THE STELLAR MASS DENSITY AND SPECIFIC STAR FORMATION RATE OF THE UNIVERSE AT z ∼ 7

By V. González, I. Labbé, R. Bouwens, G. Illingworth, M. Franx, M. Kriek, G. Brammer. 2009

229 citations recorded by the source corpus.

We use a robust sample of 11 z ∼ 7 galaxies (z850 dropouts) to estimate the stellar mass density (SMD) of the universe when it was only ∼750 Myr old. We combine the very deep optical to near-infrared photometry from the Hubble Space Telescope Advanced Camera for Surveys and NICMOS cameras with mid-infrared Spitzer Infrared Array Camera (IRAC) imaging available through the GOODS program. After carefully removing the flux from contaminating foreground sources, we have obtained reliable photometry in the 3.6 μm and 4.5 μm IRAC channels. The spectral shapes of these sources, including their rest-frame optical colors, strongly support their being at z ∼ 7 with a mean photometric redshift of 〈z〉 = 7.2 ± 0.5. We use Bruzual & Charlot synthetic stellar population models to constrain their stellar masses and star formation histories. We find stellar masses that range over (0.1–12) × 109 M☉ and average ages from 20 Myr to 425 Myr with a mean of ∼300 Myr, suggesting that in some of these galaxies most of the stars were formed at z > 8 (and probably at z ≳ 10). The best fits to the observed SEDs are consistent with little or no dust extinction, in agreement with recent results at z ∼ 4–8. The star formation rates (SFRs) are in the range from 5 to 20 M☉ yr-1. From this sample, we measure an SMD of 6.6+5.4−3.3 × 105 M☉ Mpc-3 to a limit of MUV,AB < −20 (or 0.4L*z = 3). Combined with a fiducial lower limit for their ages (80 Myr), this implies a maximum SFR density of 0.008 M☉ yr−1 Mpc−3. This is well below the critical level needed to reionize the universe at z ∼ 8 using standard assumptions. However, this result is based on luminous sources (>L*) and does not include the dominant contribution of the fainter galaxies. Strikingly, we find that the specific SFR is constant from z ∼ 7 to z ∼ 2 but drops substantially at more recent times.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/4bd71ea3d73f6c645a2e1d63bb76b6ea4b497ea2

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In Astronomy and Astrophysics

