ABSTRACT
Based on broadband/narrowband photometry and Keck DEIMOS spectroscopy, we report a redshift of z = 4.64+0.06−0.08 for AzTEC/COSMOS 1, the brightest submillimeter galaxy (SMG) in the AzTEC/COSMOS field. In addition to the COSMOS-survey X-ray to radio data, we report observations of the source with Herschel/PACS (100, 160 μm), CSO/SHARC II (350 μm), and CARMA and PdBI (3 mm). We do not detect CO(5 → 4) line emission in the covered redshift ranges, 4.56–4.76 (PdBI/CARMA) and 4.94–5.02 (CARMA). If the line is within this bandwidth, this sets 3σ upper limits on the gas mass to ≲8 × 109 M☉ and ≲5 × 1010 M☉, respectively (assuming similar conditions as observed in z ∼ 2 SMGs). This could be explained by a low CO-excitation in the source. Our analysis of the UV–IR spectral energy distribution of AzTEC 1 shows that it is an extremely young (≲50 Myr), massive (M* ∼ 1011 M☉), but compact (≲2 kpc) galaxy, forming stars at a rate of ∼1300 M☉ yr−1. Our results imply that AzTEC 1 is forming stars in a "gravitationally bound" regime in which gravity prohibits the formation of a superwind, leading to matter accumulation within the galaxy and further generations of star formation.
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1. INTRODUCTION
Submillimeter galaxies (SMGs; S850 μm>5 mJy) are ultra-luminous, dusty starbursting systems with extreme star formation rates (SFRs ∼ 100–1000 M☉ yr−1; e.g., Blain et al. 2002). The bulk of this population has been shown to lie at 2 < z < 3 (e.g., Chapman et al. 2005). However, only recently have blank-field submillimeter surveys started to discover the high-redshift (z>4) tail of the SMG distribution. To date seven z>4 SMGs have been spectroscopically confirmed (and published: three in GOODS-N, Daddi et al. 2009a, 2009b; two in COSMOS, Capak et al. 2008; Schinnerer et al. 2008; Riechers et al. 2010; Capak et al. 2011; one in ECDFS, Coppin et al. 2009, 2010; and one in A2218, Knudsen et al. 2010). These high-redshift SMGs, presenting a challenge to cosmological models of structure growth (see, e.g., Coppin et al. 2009), may alter our understanding of the role of SMGs in galaxy evolution.
Galaxies are thought to evolve in time from an initial stage with irregular/spiral morphology toward passive, very massive elliptical systems (M*>1011 M☉; e.g., Faber et al. 2007). The morphology and spectral properties of passive galaxies indicate that they have formed in a single intense burst at z>4 (e.g., Cimatti et al. 2008). SMGs represent short-lasting (≪100 Myr) starburst episodes of the highest known intensity. Thus, they would be the perfect candidates for z ∼ 2 passive galaxy progenitors. In this Letter, we report on a new z>4 SMG–AzTEC/COSMOS 1 (AzTEC 1 hereafter), the brightest SMG detected in the AzTEC–COSMOS field (Scott et al. 2008).
We adopt H0 = 70, ΩM = 0.3, ΩΛ = 0.7, use a Salpeter initial mass function, and AB magnitudes.
2. DATA
The available photometric (X-ray–radio) data for AzTEC 1 (α = 09:59:42.863, δ = +02:29:38.19) are summarized in Table 1. Its optical/IR counterpart—identified by Younger et al. (2007) in follow-up Submillimeter Array (SMA) observations of the original JCMT/AzTEC 1.1 mm detection (Scott et al. 2008)—has been targeted by the COSMOS project (Scoville et al. 2007) in more than 30 filters: ground-based optical/NIR imaging in 22 bands (Capak et al. 2007),30 Chandra (Elvis et al. 2009), GALEX (Zamojski et al. 2007), Hubble Space Telescope (HST; Scoville et al. 2007; Koekemoer et al. 2009; Leauthaud et al. 2007), Spitzer (Sanders et al. 2007), and Very Large Array (VLA; Schinnerer et al. 2007, 2010, V. Smolčić et al. 2011, in preparation; see Table 1).
