giant branch rises from it Star formation has gone on for ~1 Gyr lately it has been especially vigorous increasing at least threefold over the past 50-100 Myr

Some dwarf galaxies such as Phoenix and LGS3 are classified as intermediate between dwarf irregulars and dwarf spheroidals Almost all their stars are more than a few gigayears old but they contain a little gas and a few young stars A few stars as young as 500 Myr have been found in Fomax so this dwarf spheroidal galaxy must have had some gas until quite recently The Carina dwarf spheroidal made most of its stars in a few discrete episodes (see Figure 49) at times of peak starbirth it may have been a miniature version of Sextans A Because of their similar structures small irregulars like the Pegasus dwarf may be at an early stage while dwarf spheroidals represent the late stages in the life of a similar type of galaxy In the dwarf spheroidals which orbit close to the Galaxy or M31

00 (c) RG

GRS 8

6 MS r

4

2 nofI(R0 1 1 ~

o 2 4 6 8 10 12 14

c u Sagittariusen 8 Q) gt 6

j CO 4

AC Q) 2 ~ AGB [middot05) c

0

MS RG RR

(middotLO)

0 2 4 6 8 10 12

Tucana RG

-- shy8

6

4

2 AGB

0 0 2 4 6 8 10 12

2P

14

14

8

6

4

2

o

8

6

4

2

o

8

6

4

2

0

RG RR Ursa Minor 1

I

MS AC AGBbull bullbullbullbullbullbullbullbullbullbullbull -=J

8

6

4

2

o o 2 4 6 8 10 12 14

WMSSG NGC6S22

Draco

AGBACMS

~ RG RR ~

2P

3 ~ tTl o

[-07) I 8

AGB RG (-17) MS61 r-

4

2

0 0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14

RG Pegasus r[1Oj

MS(middotO6]

L-_J AGB

0 2 4 6 8 10 12 14

Age (Gyr)

0 2 4 6 8 10 12 14

RGmiddot DDO 210

Figure 8 Schematic plots of the star-formation histories of all Local Group dwarfs with sufficient data The labels within the individual panels specify the nature of the stellar indicators used to infer the presence of a given age component MS = main-sequence stars AGB = asymptotic giant branch stars RG = red giants RR = RR Lyr variables AC = anomalous Cepheids SG = blue and red supergiants W = Wolf-Rayet stars PN = planetary nebulae 2P means that the galaxy has an anomalously red horizontal-branch (HB) population for its (low) metallicity-that is the galaxy exhibits

18 p

I 18 0 -

(I ~~ 0

E 1

~middott~ c j -rlmiddot~ middotimiddot ()) JQ-jlk ~ 0 ~ 0

J 20 20 rmiddot~middot~~middotgt~~~1f-middot ~ ~ middot~lt(fltc 01 0

E n 22 -l 22 +- c ()) ~

0 0 0 24 0

o 05 1 15

8-R (magnitudes)

Figure 49 Left color-magnitude diagram for the Carina dwarf spheroidal galaxy Right

superposed isochrones give the locus of metal-poor stars (Z = Zo50) at ages of 3 Gyr

(solid) 7 Gyr (dotted) and 15 Gyr (dashed) we see young red clump stars close to

B - R mR = (120) and old stars on the horizontal branch Carinas distance modshy

ulus is taken as (m - M)o = 2009 dust reddening is assumed to dim stars by 0108

magnitudes in Band 0067 magnitudes in R - T Smecker-Hane A Cole Padova stellar

tracks

I ~

shy -

0

gt ~amp ~ ~ middot~~ ~t~~rS~t ~

~~ ~-( (raquo 04to 11 0 ~ 4r middot1 bullbullbullbullbull~ f~r 07r

~~ ~~1J~i1j~ 1I~~~middot~gt ~middot4 24

t~i~fj~H o 05 1 15

8-R (magnitudes)

