The UV continua and inferred stellar populations of galaxies at z ~7-9 revealed by the Hubble Ultra-Deep Field 2012 campaign

By J. Dunlop, A. B. Rogers, Ross J. McLure, Richard S. Ellis, B. Robertson, A. Koekemoer, P. Dayal, E. Curtis-Lake, V. Wild, S. Charlot and 9 more. 2012

148 citations recorded by the source corpus.

We use the new ultra-deep, near-infrared imaging of the Hubble Ultra-Deep Field (HUDF) provided by our UDF12 Hubble Space Telescope (HST) Wide Field Camera 3/IR campaign to explore the rest-frame ultraviolet (UV) properties of galaxies at redshifts z > 6.5. We present the first unbiased measurement of the average UV power-law index, 〈β〉, (fλ ∝ λ^β) for faint galaxies at z ≃ 7, the first meaningful measurements of 〈β〉 at z ≃ 8, and tentative estimates for a new sample of galaxies at z ≃ 9. Utilizing galaxy selection in the new F140W (J_140) imaging to minimize colour bias, and applying both colour and power-law estimators of β, we find 〈β〉 = −2.1 ± 0.2 at z ≃ 7 for galaxies with M_UV ≃ −18. This means that the faintest galaxies uncovered at this epoch have, on average, UV colours no more extreme than those displayed by the bluest star-forming galaxies at low redshift. At z ≃ 8 we find a similar value, 〈β〉 = −1.9 ± 0.3. At z ≃ 9, we find 〈β〉 = −1.8 ± 0.6, essentially unchanged from z ≃ 6 to 7 (albeit highly uncertain). Finally, we show that there is as yet no evidence for a significant intrinsic scatter in β within our new, robust z ≃ 7 galaxy sample. Our results are most easily explained by a population of steadily star-forming galaxies with either ≃ solar metallicity and zero dust, or moderately sub-solar (≃10–20 per cent) metallicity with modest dust obscuration (AV ≃ 0.1–0.2). This latter interpretation is consistent with the predictions of a state-of-the-art galaxy-formation simulation, which also suggests that a significant population of very-low metallicity, dust-free galaxies with β ≃ −2.5 may not emerge until M_UV > −16, a regime likely to remain inaccessible until the James Webb Space Telescope.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/5a786a36cdd8c3856d5e713520198248ec613df0

How researchers see this paper

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In Astronomy and Astrophysics

1. L. Hernquist
2. P. Hopkins
3. P. V. van Dokkum
4. Richard S. Ellis
5. M. Franx
6. R. Somerville
7. R. Dav'e
8. J. Dunlop

