Star formation in cooling flow galaxies

Spectroscopic observations of central dominant galaxies are reviewed. Through the analysis of absorption spectral features (mainly the strength of the Mg triplet at 5175 A and the break in 4000 A), both in the galaxy centers and along the radii, we will be able to impose limits on the ongoing star formation as the ultimate fate for the large amounts of accreted gas. With the same aim we will carry out a dynamical study based on velocity dispersion measurements

The Fundamental Properties of Dwarf Elliptical Galaxies in Clusters

We present preliminary results of an extensive study of the fundamental properties of dwarf elliptical galaxies (dEs) in the Coma cluster. Our study will combine HST surface photometry with ground-based UBRIJK photometry and optical spectroscopy. The combined data set will be used to investigate the intrinsic correlations among global parameters in cluster dEs, including the Fundamental Plane, the color-magnitude relation, the Faber-Jackson and Kormendy relation, and velocity dispersion versus line strength indices. These empirical correlations have provided important constraints to theoretical models of galaxy formation and evolution for "normal" elliptical galaxies. Although dEs are the most abundant galaxy population in clusters their properties remain, however, largely unknown. Our study aims to provide an essential reference for testing current theories on the formation and evolution of dEs in clusters, and understanding their relation to more massive elliptical galaxies.Comment: 10 pages. To appear in "Star Formation through Time", 2003, ASP Conf. Ser. ed. Perez, Gonzalez Delgado, Tenorio-Tagl

Empirical calibration of the \lambda 4000 \AA break

Empirical fitting functions, describing the behaviour of the \lambda 4000 \AA break, D_4000, in terms of effective temperature, metallicity and surface gravity, are presented. For this purpose, the break has been measured in 392 stars from the Lick/IDS Library. We have followed a very detailed error treatment in the reduction and fitting procedures, allowing for a reliable estimation of the break uncertainties. This calibration can be easily incorporated into stellar population models to provide accurate predictions of the break amplitude for, relatively old, composite systems.Comment: 21 pages including 7 postscript figures. Accepted for publication in Astronomy in Astrophysics Supplement Series. Table 1 will be also available at CD

Velocity Dispersions and Stellar Populations of the Most Compact and Msssive early-Type Galaxies at Redshift similar to 1

We present Gran-Telescopio-Canarias/OSIRIS optical spectra of four of the most compact and massive early-type galaxies (ETGs) in the Groth Strip Survey at redshift z similar to 1, with effective radii R-e = 0.5-2.4 kpc and photometric stellarmasses M-star = (1.2-4) x 10(11)M(circle dot). We find that these galaxies have velocity dispersions sigma = 156-236 km s(-1). The spectra are well fitted by single stellar population models with approximately 1 Gyr of age and solar metallicity. We find that (1) the dynamical masses of these galaxies are systematically smaller by a factor of similar to 6 than the published stellarmasses using BRIJK photometry, and (2) when estimating stellarmasses as 0.7xM(dyn), a combination of passive luminosity fading with mass/size growth due to minor mergers can plausibly evolve our objects to match the properties of the local population of ETGs

SHARDS: A global view of the star formation activity at z~0.84 and z~1.23

In this paper, we present a comprehensive analysis of star-forming galaxies (SFGs) at intermediate redshifts (z~1). We combine the ultra-deep optical spectro-photometric data from the Survey for High-z Absorption Red and Dead Sources (SHARDS) with deep UV-to-FIR observations in the GOODS-N field. Exploiting two of the 25 SHARDS medium-band filters, F687W17 and F823W17, we select [OII] emission line galaxies at z~0.84 and z~1.23 and characterize their physical properties. Their rest-frame equivalent widths (EW$_{\mathrm{rf}}$([OII])), line fluxes, luminosities, star formation rates (SFRs) and dust attenuation properties are investigated. The evolution of the EW$_{\mathrm{rf}}$([OII]) closely follows the SFR density evolution of the universe, with a trend of EW$_{\mathrm{rf}}$([OII])$\propto$(1+z)$^3$ up to redshift z~1, followed by a possible flattening. The SF properties of the galaxies selected on the basis of their [OII] emission are compared with complementary samples of SFGs selected by their MIR and FIR emission, and also with a general mass-selected sample of galaxies at the same redshifts. We demonstrate observationally that the UVJ diagram (or, similarly, a cut in the specific SFR) is only partially able to distinguish the quiescent galaxies from the SFGs. The SFR-M$_*$ relation is investigated for the different samples, yelding a logarithmic slope ~1, in good agreement with previous results. The dust attenuations derived from different SFR indicators (UV(1600), UV(2800), [OII], IR) are compared and show clear trends with respect to both the stellar mass and total SFR, with more massive and highly star-forming galaxies being affected by stronger dust attenuation.Comment: Replaced to match the accepted version (24 pages, 1 table, 17 figures). Published in ApJ, 812, 155 (2015): http://stacks.iop.org/0004-637X/812/15

Once in a blue stream: Detection of recent star formation in the NGC 7241 stellar stream with MEGARA