~ No ~ rkJrtiJo ~ kut ~ tONL tr ~~

bull

k~

~ NOI FJ (ouF Mli) tGzs

~ r~ o(~ ~ IOpoundyr

00

Annu Rev Astro Astrophys 199836435-506 Downloaded from arjournalsannualreviewsorg RESERVE UNIVERSITY on 1112409 For per~onal use r-~nlJY___________

MS RG RR AG WLM Inner NGC 147

I 8 8

6 6 AG

41 MS AGB ~

(a)

cr lL C) Q)

gt a3 Q)

cr

8

6

4

2

o

8

6

4

2

0

8

6

4

2

0

8

6

4

2

o

WLM Outer

MS

o 2 4 6 8

And III

~ _ ____~~_S o 2 4 6 8

MS MS (-05] bull

I 2 ~II L IIAGe

10 12 14

10

AG

12 14

8

6

4

2

o

AG AA NGC 205 Inner

AGB

o 2 4 6 8

Sculptor

MSACAGB

o 2 4 6 8

Figure 8 (Continued)

10 12

AG AR

10 12

8

6

4

2

o 2 4 6 8 10 12 14

RG AA NGC 185

MS AGB

MS rn o 2 4 6 e 10 12 14

AG

0

8

6

4

2

o

8

6 I 12P

4M2~~n ~~ AGB

I

N

0 2 4 8 8 10 12 14

~ RG RR

NGC 205 Outer ~ (ltJ9) tI1

o

AGB AGBbullbullbull

0 2 4 6 8 10 12 14

AGAR And I

_ _0~1~~~~________~ ~I 14 o 2 4 6 e 10 12 14 0 2 4 6 8 10 12 14

WMSRG LGS3 IC 1613

8 8 RG RA

6 6 MS AGB AGB ~2P 4 4

2 2

o 0 14 o 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14

Age (Gyr)

168 4 Our backyard the Local Group

E gt

Q)

U J C CJl 0

E gt c Q) I

0 0 0 0

20

22

24

26

10000

1000

100

012

V-I (magnitudes)

-1 3

Figure 420 Color-magnitude diagram for the dwarf irregular galaxy Sextans A its lumishy

nosity Lv 4 x 107 Lo at a distance d = 1400 kpc The bluest near-vertical plume

of stars rising from V - I mv (-0325) is the main sequence Stars in the

slightly redder plume beside it at V - I 0 are blue supergiants massive stars with

M 2 2Mo burning helium in their cores The red giant branch rises from the red clump

at V - I mv (0826) the stars with L 2 1000Lo and V - I 1 are red supergiantsshy

R Dohm-Palmer et al

supergiants on the parallel plume at V - I ~ O The mass of stars at V - I ~ 08 at the base of the figure is the red clump the red giant branch rises from it Star formation has gone on for ~1 Gyr lately it has been especially vigorous increasing at least threefold over the past 50-100 Myr

Some dwarf galaxies such as Phoenix and LGS3 are classified as intermediate between dwarf irregulars and dwarf spheroidals Almost all their stars are more than a few gigayears old but they contain a little gas and a few young stars A few stars as young as 500 Myr have been found in Fomax so this dwarf spheroidal galaxy must have had some gas until quite recently The Carina dwarf spheroidal made most of its stars in a few discrete episodes (see Figure 49) at times of peak starbirth it may have been a miniature version of Sextans A Because of their similar structures small irregulars like the Pegasus dwarf may be at an early stage while dwarf spheroidals represent the late stages in the life of a similar type of galaxy In the dwarf spheroidals which orbit close to the Galaxy or M31

00 (c) RG

GRS 8

6 MS r

4

2 nofI(R0 1 1 ~

o 2 4 6 8 10 12 14

c u Sagittariusen 8 Q) gt 6

j CO 4

AC Q) 2 ~ AGB [middot05) c

0

MS RG RR

(middotLO)

