The Role of Dissipation in Galaxy Mergers Sadegh Khochfar University of Oxford

Why should dissipation be important? Perez-Gonzalez et al. (2005)

Dissipation during Mergers Springel & Hernquist (2005) Star bursts occur during mergers and the strength depends on the available fuel. New born stars are not subject to the existing phase space constraints and can increase the phase space density. Carlberg (1986)

Semi-analytic Modelling Extended Press-Schechter Gas Cooling Reionising Background Star Formation Supernova Feedback Stellar Population Models Galaxy Merging via Dynamical Friction

Stellar Components Bulge Stars : Major Merger: Stellar disks get disrupted spheroid All available cold gas centre of the remnant Gas in the centre central star burst Minor Merger: Stars of satellite to bulge Gas of satellite to disk Disk Stars: Parameterisation of Schmidt-Kennicutt law

Stars in Bulges & Ellipticals 3 main distinct origins: Former disk stars quiescent Central Starburst star burst Satellite stars Springel & Hernquist (2005) star burst quiescent

Surface Mass Density Springel & Hernquist (2005) Effective radius of the Star burst component is ~ 5.7 time smaller than that of the scattered disc stars. star burst quiescent Dekel & Cox (2006)

Surface Mass Density Kauffmann et al. (2003)

Morphology Dependence Kauffmann et al. (2003) EllipticalsSpirals

Where are all the Stars? Khochfar & Silk (2006a) The most massive Galaxies at each redshift are ellipticals galaxies. With time massive disc galaxies start appearing.

Progenitors Progenitors of massive galaxies have already bulges Above M C no mergers between bulge less galaxies happen anymore no environment dependence MCMC Khochfar & Silk (2005)

Dry Mergers Khochfar & Burkert (2003) At the characteristic mass scale the mass in progenitor bulges is roughly 50% Massive spheroids form by mergers of spheroids

Dissipation in Mergers vs Mass MCMC log M  ~85 % Above M C bulges and ellipticals have on average a constant fraction of 85 % of stars made previously in disks M quiescent /M bulge

Build-Up of the Relation Early major mergers are gas-rich and tend to decrease the fraction of quiescent stars in bulges. Satellite mergers in contrast increase the fraction of the quiescent population in bulges. Khochfar & Silk (2006a)

Redshift Evolution Bulges present at earlier times are more compact and smaller than their counterparts at low redshifts. This effect is most significant for massive elliptical galaxies at high redshifts.

Environmental Dependence Kauffmann et al. (2004) Khochfar & Silk (2006a)

So far…. Present day Es with masses > M C are determined by mergers of bulge dominated systems Dissipation is more important for smaller Es except for the most massive Es at high z Dissipation is more important at higher z Dissipation is more important for Es with masses > M C

Size-Distribution Kauffmann et al. (2003) Khochfar & Silk (2006b)

Size-Distribution Khochfar & Silk (2006b) Our results suggest:

Dissipation Factor Khochfar & Silk (2006a)

Size-Evolution Massive ellipticals show a stronger size- evolution than less massive ones. The size-evolution predicted based on the star-burst component agrees well with the observations. Khochfar & Silk (2006b)

Size-Evolution Massive galaxies could be up to five times smaller at high redshifts than now, because they are more likely to be formed during a gas- rich major merger. Khochfar & Silk (2006b) Trujillo et al. (2006)

RSF-Correlations Schawinski, Khochfar et al. (2006) Feedback effects correlate with sigma but not with the luminosity

Critical Black Hole Mass-  Relation M BH AGNs with black hole masses larger than the critical black hole mass shut off star formation and prohibit it in the future. Schawinski & Khochfar et al. (2006)

The RSF-Correlation Schawinski & Khochfar et al. (2006)

The Big Picture Schawinski & Khochfar et al. (2006)

So far…. Generally the size of an E is a function of the star burst fraction Gas-rich merger result in smaller Es The observed size evolution is in agreement with the one predicted by LCDM Es of the same mass are smaller at high redshifts Most massive Es show up to a factor of 3 in size-evolution between z=0 and z=2

So far… Assuming a critical BH mass-sigma relation accounts for the trend seen in the RSF galaxies M BH -  correlation is tighter when accretion dominates BH growth M BH -L correlation is tighter when the BH growth is merger dominated

Red-Sequence & Blue-Cloud Bell et al. (2004) Baldry et al. (2006)

Modeling Approach Substructure (e.g. Kang et al. 2005) Kang et al. (2005)

Modeling Approach Substructure (e.g. Kang et al. 2005) Cooling/heating (e.g. Dekel & Birnboim 2006; Cattaneo et al. 2005) Cattaneo et al. (2005)

