Spitzer imaging of i′-drop galaxies: old stars at z≈ 6

Eyles, L.; Bunker, Andrew J.; Stanway, Elizabeth R.; Lacy, Mark; Ellis, Richard S.; Doherty, Michelle

doi:10.1111/j.1365-2966.2005.09434.x

Cited by 140 publications

(243 citation statements)

References 53 publications

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“…The local background is determined from an annulus of radius between 4 and 10 pixels. We find the source magnitude 26.0 ± 0.3, subject to a correction of −0.7 magnitude for the missing flux outside the aperture 36 . This magnitude derived from a small aperture is fainter by approximately 0.5 magnitude than that from GALFIT fitting.…”

Section: Irac Photometrymentioning

confidence: 85%

A magnified young galaxy from about 500 million years after the Big Bang

Zheng

Postman

Zitrin

et al. 2012

Nature

309

342

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The early Universe at redshift z∼6-11 marks the reionization of the intergalactic medium, following the formation of the first generation of stars. However, those young galaxies at a cosmic age of < ∼ 500 million years (Myr, at z > ∼ 10) remain largely unexplored as they are at or beyond the sensitivity limits of current large telescopes. Gravitational lensing by galaxy clusters enables the detection of high-redshift galaxies that are fainter than what otherwise could be found in the deepest images of the sky. We report the discovery of an object found in the multi-band observations of the cluster MACS1149+22 that has a high probability of being a gravitationally magnified object from the early universe. The object is firmly detected (12σ) in the two reddest bands of HST/WFC3, and not detected below 1.2 µm, matching the characteristics of z∼9 objects. We derive a robust photometric redshift of z = 9.6 ± 0.2, corresponding to a cosmic age of 490 ± 15 Myr (i.e., 3.6% of the age of the Universe).The large number of bands used to derive the redshift estimate make it one of the most accurate estimates ever obtained for such a distant object. The significant magnification by cluster lensing (a factor of ∼15) allows us to analyze the object's ultra-violet and optical luminosity in its rest-2 frame, thus enabling us to constrain on its stellar mass, star-formation rate and age. If the galaxy is indeed at such a large redshift, then its age is less than 200 Myr (at the 95% confidence level), implying a formation redshift of z f < ∼ 14. The object is the first z>9 candidate that is bright enough for detailed spectroscopic studies with JWST, demonstrating the unique potential of galaxy cluster fields for finding highly magnified, intrinsically faint galaxies at the highest redshifts.Observational cosmology has established that the age of the Universe is 13.7 billion years, and the reionization of the vast intergalactic medium (IGM) started around redshift z ∼ 11, 1 as the result of radiation from the first generation of stars. The task of probing the most distant Universe is progressively challenging: While more than 10 5 quasars have been found, only one is at z > 7; 2 while thousands of gamma-ray burst events have been recorded, only one 3 is confirmed at z=8.3; and while thousands of galaxy candidates have been found at z ∼ 6, only one has been reported at z ∼ 10, 4 which is based on a single-band detection. Galaxies at z ∼ 10 are expected to be at a magnitude of ∼ 29 (in the AB system, used hereafter) 4, 5 , near the detection limits of the deepest fields observed by Hubble Space Telescope (HST), and beyond the spectroscopic capability of even the next generation of large telescopes.In this Letter we report the discovery of a gravitationally lensed source whose most likely redshift is z ∼ 9.6. The source, hereafter called MACS1149-JD1, is selected from a near-infrared detection image at significance of 22σ. MACS1149-JD1 has a unique flux distribution characterized by a) no detection at Galaxy clusters are the largest r...

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Section: Irac Photometrymentioning

confidence: 85%

A magnified young galaxy from about 500 million years after the Big Bang

Zheng

Postman

Zitrin

et al. 2012

Nature

309

342

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“…Details of the observations have been described in detail elsewhere (Eyles et al 2005;Yan et al 2005;Stark et al 2007) so we do not discuss them further here. The 5σ limiting magnitudes of the IRAC imaging are 26.3 at 3.6 μm and 25.9 at 4.5 μm using 2.…”