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

In Instrumentation

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

Citations in the corpus

• UV-CONTINUUM SLOPES AT z  ∼  4–7 FROM THE HUDF09+ERS+CANDELS OBSERVATIONS: DISCOVERY OF A WELL-DEFINED UV COLOR–MAGNITUDE RELATIONSHIP FOR z ⩾ 4 STAR-FORMING GALAXIES (2011, methodology): “The SFR densities implied by several recent stellar mass density determinations (e.g., Stark et al. 2009; González et al. 2010; Labbé et al. 2010a,b; González et al. 2011) are presented in Figure 20, and there is remarkably good agreement over the redshift range z ∼ 4-6.”
• THE CHARACTERISTIC STAR FORMATION HISTORIES OF GALAXIES AT REDSHIFTS z ∼ 2–7 (2012, background): “16 The difference in the mean stellar mass, and hence mean specific SFR, that results from using CB11 versus Bruzual & Charlot (2003) models (the latter have been used in other studies; e.g., González et al. 2010) is negligible compared to the intrinsic dispersion in specific SFR.”
• CRITICAL STAR FORMATION RATES FOR REIONIZATION: FULL REIONIZATION OCCURS AT REDSHIFT z ≈ 7 (2012, background): “With a comoving SFR density ρ̇∗ 0.01 M yr−1 Mpc−3 at z ≈ 7 (González et al. 2010; Bouwens et al. 2011a), the observed galaxies do not produce enough ionizing photons in the Lyman continuum (LyC) to maintain a photoionized IGM against recombinations.”
• Star formation rates and masses of z∼ 2 galaxies from multicolour photometry (2010, background): “…true, the implied cosmic SFR should rapidly vanish by z ∼ 3, while this is far from happening: the cosmic SFR at z ∼ 3 is nearly as high as it is at z ∼ 2 (e.g., Hopkins & Beacom 2006), and the specific SFR at a given mass stays at the same high level all the way to z ∼ 7 (Gonzalez et al. 2010).”
• EVOLUTION OF GALAXY STELLAR MASS FUNCTIONS, MASS DENSITIES, AND MASS-TO-LIGHT RATIOS FROM z ∼ 7 TO z ∼ 4 (2010, methodology): “To obtain 6 Slightly modified, Bouwens et al. 2010, in prep. reliable IRAC fluxes we use the deblending method of Labbé et al. (2006, see also González et al. 2010; Labbé et al. 2010b,a; Wuyts et al. 2007; de Santis et al. 2007).”
• THE STAR FORMATION MASS SEQUENCE OUT TO z = 2.5 (2012, background): “Galaxies show a strong correlation between their star formation rate (SFR) and stellar mass (M⋆) from z = 0 to the earliest observed epoch, z = 7 (e.g., Brinchmann et al. 2004; Noeske et al. 2007; Elbaz et al. 2007; Daddi et al. 2007; Pannella et al. 2009; Magdis et al. 2010; González et al. 2010).”
• CANDELS: THE CONTRIBUTION OF THE OBSERVED GALAXY POPULATION TO COSMIC REIONIZATION (2012, background): “The specific star-formation rate (sSFR; starformation rate per unit mass) is remarkably constant from z∼ 4–7 (e.g., Stark et al. 2009; González et al. 2010).”
• METALLICITY-DEPENDENT QUENCHING OF STAR FORMATION AT HIGH REDSHIFT IN SMALL GALAXIES (2011, methodology): “Evolution of sSFR at Fixed Stellar Mass Another common observational method is to examine the properties of galaxies at fixed stellar mass across a range in redshift (e.g. Papovich et al. 2006; Stark et al. 2009; González et al. 2010).”
• CANDELS: THE COSMIC ASSEMBLY NEAR-INFRARED DEEP EXTRAGALACTIC LEGACY SURVEY (2011, unknown): “Furthermore, the data, though noisy, show a constant ratio of SFR to stellar mass at all redshifts z > 3 (González et al. 2010).”
• Accretion-driven evolution of black holes: Eddington ratios, duty cycles and active galaxy fractions (2011, methodology): “The grey bands indicate the uncertainties around the measured SSFR as catalogued and derived by González et al. (2010) for galaxies with stellar mass ∼ 5 × 109 − 1010M⊙.”
• THE SPECTRAL ENERGY DISTRIBUTIONS OF z ∼ 8 GALAXIES FROM THE IRAC ULTRA DEEP FIELDS: EMISSION LINES, STELLAR MASSES, AND SPECIFIC STAR FORMATION RATES AT 650 MYR (2012, methodology): “…of substantial stellar masses ∼ 109 − 1010M⊙ (Eyles et al. 2005; Yan et al. 2006; Stark et al. 2009) and stellar ages (> 300Myr) (Labbé et al. 2006; González et al. 2010; 1 Based on observations made with the NASA/ESA Hubble Space Telescope, which is operated by the Association of…”
• STELLAR POPULATIONS OF Lyα EMITTERS AT z ∼ 6–7: CONSTRAINTS ON THE ESCAPE FRACTION OF IONIZING PHOTONS FROM GALAXY BUILDING BLOCKS (2010, methodology): “We do not use two zdropout candidates reported by Capak et al. (2009) and 11 z850LP-dropouts discovered by González et al. (2010), because they are too bright (the former have J ∼ 23 and the latter J110W ∼ 26 − 27.5).”
• On the origin of the galaxy star‐formation‐rate sequence: evolution and scatter (2009, methodology): “Note, though, that the high-redshift (z 4) data have not been corrected for extinction as observations indicate that there is little or no extinction in these galaxies (Gonzalez et al. 2010).”
• DISCOVERY OF z ∼ 8 GALAXIES IN THE HUBBLE ULTRA DEEP FIELD FROM ULTRA-DEEP WFC3/IR OBSERVATIONS (2009, background): “Only ∼25 high-quality z ∼ 7 candidates are known (e.g., Bouwens et al. 2008; Oesch et al. 2009; Ouchi et al. 2009; Castellano et al. 2009; Gonzalez et al. 2009; R.J. Bouwens et al. 2009, in prep).”
• THE MOST LUMINOUS z ∼ 9–10 GALAXY CANDIDATES YET FOUND: THE LUMINOSITY FUNCTION, COSMIC STAR-FORMATION RATE, AND THE FIRST MASS DENSITY ESTIMATE AT 500 Myr (2013, methodology): “Our tests show that we can map the kernel to high precision and perform excellent subtractions (see, e.g., Labbé et al. 2010a, 2010b, 2013; González et al. 2010, 2012).”
• GOODS-HERSCHEL: STAR FORMATION, DUST ATTENUATION, AND THE FIR–RADIO CORRELATION ON THE MAIN SEQUENCE OF STAR-FORMING GALAXIES UP TO z ≃ 4 (2014, methodology): “Intriguingly enough, this underprediction of SFR conspire to create a plateau of the UV derived SSFR values atz ≥ 2 which was indeed observed in previous studies (see, e.g., Daddi et al. 2009; Stark et al. 2009; González et al. 2010).”
• A UNIFIED EMPIRICAL MODEL FOR INFRARED GALAXY COUNTS BASED ON THE OBSERVED PHYSICAL EVOLUTION OF DISTANT GALAXIES (2012, methodology): “…(1+min(z, zevo))γMS , (2) wheresS FRMS,0 is the sSFR at z=0 for M⋆ = 1011 M⊙ and βMS parametrizes the dependance of sSFR onM⋆. γMS describes the evolution of the normalization of the MS out to redshift zevo = 2.5 where this evolution flattens according to observations (e.g. González et al. 2010).”