Table 1. AzTEC 1 Photometry
| Wavelength | Band/Telescope | Flux Density (μJy) |
|---|---|---|
| 0.5–2 keV | Chandra-soft-band | <0.0003a,b |
| 1551 Å | FUV | <0.20a |
| 2307 Å | NUV | <0.09a |
| 3911 Å | u* | <0.01a |
| 4270 Å | IA427 | <0.03a |
| 4440 Å | BJ | <0.01a |
| 4640 Å | IA464 | <0.04a |
| 4728 Å | g+ | <0.03a |
| 4840 Å | IA484 | <0.03a |
| 5050 Å | IA505 | <0.04a |
| 5270 Å | IA527 | <0.03a |
| 5449 Å | VJ | <0.02a |
| 5740 Å | IA574 | 0.09 ± 0.04 |
| 6240 Å | IA624 | 0.08 ± 0.04 |
| 6295 Å | r+ | 0.12 ± 0.02 |
| 6790 Å | IA679 | 0.20 ± 0.04 |
| 7090 Å | IA709 | 0.25 ± 0.04 |
| 7110 Å | NB711 | 0.26 ± 0.10 |
| 7380 Å | IA738 | 0.24 ± 0.05 |
| 7641 Å | i+ | 0.29 ± 0.02 |
| 7670 Å | IA767 | 0.26 ± 0.05 |
| 8040 Å | F814W | 0.31 ± 0.02 |
| 8150 Å | NB816 | 0.21 ± 0.05 |
| 8270 Å | IA827 | 0.33 ± 0.06 |
| 9037 Å | z+ | 0.35 ± 0.07 |
| 12444 Å | J | <0.5a |
| 16310 Å | H | 1.03 ± 0.22 |
| 21537 Å | Ks | 1.33 ± 0.23 |
| 3.6 μm | IRAC1 | 3.87 ± 0.13 |
| 4.5 μm | IRAC2 | 4.53 ± 0.23 |
| 5.8 μm | IRAC3 | 7.90 ± 4.50 |
| 8.0 μm | IRAC4 | 13.01 ± 2.88 |
| 16 μm | IRS-16 | 12.80 ± 4.20 |
| 24 μm | MIPS-24 | 46.40 ± 4.90 |
| 70 μm | MIPS-70 | <2600a |
| 100 μm | PACS-100 | <3600a |
| 160 μm | MIPS-160 | <8200a |
| 160 μm | PACS-160 | <6900a |
| 350 μm | CSO | <15000a |
| 450 μm | SCUBA-2 | <44000a |
| 850 μm | SCUBA-2 | 16000 ± 3500 |
| 890 μm | SMA | 15600 ± 1100 |
| 1.1 mm | JCMT/AzTEC | 9300 ± 1300 |
| 1.3 mm | CARMA | 9400 ± 1600 |
| 3 mm | CARMA | <720a |
| 3 mm | PdBI | 300 ± 40 |
| 20 cm | VLA | 42.0 ± 10 |
| 90 cm | VLA | <1000a |
Notes. aThe given limits are 2σ upper limits. bCorresponds to =10−15 erg cm−2 s−1.
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Herschel (100 and 160 μm) data are drawn from the PACS Evolutionary Probe observations (D. Lutz et al. 2011, in preparation; Berta et al. 2010).
Observations at 350 μm with CSO/SHARC II were obtained during two nights in 2009 March with an average 225 GHz opacity of τ225 < 0.05. The data were reduced using the standard CRUSH tool. A total of ∼6 hr of integration time reached an rms of 10 mJy. Combined with previous data (J. Aguirre et al. 2011, in preparation) we detect no flux at 1σ = 7 mJy.
