D. Rigopoulou

The All-wavelength Extended Groth Strip International Survey (AEGIS) Data Sets

In this the first of a series of Letters, we present a panchromatic data set in the Extended Groth Strip region of the sky. Our survey, the All-Wavelength Extended Groth Strip International Survey (AEGIS), aims to study the physical properties and evolutionary processes of galaxies at z ~ 1. It includes the following deep, wide-field imaging data sets: Chandra/ACIS X-ray, GALEX ultraviolet, CFHT/MegaCam Legacy Survey optical, CFHT/CFH12K optical, Hubble Space Telescope/ACS optical and NICMOS near-infrared, Palomar/WIRC near-infrared, Spitzer/IRAC mid-infrared, Spitzer/MIPS far-infrared, and VLA radio continuum. In addition, this region of the sky has been targeted for extensive spectroscopy using the Deep Imaging Multi-Object Spectrograph (DEIMOS) on the Keck II 10 m telescope. Our survey is compared to other large multiwavelength surveys in terms of depth and sky coverage.

THE EVOLVING INTERSTELLAR MEDIUM OF STAR-FORMING GALAXIES SINCE z = 2 AS PROBED BY THEIR INFRARED SPECTRAL ENERGY DISTRIBUTIONS

Using data from the mid-infrared to millimeter wavelengths for individual galaxies and for stacked ensembles at 0.5 1012 L ☉). For galaxies within the MS, we show that the variations of specific star formation rates (sSFRs = SFR/M *) are driven by varying gas fractions. For relatively massive galaxies like those in our samples, we show that the hardness of the radiation field, U, which is proportional to the dust-mass-weighted luminosity (L IR/M dust) and the primary parameter defining the shape of the IR spectral energy distribution (SED), is equivalent to SFE/Z. For MS galaxies with stellar mass log (M */M ☉) ≥ 9.7 we measure this quantity, U, showing that it does not depend significantly on either the stellar mass or the sSFR. This is explained as a simple consequence of the existing correlations between SFR-M *, M *-Z, and M gas-SFR. Instead, we show that U (or equally L IR/M dust) does evolve, with MS galaxies having harder radiation fields and thus warmer temperatures as redshift increases from z = 0 to 2, a trend that can also be understood based on the redshift evolution of the M *-Z and SFR-M * relations. These results motivate the construction of a universal set of SED templates for MS galaxies that are independent of their sSFR or M * but vary as a function of redshift with only one parameter, U.

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.

A Large Mid-Infrared Spectroscopic and Near-Infrared Imaging Survey of Ultraluminous Infrared Galaxies: Their Nature and Evolution

We present a low-resolution mid-infrared spectroscopic survey of an unbiased sample of 62 ultraluminous infrared galaxies (ULIRGs) (LIR > 1012L⊙, z ≤ 0.3) using ISOPHOT-S on board the Infrared Space Observatory (ISO). For comparison, we also present ISOPHOT-S spectra for 23 active galactic nuclei (AGNs) and 15 starburst and normal galaxies. The line-to-continuum ratio of the 7.7 μm polycyclic aromatic hydrocarbon (PAH) emission feature is used as a discriminator between starburst and AGN activity in ULIRGs. We find that the majority of ULIRGs are predominantly powered by starbursts. The ratio of PAH over infrared luminosities, LPAH/LIR, for starburst-dominated ULIRGs is very similar to the ratio found for template starbursts. The shapes of the PAH features are sometimes unusual. Extinction has a noticeable effect on the PAH spectra of ULIRG starbursts. We have obtained high-resolution near-infrared imaging for the southern ISOPHOT-S ULIRGs in order to investigate their evolution stage. The majority (68%) of the ULIRGs imaged are double systems, and all show distorted morphologies. Of the 23 double-nuclei systems, 17 appear at linear separations between 4 and 14 kpc, with a mean separation of 6.5 kpc. Using the separations measured from our new near-infrared imaging as well as from the literature, we have examined whether ULIRGs that are advanced mergers are more AGN-like. We have found no such evidence, contrary to what is postulated by the classical evolutionary scenario. No correlation is found between the stage of merger in ULIRGs and their infrared luminosity. In fact, we find that systems in the early stages of merging may well put out maximum luminosity. We also find that the total mass of interstellar gas, as estimated from the CO (1 → 0) luminosity, does not decrease with decreasing merger separation. When both an AGN and a starburst occur concurrently in ULIRGs, we find that the starburst dominates the luminosity output. We propose that the available gas reservoir and the individual structure of the interacting galaxies plays a major role in the evolution of the system.

HerMES: The SPIRE confusion limit

We report on the sensitivity of SPIRE photometers on the Herschel Space Observatory. Specifically, we measure the confusion noise from observations taken during the Science Demonstration Phase of the Herschel Multi-tiered Extragalactic Survey. Confusion noise is defined to be the spatial variation of the sky intensity in the limit of infinite integration time, and is found to be consistent among the different fields in our survey at the level of 5.8, 6.3 and 6.8 mJy/beam at 250, 350 and 500 microns, respectively. These results, together with the measured instrument noise, may be used to estimate the integration time required for confusion-limited maps, and provide a noise estimate for maps obtained by SPIRE.

