Improved and Quality-Assessed Emission and Absorption Line Measurements in Sloan Digital Sky Survey Galaxies

Oh, Kyuseok; Sarzi, Marc; Schawinski, Kevin; Yi, Sukyoung K.

doi:10.1088/0067-0049/195/2/13

Cited by 164 publications

(223 citation statements)

References 56 publications

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“…Indeed the differences between pairs of measurements closely match those predicted by their uncertainties. The good agreement of the flux measurements obtained by Oh et al (2011) using a different approach for the removal of the stellar emission also supports the robustness of those provided by MPA-JHU database.…”

Section: Emission Lines and Stellar Continuumsupporting

confidence: 73%

Revisiting the census of low-luminosity AGN

Capetti

2011

A&A

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The aim of this paper is to revisit critically the current census of active galactic nucleus (AGN) as derived from optical spectroscopy. We considered the spectra of nearby (z < 0.1) galaxies from the Sloan Digital Sky Survey (SDSS). The equivalent width (EW) distribution of the [O III]λ5007 emission line is strongly clustered around ∼0.6 Å, extending the validity of the results we obtained for red giant ellipticals. The close connection between emission lines and stellar continuum points to stellar processes as the most likely source of the bulk of the ionizing photons in these galaxies although their emission line ratios are similar to those of active nuclei. Genuine AGN might be sought mainly among the minority (∼5-10%) of outliers, i.e., galaxies with EW 2 Å. The galaxies located in the AGN region of the spectroscopic diagnostic diagrams outnumber outliers by a factor 5-10, which casts doubts on the accuracy of the current identification of active galaxies, particularly those of LINERs of low line luminosity, 10 39 −10 40 erg s −1 . This conclusion can be tested by using spectra that cover smaller physical regions such as those that are already available in the literature of the ∼500 nearest bright galaxies, with a stellar continuum reduced by a factor of 20-100 with respect to SDSS galaxies. If the emission lines were mainly of AGN origin, their contrast against the continuum should be enhanced. Instead, their EW distribution is similar to that of the SDSS sample, with just an increase of the outlier fraction. We conclude that the number of low-luminosity AGN is currently largely overestimated with a sample purity as low as ∼10%. As a consequence the properties of low-luminosity AGN should be fundamentally revised.

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Section: Emission Lines and Stellar Continuumsupporting

confidence: 73%

Revisiting the census of low-luminosity AGN

Capetti

2011

A&A

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“…The velocity widths (deconvolved for the instrumental broadening) of [O ii]λλ3727,3729 doublet (i.e.,σ [O II] ) is found in the range of ∼ 17 ± 16 km s −1 to 194 ± 72 km s −1 in SDSS-DR7 and 6 ± 11 km s −1 to 198 ± 91 km s −1 in the SDSS-DR12 spectra with an average σ [O II] of ∼ 75 km s −1 . This is similar to a typical velocity dispersion found in the SDSS galaxies (Oh et al 2011). The KS − test does not indicate any differences between the σ [O II] in SDSS-DR7 and DR12 with p null = 0.23.…”

Section: Velocity Width Of Emission and Mass Ofsupporting

confidence: 84%

[O ii] nebular emission from Mg ii absorbers: star formation associated with the absorbing gas

Joshi

Srianand

Petitjean

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We present nebular emission associated with 198 strong Mg ii absorbers at 0.35 z 1.1 in the fibre spectra of quasars from the Sloan Digital Sky Survey. Measured and their z evolution are consistent with those of galaxies detected in deep surveys. Based on the median stacked spectra, we infer the average metallicity (log Z ∼8.3), ionization parameter (log q ∼7.5) and stellar mass (log (M/M ⊙ )∼9.3). The Mg ii systems with nebular emission typically have W 2796 2Å, Mg ii doublet ratio close to 1 and W(Fe iiλ2600)/W 2796 ∼ 0.5 as often seen in damped Lyα and 21-cm absorbers at these redshifts. This is the biggest reported sample of [O ii] emission from Mg ii absorbers at low impact parameters ideally suited for probing various feedback processes at play in z 1 galaxies.

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“…Groves et al (2012) have indeed shown that, for a fixed age of the underlying stellar population, different population synthesis models give differences in the Hβ and Hα Balmer absorption lines up to ∼2−3 Å. There are also indications that the use of different fitting procedures can lead to different measurements of line emission, in particular whenever the emission is weak (Oh et al 2011). For these reasons we prefer to adopt a simpler approach by directly measuring the underlying absorption in the Hβ line from the spectra, and use a constant correction for the Hα line.…”

Section: Contribution Of the Underlying Balmer Absorptionmentioning

confidence: 99%

“…The set of spectroscopic data in our hand is thus quite non homogeneous in terms of S/N. Since the accuracy of the fit depends on the S/N (Oh et al 2011), these spectra can be hardly used without other photometric data to constrain the star formation history of the target galaxies and measure the underlying Balmer absorption using population synthesis models.…”

Section: Contribution Of the Underlying Balmer Absorptionmentioning

confidence: 99%

Integrated spectroscopy of theHerschelReference Survey

Boselli

Hughes

Cortese

et al. 2013

A&A

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We present long-slit integrated spectroscopy of 238 late-type galaxies belonging to the Herschel Reference Survey, a volume-limited sample representative of the nearby universe. This sample has a unique legacy value since it was ideally defined for any statistical study of the multifrequency properties of galaxies spanning a wide range in morphological type and luminosity. The spectroscopic observations cover the spectral range 3600−6900 Å at a resolution R 1000 and are thus suitable for separating both the underlying absorption from the emission of the Hβ line and the two [Nii] . We used the data to study the distribution of the equivalent width of all the emission lines, of the Balmer decrement C(Hβ), and of the observed underlying Balmer absorption under Hβ (EW Hβ abs ) in this sample. Combining these new spectroscopic data with those available at other frequencies, we also study the dependence of C(Hβ) and EW Hβ abs on morphological type, stellar mass, stellar surface density, star formation rate, birthrate parameter, and metallicity in galaxies belonging to different environments (fields vs. Virgo cluster). The distribution of the equivalent width of all the emission lines, of C(Hβ) (or equivalently of A(Hα)), and of EW Hβ abs are systematically different in cluster and field galaxies. The Balmer decrement increases with the stellar mass, stellar surface density, metallicity, and star formation rate of the observed galaxies, while it is unexpectedly almost independent of the column density of the atomic and molecular gas. The dependence of C(Hβ) on stellar mass is steeper than previously found in other works. The underlying Balmer absorption does not significantly change with any of these physical parameters.

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Improved and Quality-Assessed Emission and Absorption Line Measurements in Sloan Digital Sky Survey Galaxies

Cited by 164 publications

References 56 publications

Revisiting the census of low-luminosity AGN

Revisiting the census of low-luminosity AGN

[O ii] nebular emission from Mg ii absorbers: star formation associated with the absorbing gas

Integrated spectroscopy of theHerschelReference Survey

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