- ID:
- ivo://CDS.VizieR/J/AJ/158/192
- Title:
- He II emission from Wolf-Rayet stars in MW & LMC
- Short Name:
- J/AJ/158/192
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We calibrated a technique to measure dust attenuation in star-forming galaxies. The technique utilizes the stellar-wind lines in Wolf-Rayet stars, which are widely observed in galaxy spectra. The He II 1640 and 4686 features are recombination lines whose ratio is largely determined by atomic physics. Therefore they can serve as a stellar dust probe in the same way as the Balmer lines are used as a nebular probe. We measured the strength of the He II 1640 line in 97 Wolf-Rayet stars in the Galaxy and the Large Magellanic Cloud. The reddening corrected fluxes follow a tight correlation with a fixed ratio of 7.76 for the He II 1640 to 4686 line ratio. Dust attenuation decreases this ratio. We provide a relation between the stellar E(B-V) and the observed line ratio for several attenuation laws. Combining this technique with the use of the nebular Balmer decrement allows the determination of the stellar and nebular dust attenuation in galaxies and can probe its effects at different stellar age and mass regimes, independently of the initial mass function and the star formation history. We derived the dust reddening from the He II line fluxes and compared it to the reddening from the Balmer decrement and from the slope of the ultraviolet continuum in two star-forming galaxies. The three methods result in dust attenuations which agree to within the errors. Future application of this technique permits studies of the stellar dust attenuation compared to the nebular attenuation in a representative galaxy sample.
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- ID:
- ivo://CDS.VizieR/J/ApJ/847/81
- Title:
- HeII photoionization rates of quasars
- Short Name:
- J/ApJ/847/81
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The HeII transverse proximity effect-enhanced HeII Ly{alpha} transmission in a background sightline caused by the ionizing radiation of a foreground quasar-offers a unique opportunity to probe the morphology of quasar-driven HeII reionization. We conduct a comprehensive spectroscopic survey to find z~3 quasars in the foreground of 22 background quasar sightlines with Hubble Space Telescope/COS HeII Ly{alpha} transmission spectra. With our two-tiered survey strategy, consisting of a deep pencil-beam survey and a shallow wide-field survey, we discover 131 new quasars, which we complement with known SDSS/BOSS quasars in our fields. Using a restricted sample of 66 foreground quasars with inferred HeII photoionization rates greater than the expected UV background at these redshifts ({Gamma}_QSO_^HeII^>5x10^-16^s^-1^) we perform the first statistical analysis of the HeII transverse proximity effect. Our results show qualitative evidence for a large object-to-object variance: among the four foreground quasars with the highest {Gamma}_QSO_^HeII^ only one (previously known) quasar is associated with a significant HeII transmission spike. We perform a stacking analysis to average down these fluctuations, and detect an excess in the average HeII transmission near the foreground quasars at 3{sigma} significance. This statistical evidence for the transverse proximity effect is corroborated by a clear dependence of the signal strength on {Gamma}_QSO_^HeII^. Our detection places a purely geometrical lower limit on the quasar lifetime of t_Q_>25Myr. Improved modeling would additionally constrain quasar obscuration and the mean free path of HeII-ionizing photons.
- ID:
- ivo://CDS.VizieR/J/A+A/439/129
- Title:
- HERES II. Spectroscopic analysis
- Short Name:
- J/A+A/439/129
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of analysis of "snapshot" spectra of 253 metal-poor halo stars -3.8<=[Fe/H]<=-1.5 obtained in the HERES survey. The snapshot spectra have been obtained with VLT/UVES and have typically S/N~54 per pixel (ranging from 17 to 308), R~20000, lambda=3760-4980{AA}. This sample represents the major part of the complete HERES sample of 373 stars; however, the CH strong content of the sample is not dealt with here.
