Large Scale Structure and Galaxy Properties

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A Dark Halo Survey - dynamics and
physics of satellite system

• 2007. 8. 13-17
• Changbom Park
• Korea Institute for Advanced Study (KIAS)
• A Proposal for LAMOST AS2

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Issue - motivation
? Dark matter halos surrounding galaxies, groups
clusters ? Nature of the DHs of field galaxies
- consistent with those expected in LCDM
model? ? Tracers of the halo potential 1.
satellite galaxies 2. background galaxies
behind the potential well (weak gravitational
lensing) - Information on halos through
ensemble average over large samples
(current data give 1 satellite per host) ? Time
is ripe for studying individual halos from
forthcoming redshift surveys
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Sciences from satellites A. Properties of DHs
well beyond the visible part of galaxies 1.
Radial profile 2. Dark halo mass function 3.
Mass-to-light ratio as a function M 4.
Non-sphericity of halo alignment of satellite
system 5. Large-scale distribution of dark
halos 6. Redshift evolution of dark halos B.
Properties of satellites and their DHs 7.
Physical properties of satellites 8.
Host-satellite properties environmental effects
of satellite formation
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How to use satellites to probe DHs
? Dynamics of satellite galaxies strong - the
gravitational potential of the host galaxy only
is probed weak - projected radius (use good
zsp), interlopers (effects can be corrected),
relaxation time gt t0 (do not
assume virialization) ? Define hosts and
satellites for probing DH potential given the
spherical coor. (RA, DEC, z) from a redshift
survey 1. Isolation criteria on hosts
host is brighter than any neighbor by ?m within
rplt R, ?vltV 2. Satellite conditions
fainter more than ?m' compared to their hosts
should be within rplt R', ?vltV' ? Large-scale
properties of halos - no info near the center
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Dark halo models
JE
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Radial profile and mass of halos
Prada et al. 03 Brainerd 04 - SDSS 2dF -
Decreasing sv profile well-fit by that of NFW
halos for hosts with -19.5 gt MB gt -21.5 - Virial
mass of L galaxy (MB-19.5) 1012 h-1 M? -
Host dependence of sv sv is higher for
early-type or brighter hosts indicating deeper
potential (larger mass) sv decreases faster for
early-type hosts
Conroy et al. 05, 07 - DEEP2 - Decreasing sv
profile well-fit by that of NFW halos for hosts
with -19.5 gt MB gt -21.5 - Virial mass of L
galaxy (MB-19.5) 1012 h-1 M?
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Mass/Light Ratio - dependence on L
Zaritsky et al. 97 Zaritsky White 94 - ?v
of satellites of isolated spirals indep. of HI
line width M/L L-1
McKay et al. 02 Brainerd Specian 03 - SDSS
2dF - isothermal estimator Mdyn(rlt260kpc)
2.1r s2/G - Mdyn(rlt260kpc)/L const. for L
2L for early types, but
L-1 for spirals
Prada et al. 03 - SDSS radial variation of
M/L - sv L0.3 for satellites with
rplt120kpc L0.5 at 250ltrplt350kpc - sv
Mvir0.38 for satellites with rplt120kpc
Mvir0.5 at 250ltrplt350kpc for NFW gt Mvir/L
L-0.2 at rplt120kpc const. at rp350kpc
? rather weak dependence of M/L on L
interesting to see M/L at higer lower masses
lt--gt LCDMG.Formation
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Non-sphericity of halos
Kazantzidis et al. 04 N-body hydro
simulation - projected ellipticity of 0.3 at
rrvir (not affected by rounding effects of gas
physics at the center)
Holmberg 69 Zaritsky et al. 97 Sales Lambas
04 - Holmberg effect alignment of satellites
with the minor axes of hosts
Penarrubia et al. 02 - Planar orbit decays more
quickly than the polar orbit
Agustsson Brainerd 06 - Alignment of
satellites with the major axes of hosts!
Azzaro et al. 07 - Alignment of satellites
with red hosts (red sat. in particular) gt
consistent with LCDM?
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Physics of satellite system
E hosts
f(ESat)
Ahn, Park, Choi 07 Satellite morphology
satellite density profile Mrlt-20 Morphology
conformity L sat. of L hosts increase inward
surface density profile n -2(E) -1.4(L
sat)
L hosts
E hosts
L satellites
E satellites
L hosts
L satellites
E satellite
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mass density from 20 bright nearby galaxies
Ahn, Park, Choi 07 Satellite morphology vs
environment - Clear dependence on background
density - Effects of host morphology disappears
only at r23 rvir ?Mass profile from dynamics
consistent with NFW LCDM, but satellite
density profile morphology are affected by
physical interactions with hosts
f(ESat)
E hosts
L hosts
High density
L
E
Low density
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Park, Gott, Choi 07 Galaxy pairs -
Hydrodynamic interactions within virial radius
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Some of Nearby Galactic Satellite Systems- How
do they look?
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LAMOST
Key surveys 1. Galaxy Redshift Survey,
2. Milky Way Star Survey, 3. Spectroscopic
Survey for Multi-Waveband Cross-Identification 10
7 galaxies for LSS sciences (wide field) 1.
magnitude-limited down to B20.5 with mean
z0.2 2. LRG down to r20.5 with 0.3ltzlt0.8 3.
Emission line galaxy survey 4. QSO using SDSS 5
colors
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Galaxy redshift survey 4000 fibers Resolution
R500, 1000, 2000 covering 370-900nm. Spectra of
galaxies down to B20.5m in 1.5h exposure until
N107?
LAMOST
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If the same sky coverage of SDSS, rlim19.8 to
get 107 spectra
Extinction-corrected Mag. Limit
Sky coverage wider than SDSS rlim19.2 to get
107 spectra
Fainter than r17.77
But low b coverage is not quite useful for LSS
sciences. In practice, fiber constraints
will make the limit fuzzy
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Sky Coverage