0 2 4 6 8 10 12

Tucana RG

-- shy8

6

4

2 AGB

0 0 2 4 6 8 10 12

2P

14

14

8

6

4

2

o

8

6

4

2

o

8

6

4

2

0

RG RR Ursa Minor 1

I

MS AC AGBbull bullbullbullbullbullbullbullbullbullbullbull -=J

8

6

4

2

o o 2 4 6 8 10 12 14

WMSSG NGC6S22

Draco

AGBACMS

~ RG RR ~

2P

3 ~ tTl o

[-07) I 8

AGB RG (-17) MS61 r-

4

2

0 0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14

RG Pegasus r[1Oj

MS(middotO6]

L-_J AGB

0 2 4 6 8 10 12 14

Age (Gyr)

0 2 4 6 8 10 12 14

RGmiddot DDO 210

Figure 8 Schematic plots of the star-formation histories of all Local Group dwarfs with sufficient data The labels within the individual panels specify the nature of the stellar indicators used to infer the presence of a given age component MS = main-sequence stars AGB = asymptotic giant branch stars RG = red giants RR = RR Lyr variables AC = anomalous Cepheids SG = blue and red supergiants W = Wolf-Rayet stars PN = planetary nebulae 2P means that the galaxy has an anomalously red horizontal-branch (HB) population for its (low) metallicity-that is the galaxy exhibits

18 p

I 18 0 -

(I ~~ 0

E 1

~middott~ c j -rlmiddot~ middotimiddot ()) JQ-jlk ~ 0 ~ 0

J 20 20 rmiddot~middot~~middotgt~~~1f-middot ~ ~ middot~lt(fltc 01 0

E n 22 -l 22 +- c ()) ~

0 0 0 24 0

o 05 1 15

8-R (magnitudes)

Figure 49 Left color-magnitude diagram for the Carina dwarf spheroidal galaxy Right

superposed isochrones give the locus of metal-poor stars (Z = Zo50) at ages of 3 Gyr

(solid) 7 Gyr (dotted) and 15 Gyr (dashed) we see young red clump stars close to

B - R mR = (120) and old stars on the horizontal branch Carinas distance modshy

ulus is taken as (m - M)o = 2009 dust reddening is assumed to dim stars by 0108

magnitudes in Band 0067 magnitudes in R - T Smecker-Hane A Cole Padova stellar

tracks

I ~

shy -

0

gt ~amp ~ ~ middot~~ ~t~~rS~t ~

~~ ~-( (raquo 04to 11 0 ~ 4r middot1 bullbullbullbullbull~ f~r 07r

~~ ~~1J~i1j~ 1I~~~middot~gt ~middot4 24

t~i~fj~H o 05 1 15

8-R (magnitudes)

~ No ~ rkJrtiJo ~ kut ~ tONL tr ~~

bull

k~

~ NOI FJ (ouF Mli) tGzs

~ r~ o(~ ~ IOpoundyr

00

Annu Rev Astro Astrophys 199836435-506 Downloaded from arjournalsannualreviewsorg RESERVE UNIVERSITY on 1112409 For per~onal use r-~nlJY___________

MS RG RR AG WLM Inner NGC 147

I 8 8

6 6 AG

41 MS AGB ~

(a)

cr lL C) Q)

gt a3 Q)

cr

8

6

4

2

o

8

6

4

2

0

8

6

4

2

0

8

6

4

2

o

WLM Outer

MS

o 2 4 6 8

And III

~ _ ____~~_S o 2 4 6 8

MS MS (-05] bull

I 2 ~II L IIAGe

10 12 14

10

AG

12 14

8

6

4

2

o

AG AA NGC 205 Inner

AGB

o 2 4 6 8

Sculptor

MSACAGB

o 2 4 6 8

Figure 8 (Continued)

10 12

AG AR

10 12

8

6

4

2

o 2 4 6 8 10 12 14

RG AA NGC 185

MS AGB

MS rn o 2 4 6 e 10 12 14

AG

0

8

6

4

2

o

8

6 I 12P

4M2~~n ~~ AGB

I

N

0 2 4 8 8 10 12 14

~ RG RR

NGC 205 Outer ~ (ltJ9) tI1

o

AGB AGBbullbullbull

0 2 4 6 8 10 12 14

AGAR And I

_ _0~1~~~~________~ ~I 14 o 2 4 6 e 10 12 14 0 2 4 6 8 10 12 14

WMSRG LGS3 IC 1613

8 8 RG RA

6 6 MS AGB AGB ~2P 4 4

2 2

o 0 14 o 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14

Age (Gyr)