- ID:
- ivo://CDS.VizieR/J/MNRAS/441/2
- Title:
- Herschel far-IR counterparts of SDSS galaxies
- Short Name:
- J/MNRAS/441/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study a hundred of galaxies from the spectroscopic Sloan Digital Sky Survey (SDSS) with individual detections in the far-infrared Herschel Photodetector Array Camera and Spectrometer bands (100 or 160um) and in the GALEX far-ultraviolet band up to z~0.4 in the COSMOS and Lockman Hole fields. The galaxies are divided into four spectral and four morphological types. For the star-forming and unclassifiable galaxies, we calculate dust extinctions from the ultraviolet (UV) slope, the H{alpha}/H{beta} ratio and the L_IR_/L_UV_ ratio. There is a tight correlation between the dust extinction and both L_IR_ and metallicity. We calculate SFRtotal and compare it with other star formation rate (SFR) estimates (H{alpha}, UV, SDSS) finding very good agreement between them with smaller dispersions than typical SFR uncertainties. We study the effect of mass and metallicity, finding that it is only significant at high masses for SFRH{alpha}. For the AGN and composite galaxies, we find a tight correlation between SFR and L_IR_({sigma}~0.29), while the dispersion in the SFR-L_UV_ relation is larger ({sigma}~0.57). The galaxies follow the prescriptions of the Fundamental Plane in the M-Z-SFR space.
- ID:
- ivo://CDS.VizieR/J/ApJ/736/31
- Title:
- HETDEX pilot survey. II. 1.9<z<3.8 LAEs
- Short Name:
- J/ApJ/736/31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the escape of Ly{alpha} photons from Ly{alpha} emitting galaxies (LAEs) and the overall galaxy population using a sample of 99 LAEs at 1.9<z<3.8 detected through integral-field spectroscopy of blank fields by The Hobby Eberly Telescope Dark Energy Experiment Pilot Survey. For 89 LAEs with broadband counterparts we measure ultraviolet (UV) luminosities and UV slopes, and estimate E(B-V) under the assumption of a constant intrinsic UV slope for LAEs. These quantities are used to estimate dust-corrected star formation rates (SFRs). Comparison between the observed Ly{alpha} luminosity and that predicted by the dust-corrected SFR yields the Ly{alpha} escape fraction. We also measure the Ly{alpha} luminosity function and luminosity density ({rho}_Ly{alpha}_) at 2<z<4. Using this and other measurements from the literature at 0.3<z<7.7 we trace the redshift evolution of {rho}_Ly{alpha}_. We compare it to the expectations from the star formation history of the universe and characterize the evolution of the Ly{alpha} escape fraction of galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJS/182/378
- Title:
- HI and OVI absorbers in nearby Universe
- Short Name:
- J/ApJS/182/378
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze intergalactic HI and OVI absorbers with {nu}<5000km/s in Hubble Space Telescope and Far Ultraviolet Spectroscopic Explorer spectra of 76 active galactic nuclei. The baryons traced by HI/OVI absorption are clearly associated with the extended surroundings of galaxies; for impact parameters <400kpc they are 2-4 times more numerous as those inside the galaxies. This large reservoir of matter likely plays a major role in galaxy evolution. We tabulate the fraction of absorbers having a galaxy of a given luminosity within a given impact parameter ({rho}) and velocity difference ({Delta}v), as well as the fraction of galaxies with an absorber closer than a given {rho} and {Delta}v. We identify possible "void absorbers" ({rho}>3Mpc to the nearest L_*_ galaxy), although at v<2500km/s all absorbers are within 1.5Mpc of an L>0.1L_*_ galaxy. The absorber properties depend on {rho}, but the relations are not simple correlations.
- ID:
- ivo://CDS.VizieR/J/ApJS/169/458
- Title:
- Highly excited H2 in Comets
- Short Name:
- J/ApJS/169/458
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Rotationally resolved molecular hydrogen transitions originating from excitation of highly excited rovibrational levels of the X^1^{SIGMA}^+^_g_ state have been systematically identified for the first time in the Far Ultraviolet Spectroscopic Explorer (FUSE) observation of comets C/2000 WM1 (LINEAR) and C/2001 A2 (LINEAR). Spectral assignments for the observed lines of H_2_ and other atomic and molecular species are given. All observed H_2_ transitions belong to the Lyman (B^1^{SIGMA}^+^_u_-X^1^{sigma}^+^_g_) and Werner (C^1^{PI}_u_-X^1^{SIGMA}^+^_g_) band systems. Resonant excitation of H_2_ by Ly{beta} and other solar lines is very limited.