• Minimize Galactic foreground extinction

Celestial equator
Extinction contours of Schlegel, Finkbeiner and
Davis (1998).
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Photometric catalog of SDSS galaxies down to
rlim19.7 photo-z
Magnitude limits and Survey depth
18.7
19.2
19.7
rlim17.6
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Survey of Galactic Satellite Systems Option 1
Natural outcome of blind magnitude-limited survey
Conditions 1. large sky coverage to look
into satellite systems of widely-separated
bright galaxies 2. gtgt 1mag deeper than SDSS
to significantly increase satellites observed
3. high completeness in crowded region not to
miss satellites around hosts
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LAMOST controllable fiber positioning system
Wide Field Multi-Object Spectrograph (WFMOS)
Echidnas with 5000 fibers Fiber separation
1' Fiber movability 1'
FoV 5 degrees -gt17.67
square arcminutes /fiber -gt4.2' btw fibers
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LAMOST controllable fiber positioning system
of galaxies a fiber should observe
red points actual SDSS galaxies with rlt19.2
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4
94
3
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Fiber separation 4.2' Fiber movability
4.2'-40" gt 4 tilings give 94 completeness at
rlim19.2, But with the efficiency of only 20
for the 4th one !!! 34th tilings should be made
together with other surveys If 12 tilings made,
survey is significant incomplete clustered
regions will be systematically undersampled.
1
1
2
20
3
4
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Survey of Galactic Satellite Systems Option 1
Natural outcome of blind magnitude-limited survey
Conditions 1. large sky coverage to look
into satellite systems of widely-separated
bright galaxies 2. gtgt 1mag deeper than SDSS
to significantly increase satellites observed
3. high completeness in crowded region not to
miss satellites around hosts 4. high S/N and
spectral resolution to give error(cz)ltlt100km/s
if R2000 as in SDSS, ?v30km/s --gt accurate
satellite dynamics But the LAMOST's Key Survey
might adopt rlim19.2 with R500 (??10A)
--gt ?verr gt120km/s sv of satellites

