We study the synchrotron component of the spectral energy distribution on the sample of 877 blazars using ASDC SED Builder Tool with available broadband data from the literature. Our sample includes 423 flat-spectrum radio sources (FSRQs), 361 BL Lac objects and candidates, and 93 blazars of uncertain type. We have made an estimation of the synchrotron peak frequency for the 875 objects and further classified them as high, intermediate and low synchrotron peaked sources (HSPs/ISPs/LSPs). For each source NVSS name (RA (HHMMSS) and DEC (DDMMSS) for the J2000.0 epoch), alias, redshift, R band magnitude, synchrotron peak frequency, correlation coefficient, flux density at 4.8GHz, SED class, blazar type and selection method are presented.
The chemical enrichment in the interstellar medium (ISM) of galaxies is regulated by several physical processes: star birth and death, grain formation and destruction, and galactic inflows and outflows. Understanding such processes and their relative importance is essential to following galaxy evolution and the chemical enrichment through the cosmic epochs, and to interpreting current and future observations. Despite the importance of such topics, the contribution of different stellar sources to the chemical enrichment of galaxies, for example massive stars exploding as Type II supernovae (SNe) and low-mass stars, as well as the mechanisms driving the evolution of dust grains, such as for example grain growth in the ISM and destruction by SN shocks, remain controversial from both observational and theoretical viewpoints. In this work, we revise the current description of metal and dust evolution in the ISM of local low-metallicity dwarf galaxies and develop a new description of Lyman-break galaxies (LBGs) which are considered to be their high-redshift counterparts in terms of star formation, stellar mass, and metallicity. Our goal is to reproduce the observed properties of such galaxies, in particular (i) the peak in dust mass over total stellar mass (sMdust) observed within a few hundred million years; and (ii) the decrease in sMdust at a later time. We fitted spectral energy distribution (SED) of dwarf galaxies and LBGs with the 'Code Investigating GALaxies Emission' (CIGALE), through which the total stellar mass, dust mass, and star formation rate are estimated. For some of the dwarf galaxies considered, the metal and gas content are available from the literature. We computed different prescriptions for metal and dust evolution in these systems (e.g. different initial mass functions for stars, dust condensation fractions, SN destruction, dust accretion in the ISM, and inflow and outflow efficiency), and we fitted the properties of the observed galaxies through the predictions of the models. Only some combinations of models are able to reproduce the observed trend and simultaneously fit the observed properties of the galaxies considered. In particular, we show that (i) a top-heavy initial mass function that favours the formation of massive stars and a dust condensation fraction for Type II SNe of around 50% or more help to reproduce the peak of sMdust observed after ~100Myr from the beginning of the baryon cycle for both dwarf galaxies and LBGs; (ii) galactic outflows play a crucial role in reproducing the observed decline in sMdust with age and are more efficient than grain destruction from Type II SNe both in local galaxies and at high-redshift; (iii) a star formation efficiency (mass of gas converted into stars) of a few percent is required to explain the observed metallicity of local dwarf galaxies; and (iv) dust growth in the ISM is not necessary in order to reproduce the values of sMdust derived for the galaxies under study, and, if present, the effect of this process would be erased by galactic outflows.
This paper reports the results of a modest redshift survey carried out, at generally low Galactic latitudes, in the vicinity of the South Celestial Pole. Target galaxies were selected as a 'representative' sample of underlying large-scale structures. Dimensions, approximate magnitudes and radial velocity measurements, are reported for 335 galaxies.
We explore the evolution of field early-type galaxies in a sample extracted from the ACS images of the southern GOODS field. The galaxies are selected by means of a nonparametric analysis, followed by visual inspection of the candidates with a concentrated surface brightness distribution. We furthermore exclude from the final sample those galaxies that are not consistent with an evolution into the Kormendy relation between surface brightness and size that is observed for z=0 ellipticals. The final set, which comprises 249 galaxies with a median redshift z_m_=0.71, represents a sample of early-type systems not selected with respect to color, with similar scaling relations as those of bona fide elliptical galaxies.
