Aperture Effects on Star Formation Rate, Metallicity, and Reddening

By Lisa J. Kewley, R. Jansen, Margaret J. Geller. 2005

203 citations recorded by the source corpus.

We use 101 galaxies selected from the Nearby Field Galaxy Survey to investigate the effect of aperture size on the star formation rate, metallicity, and reddening determinations for galaxies. Our sample includes galaxies of all Hubble types except ellipticals with global star formation rates (SFRs) ranging from 0.01 to 100 M⊙ yr−1, metallicities in the range 7.9≲log (O/H) + 12≲9.0, and reddening of 0≲A(V)≲3.3. We compare the SFR, metallicity, and reddening derived from nuclear spectra to those derived from integrated spectra. For apertures capturing <20% of the B26 light, the differences between nuclear and global metallicity, extinction, and SFR are substantial. Late‐type spiral galaxies show the largest systematic difference (∼0.14 dex), with nuclear metallicities greater than the global metallicities. The Sdm, Im, and Peculiar types have the largest scatter in nuclear/integrated metallicities, indicating a large range in metallicity gradients for these galaxy types, or clumpy metallicity distributions. We find little evidence for systematic differences between nuclear and global extinction estimates for any galaxy type. However, there is significant scatter between the nuclear and integrated extinction estimates for nuclear apertures containing <20% of the B26 flux. We calculate an “expected” SFR using our nuclear spectra and apply the commonly used aperture correction method. The expected SFR overestimates the global value for early‐type spirals, with large scatter for all Hubble types, particularly late types. The differences between the expected and global SFRs probably result from the assumption that the distributions of the emission‐line gas and the continuum are identical. The largest scatter (error) in the estimated SFR occurs when the aperture captures <20% of the B26 emission. We discuss the implications of these results for metallicity‐luminosity relations and star formation history studies based on fiber spectra. To reduce systematic and random errors from aperture effects, we recommend selecting samples with fibers that capture >20% of the galaxy light. For the Sloan Digital Sky Survey and the Two‐Degree Field Galaxy Redshift Survey, redshifts z>0.04 and 0.06 are required, respectively, to ensure a covering fraction >20% for galaxy sizes similar to the average size, type, and luminosity observed in our sample. Higher luminosity samples and samples containing many late‐type galaxies require a larger minimum redshift to ensure that >20% of the galaxy light is enclosed by the fiber.

Subfields: Astronomy and Astrophysics, Electrical and Electronic Engineering, Instrumentation

View Paper: https://www.semanticscholar.org/paper/6653bdd9f41207500b7a436af03ce42e5324648c