Observations at 3 mm were obtained with CARMA in E-array configuration in 2009 July. The target was observed for 8.5 hr on-source. The 3 mm receivers were tuned to 98.95 GHz (3.03 mm), with lower (upper) sidebands centered at 96.43 (101.46) GHz, respectively. Each sideband was observed with 45 31.25 MHz wide channels, leading to a total bandwidth of 2.56 GHz. The data reduction was performed with the MIRIAD package. No line emission (the CO(5→4) transition is expected at the source's redshift) was detected across the observed bands covering 4.64 < z < 4.72 and 4.94 < z < 5.02. The uv-data were imaged merging both sidebands together and using natural weighting. We infer an rms of 0.36 mJy beam−1 in the continuum map, but no detection of the source.
Using the new WideX correlator on PdBI, AzTEC 1 was observed with six antennas in 2010 April/May for ∼5.5 hr on-source. The WideX correlator covered 3.6 GHz bandwidth using polarizations centered at 101.866394 GHz. 1005+066 and 3C273 were used as phase and gain calibrators, respectively. The flux calibration error is estimated to be <10%. The naturally weighted beam is 6
38 × 501 (PA = 32°). The 3 mm continuum emission, shown in Figure 1, is detected at 7.5σ with S3 mm = 0.3 ± 0.04 mJy and unresolved. No line emission is detected across the band covering 4.56 < z < 4.76. The rms per 180 km s−1 wide channel (61.2 MHz) is 0.35 mJy beam−1.
Figure 1. PdBI 3 mm continuum image of AzTEC 1. Contours are at ±3σ, ±5σ, and ±7σ (1σ = 0.04 mJy beam−1). The inset shows the clean beam.
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Standard image High-resolution imageAzTEC 1 was spectroscopically targeted with DEIMOS on Keck II in 2008 November with clear conditions and ∼1'' seeing and a 4 hr integration time split into 30 minute exposures. The data were collected with the 830 l mm−1 grating tilted to 7900 Å and the OG550 blocker. The objects were dithered ±3'' along the slit to remove ghosting.
The data were reduced via the modified DEEP2 DEIMOS pipeline (see Capak et al. 2008). The overall instrumental throughput was determined using the standard stars HZ-44 and GD-71. Bright stars in the mask were used to determine the amount of atmospheric extinction, wavelength-dependent slit losses from atmospheric dispersion, and to correct for the A, B, and water absorption bands. The two-dimensional (2D) and one-dimensional (1D) spectra are shown in Figure 2. No strong emission lines are present in the spectrum. The continuum is clearly detected (see 2D spectrum in Figure 2), however, at low signal to noise, consistent with the faint magnitude of the source (i+ = 25.2).
Figure 2. Top panel shows the Keck II/DEIMOS 2D spectrum of AzTEC 1. Note the increase in continuum flux beyond Lyα (see also Figure 3). In the bottom panel the extracted 1D spectrum is shown. Note that the atmospheric B band (6860–6890 Å) is coincident with the expected Lyα emission line. The composite LBG spectrum is from Shapley et al. (2003).
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Standard image High-resolution image3. THE REDSHIFT OF AzTEC 1
From features in the DEIMOS spectrum, we determine a redshift for AzTEC 1 of 4.650 ± 0.005 based on the blue cutoff of Lyα. Note that in this redshift range, Lyα, the most prominent emission line that may be expected, would be attenuated by the atmospheric B band (6860–6890 Å). The 1216 Å Lyα forest break is however clearly seen in the 2D spectrum, as well as in the heavily smoothed 1D spectrum (see Figures 2 and 3). If this were the 4000 Å break at z = 0.71, we would expect strong 160 μm and 350 μm detections for any known galaxy type. As these do not exist for AzTEC 1, low redshifts (z < 1) can be ruled out. Note that the inferred high redshift is consistent with both, the source being a B-band dropout, and its FIR/radio ratio (Younger et al. 2008; Yun & Carilli 2002).