Modeling Approach Substructure (e.g. Kang et al. 2005) Cooling/heating (e.g. Dekel & Birnboim 2006; Cattaneo et al. 2005) AGN Feedback (e.g. Croton et al 2006; Bower et al 2006) Croton et al. (2005)Baldry et al. (2006)

Conclusions Dissipation is more important at high redshift Dissipation very important in the most massive Es at high redshifts Dissipation is able to account for the size evolution of Es Dissipation can account for the tightness of the M Bh -  relation Shut off of star formation is the main key to produce the color bimodality There are many different approaches to achieve a shut off which show different successes and failures

Star Formation in Elliptical Galaxies Schawinski & Khochfar et. al (2005) RSF galaxy: 1-3% Star formation in the last Gyr Sample of ~800 Es, all visually classified.

Intrinsic Scatter

Black Hole Mass-  Relation M BH AGNs in black holes with masses larger than the critical black hole mass shut down star formation and prohibit it in the future.

AGN-Feedback

Size-Evolution

Surface Brightness Kauffmann et al. (2003) Bingelli et al. (1988)

Dissipation in Mergers vs Redshift M quiescent /M bulge z Spheroids formed at early times have higher fractions of stars being formed in a star burst event

Formation Epoch of Spheroids The epoch of the last major merger is correlated with mass of the spheroid and surface mass density (fraction of quiescent stars in the bulge)

Morphology Dependence M quiescent /M bulge log M  SpiralsEllipticals

Bulges vs Ellipticals Massive bulges have on average lower fractions of star burst components then ellipticals of the same mass and hence should have lower surface mass densities

Phase Space Density Carlberg (1986) Present day spiral galaxies are not likely to merge into present day ellipticals in concordance with CDM predictions.

Summary M c is connected to spheroid formation Progenitor galaxies with massive bulges result in remnants having constant surface mass density Mass fraction in spheroids from central star bursts becomes constant above M c The star burst fraction increases with redshift In dense environments the star burst component in small galaxies is higher The fraction of star burst component is higher in ellipticals than in bulges Phase space constraints can be recovered M c is not a universal mass scale

A Universal Characteristic Mass Scale log M  M quiescent /M bulge

Age distribution Kauffmann et al. (2003)

Surface Brightness De Jong & van der Kruit (1994)

Concentrations Kauffmann et al. (2003) Higher concentration in more massive galaxies

Dissipation in Mergers vs Mass log M  M quiescent /M star burst

Formation of Bulges & Ellipticals Springel

Density Structure of Remnants without Gas Stellar dynamical properties remnants are spheroidal remnants show profile signs of interaction (e.g. tidal tails) decoupled cores 20% bulge 10% bulge no bulge

The Sloan Digital Sky Survey DR1, Kauffmann et al. (2003) 14.5 < r * < < z < galaxies, 20% of the survey Concentration indices, C=R90/R50 Galaxy size Stellar mass, M * Surface mass density,  

Spheroids Kormendy & Bender

Density Structure of Remnants without Gas Naab &Trujillo (2005) initialfinal The effective radius decreases depending on the orbit geometry and structure of the merging galaxies by a factor ~ 0.8

Density Structure of Remnants without Gas Naab &Trujillo (2005) initialfinal The effective radius decreases depending on the orbit geometry and structure of the merging galaxies by a factor ~ 0.8 Phase space density:

Elliptical/Bulge Formation Simulation by T. Naab

Parameter Space Mass ratio (e.g. Barnes & Hernquist, 1992) Bulge-to-Disc ratio (Khochfar & Burkert, 2003) Orbital parameters (Khochfar & Burkert, 2006) Spin orientation (Khochfar & Burkert, 2006) Mass to light ratios Scale length of stellar components Super-massive black hole (di Matteo et al., 2005) Gas fraction

Progenitor Bulges and R eff Shen et al. (2004) For progenitor bulges > 50% of total mass:

UV-CMR Schawinski et al. (2006) The bluest UV-upturn Galaxy is at NUV-r ~5.4 We assume all galaxies with NUV-r <5.4 have a young stellar component Multiband photometric fitting of the SED show that between 1-3% of the total stellar mass is acquired within the last Gyr. => RSF Galaxies

Working Hypothesis Intrinsic scatter in black hole masses for a given velocity dispersion is the reason for the change in the fraction of RSF-galaxies with sigma Using the fraction of RSF-galaxies with sigma it is possible to predict a critical black hole mass at a given sigma at which feedback prohibits further star formation

Intrinsic Scatter