J/ApJ/794/75 HST-COS UV spectra observations of AGNs (Stevans+, 2014)
HST-COS observations of AGNs. II. Extended survey of ultraviolet composite spectra from 159 active galactic nuclei. Stevans M.L., Shull J.M., Danforth C.W., Tilton E.M. <Astrophys. J., 794, 75 (2014)> =2014ApJ...794...75S (SIMBAD/NED BibCode)
ADC_Keywords: Active gal. nuclei ; Galaxies, spectra ; Photometry, ultraviolet ; Redshifts ; Photometry, HST ; Photometry, hydrogen-line Keywords: galaxies: active - line: profiles - quasars: emission lines - ultraviolet: galaxies Abstract: The ionizing fluxes from quasars and other active galactic nuclei (AGNs) are critical for interpreting their emission-line spectra and for photoionizing and heating the intergalactic medium. Using far-ultraviolet (FUV) spectra from the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope (HST), we directly measure the rest-frame ionizing continua and emission lines for 159 AGNs at redshifts 0.001<zAGN<1.476 and construct a composite spectrum from 475 to 1875 Å. We identify the underlying AGN continuum and strong extreme ultraviolet (EUV) emission lines from ions of oxygen, neon, and nitrogen after masking out absorption lines from the H I Lyα forest, 7 Lyman-limit systems (NHI≥1017.2/cm2) and 214 partial Lyman-limit systems (14.5<logNHI<17.2). The 159 AGNs exhibit a wide range of FUV/EUV spectral shapes, Fv∝ναν_^, typically with -2≤αν≤0 and no discernible continuum edges at 912 Å (H I) or 504 Å (He I). The composite rest-frame continuum shows a gradual break at λbr~ 1000 Å, with mean spectral index αν=-0.83±0.09 in the FUV (1200-2000 Å) steepening to αν=-1.41±0.15 in the EUV (500-1000 Å). We discuss the implications of the UV flux turnovers and lack of continuum edges for the structure of accretion disks, AGN mass inflow rates, and luminosities relative to Eddington values. Description: Here in Paper II, we enlarge our composite spectrum from 22 to 159 AGNs, confirm the validity of our early results, and explore possible variations of the EUV spectral index with AGN type and luminosity. Both studies were enabled by high-quality, moderate-resolution spectra taken with the Cosmic Origins Spectrograph installed on the HST during the 2009 May servicing mission. The COS instrument (Green et al. 2012ApJ...744...60G) was designed explicitly for point-source spectroscopy of faint targets, particularly quasars and other AGNs used as background sources for absorption-line studies of the intergalactic medium (IGM), circumgalactic medium (CGM), and interstellar medium (ISM). Our survey is based on high-quality spectra of the numerous AGNs used in these projects. Our new survey contains 159 AGNs out to z=1.476 with 16 targets at z>0.90, sufficient to probe below 600 Å by observing with G130M down to 1135 Å. File Summary:
FileName Lrecl Records Explanations
ReadMe 80 . This file table1.dat 80 159 COS Observations (159 AGN Targets Ordered by Redshift) table2.dat 47 221 Lyman-limit Systems and Partial Lyman-limit Systems
See also: J/ApJ/817/111 : HST/COS survey of z<0.9 AGNs. I. (Danforth+, 2016) Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
1- 24 A24 --- AGN AGN target's name 26- 31 A6 --- Type AGN type 33- 40 F8.6 --- z Redshift 42- 46 F5.2 --- alphal Fitted spectral index (1) 48- 53 F6.4 --- e_alphal Error in alphal 55- 61 F7.4 10-16W/m2/nm F0 Rest-frame flux normalization at 1100Å (in 10-14 erg/cm2/s/Å) 63- 67 F5.2 10-16W/m2/nm Fl Observed flux at 1300Å (in 10-14 erg/cm2/s/Å) (2) 69- 73 F5.2 [10-7W] loglLl Band luminosity at 1100Å (in erg/s) 75- 76 I2 --- S/N1 Signal-to-noise ratio at 1250Å and 1550Å for data with G130M (1132-1460Å) grating 77 A1 --- --- [,] 79- 80 I2 --- S/N2 Signal-to-noise ratio at 1250Å and 1550Å for data with G160M (1394-1798Å) grating
Note (1): Corresponds to frequency index αν=-[2+αλ]. Finn et al. (2014MNRAS.440.3317F) fitted a harder spectral index, αλ=-0.64, for J0209-0438 at z=1.131, using additional COS/G230L spectra extending to longer wavelengths. Note (2): Flux at 1300Å for SBS 1108+560 is low, owing to LyC absorption (λ<1334Å) from a LLS at z=0.46335.
Byte-by-byte Description of file: table2.dat
Bytes Format Units Label Explanations
1- 24 A24 --- AGN AGN target's name 26- 32 F7.5 --- z Redshift 34- 38 F5.2 [cm-2] logNHI Log of H I column density 40- 44 F5.3 [cm-2] e_logNHI Error in logNHI 46- 47 I2 km/s b Doppler parameter (1)
Note (1): Derived by fitting Lyα and higher Lyman series absorbers. When the Doppler parameter is unconstrained, we used mean b=25 km/s to propagate uncertainties in the continuum slope of individual spectra.
History: From electronic version of the journal References: Shull et al., Paper I, 2012ApJ...752..162S
(End) Prepared by Tiphaine Pouvreau [CDS] 27-Apr-2017
|The document above follows the rules of the Standard Description for Astronomical Catalogues.From this documentation it is possible to generate f77 program to load files into arrays or line by line|