Emission from the Ionized Gaseous Halos of Low Redshift Galaxies and Their Neighbors

Using a sample of nearly half a million galaxies, intersected by over 8 million lines of sight from the Sloan Digital Sky Survey Data Release 12, we extend our previous study of the recombination radiation emitted by the gaseous halos of nearby galaxies. We identify an inflection in the radial profile of the H$\alpha$+N[{\small II}] radial emission profile at a projected radius of $\sim 50$ kpc and suggest that beyond this radius the emission from ionized gas in spatially correlated halos dominates the profile. We confirm that this is a viable hypothesis using results from a highly simplified theoretical treatment in which the dark matter halo distribution from cosmological simulations is straightforwardly populated with gas. Whether we fit the fraction of halo gas in a cooler (T $= 12,000$ K), smooth ($c = 1$) component (0.26 for galaxies with M$_* = 10^{10.88}$ M$_\odot$ and 0.34 for those with M$_* = 10^{10.18}$ M$_\odot$) or take independent values of this fraction from published hydrodynamical simulations (0.19 and 0.38, respectively), this model successfully reproduces the radial location and amplitude of the observed inflection. We also observe that the physical nature of the gaseous halo connects to primary galaxy morphology beyond any relationship to the galaxy's stellar mass and star formation rate. We explore whether the model reproduces behavior related to the central galaxy's stellar mass, star formation rate, and morphology. We find that it is unsuccessful in reproducing the observations at this level of detail and discuss various shortcomings of our simple model that may be responsible.Comment: 10 pages, 8 figures, accepted by Ap

Emission line ratios for the Circumgalactic Medium and the "Bimodal" Nature of Galaxies

We find significantly different diagnostic emission line ratios for the circumgalactic gas associated with galaxies of stellar masses above and below $10^{10.4}$ M$_\odot$ using SDSS spectroscopy. Specifically, in a sample of 17,393 galaxies, intersected by 18,535 lines of sight at projected radii between 10 and 50 kpc, we stack measured fluxes for nebular strong emission lines, [O {\small III}] $\lambda$5007, H$\alpha$ and [N {\small II}] $\lambda6583$, and find that the gas surrounding the lower mass galaxies exhibits similar line ratios to those of gas ionized by star formation and that surrounding the higher mass galaxies similar to those of gas ionized by AGN or shocks. This finding highlights yet another characteristic of galaxies that is distinctly different above and below this stellar mass threshold, but one that is more closely connected to the gas accretion behavior hypothesized to be responsible for this dichotomy.Comment: 5 pages, 3 figures, accepted by ApJ

The Anisotropic Circumgalactic Medium of Massive Early-Type Galaxies

Using measurements of the [O III], H$\alpha$ and [N II] emission line fluxes originating in the cool (T $\sim10^4$ K) gas that populates the halos of massive early-type galaxies with stellar mass greater than $10^{10.4}$ M$_\odot$, we explore the recent conjecture that active galactic nucleus (AGN) activity preferentially removes the circumgalactic medium (CGM) along the polar (minor-axis) direction. We find deficits in the mean emission line flux of [O III] and H$\alpha$ (65 and 43%, respectively) along the polar vs. planar directions, although due to the large uncertainties in these difficult measurements the results are of marginal statistical significance (1.5$\sigma$). More robustly (97 to 99.9% confidence depending on the statistical test), diagnostic line ratios show stronger AGN ionization signatures along the polar direction at small radii than at other angles or radii. Our results are consistent with the conjecture of an anisotropic CGM in massive, early type galaxies, suggested on independent grounds, that is tied to AGN activity and begin to show the potential of CGM mapping using emission lines.Comment: 7 pages, accepted for publication in Ap

