18599222
Morphology of Luminous Infrared Galaxies in the Local Universe
We study the morphology, stellar mass and star formation rate of 159 local luminous infrared galaxies (LIRGs) using multi-color images from Data Release 2 (DR2) of the Sloan Digital Sky Survey (SDSS). The LIRGs are selected from a cross-correlation analysis between the IRAS survey and SDSS. They are all brighter than 15.9 mag in the r-band and below redshift ∼ 0.1, and can be reliably classified morphologically. The fractions of interacting/merging and normal disk galaxies are 48% and 40% respectively. The normal disk galaxies tend to have lower infrared luminosity than interacting/merging galaxies and hence become an increasingly important population at lower infrared luminosity. Our results complement and confirm the morphology evolution trend of LIRGs found by Melbourne, Koo & Le Floc’h (2005) from z ∼ 1 to z ∼ 0.1. We also find that about 75% of disk galaxies in the local LIRGs are barred, indicating that bars play an important role in triggering star formation rates & 20M⊙ yr −1 in the local universe. Subject headings: galaxies : formation infrared: galaxies galaxies: interactions galaxies: starburst galaxies spiral
119192167
GALAXY DISKS DO NOT NEED TO SURVIVE IN THE ΛCDM PARADIGM: THE GALAXY MERGER RATE OUT TO z ∼ 1.5 FROM MORPHO-KINEMATIC DATA
About two-thirds of present-day, large galaxies are spirals such as the Milky Way or Andromeda, but the way their thin rotating disks formed remains uncertain. Observations have revealed that half of their progenitors, six billion years ago, had peculiar morphologies and/or kinematics, which exclude them from the Hubble sequence. Major mergers, i.e., fusions between galaxies of similar mass, are found to be the likeliest driver for such strong peculiarities. However, thin disks are fragile and easily destroyed by such violent collisions, which creates a critical tension between the observed fraction of thin disks and their survival within the ΛCDM paradigm. Here, we show that the observed high occurrence of mergers among their progenitors is only apparent and is resolved when using morpho-kinematic observations that are sensitive to all the phases of the merging process. This provides an original way of narrowing down observational estimates of the galaxy merger rate and leads to a perfect match with predictions by state-of-the-art ΛCDM semi-empirical models with no particular fine-tuning needed. These results imply that half of local thin disks do not survive but are actually rebuilt after a gas-rich major merger occurring in the past nine billion years, i.e., two-thirds of the lifetime of the universe. This emphasizes the need to study how thin disks can form in halos with a more active merger history than previously considered and to investigate what is the origin of the gas reservoir from which local disks would reform.
54784839
The Milky Way and other spiral galaxies
Cosmologists have often considered the Milky Way as a typical spiral galaxy, and its properties have considerably influenced the current scheme of galaxy formation. Here we compare the general properties of the Milky Way disk and halo with those of galaxies selected from the SDSS. Assuming the recent measurements of its circular velocity results in the Milky Way being offset by ∼2 from the fundamental scaling relations. On the basis of their location in the (MK, Rd, Vflat) volume, the fraction of SDSS spirals like the MilkyWay is only 1.2% in sharp contrast with M31, which appears to be quite typical. Comparison of the Milky Way with M31 and with other spirals is also discussed to investigate whether or not there is a fundamental discrepancy between their mass assembly histories. Possibly the Milky Way is one of the very few local galaxies that could be a direct descendant of very distant, z = 2-3 galaxies, thanks to its quiescent history since thick disk formation.
124565590
High-spin states in near-spherical Y-88
16103411
Partially obscured quasars in the Sloan Digital Sky Survey Early Data Release
We have compiled a sample of 21 low redshift (z . 0.3), luminous active galactic nuclei (AGN) with large Balmer decrements (Hα/Hβ > 7) using the galaxy and QSO catalogs of the Sloan Digital Sky Survey Early Data Release. Using this sample we attempt to determine the fraction of quasars with large internal absorption. We find that these AGN have Strong [O III] λ5007 and broad Hα emission, and that starlight dominates the spectra in the blue band, suggesting that these objects are heavily reddened. Their narrow emission line ratios are similar to those of Seyfert 2 galaxies, yet the average [O III] λ5007 emission is ∼10 times more luminous. Applying the empirical relation between the optical continuum and the Balmer line luminosity for blue quasars, we find that the intrinsic luminosities of these 21 objects are in the range for quasars. We propose that they are obscured, intermediate type quasars analogous to type 1.8 and 1.9 Seyfert galaxies. The ratio of these optically selected, intermediate type quasars to type 1 quasars are found to be around 1, similar to that for local Seyfert galaxies. Preliminary study indicates that most of these quasars are hosted in early type galaxies. Subject headings: galaxies: active — quasars: general — galaxies: nuclei
122668197
Search for Dijet Resonances in 7 TeV pp Collisions at CMS
A search for narrow resonances in the dijet mass spectrum is performed using data corresponding to an integrated luminosity of 2.9 inverse pb collected by the CMS experiment at the LHC. Upper limits at the 95% confidence level (CL) are presented on the product of the resonance cross section, branching fraction into dijets, and acceptance, separately for decays into quark-quark, quark-gluon, or gluon-gluon pairs. The data exclude new particles predicted in the following models at the 95% CL: string resonances, with mass less than 2.50 TeV, excited quarks, with mass less than 1.58 TeV, and axigluons, colorons, and E_6 diquarks, in specific mass intervals. This extends previously published limits on these models.
