Abundance of Galaxies and Dark Matter Mario Abadi Alejandro Benítez-Llambay & Ismael Ferrero Observatorio Astronómico Universidad Nacional de Córdoba, UNC Instituto de Astronomía Teórica y Experimental CONICET-UNC Argentina November 22-29, 2013 Latin American Regional IAU Meeting Florianopolis, Brazil

Collaborators Julio Navarro (University of Victoria, Canada) Laura Sales (Harvard, United States) Sebastian Gurovich (IATE, Argentina) Stefan Gottloeber (Astrophysical Institute, Potsdam, Germany) Gustavo Yepes (Universidad Autonóma de Madrid, Spain) Yehuda Hoffman (Hebrew University of Jerusalem, Israel) Matthias Steinmetz (Astrophysical Institute, Potsdam, Germany)

Mass-Energy Content of the Universe Cosmic Microwave Background Temperature=2.735 °K (Plank Satellite 2013) fbar=4.9/26.8 ~ 18% Ordinary Matter

Mass-Energy Content of the Universe

Where are the Stars?

Credits: Duncan Forbes

Where is the Dark Matter? Aquarius Simulation Springel et al. 2008

Where is the Dark Matter? Aquarius Simulation Springel et al. 2008

Where is the Dark Matter? Aquarius Simulation Springel et al. 2008

~650 Mpc Galaxy Distribution Sloan Digital SkySurvey, ~50000 galaxies from Sloan Digital Sky Survey with redshift <z<0.05 by Baldry et al 2008 Credits: M. Blanton & Sloan Digital Sky Survey Team Milky Way Stellar mass 5x10^10 Msolar Log Stellar Mass [Msolar] Number Density of Galaxies per bin [dex^-1 Mpc^-3]

Dark Matter Halos Distribution Millennium series of Dark Matter only simulations (Springel et al 2005 & Angulo et al 2012) Dark Matter Halo Mass Number Density of Halos per bin [dex^-1 Mpc^-3]

Galaxy and Halo Mass Function At the faint end, the dark matter halo mass function is much steeper than the galaxy stellar mass function What is the relation between galaxy stellar mass and dark matter halo mass in order to reconcile these two distributions? Galaxies Baldry et al 2008 Log Mass [Msolar] Milennium Dark Matter Halos (rescaled) Number Density of per bin [dex^-1 Mpc^-3]

Galaxy Stellar Mass vs Halo Mass Abundance Matching Guo et al 2011 Log Dark Matter Halo Mass Log Stellar Mass [Msolar] Milky Way Universal Baryon Fraction fbar~0.171 Very steep relation at the low halo mass end. Essentially, no galaxies with Mgal>10^6 M  should form in halos with mass below a threshold of 10^10 M  A mechanism to select a small fraction of low-mass haloes to be galaxy hosts while leaving dark the vast majority of systems of comparable (or even higher) mass. However…

Galaxy Stellar Mass vs Halo Mass Log Dark Matter Halo Mass Log Stellar Mass [Msolar] Are these masses consistent with masses estimated from kinematic data? Isolated dwarfs HI, tidal interactions negligible and more extended rotation curves These results agree with a similar analysis done by Oh et al See also Milky Way dSphs (Boylan-Kolchin 2011a,b) Ferrero et al. 2012

1)Incorrect interpretation of the data: rotational velocity of neutral gas in dwarf irregulars is not a direct measure of its circular velocity. Gas pressure, non-circular motions and gas velocity dispersion corrections should be taken into account. 2)Baryonic effects: supernova driven gas blowouts (e.g. Navarro et al. 1996) or gravitational fluctuations created by star- forming regions (Pontzen & Governato 2012) might reduce the dark matter content of dwarf galaxies and alleviate the problem. Galaxy Stellar Mass vs Halo Mass Log Dark Matter Halo Mass Log Stellar Mass [Msolar] Ferrero et al. 2012

CLUES Simulation A cosmological numerical simulation that matches the Local Group nearby large-scale structure and the relative positions, stellar masses and morphology of its 3 main spirals: Milky Way (MW), Andromeda (M31) and Triangulum (M33). SPH-GADGET2 (Springel 2005) code with cosmic ionizing UV background, star formation, Supernova feedback and isotropic winds. Zoom-in technique with a Low res region = box of 64/h Mpc on a side High res region = roughly spherical of 2/h Mpc radius Initially, 53 millon gas plus dark matter particles mgas~6x10^4 Msolar mdark~3.5x10^5 Msolar Softening 0.14 kpc

Clues Simulations: Dark Matter Log Dark Matter Halo Mass Log Stellar Mass [Msolar] Credits: G. Yepes 1.3 Mpc/h Ferrero et al Benitez Llambay et al. 2013

Clues Simulations: Gas Log Dark Matter Halo Mass Log Stellar Mass [Msolar] Credits: K. Riebe 2Mpc/h50 kpc/h Ferrero et al Benitez Llambay et al. 2013

Star Formation Log Dark Matter Halo Mass Log Stellar Mass [Msolar] Galaxies with on-going star formation Galaxies that stopped forming stars Ferrero et al Benitez Llambay et al. 2013

Ram Pressure Stripping with the Cosmic Web Benitez-Llambay et al 2013

Galaxy Stellar Mass vs Halo Mass Log Dark Matter Halo Mass Log Stellar Mass [Msolar] Ferrero et al Benitez Llambay et al. in prep.

Reionization Benitez Llambay et al in prep

Conclusions Abundance matching implies that galaxy formation must become extremely inefficient below 10^10 Msolar in order to reconcile the galaxy stellar mass function with dark halo mass function on galactic scales. Many of the galaxies in our sample have enclosed masses much lower than expected from haloes as massive as 10^10 Msolar "Cosmic web stripping" enables the removal of baryons from low-mass halos without appealing to feedback or reionization. May help to explain the scarcity of dwarf galaxies compared with the numerous low-mass halos expected in the CDM and the large diversity of star formation histories and morphologies characteristic of faint galaxies. Further simulations and observational evidence needed.