- ID:
- ivo://CDS.VizieR/J/ApJ/872/17
- Title:
- HAZMAT. V. UV and X-ray evolution of K stars
- Short Name:
- J/ApJ/872/17
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Knowing the high-energy radiation environment of a star over a planet's formation and evolutionary period is critical in determining if that planet is potentially habitable and if any biosignatures could be detected, as UV radiation can severely change or destroy a planet's atmosphere. Current efforts for finding a potentially habitable planet are focused on M stars, yet K stars may offer more habitable conditions due to decreased stellar activity and more distant and wider habitable zones (HZs). While M star activity evolution has been observed photometrically and spectroscopically, there has been no dedicated investigation of K star UV evolution. We present the first comprehensive study of the near-UV, far-UV, and X-ray evolution of K stars. We used members of young moving groups and clusters ranging in age from 10 to 625Myr combined with field stars and their archived GALEX UV and ROSAT X-ray data to determine how the UV and X-ray radiation evolve. We find that the UV and X-ray flux incident on an HZ planet is 5-50 times lower than that of HZ planets around early-M stars and 50-1000 times lower than those around late-M stars, due to both an intrinsic decrease in K dwarf stellar activity occurring earlier than for M dwarfs and the more distant location of the K dwarf HZ.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/767/15
- Title:
- Hectospec Cluster Survey (HeCS)
- Short Name:
- J/ApJ/767/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The infall regions of galaxy clusters represent the largest gravitationally bound structures in a {Lambda}CDM universe. Measuring cluster mass profiles into the infall regions provides an estimate of the ultimate mass of these halos. We use the caustic technique to measure cluster mass profiles from galaxy redshifts obtained with the Hectospec Cluster Survey (HeCS), an extensive spectroscopic survey of galaxy clusters with MMT/Hectospec. We survey 58 clusters selected by X-ray flux at 0.1<z<0.3. The survey includes 22680 unique MMT/Hectospec redshifts for individual galaxies; 10145 of these galaxies are cluster members. For each cluster, we acquired high signal-to-noise spectra for ~200 cluster members and a comparable number of foreground/background galaxies. The cluster members trace out infall patterns around the clusters. The members define a very narrow red sequence. We demonstrate that the determination of velocity dispersion is insensitive to the inclusion of bluer members (a small fraction of the cluster population). We apply the caustic technique to define membership and estimate the mass profiles to large radii. The ultimate halo mass of clusters (the mass that remains bound in the far future of a {Lambda}CDM universe) is on average (1.99+/-0.11)M_200_, a new observational cosmological test in essential agreement with simulations. Summed profiles binned in M_200_ and in L_X_demonstrate that the predicted Navarro-Frenk-White form of the density profile is a remarkably good representation of the data in agreement with weak lensing results extending to large radius. The concentration of these summed profiles is also consistent with theoretical predictions.
- ID:
- ivo://CDS.VizieR/J/A+A/409/79
- Title:
- HELLAS2XMM survey. IV.
- Short Name:
- J/A+A/409/79
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from the photometric and spectroscopic identification of 122 X-ray sources recently discovered by XMM-Newton in the 2-10keV band (the HELLAS2XMM 1dF sample). Their flux cover the range 8x10^-15^-4x10^-13^erg/cm^2^/s and the total area surveyed is 0.9 square degrees. One of the most interesting results (which is found also in deeper surveys) is that about 20% of the hard X-ray selected sources have an X-ray to optical flux ratio (X/O) ten times or more higher than that of optically selected AGN. Unlike the faint sources found in the ultra-deep Chandra and XMM-Newton surveys, which reach X-ray (and optical) fluxes more than one order of magnitude lower than the HELLAS2XMM survey sources, many of the extreme X/O sources in our sample have R<~25 and are therefore accessible to optical spectroscopy. We report the identification of 13 sources with X/O>~10 (to be compared with 9 sources known from the deeper, pencil-beam surveys). Eight of them are narrow line QSO (seemingly the extension to very high luminosity of the type 2 Seyfert galaxies), four are broad line QSO. The results from our survey are also used to make reliable predictions about the luminosity of the sources not yet spectroscopically identified, both in our sample and in deeper Chandra and XMM-Newton samples. We then use a combined sample of 317 hard X-ray selected sources (HELLAS2XMM 1dF, Chandra Deep Field North 1Msec, Chandra SSA13 and XMM-Newton Lockman Hole flux limited samples), 221 with measured redshifts, to evaluate the cosmological evolution of the hard X-ray source's number and luminosity densities.