In Instrumentation

1. P. V. van Dokkum
2. Richard S. Ellis
3. M. Franx
4. R. Bouwens
5. J. Dunlop
6. I. Labbé
7. C. Conroy
8. P. Oesch

Citations in the corpus

• ALMA SPECTROSCOPIC SURVEY IN THE HUBBLE ULTRA DEEP FIELD: THE INFRARED EXCESS OF UV-SELECTED z = 2–10 GALAXIES AS A FUNCTION OF UV-CONTINUUM SLOPE AND STELLAR MASS (2016, background): “The impact of the scatter is asymmetric since faint blue sources – with β’s in the range of ∼ −2 to ∼ −2.3 (e.g., Wilkins et al. 2011; Dunlop et al. 2013; Kurczynski et al. 2014) – are already predicted to show essentially no dust emission and so the expected emission can only be larger when adding…”
• Ultraviolet emission lines in young low-mass galaxies at z ≃ 2: physical properties and implications for studies at z > 7 (2014, background): “Over the last several years, considerable effort has been focused on determining the distribution of UV-continuum slopes in galaxies at very high redshifts (e.g., Wilkins et al. 2011, Finkelst in et al. 2012, Rogers et al. 2013, Dunlop et al. 2013, Bouwens et al. 2012, 2013).”
• The bright end of the galaxy luminosity function at z≃7: before the onset of mass quenching? (2013, methodology): “…of β = −2.1 and β = −2.0 including the Y JHK and JHK bands respectively, are consistent with the value found for fainter galaxies at z ∼ 7 using the same fitting method (β = −2.1 ± 0.2; Rogers et al. 2013a; Dunlop et al. 2013) and using the colours directly (β = −2.33 ± 0.33; Bouwens et al. 2013).”
• The z ∼ 6 Luminosity Function Fainter than −15 mag from the Hubble Frontier Fields: The Impact of Magnification Uncertainties (2016, result): “…adopt a median value of −2.2 for the UV -continuum slope for galaxies in our simulations to match that found in the observations (e.g., Bouwens et al. 2014: see also Wilkins et al. 2011; Bouwens et al. 2012; Finkelstein et al. 2012; Dunlop et al. 2013; Rogers et al. 2014; Duncan & Conselice 2015).”
• Stellar population effects on the inferred photon density at reionization (2015, methodology): “…ultraviolet-luminous galaxies in this redshift range are directly observable (e.g Douglas et al. 2010; Stark et al. 2013; Dunlop et al. 2013), and the requirement that they maintain ionization of the intergalactic medium provides informative constraints on their Lyman…”
• UV-CONTINUUM SLOPES OF >4000 z ∼ 4–8 GALAXIES FROM THE HUDF/XDF, HUDF09, ERS, CANDELS-SOUTH, AND CANDELS-NORTH FIELDS (2013, methodology): “B.4.1 Source-By-Source Comparisons A comparison of the Dunlop et al. (2013) β measurements with our own β determinations is shown in Figure 22.”
• AN INTENSELY STAR-FORMING GALAXY AT z ∼ 7 WITH LOW DUST AND METAL CONTENT REVEALED BY DEEP ALMA AND HST OBSERVATIONS (2013, background): “We obtain β = −2.00± 0.57 for the entire system of Himiko, comparable to the average UV slope of ≃ L∗ LBGs, β = −2.09±0.22 (Bouwens et al. 2012, see also Dunlop et al. 2013).”
• New redshift z ≃ 9 galaxies in the Hubble Frontier Fields: implications for early evolution of the UV luminosity density (2014, background): “Third, such rapid evolution might also be viewed as unexpected given the known, relatively mature properties of galaxies at z ' 7 (Dunlop et al. 2012, 2013) and theoretical predictions of early structure growth (e.g. Jaacks et al. 2012; Kimm & Cen 2013; Paardekooper et al. 2013; Cai et al. 2014;…”
• The galaxy luminosity function at z ≃ 6 and evidence for rapid evolution in the bright end from z ≃ 7 to 5 (2014, methodology): “…deep near-infrared data, Willott et al. (2013) was able to measure βUV using an identical method, finding a mean value of βUV = −1.38± 0.2, which is redder than that found for fainter galaxies which tend to exhibit βUV ' −2.0 (Dunlop et al. 2013; Rogers et al. 2013; Bouwens et al. 2013).”
• A deep ALMA image of the Hubble Ultra Deep Field (2016, methodology): “…the UDF09 campaign (Oesch et al. 2010; Bouwens et al. 2010; Illingworth et al. 2013) followed by the UDF12 programme (Ellis et al. 2013; Koekemoer et al. 2013; Dunlop et al. 2013), has delivered the deepest near-infrared imaging ever achieved (reaching 30 AB mag, 5-σ) over an area of 4.5 arcmin2.”
• THE EVOLUTION OF THE GALAXY REST-FRAME ULTRAVIOLET LUMINOSITY FUNCTION OVER THE FIRST TWO BILLION YEARS (2014, background): “As a bevy of recent work has shown, this dust correction is important even out to z ~ 7–8 (e.g., Finkelstein et al. 2012b; Dunlop et al. 2013; Bouwens et al. 2014, see also Section 7).”
• REIONIZATION AFTER PLANCK: THE DERIVED GROWTH OF THE COSMIC IONIZING EMISSIVITY NOW MATCHES THE GROWTH OF THE GALAXY UV LUMINOSITY DENSITY (2015, methodology): “Alternatively, if we take ξion to be equal to 1025.2 s−1/(erg s−1 Hz−1) as R13 adopted to match with the β measurements of Dunlop et al. (2013), the relevant value of fesc is 0.20 0.04 0.05 - + (essentially identical to R13ʼs adopted value of 0.2).”
• LINE-EMITTING GALAXIES BEYOND A REDSHIFT OF 7: AN IMPROVED METHOD FOR ESTIMATING THE EVOLVING NEUTRALITY OF THE INTERGALACTIC MEDIUM (2014, background): “As such UV continuum slopes are now available for the growing body of z > 7 photometric galaxy samples(e.g. Dunlop et al. 2013; Bouwens et al. 2013), we can realize a Lyα fraction test that overcomes several of the issues associated with the earlier approach.”
• COSMIC REIONIZATION AND EARLY STAR-FORMING GALAXIES: A JOINT ANALYSIS OF NEW CONSTRAINTS FROM PLANCK AND THE HUBBLE SPACE TELESCOPE (2015, methodology): “Following Robertson et al. (2013), we adopt a fiducial escape fraction of fesc = 0.2 and, motivated by the restframe UV spectral energy distributions of z ∼ 7 − 8 galaxies (Dunlop et al. 2013), a fiducial Lyman continuum photon production efficiency of log10 ξion = 53.14 [Lyc photons s−1M−1⊙ yr].”
• UVUDF: ULTRAVIOLET THROUGH NEAR-INFRARED CATALOG AND PHOTOMETRIC REDSHIFTS OF GALAXIES IN THE HUBBLE ULTRA DEEP FIELD (2015, background): “…colors and luminosity function of high redshift galaxies (e.g., Bouwens et al. 2006; Ryan et al. 2007; Cameron & Driver 2009; Bouwens et al. 2011b; Dunlop et al. 2013; Schenker et al. 2013; McLure et al. 2013; Oesch et al. 2013; Bouwens et al. 2014), to observe the evolution in the star formation…”
• Spectroscopic detections of C iii] λ1909 Å at z ≃ 6–7: a new probe of early star-forming galaxies and cosmic reionization (2014, background): “Indeed the average stellar continuum of z ' 8 galaxies is indicative of older (100 Myr for constant star formation) stars (Dunlop et al. 2013, Labbé et al. 2013).”