K. S. Scott

The Evolution of Interstellar Medium Mass Probed by Dust Emission: ALMA Observations at z = 0.3-2

The use of submm dust continuum emission to probe the mass of interstellar dust and gas in galaxies is empirically calibrated using samples of local star forming galaxies, Planck observations of the Milky Way and high redshift submm galaxies (SMGs). All of these objects suggest a similar calibration, strongly supporting the view that the Rayleigh-Jeans (RJ) tail of the dust emission can be used as an accurate and very fast probe of the ISM in galaxies. We present ALMA Cycle 0 observations of the Band 7 (350 GHz) dust emission in 107 galaxies from z = 0.2 to 2.5. Three samples of galaxies with a total of 101 galaxies were stellar mass-selected from COSMOS to have M∗ ≃ 10 11 M⊙: 37 at z∼ 0.4, 33 at z∼ 0.9 and 31 at z= 2. A fourth sample with 6 IR luminous galaxies at z = 2 was observed for comparison with the purely mass-selected samples. From the fluxes detected in the stacked images for each sample, we find that the ISM content has decreased a factor ∼ 6 from 1−2×10 10 M⊙ at both z = 2 and 0.9 down to ∼ 2×10 9 M⊙ at z = 0.4. The IR luminous sample at z = 2 shows a further ∼ 4 times increase in MISM compared to the equivalent non-IR bright sample at the same redshift. The gas mass fractions are ∼ 2 ± 0.5,12 ± 3,14 ± 2 and 53 ± 3 % for the four subsamples (z = 0.4, 0.9, 2 and IR bright galaxies). Subject headings: cosmology: observations — cosmology: galaxy evolution ISM: clouds

[C II] Line Emission in Massive Star-forming Galaxies at z = 4.7

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [C II] 157.7 μm fine structure line and thermal dust continuum emission from a pair of gas-rich galaxies at z = 4.7, BR1202-0725. This system consists of a luminous quasar host galaxy and a bright submillimeter galaxy (SMG), while a fainter star-forming galaxy is also spatially coincident within a 4 (25 kpc) region. All three galaxies are detected in the submillimeter continuum, indicating FIR luminosities in excess of 10^(13) L_☉ for the two most luminous objects. The SMG and the quasar host galaxy are both detected in [C II] line emission with luminosities L_([CII]) = (10.0 ± 1.5) × 10^9 L_☉ and L_([CII]) = (6.5 ± 1.0) × 10^9 L_☉, respectively. We estimate a luminosity ratio L_([CII])/L_(FIR) = (8.3 ± 1.2) × 10^(–4) for the starburst SMG to the north and L [C II]/L FIR = (2.5 ± 0.4) × 10–4 for the quasar host galaxy, in agreement with previous high-redshift studies that suggest lower [C II]-to-FIR luminosity ratios in quasars than in starburst galaxies. The third fainter object with a flux density S_(340GHz) = 1.9 ± 0.3 mJy is coincident with a Lyα emitter and is detected in HST ACS F775W and F814W images but has no clear counterpart in the H band. Even if this third companion does not lie at a redshift similar to BR1202-0725, the quasar and the SMG represent an overdensity of massive, infrared luminous star-forming galaxies within 1.3 Gyr of the big bang.

The source counts of submillimetre galaxies detected at λ= 1.1 mm

The source counts of galaxies discovered at submillimetre and millimetre wavelengths provide important information on the evolution of infrared-bright galaxies. We combine the data from six blank-field surveys carried out at 1.1 mm with AzTEC, totalling 1.6 deg^2 in area with root-mean-square depths ranging from 0.4 to 1.7 mJy, and derive the strongest constraints to date on the 1.1 mm source counts at flux densities S_1100= 1–12 mJy. Using additional data from the AzTEC Cluster Environment Survey to extend the counts to S1100∼ 20 mJy, we see tentative evidence for an enhancement relative to the exponential drop in the counts at S_1100∼ 13 mJy and a smooth connection to the bright source counts at >20 mJy measured by the South Pole Telescope; this excess may be due to strong-lensing effects. We compare these counts to predictions from several semi-analytical and phenomenological models and find that for most the agreement is quite good at flux densities ≳ 4 mJy; however, we find significant discrepancies (≳ 3σ) between the models and the observed 1.1-mm counts at lower flux densities, and none of them is consistent with the observed turnover in the Euclidean-normalized counts at S_1100≲ 2 mJy. Our new results therefore may require modifications to existing evolutionary models for low-luminosity galaxies. Alternatively, the discrepancy between the measured counts at the faint end and predictions from phenomenological models could arise from limited knowledge of the spectral energy distributions of faint galaxies in the local Universe.