The results of a comprehensive analysis of continuous radio spectra of a sample of Gigahertz-Peaked Spectrum (GPS) sources are reported. The sources are selected from a flux-density-complete sample (S more or equal 200mJy at 4.8 or 5GHz) using multifrequency measurements of the RATAN-600 radio telescope and data from the CATS astrophysical catalogs support system. The analysis revealed a very small number (1-2%) of "classical" GPS objects, which is significantly less than the expected fraction of 10%. GPS galaxies are found to have narrower and steeper radio spectra than quasars. The low-frequency part of the spectrum is seen to become steeper with increasing redshift. Galaxies and quasars at the same z have comparable angular sizes, whereas their luminosities may differ by one order of magnitude. At large redshifts there is a deficit of objects with low (several GHz) peak frequencies. The number of GPS galaxies decreases sharply with redshift, and most of them are found at z between 0.01 and 1.81. GPS quasars are found at large redshifts, from 0.11 to 3.99. A quarter of the sample consists of blazars whose spectra may temporarily have a convex shape when the object is in active state.
Star-forming galaxies with nebular HeII emission contain very energetic ionizing sources of radiation, which can be considered as analogs to the major contributors of the reionization of the Universe in early epochs. It is therefore of great importance to provide a reliable absolute scale for the equivalent effective temperature (T*) for these sources. We study a sample of local (z<0.2) star-forming galaxies showing optical nebular HeII emission using the so-called softness diagrams, involving emission lines of two elements in two consecutive stages of ionization (e.g., [SII]/[SIII] vs. [OII]/[OIII]). We use for the first time the HeI/HeII ratio in these diagrams in order to explore the higher range of T* expected in these objects, and to investigate the role of possible mechanisms driving the distribution of galaxy points in these diagrams. We build grids of photoionization models covering different black-body temperatures, model cluster atmospheres, and density-bounded geometries to explain the conditions observed in the sample. We verified that the use of the softness diagrams including the emission-line ratio HeI/HeII combined with black-body photoionization models can provide an absolute scale of T* for these objects. The application of a Bayesian-like code indicates T* in the range 50-80kK for the sample of galaxies, with a mean value higher than 60kK. The average of these high temperature values can only be reproduced using cluster model populations with nearly metal-free stars, although such ionizing sources cannot explain either the highest T* values, beyond 1{sigma}, or the dispersion observed in the softness diagrams. According to our photoionization models, most sample galaxies could be affected to some extent by ionizing photon leaking, presenting a mean photon absorption fraction of 26% or higher depending on the metallicity assumed for the ionizing cluster. The entire range of HeI/HeII, [SII]/[SIII], and [OII]/[OIII] ratios for these HeII-emitting galaxies is reproduced with our models, combining nearly metal-free ionizing clusters and photon leaking under different density-bounded conditions.
We measure the strength, frequency, and timescale of tidally triggered star formation at redshift z=0.08-0.38 in a spectroscopically complete sample of galaxy pairs drawn from the magnitude-limited redshift survey of 9825 Smithsonian Hectospec Lensing Survey galaxies with R<20.3. To examine the evidence for tidal triggering, we identify a volume-limited sample of major (|{Delta}M_R_|<1.75, corresponding to mass ratio >1/5) pair galaxies with M_R_<-20.8 in the redshift range z=0.08-0.31.
