5-micron photometry of late-type dwarfs

We present narrowband-M photometry of nine low-mass dwarfs with spectral types ranging from M2.5 to L0.5. Combining the (L'-M') colours derived from our observations with data from the literature, we find colours consistent with a Rayleigh-Jeans flux distribution for spectral types earlier than M5, but enhanced F_3.8/F_4.7 flux ratios (negative (L'-M') colours) at later spectral types. This probably reflects increased absorption at M' due to the CO fundamental band. We compare our results against recent model predictions and briefly discuss the implications.Comment: accepted for the Astronomical Journa

Risky Decisions and Decision Support - Does Stress Make a Difference?

Studies of human decision making have demonstrated that stress exacerbates risk taking. Since all decisions involve some element of risk, stress has critical impact on decision quality. Decisions are found to improve with stress up to an optimal threshold beyond which deterioration is observed. However, few studies have examined the psychological experiences underlying risk-taking behavior in conjunction with stress creators. In this paper we propose a research framework that integrates pre-conditions of stress (perceptions of high gain/loss, risk, complexity, and organizational pressure) with observed psychological experiences (time pressure, uncertainty, information overload, and dynamism) that potentially result in risky decision making. This framework suggests that decision support systems have the potential of mitigating or enhancing the psychological perceptions of stress and, hence, impacting decision quality. Empirical testing of a component of this framework provided interesting preliminary results. Subjects experiencing high stress indicated the same levels of perceived uncertainty and dynamism as subjects exposed to low stress, suggesting that use of a decision support system mitigated the perceptions of dynamism and uncertainty for the high stress group. Contrary to hypotheses, the use of a decision support system did not mitigate perceptions of information overload

Constraining massive gravity with recent cosmological data

A covariant formulation of a theory with a massive graviton and no negative energy state has been recently proposed as an alternative to the usual General Relativity framework. For a spatially flat homogenous and isotropic universe, the theory introduces modified Friedmann equations where the standard matter term is supplemented by four effective fluids mimicking dust, cosmological constant, quintessence and stiff matter, respectively. We test the viability of this massive gravity formulation by contrasting its theoretical prediction to the Hubble diagram as traced by Type Ia Supernovae (SNeIa) and Gamma Ray Bursts (GRBs), the $H(z)$ measurements from passively evolving galaxies, Baryon Acoustic Oscillations (BAOs) from galaxy surveys and the distance priors from the Cosmic Microwave Background Radiation (CMBR) anisotropy spectrum. It turns out that the model is indeed able to very well fit this large dataset thus offering a viable alternative to the usual dark energy framework. We finally set stringent constraints on its parameters also narrowing down the allowed range for the graviton mass.Comment: 10 pages, 1 figure, 2 tables, accepted for publication on Physical Review

The Rest-Frame Optical Luminosity Density, Color, and Stellar Mass Density of the Universe from z=0 to z=3

We present the evolution of the rest-frame optical luminosity density, of the integrated rest-frame optical color, and of the stellar mass density for a sample of Ks-band selected galaxies in the HDF-S. We derived the luminosity density in the rest-frame U, B, and V-bands and found that the luminosity density increases by a factor of 1.9+-0.4, 2.9+-0.6, and 4.9+-1.0 in the V, B, and U rest-frame bands respectively between a redshift of 0.1 and 3.2. We derived the luminosity weighted mean cosmic (U-B)_rest and (B-V)_rest colors as a function of redshift. The colors bluen almost monotonically with increasing redshift; at z=0.1, the (U-B)_rest and (B-V)_rest colors are 0.16 and 0.75 respectively, while at z=2.8 they are -0.39 and 0.29 respectively. We derived the luminosity weighted mean M/LV using the correlation between (U-V)_rest and log_{10} M/LV which exists for a range in smooth SFHs and moderate extinctions. We have shown that the mean of individual M/LV estimates can overpredict the true value by ~70% while our method overpredicts the true values by only ~35%. We find that the universe at z~3 had ~10 times lower stellar mass density than it does today in galaxies with LV>1.4 \times 10^{10} h_{70}^-2 Lsol. 50% of the stellar mass of the universe was formed by $z~1-1.5. The rate of increase in the stellar mass density with decreasing redshift is similar to but above that for independent estimates from the HDF-N, but is slightly less than that predicted by the integral of the SFR(z) curve.Comment: 19 pages, 12 figures, Accepted for Publication in the Dec. 20, 2003 edition of the Astrophysical Journal. Minor changes made to match the accepted version including short discussions on the effects of clustering and on possible systematic effects resulting from photometric redshift error

