Galaxy formation and evolution

Abstract:

We present a multi-wavelength, UV-to-radio analysis for a sample of massive (M * ∼ 10¹⁰ M ⊙) IRAC- and MIPS 24 μm detected Lyman break galaxies (LBGs) with spectroscopic redshifts z 3 in the GOODS-North field. For LBGs without individual 24 μm detections, we employ stacking techniques at 24 μm, 1.1mm, and 1.4GHz to construct the average UV-to-radio spectral energy distribution and find it to be consistent with that of a luminous infrared galaxy with L IR = 4.5 ^+1.1 -2.3 × 10¹¹ L ⊙ and a specific star formation rate of 4.3 Gyr^-1 that corresponds to a mass doubling time 230 Myr. On the other hand, when considering the 24 μm detected LBGs we find among them galaxies with L IR>10 ¹² L ⊙, indicating that the space density of z 3 UV-selected ultra-luminous infrared galaxies (ULIRGs) is (1.5 0.5) × 10^-5 Mpc^-3. We compare measurements of star formation rates from data at different wavelengths and find that there is tight correlation (Kendall's τ>99.7%) and excellent agreement between the values derived from dust-corrected UV, mid-IR, millimeter, and radio data for the whole range of L IR up to L IR 10¹³ L ⊙. This range is greater than that for which the correlation is known to hold at z ∼ 2, possibly due to the lack of significant contribution from polycyclic aromatic hydrocarbons to the 24 μm flux at z ∼ 3. The fact that this agreement is observed for galaxies with L IR> 10¹² L ⊙ suggests that star formation in UV-selected ULIRGs, as well as the bulk of star formation activity at this redshift, is not embedded in optically thick regions as seen in local ULIRGs and submillimeter-selected galaxies at z = 2. © 2010 The American Astronomical Society. All rights reserved.

Abstract:

Aims. We aim to demonstrate that the Herschel-ATLAS (H-ATLAS) is suitable for a blind and unbiased survey for debris disks by identifying candidate debris disks associated with main sequence stars in the initial science demonstration field of the survey. We show that H-ATLAS reveals a population of far-infrared/sub-mm sources that are associated with stars or star-like objects on the SDSS main-sequence locus. We validate our approach by comparing the properties of the most likely candidate disks to those of the known population. Methods. We use a photometric selection technique to identify main sequence stars in the SDSS DR7 catalogue and a Bayesian Likelihood Ratio method to identify H-ATLAS catalogue sources associated with these main sequence stars. Following this photometric selection we apply distance cuts to identify the most likely candidate debris disks and rule out the presence of contaminating galaxies using UKIDSS LAS K-band images. Results. We identify 78 H-ATLAS sources associated with SDSS point sources on the main-sequence locus, of which two are the most likely debris disk candidates: H-ATLAS J090315.8 and H-ATLAS J090240.2. We show that they are plausible candidates by comparing their properties to the known population of debris disks. Our initial results indicate that bright debris disks are rare, with only 2 candidates identified in a search sample of 851 stars. We also show that H-ATLAS can derive useful upper limits for debris disks associated with Hipparcos stars in the field and outline the future prospects for our debris disk search programme. © 2010 ESO.

Abstract:

We present observations of a very massive galaxy at z = 1.82 that show that its morphology, size, velocity dispersion, and stellar population properties are fully consistent with those expected for passively evolving progenitors of today's giant ellipticals. These findings are based on a deep optical rest-frame spectrum obtained with the Multi-Object InfraRed Camera and Spectrograph on the Subaru Telescope of a high-z passive galaxy candidate (pBzK) from the COSMOS field, for which we accurately measure its redshift of z = 1.8230 and obtain an upper limit on its velocity dispersion σ* < 326 km s^-1. By detailed stellar population modeling of both the galaxy broadband spectral energy distribution and the rest-frame optical spectrum, we derive a star formation-weighted age and formation redshift of tsf ≃ 1-2 Gyr and zform ≃ 2.5-4, and a stellar mass of M * ≃ (3-4) × 10¹¹ M⊙. This is in agreement with a virial mass limit of Mvir < 7 × 10¹¹ M⊙, derived from the measured σ* value and stellar half-light radius, as well as with the dynamical mass limit based on the Jeans equations. In contrast to previously reported super-dense passive galaxies at z ∼ 2, the present galaxy at z = 1.82 appears to have both size and velocity dispersion similar to early-type galaxies in the local universe with similar stellar mass. This suggests that z 2 massive and passive galaxies may exhibit a wide range of properties, then possibly following quite different evolutionary histories from z ∼ 2 to z = 0. © 2010 The American Astronomical Society. All rights reserved.

Abstract:

We present spectral energy distributions (SEDs) for 68 Herschel sources detected at 5σ at 250, 350 and 500 μm in the HerMES SWIRE-Lockman field. We explore whether existing models for starbursts, quiescent star-forming galaxies and active galactic nucleus dust tori are able to model the full range of SEDs measured with Herschel. We find that while many galaxies ( 56 per cent) are well fitted with the templates used to fit IRAS, Infrared Space Observatory (ISO) and Spitzer sources, for about half the galaxies two new templates are required: quiescent ('cirrus') models with colder (10-20 K) dust and a young starburst model with higher optical depth than Arp 220. Predictions of submillimetre fluxes based on model fits to 4.5-24 μm data agree rather poorly with the observed fluxes, but the agreement is better for fits to 4.5-70 μm data. Herschel galaxies detected at 500 μm tend to be those with the highest dust masses. © 2010 The Authors. Journal compilation © 2010 RAS.

Abstract:

We present the results of our search for high-redshift Lyman-break galaxies over the GOODS-South field. We use Hubble Space Telescope (HST)-ACS data in B, V, i′ & z′, Very Large Telescope (VLT)-ISAAC J and Ks, Spitzer-Infrared Array Camera (IRAC) 3.6, 4.5, 5.8 and 8.0 μm data in conjunction with the new HAWK-I Y-band science verification data to search for dropout galaxies in the redshift range 6 < z < 9. We survey ≈119 arcmin² to YAB = 25.7 (5σ), of which 37.5 arcmin² reaches YAB = 25.9. Candidate z′ and Y dropouts were selected on the basis of a colour cut of (Y - J)AB > 0.75 mag and (z′ - Y)AB > 1.0 mag, respectively. We find no robust Y-drops (z ≈ 9) brighter than JAB < 25.4. In our search for z′-band dropouts (z ≈ 6.5-7.5), we identify four possible candidates, two with z′-drop colours and clear Spitzer-IRAC detections and two less likely candidates. We also identify two previously known Galactic T-dwarf stellar contaminants with these colours, and two likely transient objects seen in the Y-band data. The implications if all or none of our candidates is real on the ultraviolet galaxy luminosity functions at z > 6.5 are explored. We find our number of z′-drop candidates to be insufficient based on the expected number of z′ drops in a simple no-evolution scenario from the z = 3 Lyman-break galaxy luminosity function but we are consistent with the observed luminosity function at z ≈ 6 (if all our candidates are real). However, if one or both of our best z′-drop candidates are not z > 6.5 galaxies, this would demand evolution of the luminosity function at early epochs, in the sense that the number density of ultraviolet luminous star- forming galaxies at z > 7 is less than at z ~ 6. We show that the future surveys to be conducted with the European Southern Observatory VISTA telescope over the next 5 yr will be able to measure the bulk of the luminosity function for both z′ and Y dropouts and thus provide the strongest constraints on the level of star-formation within the epoch of reionization. © 2010 The Authors. Journal compilation. © 2010 RAS.