CANDELS: THE EVOLUTION OF GALAXY REST-FRAME ULTRAVIOLET COLORS FROM z = 8 TO 4

By S. Finkelstein, C. Papovich, B. Salmon, K. Finlator, Mark Dickinson, H. Ferguson, M. Giavalisco, A. Koekemoer, Naveen A. Reddy, R. Bassett and 11 more. 2011

230 citations recorded by the source corpus.

We study the evolution of galaxy rest-frame ultraviolet (UV) colors in the epoch 4 ≲ z ≲ 8. We use new wide-field near-infrared data in the Great Observatories Origins Deep Survey-South field from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, Hubble Ultra Deep Field (HUDF) 2009, and Early Release Science programs to select galaxies via photometric redshift measurements. Our sample consists of 2812 candidate galaxies at z ≳ 3.5, including 113 at z ≃ 7–8. We fit the observed spectral energy distribution to a suite of synthetic stellar population models and measure the value of the UV spectral slope (β) from the best-fit model spectrum. We run simulations to show that this measurement technique results in a smaller scatter on β than other methods, as well as a reduced number of galaxies with catastrophically incorrect β measurements (i.e., Δβ > 1). We find that the median value of β evolves significantly from −1.82+0.00− 0.04 at z = 4 to −2.37+0.26− 0.06 at z = 7. Additionally, we find that faint galaxies at z = 7 have β = −2.68+0.39− 0.24 (∼ −2.4 after correcting for observational bias); this is redder than previous claims in the literature and does not require “exotic” stellar populations (e.g., very low metallicities or top-heavy initial mass functions) to explain their colors. This evolution can be explained by an increase in dust extinction, from low amounts at z = 7 to AV ∼ 0.5 mag at z = 4. The timescale for this increase is consistent with low-mass asymptotic giant branch stars forming the bulk of the dust. We find no significant (<2σ) correlation between β and MUV when measuring MUV at a consistent rest-frame wavelength of 1500 Å. This is particularly true at bright magnitudes, though our results do show evidence for a weak correlation at faint magnitudes when galaxies in the HUDF are considered separately, hinting that dynamic range in sample luminosities may play a role. We do find a strong correlation between β and the stellar mass at all redshifts, in that more massive galaxies exhibit redder colors. The most massive galaxies in our sample have similarly red colors at each redshift, implying that dust can build up quickly in massive galaxies and that feedback is likely removing dust from low-mass galaxies at z ⩾ 7. Thus, the stellar-mass—metallicity relation, previously observed up to z ∼ 3, may extend out to z = 7–8.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/e2fe5c0e70f3b8440f4f7960dde4fa65edc8c83a

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In Astronomy and Astrophysics

1. P. V. van Dokkum
2. Richard S. Ellis
3. L. Hernquist
4. P. Hopkins
5. M. Franx
6. C. Conroy
7. R. Bouwens
8. R. Somerville

