Multiple rooks of chess - a generic integral field unit deployment technique

A new field re-configuration technique, Multiple Rooks of Chess (MRC), for multiple deployable Integral Field Spectrographs has been developed. The method involves mechanical geometry as well as an optimized deployment algorithm. The geometry is found to be simple for mechanical implementation. The algorithm initially assigns the IFUs to the target objects and then devises the movement sequence based on the current and the desired IFU positions. The reconfiguration time using the suitable actuators which runs at 20 cm/s is found to be a maximum of 25 seconds for the circular DOTIFS focal plane (180 mm diameter). The Geometry Algorithm Combination (GAC) has been tested on several million mock target configurations with object-to-IFU ({\tau} ) ratio varying from 0.25 to 16. The MRC method is found to-be efficient in target acquisition in terms of field revisit and deployment time without any collision or entanglement of the fiber bundles. The efficiency of the technique does not get affected by the increase in number density of target objects. The technique is compared with other available methods based on sky coverage, flexibility and overhead time. The proposed geometry and algorithm combination is found to have an advantage in all of the aspects.Comment: 18 Pages, 13 Figures, 1 Tabl

Rest-frame ultra-violet spectra of massive galaxies at z=3: evidence of high-velocity outflows

Galaxy formation models invoke the presence of strong feedback mechanisms that regulate the growth of massive galaxies at high redshifts. In this paper we aim to: (1) confirm spectroscopically the redshifts of a sample of massive galaxies selected with photometric redshifts z > 2.5; (2) investigate the properties of their stellar and interstellar media; (3) detect the presence of outflows, and measure their velocities. To achieve this, we analysed deep, high-resolution (R~2000) FORS2 rest-frame UV spectra for 11 targets. We confirmed that 9 out of 11 have spectroscopic redshifts z > 2.5. We also serendipitously found two mask fillers at redshift z > 2.5, which originally were assigned photometric redshifts 2.0 < z < 2.5. In the four highest-quality spectra we derived outflow velocities by fitting the absorption line profiles with models including multiple dynamical components. We found strongly asymmetric, high-ionisation lines, from which we derived outflow velocities ranging from 480 to 1518 km/s. The two galaxies with highest velocity show signs of AGN. We revised the spectral energy distribution fitting U-band through 8 micron photometry, including the analysis of a power-law component subtraction to identify the possible presence of active galactic nuclei (AGN). The revised stellar masses of all but one of our targets are >1e10 Msun, with four having stellar masses > 5e10 Msun. Three galaxies have a significant power-law component in their spectral energy distributions, which indicates that they host AGN. We conclude that massive galaxies are characterised by significantly higher velocity outflows than the typical Lyman break galaxies at z ~ 3. The incidence of high-velocity outflows (~40% within our sample) is also much higher than among massive galaxies at z < 1, which is consistent with the powerful star formation and nuclear activity that most massive galaxies display at z > 2.Comment: 17 pages, 14 figures, Accepted for publication in A&

MOONS: The New Multi-Object Spectrograph for the VLT

MOONS is the new Multi-Object Optical and Near-infrared Spectrograph currently under construction for the Very Large Telescope (VLT) at ESO. This remarkable instrument combines, for the first time, the collecting power of an 8-m telescope, 1000 fibres with individual robotic positioners, and both low- and high-resolution simultaneous spectral coverage across the 0.64-1.8 micron wavelength range. This facility will provide the astronomical community with a powerful, world-leading instrument able to serve a wide range of Galactic, extragalactic and cosmological studies. Construction is now proceeding full steam ahead and this overview article presents some of the science goals and the technical description of the MOONS instrument. More detailed information on the MOONS surveys is provided in the other dedicated articles in this Messenger issue.STFC ER

The role of black hole mass in quasar radio activity

We use a homogeneous sample of about 300, 0.3 <~ z <~ 3, radio-loud quasars drawn from the FIRST and 2dF QSO surveys to investigate a possible dependence of radio activity on black-hole mass. By analyzing composite spectra for the populations of radio-quiet and radio-loud QSOs -- chosen to have the same redshift and luminosity distribution -- we find with high statistical significance that radio-loud quasars are on average associated with black holes of masses ~10^{8.6} M_sun, about twice as large as those measured for radio-quiet quasars (~10^{8.3} M_sun). We also find a clear dependence of black hole mass on optical luminosity of the form log (M_BH/M_sun)_{RL}= 8.57(\pm 0.06) - 0.27(\pm 0.06) (M_B + 24.5) and log (M_BH/M_sun)_{RQ}= 8.43(\pm 0.05) -0.32(\pm 0.06) (M_B + 24.5), respectively for the case of radio-loud and radio-quiet quasars. It is intriguing to note that these two trends run roughly parallel to each other, implying that radio-loud quasars are associated to black holes more massive than those producing the radio-quiet case at all sampled luminosities. On the other hand, in the case of radio-loud quasars, we find evidence for only a weak (if any) dependence of the black hole mass on radio power. The above findings seem to support the belief that there exists -- at a given optical luminosity -- a threshold black hole mass associated with the onset of significant radio activity such as that of radio-loud QSOs; however, once the activity is triggered, there appears to be very little connection between black hole mass and level of radio output.Comment: 10 pages, 10 figures, minor changes to match the accepted versio