We derive rotation curves, surface brightness profiles, and oxygen abundance distributions for 147 late-type galaxies using the publicly available spectroscopy obtained by the MaNGA survey. Changes of the central oxygen abundance (O/H)_0_, the abundance at the optical radius (O/H)_R25_, and the abundance gradient with rotation velocity V_rot_ were examined for galaxies with rotation velocities from 90km/s to 350km/s. We find that each relation shows a break at V_rot_^*^~200km/s. The central (O/H)_0_ abundance increases with rising V_rot_ and the slope of the (O/H)_0_-V_rot_ relation is steeper for galaxies with V_rot_<=V_rot_^*^. The mean scatter of the central abundances around this relation is 0.053 dex. The relation between the abundance at the optical radius of a galaxy and its rotation velocity is similar; the mean scatter in abundances around this relation is 0.081 dex. The radial abundance gradient expressed in dex/kpc flattens with the increase of the rotation velocity. The slope of the relation is very low for galaxies with V_rot_>=V_rot_^*^. The abundance gradient expressed in dex/R_25_ is roughly constant for galaxies with V_rot_<=V_rot_^*^, flattens towards V_rot_^*^, and then again is roughly constant for galaxies with V_rot_>=V_rot_^*^. The change of the gradient expressed in terms of dex/h_d_ (where h_d_ is the disc scale length), in terms of dex/R_e,d_ (where R_e,d_ is the disc effective radius), and in terms of dex/R_e,g_ (where R_e,g_ is the galaxy effective radius) with rotation velocity is similar to that for gradient in dex/R_25_. The relations between abundance characteristics and other basic parameters (stellar mass, luminosity, and radius) are also considered.
This paper presents optical long-slit spectroscopic observations of 105 barred Markarian IRAS galaxies. These observations are used to determine the spectral type (starburst or Seyfert) of emission-line regions in the nucleus and along the bar of the galaxies, in order to define a homogeneous sample of Starburst Nucleus Galaxies (SBNGs). Our selection criteria (ultraviolet excess, far infrared emission and barred morphology) have been very efficient for selecting star-forming galaxies, since our sample of 221 emission-line regions includes 82% nuclear or extranuclear starbursts. The contamination by Seyferts is low (9%). The remaining galaxies (9%) are objects with ambiguous classification (HII or LINER). The dust content and H{alpha} luminosity increase towards the nuclei of the galaxies. No significant variation of the electron density is found between nuclear and bar HII regions. However, the mean H{alpha} luminosity and electron density in the bar are higher than in typical disk HII regions. We investigate different mechanisms for explaining the excess of nitrogen emission observed in our starburst nuclei. There is no evidence for the presence of a weak hidden active galactic nucleus in our starburst galaxies. The cause of this excess is probably a selective enrichment of nitrogen in the nuclei of the galaxies, following a succession of short and intense bursts of star formation. Our sample of SBNGs, located at a mean redshift of 0.015, has moderate H{alpha} (10^41^erg/s) and far infrared (10^10^L{sun}) luminosities. The types are distributed equally among early- and late-type giant spirals with a slight preference for Sbc/Sc types because of their barred morphology. The majority (62%) of SBNGs are isolated with no sign of gravitational interaction. In terms of distance, luminosity and level of interaction, SBNGs are intermediate between HII galaxies and luminous infrared galaxies.
Using Hubble Space Telescope photometry to measure star formation histories, we age-date the stellar populations surrounding supernova remnants (SNRs) in M31 and M33. We then apply stellar evolution models to the ages to infer the corresponding masses for their supernova progenitor stars. We analyze 33 M33 SNR progenitors and 29 M31 SNR progenitors in this work. We then combine these measurements with 53 previously published M31 SNR progenitor measurements to bring our total number of progenitor mass estimates to 115. To quantify the mass distributions, we fit power laws of the form dN/dM{prop.to}M^-{alpha}^. Our new larger sample of M31 progenitors follows a distribution with {alpha}=4.4_-0.4_^+0.4^, and the M33 sample follows a distribution with {alpha}=3.8_-0.5_^+0.4^. Thus both samples are consistent within the uncertainties, and the full sample across both galaxies gives {alpha}=4.2_-0.3_^+0.3^. Both the individual and full distributions display a paucity of massive stars when compared to a Salpeter initial mass function, which we would expect to observe if all massive stars exploded as SN that leave behind observable SNR. If we instead fix {alpha}=2.35 and treat the maximum mass as a free parameter, we find M_max_~35-45 M_{sun}_, indicative of a potential maximum cutoff mass for SN production. Our results suggest that either SNR surveys are biased against finding objects in the youngest (<10 Myr old) regions, or the highest mass stars do not produce SNe.
