Overview of the LISA mission and R&D developments at the APC

International audienceThe study of the gravitational waves opens a new window for the observation of the universe. Completing the observations obtained from electro-magnetic waves, neutrinos and cosmic rays, the gravitational waves will provide informations on the most violent phenomena in the universe, as supernova explosions, collisions of binary systems or mergers of black holes. Their study will thus increase our knowledge in astrophysics, but also in cosmology and fundamental physics. This paper will make a short presentation of the future space interferometer LISA, aiming at detecting gravitational waves, and presents an overview of the R&D developments for LISA at the APC laboratory

LISA ON TABLE: AN OPTICAL SIMULATOR FOR LISA

LISA, the first space project for detecting gravitational waves, relies on two main technical challenges: the free falling masses and an outstanding precision on phase shift measurements (a few pm on 5 Mkm in the LISA band). The technology of the free falling masses, i.e. their isolation to forces other than gravity and the capability for the spacecraft to precisely follow the test masses, will soon be tested with the technological LISA Pathfinder mission. The performance of the phase measurement will be achieved by at least two stabilization stages: a pre-stabilisation of the laser frequency at a level of 10-13 (relative frequency stability) will be further improved by using numerical algorithms, such as Time Delay Interferometry, which have been theoretically and numerically demonstrated to reach the required performance level (10-21). Nevertheless, these algorithms, though already tested with numerical model of LISA, require experimental validation, including 'realistic' hardware elements. Such an experiment would allow to evaluate the expected noise level and the possible interactions between subsystems. To this end, the APC is currently developing an optical benchtop experiment, called LISA On Table (LOT), which is representative of the three LISA spacecraft. A first module of the LOT experiment has been mounted and is being characterized. After completion this facility may be used by the LISA community to test hardware (photodiodes, phasemeters) or software (reconstruction algorithms) components

High resolution numerical study of the Algiers 2001 flash flood: sensitivity to the upper-level potential vorticity anomaly

From 9 to 11 November 2001, intense cyclogenesis affected the northern coasts of Africa and more particularly the densely populated city of Algiers. During the morning of 10 November, more than 130 mm of precipitation was recorded at Bouzareah and resulted in mudslides which devastated the Bab-el-Oued district. This disaster caused more than 700 casualties and catastrophic damage. Like many other heavy rainstorms in the western Mediterranean, this event was associated with the presence of an upper-level trough materialized by a deep stratospheric intrusion and characterized by high potential vorticity values. In this study, the impact of this synoptic structure on the localization and intensity of the precipitation which affected Algiers is investigated using a potential vorticity (PV) inversion method coupled for the first time with the French non-hydrostatic MESO-NH model. A set of perturbed synoptic environments was designed by slightly modifying the extent and the intensity of the coherent potential vorticity structures in the operational ARPEGE analysis. It is shown that such modifications may have a strong impact on the fine-scale precipitation forecast in the Algiers region, thereby demonstrating the fundamental role played by the potential vorticity anomaly during this exceptional meteorological event

Quasars probing intermediate redshift star-forming galaxies

We present a sample of 46 [OIII]-emitting galaxies at z<0.8 detected in the fibre spectra of quasars from the SDSS-DR7 through an automatic search procedure. We also detect [OII] and Hb emission lines from most of these galaxies in the SDSS spectra. We study both the emission and absorption properties of a sub-sample of 17 galaxies in the redshift range z=0.4-0.7, where MgII lines are covered by the SDSS spectra. The measured lower-limits on the star-formation rates of these galaxies are in the range 0.2-20 M_sun/yr. The emission line luminosities and (O/H) metallicities from R23 measured in this sample are similar to what is found in normal galaxies at these redshifts. Thus, this constitutes a unique sample of intermediate redshift star-forming galaxies where we can study the QSO absorber - galaxy connection. Strong MgII (W>1A) as well as MgI absorption lines are detected in the QSO spectra at the redshift of most of these galaxies. Strong FeII (W>1A) absorption lines are also generally detected whenever the appropriate wavelength ranges are covered. This suggests that most of these systems could be bona-fide Damped Lyman-alpha systems. We investigate various possible relations between the MgII rest equivalent widths and the emission line properties. We find a possible (2 sigma) correlation between the emission-line metallicity of the galaxies and the MgII rest equivalent width of the absorbers [truncated].Comment: 15 pages, 11 figures, 5 tables. accepted for publication in MNRA

2D Kinematics and Physical Properties of z~3 Star-Forming Galaxies

We present results from a study of the kinematic structure of star-forming galaxies at redshift z~3 selected in the VVDS, using integral-field spectroscopy of rest-frame optical nebular emission lines, in combination with rest-frame UV spectroscopy, ground-based optical/near-IR and Spitzer photometry. We also constrain the underlying stellar populations to address the evolutionary status of these galaxies. We infer the kinematic properties of four galaxies: VVDS-20298666, VVDS-020297772, VVDS-20463884 and VVDS-20335183 with redshifts z = 3.2917, 3.2878, 3.2776, and 3.7062, respectively. While VVDS-20463884 presents an irregular velocity field with a peak in the local velocity dispersion of the galaxy shifted from the centre of the galaxy, VVDS-20298666 has a well-resolved gradient in velocity over a distance of ~4.5 kpc with a peak-to-peak amplitude of v = 91 km/s . We discovered that the nearby galaxy, VVDS-020297772 (which shows traces of AGN activity), is in fact a companion at a similar redshift with a projected separated of 12 kpc. In contrast, the velocity field of VVDS-020335183 seems more consistent with a merger on a rotating disk. However, all of the objects have a high local velocity dispersion (sigma ~ 60-70 km/s), which gives v/sigma < 1. It is unlikely that these galaxies are dynamically cold rotating disk of ionized gas.Comment: 14 pages and 16 figure

