Galaxies…. + On the largest scales… they trace the cosmic structure as the “living fossils” of the earliest density fluctuations of the universe They are luminous tracers of the process of gravitation contraction embedded in a universal expansion + On cluster scales… they act as trace particles of the most massive cosmic structures They dynamically weigh the high end of the overdensity regime, and contribute intracluster baryonic gas, the luminous tracer of the of cluster dark matter “halos” + On group scales… merging relics and distribution of luminosities echo the dynamic responses of intermediate mass scales They provide insights to the dynamics that drives the star formation, chemical evolution, and our origins … but, to get to the heart and soul, we need to know the detailed processes…

How does baryonic gas respond as it accretes into a dark matter halo? How does this response realize galaxies as we observe them? When cooling time < dynamical time: gas cools on time scales shorter than the accretion cycle; accretion mode is “cold” When cooling time > dynamical time: Gas shock heats on time scales shorter than accretion cycle; accretion mode is “hot” Dynamical time ~  -1/2 Cooling time ~  -1  -1 (Z) Cooling time Dynamical time ~  -1/2  -1 (Z) Though density at given R in halo depends upon concentration of DM halo density profile, this density dependent time scales set up a “transition”, or “critical” mass that segregates the accretion modes in the halos of galaxies of different masses Since halo mass increases with time, but the density of circum-galactic gas decreases, this sets up a fairly simple scenario for understanding galaxy evolution… Gas is the key….

Time/Age, Gyr Spherical Models conducted by Dekel & Birnboim (2003,2006) Higher Mass DM halos: Shock set up within 1-2 Gyr with T>10 5 K (with much hotter gas) at R~0.1 R vir ; shock maintained thereafter; cold gas accretion onto galaxy suppressed Lower Mass DM halos: Gas accretes cold until mass grows above some threshold, then shock set up at R~0.1 R vir ; shock maintained thereafter, but while halo at intermediate mass, some cold material penetrates to galaxy Dekel & Birnboim (2006)

M crit = Critical Mass ~ M sun Three Regimes of accretion: 1.M<M crit : cold mode directly onto galaxy at all redshifts though decreasing with decreasing z; cold mode remains important mode of accretion onto galaxies 2.M>M crit high z : hot shocked accretion onto halo; cold stream penetration by filaments continue to accrete onto galaxy 3.M>M crit low z : hot shocked accretion; cold stream disruption; accretion onto halo, but accretion onto galaxy suppressed Dynamical time ~  -1/2 = (1+z) -3/2 Cooling time ~  -1  -1 (Z) = (1+z) -3  -1 (Z) Cooling time Dynamical time ~ (1+z) -3/2  -1 (Z) The Transition Mass…. What do full blown cosmological simulations reveal?

Gas Phases in Simulations in  -T plane…. ICM – intracluster medium WHIM – warm/hot ionized medium and hot halo component Diffuse IGM – filaments Cold Halo Gas – accreting, post shocked cooled ISM – within galaxies Van de Voort & Schaye (2011)

R vir M > M crit : shock heated halo, cold flows disrupted, accretion onto galaxy suppressed; minor satellites form, become “dry” M = M crit : shock heated halo, cold flows partially disrupted, accretion onto galaxy can occur; halos contain multiphase gas M < M crit : cold flow accretion directly onto galaxy; star formation efficient, SNe driven winds efficient, resulting in complex multi-phase halos Van de Voort & Schaye (2011) Accretion and Mass….

M > M crit : shock heated halo, cold flows disrupted, accretion onto galaxy suppressed; minor satellites form, become “dry” M = M crit : shock heated halo, cold flows partially disrupted, accretion onto galaxy can occur; halos contain multiphase gas M < M crit : cold flow accretion directly onto galaxy; star formation efficient, SNe driven winds efficient, resulting in complex multi-phase halos Van de Voort & Schaye (2011) Accretion and Mass….

We have now build a sample of 200+ z=0.1-1 Galaxies…. Measured: M B, M R, M K B-R color B-K color Impact parameter, D MgII EWs; 58 w/ stringent limits Deduce: Stellar population (SPS models) SP ages, metallicities, masses Virial Masses (halo matching) Virial radii, temperatures For ~100 have HST/SDSS images: + Morphologies + Inclinations + QSO-major axis position angle Nielsen etal (2012), inprep EW vs D (7.8  ) Worth noting is the large amount scatter… Many studies attempt to explain as a 2 nd parameter, for example, galaxy luminosity (see Chen etal 2010) Scatter could be a result of a mutli-variate dependence (can it be reduced?) Can its reduction provide new insights into gaseous halos?

