J. Kamenetzky

A dust-obscured massive maximum-starburst galaxy at a redshift of 6.34

Massive present-day early-type (elliptical and lenticular) galaxies probably gained the bulk of their stellar mass and heavy elements through intense, dust-enshrouded starbursts—that is, increased rates of star formation—in the most massive dark-matter haloes at early epochs. However, it remains unknown how soon after the Big Bang massive starburst progenitors exist. The measured redshift (z) distribution of dusty, massive starbursts has long been suspected to be biased low in z owing to selection effects, as confirmed by recent findings of systems with redshifts as high as ∼5 (refs 2–4). Here we report the identification of a massive starburst galaxy at z = 6.34 through a submillimetre colour-selection technique. We unambiguously determined the redshift from a suite of molecular and atomic fine-structure cooling lines. These measurements reveal a hundred billion solar masses of highly excited, chemically evolved interstellar medium in this galaxy, which constitutes at least 40 per cent of the baryonic mass. A ‘maximum starburst’ converts the gas into stars at a rate more than 2,000 times that of the Milky Way, a rate among the highest observed at any epoch. Despite the overall downturn in cosmic star formation towards the highest redshifts, it seems that environments mature enough to form the most massive, intense starbursts existed at least as early as 880 million years after the Big Bang.

The detection of a population of submillimeter-bright, strongly lensed galaxies

Through a Lens Brightly Astronomical sources detected in the submillimeter range are generally thought to be distant, dusty galaxies undergoing a vigorous burst of star formation. They can be detected because the dust absorbs the light from stars and reemits it at longer wavelengths. Their properties are still difficult to ascertain, however, because the combination of interference from dust and the low spatial resolution of submillimeter telescopes prevents further study at other wavelengths. Using data from the Herschel Space Telescope, Negrello et al. (p. 800) showed that by searching for the brightest sources in a wide enough area in the sky it was possible to detect gravitationally lensed submillimeter galaxies with nearly full efficiency. Gravitational lensing occurs when the light of an astronomical object is deflected by a foreground mass. This phenomenon increases the apparent brightness and angular size of the lensed objects, making it easier to study sources that would be otherwise too faint to probe. Data from the Herschel Space Observatory unveils distant, dusty galaxies invisible to optical telescopes. Gravitational lensing is a powerful astrophysical and cosmological probe and is particularly valuable at submillimeter wavelengths for the study of the statistical and individual properties of dusty star-forming galaxies. However, the identification of gravitational lenses is often time-intensive, involving the sifting of large volumes of imaging or spectroscopic data to find few candidates. We used early data from the Herschel Astrophysical Terahertz Large Area Survey to demonstrate that wide-area submillimeter surveys can simply and easily detect strong gravitational lensing events, with close to 100% efficiency.

An Overview of the Dwarf Galaxy Survey

The Dwarf Galaxy Survey (DGS) program is studying low-metallicity galaxies using 230 hr of farinfrared (FIR) and submillimetre (submm) photometric and spectroscopic observations of the Herschel Space Observatory and draws from this a rich database of a wide range of wavelengths tracing the dust, gas and stars. This sample of 50 galaxies includes the largest metallicity range achievable in the local Universe including the lowest metallicity (Z) galaxies, 1/50 Z., and spans four orders of magnitude in star formation rates. The survey is designed to get a handle on the physics of the interstellar medium (ISM) of low metallicity dwarf galaxies, especially their dust and gas properties and the ISM heating and cooling processes. The DGS produces PACS and SPIRE maps of low-metallicity galaxies observed at 70, 100, 160, 250, 350, and 500 mu m with the highest sensitivity achievable to date in the FIR and submm. The FIR fine-structure lines, [CII] 158 mu m, [OI] 63 mu m, [OI] 145 mu m, [OIII] 88 mu m, [NIII] 57 mu m, and [NII] 122 and 205 mu m have also been observed with the aim of studying the gas cooling in the neutral and ionized phases. The SPIRE FTS observations include many CO lines (J = 4-3 to J = 13-12), [NII] 205 mu m, and [CI] lines at 370 and 609 mu m. This paper describes the sample selection and global properties of the galaxies and the observing strategy as well as the vast ancillary database available to complement the Herschel observations. The scientific potential of the full DGS survey is described with some example results included.

Measurements of CO Redshifts with Z-Spec for Lensed Submillimeter Galaxies Discovered in the H-ATLAS Survey

