J/ApJS/177/39 Survey of low-redshift OVI absorbers (Tripp+, 2008) ================================================================================ A high-resolution survey of low-redshift QSO absorption lines: statistics and physical conditions of O VI absorbers. Tripp T.M., Sembach K.R., Bowen D.V., Savage B.D., Jenkins E.B., Lehner N., Richter P. =2008ApJS..177...39T ================================================================================ ADC_Keywords: Spectra, ultraviolet ; Redshifts ; QSOs ; Spectroscopy Keywords: cosmology: observations - intergalactic medium quasars: absorption lines Abstract: Using high-resolution ultraviolet spectra of 16 low-z QSOs obtained with the E140M echelle mode of the Space Telescope Imaging Spectrograph, we study the physical conditions and statistics of OVI absorption in the intergalactic medium (IGM) at z<0.5. We identify 51 intervening (z_abs_30m{AA}, the number of OVI absorbers per unit redshift dN/dz=15.6^+2.9^_-2.4_(21.0^+3.2^_-2.8_), and this decreases to dN/dz=0.9^+1.0^_-0.5_(0.3^+0.7^_-0.3_) for W_r_>300m{AA}. The number per redshift increases steeply as z_abs_ approaches z_QSO_; we find that dN/dz is ~3-10 times higher within 2500km/s of z_QSO_. The most striking difference between intervening and proximate systems is that some proximate absorbers have substantially lower HI/OVI ratios. Description: Our survey of low-redshift OVI absorbers is based primarily on high-resolution ultraviolet (UV) spectroscopy of QSOs acquired with the E140M echelle mode of STIS (from 1999 January to 2003 May). File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file list.dat 52 16 QSO's list table2.dat 114 179 OVI absorbers: integrated total equivalent widths and column densities table3.dat 204 245 Profile-fitting parameters for intervening and proximate OVI absorbers table7.dat 73 38 *Column density ratios and temperature constraints of well-aligned components in intervening OVI absorbers notes.dat 79 65 Notes from table 2 appendix.dat 80 490 Appendix: comments on line identification, blending, hot pixel contamination, and saturation in individual systems -------------------------------------------------------------------------------- Note on table7.dat: This table lists data for components with OVI and HI components that have aligned centroids (see section 2.3.2). -------------------------------------------------------------------------------- See also: VII/23 : Absorption Lines in QSO Spectra (Ellis+ 1978) J/ApJS/77/203 : QSO absorption systems (Junkkarinen+ 1991) J/AJ/112/62 : Quasar absorption-line systems (Tanner+ 1996) J/ApJS/122/355 : Properties of low z QSO absorption systems (Vanden Berk+ 1999) J/ApJ/599/116 : UV properties of absorbed quasars (Vestergaard+, 2003) Byte-by-byte Description of file: list.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 12 A12 --- QSO QSO name 17- 18 I2 h RAh Right ascension (J2000) 20- 21 I2 min RAm Right ascension (J2000) 23- 26 F4.1 s RAs Right ascension (J2000) 28 A1 --- DE- Declination sign (J2000) 29- 30 I2 deg DEd Declination (J2000) 32- 33 I2 arcmin DEm Declination (J2000) 35- 36 I2 arcsec DEs Declination (J2000) 39- 52 A14 --- Name QSO JHHMM+DDMM name -------------------------------------------------------------------------------- Byte-by-byte Description of file: table2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 12 A12 --- QSO Target QSO name 14- 20 F7.5 --- zabs Absorber systemic redshift (1) 22- 33 A12 --- Ion Species and transition used to measure EWr & logN 34- 36 A3 --- n_Ion [eghjkmo, ] Note(s) on species in notes.dat file 38 A1 --- l_EWr [~ ] Limit flag on EWr 39- 44 F6.1 0.1pm EWr ?=- Rest-frame integrated equivalent width 46- 49 F4.1 0.1pm e_EWr ? Error on EWr 50 A1 --- n_EWr [xfil] Note on EWr in notes.dat file 52- 53 A2 --- l_logN [>=~ ] Limit flag on logN 54- 58 F5.2 [-] logN ?=- Directly integrated apparent column density 60- 63 F4.2 [-] E_logN ? Positive error on logN 65- 68 F4.2 [-] e_logN ? Negative error on logN 69 A1 --- n_logN [abdikfln] Note on logN in notes.dat file 71- 74 I4 km/s Vel1 ?=- Velocity centroid of component 1 (2) 76- 79 I4 km/s Vel2 ? Velocity centroid of component 2 (2) 81- 83 I3 km/s Vel3 ? Velocity centroid of component 3 (2) 85- 87 I3 km/s Vel4 ? Velocity centroid of component 4 (2) 89- 91 I3 km/s Vel5 ? Velocity centroid of component 5 (2) 93- 95 I3 km/s Vel6 ? Velocity centroid of component 6 (2) 97- 99 I3 km/s Vel7 ? Velocity centroid of component 7 (2) 101-103 I3 km/s Vel8 ? Velocity centroid of component 8 (2) 105-107 I3 km/s Vel9 ? Velocity centroid of component 9 (2) 109 A1 --- n_Vel1 [c] Note on component velocity (3) 111-114 A4 --- Spec Spectrograph used for the measurement -------------------------------------------------------------------------------- Note (1): Which in this paper is defined by the centroid of the strongest component detected in the OVI profiles. Note (2): Derived from Voigt-profile fitting (see Table 3). Note (3): 'c' for an optically thick Lyman limit absorber: all available Lyman series lines are strongly saturated and, consequently, cannot be used to derive reliable constraints on the HI component structure. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table3.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 12 A12 --- QSO Target QSO name 14- 20 F7.5 --- zabs Absorber systemic redshift (1) 22- 37 A16 --- Class Classification (2) 39- 41 A3 --- Ion Species 43-146 A104 --- line Fitted lines 148-151 I4 km/s Vel ?=- Velocity centroid (3) 153-154 I2 km/s e_Vel ? Error on Vel 155 A1 --- u_Vel Uncertainty flag on Vel (3) 157-159 I3 km/s b ?=- Doppler parameter (3) 161-162 I2 km/s E_b ? Positive error on b 164-165 I2 km/s e_b ? Negative error on b 166 A1 --- u_b Uncertainty flag on b (3) 168-169 A2 --- l_logN [>~ ] Limit flag on logN 170-174 F5.2 [cm-2] logN ?