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Title: Our New View of the Local Group


1
Our New View of the Local Group
Steven Majewski Irvine, March 2007
2
Recent Local Group Observational Advances
  • New Members (Dwarf Galaxies) of the LG
  • New Luminous Halos of the LG
  • New Tidal Streams of the LG
  • Other New Structural Features of the LG
  • Some New Constraints for the LG

3
1. A Bevy of New Dwarf Systems Milky Way Ursa
Major I Willman et al. 2005 Bootes Belokurov
et al. 2006 Canes Venatici I Zucker et al.
2006aUrsa Major II Zucker et al. 2006b Coma
Berenices Belokurov et al. 2007 Canes Venatici
II ibid SEGUE 1 ibid Hercules ibid Leo
IV ibid Leo T Irwin et al. 2007
4
1. A Bevy of New Dwarf Systems M31 And
IX Zucker et al. 2004 And X Zucker et al.
2006c And XI Martin et al. 2006 And XII
ibid And XIII ibid And XIV Majewski et al.
2007
5
1. A Bevy of New Dwarf Systems Milky Way L
(Lsun) D (kpc) Rcore(pc) Ursa Major
I 1x104 100 290 Bootes 2x104 60 230 Canes
Venatici I 1x105 220 550Ursa Major II 3x103
30 125 Coma Berenices 2x103 45 70 Canes
Venatici II 7x103 150 135 SEGUE 1 1x103 25
30 Hercules 2x104 140 310 Leo
IV 1x104 160 150 Leo T (200 Myr
pop) 6x104 420 170 HI 2x105
6
1. A Bevy of New Dwarf Systems M31 L
(Lsun) D (kpc) Rcore(pc) And IX 1.7x105
805 gt500 And X 1.4x105 700 270 And
XI 6.9x104 780 115 And XII
3.0x104 780 125 And XIII 4.8x104 780 115
And XIV 2.0x105 740 623
7
1. A Bevy of New Dwarf Systems in Local
Group M (sun) M/L (sun) UMa I 107
500 Kleyna et al. 2005 Boo 1x107
130-680 Munoz et al. 2006 And IX 1.6x107
93 Chapman et al. 05 And XIV
3.3x107 165 Majewski et al. 07 Also, Martin
et al. (submitted) on several of the newly
found MW dSphs
8
1. A Bevy of New Dwarf Systems Milky Way
Gilmore et al. 2007, astro-ph/0703308
Mateo trend of constant dSph mass seems to
hold.
9
Do these solve the missing satellites?
Moore et al. (1999), Kaufmann et al. (1993),
Klypin et al. (1999)
number
mass
  • Are there enough to fill the gap? SDSS
    footprint 1/5 of sky - another 40-50 of these
    in MW.
  • Not all masses represented

10
why are the darkest satellites also the most
distorted?
Bootes
Can Ven
Ursa Major
Ursa Minor
Belokurov et al. 2006
Zucker et al. 2006
Willman et al. 2005
Palma et al. 2003
(M/L)c 130-680
(M/L)c ??
(M/L)c 47-95
(M/L)c 500
Palma et al. 2003
Munoz et al. 2006
Kleyna et al. 2005
11
Andromeda Dwarf Galaxies
Currently, 13 dSphs (And I-III, V-XIV) and 4 dEs
(M32, M110, NGC 147, NGC 185).
Martin et al. (2006) note tight concentration of
their four newlyfound objects despite their
large survey area (and add And XIV?).Interesting
alignment of 10 objectswithin 7 kpc projected
distance of a single radial vector over 260
kpc. M31 dynamical families Koch Grebel
2006 McConnachie Irwin 2006 Metz et al.
2007Reminiscent of Milky Way alignment
suggestions Kunkel 1979, Lynden-Bell 1980,
Lynden-Bell Lynden-Bell 1995, Majewski
1993,Fusi Pecci et al. 1993 Palma et al.
2002 Filaments? Kroupa et al. 2005, Kang et al.
2005, Libeskind et al. 2005, 2007, Wang et al.
2005, Zentner et al. 2005
Martin et al. (2007) map
AndXIV
12
2. Newly Found Local Group Luminous Halos M31
Background - Milky Way vs M31 Properties of
Milky Way Halo Age - old, 12 Gyr
Chemical composition - metal poor, Fe/H
-1.5 Surface brightness profile -
power law, R-2 Properties of M31
Halo Age - both intermediate age and
old populations, 6-12 Gyr Chemical
composition - metal rich, Fe/H -0.5
Surface brightness profile - de Vaucouleurs,
R1/4
Inner Spheroid
Brown et al. (2003)
Durrell, Harris, Pritchet (2004) Durrell,
Harris, Pritchet (2001) Bellazzini et al. (2003)
Pritchet van den Bergh (1994)
13
Remote Outer Halo of M31
Majewski/Ostheimer KPNO 4-m/MOSAIC DDO51 filter
14
2. Newly Found Local Group Luminous Halos M31
Isolating a clean sample of M31 RGB stars Use
probability distribution functions based on 5
photometric/spectroscopic diagnostics to
eliminate foreground Milky Way dwarfs. 1.)
Radial Velocity 2.)DDO51 photometry 3.)
Na I equivalent width 4.) Position in the
CMD 5.) Fe/Hphot vs Fe/Hspec
Gilbert et al. (2006, ApJ, 652, 1188)
February 23rd, 2007