We present new observations from Z-Spec, a broadband 185-305 GHz spectrometer, of five submillimeter bright lensed sources selected from the Herschel-Astrophysical Terahertz Large Area Survey science demonstration phase catalog. We construct a redshift-finding algorithm using combinations of the signal to noise of all the lines falling in the Z-Spec bandpass to determine redshifts with high confidence, even in cases where the signal to noise in individual lines is low. We measure the dust continuum in all sources and secure CO redshifts for four out of five (z ~ 1.5-3). In one source, SDP.17, we tentatively identify two independent redshifts and a water line, confirmed at z = 2.308. Our sources have properties characteristic of dusty starburst galaxies, with magnification-corrected star formation rates of 10^(2–3) M_☉ yr^(–1). Lower limits for the dust masses (~a few 10^8 M_☉) and spatial extents (~1 kpc equivalent radius) are derived from the continuum spectral energy distributions, corresponding to dust temperatures between 54 and 69 K. In the local thermodynamic equilibrium (LTE) approximation, we derive relatively low CO excitation temperatures (≲100 K) and optical depths (τ ≲ 1). Performing a non-LTE excitation analysis using RADEX, we find that the CO lines measured by Z-Spec (from J = 4 → 3 to 10 → 9, depending on the galaxy) localize the best solutions to either a high-temperature/low-density region or a low/temperature/high-density region near the LTE solution, with the optical depth varying accordingly. Observations of additional CO lines, CO(1-0) in particular, are needed to constrain the non-LTE models.

HERSCHEL-SPIRE IMAGING SPECTROSCOPY OF MOLECULAR GAS IN M82

We present new Herschel-SPIRE imaging spectroscopy (194-671 mu m) of the bright starburst galaxy M82. Covering the CO ladder from J = 4 -\textgreater 3 to J = 13 -\textgreater 12, spectra were obtained at multiple positions for a fully sampled similar to 3 x 3 arcmin map, including a longer exposure at the central position. We present measurements of (CO)-C-12, (CO)-C-13, [CI], [NII], HCN, and HCO+ in emission, along with OH+, H2O+, and HF in absorption and H2O in both emission and absorption, with discussion. We use a radiative transfer code and Bayesian likelihood analysis to model the temperature, density, column density, and filling factor of multiple components of molecular gas traced by (CO)-C-12 and (CO)-C-13, adding further evidence to the high-J lines tracing a much warmer (similar to 500 K), less massive component than the low-J lines. The addition of (CO)-C-13 (and [CI]) is new and indicates that [CI] may be tracing different gas than (CO)-C-12. No temperature/density gradients can be inferred from the map, indicating that the single-pointing spectrum is descriptive of the bulk properties of the galaxy. At such a high temperature, cooling is dominated by molecular hydrogen. Photon-dominated region (PDR) models require higher densities than those indicated by our Bayesian likelihood analysis in order to explain the high-J CO line ratios, though cosmic-ray-enhanced PDR models can do a better job reproducing the emission at lower densities. Shocks and turbulent heating are likely required to explain the bright high-J emission.

SUBMILLIMETER LINE SPECTRUM OF THE SEYFERT GALAXY NGC 1068 FROM THE HERSCHEL-SPIRE FOURIER TRANSFORM SPECTROMETER*

The first complete submillimeter spectrum (190-670 mu m) of the Seyfert 2 galaxy NGC 1068 has been observed with the SPIRE Fourier transform spectrometer on board the Herschel Space Observatory. The sequence of CO lines (J(up) = 4-13), lines from H2O, the fundamental rotational transition of hydrogen fluoride, two o-H2O+ lines, and one line each from CH+ and OH+ have been detected, together with the two [C I] lines and the [N II] 205 mu m line. The observations in both single pointing mode with sparse image sampling and in mapping mode with full image sampling allow us to disentangle two molecular emission components, one due to the compact circumnuclear disk (CND) and one from the extended region encompassing the star-forming ring (SF-ring). Radiative transfer models show that the two CO components are characterized by densities of n(H-2) = 10(4.5) and 10(2.9) cm(-3) and temperatures of T-kin = 100 K and 127 K, respectively. A comparison of the CO line intensities with the photodissociation region (PDR) and X-ray-dominated region (XDR) models, together with the other observational constraints, such as the observed CO surface brightness and the radiation field, indicates that the best explanation for the CO excitation of the CND is an XDR with a density of n(H-2) similar to 10(4) cm(-3) and an X-ray flux of 9 erg s(-1) cm(-2), consistent with illumination by the active galactic nucleus, while the CO lines in the SF-ring are better modeled by a PDR. The detected water transitions, together with those observed with the Herschel PACS spectrometer, can be modeled by a large velocity gradient model with low temperature (T-kin similar to 40 K) and high density (n(H-2) in the range 10(6.7)-10(7.9) cm(-3)). The emission of H2O+ and OH+ are in agreement with PDR models with cosmic-ray ionization. The diffuse ionized atomic component observed through the [N II] 205 mu m line is consistent with previous photoionization models of the starburst.

Discovery of a Multiply Lensed Submillimeter Galaxy in Early HerMES Herschel/SPIRE Data

We report the discovery of a bright (

A Survey of the Molecular ISM Properties of Nearby Galaxies Using the Herschel FTS

f(250\mum) > 400

Redshift determination and co line excitation modeling for the multiply lensed galaxy hlsw-01

mJy), multiply-lensed submillimeter galaxy \obj\ in {\it Herschel}/SPIRE Science Demonstration Phase data from the HerMES project. Interferometric 880\mum\ Submillimeter Array observations resolve at least four images with a large separation of

THE REDSHIFT DISTRIBUTION OF DUSTY STAR-FORMING GALAXIES FROM THE SPT SURVEY

\sim 9\arcsec