Dust in the reionization era: ALMA observations of a zz=8.38 Galaxy

We report on the detailed analysis of a gravitationally-lensed Y-band dropout, A2744_YD4, selected from deep Hubble Space Telescope imaging in the Frontier Field cluster Abell 2744. Band 7 observations with the Atacama Large Millimeter Array (ALMA) indicate the proximate detection of a significant 1mm continuum flux suggesting the presence of dust for a star-forming galaxy with a photometric redshift of $z\simeq8$. Deep X-SHOOTER spectra confirms the high redshift identity of A2744_YD4 via the detection of Lyman $\alpha$ emission at a redshift $z$=8.38. The association with the ALMA detection is confirmed by the presence of [OIII] 88$\mu$m emission at the same redshift. Although both emission features are only significant at the 4 $\sigma$ level, we argue their joint detection and the positional coincidence with a high redshift dropout in the HST images confirms the physical association. Analysis of the available photometric data and the modest gravitational magnification ($\mu\simeq2$) indicates A2744_YD4 has a stellar mass of $\sim$ 2$\times$10$^9$ M$_{\odot}$, a star formation rate of $\sim20$ M$_{\odot}$/yr and a dust mass of $\sim$6$\times$10$^{6}$ M$_{\odot}$. We discuss the implications of the formation of such a dust mass only $\simeq$200 Myr after the onset of cosmic reionisation.Comment: Accepted for publication in ApJ

THE BOSS EMISSION-LINE LENS SURVEY. IV. SMOOTH LENS MODELS for the BELLS GALLERY SAMPLE

We present \textsl{Hubble Space Telescope} (\textsl{HST}) F606W-band imaging observations of 21 galaxy-Ly$\alpha$ emitter lens candidates in the Baryon Oscillation Spectroscopic Survey (BOSS) Emission-Line Lens Survey (BELLS) for GALaxy-Ly$\alpha$ EmitteR sYstems (BELLS GALLERY) survey. 17 systems are confirmed to be definite lenses with unambiguous evidence of multiple imaging. The lenses are primarily massive early-type galaxies (ETGs) at redshifts of approximately $0.55$, while the lensed sources are Ly$\alpha$ emitters (LAEs) at redshifts from 2 to 3. Although the \textsl{HST} imaging data are well fit by smooth lens models consisting of singular isothermal ellipsoids in an external shear field, a thorough exploration of dark substructures in the lens galaxies is required. The Einstein radii of the BELLS GALLERY lenses are on average $60\%$ larger than those of the BELLS lenses because of the much higher source redshifts which will allow a detailed investigation of the radius evolution of the mass profile in ETGs. With the aid of the average $\sim 13 \times$ lensing magnification, the LAEs are resolved to comprise individual star-forming knots of a wide range of properties with characteristic sizes from less than 100 pc to several kpc, rest-frame far UV apparent AB magnitudes from 29.6 to 24.2, and typical projected separations of 500 pc to 2 kpc.Comment: 15 pages, 4 figures, minor edits to match the ApJ published versio

A Population of Dust-rich Quasars at z ~ 1.5

We report Herschel SPIRE (250, 350, and 500 μm) detections of 32 quasars with redshifts 0.5 ≤z < 3.6 from the Herschel Multi-tiered Extragalactic Survey (HerMES). These sources are from a MIPS 24 μm flux-limited sample of 326 quasars in the Lockman Hole Field. The extensive multi-wavelength data available in the field permit construction of the rest-frame spectral energy distributions (SEDs) from ultraviolet to the mid-infrared for all sources, and to the far-infrared (FIR) for the 32 objects. Most quasars with Herschel FIR detections show dust temperatures in the range of 25-60 K, with a mean of 34 K. The FIR luminosities range from 10^(11.3) to 10^(13.5) L_☉, qualifying most of their hosts as ultra- or hyper-luminous infrared galaxies. These FIR-detected quasars may represent a dust-rich population, but with lower redshifts and fainter luminosities than quasars observed at ~1 mm. However, their FIR properties cannot be predicted from shorter wavelengths (0.3-20 μm, rest frame), and the bolometric luminosities derived using the 5100 Å index may be underestimated for these FIR-detected quasars. Regardless of redshift, we observed a decline in the relative strength of FIR luminosities for quasars with higher near-infrared luminosities

SHARDS frontier fields: physical properties of a low-mass Lyα emitter at z = 5.75

