Understanding formation of galaxies from their environments

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Understanding formation of galaxies from their
environments

• Yipeng Jing
• Shanghai Astronomical Observatory

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A brief overview of structure formation

• A concordance LCDM model emerged
• Structures form from bottom up
• Most basic properties of dark matter halos well
  understood now,
• Number density approximately by PS
• Internal structure by NFW profile
• Halos are triaxial with larger halos being more
  elongated
• Halos are pointed along nearby filaments also
  pointed preferentially to each other
• Halos are slowly rotating with the spin parameter
  0.05 spin parameters are log-normal distributed
• Rotation preferentially along the minor axis of
  halos

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Structure formation
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Physical processes of galaxy formation

• Gas cooling and disk galaxy formation
• Galaxies falling into bigger halos with halos
  merges ram pressure and tidal stripping may take
  away hot gas and even cold gas from satellite
  galaxies
• Mergers of gaseous galaxies lead to starbursts
• dry mergers are important as well formation of E
  galaxies
• Black holes grow with merges and accretion
• Supernova feedback and AGN feedback

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• JYP Suto, Y. 2000, ApJ, 529, L69

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Okamoto et al. 2005, MNRAS, 363,129
Formation of galactic disk depends on the
formation of stars and the feedback much more
complicated than the conventional disk formation
scenario by Fall and Efstathiou (1980)
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Physical processes of galaxy formation

• Gas cooling and disk galaxy formation
• Galaxies falling into bigger halos with halos
  merges ram pressure and tidal stripping may take
  away hot gas and cold gas from satellite
  galaxies
• Mergers of gaseous galaxies lead to starbursts
• dry mergers are important as well formation of E
  galaxies
• Black holes grows with merges and accretion
• Supernova feedback and AGN feedback

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Strangulation hot gas stripping
Gravitational tidal force can remove cold gas and
even part of stellar mass of a satellite galaxy
Wang, H.Y., Jing et al., in preparation
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Physical processes of galaxy formation

• Gas cooling and disk galaxy formation
• Galaxies falling into bigger halos with halos
  merges ram pressure and tidal stripping may take
  away hot gas and even cold gas from satellite
  galaxies
• Mergers of gaseous galaxies lead to starbursts
• dry mergers are important as well formation of E
  galaxies
• Black holes grows with merges and accretion
• Supernova feedback and AGN feedback

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• Hierarchical formation, galaxies falling into
  bigger halos, and galaxies mergers

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Physical processes of galaxy formation

• Gas cooling and disk galaxy formation
• Galaxies falling into bigger halos with halos
  merges ram pressure and tidal stripping may take
  away hot gas and even cold gas from satellite
  galaxies
• Mergers of gaseous galaxies lead to starbursts
• dry mergers are important as well formation of E
  galaxies
• Black holes grows with merges and accretion
• Supernova feedback and AGN feedback

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Spectroscopic (redshift) survey of 106
galaxies Sloan Digital Sky Survey (SDSS)
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Orientation of central galaxies relative to host
halos

• Yang X.H., et al. astroph/0601040, MN, 2006
• Kang X., et al. , MN, 2007

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Isodensity Surfaces of halos

• Use SPH method to get the density for each
  particle and form the isodensity surfaces (Jing
  Suto 2002)

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Why do we do this?

• Understanding disk formation
• Relation with the rotation (spin) of the dark
  matter halos
• Dynamical evolution
• Understanding elliptical formation
• Major merges

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Observational Sample

• SDSS DR2
• Halo based groups (unique!) selected from SDSS
  (Yang et al. 2005 MNRAS 356, 1293)
• Useful information
• Central and satellites
• Mass of the halos
• Color of the group members

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Alignment for the whole sample

• f N(?) /N_ran(?)
• 24,728 pairs

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Dependences on the color
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Dependences on group mass
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Which satellites contributed ?
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Summary for the observation

• Satellites align with the major axis of the
  centrals, in contrast with the classic
  Holmberg(1969) effect
• The effect stronger for red centrals/satellites
  vanishes for blue centrals have chance to have
  our Milky Way
• Stronger for richer systems
• Stronger for satellites at smaller halo-centric
  distance

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Jing Suto 2002
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Jing Suto 2002
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Jing Suto (2002)
Radius R
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Semi-analytical modeling of galaxy formation
based on N-body simulations

• Physical processes heating, cooling, star
  formation and feedback, chemical evolution, dust
  extinction, SSP, galaxy mergers and morphology
  transformation (quite complete compared with
  previous works)
• Subhalos well resolved Galaxy mergers are dealt
  with much better than previous works
• Cooling time scale is longer than standard flat
  faint end of LF
• Cut off cooling in massive halos with AGN
  formation and feedback
• Kang X., YPJ, H.J.Mo, G. Boerner (2005)
• Kang, Jing, Silk, 2006

