- ID:
- ivo://CDS.VizieR/J/A+A/570/A69
- Title:
- GALEX Ultraviolet Virgo Cluster Survey. IV.
- Short Name:
- J/A+A/570/A69
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the role of the environment on galaxy evolution using a sample of 868 galaxies in the Virgo cluster and in its surrounding regions that are selected from the GALEX Ultraviolet Virgo Cluster Survey (GUViCS) with the purpose of understanding the origin of the red sequence in dense environments. The sample spans a wide range in morphological types (from dwarf ellipticals to Im and BCD) and stellar masses (10^7^<=M_star_<=10^11.5^M_{sun}_). We collected multifrequency data covering the whole electromagnetic spectrum for most of the galaxies, including UV, optical, mid- and far-infrared imaging data, as well as optical and HI spectroscopic data. We first identify the different dynamical substructures that compose the Virgo cluster, and we calculate the local density of galaxies using different methods. We then study the distribution of galaxies belonging to the red sequence, the green valley, and the blue cloud within the different cluster substructures or as a function of galaxy density. Our analysis indicates that all the most massive galaxies M_star_>=10^11^M_{sun}_) are slow rotators and are the dominant galaxies of the different cluster substructures, which are generally associated with a diffuse X-ray emission. They are probably the result of major merging events that occurred at early epochs, as also indicated by their very old stellar populations. Slow rotators of lower stellar mass (10^8.5^<=M_star_<=10^11^M_{sun}_) are also preferentially located within the different high-density substructures of the cluster. Their position in the velocity space indicates that they are virialised within the cluster; thus, they are Virgo members since its formation. They have been shaped by gravitational perturbations occurring within the infalling groups that later form the cluster (pre-processing). On the contrary, low-mass star-forming systems are extremely rare in the inner regions of the Virgo cluster A, where the density of the intergalactic medium is at its maximum. Our ram pressure stripping models consistently indicate that these star-forming systems can be rapidly deprived of their interstellar medium during their interaction with the intergalactic medium. The lack of gas quenches their star-formation activity transforming them into quiescent dwarf ellipticals. This mild transformation does not perturb the kinematic properties of these galaxies, which still have rotation curves typical of star-forming systems.
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- ID:
- ivo://CDS.VizieR/J/ApJ/789/135
- Title:
- Gamma-ray bright blazars spectrophotometry
- Short Name:
- J/ApJ/789/135
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present {gamma}-ray, X-ray, ultraviolet, optical, and near-infrared light curves of 33 {gamma}-ray bright blazars over 4 years that we have been monitoring since 2008 August with multiple optical, ground-based telescopes and the Swift satellite, and augmented by data from the Fermi Gamma-ray Space Telescope and other publicly available data from Swift. The sample consists of 21 flat-spectrum radio quasars (FSRQs) and 12 BL Lac objects (BL Lacs). We identify quiescent and active states of the sources based on their {gamma}-ray behavior. We derive {gamma}-ray, X-ray, and optical spectral indices, {alpha}_{gamma}_, {alpha}_X_, and {alpha}_o_, respectively (F_{nu}_{prop.to}{nu}^{alpha}^), and construct spectral energy distributions during quiescent and active states. We analyze the relationships between different spectral indices, blazar classes, and activity states. We find (1) significantly steeper {gamma}-ray spectra of FSRQs than for BL Lacs during quiescent states, but a flattening of the spectra for FSRQs during active states while the BL Lacs show no significant change; (2) a small difference of {alpha}_X_ within each class between states, with BL Lac X-ray spectra significantly steeper than in FSRQs; (3) a highly peaked distribution of X-ray spectral slopes of FSRQs at ~ -0.60, but a very broad distribution of {alpha}_X_of BL Lacs during active states; (4) flattening of the optical spectra of FSRQs during quiescent states, but no statistically significant change of {alpha}_o_ of BL Lacs between states; and (5) a positive correlation between optical and {gamma}-ray spectral slopes of BL Lacs, with similar values of the slopes. We discuss the findings with respect to the relative prominence of different components of high-energy and optical emission as the flux state changes.
