Gustavo YepesUniversidad Autónoma de Madrid

KNAWInternational Colloquium on COSMIC VOIDS

Amsterdam 2006

COLLABORATORSCOLLABORATORS

Matthias Hoeft (IU. Bremen)Matthias Hoeft (IU. Bremen)

Stefan Gottlöber (AIP)Stefan Gottlöber (AIP)

Volker Springel (MPG)Volker Springel (MPG)

CDM Mass function in void regionsCDM Mass function in void regions

High-resolution N-body Simulations Gottlöber et al 2003

The missing dwarf galaxy The missing dwarf galaxy problem in void regionsproblem in void regions

● If If CDM comology is correct there should be a lot of small halos CDM comology is correct there should be a lot of small halos (Vc < 20 km/s ) in voids. Same problem as satellites of galaxies: (Vc < 20 km/s ) in voids. Same problem as satellites of galaxies: too much substructure in CDM models.too much substructure in CDM models.

● No galaxies brighter than MNo galaxies brighter than MBB=-11 (Karanchentsev talk) found in =-11 (Karanchentsev talk) found in local voids.local voids.

● What happens with baryons of small halos in voids?What happens with baryons of small halos in voids?– Are they visible but very faint?. Magnitude, colors. (Red Dwarfs)Are they visible but very faint?. Magnitude, colors. (Red Dwarfs)– Are they just baryonless dark halos?Are they just baryonless dark halos?

● What are the physical mechanisms ?What are the physical mechanisms ?– Gas evaporation by UV photoionization Gas evaporation by UV photoionization – Supernova feedback (e.g Dekel & Silk) Supernova feedback (e.g Dekel & Silk)

● What is the typical halo mass for this to happen?What is the typical halo mass for this to happen?

GALAXY FORMATION GALAXY FORMATION IN VOIDS IN VOIDS

M. Hoeft, G. Yepes, S. Gottlober and V. Springel, M. Hoeft, G. Yepes, S. Gottlober and V. Springel, MNRAS 2006, 371, 401MNRAS 2006, 371, 401

And And Matthias Hoeft’s talk tomorrowMatthias Hoeft’s talk tomorrow

HIGH RESOLUTION HIGH RESOLUTION CDM CDM VOID SIMULATIONS VOID SIMULATIONS

MULTIMASS TECHNIQUEMULTIMASS TECHNIQUEMulti-mass technique to achieve high resolution:Re-Simulated void areas from large computational boxes by resampling particles of incresing mass away from the refined region:

Original intial conditions set up to 20483 particles in a big (50-80 Mpc) box.

S. Gottloeber’s void finding algorithm:Spherical void regions are selected as maximum spheres that do not contain any large (> 2x1011 M)halo

(G)ASTROPHYSICAL (G)ASTROPHYSICAL PROCESSESPROCESSES

● To study in detail the galaxy formation process we take into account:

● Radiative and Compton cooling● UV-photoionization● Multiphase ISM.● Star Formation.● Star-Gas back-reactions

– SN’s thermal Feedbacks: Cloud Evaporation and gas reheating – Stelar Winds

● Springel-Hernquist (2003) implementation of multiphase SPH modeling in GADGET-2.

VOIDS FROM A 80/h Mpc Box

1024102433 effective particle in void region effective particle in void region MMgas gas = = 5.5106 M MMdark dark = = 3.4107 M Smoothing= 2 kpcSmoothing= 2 kpc

20/h Mpc20/h Mpc Simulations done with GADGET2Simulations done with GADGET2Primordial CoolingPrimordial CoolingPhotoionization Photoionization Multiphase mediumMultiphase mediumStar formationStar formationFeedback Feedback ThermalThermal Kinetic (Winds)Kinetic (Winds)

15/h Mpc15/h Mpc

Void with 10243 effective particles (7 million particles )

– Mgas = 1.5106 M

– Mdark= 8.2106 M

Spatial smoothing= 2 kpc

Same void was resimulated with full resolution 20483 ( 43 million particles in total)

– Mgas 2 105 M

– Mdark 106 M

– Spatial smoothing= • 0.5 kpc comoving

(ULTRA)HIGH-RESOLUTION (ULTRA)HIGH-RESOLUTION SIMULATIONS OF VOIDS SIMULATIONS OF VOIDS

50/h Mpc Box 50/h Mpc Box

10/h Mpc10/h Mpc

Different feedback parameters

List of simulationsList of simulationsHoeft et al 2006, MNRAS Hoeft et al 2006, MNRAS 371, 401

++Simulations with Kinetic Feedback (stellar winds)Simulations with Kinetic Feedback (stellar winds)

With different values of With different values of (fraction of E(fraction of ESNSN that goes into wind that goes into wind

Halo Mass function in VoidsHalo Mass function in Voids

Baryon fractionBaryon fraction

Halos belowfew times109 Msun

arebaryon-poor

Characteristicmass scaledepends onredshift

Characteristic Mass of UV evaporationCharacteristic Mass of UV evaporation

Characteristic massCharacteristic mass Mc

baryon-rich

baryon-poor

Mc risessignificantlywith z

Halo may startbaryon-richand becomelaterbaryon-poor

Tentry

What is the characteristic Mass?What is the characteristic Mass?