Figure 3. UV-IR SED of AzTEC 1 (symbols). The spectral template, best fit to the multi-band photometry (filled symbols) and the binned DEIMOS spectrum (open symbols), redshifted to the most probable redshift (z = 4.64) is also plotted (in red). The redshift probability distribution p ∝ exp(−0.5χ2) is shown in the inset. The median redshift and 1σ uncertainties (z = 4.64+0.06−0.08), as well as the degrees of freedom (dof) and the total χ2 of the best fit, are indicated in the top left.
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Standard image High-resolution imageDue to (1) the low signal-to-noise ratio, (2) the general absence of strong emission lines, and (3) the atmospheric B-band bias at the expected position of Lyα, we utilize the photometric data available for AzTEC 1 along with the spectrum to refine our redshift estimate. Using 31 NUV–NIR photometric measurements (Table 1) and the binned spectrum, we constrain the redshift via a χ2 minimization spectral energy distribution (SED) fitting technique described in detail by Ilbert et al. (2009). Our best-fit results, as well as the redshift probability [exp(−χ2/2)] distribution, are shown in Figure 3. We find a redshift of z = 4.64+0.06−0.08, where the errors are drawn from the 68% confidence interval. Note that this analysis yields also a secondary redshift peak at z = 4.44, albeit with a significantly lower probability than that at z = 4.64
As it is possible that heavy extinction in the UV biases UV–NIR-derived photometric redshifts toward higher values, we estimate the photometric redshift using FIR–radio data via a Monte Carlo approach, described in detail in Aretxaga et al. (2003). We find that the upper limits at λ < 450 μm strongly suggest z>4.0 (at ∼90% confidence). The redshift probability distribution reaches a plateau with equally plausible solutions between z = 4.5 and z = 6.0, supporting the optical–IR redshift solution.
The inferred most probable redshift z = 4.64 (based on UV–NIR data) is close to the spectroscopically determined redshift of z = 4.65 and supported by the FIR–radio data. Thus, hereafter we take z = 4.64+0.06−0.08 as the best estimate for the redshift of AzTEC 1.
4. SPECTRAL ENERGY DISTRIBUTION OF AzTEC 1
In Figure 4 we show the SED of AzTEC 1. Fixing the redshift to z = 4.64 (Section 3), we fit the UV–NIR SED using various model spectrum libraries. For each model we compute the total χ2 and define the most probable parameter values and their errors from the probability distribution function. Using the Bruzual & Charlot (2003) library (see Smolčić et al. 2008 for details) the UV–NIR SED is best described by a 740+200−60 Myr old starburst with SFR = 410 ± 50 M☉ yr−1, an extinction of AV = 2 ± 0.2 mag, and a stellar mass of M* = (1.5 ± 0.2) × 1011 M☉ (see the top panel in Figure 4). We find consistent results when using the Maraston et al. (2003) library. However, as pointed out by Maraston et al. (2010), using exponentially decaying star formation histories as above some of the free parameters may be poorly parameterized in young starburst galaxies whose SED is dominated by the youngest stellar populations that outshine the old ones. Thus, we additionally fit to the optical–NIR SED of AzTEC 1 the model library presented in Efstathiou et al. (2000), specifically developed for starburst galaxies. These (UV-mm) models are treated as an ensemble of optically thick giant molecular clouds (GMCs) centrally illuminated by recently formed stars. The evolution of the stellar population within the GMC is modeled using the Bruzual & Charlot (2003) stellar population synthesis models. The Efstathiou et al. (2000) models yield a 37 ± 4 Myr old starburst with AV = 100 ± 20 and SFR = 1300 ± 150 M☉ yr−1.
Figure 4. UV–NIR (top) and IR (bottom) SED of AzTEC 1. The best-fit model spectra from the Maraston et al. (2003, gray) and Bruzual & Charlot (2003, black) library to the UV–NIR SED and Lagache et al. (2003) library to the IR SED are also shown (see the text for details).
