- ID:
- ivo://CDS.VizieR/J/ApJ/655/851
- Title:
- Wolf-Rayet galaxies in the SDSS
- Short Name:
- J/ApJ/655/851
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use a large sample of 174 Wolf-Rayet (W-R) galaxies drawn from the Sloan Digital Sky Survey to study whether and how the slope of the stellar initial mass function depends on metallicity. We calculate for each object its oxygen abundance, according to which we divide our sample into four metallicity subsamples. For each subsample, we then measure three quantities: the equivalent width of the H{beta} emission line, the equivalent width of the W-R bump around 4650{AA}, and the W-R bump-to-Hbeta intensity ratio, and compare to the predictions of the same quantities by evolutionary synthesis models of Schaerer & Vacca (1998ApJ...497..618S).
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Search Results
- ID:
- ivo://CDS.VizieR/J/A+A/439/265
- Title:
- Wolf-Rayet population in M83
- Short Name:
- J/A+A/439/265
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalogue of non-nuclear regions containing Wolf-Rayet stars in the metal-rich spiral galaxy M 83 (NGC 5236). From a total of 283 candidate regions identified using He II {lambda}4686 imaging with VLT-FORS2, Multi Object Spectroscopy of 198 regions was carried out, confirming 132 WR sources. From this sub-sample, an exceptional content of ~1035+/-300 WR stars is inferred, with N(WC)/N(WN) ~ 1.2, continuing the trend to larger values at higher metallicity amongst Local Group galaxies, and greatly exceeding current evolutionary predictions at high metallicity.
- ID:
- ivo://CDS.VizieR/J/MNRAS/381/418
- Title:
- Wolf-Rayet population in NGC 1313
- Short Name:
- J/MNRAS/381/418
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a VLT/FORS1 survey of Wolf-Rayet (WR) stars in the spiral galaxy NGC 1313. In total, 94 WR candidate sources have been identified from narrow-band imaging. Of these, 82 have been spectroscopically observed, for which WR emission features are confirmed in 70 cases, one of which also exhibits strong nebular HeII{lambda}4686 emission. We also detect strong nebular HeII{lambda}4686 emission within two other regions of NGC 1313, one of which is a possible supernova remnant. Nebular properties confirm that NGC 1313 has a metal content log(O/H)+12=8.23+/-0.06, in good agreement with previous studies. From continuum-subtracted H{alpha} images we infer a global star formation rate of 0.6M_{sun}/yr. Using template LMC WR stars, spectroscopy reveals that NGC 1313 hosts a minimum of 84 WR stars. Our census comprises 51 WN stars, including a rare WN/C transition star plus 32 WC stars. In addition, we identify one WO star which represents the first such case identified beyond the Local Group. The bright giant HII region PES 1, comparable in H{alpha} luminosity to NGC 595 in M 33, is found to host a minimum of 17 WR stars. The remaining photometric candidates generally display photometric properties consistent with WN stars, such that we expect a global WR population of ~115 stars with N(WR)/N(O)~0.01 and N(WC)/N(WN)~0.4.
- ID:
- ivo://CDS.VizieR/J/A+A/526/A116
- Title:
- W Virginis high-resolution spectra
- Short Name:
- J/A+A/526/A116
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this work was to perform a multiphase spectroscopic study of W Vir which represents stars of the class of Population II cepheids, in order to trace the behaviour of emission features in different lines, and to use the data to describe the dynamical processes in the atmosphere of this star associated with the shock wave propagation.
- ID:
- ivo://CDS.VizieR/J/A+A/649/A39
- Title:
- xCOLD GASS and xGASS. Metallicity gradients
- Short Name:
- J/A+A/649/A39
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- The xGASS and xCOLD GASS surveys have measured the atomic (HI) and molecular gas (H_2_) content of a large and representative sample of nearby galaxies (redshift range of 0.01<z<0.05). We present optical longslit spectra for a subset of the xGASS and xCOLD GASS galaxies to investigate the correlation between radial metallicity profiles and cold gas content. In addition to data from Moran et al. (2012ApJ...745...66M), this paper presents new optical spectra for 27 galaxies in the stellar mass range of 9.0<=logMstar[Msun]<=10.0. The longslit spectra were taken along the major axis of the galaxies, allowing us to obtain radial profiles of the gas-phase oxygen abundance (12+log(O/H)). The slope of a linear fit to these radial profiles is defined as the metallicity gradient. We investigated correlations between these gradients and global galaxy properties, such as star formation activity and gas content. In addition, we examined the correlation of local metallicity measurements and the global HI mass fraction. We obtained two main results: (i) the local metallicity is correlated with the global HI mass fraction, which is in good agreement with previous results. A simple toy model suggests that this correlation points towards a 'local gas regulator model'; (ii) the primary driver of metallicity gradients appears to be stellar mass surface density (as a proxy for morphology). This work comprises one of the few systematic observational studies of the influence of the cold gas on the chemical evolution of star-forming galaxies, as considered via metallicity gradients and local measurements of the gas-phase oxygen abundance. Our results suggest that local density and local HI mass fraction are drivers of chemical evolution and the gas-phase metallicity.
