Probing Outflows in z= 1~2 Galaxies through FeII/FeII* Multiplets

We report on a study of the 2300-2600\AA FeII/FeII* multiplets in the rest-UV spectra of star-forming galaxies at 1.0<z<2.6 as probes of galactic-scale outflows. We extracted a mass-limited sample of 97 galaxies at z~1.0-2.6 from ultra-deep spectra obtained during the GMASS spetroscopic survey in the GOODS South field with the VLT and FORS2. We obtain robust measures of the rest equivalent width of the FeII absorption lines down to a limit of W_r>1.5 \AA and of the FeII* emission lines to W_r>0.5 \AA. Whenever we can measure the systemic redshift of the galaxies from the [OII] emission line, we find that both the FeII and MgII absorption lines are blueshifted, indicative that both species trace gaseous outflows. We also find, however, that the FeII gas has generally lower outflow velocity relative to that of MgII. We investigate the variation of FeII line profiles as a function of the radiative transfer properties of the lines, and find that transitions with higher oscillator strengths are more blueshifted in terms of both line centroids and line wings. We discuss the possibility that FeII lines are suppressed by stellar absorptions. The lower velocities of the FeII lines relative to the MgII doublet, as well as the absence of spatially extended FeII* emission in 2D stacked spectra, suggest that most clouds responsible for the FeII absorption lie close (3~4 kpc) to the disks of galaxies. We show that the FeII/FeII* multiplets offer unique probes of the kinematic structure of galactic outflows.Comment: 53 pages, 22 Figures, accepted for publication in ApJ, revised according to referee comment

The Formation of Ultra Diffuse Galaxies in Cored Dark Matter Halos Through Tidal Stripping and Heating

We propose that the Ultra-Diffuse Galaxy (UDG) population represents a set of satellite galaxies born in $\sim10^{10}-10^{11}$ M$_\odot$ halos, similar to field dwarfs, which suffer a dramatic reduction in surface brightness due to tidal stripping and heating. This scenario is observationally motivated by the radial alignment of UDGs in Coma as well as the significant dependence of UDG abundance on cluster mass. As a test of this formation scenario, we apply a semi-analytic model describing the change in stellar mass and half-light radius of dwarf satellites, occupying either cored or cuspy halos, to cluster subhalos in the Illustris-dark simulation. Key to this model are results from simulations which indicate that galaxies in cored dark-matter halos expand significantly in response to tidal stripping and heating, whereas galaxies in cuspy halos experience limited size evolution. Our analysis indicates that a population of tidally-stripped dwarf galaxies, residing in cored halos (like those hosting low-surface brightness field dwarfs), is able to reproduce the observed sizes and stellar masses of UDGs in clusters remarkably well.Comment: Resubmitted to MNRAS; comments welcome

Spatial Locality of Galaxy Correlation Function in Phase Space: Samples from the 2MASS Extended Source Catalog

We analyze the statistical properties and dynamical implications of galaxy distributions in phase space for samples selected from the 2MASS Extended Source Catalog. The galaxy distribution is decomposed into modes $\delta({\bf k, x})$ which describe the number density perturbations of galaxies in phase space cell given by scale band $\bf k$ to ${\bf k}+\Delta {\bf k}$ and spatial range $\bf x$ to ${\bf x}+\Delta {\bf x}$. In the nonlinear regime, $\delta({\bf k, x})$ is highly non-Gaussian. We find, however, that the correlations between $\delta({\bf k, x})$ and $\delta({\bf k', x'})$ are always very weak if the spatial ranges (${\bf x}$, ${\bf x}+\Delta {\bf x}$) and (${\bf x'}$, ${\bf x'}+\Delta {\bf x'}$) don't overlap. This feature is due to the fact that the spatial locality of the initial perturbations is memorized during hierarchical clustering. The highly spatial locality of the 2MASS galaxy correlations is a strong evidence for the initial perturbations of the cosmic mass field being spatially localized, and therefore, consistent with a Gaussian initial perturbations on scales as small as about 0.1 h$^{-1}$ Mpc. Moreover, the 2MASS galaxy spatial locality indicates that the relationship between density perturbations of galaxies and the underlying dark matter should be localized in phase space. That is, for a structure consisting of perturbations on scales from $k$ to $k+\Delta {k}$, the nonlocal range in the relation between galaxies and dark matter should {\it not} be larger than $|{\Delta {\bf x}}|=2\pi/|\Delta {\bf k}|$. The stochasticity and nonlocality of the bias relation between galaxies and dark matter fields should be no more than the allowed range given by the uncertainty relation $|{\Delta {\bf x}|| \Delta{\bf k}}|=2\pi$.Comment: 27 pages, 9 figures, accepted by Ap