Complex decay chains of top and bottom squarks

Current searches for the top squark mostly focus on the decay channels of $\tilde{t}_1 \rightarrow t \chi_1^0$ or $\tilde{t}_1 \rightarrow b \chi_1^\pm \rightarrow bW \chi_1^0$, leading to $tt/bbWW+\not\mathrel{E}_T$ final states for top squark pair production at the LHC. In supersymmetric scenarios with light gauginos other than the neutralino lightest supersymmetric particle (LSP), different decay modes of the top squark could be dominant, which significantly weaken the current top squark search limits at the LHC. Additionally, new decay modes offer alternative discovery channels for top squark searches. In this paper, we study the top squark and bottom squark decay in the Bino-like LSP case with light Wino or Higgsino next-to-LSPs (NLSPs), and identify cases in which additional decay modes become dominant. We also perform a collider analysis for top squark pair production with mixed top squark decay final states of $\tilde{t}_1 \to t {\chi}_2^0 \to th {\chi}_1^0$, $\tilde{t}_1 \to b {\chi}_1^\pm \to bW {\chi}_1^0$, leading to the $bbbbjj\ell+\not\mathrel{E}_T$ collider signature. The branching fraction for such decay varies between 25\% and 50\% for a top squark mass larger than 500 GeV with $M_2=M_1+150$ GeV. At the 14 TeV LHC with 300 ${\rm fb}^{-1}$ integrated luminosity, the top squark can be excluded up to about 1040 GeV at the 95\% C.L., or be discovered up to 940 GeV at 5$\sigma$ significance.Comment: 28 pages, 13 figure

Hydrogen Emission from the Ionized Gaseous Halos of Low Redshift Galaxies

Using a sample of nearly half million galaxies, intersected by over 7 million lines of sight from the Sloan Digital Sky Survey Data Release 12, we trace H$\alpha$ + [N{\small II}] emission from a galactocentric projected radius, $r_p$, of 5 kpc to more than 100 kpc. The emission flux surface brightness is $\propto r_p^{-1.9 \pm 0.4}$. We obtain consistent results using only the H$\alpha$ or [N{\small II}] flux. We measure a stronger signal for the bluer half of the target sample than for the redder half on small scales, $r_p <$ 20 kpc. We obtain a $3\sigma$ detection of H$\alpha$ + [N{\small II}] emission in the 50 to 100 kpc $r_p$ bin. The mean emission flux within this bin is $(1.10 \pm 0.35) \times 10^{-20}$ erg cm$^{-2}$ s$^{-1}$ \AA$^{-1}$, which corresponds to $1.87 \times 10^{-20}$ erg cm$^{-2}$ s$^{-1}$ arcsec$^{-2}$ or 0.0033 Rayleigh. This detection is 34 times fainter than a previous strict limit obtained using deep narrow-band imaging. The faintness of the signal demonstrates why it has been so difficult to trace recombination radiation out to large radii around galaxies. This signal, combined with published estimates of n$_{\rm H}$, lead us to estimate the temperature of the gas to be 12,000 K, consistent with independent empirical estimates based on metal ion absorption lines and expectations from numerical simulations.Comment: 12 pages, 13 figure

On the Effect of Environment on Line Emission from the Circumgalactic Medium

We measure differences in the emission-line flux from the circumgalactic medium (CGM) of galaxies in different environments. Such differences could be a critical clue in explaining a range of galaxy properties that depend on environment. Using large samples of stacked archival spectra from the Sloan Digital Sky Survey, we find that the H alpha + [N II] emission-line flux from the CGM within 50 kpc of similar to L* galaxies is lower both for galaxies that lie within a projected distance of similar to 500 kpc from a massive (M-* > 10(11) M-circle dot) galaxy and for galaxies in richer/denser environments. The environmental differences are statistically significant even after we control for galaxy mass and morphology. We interpret these observations as a direct signature of environmentally caused strangulation. We present a simple, heuristic model for the effect of a massive parent galaxy. In this model, the CGM cool gas fraction within 50 kpc is significantly decreased for galaxies that lie within 700 kpc of a massive galaxy, with about 80% of the cool gas removed even when the galaxy is at a distance of 500 kpc from its massive parent. However, we discuss alternative physical causes for the observed behavior and discuss ways forward in addressing open questions.NSF [AST-171384]; Sloan Foundation Fellowship; Alfred P. Sloan Foundation; National Science Foundation; U.S. Department of Energy Office of Science; University of Arizona; Brazilian Participation Group; Brookhaven National Laboratory; Carnegie Mellon University, University of Florida; French Participation Group; German Participation Group; Harvard University; Instituto de Astrofisica de Canarias; Michigan State/Notre Dame/JINA Participation Group; Johns Hopkins University; Lawrence Berkeley National Laboratory; Max Planck Institute for Astrophysics; Max Planck Institute for Extraterrestrial Physics, New Mexico State University, New York University; Pennsylvania State University, University of Portsmouth; Princeton University; Spanish Participation Group, University of Tokyo, University of Utah; Yale UniversityThis item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at [email protected]