GMRT mini-survey to search for 21-cm absorption in Quasar-Galaxy Pairs at z~0.1

We present the results from our 21-cm absorption survey of a sample of 5 quasar-galaxy pairs (QGPs), with the redshift of the galaxies in the range 0.03<zg<0.18, selected from the SDSS. The HI 21-cm absorption was searched towards the 9 sight lines with impact parameters ranging from 10 to 55 kpc using GMRT. 21-cm absorption was detected only in one case i.e. towards the Quasar (zq=2.625 SDSS J124157.54+633241.6)-galaxy (zg=0.143 SDSS J124157.26+633237.6) pair with the impact parameter 11 kpc. The quasar sight line in this case pierces through the stellar disk of a galaxy having near solar metallicity (i.e (O/H)+12=8.7) and star formation rate uncorrected for dust attenuation of 0.1 M_odot/yr. The quasar spectrum reddened by the foreground galaxy is well fitted with the Milky Way extinction curve (with an Av of 0.44) and the estimated HI column density is similar to the value obtained from 21-cm absorption assuming spin temperature of 100K. Combining our sample with the z<0.1 data available in the literature, we find the detectability of 21-cm absorption with integrated optical depth greater than 0.1 km\s to be 50% for the impact parameter less than 20 kpc. Using the surface brightness profiles and relationship between the optical size and extent of the HI disk known for nearby galaxies, we conclude that in most of the cases of 21-cm absorption non-detection, the sight lines may not be passing through the HI gas. We also find that in comparison to the absorption systems associated with these QGPs, z<1 DLAs with 21-cm absorption detections have lower CaII equivalent widths despite having higher 21-cm optical depths and smaller impact parameters. This suggests that the current sample of DLAs may be a biased population that avoids sight lines through dusty star-forming galaxies. A systematic survey of QGPs is needed to confirm these findings and understand the nature of 21-cm absorbers.Comment: 17 pages, 5 tables, 19 figures, accepted for publication in MNRAS (abstract abridged

Emission-lines calibrations of the Star Formation Rate from the Sloan Digital Sky Survey

Our goal is to study the existing star formation rate calibrations based on emission-line luminosities and to provide new ones. We use the SDSS data release DR4, which gives star formation rates and emission-line luminosities of more than 100000 star-forming galaxies. We confirm that the best results are obtained with the Halpha calibration. This calibration has an uncertainty of 0.17 dex. We show that one has to check carefully the method used to derive the dust attenuation and to use the adequate calibration: in some cases, the standard scaling law has to be replaced by a more general power law. When data is corrected for dust attenuation but the Halpha emission line not observed, the use of the Hbeta emission line, has to be preferred to the [OII]3727 emission line. In the case of uncorrected data, the correction for dust attenuation can be assumed as a constant value but we show that such method leads to poor results, in terms of dispersion and residual slope. Self-consistent corrections, based e.g. on the absolute magnitude, give better results in terms of dispersion but still suffer from systematic shifts, and/or residual slopes. The best results with data not corrected for dust attenuation are obtained when using the observed [OII]3727 and Hbeta emission lines together. This calibration has an uncertainty of 0.23 dex

Quantum cascade laser frequency stabilisation at the sub-Hz level

Quantum Cascade Lasers (QCL) are increasingly being used to probe the mid-infrared "molecular fingerprint" region. This prompted efforts towards improving their spectral performance, in order to reach ever-higher resolution and precision. Here, we report the stabilisation of a QCL onto an optical frequency comb. We demonstrate a relative stability and accuracy of 2x10-15 and 10-14, respectively. The comb is stabilised to a remote near-infrared ultra-stable laser referenced to frequency primary standards, whose signal is transferred via an optical fibre link. The stability and frequency traceability of our QCL exceed those demonstrated so far by two orders of magnitude. As a demonstration of its capability, we then use it to perform high-resolution molecular spectroscopy. We measure absorption frequencies with an 8x10-13 relative uncertainty. This confirms the potential of this setup for ultra-high precision measurements with molecules, such as our ongoing effort towards testing the parity symmetry by probing chiral species

CITY AUTOMATED TRANSPORT SYSTEM (CATS): THE LEGACY OF AN INNOVATIVE EUROPEAN PROJECT

CATS is a collaborative European project promoting driverless vehicles that ended in December 2014. This contribution explains how the project evolved, including the handling of unexpected events and concentrating on lessons learned. The constructor and vehicle had to be changed for economic reasons in the middle of the project timeline. A second constructor went bankrupt, although access to his vehicles could be secured. For security and legal reasons, part of the final demonstration was relocated at short notice to the EPFL campus in Lausanne, Switzerland, where around 1600 people were transported during 16 days of vehicle operation. Reactions to the driverless vehicle concept were overwhelmingly positive. Implications for the acceptability of driverless vehicles in Europe and elsewhere are discussed