In this work we study the striking case of a narrow blue stream around the NGC 7241 galaxy and its foreground dwarf companion. We want to figure out if the stream was generated by tidal interaction with NGC 7241 or it first interacted with the foreground dwarf companion and later both fell together towards NGC 7241. We use four sets of observations, including a follow-up spectroscopic study with the MEGARA instrument at the 10.4-m Gran Telescopio Canarias. Our data suggest that the compact object we detected in the stream is a foreground Milky Way halo star. Near this compact object we detect emission lines overlapping a bluer and fainter blob of the stream that is clearly visible in both ultra-violet and optical deep images. From its heliocentric systemic radial velocity (Vsyst= 1548.58+/-1.80 km s^-1) and new UV and optical broad-band photometry, we conclude that this over-density could be the actual core of the stream, with an absolute magnitude of M_g ~ -10 and a (g-r) = 0.08 +/- 0.11, consistent with a remnant of a low-mass dwarf satellite undergoing a current episode of star formation. From the width of the stream and assuming a circular orbit, we calculate that the progenitor mass can be the typical of a dwarf galaxy, but it could also be substantially lower if the stream is on a very radial orbit or it was created by tidal interaction with the companion dwarf instead of with NGC 7241. Finally, we find that blue stellar streams containing star formation regions are commonly predicted by high-resolution cosmological simulations of galaxies lighter than the Milky Way. This scenario is consistent with the processes explaining the bursty star formation history of some dwarf satellites, which are followed by a gas depletion and a fast quenching once they enter within the virial radius of their host galaxies for the first time.Comment: 12 pages, 5 figures, accepted for publication in Astronomy & Astrophysic

Hunt for new phenomena using large jet multiplicities and missing transverse momentum with ATLAS in 4.7 fb−1 of s√=7TeV proton-proton collisions

Results are presented of a search for new particles decaying to large numbers of jets in association with missing transverse momentum, using 4.7 fb−1 of pp collision data at s√=7TeV collected by the ATLAS experiment at the Large Hadron Collider in 2011. The event selection requires missing transverse momentum, no isolated electrons or muons, and from ≥6 to ≥9 jets. No evidence is found for physics beyond the Standard Model. The results are interpreted in the context of a MSUGRA/CMSSM supersymmetric model, where, for large universal scalar mass m 0, gluino masses smaller than 840 GeV are excluded at the 95% confidence level, extending previously published limits. Within a simplified model containing only a gluino octet and a neutralino, gluino masses smaller than 870 GeV are similarly excluded for neutralino masses below 100 GeV

Observation of a new chi_b state in radiative transitions to Upsilon(1S) and Upsilon(2S) at ATLAS

The chi_b(nP) quarkonium states are produced in proton-proton collisions at the Large Hadron Collider (LHC) at sqrt(s) = 7 TeV and recorded by the ATLAS detector. Using a data sample corresponding to an integrated luminosity of 4.4 fb^-1, these states are reconstructed through their radiative decays to Upsilon(1S,2S) with Upsilon->mu+mu-. In addition to the mass peaks corresponding to the decay modes chi_b(1P,2P)->Upsilon(1S)gamma, a new structure centered at a mass of 10.530+/-0.005 (stat.)+/-0.009 (syst.) GeV is also observed, in both the Upsilon(1S)gamma and Upsilon(2S)gamma decay modes. This is interpreted as the chi_b(3P) system.Comment: 5 pages plus author list (18 pages total), 2 figures, 1 table, corrected author list, matches final version in Physical Review Letter

Search for displaced vertices arising from decays of new heavy particles in 7 TeV pp collisions at ATLAS

We present the results of a search for new, heavy particles that decay at a significant distance from their production point into a final state containing charged hadrons in association with a high-momentum muon. The search is conducted in a pp-collision data sample with a center-of-mass energy of 7 TeV and an integrated luminosity of 33 pb^-1 collected in 2010 by the ATLAS detector operating at the Large Hadron Collider. Production of such particles is expected in various scenarios of physics beyond the standard model. We observe no signal and place limits on the production cross-section of supersymmetric particles in an R-parity-violating scenario as a function of the neutralino lifetime. Limits are presented for different squark and neutralino masses, enabling extension of the limits to a variety of other models.Comment: 8 pages plus author list (20 pages total), 8 figures, 1 table, final version to appear in Physics Letters

Measurements of Higgs boson production and couplings in diboson final states with the ATLAS detector at the LHC

Measurements are presented of production properties and couplings of the recently discovered Higgs boson using the decays into boson pairs, H →γ γ, H → Z Z∗ →4l and H →W W∗ →lνlν. The results are based on the complete pp collision data sample recorded by the ATLAS experiment at the CERN Large Hadron Collider at centre-of-mass energies of √s = 7 TeV and √s = 8 TeV, corresponding to an integrated luminosity of about 25 fb−1. Evidence for Higgs boson production through vector-boson fusion is reported. Results of combined fits probing Higgs boson couplings to fermions and bosons, as well as anomalous contributions to loop-induced production and decay modes, are presented. All measurements are consistent with expectations for the Standard Model Higgs boson