UC Santa Cruz
15
2. Newly Found Local Group Luminous Halos M31
Surface Brightness Star-counts in outer fields
(R gt 60 kpc) well above extrapolation of Sersic
inner spheroid. Best fit power law R-2.6 halo.
Guhathakurta et al. (2005, astro-ph/0502366)
February 23rd, 2007


UC Santa Cruz
16
2. Newly Found Local Group Luminous Halos M31
Metallicity
Kalirai et al. (2006, ApJ, 648, 389)
Fe/Hspec -1.24 ? 0.12 (? 0.85) Fe/Hphot
-1.48 ? 0.11 (? 0.73) ?/Fe 0.3
17
Background Image of Night Sky from Stellarium
Planetarium
18
2. Newly Found Local Group Luminous Halos M33
  • Several Recent Surveys
  • RR Lyrae Stars
  • Pritzl et al. (2006 AAS)
  • Sarajedini et al. (2006)
  • Giant Stars - photometric
  • Brooks, Wilson Harris (2004)
  • Giant Stars - photometric spectroscopic
  • Smecker-Hane et al. group (2004, 2005, 2006 AAS)
  • McConnachie et al. (2004, 2006)
  • Globular Clusters
  • Schommer et al. (1991)
  • Sarajedini et al. (1998, 2000)
  • Chandar et al. (2002)

19
2. Newly Found Local Group Luminous Halos M33
  • Generally find
  • Halo field metal-poor, like Milky Way and
    Andromeda (Fe/H -1.5), despite 10 less
    massive
  • M33 halo clusters, 5-7 Gyr age range (accretion?
    fragments?)
  • One possible reported substructure/tail
    (McConnachie et al. 2006) though no strong
    indicators of substructure (Sarajedini 2006).

20
2. Newly Found Local Group Halos M33
  • Sarajedini (2006) argues M33 in superhalo of
    M31
  • M31 tidal field disrupts/dilutes M33 streams,
    but leaves M33 clusters.
  • M33 halo matches M31 metallicity trend.

21
2. A Stellar Halo Around the Large Magellanic
Cloud?
12 deg2 Carina dSph Study -- Munoz et al. (2005)
Carina
MagellanMIKE echellespectroscopy
Discovered moving group of foreround LMC stars
sv 10 km/s, correct distance, metallicity
Extreme RV, similar to LMC
22
But
Linking fields
23 deg 20 kpc
23
If bound, implies LMC larger, twice as massive
than previously thought
Minimum rt??
24
  • Spectroscopic Survey

Carina field
25
  • Velocity Trend of LMC stars Carina 330 group

van der Marel 2003 model
Disk extrapolated
Halo extrapolated
Munoz et al. 2006
26
Other fields whereLMC population detected
27
2. A Stellar Halo Around the Large Magellanic
Cloud?
  • New moving group with LMC-like properties (CMD
    position, metallicity, velocity trend) at 22O
    from LMC center.
  • If unbound debris, not favorably placed to be
    stellar counterpart of HI stream.
  • If bound stellar halo, LMC larger than
    previously thought (radius 20 kpc) and 2-3x
    more massive 2-3x1010 Msun
  • If halo, it is considerably more metal rich
    (Fe/H -0.6)than M31, M33, Milky Way halo.

28
2. Luminous Halos Around LG dSphs?
Van Agt 1970s, Eskridge 1980s, Irwin
Hatzidimitriou 1995,
29
3. New Halo Streams Milky Way
SDSS Field of Streams (Belokurov et al.,
Grillmair et al.)
Grillmair figure in Unwin et al. (2007)
30
3. New Halo Streams M31
31
Giant Stream and Young Shell System in M31
NE Shelf
W Shelf
Giant S Stream
Star-Count Map(Irwin et al. 2005)
Fardal, Guhathakurta, Babul, McConnachie 2006
(astro-ph/0609050)
32
3. Halo Substructure M31
Substructure
Gilbert et al. (2007, astro-ph/0703029)
33
3. Halo Substructure M31
Gilbert et al. (2007, astro-ph/0703029)
Ferguson et al. (2002, AJ, 124, 1452) map
34
3. Halo Substructure M31
Gilbert et al. (2007, astro-ph/0703029)
February 23rd, 2007