Faint radio-loud quasars: clues to their evolution

The quasar sample selected by cross-correlating the FIRST and the 2dF Quasar Redshift Surveys allows us to explore, for the first time, the faint end of the radio and optical luminosity functions up to z = 2.2. We find indications (~3 \sigma) of a negative evolution for these faint sources at z > 1.8, both in radio and optical bands. This corresponds to a decrement in the space density of faint quasars of about a factor 2 at z=2.2 and confirms the presence of a differential evolution for the population of radio-active quasars. The faint end of both luminosity functions flattens and the comparison with the (optical) number density of the whole quasar population supports a dependence of the fraction of radio detected quasars on the optical luminosity. A progressive decrease in the fraction of quasars in the whole radio source population can be consistently accounted for within the `receding torus' scenario. The population of low luminosity quasars, which the FIRST-2dF detects, appears to depart from the `classical' scheme for radio-loud quasars.Comment: 11 pages, 7 figures, accepted for publication in MNRA

MOONS:The New Multi-Object Spectrograph for the VLT

MOONS is the new Multi-Object Optical and Near-infrared Spectrograph currently under construction for the Very Large Telescope (VLT) at ESO. This remarkable instrument combines, for the first time, the collecting power of an 8-m telescope, 1000 fibres with individual robotic positioners, and both low- and high-resolution simultaneous spectral coverage across the 0.64-1.8 micron wavelength range. This facility will provide the astronomical community with a powerful, world-leading instrument able to serve a wide range of Galactic, extragalactic and cosmological studies. Construction is now proceeding full steam ahead and this overview article presents some of the science goals and the technical description of the MOONS instrument. More detailed information on the MOONS surveys is provided in the other dedicated articles in this Messenger issue

Determining the stellar masses of submillimetre galaxies: the critical importance of star formation histories

Submillimetre (submm) galaxies are among the most rapidly star-forming and most massive high-redshift galaxies; thus, their properties provide important constraints on galaxy evolution models. However, there is still a debate about their stellar masses and their nature in the context of the general galaxy population. To test the reliability of their stellar mass determinations, we used a sample of simulated submm galaxies for which we derived stellar masses via spectral energy distribution (SED) modelling (with Grasil, Magphys, Hyperz and LePhare) adopting various star formation histories (SFHs). We found that the assumption of SFHs with two independent components leads to the most accurate stellar masses. Exponentially declining SFHs (tau) lead to lower masses (albeit still consistent with the true values), while the assumption of single-burst SFHs results in a significant mass underestimation. Thus, we conclude that studies based on the higher masses inferred from fitting the SEDs of real submm galaxies with double SFHs are most likely to be correct, implying that submm galaxies lie on the high-mass end of the main sequence of star-forming galaxies. This conclusion appears robust to assumptions of whether or not submm galaxies are driven by major mergers, since the suite of simulated galaxies modelled here contains examples of both merging and isolated galaxies. We identified discrepancies between the true and inferred stellar ages (rather than the dust attenuation) as the primary determinant of the success/failure of the mass recovery. Regardless of the choice of SFH, the SED-derived stellar masses exhibit a factor of ~2 scatter around the true value; this scatter is an inherent limitation of the SED modelling due to simplified assumptions. Finally, we found that the contribution of active galactic nuclei does not have any significant impact on the derived stellar masses.Comment: Accepted to A&A. 11 pages, 9 figures, 1 table. V2 main changes: 1) discussion of the stellar age as the main parameter influencing the success of an SED model (Fig. 4, 5, 7); 2) discussion of the age-dust degeneracy (Fig 9); 3) the comparison of real and simulated submm galaxies (Fig 1

The Radio Loud / Radio Quiet dichotomy: news from the 2dF QSO Redshift Survey

We present a detailed analysis of a sample of radio-detected quasars, obtained by matching together objects from the FIRST and 2dF Quasar Redshift Surveys. The dataset consists of 113 sources, spanning a redshift range 0.3 < z < 2.2, with optical magnitudes 18.25 < b_J < 20.85 and radio fluxes S_{1.4 GHz} < 1 mJy. These objects exhibit properties such as redshift and colour distribution in full agreement with those derived for the whole quasar population, suggestive of an independence of the mechanism(s) controlling the birth and life-time of quasars of their level of radio emission. The long debated question of radio-loud (RL)/radio-quiet (RQ) dichotomy is then investigated for the combined FIRST-2dF and FIRST-LBQS sample, since they present similar selection criteria. We find the fraction of radio detections to increase with magnitude from < 3% at the faintest levels up to 20% for the brightest sources. The classical RL/RQ dichotomy, in which the distribution of radio-to-optical ratios and/or radio luminosities shows a lack of sources, is ruled out by our analysis. We also find no tight relationship between optical and radio luminosities for sources in the considered sample, result that tends to exclude the mass of the quasar black hole as the physical quantity associated to the level of radio emission.Comment: 11 pages, 14 figures, accepted by MNRA