G. Cupani

X-shooter spectroscopy of young stellar objects - IV. Accretion in low-mass stars and substellar objects in Lupus

We present X-Shooter/VLT observations of a sample of 36 accreting low-mass stellar and sub-stellar objects (YSOs) in the Lupus star forming region, spanning a range in mass from ~0.03 to ~1.2Msun, but mostly with 0.1Msun < Mstar < 0.5Msun. Our aim is twofold: firstly, analyse the relationship between excess-continuum and line emission accretion diagnostics, and, secondly, to investigate the accretion properties in terms of the physical properties of the central object. The accretion luminosity (Lacc), and from it the accretion rate (Macc), is derived by modelling the excess emission, from the UV to the near-IR, as the continuum emission of a slab of hydrogen. The flux and luminosity (Ll) of a large number of emission lines of H, He, CaII, etc., observed simultaneously in the range from ~330nm to 2500nm, were computed. The luminosity of all the lines is well correlated with Lacc. We provide empirical relationships between Lacc and the luminosity of 39 emission lines, which have a lower dispersion as compared to previous relationships in the literature. Our measurements extend the Pab and Brg relationships to Lacc values about two orders of magnitude lower than those reported in previous studies. We confirm that different methodologies to measure Lacc and Macc yield significantly different results: Ha line profile modelling may underestimate Macc by 0.6 to 0.8dex with respect to Macc derived from continuum-excess measures. Such differences may explain the likely spurious bi-modal relationships between Macc and other YSOs properties reported in the literature. We derive Macc in the range 2e-12 -- 4e-8 Msun/yr and conclude that Macc is proportional to Mstar^1.8(+/-0.2), with a dispersion lower by a factor of about 2 than in previous studies. A number of properties indicate that the physical conditions of the accreting gas are similar over more than 5 orders of magnitude in Macc.

X-shooter spectroscopy of young stellar objects - II. Impact of chromospheric emission on accretion rate estimates

Context. The lack of knowledge of photospheric parameters and the level of chromospheric activity in young low-mass pre-main sequence stars introduces uncertainties when measuring mass accretion rates in accreting (Class II) Young Stellar Objects. A detailed investigation of the effect of chromospheric emission on the estimates of mass accretion rate in young low-mass stars is still missing. This can be undertaken using samples of young diskless (Class III) K and M-type stars. Aims. Our goal is to measure the chromospheric activity of Class III pre main sequence stars to determine its effect on the estimates of accretion luminosity (Lacc) and mass accretion rate (Macc) in young stellar objects with disks. Methods. Using VLT/X-Shooter spectra we have analyzed a sample of 24 non-accreting young stellar objects of spectral type between K5 and M9.5. We identify the main emission lines normally used as tracers of accretion in Class II objects, and we determine their fluxes in order to estimate the contribution of the chromospheric activity to the line luminosity. Results. We have used the relationships between line luminosity and accretion luminosity derived in the literature for Class II objects to evaluate the impact of chromospheric activity on the accretion rate measurements. We find that the typical chromospheric activity would bias the derived accretion luminosity by Lacc,noise< 10-3Lsun, with a strong dependence with the Teff of the objects. The noise on Macc depends on stellar mass and age, and the typical values of log(Macc,noise) range between -9.2 to -11.6Msun/yr. Conclusions. Values of Lacc< 10-3Lsun obtained in accreting low-mass pre main sequence stars through line luminosity should be treated with caution as the line emission may be dominated by the contribution of chromospheric activity.

Metals in the IGM approaching the re-ionization epoch: results from X-shooter at the VLT

We present the results of observations taken with the X-shooter spectrograph devoted to the study of quasars at z ∼ 6. This paper focuses on the properties of metals at high redshift traced, in particular, by the C IV doublet absorption systems. Six objects were observed with resolutions �27 and 34 km s −1 in the visual, and 37.5 and 53.5 km s −1 in the near-infrared. We detected 102 C IV lines in the range: 4.35 <z< 6.2 of which 27 are above z ∼ 5. Thanks to the characteristics of resolution and spectral coverage of X-shooter, we could also detect 25 Si IV doublets associated with the C IV at z 5. The column density distribution function of the C IV line sample is observed to evolve in redshift for z 5.3, with respect to the normalization defined by low-redshift (1.5 <z <4) C IV lines. This behaviour is reflected in the redshift evolution of the C IV cosmic mass density, � C IV, of lines with column density in the range 13.4 < log N(C IV) < 15, which is consistent with a drop of a factor of ∼ 2f or z 5.3. Considering only the stronger C IV lines (13.8 < log N(C IV) < 15), � C IV gently rises by a factor of ∼10 between z � 6.2 and z � 1.5 with a possible flattening towards z ∼ 0. The increase is well fitted by a power law: � C IV = (2 ± 1) × 10 −8 [(1 + z)/4] −3.1±0.1 .A n insight into the properties of the C IV absorbers and their evolution with redshift is obtained by comparing the observed column densities of associated C IV ,S iIV and C II absorptions with the output of a set of CLOUDY photoionization models. As already claimed by cosmological simulations, we find that C IV is a good tracer of the metallicity in the low-density intergalactic medium (IGM) gas at z ∼ 5−6 while at z ∼ 3 it arises in gas with overdensity δ ∼ 100.