=- Column density of individual components (4) 176-179 F4.2 [cm-2] e_logN ? Error on logN 180 A1 --- u_logN Uncertainty flag on logN (3) 182-201 A20 --- Type Component number (type) (5) 203-204 I2 --- Note ? See comments in "appendix.dat" file -------------------------------------------------------------------------------- Note (1): In this paper, we use the centroid of the strongest OVI component to define the systemic redshift of the absorber. Note (2): Absorber classification: (Prox) = absorption systems detected within 5000km/s of the QSO redshift (Proximate absorbers) (Int) = systems that are displaced by more than 5000km/s from z_QSO_ (Intervening systems). simple = systems in which all HI and OVI components are aligned (see section 2.3.2) complex = absorbers that show significant velocity offsets between HI and OVI components. Note (3): For each component, we list the velocity centroid (Vel), Doppler parameter (b), and column density (N) obtained from Voigt-profile fitting using the software of Fitzpatrick & Spitzer (1997ApJ...475..623F). The listed parameter uncertainties primarily reflect the random noise in the measurements. In some cases, systematic uncertainties due to effects such as line saturation and blending can be larger than the formal uncertainties listed in the table. For these more uncertain measurements, we list the formal error bars indicated by the fitting, but we flag the measurements with a colon. Comments on the source of the additional systematic uncertainties are presented in the Appendix. Note (4): Column densities of individual components detected in each OVI absorption system (some OVI absorbers show only one component, but many of the systems have multiple components). Note (5): For convenience, we number the components in each absorption system, and we indicate whether the OVI and HI components are aligned or offset from each other. If the components are aligned, we give the HI and OVI components the same number, and if a component is offset, it is given a unique number. For example, in the 3C 249.1 system at z_abs_=0.24676, we identify two HI components at v=-79+/-3km/s (component 1) and v=0+/-1km/s (component 2), and we find one OVI component at v=0+/-3km/s. The OVI component is aligned with HI component 2, and thus, the OVI component is also identified as component 2. By using the same component numbers for aligned HI and OVI cases, the reader can easily identify which components are matched together from Table 3. -------------------------------------------------------------------------------- Byte-by-byte Description of file: table7.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 12 A12 --- QSO Target QSO name 14- 20 F7.5 --- zabs Absorption system redshift 22- 24 I3 km/s Vel Velocity of the particular component (1) 26 A1 --- l_logTb Limit flag on logTb 27- 30 F4.2 [K] logTb Temperature upper limit, OVI only (2) 32 A1 --- l_logT Limit flag on logT 33- 36 F4.2 [K] logT 3{sigma} upper limit on T, OVI only (3) 38- 41 F4.2 [K] logTb2 ?=- Best measurement of the gas temperature, HI+OVI (4) 43 A1 --- l_logT2 Limit flag on logT2 44- 47 F4.2 [K] logT2 ?=- 3{sigma} upper limit on the temperature, HI+OVI (5) 49- 50 I2 km/s b ? Nonthermal broadening component corresponding to logTb2 52- 56 F5.2 [-] logN(H/O) Log of the HI/OVI column-density ratio 58 A1 --- l_logN(C/O) Limit flag on logNC/O 59- 63 F5.2 [-] logN(C/O) ?=- Log of the CIII/OVI column-density ratio 65- 73 A9 --- Class Absorber classification (6) -------------------------------------------------------------------------------- Note (1): From which the temperature and columns density ratios were measured. Note (2): Implied by the best-fit OVI b-value (eq. [7]: T=mb^2^/2k=A(b/0.129)^2^ where A is the atomic mass number and the numerical coefficient assumes that b is in km/s and T is in Kelvin). Note (3): Indicating by propagating the uncertainty in b(OVI) through eq. (7). Note (4): Found by solving eq. (8) using the OVI and HI b-values (logT, with T measured in degrees kelvin). Note (5): Found by propagating the b-value uncertainties through eq. (8): b^2^=0.129^2^x(T/A)+b^2^_nt_ where b_nt_ is a nonthermal broadening term. Note (6): Absorber classification: Complex = systems that show significant velocity offsets between low-ionization and high-ionization line Simple = absorbers that are entirely composed of aligned HI and OVI components Simple* = indicate that the majority of the OVI and HI profiles are well aligned and can be analyzed as a single-phase system Uncertain = in some instances, the HI profiles and component centroids are poorly constrained, e.g., if the absorber is a black Lyman-limit system presenting only badly saturated Lyman series lines or if HI is not detected at all (as found in several systems near the QSO redshifts); in these cases, we list the classification as uncertain. -------------------------------------------------------------------------------- Byte-by-byte Description of file: notes.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1 A1 --- Note Note designation 3- 79 A77 --- Text Text of note -------------------------------------------------------------------------------- Byte-by-byte Description of file: appendix.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 2 I2 --- Note Note number 4- 80 A77 --- Text Text of note -------------------------------------------------------------------------------- Nomenclature note : <[TSB2008] QSO JHHMM+DDMM abs N.NNNNN> in Simbad. History: From electronic version of the journal ================================================================================ (End) Emmanuelle Perret [CDS] 24-Sep-2009