- ID:
- ivo://CDS.VizieR/J/A+A/627/A100
- Title:
- HESS and Suzaku observations of Vela X
- Short Name:
- J/A+A/627/A100
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Pulsar Wind Nebulae (PWNe) represent the most prominent population of Galactic very-high-energy gamma-ray sources and are thought to be an efficient source of leptonic cosmic rays. Vela X is a nearby middle-aged PWN, which shows bright X-ray and TeV gamma-ray emission toward an elongated structure called the cocoon. Since TeV emission is likely inverse-Compton emission of electrons, predominantly from interactions with the cosmic microwave background, while X-ray emission is synchrotron radiation of the same electrons, we aim to derive the properties of the relativistic particles and of magnetic fields with minimal modelling. We use data from the Suzaku XIS to derive the spectra from three compact regions in Vela X covering distances from 0.3pc to 4pc from the pulsar along the cocoon. We obtain gamma-ray spectra of the same regions from H.E.S.S. observations and fit a radiative model to the multi-wavelength spectra. The TeV electron spectra and magnetic field strengths are consistent within the uncertainties for the three regions, with energy densities of the order 10^-12^erg/cm^-3^. The data indicate the presence of a cutoff in the electron spectrum at energies of 100TeV and a magnetic field strength of 6G. Constraints on the presence of turbulent magnetic fields are weak. The pressure of TeV electrons and magnetic fields in the cocoon is dynamically negligible, requiring the presence of another dominant pressure component to balance the pulsar wind at the termination shock. Sub-TeV electrons cannot account completely for the missing pressure, that may be provided either by relativistic ions or from mixing of the ejecta with the pulsar wind. The electron spectra are consistent with expectations from transport scenarios dominated either by advection via the reverse shock or by diffusion, but for the latter the role of radiative losses near the termination shock needs to be further investigated in the light of the measured cutoff energies. Constraints on turbulent magnetic fields and the shape of the electron cutoff can be improved by spectral measurements in the energy range >~10keV.
- ID:
- ivo://CDS.VizieR/J/A+A/470/787
- Title:
- High energy peaked BL Lacs optical spectros.
- Short Name:
- J/A+A/470/787
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The multi-frequency sedentary survey is a flux-limited, statistically well-defined sample of highly X-ray dominated (i.e., with a very high X-ray to radio flux ratio) BL Lacertae objects, which includes 150 sources. In this paper, the third of the series, we report the results of a dedicated optical spectroscopy campaign that, together with results from other independent optical follow-up programs, led to the spectroscopic identification of all sources in the sample. We carried out a systematic spectroscopic campaign for the observation of all unidentified objects of the sample using the ESO 3.6m, the KPNO 4m, and the TNG optical telescopes.
- ID:
- ivo://CDS.VizieR/J/A+A/335/467
- Title:
- High galactic latitude RASS X-ray sources
- Short Name:
- J/A+A/335/467
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a summary of spectroscopic identifications for a complete sample of bright soft high galactic latitude X-ray sources drawn from the ROSAT All-Sky Survey which have PSPC count-rates CR>0.5cts/s and hardness ratios HR1<0. Of a total of 397 sources, 270 had catalogued counterparts although most of these were not previously known as X-ray sources; of the remaining 127 sources neither X-ray nor optical properties were previously known. Of the whole sample of very soft X-ray sources 155 were also discovered by the Wide-Field-Camera on board ROSAT. We present spectroscopic identifications of 108 sources and other identifications for further 18 sources; 1 source remains unidentified so far. In practically all cases a unique optical counterpart exists facilitating identification. The largest source classes are AGN, magnetic cataclysmic variables, and hot white dwarfs.
- ID:
- ivo://CDS.VizieR/J/A+A/347/47
- Title:
- High galactic latitude RASS X-ray sources. II.