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Predictions from Semi-analytical model
Numerical Simulation

• Difficulty to predict the orientation of the
  central galaxies
• Spiral galaxies may not be related to halo spin
  from recent simulations
• Ellipticals detailed simulation of mergers
• Useful constraints from the observation

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Assumption on the orietation of the central galaxy

• Central galaxy aligns perfectly with the dark
  matter within r_vir or within 0.3 r_vir

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Predictions from Semi-analytical model
Numerical Simulation

• Difficulty to predict the orientation of the
  central galaxies
• Spiral galaxies may not be related to halo spin
  from recent simulations
• Ellipticals detailed simulation of mergers
• Useful constraints from the observation

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If some misalignment between the central galaxy
and its host halo

• Gaussian distribution with the width
• 60 degrees for blue
• 30 degrees for red

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Dependence on halo mass
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• Schematic picture to explain the alignment

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Conclusions from the modeling

• The alignment effect is explained if
• the red central has some mis-alignment with the
  host halo(Gaussian width 30degrees)
• the blue central has more (60 degrees)
• Color and halo mass dependences explained
• Important Implications Is the disk of spirals
  determined by the spin of the host? Intrinsic
  alignment for weak lensing?

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Color of centrals and satellites

• To understand
• Hot gas stripping
• Cold gas and stars stripping by tides
• AGN activity

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Fraction of blue galaxies
Weinmann et al. 2006
More severe for more massive clusters But hot
gas not stripped immediately!
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Astroph/0709.1354 downsizing
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Monaco et al. 2006, ApJ
Downsizing requires satellite galaxies to lose a
significant amount of stars before merging into
the central galaxies
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A few points for the future work

• Hot gas stripped not immediately after falling
  into the host need more work to quantify this
• Stars of satellites must be stripped out by
  tides existence of the IC stars
• In order to keep the central galaxies red, blue
  components of satellites must be removed

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Interaction-induced star formation enhancement
(Li et al. 2008a)

• Sample selection
• SDSS DR4 400,000 galaxies rlt17.7
• Use emission line diagram to select star-forming
  galaxies rlt17.6
• Use SFR/M, specific star formation rate as the
  star formation strength

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Clustering properties Overall comparison for
different types
Brinchmann et al. 2004
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Methods

• cross correlation function with spectroscopic
  sample of all galaxies neighbour counts
• Enhancement function with reference to galaxies
  in a photometric sample to limiting magnitude
  19 other limits18.5 and 19.5 also used, to study
  the effect of companions mass
• Morphology --- sign of interaction

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Clustering properties high/low SFR/M
Projected cross-correlation function
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Clustering properties As a function of SFR/M,
at different scales
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Interaction-induced enhancement function
dependence on mass of the SF galaxy
Average boot of SFR/M as a function of the
distance to the nearest neighbor in rlt19 but
r-r_sfglt1.4
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Weak dependence on mass of the companion
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Dependence on the concentration of star-forming
galaxies
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Highly concentrated star forming galaxies, as
ellipticals
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neighbour counts of SF galaxies lt30 have a
neighbor at r_plt100 kpc/h
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high SFR/M star forming without a neighbour
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Summary

• SF galaxies have more close neighbors
• High SF galaxies are small in small halos with
  cold gas low SF galaxies are bigger in larger
  halos without gas
• little dependence found on mass of the companion
  
• Interaction increases SF with decrease of the
  scaled separation
• Strong star forming galaxies are more
  concentrated, consistent with the merging
  scenario
• High SF galaxies do not necessarily have close
  neighbors, but many are post mergers

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Are AGN the products of galaxy mergers?

• Li, C et al. (2008b)

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Clustering properties Overall comparison for
different types
Brinchmann et al. 2004
L(O III)/M_bh indicator for the strength of
accretion rate
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Matched sample in redshift, stellar mass and 4000
A break index D4000
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Strong star formation of AGN! but are these stars
the same as in the starburst or produced with the
black hole accretion ?
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Conclusion

• no evidence that enhanced AGN activity is also
  connected with interactions
• Open questions
• are young stars produced with accretion?
• Are AGN post-merger events?
• Our results consistent with the picture
• merger, starburst, AGN (with or without young
  stars formed)

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Final Remarks

• The observations have provided important clues to
  the important processes of galaxy formation, but
  the interpretation is far from definite
• Detailed theoretical modeling, especially
  numerical simulations, are needed.