arXiv subjects

G. Magris C.

Publications and source records attributed to G. Magris C..

3 recordsLinked to original sources

arXiv2017

Galaxy properties from J-PAS narrow-band photometry

We study the consistency of the physical properties of galaxies retrieved from SED-fitting as a function of spectral resolution and signal-to-noise ratio (SNR). Using a selection of physically motivated star formation histories, we set up a control sample of mock galaxy spectra representing observations of the local universe in high-resolution spectroscopy, and in 56 narrow-band and 5 broad-band photometry. We fit the SEDs at these spectral resolutions and compute their corresponding the stellar mass, the mass- and luminosity-weighted age and metallicity, and the dust extinction. We study the biases, correlations, and degeneracies affecting the retrieved parameters and explore the rôle of the spectral resolution and the SNR in regulating these degeneracies. We find that narrow-band photometry and spectroscopy yield similar trends in the physical properties derived, the former being considerably more precise. Using a galaxy sample from the SDSS, we compare more realistically the results obtained from high-resolution and narrow-band SEDs (synthesized from the same SDSS spectra) following the same spectral fitting procedures. We use results from the literature as a benchmark to our spectroscopic estimates and show that the prior PDFs, commonly adopted in parametric methods, may introduce biases not accounted for in a Bayesian framework. We conclude that narrow-band photometry yields the same trend in the age-metallicity relation in the literature, provided it is affected by the same biases as spectroscopy; albeit the precision achieved with the latter is generally twice as large as with the narrow-band, at SNR values typical of the different kinds of data.

astro-ph.GA↗

arXiv2005

Nanodiamond dust and the far-ultraviolet quasar break

We explore the possibility that the steepening observed shortward of 1000A in the energy distribution of quasars may result from absorption by dust, being either intrinsic to the quasar environment or intergalactic. We find that a dust extinction curve consisting of nanodiamonds, composed of terrestrial cubic diamonds or with surface impurities as found in carbonaceous chondrite meteorites, such as Allende, is successful in reproducing the sharp break observed. The intergalactic dust model is partially successful in explaining the shape of the composite energy distribution, but must be discarded in the end, as the amount of crystalline dust required is unreasonable and would imply an improbable fine tuning among the dust formation processes. The alternative intrinsic dust model requires a mixture of both cubic diamonds and Allende nanodiamonds and provide a better fit of the UV break. The gas column densities implied are of the order 10^{20} cm^{-2} assuming solar metallicity for carbon and full depletion of carbon into dust. The absorption only occurs in the ultraviolet and is totally negligible in the visible. The minimum dust mass required is of the order ~ 0.003 r_{pc}^{2}M_o, where r_{pc} is the distance in parsec between the dust screen and the continuum source. The intrinsic dust model reproduces the flux {\it rise} observed around 660A in key quasar spectra quite well. We present indirect evidence of a shallow continuum break near 670A (18.5 eV), which would be intrinsic to the quasar continuum.

astro-ph↗

arXiv2003

ADEMIS: A Library of Evolutionary Models for Emission-Line Galaxies: I- Dustfree Models

We present an extensive set of stellar population synthesis models, which self-consistently include the (optical--far-UV) continuum emission from stars as well as the resulting emission-line spectrum from photoionized gas surrounding massive stars during their main sequence life-time. The models are presented as a compiled library, ADEMIS, available electronically. ADEMIS contains the equivalent widths and the intensities of the lines [OII]3727, Hbeta, [OIII]5007, Halpha, [NII]6584, which were calculated assuming a metallicity of 0.2, 0.4, 1.0, and 1.5 Zo and a wide range of ionization parameters. We investigate the regime of continuous star formation, assuming a Salpeter initial mass function, whose upper mass limit is an input parameter. The calculated equivalent width models, which are function of the burst age, are compared with the Jansen et al. atlas of integrated spectra for nearby galaxies. We reproduce the observed properties of galaxies along the full Hubble sequence and suggest how the metallicity and age of such galaxies might be be roughly estimated.

astro-ph↗