00 (c) RG

GRS 8

6 MS r

4

2 nofI(R0 1 1 ~

o 2 4 6 8 10 12 14

c u Sagittariusen 8 Q) gt 6

j CO 4

AC Q) 2 ~ AGB [middot05) c

0

MS RG RR

(middotLO)

0 2 4 6 8 10 12

Tucana RG

-- shy8

6

4

2 AGB

0 0 2 4 6 8 10 12

2P

14

14

8

6

4

2

o

8

6

4

2

o

8

6

4

2

0

RG RR Ursa Minor 1

I

MS AC AGBbull bullbullbullbullbullbullbullbullbullbullbull -=J

8

6

4

2

o o 2 4 6 8 10 12 14

WMSSG NGC6S22

Draco

AGBACMS

~ RG RR ~

2P

3 ~ tTl o

[-07) I 8

AGB RG (-17) MS61 r-

4

2

0 0 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14

RG Pegasus r[1Oj

MS(middotO6]

L-_J AGB

0 2 4 6 8 10 12 14

Age (Gyr)

0 2 4 6 8 10 12 14

RGmiddot DDO 210

Figure 8 Schematic plots of the star-formation histories of all Local Group dwarfs with sufficient data The labels within the individual panels specify the nature of the stellar indicators used to infer the presence of a given age component MS = main-sequence stars AGB = asymptotic giant branch stars RG = red giants RR = RR Lyr variables AC = anomalous Cepheids SG = blue and red supergiants W = Wolf-Rayet stars PN = planetary nebulae 2P means that the galaxy has an anomalously red horizontal-branch (HB) population for its (low) metallicity-that is the galaxy exhibits

18 p

I 18 0 -

(I ~~ 0

E 1

~middott~ c j -rlmiddot~ middotimiddot ()) JQ-jlk ~ 0 ~ 0

J 20 20 rmiddot~middot~~middotgt~~~1f-middot ~ ~ middot~lt(fltc 01 0

E n 22 -l 22 +- c ()) ~

0 0 0 24 0

o 05 1 15

8-R (magnitudes)

Figure 49 Left color-magnitude diagram for the Carina dwarf spheroidal galaxy Right

superposed isochrones give the locus of metal-poor stars (Z = Zo50) at ages of 3 Gyr

(solid) 7 Gyr (dotted) and 15 Gyr (dashed) we see young red clump stars close to

B - R mR = (120) and old stars on the horizontal branch Carinas distance modshy

ulus is taken as (m - M)o = 2009 dust reddening is assumed to dim stars by 0108

magnitudes in Band 0067 magnitudes in R - T Smecker-Hane A Cole Padova stellar

tracks

I ~

shy -

0

gt ~amp ~ ~ middot~~ ~t~~rS~t ~

~~ ~-( (raquo 04to 11 0 ~ 4r middot1 bullbullbullbullbull~ f~r 07r

~~ ~~1J~i1j~ 1I~~~middot~gt ~middot4 24

t~i~fj~H o 05 1 15

8-R (magnitudes)

~ No ~ rkJrtiJo ~ kut ~ tONL tr ~~

bull

k~

~ NOI FJ (ouF Mli) tGzs

~ r~ o(~ ~ IOpoundyr

00

Annu Rev Astro Astrophys 199836435-506 Downloaded from arjournalsannualreviewsorg RESERVE UNIVERSITY on 1112409 For per~onal use r-~nlJY___________