Section: The Goods Fieldsmentioning

confidence: 99%

Properties ofz~ 3–6 Lyman break galaxies

Barros

Schaerer

Stark

2014

A&A

156

205

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Context. To gain insight on the mass assembly and place constraints on the star formation history (SFH) of Lyman break galaxies (LBGs), it is important to accurately determine their properties. Aims. We estimate how nebular emission and different SFHs affect parameter estimation of LBGs.Methods. We present a homogeneous, detailed analysis of the spectral energy distribution (SED) of ∼1700 LBGs from the GOODS-MUSIC catalogue with deep multi-wavelength photometry from the U band to 8 μm to determine stellar mass, age, dust attenuation, and star formation rate. Using our SED fitting tool, which takes into account nebular emission, we explore a wide parameter space. We also explore a set of different star formation histories. Results. Nebular emission is found to significantly affect the determination of the physical parameters for the majority of z ∼ 3−6 LBGs. We identify two populations of galaxies by determining the importance of the contribution of emission lines to broadband fluxes. We find that ∼65% of LBGs show detectable signs of emission lines, whereas ∼35% show weak or no emission lines. This distribution is found over the entire redshift range. We interpret these groups as actively star-forming and more quiescent LBGs, respectively. We find that it is necessary to considerer SED fits with very young ages (<50 Myr) to reproduce some colours affected by strong emission lines. Other arguments favouring episodic star formation and relatively short star formation timescales are also discussed. Considering nebular emission generally leads to a younger age, lower stellar mass, higher dust attenuation, higher star formation rate, and a large scatter in the SFR-M relation. Our analysis yields a trend of increasing specific star formation rate with redshift, as predicted by recent galaxy evolution models. Conclusions. The physical parameters of approximately two thirds of high redshift galaxies are significantly modified when we account for nebular emission. The SED models, which include nebular emission shed new light on the properties of LBGs with numerous important implications.

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“…Egami et al 2005;Schaerer & Pelló 2005;Eyles et al 2005;Verma et al 2007;Yabe et al 2009;Stark et al 2009;Lee et al 2010;Schaerer & de Barros 2010;González et al 2011), some of them imposing no dust attenuation, motivated by the blue UV slopes observed at high redshift. Notable examples are the work of Finlator et al (2007) who analyzed 6 galaxies at z > 5.5 with different SFHs, including rising ones taken from they hydrodynamic simulations.…”

Section: Introductionmentioning

confidence: 99%

Properties ofz ~ 3–6 Lyman break galaxies

Schaerer

Barros

Sklias

2012

A&A

150

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Context. The existence of a relation between the star formation rate (SFR) and stellar mass (M ) of galaxies, and the evolution of the specific star formation rate (sSFR = SFR/M ) are key questions for the understanding of early galaxy formation and evolution. Aims. We examine the dependence of derived physical parameters of distant Lyman break galaxies (LBGs) on the assumed star formation histories (SFHs) and age priors, their implications on the SFR-mass relation, and we propose observational tests to better constrain these quantities using IR observations and emission line studies. Methods. We use our spectral energy distribution (SED) fitting tool including the effects of nebular emission. We analyze a large sample of LBGs from redshift z ∼ 3 to 6, assuming five different star formation histories, extending thereby our first analysis of this sample , A&A, submitted, Paper II). In addition we predict the IR luminosities consistently with the SED fits, assuming that all radiation absorbed by dust is reemitted in the IR. Results. Compared to "standard" SED fits assuming constant SFR and neglecting nebular lines, models assuming variable SFHs yield systematically lower stellar masses, higher extinction, higher SFR, higher IR luminosities, and a wider range of equivalent widths for optical emission lines. Exponentially declining and delayed SFHs yield basically identical results. Exponentially rising SFHs with variable timescales yield similar masses, but somewhat higher extinction than exponentially declining ones. Distinguishing these SFHs from the currently available data is difficult. We find significant deviations between the derived SFR and IR luminosity from the commonly used SFR(IR) or SFR(IR+UV) calibration, due to differences in the SFHs and ages. For most LBGs at z > ∼ 3 we find that the standard calibrations will underestimate the true, current SFR derived from the SED fits, due to assumptions inconsistent with the SED models. Models with variable SFHs, favored statistically, yield generally a large scatter in the SFR-mass relation. We show the dependence of this scatter on assumptions of the SFH, the introduction of an age prior, and on the extinction law. We show that the true scatter in the SFR-mass relation can be significantly larger than inferred using SFR(UV) and/or SFR(IR), if the true star formation histories are variable and relatively young populations are present. We show that different SFHs, and hence differences in the derived SFR-mass relation and in the specific star formation rates, can be tested/constrained observationally with future IR observations with ALMA. Measurement of emission lines, such as Hα and [O ii] λ3727, can also provide useful constraints on the SED models, and hence test the predicted physical parameters. Conclusions. Important results such as the finding of a large scatter in the SFR-mass relation at high-z and an increase of the specific star formation rate with redshift above z > ∼ 3 (cf. Paper II) can be tested observationally using IR observations and m...

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Spitzer imaging of i′-drop galaxies: old stars at z≈ 6

Cited by 140 publications

References 53 publications

A magnified young galaxy from about 500 million years after the Big Bang

A magnified young galaxy from about 500 million years after the Big Bang

Properties ofz~ 3–6 Lyman break galaxies

Properties ofz ~ 3–6 Lyman break galaxies

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