CEA Bolometer Arrays: the First Year in Space

The CEA/LETI and CEA/SAp started the development of far-infrared filled bolometer arrays for space applications over a decade ago. The unique design of these detectors makes possible the assembling of large focal planes comprising thousands of bolometers running at 300 mK with very low power dissipation. Ten arrays of 16x16 pixels were thoroughly tested on the ground, and integrated in the Herschel/PACS instrument before launch in May 2009. These detectors have been successfully commissioned and are now operating in their nominal environment at the second Lagrangian point of the Earth-Sun system. In this paper we briefly explain the functioning of CEA bolometer arrays, and we present the properties of the detectors focusing on their noise characteristics, the effect of cosmic rays on the signal, the repeatability of the measurements, and the stability of the system

Mid-infrared and optical spectroscopy of ultraluminous infrared galaxies: A comparison

New tools from Infrared Space Observatory (ISO) mid-infrared spectroscopy have recently become available to determine the power sources of dust-obscured ultraluminous infrared galaxies (ULIRGs). We compare ISO classifications - starburst or active galactic nucleus (AGN) - with classifications from optical spectroscopy, and with optical/near-infrared searches for hidden broad-line regions. The agreement between mid-infrared and optical classification is excellent if optical LINER spectra are assigned to the starburst group. The starburst nature of ULIRG LINERs strongly supports the suggestion that LINER spectra in infrared-selected galaxies, rather than being an expression of the AGN phenomenon, are due to shocks that are probably related to galactic superwinds. Differences between ISO and optical classification provide clues on the evolution of ULIRGs and on the configuration of obscuring dust. We find few ISO AGN with optical HII or LINER identification, suggesting that highly obscured AGN exist but are not typical for the ULIRG phenomenon in general. Rather, our results indicate that strong AGN activity, once triggered, quickly breaks the obscuring screen at least in certain directions, thus becoming detectable over a wide wavelength range.Comment: aastex, 1 eps figure. Accepted by ApJ (Letters

A Far-infrared Characterization of 24 μm Selected Galaxies at 0 < z < 2.5 using Stacking at 70 μm and 160 μm in the COSMOS Field

We present a study of the average properties of luminous infrared galaxies detected directly at 24 μm in the COSMOS field using a median stacking analysis at 70 μm and 160 μm. Over 35,000 sources spanning 0 ≤ z ≤ 3 and 0.06 mJy ≤ S_(24) ≤ 3.0 mJy are stacked, divided into bins of both photometric redshift and 24 μm flux. We find no correlation of S_(70)/S_(24) flux density ratio with S_(24), but find that galaxies with higher S_(24) have a lower S_(160)/S_(24) flux density ratio. These observed ratios suggest that 24 μm selected galaxies have warmer spectral energy distributions (SEDs) at higher mid-IR fluxes, and therefore have a possible higher fraction of active galactic nuclei. Comparisons of the average S_(70)/S_(24) and S_(160)/S_(24) colors with various empirical templates and theoretical models show that the galaxies detected at 24 μm are consistent with "normal" star-forming galaxies and warm mid-IR galaxies such as Mrk 231, but inconsistent with heavily obscured galaxies such as Arp 220. We perform a χ^2 analysis to determine best-fit galactic model SEDs and total IR luminosities for each of our bins. We compare our results to previous methods of estimating L IR and find that previous methods show considerable agreement over the full redshift range, except for the brightest S_(24) sources, where they overpredict the bolometric IR luminosity at high redshift, most likely due to their warmer dust SED. We present a table that can be used as a more accurate and robust method for estimating bolometric infrared luminosity from 24 μm flux densities

CHARACTERIZATION OF LABELED PROGENITOR DERIVED ENDOTHELIAL CELLS FOR TISSUE ENGINEERING APPLICATIONS

Oral Communication presented at the ";Forum des Jeunes Chercheurs";, Brest (France) 2011