Infrared power-law galaxies in the chandra deep field-south: Active galactic nuclei and ultraluminous infrared galaxies

We investigate the nature of a sample of 92 Spitzer MIPS 24 � m–selected galaxies in the CDF-S, showing powerlaw–like emission in the Spitzer IRAC 3.6–8 � m bands. The main goal is to determine whether the galaxies not detectedinX-rays (47%ofthesample)arepartofthehypotheticalpopulationofobscuredAGNsnotdetectedevenin deep X-ray surveys. The majority of the IR power-law galaxies are ULIRGs at z > 1, and those with LIRG-like IR luminosities are usually detected in X-rays. The optical-to-IR SEDs of the X-ray–detected galaxies are almost equally divided between aBLAGN SED class (similar to anopticallyselected QSO) and an NLAGN SED (similar to the BLAGN SED but with an obscured UV/optical continuum). A small fraction of SEDs resemble warm ULIRGs (e.g., Mrk 231). Most galaxies not detected in X-rays have SEDs in the NLAGN+ULIRG class as they tend to be optically fainter and possibly more obscured. Moreover, the IR power-law galaxies have SEDs significantly different from those of high-z (zsp > 1) IR (24 � m) selected and optically bright (VVDS IAB � 24) star-forming galaxies whoseSEDsshow averyprominent stellar bumpat1.6 � m.ThegalaxiesdetectedinX-rays have2–8keVrest-frame luminosities typical ofAGNs. Thegalaxies notdetectedinX-rayshave global X-ray–to–mid-IR SED properties that make them good candidates to contain IR-bright X-ray–absorbed AGNs. If all these sources are actually obscured AGNs, we would observe a ratio of obscured to unobscured 24 � m–detected AGNs of 2:1, whereas models predict a ratio of up to 3:1. Additional studies using Spitzer to detect X-ray–quiet AGNs are likely to find more such obscured sources. Subject headings: galaxies: active — galaxies: high-redshift — infrared: galaxies — X-rays: galaxies Online material: color figuresWe investigate the nature of a sample of 92 Spitzer/MIPS 24 μm selected galaxies in the CDFS, showing power law-like emission in the Spitzer/IRAC 3.6– 8μm bands. The main goal is to determine whether the galaxies not detected in X-rays (47% of the sample) are part of the hypothetical population of obscured AGN not detected even in deep X-ray surveys. The majority of the IR powerlaw galaxies are ULIRGs at z > 1, and those with LIRG-like IR luminosities are usually detected in X-rays. The optical to IR spectral energy distributions (SEDs) of the X-ray detected galaxies are almost equally divided between a BLAGN SED class (similar to an optically selected QSO) and a NLAGN SED (similar to the BLAGN SED but with an obscured UV/optical continuum). A small fraction of SEDs resemble warm ULIRG galaxies (e.g., Mrk 231). Most galaxies not detected in X-rays have SEDs in the NLAGN+ULIRG class as they tend to be optically fainter, and possibly more obscured. Moreover, the IR powerlaw galaxies have SEDs significantly different from those of high-z (zsp > 1) IR (24 μm) selected and optically bright (VVDS IAB ≤ 24) star-forming galaxies Departamento de Astrof́ısica Molecular e Infrarroja, Instituto de Estructura de la Materia, CSIC, E28006 Madrid, Spain; e-mail: aalonso@damir.iem.csic.es Steward Observatory, The University of Arizona, 933 N. Cherry, Tucson, AZ 85721 Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK Department of Astrophysics, Oxford University, Keble Rd, Oxford, OX1 3RH, UK Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138 Columbia Astrophysics Laboratory, Columbia University Pupin Laboratories, 550 W. 120th St., Rm 1418, NY, 10027 Department of Astronomy and Astrophysics; The Pennsylvania State University; 525 Davey Lab; University Park, PA 16802 Institut d’Astrophysique Spatiale, bât 121, Université Paris Sud, F-91405 Orsay Cedex, France

The Nature and Evolution of Ultraluminous Infrared Galaxies:A Mid-Infrared Spectroscopic Survey

We report the first results of a low-resolution mid-infrared spectroscopic survey of an unbiased, far-infrared-selected sample of 60 ultraluminous infrared galaxies (ULIRGs) (LIR

ISOCAM-CVF 5-12 Micron Spectroscopy of Ultraluminous Infrared Galaxies*

{r IR}

HerMES : SPIRE galaxy number counts at 250, 350, and 500 μm

-->

Ultraluminous Infrared Galaxies: QSOs in Formation?

t SUBgt {r IR}t/SUBgt