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Standard image High-resolution image
We fit the IR portion of the SED of AzTEC 1 (fixing z = 4.64) using the Chary & Elbaz (2001, CE hereafter), Dale & Helou (2002), and Lagache et al. (2003) models. The best-fit IR model, shown in Figure 4 (bottom panel), is a Lagache et al. (2003) template with a total IR (8–1000 μm) luminosity of 2.9 × 1013 L☉ and an FIR (60–1000 μm) luminosity of 9 × 1012 L☉. For comparison, the CE SED models yield the second best fit with integrated luminosities a factor of 3–4 higher. Converting the (8–1000 μm) IR luminosity to an SFR, using the Kennicutt (1998) conversion, we find an SFR of ∼1600 M☉ yr−1. To obtain the dust temperature and dust mass in AzTEC 1, we perform a gray-body dust model fit to the data as described in detail in Aravena et al. (2008). Using β = 1.5 and β = 2 we consistently find a dust temperature of TD ∼ 50 K and dust mass of MD ∼ 1.5 × 109 M☉ (while the IR luminosity is within a factor of two compared to that given above).
5. DISCUSSION
5.1. Lack of Molecular Gas?
Based on observations of AzTEC 1 from radio to X-rays, and a Keck II/DEIMOS spectrum, we have shown that AzTEC 1 is an LFIR = 9 × 1012 L☉ starburst galaxy at z = 4.64+0.06−0.08 (the given errors are 1σ uncertainties). However, contrary to expectations our searches for the CO(5→4) transition line (νRF = 576.268 GHz) in this galaxy with the PdBI/CARMA interferometers have yielded no detection. Assuming a line width of 500 km s-1 the 3σ limits in the line luminosity based on PdBI and CARMA observations are estimated to be L'CO ≲ 9.8 × 109 K km s-1 pc2 (4.56 < z < 4.76) and L'CO ≲ 6.5 × 1010 K km s-1 pc2 (4.64 < z < 4.72 and 4.94 < z < 5.02), respectively. Taking Mgas/L'CO = 0.8 M☉ (K km s-1 pc2)−1 (Downes & Solomon 1998) implies 3σ gas mass upper limits of Mgas ≲ 8 × 109 M☉ (4.56 < z < 4.76) and Mgas ≲ 5 × 1010 M☉ (4.94 < z < 5.02). Turning the arguments around (1) assuming a typical L'CO–LFIR conversion (Riechers et al. 2006) the FIR luminosity inferred here for AzTEC 1, LFIR = 9 × 1012 L☉, yields an expected CO luminosity of L'CO ≈ 4 × 1010 K km s-1 pc2, and (2) assuming a gas-to-dust-ratio of 50–150 (e.g., Calzetti et al. 2000), and Mgas/L'CO = 0.8 M☉ (K km s-1 pc2)−1 the dust mass we inferred here for AzTEC 1 (MD ∼ 1.5 × 109 M☉) translates into a line luminosity of L'CO ∼ (9–30) × 1010 K km s-1 pc2. Such a gas reservoir should have been detected (especially with the more sensitive PdBI observations) within our interferometric observations in the 3 mm band. Below we discuss a few possibilities why the CO(5→4) line was not detected.
First, it is possible that the systemic redshift of the source is outside the bandwidth range covered with our interferometric observations (encompassing redshift ranges of 4.56–4.76 and 4.94–5.02). Our UV–NIR analysis of the SED yields a 68% probability that the redshift of the source is within 4.56 < z < 4.70. However, we also find a second redshift peak at z ∼ 4.44 in our redshift probability distribution (see Figure 3). Furthermore, the systemic (CO) redshift of the source is not necessarily expected to coincide with the one inferred from UV–NIR data (typical velocity offsets are several hundred km s-1 for narrow-line objects). Thus, it is possible that the CO redshift is outside the range covered by our interferometric observations. Note, however, that if this were the case, it would not significantly alter the results of our SED analysis (Section 4). Alternatively, assuming the systemic redshift is within the covered bandwidth, the CO(5→4) non-detection could be explained by a low CO-excitation resulting in a low line brightness of the CO(5→4) transition. Assuming a CO 5→4 to 1→0 line brightness temperature ratio of ∼1/3, as found for the z>4 SMG GN20 (Carilli et al. 2010), the PdBI 3σ limit in the CO(1→0) line is L'CO ≲ 3 × 1010 K km s-1 pc2. This is roughly consistent with the CO–FIR relation. Furthermore, an uncertainty of a factor of a few in the inferred dust mass (including possible active galactic nucleus heating) and the Mgas/L'CO conversion factor makes this limit also roughly consistent with L'CO estimated from AzTEC 1's dust mass. Thus, a low CO-excitation in AzTEC 1 may explain the non-detection of CO(5→4).
