Star-formation rates and forbidden O II emission in blue galaxies

Gallagher, John S.; Hunter, D. A.; Bushouse, H.

doi:10.1086/115015

Cited by 136 publications

(174 citation statements)

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“…The strong, low ionization [O II] λλ 3727,3729 doublet is often used as a star-formation rate indicator in the absence of Hα measurements (e.g. Gallagher et al 1989;Lilly et al 1996;Kennicutt 1998;Rosa-González et al 2002;Kewley et al 2004 Cardelli et al 1989 extinction law). The Hα and Hβ emission lines originate from recombination to the n = 2 level of hydrogen, and therefore the intrinsic Hα/Hβ ratio can be accurately calculated using the relative lifetimes of the Hα (3 → 2) and Hβ (4 → 2) transitions.…”

Section: Motivationmentioning

confidence: 99%

Starburst–AGN mixing – II. Optically selected active galaxies

Davies

Kewley

et al. 2014

Monthly Notices of the Royal Astronomical Society

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We use 4 galaxies from the Calar Alto Legacy Integral Field Area (CALIFA) survey with clear signs of accretion onto supermassive black holes to investigate the relative contribution of star-formation and active galactic nucleus (AGN) activity to the lineemission of each galaxy as a function of radius. The combination of star-formation and AGN activity produces curved "mixing sequences" on standard optical diagnostic diagrams, and the fraction of emission due to AGN activity decreases smoothly with distance from the centre of the galaxy. We use the AGN activity profiles to calculate the size of the AGN narrow line regions, which have radii of ∼ 6.3 kpc. We calculate the fractional contribution of the star-formation and the AGN activity to the global Hα, [O II] λλ 3727,3729 and [O III] λ 5007 luminosities of each galaxy, and show that both ionization sources contribute significantly to the emission in all three lines. We use weighted combinations of stellar and AGN photoionization models to produce mixing models, which are consistent with observations for 85 percent of spaxels across the galaxies in our sample. We also present a new diagnostic for starburst-AGN mixing which requires only the [O II], [O III] and Hβ emission lines, and can therefore be used to calculate AGN fractions up to z ∼ 0.85 in the optical and z ∼ 3.5 in the nearinfrared. We anticipate that this diagnostic will facilitate studies of the properties of AGN ionizing radiation fields and the relative optical contribution of star-formation and AGN activity over cosmic time.

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Section: Motivationmentioning

confidence: 99%

Starburst–AGN mixing – II. Optically selected active galaxies

Davies

Kewley

et al. 2014

Monthly Notices of the Royal Astronomical Society

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“…for R < ∼ R SF , with R SF on the order of ∼1 kpc) and is practically negligible for larger radii where the evolved stellar LSB host entirely dominates the line-of-sight intensity (P02, Knollmann 2004). More generally, even though ne in local SFDGs may protrude beyond R SF (Hunter & Gallagher 1985;Gallagher et al 1989;Hunter & Gallagher 1990Meurer et al 1992;Marlowe et al 1995;Ferguson et al 1996;Martin 1998;Bomans 2002;Cairós et al 2002, among others), its extremely low surface brightness means it has no impact on surface photometry (P02, Knollmann 2004). As an example, even for BCDs with strong ongoing SF activity, corrections of integral photometric quantities for ne do not exceed ≈0.1 mag (Salzer et al 1989).…”

Section: Zw 18 As Local Morphological Template For Rapidly Assemblimentioning

confidence: 99%

I Zw 18 as morphological paradigm for rapidly assembling high-zgalaxies

Papaderos

Östlin

2012

A&A

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Context. I Zw 18, ever since regarded as the prototypical blue compact dwarf (BCD) galaxy, is, quite ironically, the most atypical BCD known. This is because its large low-surface brightness (LSB) envelope is not due to an old underlying stellar host, as invariably is the case for typical BCDs, but is entirely due to extended nebular emission. Aims. Our goal is to explore I Zw 18 and its detached C component I Zw 18 C down to an unprecedently faint surface brightness μ (mag/ ) level in order to gain further insight into the structural properties and evolutionary history of this enigmatic galaxy pair. Methods. We present a photometric analysis of the entire set of archival HST ACS V, R and I band data for I Zw 18. Results. Radial color profiles for I Zw 18 C reveal blue and practically constant colors (0 ± 0.05) down to μ ∼ 27.6, and a previously undisclosed, slightly redder (V − I ≈ 0.2), stellar population in its extreme periphery (μ ∼ 29). We argue that stellar diffusion over τ ∼ 10 8 yr and the associated stellar mass filtering effect can consistently account for the observed properties of the stellar component in the outskirts of I Zw 18 C. This process, in combination with propagating star formation with a mean velocity of ∼20 km s −1 can reproduce all essential characteristics of I Zw 18 C within ∼τ. An extremely faint substrate of older stars cannot be ruled out but does not need to be postulated. As for I Zw 18, we find that nebular emission (ne) extends out to ∼16 stellar scale lengths, shows a nearly exponential outer profile, and provides at least one third of the total optical emission. Nebular emission dominates already at μ ∼ 23.5, as evident from e.g. the uniform and extremely blue (V − I ≈ -1, R − I ≈ -1.4) colors of the LSB envelope of I Zw 18. Conclusions. The case of I Zw 18 suggests caution in studies of distant galaxies in dominant stages of their evolution, rapidly assembling their stellar mass at high specific star formation rates (SSFRs). It calls attention to the fact of ne not necessarily being cospatial with the underlying ionizing and non-ionizing stellar background. It also does not have to scale with the background surface density. The prodigious energetic output during dominant phases of galaxy evolution may result in large exponential ne envelopes, extending much beyond the still compact stellar component, just like in I Zw 18. Therefore, the morphological paradigm of I Zw 18, while probably unique in the nearby Universe, may be ubiquitous among high-SSFR galaxies at high redshift. Using I Zw 18 as reference, we show that extended ne may introduce substantial observational biases and affect several of the commonly studied fundamental galaxy relations. Among others, we show that the surface brightness profiles of distant morphological analogs to I Zw 18 may be barely distinguishable from Sérsic profiles with an exponent 2 < ∼ η < ∼ 5, thus mimicking the profiles of massive galaxy spheroids.