UC Santa Cruz
35
NGC 205 ObservationsKeck / DEIMOS multislit
spectroscopy
3. Halo Substructure M31
  • Integrated light spectra cannont probe beyond
    effective radius
  • Geha et al. target individual red giant branch
    stars
  • Accurate radial velocities for 723 red giant
    stars in NGC 205

Geha, Guhathakurta, Rich Cooper 2006, AJ
36
3. Halo Substructure M31
Keck/DEIMOS studies of NGC 147, NGC 205, NGC 185
underway.
Geha et al. (2006, AJ, 131, 332)
37
4. Other New Structural Features Bars
  • Milky Way bar in gas -- Binney et al. 1991
  • Stellar feature -- Blitz Spergel 1991,
    Weinberg 1992
  • Milky Way bar in 2MASS carbon stars --
  • Skrutskie et al. 2001, Cole Weinberg 2002

38
An Unobstructed Wide-field View in the Near
Infrared
4. The M31s Boxy Bulge and Central Bar
Lindblad 1956, Stark 1977, Stark Binney 1994,
Berman 2001
BVRZ
Beaton et al. 2006, ApJL, in press
(astro-ph/0605239)
39
M31s Boxy Bulge and Central BarDetailed
Comparison to Dynamical Models
4. Other New Structural Features The M31 Bar
Athanassoula Beaton 2006 (astro-ph/0605090)
Effect of changing inclination
Effect of changing bar angle
40
4. Other New Structural Features Vast
Extended Stellar Disk Around M31
  • Ibata et al. (2005)
  • 15 to 40 kpc
  • circular orbits
  • velocity disperion 30 km/s
  • significant metallicity range
  • Fe/H -0.9 /- 0.2
  • continues central exponential scalelength 5.1
    kpc
  • 10 disk light

accretion
41
5. New Constraints Mass of M31
Andromeda XIV SRM, Beaton, Patterson, Kalirai,
Geha, Munoz,Seigar, Guhathakurta, Bullock, Rich,
Gilbert, Reitzel (2007)
162 kpc
AndXIV
Martin et al. (2007) map
42
5. New Constraints Mass of M31
-203 km/s velocity relative to M31
43
5. New Constraints Mass of M31
  • Seigar et al. (2007) cosmologically-motivated
    M31 mass model constrained by Ha, HI rotation
    curves 2MASS.
  • virial mass 8.5-12.3 x 1011 Msun, slightly
    higher than virial mass estimates 8 x 1011 Msun

projected radius
radial velocity only
Either And XIV unbound to M31, or M31 more
massive
44
5. New Constraints Origin of Magellanic Stream,
  • Recent Observations
  • HIPASS high spatial resolution survey discovers
    leading arm
  • Bifurcation of Stream
  • (Putman et al. 1998, 2003)
  • High velocity resolution looks at the MCs
    Stream (Staveley-Smith et al. 2003, Brüns et al.
    2005)

Putman et al. 2003
Putman et al. 1998
Brüns et al. 2005
45
5. New Constraints Origin of Magellanic Stream,
LMC/SMC/MW Interaction from Magellanic Stream
  • Recent Models
  • Ram pressure models can reproduce most
    observations. But no Leading Arm (Mastropietro
    et al. 2004)
  • Tidal models reproduce correct Leading Arm shape
  • Stream bifurcation (LMC crashed through Stream)
    (Connors et al. 2005)

Mastropietro et al. 2004
Observations
Model
Connors et al. 2005
46
Leiden/Argentine/Bonn (LAB) All-sky HI Survey
  • Combination of Leiden/Dwingeloo Survey with the
    Instituto Argentino de Radioastronomia Survey
    (Kalberla et al. 2005)
  • Stray radiation correction
  • All-sky survey covering 450 lt
    VLSR lt 400 km/s.

Kalberla et al. 2005
  • Spatial resolution 0.5, velocity resolution
    1.3 km/s, rms TB 0.09 K

47
Database of Gaussians(Nidever, Majewski Burton
2006)
Typical Decomposition
  • Decomposed the LAB database (several weeks on
    multiple computers)
  • Whole sky decomposed into 1,375,993 Gaussians

Brightness Temperature
Velocity
48
Latitude
  • Plotting Gaussian centers in PPV space -
    clarifies structure - enables systematic
    tracking (even across MW mid-plane)

Velocity
Magellanic Longitude
49
  • Two trailing filaments seen at head of Stream
  • One filament can be tracked to the LMC
  • Other filament possibly from the SMC/Bridge
    region?