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Option 2 A separate survey around selected area
of the sky
1. survey area 5 x 20 for example 2. rlim
19.7 2 mag deeper than SDSS 3. 5 tilings to
reach completeness gt 90 4. spectral resolution
R2000 But bright nearby host galaxies are
rare (lt40h-1Mpc) 3 galaxies with Mrlt-20
(lt80 h-1Mpc) 20 in 100 ? For farther
hosts the size of satellite systems becomes lt 15'
satellites become too faint
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Bright galaxies added Extinction, K-correction,
L-evolution corrected
L
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Targeted Survey Select hosts at d50100 h-1Mpc
in underdense regions Satellite system of
rp400h-1kpc subtends 14' 28' on the sky
100
50
rlim19.2
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Option 3 A separate survey of satellites around
selected hosts
1. select hosts located at 40 lt d lt 80 h-1Mpc
r350h-1kpc radius of a satellite system
subtends 30'gt?gt15' 2. Down to rlim 19.7, there
are 20050 galaxies within r30'15' circles
---gt needs to make 45 tilings just for the
region highly inefficient! This
is optimal for individually movable fiber
spectroscopy!
host
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Option 4 Ask neighbors to do the extra job
1. Galaxy survey as planned originally
down to r19.219.4 with R500, over gt10000?
2. Find satellite candidates of all galaxies
within d100h-1Mpc 3. Give the list to AS2, for
example, for spectroscopy with R2000
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SDSS LSS DR5 in (?, ?)
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5 slice
(Park et al. 2005)
Park Gott (1994) SDSS Project Book
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AS2 - After Sloan II
Massive Spectroscopic Surveys of the Distant
Universe, the Milky Way Galaxy, and Extra-Solar
Planetary System
Program 6 yrs from mid-2008 to
mid-2014 Telescope APO 2.5m with 7 deg.
FoV Spectrograph 3700 9800A, R2400, 1000
fibers, 2" diameter Surveys 1. BOSS - redshifts
of 1.5M LRGs 160,000 high-z QSOs (mid2009
mid2014) 2. SEGUE 2 - 250,000 stars down to
g19 3. APO Galactic Evolution Experiment
(APOGEE) - 100,000 stars down to H13.5 towards
inner Galaxy 4. MARVELS - planets from vr of
11,000 stars
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AS2 -BOSS
1.5M LRGs at 0.2ltzlt0.7 160,000 QSOs at
2.3ltzlt2.8 in 10,000 square degrees LRGs down to
i20 lt use photo-z to select bright objects in
the right r-range. (will be no close
objects!)
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Forecast of AS2
w(a) wpwa(ap-a)
err(OK) 0.002, err(wp) 0.05, err(wp)0.37
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WFMOS sparse sampling !!!
surface density 33000/deg2 down to r22.7
A possibility AS2's 1000 fibers 850 for LRGs,
50 for QSOs, 100 for other sciences
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Ancillary sciences for AS2 are being collected
We propose follow-up observations of satellite
candidates from the LAMOST. 2000 tilings covering
10000 square degrees There are 2000 galaxies
with Mrlt-20 dlt90h-1Mpc ---gt if 10 satellites
per host, each tile needs 10 fibers for
satellites and the final of satellites
is 20,000. ---gt fainter but isolated hosts...
Survey strategy has to be matched
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rlim19.7, 40 fibers
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Hosts at underdense region 1. Biased but
well-defined sample --gt can be compared with
models 2. Good probes for DHs 3. DH study for
individual galaxies (not statistical)
rvirial400h-1kpc
rvirial300h-1kpc
?/?blt3 most galaxies are farther than rvirial
from their neighbors
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Summary
1. Satellite dynamics as a probe of galactic
scale dark halos 2. Satellite physics. Galaxy
formation in dark halo environment 3. more
usage... 4. Proposal for a joint survey of
satellites with AS2 not asking for an extra
survey, but careful coordination of the survey.
The survey should be made on time !!!
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