MS RG RR AG WLM Inner NGC 147

I 8 8

6 6 AG

41 MS AGB ~

(a)

cr lL C) Q)

gt a3 Q)

cr

8

6

4

2

o

8

6

4

2

0

8

6

4

2

0

8

6

4

2

o

WLM Outer

MS

o 2 4 6 8

And III

~ _ ____~~_S o 2 4 6 8

MS MS (-05] bull

I 2 ~II L IIAGe

10 12 14

10

AG

12 14

8

6

4

2

o

AG AA NGC 205 Inner

AGB

o 2 4 6 8

Sculptor

MSACAGB

o 2 4 6 8

Figure 8 (Continued)

10 12

AG AR

10 12

8

6

4

2

o 2 4 6 8 10 12 14

RG AA NGC 185

MS AGB

MS rn o 2 4 6 e 10 12 14

AG

0

8

6

4

2

o

8

6 I 12P

4M2~~n ~~ AGB

I

N

0 2 4 8 8 10 12 14

~ RG RR

NGC 205 Outer ~ (ltJ9) tI1

o

AGB AGBbullbullbull

0 2 4 6 8 10 12 14

AGAR And I

_ _0~1~~~~________~ ~I 14 o 2 4 6 e 10 12 14 0 2 4 6 8 10 12 14

WMSRG LGS3 IC 1613

8 8 RG RA

6 6 MS AGB AGB ~2P 4 4

2 2

o 0 14 o 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14

Age (Gyr)

18 p

I 18 0 -

(I ~~ 0

E 1

~middott~ c j -rlmiddot~ middotimiddot ()) JQ-jlk ~ 0 ~ 0

J 20 20 rmiddot~middot~~middotgt~~~1f-middot ~ ~ middot~lt(fltc 01 0

E n 22 -l 22 +- c ()) ~

0 0 0 24 0

o 05 1 15

8-R (magnitudes)

Figure 49 Left color-magnitude diagram for the Carina dwarf spheroidal galaxy Right

superposed isochrones give the locus of metal-poor stars (Z = Zo50) at ages of 3 Gyr

(solid) 7 Gyr (dotted) and 15 Gyr (dashed) we see young red clump stars close to

B - R mR = (120) and old stars on the horizontal branch Carinas distance modshy

ulus is taken as (m - M)o = 2009 dust reddening is assumed to dim stars by 0108

magnitudes in Band 0067 magnitudes in R - T Smecker-Hane A Cole Padova stellar

tracks

I ~

shy -

0

gt ~amp ~ ~ middot~~ ~t~~rS~t ~

~~ ~-( (raquo 04to 11 0 ~ 4r middot1 bullbullbullbullbull~ f~r 07r

~~ ~~1J~i1j~ 1I~~~middot~gt ~middot4 24

t~i~fj~H o 05 1 15

8-R (magnitudes)

~ No ~ rkJrtiJo ~ kut ~ tONL tr ~~

bull

k~

~ NOI FJ (ouF Mli) tGzs

~ r~ o(~ ~ IOpoundyr

00

Annu Rev Astro Astrophys 199836435-506 Downloaded from arjournalsannualreviewsorg RESERVE UNIVERSITY on 1112409 For per~onal use r-~nlJY___________

MS RG RR AG WLM Inner NGC 147

I 8 8

6 6 AG

41 MS AGB ~

(a)

cr lL C) Q)

gt a3 Q)

cr

8

6

4

2

o

8

6

4

2

0

8

6

4

2

0

8

6

4

2

o

WLM Outer

MS

o 2 4 6 8

And III

~ _ ____~~_S o 2 4 6 8

MS MS (-05] bull

I 2 ~II L IIAGe

10 12 14

10

AG

12 14

8

6

4

2

o

AG AA NGC 205 Inner

AGB

o 2 4 6 8

Sculptor

MSACAGB

o 2 4 6 8

Figure 8 (Continued)

10 12

AG AR

10 12

8

6

4

2

o 2 4 6 8 10 12 14

RG AA NGC 185

MS AGB

MS rn o 2 4 6 e 10 12 14

AG

0

8

6

4

2

o

8

6 I 12P

4M2~~n ~~ AGB

I

N

0 2 4 8 8 10 12 14

~ RG RR

NGC 205 Outer ~ (ltJ9) tI1

o

AGB AGBbullbullbull

0 2 4 6 8 10 12 14

AGAR And I

_ _0~1~~~~________~ ~I 14 o 2 4 6 e 10 12 14 0 2 4 6 8 10 12 14

WMSRG LGS3 IC 1613

8 8 RG RA

6 6 MS AGB AGB ~2P 4 4

2 2

o 0 14 o 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14

Age (Gyr)