We analyze the properties of a multiply-imaged Lyman-alpha (Lya) emitter at z=5.75 identified through SHARDS Frontier Fields intermediate-band imaging of the Hubble Frontier Fields (HFF) cluster Abell 370. The source, A370-L57, has low intrinsic luminosity (M_UV~-16.5), steep UV spectral index (\beta=-2.4+/-0.1), and extreme rest-frame equivalent width of Lya (EW(Lya)=420+180-120 \AA). Two different gravitational lens models predict high magnification (\mu~10--16) for the two detected counter-images, separated by 7", while a predicted third counter-image (\mu~3--4) is undetected. We find differences of ~50% in magnification between the two lens models, quantifying our current systematic uncertainties. Integral field spectroscopy of A370-L57 with MUSE shows a narrow (FWHM=204+/-10 km/s) and asymmetric Lya profile with an integrated luminosity L(Lya)~10^42 erg/s. The morphology in the HST bands comprises a compact clump (r_e<100 pc) that dominates the Lya and continuum emission and several fainter clumps at projected distances <1 kpc that coincide with an extension of the Lya emission in the SHARDS F823W17 and MUSE observations. The latter could be part of the same galaxy or an interacting companion. We find no evidence of contribution from AGN to the Lya emission. Fitting of the spectral energy distribution with stellar population models favors a very young (t<10 Myr), low mass (M*~10^6.5 Msun), and metal poor (Z<4x10^-3) stellar population. Its modest star formation rate (SFR~1.0 Msun/yr) implies high specific SFR (sSFR~2.5x10^-7 yr^-1) and SFR density (Sigma_SFR ~ 7-35 Msun/yr/kpc^2). The properties of A370-L57 make it a good representative of the population of galaxies responsible for cosmic reionization.Comment: 14 pages, 8 figures, 4 tables. Accepted for publication in Ap

MAMBO 1.2mm observations of luminous starbursts at z~2 in the SWIRE fields

We report on--off pointed MAMBO observations at 1.2 mm of 61 Spitzer-selected star-forming galaxies from the SWIRE survey. The sources are selected on the basis of bright 24um fluxes (f_24um>0.4mJy) and of stellar dominated near-infrared spectral energy distributions in order to favor z~2 starburst galaxies. The average 1.2mm flux for the whole sample is 1.5+/-0.2 mJy. Our analysis focuses on 29 sources in the Lockman Hole field where the average 1.2mm flux (1.9+/-0.3 mJy) is higher than in other fields (1.1+/-0.2 mJy). The analysis of the sources multi-wavelength spectral energy distributions indicates that they are starburst galaxies with far-infrared luminosities ~10^12-10^13.3 Lsun, and stellar masses of ~0.2-6 x10^11 M_sun. Compared to sub-millimeter selected galaxies (SMGs), the SWIRE-MAMBO sources are among those with the largest 24um/millimeter flux ratios. The origin of such large ratios is investigated by comparing the average mid-infrared spectra and the stacked far-infrared spectral energy distributions of the SWIRE-MAMBO sources and of SMGs. The mid-infrared spectra exhibit strong PAH features, and a warm dust continuum. The warm dust continuum contributes to ~34% of the mid-infrared emission, and is likely associated with an AGN component. This constribution is consistent with what is found in SMGs. The large 24um/1.2mm flux ratios are thus not due to AGN emission, but rather to enhanced PAH emission compared to SMGs. The analysis of the stacked far-infrared fluxes yields warmer dust temperatures than typically observed in SMGs. Our selection favors warm ultra-luminous infrared sources at high-z, a class of objects that is rarely found in SMG samples. Our sample is the largest Spitzer-selected sample detected at millimeter wavelengths currently available.Comment: Accepted for publication in ApJ (51 pages; 16 figures). The quality of some figures has been degraded for arXiv purposes. Full resolution version available at this http://www.iasf-milano.inaf.it/~polletta/mambo_swire/lonsdale08_ApJ_accepted.pd

Star formation rates in luminous quasars at 2 <z< 3

We investigate the relation between star formation rates (M ˙ s M˙s ) and AGN properties in optically selected type 1 quasars at 2 < z < 3 using data from Herschel and the SDSS. We find that M ˙ s M˙s remains approximately constant with redshift, at 300 ± 100 M⊙ yr−1. Conversely, M ˙ s M˙s increases with AGN luminosity, up to a maximum of ∼ 600 M⊙ yr−1, and with C IV FWHM. In context with previous results, this is consistent with a relation between M ˙ s M˙s and black hole accretion rate (M ˙ bh M˙bh ) existing in only parts of the z−M ˙ s −M ˙ bh z−M˙s−M˙bh plane, dependent on the free gas fraction, the trigger for activity, and the processes that may quench star formation. The relations between M ˙ s M˙s and both AGN luminosity and C IV FWHM are consistent with star formation rates in quasars scaling with black hole mass, though we cannot rule out a separate relation with black hole accretion rate. Star formation rates are observed to decline with increasing C IV equivalent width. This decline can be partially explained via the Baldwin effect, but may have an additional contribution from one or more of three factors; Mi is not a linear tracer of L2500, the Baldwin effect changes form at high AGN luminosities, and high C IV EW values signpost a change in the relation between M ˙ s M˙s and M ˙ bh M˙bh . Finally, there is no strong relation between M ˙ s M˙s and Eddington ratio, or the asymmetry of the C IV line. The former suggests that star formation rates do not scale with how efficiently the black hole is accreting, while the latter is consistent with C IV asymmetries arising from orientation effects