5.2. Mode of Star Formation
Our analysis of the UV–radio SED of AzTEC 1 implies that AzTEC 1 is an extremely young and massive galaxy, forming stars at a rate of ∼1300 M☉ yr−1 at z = 4.6. In general, vigorous star formation induces strong negative feedback that can terminate (and then self-regulate) the starburst by dispersing and expelling gas from the gravitational potential well (Elmegreen 1999; Scoville 2003; Thompson et al. 2005; Riechers et al. 2009). This sets a number of physical limits on the starburst. Assuming that (1) the maximum intensity of a radiation-pressure supported starburst is determined by the Eddington limit for dust, (2) a constant gas-to-dust ratio with radius, and (3) that the disk is self-regulated (i.e., Toomre Q ∼ 1) such an Eddington limited starburst will have an SFR surface density ΣSFR ∼ 1000 M☉ yr−1 kpc−2, an FIR luminosity surface density FFIR ∼ 1013 L☉ kpc−2, and an effective temperature of 88 K (see Equations (33)–(36) in Thompson et al. 2005).
An SFR of ∼1300 M☉ yr−1 in AzTEC 1 (based on the NUV–NIR SED fit) then implies an SFR surface density of ΣSFR = SFR/(πr2) ≳ 420 M☉ yr−1 kpc−2 (assuming r ≲ 1 kpc based on SMA imaging; Younger et al. 2008). The inferred value does not violate the Eddington limited starburst models. The FIR luminosity surface density in AzTEC 1, FFIR = LFIR/(πr2) ≳ 2.8 × 1012 L☉ kpc−1, and the dust temperature of ∼50 K support that the starburst in AzTEC 1 is consistent, but not in violation of its Eddington limit.
It is noteworthy that the inferred value of the SFR surface density for AzTEC 1 is somewhat higher compared to SMGs at z ∼ 2, which typically have ΣSFR ∼ 80 M☉ yr−1 kpc−2 (Tacconi et al. 2006), pointing to the compactness of the star formation region in AzTEC 1. Tacconi et al. have shown that z ∼ 2 SMGs are well described within a starburst picture (Elmegreen 1999) in which star formation cannot self-regulate and thus a significant fraction of gas is converted into stars in only a few times the dynamical timescale. Continuing this line of reasoning, we make use of a detailed hydrodynamical study of matter deposition in young assembling galaxies performed by Silich et al. (2010). We estimate that AzTEC 1 is forming stars in a "gravitationally bound" regime in which gravity prohibits the formation of a superwind, leading to matter accumulation within the galaxy and further generations of star formation. Specifically, Silich et al. show that there are three hydrodynamic regimes that develop in starbursting galaxies: (1) generation of a superwind, that expels matter from the star-forming region, (2) a "gravitationally bound" regime, in which gravity prohibits the formation of a superwind and contains the matter within the galaxy, and (3) an intermediate, bimodal regime. The specific regime is dependent on the SFR and the size of the star formation region in the galaxy (see Figure 1 in Silich et al. 2010). Taking the size of the star-forming region in AzTEC 1 to be ∼1 kpc (Younger et al. 2008), its SFR ∼ 1300 M☉ yr−1 yields that, consistent with SCUBA detected galaxies, AzTEC 1 is forming stars in the gravitationally bound regime.