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Astronomy and Astrophysics

In Electrical and Electronic Engineering

In Instrumentation

Citations in the corpus

GALAXY PAIRS IN THE SLOAN DIGITAL SKY SURVEY. I. STAR FORMATION, ACTIVE GALACTIC NUCLEUS FRACTION, AND THE LUMINOSITY/MASS–METALLICITY RELATION (2008, background): “Although aperture effects are likely to affect galaxy metallicities (Kewley et al. 2005; Ellison & Kewley 2005) we do not make any a priori cuts in CF.”
THE MASS–METALLICITY RELATION WITH THE DIRECT METHOD ON STACKED SPECTRA OF SDSS GALAXIES (2012, background): “In particular, the galaxies with very low stellar masses and metallicities that define the low mass end of the MZR tend to be compact and have homogeneous metallicities (e.g., Kobulnicky & Skillman 1997), although many of these are excluded by the criteria proposed by Kewley et al. (2005).”
A COMPREHENSIVE ANALYSIS OF UNCERTAINTIES AFFECTING THE STELLAR MASS–HALO MASS RELATION FOR 0 < z < 4 (2010, background): “For galaxies containing both a bulge and a disk, or galaxies with radial gradients, the spectra will therefore not provide a fair sample of the entire galaxy (e.g., Kewley et al. 2005); furthermore, this bias will be a function of redshift.”
Optical Star Formation Rate Indicators (2005, unknown): “Kewley et al. (2005), however, find that extinction does not depend on enclosed light fraction based on a comparison of integrated and nuclear spectra in the NFGS.”
Galaxy And Mass Assembly (GAMA): Spectroscopic analysis (2013, background): “Kewley et al. (2005) highlight, for example, how aperture effects can bias the estimate of star formation rate, nebular metallici y and obscuration in galaxies.”
THE COSMIC CORE-COLLAPSE SUPERNOVA RATE DOES NOT MATCH THE MASSIVE-STAR FORMATION RATE (2011, background): “For example, the known aperture bias from the finite SDSS fiber diameter is most critical for low-redshift galaxies like those in the LOSS survey (Kewley et al. 2005).”
Metallicities and Physical Conditions in Star-forming Galaxies at z ~ 1.0-1.5 (2008, background): “The third criterion is required to avoid significant aperture effects on the flux ratios (Kewley et al. 2005; Tremonti et al. 2004).”
OPTICAL SPECTROSCOPY AND NEBULAR OXYGEN ABUNDANCES OF THE SPITZER/SINGS GALAXIES (2010, methodology): “…that the metallicities derived from the SDSS 3′′ diameter fiber spectra may be too high by ∼0.1 dex due to aperture bias (Tremonti et al. 2004; Kewley et al. 2005). this experiment by obtaining high-quality electron temperature measurements of 28 H ii regions in the nearby late-type galaxy…”
Predicting dust extinction from the stellar mass of a galaxy (2010, background): “…Hα flux is the assumption that the radial distributions of Hα flux and stellar continuum are comparable – both Brinchmann et al. (2004) and Kewley et al. (2005) found that this is an acceptable approximation, if at least 20 per cent of the light of a galaxy is contained within the…”
Minor Galaxy Interactions: Star Formation Rates and Galaxy Properties (2007, background): “Kewley et al. (2005) demonstrate that a covering fraction of >20% is necessary to avoid substantial differences in nuclear and global measurements of star formation rates, extinction, and metallicity in their sample of 101 galaxies from the Nearby Field Galaxy Survey (Jansen et al. 2000a, 2000b).”
Gas metallicity diagnostics in star-forming galaxies (2006, background): “Kewley et al. (2005) reported that the introduced systematic error of the metallicity determination reaches up to ∼40% when the fiber covers only 20% of the total g′-band photons (see also Tremonti et al. 2004).”
Clues to the Origin of the Mass-Metallicity Relation: Dependence on Star Formation Rate and Galaxy Size (2007, methodology): “Once aperture effects and the use of a single metallicity diagnostic (e.g., Ellison & Kewley 2006; Kewley et al. 2005; Savaglio et al. 2005; Erb et al. 2006; Kewley & Ellison 2007) are accounted for, there is an offset to lower metallicities by about 0.3 dex for a galaxy of given mass at compared…”
Metallicity and Nuclear Star Formation in Nearby Galaxy Pairs: Evidence for Tidally Induced Gas Flows (2005, background): “This selection ensures that (1) we compare similar size galaxies to minimise aperture effects (see Kewley et al. 2005, for a discussion of aperture effects in the NFGS sample), and (2) there are sufficient numbers of galaxies in each 1-Mag luminosity bin for comparison.”
A fundamental plane for field star-forming galaxies (2010, background): “The lower limit in redshift ensures covering> 20% of the galaxy light, which is the minimum required to avoid domination of the spectrum by aperture eff cts (Kewley et al. 2005).”
The star formation activity of IllustrisTNG galaxies: main sequence, UVJ diagram, quenched fractions, and systematics (2018, background): “…is outlined by several authors who have highlighted the importance of quantifying the effect of apertures in measuring galaxies’ SFRs (Richards et al. 2016), both in the observational data (Kewley et al. 2005) and also in comparison with the predictions of theoretical model (Guidi et al. 2016).”
Metallicity Calibrations and the Mass-Metallicity Relation for Star-forming Galaxies (2008, methodology): “Covering fractions of 20 − 30% correspond to diameters of ∼ 5 kpc for the mean size of nearby star-forming galaxies (Kewley et al. 2005).”