The star formation rate of the Universe at z~ 6 from the Hubble Ultra-Deep Field

By A. Bunker, E. Stanway, Richard S. Ellis, R. G. M. U. O. Exeter, I. O. Astronomy, Cambridge, Caltech Astronomy. 2004

234 citations recorded by the source corpus.

We determine the abundance of i′-band dropouts in the recently released HST/ACS Hubble Ultra-Deep Field (UDF). Because the majority of these sources are likely to be z≈ 6 galaxies whose flux decrement between the F775W i′-band and F850LP z′-band arises from Lyman-α absorption, the number of detected candidates provides a valuable upper limit to the unextincted star formation rate at this redshift. We demonstrate that the increased depth of UDF enables us to reach an 8 σ limiting magnitude of z′AB= 28.5 (equivalent to 1.5 h−270 M⊙ yr−1 at z= 6.1, or 0.1 L⋆UV for the z≈ 3U-drop population), permitting us to address earlier ambiguities arising from the unobserved form of the luminosity function. We identify 54 galaxies (and only one star) at z′AB 1.3 over the deepest 11-arcmin2 portion of the UDF. The characteristic luminosity (L⋆) is consistent with values observed at z≈ 3. The faint end slope (α) is less well constrained, but is consistent with only modest evolution. The main change appears to be in the number density (Φ*). Specifically, and regardless of possible contamination from cool stars and lower-redshift sources, the UDF data support our previous result that the star formation rate at z≈ 6 was approximately six times less than at z≈ 3. This declining comoving star formation rate [0.005 h70 M⊙ yr−1 Mpc−3 at z≈ 6 at LUV > 0.1 L⋆ for a Salpeter initial mass function (IMF)] poses an interesting challenge for models which suggest that LUV > 0.1 L⋆ star-forming galaxies at z≃ 6 reionized the Universe. The short-fall in ionizing photons might be alleviated by galaxies fainter than our limit, or a radically different IMF. Alternatively, the bulk of reionization might have occurred at z≫ 6.

Subfields: Astronomy and Astrophysics, Instrumentation

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In Astronomy and Astrophysics

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

In Instrumentation

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

Citations in the corpus

• Galaxy UV-luminosity function and reionization constraints on axion dark matter (2014, background): “…function is a measure of the number density, per absolute magnitude, of the star-forming galaxies that are likely to be the primary driver of reionisation (Madau, Haardt & Rees 1999; Bunker et al. 2004; Yan & Windhorst 2004; Oesch et al. 2009; Kuhlen & Faucher-Giguère 2012; Robertson et al. 2013).”
• Measurements of the UV background at 4.6 < z < 6.4 using the quasar proximity effect (2010, background): “Direct searches for these sources atz & 6 − 10 have taken advantage of recent very deep optical and near-infrared imaging from both the ground and space (Bunker et al. 2004; Bouwens et al. 2006; Yoshida etal.”
• Keeping the Universe ionized: photoheating and the clumping factor of the high-redshift intergalactic medium (2008, background): “6 (e.g. Stanway, Bunker, & McMahon 2003; Lehnert & Bremer 2003; Bunker et al. 2004; Bouwens et al. 2004; Yan & Windhorst 2004; Sawicki & Thompson 2006; Bouwens et al. 2006; Mannucci et al. 2007; Oesch et al. 2008; Bouwens et al. 2008), on the other hand, may imply star formation rate (SFR)…”
• The Universe Is Reionizing at z ∼ 7: Bayesian Inference of the IGM Neutral Fraction Using Lyα Emission from Galaxies (2017, background): “…in these galaxies are likely the primary sources of reionizing photons (e.g., Lehnert & Bremer 2003; Bouwens et al. 2003; Yan & Windhorst 2004; Bunker et al. 2004; Finkelstein et al. 2012a; Robertson et al. 2013; Schmidt cmason@astro.ucla.edu et al. 2014), though a contribution from AGN…”
• The Connection between Galaxies and Intergalactic Absorption Lines at Redshift 2 ≲ z ≲ 3 (2005, background): “(In fact it appears to be significantly lower at z >∼ 5; Bunker et al. 2004.)”
• The Mass Assembly Histories of Galaxies of Various Morphologies in the GOODS Fields (2005, background): “…(UV continua, recombination lines and submm emission) has enabled determinations of the co-moving star formation (SF) density at various redshifts whose rise and decline around z ≃ 2 points to the epoch when most stars were born (e.g. Rudnick et al. 2003; Bouwens et al. 2003; Bunker et al. 2004).”
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• Observational Constraints on Cosmic Reionization (2006, background): “…D., Blakeslee, J. P., & Franx, M. 2006, ApJ, in press (astro-ph/0509641) Bowman et al. 2005Bowman, J, Morales, M., Hewitt, J. 2005, ApJ, 638, 20-28 Bunker et al. 2004Bunker, A. J., Stanway, E. R., Ellis, R. S., & McMahon, R. G. 2004, MNRAS, 355: 374-384 Carilli et al 2004aCarilli, C., Gnedin, N.,…”
• Intergalactic Photon Spectra from the Far-IR to the UV Lyman Limit for 0 < z < 6 and the Optical Depth of the Universe to High-Energy Gamma Rays (2005, background): “This later assumption is supported by the recent Hubble deep survey results (Bunker et al. 2004 and references therein; Bouwens, R.J., Illingworth, G.D., Blakeslee, J.P. & Franx, M. 2005) which indicate that the average star formation rate is dropping off significantly at a redshift of 6.”
• The contribution of high-redshift galaxies to cosmic reionization: New results from deep WFC3 imaging of the Hubble Ultra Deep Field (2009, methodology): “We thank Richard McMahon, Jim Dunlop, Ross McLure, Masami Ouchi, Bahram Mobasher and Michele Cirasuolo for many useful discussions about Lyman break galaxies at high redshift.”
• Galaxies in the Hubble Ultra Deep Field. I. Detection, Multiband Photometry, Photometric Redshifts, and Morphology (2006, background): “Addressing the issue of reionization, previous authors (Bunker et al. 2004; Stanway et al. 2005; Yan & Windhorst 2004; Bouwens et al. 2005) have identified i′-dropouts in the UDF.”
• The Subaru/XMM-Newton Deep Survey (SXDS). IV. Evolution of Lyα Emitters from z = 3.1 to 5.7 in the 1 deg2 Field: Luminosity Functions and AGN (2007, background): “TheUVLFs of dropout galaxies show a significant decrease in luminosity and/or number density from z 4 to 6 (e.g., Lehnert & Bremer 2003; Ouchi et al. 2004a; Shimasaku et al. 2005; Bunker et al. 2004).”
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