In Instrumentation

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

Citations in the corpus

• THE UV LUMINOSITY FUNCTION OF STAR-FORMING GALAXIES VIA DROPOUT SELECTION AT REDSHIFTS z ∼ 7 AND 8 FROM THE 2012 ULTRA DEEP FIELD CAMPAIGN (2012, background): “Extending 0.25 magnitudes fainter in UV luminosity than any previous study, our determination of αz∼8 = −1.94 +0.21 −0.24 provides increased support for this evolution, in concert with the αz∼8 = −2.02 +0.22 −0.23 found by McLure et al. (2012).”
• THE EVOLUTION OF THE GALAXY REST-FRAME ULTRAVIOLET LUMINOSITY FUNCTION OVER THE FIRST TWO BILLION YEARS (2014, methodology): “…to sustain an ionized IGM by z ~ 6, and perhaps as high as z = 7–8, if one assumes that galaxies at least 5 mag below the detection limit of HST exist (e.g., Finkelstein et al. 2012a; Robertson et al. 2013); however, the unknown ionizing photon escape fraction is a major systematic uncertainty.”
• UV LUMINOSITY FUNCTIONS AT REDSHIFTS z ∼ 4 TO z ∼ 10: 10,000 GALAXIES FROM HST LEGACY FIELDS (2014, background): “…one could consider selecting z ∼ 4-10 samples based on the best-fit photometric redshift or redshift likelihood contours (e.g., McLure et al. 2010; Finkelstein et al. 2012; Bradley et al. 2013: see Figure 1 [right]), our Lyman-Break selection procedure has the advantage of greater simplicity…”
• NEW CONSTRAINTS ON COSMIC REIONIZATION FROM THE 2012 HUBBLE ULTRA DEEP FIELD CAMPAIGN (2013, background): “In the intervening period before the UDF12 data was acquired, several workers argued against such extreme values (Finkelstein et al. 2010, 2012; McLure et al. 2011; Dunlop et al. 2012a; Bouwens et al. 2012a; Rogers et al. 2012).”
• KECK SPECTROSCOPY OF 3 < z < 7 FAINT LYMAN BREAK GALAXIES: THE IMPORTANCE OF NEBULAR EMISSION IN UNDERSTANDING THE SPECIFIC STAR FORMATION RATE AND STELLAR MASS DENSITY (2012, background): “Galaxies at higher redshifts have bluer UV continuua (e.g., Bouwens et al. 2012b, Finkelstein et al. 2012), reducing the dust-corrected SFR for a given MUV.”
• THE EVOLUTION OF THE GALAXY STELLAR MASS FUNCTION AT z = 4–8: A STEEPENING LOW-MASS-END SLOPE WITH INCREASING REDSHIFT (2015, methodology): “…2011; Oesch et al. 2012; Schenker et al. 2013b; Lorenzoni et al. 2013; Finkelstein et al. 2015; Bouwens et al. 2015), the rest-frame UV spectral slope (e.g., Finkelstein et al. 2012; Bouwens et al. 2014), and the cosmic star formation rate density (SFRD; see Madau & Dickinson 2014 for a review).”
• The Dearth of z ∼ 10 Galaxies in All HST Legacy Fields—The Rapid Evolution of the Galaxy Population in the First 500 Myr (2017, methodology): “…out to z ∼ 8, large galaxy samples have now been identified and used for the study of galaxy build up (e.g. Bouwens et al. 2011b, 2015; Bradley et al. 2014; Finkelstein et al. 2012a; Schenker et al. 2013; McLure et al. 2013; Schmidt et al. 2014; Barone-Nugent et al. 2014; Stefanon et al. 2017b).”
• REIONIZATION AFTER PLANCK: THE DERIVED GROWTH OF THE COSMIC IONIZING EMISSIVITY NOW MATCHES THE GROWTH OF THE GALAXY UV LUMINOSITY DENSITY (2015, background): “…universe (e.g., Choudhury & Ferrara 2006; Bolton & Haehnelt 2007; Oesch et al. 2009; Trenti et al. 2010; Alvarez et al. 2012; Bouwens et al. 2012a; Finkelstein et al. 2012a; Haardt & Madau 2012 [HM12]; Kuhlen & FaucherGiguère 2012 [KF12]; Shull et al. 2012; Robertson et al. 2013 [R13], 2015…”
• A new multifield determination of the galaxy luminosity function at z = 7-9 incorporating the 2012 Hubble Ultra-Deep Field imaging (2012, methodology): “52 22 v3 [ as tr oph the Universe (e.g. Robertson et al. 2010; Finkelstein et al. 2012; Kuhlen & Faucher-Giguére 2012), and, if so, providing more detailed information on how reionization proceeded (as compared to the integrated constraints on ‘instantaneous’ reionization provided by current…”
• A CENSUS OF STAR-FORMING GALAXIES IN THE Z ∼ 9–10 UNIVERSE BASED ON HST+SPITZER OBSERVATIONS OVER 19 CLASH CLUSTERS: THREE CANDIDATE Z ∼ 9–10 GALAXIES AND IMPROVED CONSTRAINTS ON THE STAR FORMATION RATE DENSITY AT Z ∼ 9.2 (2012, methodology): “We take the UV -continuum slope β of galaxies in our simulations to have a mean value and 1σ scatter of −2.3 and 0.45, respectively, to match the observed trends extrapolated to z ∼ 8-9 (Bouwens et al. 2012b; Finkelstein et al. 2012; Bouwens et al. 2014a).”
• THE ORIGIN AND OPTICAL DEPTH OF IONIZING RADIATION IN THE “GREEN PEA” GALAXIES (2013, background): “Estimates of the galactic escape fraction necessary to sustain reionization range from < 13% to ≥ 50%, depending on the luminosity function and redshift assumed (Finkelstein et al. 2012).”
• UV-CONTINUUM SLOPES OF >4000 z ∼ 4–8 GALAXIES FROM THE HUDF/XDF, HUDF09, ERS, CANDELS-SOUTH, AND CANDELS-NORTH FIELDS (2013, methodology): “In particular, Finkelstein et al. (2012) measure bluer β’s for the brightest z ∼ 4 sources than we measure and redder β’s for the faintest z ∼ 4 sources.”
• The UV continua and inferred stellar populations of galaxies at z ~7-9 revealed by the Hubble Ultra-Deep Field 2012 campaign (2012, background): “Specifically, Finkelstein et al. (2010) reported 〈β〉 = −3.07 ± 0.51, while Finkelstein et al. (2012) reported a median value of 〈β〉 = −2.68+0.39−0.24 which becomes −2.45 after bias correction.”
• Directly Observing the Galaxies Likely Responsible for Reionization (2016, background): “These parameters together combine to provide a distribution of UV slopes β, designed to match the distribution we expect in galaxies at these redshifts (Finkelstein et al. 2012; Bouwens et al. 2014).”
• THE RELATION BETWEEN STAR FORMATION RATE AND STELLAR MASS FOR GALAXIES AT 3.5 ⩽ z ⩽ 6.5 IN CANDELS (2014, background): “Finkelstein et al. (2012a) concluded that if galaxies are the main contributors to reionization, then the escape fraction must be fesc < 0.34, or fesc < 0.13 (2σ) at z ∼ 6 if the luminosity function extends to fainter galaxies than those observed, in order for the inferred ionization from galaxies…”
• 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).”