~ No ~ rkJrtiJo ~ kut ~ tONL tr ~~

bull

k~

~ NOI FJ (ouF Mli) tGzs

~ r~ o(~ ~ IOpoundyr

00

Annu Rev Astro Astrophys 199836435-506 Downloaded from arjournalsannualreviewsorg RESERVE UNIVERSITY on 1112409 For per~onal use r-~nlJY___________

MS RG RR AG WLM Inner NGC 147

I 8 8

6 6 AG

41 MS AGB ~

(a)

cr lL C) Q)

gt a3 Q)

cr

8

6

4

2

o

8

6

4

2

0

8

6

4

2

0

8

6

4

2

o

WLM Outer

MS

o 2 4 6 8

And III

~ _ ____~~_S o 2 4 6 8

MS MS (-05] bull

I 2 ~II L IIAGe

10 12 14

10

AG

12 14

8

6

4

2

o

AG AA NGC 205 Inner

AGB

o 2 4 6 8

Sculptor

MSACAGB

o 2 4 6 8

Figure 8 (Continued)

10 12

AG AR

10 12

8

6

4

2

o 2 4 6 8 10 12 14

RG AA NGC 185

MS AGB

MS rn o 2 4 6 e 10 12 14

AG

0

8

6

4

2

o

8

6 I 12P

4M2~~n ~~ AGB

I

N

0 2 4 8 8 10 12 14

~ RG RR

NGC 205 Outer ~ (ltJ9) tI1

o

AGB AGBbullbullbull

0 2 4 6 8 10 12 14

AGAR And I

_ _0~1~~~~________~ ~I 14 o 2 4 6 e 10 12 14 0 2 4 6 8 10 12 14

WMSRG LGS3 IC 1613

8 8 RG RA

6 6 MS AGB AGB ~2P 4 4

2 2

o 0 14 o 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14

Age (Gyr)

00

Annu Rev Astro Astrophys 199836435-506 Downloaded from arjournalsannualreviewsorg RESERVE UNIVERSITY on 1112409 For per~onal use r-~nlJY___________

MS RG RR AG WLM Inner NGC 147

I 8 8

6 6 AG

41 MS AGB ~

(a)

cr lL C) Q)

gt a3 Q)

cr

8

6

4

2

o

8

6

4

2

0

8

6

4

2

0

8

6

4

2

o

WLM Outer

MS

o 2 4 6 8

And III

~ _ ____~~_S o 2 4 6 8

MS MS (-05] bull

I 2 ~II L IIAGe

10 12 14

10

AG

12 14

8

6

4

2

o

AG AA NGC 205 Inner

AGB

o 2 4 6 8

Sculptor

MSACAGB

o 2 4 6 8

Figure 8 (Continued)

10 12

AG AR

10 12

8

6

4

2

o 2 4 6 8 10 12 14

RG AA NGC 185

MS AGB

MS rn o 2 4 6 e 10 12 14

AG

0

8

6

4

2

o

8

6 I 12P

4M2~~n ~~ AGB

I

N

0 2 4 8 8 10 12 14

~ RG RR

NGC 205 Outer ~ (ltJ9) tI1

o

AGB AGBbullbullbull

0 2 4 6 8 10 12 14

AGAR And I

_ _0~1~~~~________~ ~I 14 o 2 4 6 e 10 12 14 0 2 4 6 8 10 12 14

WMSRG LGS3 IC 1613

8 8 RG RA

6 6 MS AGB AGB ~2P 4 4

2 2

o 0 14 o 2 4 6 8 10 12 14 0 2 4 6 8 10 12 14

Age (Gyr)