In summary, our analysis of the properties of AzTEC 1 points to an extremely young and massive galaxy, forming stars at a rate of ∼1300 M☉ yr−1 at z = 4.6. We find that it has already assembled a stellar mass of 1.5 × 1011 M☉, in a region covering only ∼1–2 kpc in total extent (based on HST and SMA imaging; see Younger et al. 2007, 2008) yielding that AzTEC 1 is a compact massive galaxy at z = 4.6.
The high stellar mass and compactness of AzTEC 1 resemble that of a recently identified population of quiescent, passively evolving, already massive (typically M* = 1.7 × 1011 M☉), but compact galaxies at z ∼ 2 (e.g., van Dokkum et al. 2008) deemed to evolve into the most massive red-and-dead galaxies at z ∼ 0. The upper gas mass limit inferred for AzTEC 1 (although quite uncertain) is ∼1010 M☉. If AzTEC 1 continues to form stars at the current rate, it will deplete the available gas in Mgas/SFR ∼ 6 Myr (assuming 100% efficiency). Unless further gas is supplied and high levels of star formation are induced, the galaxy's stellar body will have time to age and redden till z ∼ 2–3.
The surface density of the (likely still incomplete) sample of three confirmed z>4 SMGs in the AzTEC-COSMOS field (0.3 deg2) is ≳10 deg−2. This is already higher than ∼7 deg−2 predicted by semi-analytic models of structure growth (e.g., Baugh et al. 2005; see also Coppin et al. 2009, 2010). Thus, further studies of z>4 SMGs are key to understand the SMG population (e.g., Wall et al. 2008) and its cosmological role.
6. CONCLUSIONS
Based on UV-FIR observations of AzTEC 1, and a Keck II/DEIMOS spectrum, we have shown that AzTEC 1 is an LFIR = 9 × 1012 L☉ starburst at z = 4.64+0.06−0.08 (with a secondary, less likely, redshift probability peak at z ∼ 4.44). Based on our revised FIR values we find that AzTEC 1 fits comfortably within the limits of a maximal starburst, and that it forms stars in a gravitationally bound regime which traps the gas within the galaxy leading to formation of new generations of stars. Our SED analysis yields that AzTEC 1 is an extremely young (≲50 Myr), massive (M* ∼ 1011 M☉), but compact (≲2 kpc) galaxy, forming stars at a rate of ∼1300 M☉ yr−1 at z = 4.64. These interesting properties suggest that AzTEC 1 may be a candidate of progenitors of quiescent, already massive, but very compact galaxies regularly found at z ∼ 2, and thought to evolve into the most massive, red-and-dead galaxies found in the local universe.
The authors acknowledge the significant cultural role that the summit of Mauna Kea has within the indigenous Hawaiian community; NASA grants HST-GO-09822 (contracts 1407, 1278386; SSC); HST-HF-51235.01 (contract NAS 5-26555; STScI); GO7-8136A; Blancheflor Boncompagni Ludovisi foundation (F.C.); French Agene National de la Recheche fund ANR-07-BLAN-0228; CNES; Programme National Cosmologie et Galaxies; UKF; DFG; DFG Leibniz Prize (FKZ HA 1850/28-1); European Union's Seventh Framework programme (grant agreement 229517); making use of the NASA/IPAC IRSA, by JPL/Caltech, under contract with the National Aeronautics and Space Administration; IRAM PdBI supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain); CARMA supported by the states of California, Illinois, and Maryland, the Gordon and Betty Moore Foundation, the Eileen and Kenneth Norris Foundation, the Caltech Associates, and NSF.
Footnotes
- *
Based on observations with the W. M. Keck Observatory, the Canada–France–Hawaii Telescope, the United Kingdom Infrared Telescope, the Subaru Telescope, the NASA/ESA Hubble Space Telescope, the NASA Spitzer Telescope, the Caltech Sub-mm Observatory, the Smithsonian Millimeter Array, and the National Radio Astronomy Observatory. Herschel is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA.
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An updated version of the UV–NIR catalog, available at http://irsa.ipac.caltech.edu/data/COSMOS/tables/photometry, has been used.