Simulation and pilot plant measurement for CO2 absorption with mixed amines

AbstractCO2 solubility in an aqueous tertiary amine solution was measured, and thermodynamic models Kent-Eisenberg and Clegg-Pitzer were used to correlate CO2 solubility. Process simulation was also carried out with these models, and simulation results are compared with pilot plant measurement data. The results show that the mixed amine solution of the tertiary amine with MEA could save regeneration energy about 20% compared with 30% MEA aqueous solution

Star Formation and Clumps in Cosmological Galaxy Simulations with Radiation Pressure Feedback

Cosmological simulations of galaxies have typically produced too many stars at early times. We study the global and morphological effects of radiation pressure (RP) in eight pairs of high-resolution cosmological galaxy formation simulations. We find that the additional feedback suppresses star formation globally by a factor of ~2. Despite this reduction, the simulations still overproduce stars by a factor of ~2 with respect to the predictions provided by abundance matching methods for halos more massive than 5E11 Msun/h (Behroozi, Wechsler & Conroy 2013). We also study the morphological impact of radiation pressure on our simulations. In simulations with RP the average number of low mass clumps falls dramatically. Only clumps with stellar masses Mclump/Mdisk <= 5% are impacted by the inclusion of RP, and RP and no-RP clump counts above this range are comparable. The inclusion of RP depresses the contrast ratios of clumps by factors of a few for clump masses less than 5% of the disk masses. For more massive clumps, the differences between and RP and no-RP simulations diminish. We note however, that the simulations analyzed have disk stellar masses below about 2E10 Msun/h. By creating mock Hubble Space Telescope observations we find that the number of clumps is slightly reduced in simulations with RP. However, since massive clumps survive the inclusion of RP and are found in our mock observations, we do not find a disagreement between simulations of our clumpy galaxies and observations of clumpy galaxies. We demonstrate that clumps found in any single gas, stellar, or mock observation image are not necessarily clumps found in another map, and that there are few clumps common to multiple maps.Comment: 13 pages, 6 figures, submitted to MNRA

Evidence of Environmental Quenching at Redshift z ~ 2

We report evidence of environmental quenching among galaxies at redshift ~ 2, namely the probability that a galaxy quenches its star formation activity is enhanced in the regions of space in proximity of other quenched, more massive galaxies. The effect is observed as strong clustering of quiescent galaxies around quiescent galaxies on angular scales \theta < 20 arcsec, corresponding to a proper(comoving) scale of 168 (502) kpc at z = 2. The effect is observed only for quiescent galaxies around other quiescent galaxies; the probability to find star-forming galaxies around quiescent or around star-forming ones is consistent with the clustering strength of galaxies of the same mass and at the same redshift, as observed in dedicated studies of galaxy clustering. The effect is mass dependent in the sense that the quenching probability is stronger for galaxies of smaller mass ($\rm{M_*<10^{10} Msun}$) than for more massive ones, i.e. it follows the opposite trend with mass relative to gravitational galaxy clustering. The spatial scale where the effect is observed suggests these environments are massive halos, in which case the observed effect would likely be satellite quenching. The effect is also redshift dependent in that the clustering strength of quiescent galaxies around other quiescent galaxies at z = 1.6 is ~ 1.7 times larger than that of the galaxies with the same stellar mass at z = 2.6. This redshift dependence allows for a crude estimate of the time scale of environmental quenching of low-mass galaxies, which is in the range 1.5 - 4 Gyr, in broad agreement with other estimates and with our ideas on satellite quenching.Comment: 12 pages, 9 figures, Accepted for publication in Ap

Kpc-scale Properties of Emission-line Galaxies

We perform a detailed study of the resolved properties of emission-line galaxies at kpc-scale to investigate how small-scale and global properties of galaxies are related. 119 galaxies with high-resolution Keck/DEIMOS spectra are selected to cover a wide range in morphologies over the redshift range 0.2<z<1.3. Using the HST/ACS and HST/WFC3 imaging data taken as a part of the CANDELS project, for each galaxy we perform SED fitting per resolution element, producing resolved rest-frame U-V color, stellar mass, star formation rate, age and extinction maps. We develop a technique to identify blue and red "regions" within individual galaxies, using their rest-frame color maps. As expected, for any given galaxy, the red regions are found to have higher stellar mass surface densities and older ages compared to the blue regions. Furthermore, we quantify the spatial distribution of red and blue regions with respect to both redshift and stellar mass, finding that the stronger concentration of red regions toward the centers of galaxies is not a significant function of either redshift or stellar mass. We find that the "main sequence" of star forming galaxies exists among both red and blue regions inside galaxies, with the median of blue regions forming a tighter relation with a slope of 1.1+/-0.1 and a scatter of ~0.2 dex compared to red regions with a slope of 1.3+/-0.1 and a scatter of ~0.6 dex. The blue regions show higher specific Star Formation Rates (sSFR) than their red counterparts with the sSFR decreasing since z~1, driver primarily by the stellar mass surface densities rather than the SFRs at a giver resolution element.Comment: 17 pages, 17 figures, Submitted to the Ap