00

Annu Rev Astro Astrophys 199836435-506 Downloaded from arjoumals annualreviewsorg by CASE WESTERN RESERVE UNIVERSITY on 1112409 For personal use only

(c) GR8 _--_RG -

8 8

6

4

MS r

6

4

2 no AGB 2

O~~----------------------------------- o

a LL en 8 Q) gt 6

~ t13 4

Q) 2

II 0

8

6

4

2

0

o 2 4 6 8 10 12

MS RG RR Sagittarius

(-10)

AC _ MS AGB [-o5]

J 0 2 4 6 8 10 12

Tucana ~

AGB -_ --_ - -shy 0 2 4 6 8 10 12

2P

14

14

14

8

6

4

2

o

8

6

4

2

0

I RG RR Draco 1

2P

Lshy

o 2 4

AGBACMS ~

6 8 10 12

I

14

RG DOD 210

MSr------ --- - --

0 2 4 6 8 10 12 14

Ursa Minor RG RR

8

6

4

2 _~_s AC AGB --__ __

o o 2 4 6 8 10 12 14

WMSSG NGC 6822 ()7]

8 AGB RG [-17]

6

4 I 2

0 0 2 4 6 8 10 12 14

RG Pegasus

MS()6) AGB

L r ~

0 2 4 6 8 10 12 14

Age (Gyr)

+gt +gt

~ ~ tT1 o

Figure 8 Schematic plots of the star-formation histories of all Local Group dwarfs with sufficient data The labels within the individual panels specify the nature of the stellar indicators used to infer the presence of a given age component MS = main-sequence stars AGB = asymptotic giant branch stars RG = red giants RR = RR Lyr variables AC = anomalous Cepheids SG = blue and red supergiants W = Wolf-Rayet stars PN = planetary nebulae 2P means that the galaxy has an anomalously red horizontal-branch (lIB) population for its (low) metallicity-that is the galaxy exhibits

middot SIw--~ks~ 0 ~ cJaL~ CCU 6e ~

l[l ~ tJ0cfdeg ~ ~~

oL~ oS cJc -01111~~fIl ~~

~i3 ~od cO spound

~~~ ~~~~

-----

166 4 Our backyard the Local Group

I I II I ~ 12 shy

~

+ +

s bull

+ M32

nuclez ()

-~ (j

CQ --- 16 r

~

s +

~ 20 -~

-tgt

- ~

b rshy

-24 ~

Malin 1 -I L

-24 -20 -16 -12 -8 absolute blue magnitude

Figure 418 Dwarf and giant galaxies occupy different regions in a plot of absolute Vshy

magnitude and measured central surface brightness because of seeing the true peak

brightness may be higher At left luminous elliptical galaxies and the bulges of disk

systems have very high surface brightness at their centers The rightmost of the dE

points (filled circles) represent what this text calls dwarf spheroidals open circles mark

irregular and dwarf irregular galaxies Disks of spiral galaxies are markedS Malin 1 is

a low-surf~ b~tness galaxy see Section 51 - B Binggeli

~Ja~ co~~

~6 cM~-tD 5 ~

p-t --~~~VJ

-----

166 4 Our backyard the Local Group

I I II I ~ 12 shy

~

+ +

s bull

+ M32

nuclez ()

-~ (j

CQ --- 16 r

~

s +

~ 20 -~

-tgt

- ~

b rshy

-24 ~

Malin 1 -I L

-24 -20 -16 -12 -8 absolute blue magnitude

Figure 418 Dwarf and giant galaxies occupy different regions in a plot of absolute Vshy

magnitude and measured central surface brightness because of seeing the true peak

brightness may be higher At left luminous elliptical galaxies and the bulges of disk

systems have very high surface brightness at their centers The rightmost of the dE

points (filled circles) represent what this text calls dwarf spheroidals open circles mark

irregular and dwarf irregular galaxies Disks of spiral galaxies are markedS Malin 1 is

a low-surf~ b~tness galaxy see Section 51 - B Binggeli

~Ja~ co~~

~6 cM~-tD 5 ~

p-t --~~~VJ