Galaxy Counts at 24 Microns in the SWIRE Fields

This paper presents galaxy source counts at 24 microns in the six Spitzer Wide-field InfraRed Extragalactic (SWIRE) fields. The source counts are compared to counts in other fields, and to model predictions that have been updated since the launch of Spitzer. This analysis confirms a very steep rise in the Euclidean-normalized differential number counts between 2 mJy and 0.3 mJy. Variations in the counts between fields show the effects of sample variance in the flux range 0.5-10 mJy, up to 100% larger than Poisson errors. Nonetheless, a "shoulder" in the normalized counts persists at around 3 mJy. The peak of the normalized counts at 0.3 mJy is higher and narrower than most models predict. In the ELAIS N1 field, the 24 micron data are combined with Spitzer-IRAC data and five-band optical imaging, and these bandmerged data are fit with photometric redshift templates. Above 1 mJy the counts are dominated by galaxies at z less than 0.3. By 300 microJy, about 25% are between z ~ 0.3-0.8, and a significant fraction are at z ~ 1.3-2. At low redshifts the counts are dominated by spirals, and starbursts rise in number density to outnumber the spirals' contribution to the counts below 1 mJy.Comment: 10 pages, 8 figures, accepted 3 November 2007 for publication in The Astronomical Journal, formatted with emulateapj styl

SWIRE: The SIRTF Wide‐Area Infrared Extragalactic Survey

The SIRTF Wide-Area Infrared Extragalactic Survey (SWIRE), the largest SIRTF Legacy program, is a wide-area imaging survey to trace the evolution of dusty, star-forming galaxies, evolved stellar populations, and active galactic nuclei (AGNs) as a function of environment, from redshifts to the current z ∼ 3 epoch. SWIRE will survey seven high-latitude fields, totaling 60–65 deg2 in all seven SIRTF bands: Infrared Array Camera (IRAC) 3.6, 4.5, 5.6, and 8 mm and Multiband Imaging Photometer for SIRTF (MIPS) 24, 70, and 160 mm. Extensive modeling suggests that the Legacy Extragalactic Catalog may contain in excess of 2 million IR-selected galaxies, dominated by (1) ∼150,000 luminous infrared galaxies (LIRGs; LFIR 1 1011 L,) detected by MIPS (and significantly more detected by IRAC), ∼7000 of these with ; (2) 1 million IRAC- z 1 2 detected early-type galaxies (∼ with and ∼10,000 with ); and (3) ∼20,000 classical AGNs 5 2 # 10 z 1 1 z 1 2 detected with MIPS, plus significantly more dust-obscured quasi-stellar objects/AGNs among the LIRGs. SWIRE will provide an unprecedented view of the evolution of galaxies, structure, and AGNs. The key scientific goals of SWIRE are (1) to determine the evolution of actively star forming and passively evolving galaxies in order to understand the history of galaxy formation in the context of cosmic structure formation; (2) to determine the evolution of the spatial distribution and clustering of evolved galaxies, starbursts, and AGNs in the key redshift range over which much of cosmic evolution has occurred; and (3) to 0.5 ! z ! 3 determine the evolutionary relationship between “normal galaxies” and AGNs and the contribution of AGN accretion energy versus stellar nucleosynthesis to the cosmic backgrounds. The large area of SWIRE is important to establish statistically significant population samples over enough volume cells that we can resolve the star formation history as a function of epoch and environment, i.e., in the context of structure formation. The large volume is also optimized for finding rare objects. The SWIRE fields are likely to become the next generation of large “cosmic windows” into the extragalactic sky. They have been uniquely selected to minimize Galactic cirrus emission over large scales. The Galaxy Evolution Explorer will observe them as part of its deep 100 deg2 survey, as will Herschel. SWIRE includes ∼9 deg2 of the unique large-area XMM Large Scale Structure hard X-ray imaging survey and is partly covered by the UKIDSS deep J and K survey. An extensive optical/near-IR imaging program is underway from the ground. The SWIRE data are nonproprietary; catalogs and images will be released twice yearly, beginning about 11 months after SIRTF launch. Details of the data products and release schedule are presented