Optical Spectral Signatures of Dusty Starburst Galaxies

We analyse the optical spectral properties of the complete sample of Very Luminous Infrared Galaxies presented by Wu et al. (1998a,b) and we find a high fraction (~50 %) of spectra showing both a strong H_delta line in absorption and relatively modest [OII] emission (e(a) spectra). The e(a) signature has been proposed as an efficient method to identify dusty starburst galaxies and we study the star formation activity and the nature of these galaxies, as well as the effects of dust on their observed properties. We examine their emission line characteristics, in particular their [OII]/H_alpha ratio, and we find this to be greatly affected by reddening. A search for AGN spectral signatures reveals that the e(a)'s are typically HII/LINER galaxies. We compare the star formation rates derived from the FIR luminosities with the estimates based on the H_alpha line and find that the values obtained from the optical emission lines are a factor of 10-70 (H_alpha) and 20-140 ([OII]) lower than the FIR estimates (50-300 M_sun yr^-1). We then study the morphological properties of the e(a) galaxies, looking for a near companion or signs of a merger/interaction. In order to explore the evolution of the e(a) population, we present an overview of the available observations of e(a)'s in different environments both at low and high redshift. Finally, we discuss the role of dust in determining the e(a) spectral properties and we propose a scenario of selective obscuration in which the extinction decreases with the stellar age.Comment: 26 pages, Latex, including 7 postscript figures, accepted for publication in the Astrophysical Journa

First mid-infrared spectrum of a faint high-z galaxy: Observations of CFRS 14.1157 with the Infrared Spectrograph on the Spitzer Space Telescope

The unprecedented sensitivity of the Infrared Spectrograph on the Spitzer Space Telescope allows for the first time the measurement of mid-infrared spectra from 14 to 38 microns of faint high-z galaxies. This unique capability is demonstrated with observations of sources having 16 micron fluxes of 3.6 mJy (CFRS 14.1157) and 0.35 mJy (CFRS 14.9025). A spectral-fitting technique is illustrated which determines the redshift by fitting emission and absorption features characteristic of nearby galaxies to the spectrum of an unknown source. For CFRS 14.1157, the measured redshift is z = 1.00+/-0.20 in agreement with the published result of z = 1.15. The spectrum is dominated by emission from an AGN, similar to the nucleus of NGC 1068, rather than a typical starburst with strong PAH emission like M82. Such spectra will be crucial in characterizing the nature of newly discovered distant galaxies, which are too faint for optical follow-up.Comment: Accepted in ApJ Sup. Spitzer Special Issue, 4 pages, 5 figure

VLT-ISAAC near-IR Spectroscopy of ISO selected Hubble Deep Field South Galaxies

We report the results of near-infrared VLT-ISAAC spectroscopy of a sample of 12 galaxies at z = 0.4-1.4, drawn from the ISOCAM survey of the Hubble Deep Field South. We find that the rest frame R-band spectra of the ISOCAM galaxies resemble those of powerful dust-enshrouded starbursts. Halpha emission is detected in 11 out of 12 objects down to a flux limit of 7x10^(-17) erg/cm^2/s, corresponding to a luminosity limit of 10^41 erg/s at z = 0.6, (for an Ho = 50 and Omega = 0.3 cosmology). From the Halpha luminosities in these galaxies we derive estimates of the star formation rate in the range 2--50 Mo/yr for stellar masses 1--100 Mo. The raw Halpha-based star formation rates are an order of magnitude or more lower than SFR(FIR) estimates based on ISOCAM LW3 fluxes. If the Halpha emission is corrected for extinction the median offset is reduced to a factor of 3. The sample galaxies are part of a new population of optically faint but infrared--luminous active starburst galaxies, which are characterized by an extremely high rate of evolution with redshift up to z~1.5 and expected to contribute significantly to the cosmic far-IR extragalactic background.Comment: Accepted for publication in the Astrophysical Journal Letters, 16 pages, 2 figure