- Short Name:
- J/A+A/347/47
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a summary of spectroscopic identifications of bright soft high galactic latitude X-ray sources from the ROSAT All-Sky Survey with total PSPC count rates 0.11<CR<0.5cts/s and hardness ratios HR1<0. This study supplements the identification program of a complete sample of sources with CR>=0.5cts/s presented previously. Spectroscopic identifications are presented for 70 of 77 sources, 5 sources are identified by other means, and subsidiary information is given for 2 as yet unidentified sources. In practically all cases, a unique optical counterpart exists. As for the brighter fraction of the sample, the largest source classes are Seyfert 1 galaxies, magnetic cataclysmic variables, and hot white dwarfs. In the Galactic Pole caps at |b|>400, Seyfert galaxies dominate, whereas at intermediate latitudes galactic objects as magnetic cataclysmic variables and white dwarfs become relatively more frequent.
- ID:
- ivo://CDS.VizieR/J/MNRAS/471/1766
- Title:
- High-redshift AGN feedback in SZ clusters
- Short Name:
- J/MNRAS/471/1766
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of active galactic nucleus (AGN) feedback at higher redshifts (0.3<z<1.2) using Sunyaev-Zel'dovich selected samples of clusters from the South Pole Telescope and Atacama Cosmology Telescope surveys. In contrast to studies of nearby systems, we do not find a separation between cooling flow (CF) clusters and non-CF clusters based on the radio luminosity of the central radio source (cRS). This lack may be due to the increased incidence of galaxy-galaxy mergers at higher redshift that triggers AGN activity. In support of this scenario, we find evidence for evolution in the radio-luminosity function of the cRS, while the lower luminosity sources do not evolve much, the higher luminosity sources show a strong increase in the frequency of their occurrence at higher redshifts. We interpret this evolution as an increase in high-excitation radio galaxies (HERGs) in massive clusters at z>0.6, implying a transition from HERG-mode accretion to lower power low-excitation radio galaxy (LERG)-mode accretion at intermediate redshifts. Additionally, we use local radio-to-jet power scaling relations to estimate feedback power and find that half of the CF systems in our sample probably have enough heating to balance cooling. However, we postulate that the local relations are likely not well suited to predict feedback power in high-luminosity HERGs, as they are derived from samples composed mainly of lower luminosity LERGs.
- ID:
- ivo://CDS.VizieR/J/ApJ/897/177
- Title:
- 142 high-redshift blazars at the cosmic dawn
- Short Name:
- J/ApJ/897/177
- Date:
- 11 Mar 2022
- Publisher:
- CDS
- Description:
- The uncharted territory of the high-redshift (z>~3) universe holds the key to understanding the evolution of quasars. In an attempt to identify the most extreme members of the quasar population, that is, blazars, we have carried out a multiwavelength study of a large sample of radio-loud quasars beyond z=3. Our sample consists of nine {gamma}-ray-detected blazars and 133 candidate blazars selected based on the flatness of their soft X-ray spectra (0.3-10keV photon index <~1.75), including 15 with Nuclear Spectroscopic Telescope Array (NuSTAR) observations. The application of the likelihood profile stacking technique reveals that the high-redshift blazars are faint {gamma}-ray emitters with steep spectra. The high-redshift blazars host massive black holes (<logM_BH,M{odot}_>>9) and luminous accretion disks (<L_disk_>>10^46^erg/s). Their broadband spectral energy distributions are found to be dominated by high-energy radiation, indicating their jets are among the most luminous ones. Focusing on the sources exhibiting resolved X-ray jets (as observed with the Chandra satellite), we find the bulk Lorentz factor to be larger with respect to other z>3 blazars, indicating faster moving jets. We conclude that the presented list of high-redshift blazars may act as a reservoir for follow-up observations, such as with NuSTAR, to understand the evolution of relativistic jets at the dawn of the universe.
- ID:
- ivo://CDS.VizieR/J/ApJ/693/8
- Title:
- High-redshift QSOs in the COSMOS survey
- Short Name:
- J/ApJ/693/8
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new measurement of the space density of high-redshift (z~3.0-4.5), X-ray-selected quasi-stellar objects (QSOs) obtained by exploiting the deep and uniform multiwavelength coverage of the COSMOS survey. We have assembled a large (40 objects), homogeneous sample of z>3 QSOs with X-ray flux F0.5-2keV>10^-15^erg/cm^2^/s, and available spectroscopic (22) or photometric (18) redshifts. We discuss their optical (color-color diagrams) and X-ray properties, their number counts and space densities and compare our findings with previous works and model predictions.