Listen to Matthias Hoeft’s talk tomorrowListen to Matthias Hoeft’s talk tomorrowDensity –Temperature phase diagramDensity –Temperature phase diagram

Cold mode of galactic gasaccretion: gas creeps alongthe equilibrium line between heating and Cooling (Keres et al. 04)

For gas to be able to enter the instabilty branch, need to be heated above Tentry temperature.

Mc can be viewed as the critical mass for which the virial temperature of gas inside is above the entry temperature of the thermal unstable regime.

New Filtering Mass EstimateNew Filtering Mass Estimate(M. Hoeft’s talk tomorrow)(M. Hoeft’s talk tomorrow)

Smoothing of baryonicSmoothing of baryonicFluctuations due to Fluctuations due to counteracting pressure counteracting pressure gradiantsgradiants

MMf f = = 4/3 22a/ka/kff))33

Mass accretion histories and Mass accretion histories and gas condensation in void halosgas condensation in void halos

MMcc

Age of stars in void halosAge of stars in void halos

In small halosstars can onlybe formed at highredshift

Stellar mass functionStellar mass function

Thermal feedbackThermal feedback

Mass-Luminosity functionMass-Luminosity function

z=0z=0

Bruzual & Charlot 03

SPSM

Thermal feedbackThermal feedback

Strong wind modelStrong wind model

Mass-Luminosity functionMass-Luminosity function

z=0z=0

Cum. Luminosity functionCum. Luminosity function

High ResolutionHigh ResolutionBasicBasic

Small WindsSmall Winds

Luminosity functionLuminosity function

Wind 0.15Wind 0.15

Wind 0.05Wind 0.05

Wind 0.4 Wind 0.4

Wind 0.25Wind 0.25

Kinetic Feedback: Kinetic Feedback: Energy in windsEnergy in winds

Luminosity functionLuminosity function

Effects of UV fluxEffects of UV flux

UV=0UV=0

UV*100UV*100

UV*0.1UV*0.1

UV*10UV*10

UV*0.01UV*0.01

COLOR-MAGNITUDE

COLOR-MAGNITUDEUV Normalization

COLOR-MAGNITUDEUV Normalization

COLOR-MAGNITUDEUV Normalization

COLOR-MAGNITUDEWind Energy

COLOR-MAGNITUDEWind Energy

Filtering Mass at z=0

McMc

Mean age of starsMean age of stars Mean Metallicity of starsMean Metallicity of stars

DWARF GALAXIES IN GROUPS:Same resolution than void

simulations (10243 effective)11.5 million total particles

4.5 million gas4.5 million high-res dark

Dwarfs in voids and groupsDwarfs in voids and groups

CONCLUSIONS CONCLUSIONS At present, halos below Mlim~ 7x109 M (vc ~27 km/s) are photo-evaporated and have few baryon content, either cold gas or stars. This mass scale decreases with redshift. Very small dependence of UV flux.Halos can condense baryons and form stars early than reionization redshift. Seems enough for them to shine today.UV-photoheating not able to suppress most of the small galaxies: Does not solve the problem of excess of substructure of CDM .Thermal feedback (as implemented in the simulations) does not play a significant role in keeping gas out of small halos. Kinetic feedback (winds) is very efficient in suppressing star-formation provided that a substantial fraction of ESN goes into wind energy. Need more work on feedback modeling.Dwarfs ending up in other environments (e.g groups) have similar properties as long as they have not experience substantial interactions with the host halo.

THANK YOU

Commercial (Free of charge):Commercial (Free of charge):

MNCPMNCPThe MareNostrum Numerical Cosmology ProjectThe MareNostrum Numerical Cosmology Project

http://astro.ft.uam.es/marenostrum

• MareNostrum Universe SimulationMareNostrum Universe Simulation:2x10243 500/h Mpc SPH

• MN High z Galaxy Formation SimulationMN High z Galaxy Formation Simulation:2x10243 50/h Mpc SPH +gastrophysics

• MN Local Universe Constrained SimulationsMN Local Universe Constrained Simulations• 2x10243 64 to 320/h Mpc boxes N-body , SPH+gastrophysics