- ID:
- ivo://CDS.VizieR/J/ApJ/727/46
- Title:
- Highly ionized plasmas in the Milky Way
- Short Name:
- J/ApJ/727/46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The cooling transition temperature gas in the interstellar medium (ISM), traced by the high ions, SiIV, CIV, NV, and OVI, helps to constrain the flow of energy from the hot ISM with T>10^6^K to the warm ISM with T<2x10^4^K. We investigate the properties of this gas along the lines of sight to 38 stars in the Milky Way disk using 1.5-2.7km/s resolution spectra of SiIV, CIV, and NV absorption from the Space Telescope Imaging Spectrograph, and 15km/s resolution spectra of OVI absorption from the Far Ultraviolet Spectroscopic Explorer. The absorption by SiIV and CIV exhibits broad and narrow components while only broad components are seen in NV and OVI. The narrow components imply gas with T<7x10^4^K and trace two distinct types of gas.
- ID:
- ivo://CDS.VizieR/J/ApJ/725/394
- Title:
- High-redshift Ly{alpha} emitters
- Short Name:
- J/ApJ/725/394
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an atlas of 88 z~5.7 and 30 z~6.5 Ly{alpha} emitters obtained from a wide-field narrowband survey. We combined deep narrowband imaging in 120{AA} bandpass filters centered at 8150{AA} and 9140{AA} with deep BVRIz broadband imaging to select high-redshift galaxy candidates over an area of 4180arcmin^2^. The goal was to obtain a uniform selection of comparable depth over the seven targeted fields in the two filters. For the GOODS-North region of the Hubble Deep Field-North field, we also selected candidates using a 120{AA} filter centered at 9210{AA}. We made spectroscopic observations with Keck DEIMOS of nearly all the candidates to obtain the final sample of Ly{alpha} emitters. At the 3.3{AA} resolution of the DEIMOS observations the asymmetric profile for Ly{alpha} emission can be clearly seen in the spectra of nearly all the galaxies. We show that the spectral profiles are surprisingly similar for many of the galaxies and that the composite spectral profiles are nearly identical at z=5.7 and z=6.5.
- ID:
- ivo://CDS.VizieR/J/ApJS/211/28
- Title:
- High resolution EUV spectrum of N_2_
- Short Name:
- J/ApJS/211/28
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analyzed high-resolution (FWHM=0.2{AA}) extreme-ultraviolet (EUV, 800-1350{AA}) laboratory emission spectra of molecular nitrogen excited by an electron impact at 20 and 100eV under (mostly) optically thin, single-scattering experimental conditions. A total of 491 emission features were observed from N_2_ electronic-vibrational transitions and atomic N I and N II multiplets and their emission cross sections were measured. Molecular emission was observed at vibrationally excited ground-state levels as high as v"=17, from the a^1^{Pi}_g_, b^1^{Pi}_u_, and b'^1^{Sigma}_u_^+^ excited valence states and the Rydberg series c'_n+1_^1^{Sigma}_u_^+^, c_n_^1^{Pi}_u_, and o_n_^1^{Pi}_u_ for n between 3 and 9. The frequently blended molecular emission bands were disentangled with the aid of a sophisticated and predictive quantum-mechanical model of excited states that includes the strong coupling between valence and Rydberg electronic states and the effects of predissociation. Improved model parameters describing electronic transition moments were obtained from the experiment and allowed for a reliable prediction of the vibrationally summed electronic emission cross section, including an extrapolation to unobserved emission bands and those that are optically thick in the experimental spectra. Vibrationally dependent electronic excitation functions were inferred from a comparison of emission features following 20 and 100eV electron-impact collisional excitation. The electron-impact-induced fluorescence measurements are compared with Cassini Ultraviolet Imaging Spectrograph observations of emissions from Titan's upper atmosphere.