- ID:
- ivo://CDS.VizieR/J/ApJ/813/51
- Title:
- {gamma}-ray to IR study of the blazar CTA 102
- Short Name:
- J/ApJ/813/51
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We perform a multi-wavelength polarimetric study of the quasar CTA 102 during an extraordinarily bright {gamma}-ray outburst detected by the Fermi Large Area Telescope in 2012 September-October when the source reached a flux of F_>100MeV_=5.2+/-0.4x10^-6^photons/cm2/s. At the same time, the source displayed an unprecedented optical and near-infrared (near-IR) outburst. We study the evolution of the parsec-scale jet with ultra-high angular resolution through a sequence of 80 total and polarized intensity Very Long Baseline Array images at 43GHz, covering the observing period from 2007 June to 2014 June. We find that the {gamma}-ray outburst is coincident with flares at all the other frequencies and is related to the passage of a new superluminal knot through the radio core. The powerful {gamma}-ray emission is associated with a change in direction of the jet, which became oriented more closely to our line of sight ({theta}~1.2{deg}) during the ejection of the knot and the {gamma}-ray outburst. During the flare, the optical polarized emission displays intra-day variability and a clear clockwise rotation of electric vector position angles (EVPAs), which we associate with the path followed by the knot as it moves along helical magnetic field lines, although a random walk of the EVPA caused by a turbulent magnetic field cannot be ruled out. We locate the {gamma}-ray outburst a short distance downstream of the radio core, parsecs from the black hole. This suggests that synchrotron self-Compton scattering of NIR to ultraviolet photons is the probable mechanism for the {gamma}-ray production.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A132
- Title:
- GAS II. UV luminosity functions & InfraRed eXcess
- Short Name:
- J/A+A/627/A132
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Dust is a crucial component of the interstellar medium of galaxies. The presence of dust strongly affects the light produced by stars within a galaxy. As these photons are our main information vector to explore the stellar mass assembly and therefore understand a galaxy's evolution, modeling the luminous properties of galaxies and taking into account the impact of the dust is a fundamental challenge for semi-analytical models. We present the complete prescription of dust attenuation implemented in the new semi-analytical model (SAM): G.A.S. . This model is based on a two-phase medium originating from a physically motivated turbulent model of gas structuring (G.A.S. I paper). Dust impact is treated by taking into account three dust components: Polycyclic Aromatic Hydrocarbons, Very Small Grains, and Big Grains. All three components evolve in both a diffuse and a fragmented/dense gas phase. Each phase has its own stars, dust content and geometry. Dust content evolves according to the metallicity of it associated phase. The G.A.S. model is used to predict both the UV and the IR luminosity functions from z=9.0 to z=0.1. Our two-phase ISM prescription catches very well the evolution of UV and IR luminosity functions. We note a small overproduction of the IR luminosity at low redshift (z<0.5). We also focus on the Infrared-Excess (IRX) and explore its dependency with the stellar mass, UV slope, stellar age, metallicity and slope of the attenuation curves. Our model predicts large scatters for relations based on IRX, especially for the IRX- relation. Our analysis reveals that the slope of the attenuation curve is more driven by absolute attenuation in the FUV band than by disk inclination.We confirm that the age of the stellar population and the slope of the attenuation curve can both shift galaxies below the fiducial star-birth relation in the IRX- diagram. Main results presented in this paper (e.g. luminosity functions) and in the two other associated G.A.S. papers are stored and available in the GALAKSIENN library through the ZENODO platform.
- ID:
- ivo://CDS.VizieR/J/ApJ/776/74
- Title:
- GASS VII. Bivariate HI-stellar mass function
- Short Name:
- J/ApJ/776/74