AzTEC half square degree survey of the SHADES fields - II : Identifications, redshifts and evidence for large-scale structure

The Astronomical Thermal Emission Camera (AzTEC) 1.1u2009mm survey of the two SCUBA HAlf Degree Extragalactic Survey (SHADES) fields is the largest (0.7u2009deg2) blank-field millimetre-wavelength (mm-wavelength) survey undertaken to date at a resolution of ≃18u2009arcsec and a depth of ≃1u2009mJy. We have used the deep optical to radio multiwavelength data in the SHADES Lockman Hole East and SXDF/UDS fields to obtain galaxy identifications for ≃64 per cent (≃80 per cent including tentative identifications) of the 148 AzTEC-SHADES 1.1u2009mm sources reported by Austermann et al., exploiting deep radio and 24 μm data complemented by methods based on 8 μm flux density and red optical–infrared (i − K) colour. This unusually high identification rate can be attributed to the relatively bright mm-wavelength flux density threshold, combined with the relatively deep supporting multifrequency data now available in these two well-studied fields. We have further exploited the optical–mid-infrared–radio data to derive an ≃60 per cent (≃75 per cent including tentative identifications) complete redshift distribution for the AzTEC-SHADES sources, yielding a median redshift of z ≃ 2.2, with a high-redshift tail extending to at least z ≃ 4. Despite the larger area probed by the AzTEC survey relative to the original SCUBA-SHADES imaging, the redshift distribution of the AzTEC sources is consistent with that displayed by the SCUBA sources, and reinforces tentative evidence that the redshift distribution of mm/submm sources in the Lockman Hole field is significantly different from that found in the SXDF/UDS field. Comparison with simulated surveys of similar scale extracted from semi-analytic models based on the Millennium simulation indicates that this is as expected if the mm/submm sources are massive (M > 1011u2009M⊙) star-forming galaxies tracing large-scale structures over scales of 10–20u2009Mpc. This confirms the importance of surveys covering several deg2 (as now underway with SCUBA2) to obtain representative samples of bright (sub)mm-selected galaxies. This work provides a foundation for the further exploitation of the Spitzer and Herschel data in the SHADES fields in the study of the stellar masses and specific star formation rates of the most active star-forming galaxies in cosmic history.

HIGH SPECTRAL RESOLUTION MEASUREMENT OF THE SUNYAEV-ZEL'DOVICH EFFECT NULL WITH Z-Spec

The Sunyaev-Zeldovich (SZ) effect spectrum crosses through a null where ΔT CMB = 0 near ν0 = 217 GHz. In a cluster of galaxies, ν0 can be shifted from the canonical thermal SZ effect value by corrections to the SZ effect scattering due to the properties of the inter-cluster medium. We have measured the SZ effect in the hot galaxy cluster RX J 1347.5 – 1145 with Z-Spec, an R ~ 300 grating spectrometer sensitive between 185 and 305 GHz. These data comprise a high spectral resolution measurement around the null of the SZ effect and clearly exhibit the transition from negative to positive ΔT CMB over the Z-Spec band. The SZ null position is measured to be ν0 = 225.8 ± 2.5(stat.) ± 1.2(sys.) GHz, which differs from the canonical null frequency by 3.0σ and is evidence for modifications to the canonical thermal SZ effect shape. Assuming the measured shift in ν0 is due only to relativistic corrections to the SZ spectrum, we place the limit kT e = 17.1 ± 5.3 keV from the zero-point measurement alone. By simulating the response of the instrument to the sky, we are able to generate likelihood functions in {y 0, T e, v pec} space. For v pec = 0 km s–1, we measure the best-fitting SZ model to be y 0 = 4.6+0.6 – 0.9 × 10–4, T e, 0 = 15.2+12 – 7.4 keV. When v pec is allowed to vary, a most probable value of v pec = + 450 ± 810 km s–1 is found.

Early Science with the Large Millimeter Telescope: CO and [C ii] Emission in the z = 4.3 AzTEC J095942.9+022938 (COSMOS AzTEC-1)

Measuring redshifted CO line emission is an unambiguous method for obtaining an accurate redshift and total cold gas content of optically faint, dusty starburst systems. Here, we report the first successful spectroscopic redshift determination of AzTEC J095942.9+022938 (COSMOS AzTEC-1), the brightest 1.1mm continuum source found in the AzTEC/JCMT survey (Scott et al. 2008), through a clear detection of the redshifted CO (4-3) and CO (5-4) lines using the Redshift Search Receiver on the Large Millimeter Telescope. The CO redshift of

AzTEC/ASTE 1.1-mm survey of SSA22: Counterpart identification and photometric redshift survey of submillimetre galaxies

z=4.3420pm0.0004

satmc: Spectral energy distribution Analysis Through Markov Chains

is confirmed by the detection of the redshifted 158 micron [C II] line using the Submillimeter Array. The new redshift and Herschel photometry yield

X-ray detections of submillimetre galaxies: active galactic nuclei versus starburst contribution

L_{FIR}=(1.1pm0.1)times 10^{13} L_odot

Calculating the transfer function of noise removal by principal component analysis and application to AzTEC deep-field observations

and