- ID:
- ivo://CDS.VizieR/J/AJ/159/245
- Title:
- Xinglong optical spectra of UGC3223 in 4 epochs
- Short Name:
- J/AJ/159/245
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The discovery of spectral type transition of active galactic nuclei (AGNs), the so-called "changing-look" (CL) phenomenon, challenges the widely accepted AGN paradigm, not only in the orientation-based unified model, but also in the standard disk model. In past decades, only a couple of nearby repeat changing-look active galactic nuclei (CL-AGNs) have been identified. Here we report spectroscopic observations of UGC3223 over the course of 18yr, from 2001 onwards. Combining the spectrum taken in 1987 by Stirpe, we have witnessed its type transitions from 1.5 to 2.0 to 1.8 over 32yr, and captured a long-lived (at least 10 yr) thorough "turn-off" state with a spectrum typical of a Seyfert 2 galaxy. The long-term thorough turn-off state probably suggests a once-dormant and an awakening central engine in UGC3223. We argue that the (dis)appearance of the broad Balmer emission lines can be explained by the disk-wind broad-line region model given the evolution of the calculated Eddington ratio of accretion of the supermassive black hole.
- ID:
- ivo://CDS.VizieR/J/ApJ/887/15
- Title:
- Xinglong spectra of two changing-look SDSS AGNs
- Short Name:
- J/ApJ/887/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report a spectroscopic identification of two new changing-look active galactic nuclei (CL-AGNs): SDSSJ104705.16+544405.8 and SDSSJ120447.91+170256.8, both with a "turn-off" type transition from type-1 to type-1.8/1.9. The identification is arrived at through a follow-up spectroscopic observation of the five CL-AGNs candidates that are extracted from the sample recently released in MacLeod+ (2019, J/ApJ/874/8). The candidates are extracted by the authors from the Sloan Digit Sky Survey Data Release 7, and are spectroscopically confirmed quasars with large amplitude variability. By compiling a sample of 26 previously identified CL-AGNs, we confirm the claim by MacLeod+ that CL-AGNs tend to be biased against a low Eddington ratio, and identify an overlap between the CL-AGNs at their dim state and the so-called intermediate-type AGNs. The overlap implies that there two populations of the intermediate-type AGNs with different origins. One is due to the torus orientation effect, and the other to the intrinsic change of the accretion rate of the central supermassive black holes.
- ID:
- ivo://CDS.VizieR/J/MNRAS/449/1422
- Title:
- 2XMM AGN X-ray and mid-IR luminosities
- Short Name:
- J/MNRAS/449/1422
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have determined the relation between the AGN luminosities at rest-frame 6{mu}m associated with the dusty torus emission and at 2-10keV energies using a complete, X-ray-flux-limited sample of 232 AGN drawn from the Bright Ultra-hard XMM-Newton Survey. The objects have intrinsic X-ray luminosities between 10^42^ and 10^46^erg/s and redshifts from 0.05 to 2.8. The rest-frame 6{mu}m luminosities were computed using data from the Wide-field Infrared Survey Explorer and are based on a spectral energy distribution decomposition into AGN and galaxy emission. The best-fitting relationship for the full sample is consistent with being linear, L_6{mu}m_{prop.to}L_2-10keV_^0.99+/-0.03^, with intrinsic scatter, {Delta}logL_6{mu}m_~0.35dex. The L_6{mu}m_/L_2-10keV_ luminosity ratio is largely independent of the line-of-sight X-ray absorption. Assuming a constant X-ray bolometric correction, the fraction of AGN bolometric luminosity reprocessed in the mid-IR decreases weakly, if at all, with the AGN luminosity, a finding at odds with simple receding torus models. Type 2 AGN have redder mid-IR continua at rest-frame wavelengths <12{mu}m and are overall ~1.3-2 times fainter at 6{mu}m than type 1 AGN at a given X-ray luminosity. Regardless of whether type 1 and type 2 AGN have the same or different nuclear dusty toroidal structures, our results imply that the AGN emission at rest-frame 6{mu}m is not isotropic due to self-absorption in the dusty torus, as predicted by AGN torus models. Thus, AGN surveys at rest-frame ~6{mu}m are subject to modest dust obscuration biases.
- ID:
- ivo://CDS.VizieR/J/PAZh/45/464
- Title:
- 3XMM-DR4 QSO candidates optical spectroscopy
- Short Name:
- J/PAZh/45/464
- Date:
- 22 Feb 2022
- Publisher:
- CDS
- Description:
- We present the results of optical spectroscopy for 58 quasar candidates at photometric redshifts z>~3, 57 of which enter into the Khorunzhev et al. (2016, Cat. J/PAZh/42/313) catalog (K16). This is a catalog of quasar candidates and known type 1 quasars selected among the X-ray sources of the 3XMM-DR4 catalog of the XMM-Newton serendipitous survey. At first we have performed spectroscopy for a quasi-random sample of 19 candidates at the 1.6-m AZT-33IK telescope of the Sayan Solar Observatory and the 6-m BTA telescope of the Special Astrophysical Observatory (SAO RAS). Then we have continued the observation for 39 X-ray bright candidates that could be used for the X-ray luminosity function construction (see Khorunzhev et al. 2018AstL...44..500K). The spectra at AZT-33IK were taken with the new low- and medium-resolution ADAM spectrograph that was produced and installed on the telescope in 2015. One of the most distant (z=5.08) optically bright (i=21) quasars ever detected in X-ray surveys has been discovered.
- ID:
- ivo://CDS.VizieR/J/A+A/439/1149
- Title:
- XMM spectroscopy of TWA 5
- Short Name:
- J/A+A/439/1149
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of X-ray spectroscopy for TWA 5, a member of the young TW Hydrae association, observed with XMM-Newton. TWA 5 is a multiple system which shows H{alpha} emission, a signature typical of classical T Tauri stars, but no infrared excess. From this analysis of the RGS and EPIC spectra, we have derived the emission measure distribution vs. temperature of the X-ray emitting plasma, its abundances, and the electron density.