LMC
LMC filament
Velocity
Bridge
SMC
SMC/Bridge filament
Magellanic Longitude
50
Can track both filaments all the way along Stream
  • Well separated either in velocity or space.
  • Use space-velocity criteria for upper part of
    the Stream
  • Spatial criteria for the lower part of the Stream

LMC filament
SMC/Bridge filament
51
5. New Constraints Origin of Magellanic Stream
52
LMC filament originates in the 30 Dor Region
5. Origin of Magellanic Stream
after velocity mask
  • Can track the LMC filament back to its origin in
    the 30 Dor region using velocity cuts
  • One birthplace of the Magellanic Stream
  • Site of extreme star formation. Rich in HI, CO,
    H2, GMCs and young stellar clusters

Magellanic Latitude
Magellanic Longitude
53
Distinctive Oscillating Pattern
  • Whats causing it?
  • Double helix?
  • LMC SMC tumbling about each other?

Velocity
Magellanic Longitude
54
Are the Filaments Wrapping Around Each Other?
  • If so
  • Proves that LMC and SMC bound to one another.
  • Could be used to trace LMC SMC orbit
    dynamical history

Velocity
Magellanic Longitude
55
But Filaments Are Not Wrapping
  • LMC filament spiraling on its own
  • Suggests more parallelbulk motion of LMC and
    SMC

Velocity
56
Distinctive Oscillating Pattern
  • Possibly an imprint of LMC rotation.
  • If so, can estimate drift rate
  • Measure- Velocity Amplitude 23 km/s
    - Peak-to-peak 20 deg- 30 Dor LMC Radius 2.5
    deg2.2 kpc
  • Derive - Period 0.6 Gyr - Drift Rate 84
    km/s- Age of 110 deg Stream 1 Gyr

Magellanic Latitude
Magellanic Longitude
57
5. New Constraints Origin of Magellanic Stream
Supergiant shells cluster age sequences -
further evidence for blow out from 30 Dor? - see
new models by Gurtina Besla (CfA, in prep.)
Suggests neither tidal forces nor ram pressure
origin of Stream
58
5. New Constraints dSph Surveys to Large Radii
Larger areas with greater sensitivity
Majewski et al. 2000, 2005Munoz et al. 2006
Westfall et al. 2006
Palma et al. 2003
Sohn et al. 2007
Majewski et al. 2003
59
5. New Constraints dSph Surveys to Large Radii
Larger areas with greater sensitivity
Majewski et al. 2000, 2005Munoz et al. 2006
Westfall et al. 2006
Munoz et al. 2005
Munoz et al. 2005
Mateo et al. 1998Sohn et al. 2007
Ibata et al. 1996Majewski et al., in prep.
60
5. New Constraints dSph Surveys to Large Radii
Larger areas with greater sensitivity
Multicomponent models, extended dark matter halos
to account for large velocity dispersions at
large radii Lokas 2002 Kleyna et al.
2002 Walker et al. 2006a, b Maschenko et al.
2006 Read et al. 2006 Koch et al.
2007 Wilkinson et al. 2006 Gilmore et al. 2007
see also Strigari talk
61
Two examples where tidal disruption seems
compelling
Munoz et al. (2006) Carina study
The distribution of Carina RV members shows
preference to lie along major axis, and to have
greater ellipticity with radius, as would be
expected for tidal debris.
62
Two examples where tidal disruption seems
compelling
Sohn et al. (2007) Leo I study, see also Walker
et al. talk
63
and where tidally disrupting (MFL) models
actually work (Munoz, Majewski, Johnston
2007)
Red Lines Best fitting models
  • Best Model properties
  • - Run for 6 orbits (9 Gyrs).
  • - Initial mass 3.8 x 107 MSUN.
  • - Mass Loss Rate 10 orbit-1.

Very Interesting M/L 40 (M/L)SUN In
agreement with results from core-fitting/central
velocity dispersion.
64
(Munoz, Majewski, Johnston 2007)
-Best Models Highly radial orbits with
parameters similar to the ones found by Piatek et
al. (2003) from proper motion measurements.
65
Mass Follows Light Model -- Leo I
Red Dots Best fitting model
  • Best Model properties
  • - Run for 2 orbits (12 Gyrs).
  • - Initial mass 4.0 x 107 MSUN.
  • - Mass Loss Rate 2 Gyr-1.

M/L 5 (M/L)SUN In agreement with
results from core-fitting/central velocity
dispersion.
Sohn et al. 2007, ApJ, in press
66
Some MW dSphs peeled away into the MFL regime?
M/L from central sv2
true M/L
Bullock Johnston two-component models see also
Klimentowski et al. (2006)
67
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