54687140
Bosonic anomalies, induced fractional quantum numbers, and degenerate zero modes: The anomalous edge physics of symmetry-protected topological states
The boundary of symmetry-protected topological states (SPTs) can harbor new quantum anomaly phenomena. In this work, we characterize the bosonic anomalies introduced by the 1+1D non-onsite-symmetric gapless edge modes of 2+1D bulk bosonic SPTs with a generic finite Abelian group symmetry (isomorphic to $G=\prod_i Z_{N_i}=Z_{N_1} \times Z_{N_2} \times Z_{N_3} \times ...$). We demonstrate that some classes of SPTs (termed "Type II") trap fractional quantum numbers (such as fractional $Z_N$ charges) at the 0D kink of the symmetry-breaking domain walls; while some classes of SPTs (termed "Type III") have degenerate zero energy modes (carrying the projective representation protected by the unbroken part of the symmetry), either near the 0D kink of a symmetry-breaking domain wall, or on a symmetry-preserving 1D system dimensionally reduced from a thin 2D tube with a monodromy defect 1D line embedded. More generally, the energy spectrum and conformal dimensions of gapless edge modes under an external gauge flux insertion (or twisted by a branch cut, i.e., a monodromy defect line) through the 1D ring can distinguish many SPT classes. We provide a manifest correspondence from the physical phenomena, the induced fractional quantum number and the zero energy mode degeneracy, to the mathematical concept of cocycles that appears in the group cohomology classification of SPTs, thus achieving a concrete physical materialization of the cocycles. The aforementioned edge properties are formulated in terms of a long wavelength continuum field theory involving scalar chiral bosons, as well as in terms of Matrix Product Operators and discrete quantum lattice models. Our lattice approach yields a regularization with anomalous non-onsite symmetry for the field theory description. We also formulate some bosonic anomalies in terms of the Goldstone-Wilczek formula.
118498886
Dense molecular gas in nearby gas-rich active galaxies
We present 3-mm observations obtained with the Institut de Radioastronomie Millimetrique (IRAM) 30-m telescope for 10 nearby gas-rich active galaxies spanning three orders of magnitude in infrared luminosity. Emission lines of HCO+(1–0), HCN(1–0) and C2H(1–0) were simultaneously detected in most galaxies of our sample. We also tentatively detected the rare isotopic species H13CN, HC15N and H13CO+ in up to four galaxies (IC 694, NGC 3690, NGC 4258 and NGC 6240). Our estimation shows that the optical depth of HCN is low to moderate in these galaxies (τ∼ 1–5). After comparing the intensity ratios of different molecular emission lines (HCN/HCO+, C2H/HCN and C2H/HCO+) with the infrared luminosity (LIR), we find that in the infrared luminous sample of five composite (AGN+starburst) galaxies these ratios vary with LIR: the HCN/HCO+ ratio increases with LIR, which is consistent with previous studies, while there is a slight trend in the composite galaxies that both C2H/HCN and C2H/HCO+ ratios decrease with increasing LIR. Although our sample is limited, this trend may possibly imply a relation between the overall gas density and the infrared luminosity of galaxies.
123717372
Search for quark compositeness in dijet angular distributions from pp collisions at $ \sqrt {s} = 7{ } $ TeV
A bstractA search for quark compositeness using dijet angular distributions from pp collisions at $ \sqrt {s} = 7 $ TeV is presented. The search has been carried out using a data sample corresponding to an integrated luminosity of 2.2 fb−1, recorded by the CMS experiment at the LHC. Normalized dijet angular distributions have been measured for dijet invariant masses from 0.4 TeV to above 3 TeV and compared with a variety of contact interaction models, including those which take into account the effects of next-to-leading-order QCD corrections. The data are found to be in agreement with the predictions of perturbative QCD, and lower limits are obtained on the contact interaction scale, ranging from 7.5 up to 14.5 TeV at 95 % confidence level.