Dust Biasing of Damped Lyman Alpha Systems: a Bayesian Analysis

If damped Lyman alpha systems (DLAs) contain even modest amounts of dust, the ultraviolet luminosity of the background quasar can be severely diminished. When the spectrum is redshifted, this leads to a bias in optical surveys for DLAs. Previous estimates of the magnitude of this effect are in some tension; in particular, the distribution of DLAs in the column-density -- metallicity plane has led to claims that we may be missing a considerable fraction of metal rich, high column density DLAs, whereas radio surveys do not unveil a substantial population of otherwise hidden systems. Motivated by this tension, we perform a Bayesian parameter estimation analysis of a simple dust obscuration model. We include radio and optical observations of DLAs in our overall likelihood analysis and show that these do not, in fact, constitute conflicting constraints. Our model gives statistical limits on the biasing effects of dust, predicting that only 7% of DLAs are missing from optical samples due to dust obscuration; at 2 sigma confidence, this figure takes a maximum value of 17%. This contrasts with recent claims that DLA incidence rates are underestimated by 30 -- 50%. Optical measures of the mean metallicities of DLAs are found to underestimate the true value by just 0.1 dex (or at most 0.4 dex, 2 sigma confidence limit), in agreement with the radio survey results of Akerman et al. The quantity most affected by dust biasing is the total cosmic density of metals in DLAs, Omega_{Z,DLA}, which is underestimated in optical surveys by a factor of approximately two. (Abridged.)Comment: 12 pages,8 figures, accepted for publication in MNRAS. Minor update with slightly expanded detail on previous completeness limits and forecasts for future radio survey

Multiphase Powerful Outflows Detected in High-z Quasars

open10siWe acknowledge financial support from NASA via the grants 80NSSC19K0955 and NNX16AH33G. M.Ga. acknowledges partial support by NASA Chandra GO8-19104X/GO920114X and HST GO-15890.020-A. M.Gi. is supported by the "Programa de Atraccion de Talento" of the Comunidad de Madrid, grant number 2018-T1/TIC-11733. We thank Daniel Proga, Bing Zhang, Cristian Saez, Monika Moscibrodzka, and Tim Waters for useful comments and suggestions. We greatly appreciate the useful comments made by the referee. Scientific results reported in this article are based partly on observations made by the Chandra X-ray Observatory (CXO) and XMMNewton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA. This publication makes use of data from the Sloan Digital Sky Survey (SDSS).We present results from a comprehensive study of ultrafast outflows (UFOs) detected in a sample of 14 quasars, 12 of which are gravitationally lensed, in a redshift range of 1.41-3.91, near the peak of the active galactic nucleus (AGN) and star formation activity. New XMM-Newton observations are presented for six of them, which were selected to be lensed and contain a narrow absorption line (NAL) in their UV spectra. Another lensed quasar was added to the sample, albeit already studied because it was not searched for UFOs. The remaining seven quasars of our sample are known to contain UFOs. The main goals of our study are to infer the outflow properties of high-z quasars, constrain their outflow induced feedback, study the relationship between the outflow properties and the properties of the ionizing source, and compare these results to those of nearby AGN. Our study adds six new detections (> 99% confidence) of UFOs at z > 1.4, almost doubling the current number of cases. Based on our survey of six quasars selected to contain a NAL and observed with XMM-Newton, the coexistence of intrinsic UV NALs and UFOs is found to be significant in >83% of these quasars suggesting a link between multiphase AGN feedback properties of the meso- and microscale. The kinematic luminosities of the UFOs of our high-z sample are large compared to their bolometric luminosities (median of L K/L Bol ⪆ 50%). This suggests they provide efficient feedback to influence the evolution of their host galaxies and that magnetic driving may be a significant contributor to their acceleration.openChartas G.; Cappi M.; Vignali C.; Dadina M.; James V.; Lanzuisi G.; Giustini M.; Gaspari M.; Strickland S.; Bertola E.Chartas G.; Cappi M.; Vignali C.; Dadina M.; James V.; Lanzuisi G.; Giustini M.; Gaspari M.; Strickland S.; Bertola E