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the bivariate neutral atomic hydrogen (HI)-stellar mass function (HISMF) {phi}(M_HI_, M_{star}_) for massive (logM_*_/M_{sun}_>10) galaxies derived from a sample of 480 local (0.025<z<0.050) galaxies observed in H I at Arecibo as part of the GALEX Arecibo SDSS Survey. We fit six different models to the HISMF and find that a Schechter function that extends down to a 1% HI gas fraction, with an additional fractional contribution below that limit, is the best parameterization of the HISMF. We calculate {Omega}_HI,M_{star}__>10^10^ and find that massive galaxies contribute 41% of the H I density in the local universe. In addition to the binned HISMF, we derive a continuous bivariate fit, which reveals that the Schechter parameters only vary weakly with stellar mass: M_HI_^*^, the characteristic H I mass, scales as M_{star}_^0.39^; {alpha}, the slope of the HISMF at moderate H I masses, scales as M_{star}_^0.07^; and f, the fraction of galaxies with HI gas fraction greater than 1%, scales as M_{star}_^-0.24^. The variation of f with stellar mass should be a strong constraint for numerical simulations. To understand the physical mechanisms that produce the shape of the HISMF, we redefine the parameters of the Schechter function as explicit functions of stellar mass and star formation rate (SFR) to produce a trivariate fit. This analysis reveals strong trends with SFR. While M_HI_^*^ varies weakly with stellar mass and SFR (M_HI_^*^{prop.to}M_{star}_^0.22^, M_HI_^*^{prop.to}SFR^-0.03^), {alpha} is a stronger function of both stellar mass and especially SFR ({alpha}{prop.to}M_{star}_^0.47^, {alpha}{prop.to}SFR^0.95^). The HISMF is a crucial tool that can be used to constrain cosmological galaxy simulations, test observational predictions of the H I content of populations of galaxies, and identify galaxies whose properties deviate from average trends.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A34
- Title:
- GC hot UV-bright stars model spectra
- Short Name:
- J/A+A/627/A34
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have performed a census of the UV-bright population in 78 globular clusters using wide-field UV telescopes. This population includes a variety of phases of post-horizontal branch (HB) evolution, including hot post-asymptotic giant branch (AGB) stars, and post-early AGB stars. There are indications that old stellar systems like globular clusters produce fewer post-(early) AGB stars than currently predicted by evolutionary models, but observations are still scarce. We wish to derive effective temperatures, surface gravities, and helium abundances of the luminous hot UV-bright stars in these clusters to determine their evolutionary status and compare the observed numbers to predictions from evolutionary theory. We obtained FORS2 spectroscopy of 11 of these UV-selected objects (covering a range of -2.3<[Fe/H]<-1.0), which we (re-)analysed together with previously observed data. We used model atmospheres of different metallicities, including super-solar ones. Where possible, we verified our atmospheric parameters using UV spectrophotometry and searched for metal lines in the optical spectra. We calculated evolutionary sequences for four metallicity regimes and used them together with information about the HB morphology of the globular clusters to estimate the expected numbers of post-AGB stars. We find that metal-rich model spectra are required to analyse stars hotter than 40000 K. Seven of the eleven new luminous UV-bright stars are post-AGB or post-early AGB stars, two are evolving away from the HB, one is a foreground white dwarf, and another is a white dwarf merger. Taking into account published information on other hot UV-bright stars in globular clusters, we find that the number of observed hot post-AGB stars generally agrees with the predicted values, although the numbers are still low. Spectroscopy is clearly required to identify the evolutionary status of hot UV-bright stars. For hotter stars, metal-rich model spectra are required to reproduce their optical and UV spectra, which may affect the flux contribution of hot post-AGB stars to the UV spectra of evolved populations. Adding published information on other hot UV-bright stars in globular clusters, we find that the number of observed hot post-AGB stars generally agrees with the predicted values, although the numbers are still low.
- ID:
- ivo://CDS.VizieR/J/MNRAS/445/1745
- Title:
- Giant Gemini GMOS survey. I.
- Short Name:
- J/MNRAS/445/1745
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present spectra of 163 quasars at z_em_>4.4 taken with the Gemini Multi Object Spectrometers, the largest publicly available sample of high-quality (signal-to-noise ratio S/N~20 per 1.85{AA} pixel) low-resolution (full width at half maximum FWHM~320km/s) rest-frame ultraviolet quasar spectra at these redshifts. The sample was selected from SDSS Data Release 7 with the aim to obtain high-S/N follow-up spectra of the intergalactic HI Lyman series and Lyman continuum absorption at high redshift. Each quasar was observed with the GMOS B600 (FWHM~320km/s) and R400 (FWHM~360km/s) gratings to cover the rest-frame wavelength range from ~850 to ~1500{AA}. Here we make the spectra available in reduced form. The accompanying paper presents a detailed description the sample and a measurement of the mean free path to Lyman limit photons in the IGM, based on stacked rest-frame quasar spectra.
- ID:
- ivo://CDS.VizieR/J/ApJ/797/50
- Title:
- Global energetics of solar flares. I.