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“…Collisions between the same free electrons and singly ionized oxygen atoms produce the excited states that decay via the [O II] jj3726, 3729 transitions. It is therefore not surprising that the [O II] and Ha Ñuxes are correlated (e.g., Gallagher et al 1989 ;Kennicutt 1992a ;Tresse et al 1999). The empirical relation among the bluest local galaxies shows a scatter of a factor of 3 about the mean [O II] versus Hb relation, (Gallagher et al 1989 (Osterbrock 1989).…”

Section: Star Formation Rate Estimatesmentioning

confidence: 99%

“…It is therefore not surprising that the [O II] and Ha Ñuxes are correlated (e.g., Gallagher et al 1989 ;Kennicutt 1992a ;Tresse et al 1999). The empirical relation among the bluest local galaxies shows a scatter of a factor of 3 about the mean [O II] versus Hb relation, (Gallagher et al 1989 (Osterbrock 1989). Throughout this paper we adopt as a representative extinction A B \ 1.0 correction for dwarf irregular galaxies (e.g., Martin 1997), and the reddened Ha Ñux is predicted to be This 1.17F *O II+ .…”

Section: Star Formation Rate Estimatesmentioning

confidence: 99%

“…The major limitation of this method is the limited accuracy of [O II] as a tracer of the number of young massive stars. Fortunately, the [O II] Ñux from nearby galaxies correlates with their Ha luminosity, which is a direct measure of the SFR (Gallagher, Bushouse, & Hunter 1989 ;Kennicutt 1992a ;Tresse et al 1999). The scatter in this relation and uncertainty regarding the amount of attenuation from dust in the galaxies limit how accurately we can estimate SFRs for the objects we Ðnd, but the method does identify a much larger sample of candidates for follow-up studies than has previously been available.…”

Section: Introductionmentioning

confidence: 99%

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An Emission‐Line Search for Star‐forming Dwarf Galaxies toward Abell 851

Martin

Lotz

Ferguson

2000

ApJ

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We present deep images of the redshift z \ 0.41 galaxy cluster Abell 851 (Cl 0939]4713) including a narrow bandwidth image of the redshifted [O II] jj3726, 3729 line emission. The [O II] doublet is the most accessible tracer of star formation out to redshifts near unity, and we use it to identify candidates for star-forming galaxies. The galaxies selected lie within a projected clustercentric distance of 2 Mpc and have line-of-sight velocities with respect to the cluster in the range of^1460 km s~1. The sample is complete to magnitude for galaxies with emission-line equivalent widths greater than m 5129 (AB) \ 24.0 about 11 in the observed frame. The sample is contaminated by foreground galaxies with a steep 4000 A break across the Ðlters and possibly Lya emitters at z \ 3.31, but such galaxies can be identiÐed using A color, brightness, and equivalent-width criteria. Excluding the likely interlopers, the number density of star-forming galaxies near Cl 0939]4713 is still at least 3È4 times higher than that of a similar column through the Ðeld at z \ 0.4. Galaxies in the cluster sample have lower [O II] equivalent widths than similarly selected Ðeld galaxies at z D 0.4, however, and we suggest that while the density of galaxies is higher in the cluster the star formation activity in individual galaxies is suppressed relative to their counterparts in the Ðeld. The relatively small enhancement in the surface density of the [O II]-selected population toward the cluster core leads us to believe the [O II]-selected galaxies reside in the outer regions of the cluster. We identify a population of starburst galaxies among the [O II] emitters based on their blue g[i color. The majority of the [O II]-selected galaxies appear to be related to the normal spiral galaxy population, but the bursting population is dominated by intrinsically faint galaxies of below average size. We suggest that this population is composed primarily of dwarf galaxies and discuss their relation to the dwarf galaxies in present-day clusters.

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Star-formation rates and forbidden O II emission in blue galaxies

Cited by 136 publications

References 0 publications

Starburst–AGN mixing – II. Optically selected active galaxies

Starburst–AGN mixing – II. Optically selected active galaxies

I Zw 18 as morphological paradigm for rapidly assembling high-zgalaxies

An Emission‐Line Search for Star‐forming Dwarf Galaxies toward Abell 851

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