2007MNRAS.374..910E

Query : 2007MNRAS.374..910E

2007MNRAS.374..910E - Mon. Not. R. Astron. Soc., 374, 910-930 (2007/January-3)

The stellar mass density at z ~ 6 from Spitzer imaging of i'-drop galaxies.

EYLES L.P., BUNKER A.J., ELLIS R.S., LACY M., STANWAY E.R., STARK D.P. and CHIU K.

Abstract (from CDS):

We measure the ages, stellar masses, and star formation histories of z ∼ 6 galaxies, observed within 1 Gyr of the big bang. We use imaging from the Hubble Space Telescope (HST) and the Spitzer Space Telescope from the public `Great Observatories Origins Deep Survey' (GOODS), coupled with ground-based near-infrared imaging, to measure their spectral energy distributions (SEDs) from 0.8-5µm, spanning the rest-frame ultraviolet (UV) and optical. From our sample of ~50 `i'-drop' Lyman-break star-forming galaxies in GOODS-South with z'AB< 27, we focus on ~30 with reliable photometric or spectroscopic redshifts. Half of these are confused with foreground sources at Spitzer resolution, but from the 16 with clean photometry we find that a surprisingly large fraction (40 per cent) have evidence for substantial Balmer/4000-Å spectral breaks. This indicates the presence of old underlying stellar populations that dominate the stellar masses. For these objects, we find ages of ∼200-700Myr, implying formation redshifts of 7 ≤ zf≤ 18, and large stellar masses in the range ∼1-3x1010M☉. Analysis of seven i'-drops that are undetected at 3.6µm indicates that these are younger, considerably less massive systems. We calculate that emission line contamination should not severely affect our photometry or derived results. Using SED fits out to 8µm, we find little evidence for substantial intrinsic dust reddening in our sources. We use our individual galaxy results to obtain an estimate of the global stellar mass density at z ∼ 6. Correcting for incompleteness in our sample, we find the z ∼ 6 comoving stellar mass density to be 2.5x106M☉/Mpc3. This is a lower limit, as post-starburst and dust-obscured objects, and also galaxies below our selection thresholds, are not accounted for. From our results, we are able to explore the star formation histories of our selected galaxies, and we suggest that the past global star formation rate may have been much higher than that observed at the z ∼ 6 epoch. The associated UV flux we infer at z > 7 could have played a major role in reionizing the Universe.

Abstract Copyright: 2006 The Authors. Journal compilation © 2006 RAS

Journal keyword(s): galaxies: evolution - galaxies: formation - galaxies: high-redshift - galaxies: starburst - galaxies: stellar content

Nomenclature: Table 1: [EBE2007] NN-NNNNN N=31.

Simbad objects: 40

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Number of rows : 40
N Identifier Otype ICRS (J2000)
RA 		ICRS (J2000)
DEC 		Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2026 		#notes
1 NAME HCM 6A EmG 02 39 54.737 -01 33 32.24           ~ 50 0
2 GOODS-MUSIC 8079 G 03 32 13.072 -27 49 00.76           ~ 3 0
3 GOODS-MUSIC 10793 EmG 03 32 13.41 -27 46 46.3           ~ 6 0
4 GOODS-MUSIC 9235 EmG 03 32 14.7383 -27 47 58.747   28.1763     27.2817 ~ 14 0
5 GOODS-MUSIC 15176 G 03 32 15.25 -27 43 08.9           ~ 3 0
6 GOODS J033217.81-275441.6 G 03 32 17.8079 -27 54 41.581   29.3482       ~ 4 0
7 [BIB2006] CDFS-2181947466 G 03 32 18.1867 -27 47 46.640   29.667 27.995 26.29 25.2328 ~ 18 1
8 GOODS-MUSIC 8187 EmG 03 32 18.298 -27 48 55.63           ~ 9 0
9 GOODS J033222.28-275257.2 G 03 32 22.2795 -27 52 57.210           ~ 14 0
10 GOODS-MUSIC 959 G 03 32 23.8413 -27 55 11.639           ~ 12 0
11 GOODS-MUSIC 9234 EmG 03 32 24.7974 -27 47 58.811         28.0406 ~ 16 0
12 NAME CDFS 3223-4627 G 03 32 25.1100 -27 46 35.674           ~ 9 0
13 GOODS-MUSIC 499 EmG 03 32 25.6058 -27 55 48.677         26.1883 ~ 33 0
14 GOODS-MUSIC 9858 G 03 32 27.38 -27 47 28.2           ~ 8 0
15 GOODS-MUSIC 15047 EmG 03 32 27.88 -27 43 15.6           ~ 10 0
16 NAME GOODS Southern Field reg 03 32 28.0 -27 48 30           ~ 1623 1
17 NAME Chandra Deep Field-South reg 03 32 28.0 -27 48 30           ~ 2282 1
18 GOODS-MUSIC 16458 G 03 32 29.01 -27 42 07.8           ~ 8 0
19 GOODS-MUSIC 4264 G 03 32 31.1984 -27 52 06.146           ~ 4 0
20 GOODS J033232.46-274001.9 G 03 32 32.4593 -27 40 01.927         28.6029 ~ 6 0
21 [BIB2006] CDFS-2331939491 G 03 32 33.1942 -27 39 49.111         27.6307 ~ 10 0
22 GOODS-MUSIC 13076 G 03 32 35.36 -27 44 57.1           ~ 5 0
23 GOODS-MUSIC 15052 G 03 32 36.345 -27 43 15.50           ~ 7 0
24 GOODS-MUSIC 10898 EmG 03 32 36.470 -27 46 41.44   29.56 31.02   26.54 ~ 25 0
25 GOODS-MUSIC 4361 G 03 32 36.83 -27 52 01.0           ~ 6 0
26 GOODS-MUSIC 16461 G 03 32 37.953 -27 42 07.60           ~ 11 0
27 NAME HUDF-J2 G 03 32 38.72681 -27 48 39.8845           ~ 26 1
28 EIS-DEEP CDFS-4 J 1 1349 BD? 03 32 38.8006 -27 49 53.656           ~ 19 0
29 GOODS-MUSIC 5207 G 03 32 38.9598 -27 51 16.628         27.9857 ~ 6 0
30 NAME Hubble Ultra Deep Field reg 03 32 39.0 -27 47 29           ~ 1900 0
31 GOODS-MUSIC 3912 EmG 03 32 39.0288 -27 52 23.104         27.0612 ~ 14 0
32 CXOCDFS J033240.0-274815 EmG 03 32 40.013 -27 48 14.99     29.013   26.7186 ~ 55 0
33 GLARE 3011 EmG 03 32 43.10 -27 45 17.6           ~ 6 0
34 GLARE 3002 EmG 03 32 43.34 -27 49 20.3           ~ 11 0
35 GLARE 3001 EmG 03 32 46.0406 -27 49 29.715         28.4753 ~ 31 0
36 GLARE 3030 EmG 03 32 48.94 -27 46 51.4           ~ 6 0
37 GOODS-MUSIC 10580 EmG 03 32 49.9821 -27 46 56.182         27.6131 ~ 12 0
38 GOODS-MUSIC 9135 G 03 32 52.2173 -27 48 04.776         28.4255 ~ 9 0
39 GOODS-MUSIC 7818 G 03 32 54.1007 -27 49 15.951           ~ 11 0
40 HD 42581B BD* 06 10 34.80 -21 52 00.0           T6.5 549 0

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