- Short Name:
- J/ApJ/797/50
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first part of a project on the global energetics of solar flares and coronal mass ejections that includes about 400 M- and X-class flares observed with Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). We calculate the potential (E_p_), the nonpotential (E_np_) or free energies (E_free_=E_np_-E_p_), and the flare-dissipated magnetic energies (E_diss_). We calculate these magnetic parameters using two different NLFFF codes: the COR-NLFFF code uses the line-of-sight magnetic field component B_z_ from HMI to define the potential field, and the two-dimensional (2D) coordinates of automatically detected coronal loops in six coronal wavelengths from AIA to measure the helical twist of coronal loops caused by vertical currents, while the PHOT-NLFFF code extrapolates the photospheric three-dimensional (3D) vector fields. We find agreement between the two codes in the measurement of free energies and dissipated energies within a factor of <~3. The size distributions of magnetic parameters exhibit powerlaw slopes that are approximately consistent with the fractal-diffusive self-organized criticality model. The magnetic parameters exhibit scaling laws for the nonpotential energy, E_np_{propto}E_p_^1.02^, for the free energy, E_free_{propto}E_p_^1.7^ and E_free_{propto}B_{phi}_^1.0^L^1.5^, for the dissipated energy, E_diss_{propto}E_p_^1.6^ and E_diss_{propto}E_free_^0.9^ , and the energy dissipation volume, V{propto}E_diss_^1.2^. The potential energies vary in the range of E_p_=1x10^31^-4x10^33^erg, while the free energy has a ratio of E_free_/E_p_{approx}1%-25%. The Poynting flux amounts to F_flare_{approx}5x10^8^-10^10^erg/cm2/s during flares, which averages to F_AR_{approx}6x10^6^erg/cm2/s during the entire observation period and is comparable with the coronal heating rate requirement in active regions.
- ID:
- ivo://CDS.VizieR/J/ApJ/802/53
- Title:
- Global energetics of solar flares. II.
- Short Name:
- J/ApJ/802/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the second part of a project on the global energetics of solar flares and coronal mass ejections that includes about 400 M- and X-class flares observed with the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) during the first 3.5yr of its mission. In this Paper II we compute the differential emission measure (DEM) distribution functions and associated multithermal energies, using a spatially-synthesized Gaussian DEM forward-fitting method. The multithermal DEM function yields a significantly higher (by an average factor of ~14), but more comprehensive (multi-) thermal energy than an isothermal energy estimate from the same AIA data. We find a statistical energy ratio of E_th_/E_diss_~2-40% between the multithermal energy E_th_ and the magnetically dissipated energy E_diss_, which is an order of magnitude higher than the estimates of Emslie et al. (2012ApJ...759...71E). For the analyzed set of M- and X-class flares we find the following physical parameter ranges: L=10^8.2^-10^9.7^cm for the length scale of the flare areas, T_p_=10^5.7^-10^7.4^K for the DEM peak temperature, T_w_=10^6.8^-10^7.6^K for the emission measure-weighted temperature, n_p_=10^10.3^-10^11.8^/cm3 for the average electron density, EM_p_=10^47.3^-10^50.3^/cm3 for the DEM peak emission measure, and E_th_=10^26.8^-10^32.0^erg for the multithermal energies. The deduced multithermal energies are consistent with the RTV scaling law E_th,RTV_=73x10^-10^T_p_^3^L_p_^2^, which predicts extremal values of E_th,max_~1.5x10^33^erg for the largest flare and E_th,min_~1x10^24^erg for the smallest coronal nanoflare. The size distributions of the spatial parameters exhibit powerlaw tails that are consistent with the predictions of the fractal-diffusive self-organized criticality model combined with the RTV scaling law.
- ID:
- ivo://CDS.VizieR/J/ApJ/831/105
- Title:
- Global energetics of solar flares. IV. CME
- Short Name:
- J/ApJ/831/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This study entails the fourth part of a global flare energetics project, in which the mass m_cme_, kinetic energy E_kin_, and the gravitational potential energy E_grav_ of coronal mass ejections (CMEs) is measured in 399 M and X-class flare events observed during the first 3.5 years of the Solar Dynamics Observatory (SDO) mission, using a new method based on the extreme ultraviolet (EUV) dimming effect. EUV dimming is modeled in terms of a radial adiabatic expansion process, which is fitted to the observed evolution of the total emission measure of the CME source region. The model derives the evolution of the mean electron density, the emission measure, the bulk plasma expansion velocity, the mass, and the energy in the CME source region. The EUV dimming method is truly complementary to the Thomson scattering method in white light, which probes the CME evolution in the heliosphere at r>~2R_{sun}_, while the EUV dimming method tracks the CME launch in the corona. We compare the CME parameters obtained in white light with the LASCO/C2 coronagraph with those obtained from EUV dimming with the Atmospheric Imaging Assembly onboard the SDO for all identical events in both data sets. We investigate correlations between CME parameters, the relative timing with flare parameters, frequency occurrence distributions, and the energy partition between magnetic, thermal, nonthermal, and CME energies. CME energies are found to be systematically lower than the dissipated magnetic energies, which is consistent with a magnetic origin of CMEs.