MgII EW and Galaxy Virial Mass? Expectations: Halos with M vir > M crit dominated by hot T vir gas; MgII should not survive >>> smaller MgII EW Halos with M vir < M crit lower T vir; thus dominated by cold mode accretion; MgII should survive >>> larger MgII EW Keres etal (2005,2009) Indeed, the cosmological simulations predict that the fraction of cold mode accretion gas diminishes with increasing M vir

MgII EW and Galaxy Virial Mass? Expectations: Halos with M vir > M crit dominated by hot T vir gas; MgII should not survive >>> smaller MgII EW Halos with M vir < M crit lower T vir; thus dominated by cold mode accretion; MgII should survive >>> larger MgII EW Using a statistical sample of LRGs, Bouche etal (2006) employed galaxy-galaxy x-corr and dark matter bias model to estimate galaxy masses, then employed galaxy-absorber x-corr to create statistical relation between MgII EW and galaxy virial mass – found 3  anti-correlation. Gauthier etal (2009, 2010) found 1.5  … suggest confirmation of simulations and that scatter in EW vs D may have some dependence on galaxy virial mass? Bouche’ etal (2006)

MgII EW and Galaxy Virial Mass? Expectations: Halos with M vir > M crit dominated by hot T vir gas; MgII should not survive >>> smaller MgII EW Halos with M vir < M crit lower T vir; thus dominated by cold mode accretion; MgII should survive >>> larger MgII EW Using halo abundance matching of Trujillo-Gomez  we obtain virial masses from M R for each galaxy. We find no correlation between MgII EW and galaxy M vir

MgII EW and Galaxy Virial Mass? Our sensitivity to MgII EW is factor of 100 deeper (0.03 angstroms) Still no evidence for correlation Whatever dictates MgII absorption strength, it is not primarily a halo mass dependence Whereas galaxies with EW>0.3 are selected by absorption, those with EW<0.3 are not (and in some cases these stringent limits may indicate a true lack of MgII absorbing gas along sightline) … so not clearly a selection effect Nielsen etal (2012), inprep

Having Deduced Galaxy Virial Masses and Radii…. MgII EW vs D/R vir yields a 9.8  anti-correlation; best fit with a power-law Nielsen etal (2012), inprep Strongly suggests that EW strongly depends upon location with respect to virial radius of galaxy dark matter halo

Gas density decreases by 2-3 orders of magnitude between R vir Gas temperature increases by order of magnitude between R vir z=0 Cold Mode (blue) …. Van de Voort etal (2011) Statistical Expectation based upon Simulations?... These trends, if properties of real galaxies, conspire to have MgII EW decrease uniformly with R/R vir Scatter would be expected since D is projected R

The HI Absorbing Complex! 1600 km/s of Neutral Hydrogen Absorption 58 kpc from G1 G1 is massive elliptical log M vir /M sun =13.7 D/R vir = 0.1 T vir = 10 7 K solar metallicity SP z=4 “red and dead” In such galaxies, at z<1, infalling filaments, cold mode accretion penetrate no further than D/R vir =0.5 Thus, even though the galaxy is probed at D/R vir =0.1 in projection, the gas probed in HI absorption likely arises in the outer halo, near the virial radius, and/or beyond the virial radius Keres et al (2009) R vir

Concluding Remarks… 1.Observational data and simulations are reaching a point where direct comparisons on using case-by-case studies can test theory of galaxy evolution 2.The key ingredients for galaxies are masses and stellar populations, metallicities, age, and morphologies 3.Theory challenged by lack of Mass relation, but supported by highly significant D/R vir anti-correlation with MgII EW 4.The G1 HI complex is a fascinating confirmation of the shut down of cold accretion by intermediate redshifts in massive galaxies; the G2 galaxy/absorber is a challenge to simulations, since the hot accretion appears to be operating 5.The MgII orientation effect (which we are continuing to explore), suggests that either low ionization components of winds and/or infall are dominant along the principle axes of galaxies; yet the lack of MgII absorption can be present at all projected orientations (hot gas not traced by MgII)…? T H A N K Y O U !!!