%0 Generic %1 stern2016universal %A Stern, Jonathan %A Hennawi, Joseph F. %A Prochaska, J. Xavier %A Werk, Jessica K. %D 2016 %K cgm density low-z profile %T A Universal Density Structure for Circum-Galactic Gas %U http://arxiv.org/abs/1604.02168 %X We develop a new method to constrain the physical conditions in the cool (~10^4 K) circumgalactic medium (CGM) from measurements of ionic columns densities, under two main assumptions: that the cool CGM spans a large range of gas densities, and that small high-density clouds are hierarchically embedded in large low-density clouds. The new method combines (or `stacks') the information available from different sightlines during the photoionization modeling, thus yielding significantly tighter constraints on the CGM properties compared to traditional methods which model each sightline individually. Applying this new technique to the COS-Halos survey of low-redshift ~L* galaxies, we find that we can reproduce all observed ion columns in all 44 galaxies in the sample, from the low-ions to OVI, with a single universal density structure for the cool CGM. The gas densities span the range 50 < \rho/\rho_mean < 5x10^5 (\rho_mean is the cosmic mean), while the physical size of individual clouds scales as ~\rho^-1, from ~35 kpc of the low density OVI clouds to ~6 pc of the highest density low-ion clouds. The cloud sizes are too small for this density structure to be driven by self-gravity, thus its physical source is unclear. We find a total cool CGM mass within the virial radius of 1.3x10^10 M_sun (~1% of the halo mass), distributed rather uniformly over the four decades in density. The mean cool gas density profile scales as R^-1.0, where R is the distance from the galaxy center. We construct a 3D model of the cool CGM based on our results, which we argue are a benchmark for the CGM structure in hydrodynamic simulations. Our results can be tested by measuring the coherence scales of different ions, using absorption line measurements along multiple sightlines towards lensed quasars.

@misc{stern2016universal, abstract = {We develop a new method to constrain the physical conditions in the cool (~10^4 K) circumgalactic medium (CGM) from measurements of ionic columns densities, under two main assumptions: that the cool CGM spans a large range of gas densities, and that small high-density clouds are hierarchically embedded in large low-density clouds. The new method combines (or `stacks') the information available from different sightlines during the photoionization modeling, thus yielding significantly tighter constraints on the CGM properties compared to traditional methods which model each sightline individually. Applying this new technique to the COS-Halos survey of low-redshift ~L* galaxies, we find that we can reproduce all observed ion columns in all 44 galaxies in the sample, from the low-ions to OVI, with a single universal density structure for the cool CGM. The gas densities span the range 50 < \rho/\rho_mean < 5x10^5 (\rho_mean is the cosmic mean), while the physical size of individual clouds scales as ~\rho^-1, from ~35 kpc of the low density OVI clouds to ~6 pc of the highest density low-ion clouds. The cloud sizes are too small for this density structure to be driven by self-gravity, thus its physical source is unclear. We find a total cool CGM mass within the virial radius of 1.3x10^10 M_sun (~1% of the halo mass), distributed rather uniformly over the four decades in density. The mean cool gas density profile scales as R^-1.0, where R is the distance from the galaxy center. We construct a 3D model of the cool CGM based on our results, which we argue are a benchmark for the CGM structure in hydrodynamic simulations. Our results can be tested by measuring the coherence scales of different ions, using absorption line measurements along multiple sightlines towards lensed quasars.}, added-at = {2016-04-11T17:55:01.000+0200}, author = {Stern, Jonathan and Hennawi, Joseph F. and Prochaska, J. Xavier and Werk, Jessica K.}, biburl = {https://www.bibsonomy.org/bibtex/24d792b8a4e9fa792d33e8a025d8057a5/miki}, description = {[1604.02168] A Universal Density Structure for Circum-Galactic Gas}, interhash = {70a3198fea5210e78e2a13363852afc7}, intrahash = {4d792b8a4e9fa792d33e8a025d8057a5}, keywords = {cgm density low-z profile}, note = {cite arxiv:1604.02168Comment: Submitted to ApJ}, timestamp = {2016-04-11T17:55:01.000+0200}, title = {A Universal Density Structure for Circum-Galactic Gas}, url = {http://arxiv.org/abs/1604.02168}, year = 2016 }