New constraints on the free-streaming of warm dark matter from intermediate and small scale Lyman-alpha forest data

We present new measurements of the free-streaming of warm dark matter (WDM) from Lyman-α flux-power spectra. We use data from the medium resolution, intermediate redshift XQ-100 sample observed with the X-shooter spectrograph (z = 3 – 4.2) and the high-resolution, high-redshift sample used in Viel et al. (2013) obtained with the HIRES/MIKE spectrographs (z = 4.2 - 5.4). Based on further improved modelling of the dependence of the Lyman-α flux-power spectrum on the free-streaming of dark matter, cosmological parameters, as well as the thermal history of the intergalactic medium (IGM) with hydrodynamical simulations, we obtain the following limits, expressed as the equivalent mass of thermal relic WDM particles. The XQ-100 flux power spectrum alone gives a lower limit of 1.4 keV, the re-analysis of the HIRES/MIKE sample gives 4.1 keV while the combined analysis gives our best and significantly strengthened lower limit of 5.3 keV (all 2σ C.L.). The further improvement in the joint analysis is partly due to the fact that the two data sets have different degeneracies between astrophysical and cosmological parameters that are broken when the data sets are combined, and more importantly on chosen priors on the thermal evolution. These results all assume that the temperature evolution of the IGM can be modelled as a power law in redshift. Allowing for a non-smooth evolution of the temperature of the IGM with sudden temperature changes of up to 5000K reduces the lower limit for the combined analysis to 3.5 keV. A WDM with smaller thermal relic masses would require, however, a sudden temperature jump of 5000K or more in the narrow redshift interval z = 4.6 - 4.8, in disagreement with observations of the thermal history based on high-resolution resolution Lyman-α forest data and expectations for photo-heating and cooling in the low density IGM at these redshifts.

Strongly star-forming rotating disks in a complex merging system at z = 4.7 as revealed by ALMA

We performed a kinematical analysis of the [CII] line emission of the BR 1202-0725 system at z 4:7 using ALMA Science Verification observations. The most prominent sources of this system are a quasar and a submillimeter galaxy, separated by a projected distance of about 24 kpc and characterized by very high star-formation rates, higher than 1000 M yr 1 . However, the ALMA observations reveal that these galaxies apparently have undisturbed rotating disks, which is at variance with the commonly accepted scenario in which strong star formation activity is induced by a major merger. We also detected faint components which, after spectral deblending, were spatially resolved from the main quasar (QSO) and submillimeter galaxy (SMG) emissions. The relative velocities and positions of these components are compatible with orbital motions within the gravitational potentials generated by the QSO host galaxy and the SMG, suggesting that they are smaller galaxies in interaction or gas clouds in accretion flows of tidal streams. Moreover, we did not find any clear spectral evidence for outflows caused by AGN or stellar feedback. This suggests that the high star formation rates might be induced by interactions or minor mergers with these companions, whichdo not a ect the large-scale kinematics of the disks, however. Alternatively, the strong star formation may be fueled by the accretion of pristine gas from the host halo. Our kinematical analysis also indicates that the QSO and the SMG have similar dynamical masses, mostly in the form of molecular gas, and that the QSO host galaxy and the SMG are seen close to face-on with slightly di erent disk inclinations: the QSO host galaxy is seen almost face-on (i 15 ), while the SMG is seen at higher inclinations (i 25 ). Finally, the ratio between the black hole mass of the QSO, obtained from new XShooter spectroscopy, and the dynamical mass of the host galaxy is similar to value found in very massive local galaxies, suggesting that the evolution of black hole galaxy relations is probably better studied with dynamical than with stellar host galaxy masses.

On the Evolution of the Cosmic Ionizing Background

We study the observed cosmic ionizing background as a constraint on the nature of the sources responsible for the reionization of the Universe. In earlier work, we showed that extrapolations of the Ultra-Violet Luminosity Function (LF) of Lyman Break Galaxies (LBGs) at fixed Lyman continuum photon escape fraction are not able to reproduce the redshift evolution of this background. Here, we employ extrapolations of the high-z LFs to describe the contribution of LBGs to the ionizing photon rate, taking into account the smoothing of the baryonic perturbations, due to the background itself (i.e. the filtering mass), as well as a possible sharp increase of the escape fraction in dwarf galaxies. Under the hypothesis of a dominant contribution of LBGs to cosmic reionization, our results suggest that sources fainter than the current observational limits should be characterised by escape fractions of the order of ~0.1-0.3 (larger than the current estimates for bright galaxies) to account for a z>6 reionization and the measured evolution of cosmic ionizing background, at the same time. The contribution to the background from quasars turns out to be relevant at z<3. Overall, our results support the case for dedicated observations of faint galaxies in the rest-frame UV, in order to better determine their physical properties. Observed escape fractions outside our proposed range bear relevant consequences on the nature of the astrophysical sources responsible for cosmic reionization and/or its buildup process.

The evolution of neutral gas in damped Lyman α systems from the XQ-100 survey

We present a sample of 38 intervening Damped Lyman

High-resolution spectroscopy of a young, low-metallicity optically-thin L = 0.02L* star-forming galaxy at z = 3.12

\alpha

The ultracool dwarf DENIS-P J104814.7-395606 - Chromospheres and coronae at the low-mass end of the main-sequence

(DLA) systems identified towards 100

The First X-shooter Observations of Jets from Young Stars

z>3.5