arXiv subjects

Antonio D. Montero-Dorta

Publications and source records attributed to Antonio D. Montero-Dorta.

59 records · Page 4Linked to original sources

arXiv2011

Fiber Assignment in Next-generation Wide-field Spectrographs

We present an optimized algorithm for assigning fibers to targets in next-generation fiber-fed multi-object spectrographs. The method, that we named draining algorithm, ensures that the maximum number of targets in a given target field is observed in the first few tiles. Using randomly distributed targets and mock galaxy catalogs we have estimated that the gain provided by the draining algorithm as compared to a random assignment can be as much as 2% for the first tiles. This would imply for a survey like BigBOSS saving for observation several hundred thousand objects or, alternatively, reducing the covered area in ~350 sq. deg. An important advantage of this method is that the fiber collision problem can be solved easily and in an optimal way. We also discuss additional optimizations of the fiber positioning process. In particular, we show that allowing for rotation of the focal plane can improve the efficiency of the process in ~3.5-4.5% even if only small adjustments are permitted (up to 2 deg). For instruments that allow large rotations of the focal plane the expected gain increases to ~5-6%. These results, therefore, strongly support focal plane rotation in future spectrographs, as far as the efficiency of the fiber positioning process is concerned. Finally, we discuss on the implications of our optimizations and provide some basic hints for an optimal survey strategy based on the number of targets per positioner.

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arXiv2008

The SDSS DR6 Luminosity Functions of Galaxies

We present number counts, luminosity functions (LFs) and luminosity densities of galaxies obtained using the Sloan Digital Sky Survey Sixth Data Release in all SDSS photometric bands. Thanks to the SDSS DR6, galaxy statistics have increased by a factor of ~9 in the u-band and by a factor of ~4-5 in the rest of the SDSS bands with respect to the previous work of Blanton et al. (2003b). In addition, we have achieved a high redshift completeness in our galaxy samples. Firstly, by making use of the survey masks, provided by the NYU-VAGC DR6, we have been able to define an area on the sky of high angular redshift completeness. Secondly, we guarantee that brightness-dependent redshift incompleteness is small within the magnitude ranges that define our galaxy samples. With these advances, we have estimated very accurate SDSS DR6 LFs in both the bright and the faint end. In the {0.1}^r-band, our SDSS DR6 luminosity function is well fitted by a Schechter LF with parameters Phi_{*}=0.90 +/- 0.07$, M_{*}-5log_{10}h=-20.73 +/- 0.04 and alpha=-1.23 +/- 0.02. As compared with previous results, we find some notable differences. In the bright end of the {0.1}^u-band luminosity function we find a remarkable excess, of ~1.7 dex at M_{{0.1}^u}=-20.5, with respect to the best-fit Schechter LF. This excess weakens in the {0.1}^g-band, fading away towards the very red {0.1}^z-band. A preliminary analysis on the nature of this bright-end bump reveals that it is mostly comprised of active galaxies and QSOs. It seems, therefore, that an important fraction of this exceeding luminosity may come from nuclear activity. In the faint end of the SDSS DR6 luminosity functions, where we can reach 1-1.5 magnitudes deeper than the previous SDSS LF estimation, we obtain a steeper slope [ABRIDGED].

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arXiv2008

The DEEP2 Galaxy Redshift Survey: The Red Sequence AGN Fraction and its Environment and Redshift Dependence

We measure the dependence of the AGN fraction on local environment at z~1, using spectroscopic data taken from the DEEP2 Galaxy Redshift Survey, and Chandra X-ray data from the All-Wavelength Extended Groth Strip International Survey (AEGIS). To provide a clean sample of AGN we restrict our analysis to the red sequence population; this also reduces additional colour-environment correlations. We find evidence that high redshift LINERs in DEEP2 tend to favour higher density environments relative to the red population from which they are drawn. In contrast, Seyferts and X-ray selected AGN at z~1 show little (or no) environmental dependencies within the same underlying population. We compare these results with a sample of local AGN drawn from the SDSS. Contrary to the high redshift behaviour, we find that both LINERs and Seyferts in the SDSS show a slowly declining red sequence AGN fraction towards high density environments. Interestingly, at z~1 red sequence Seyferts and LINERs are approximately equally abundant. By z~0, however, the red Seyfert population has declined relative to the LINER population by over a factor of 7. We speculate on possible interpretations of our results.

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arXiv2006

The Halo Mass Function Redshift Dependence

It has recently been shown that the correct halo mass function high mass behaviour may be obtained by an appropriate treatment of the all-mass-at-center problem. Here we show that the treatment of this problem leads to an accumulated mass fraction, F, which is not a universal function of the linear variance of the density contrast, but depends also on the shape of the power spectrum. For relevant power spectra F is a universal function of two quantities: the linear variance and a quantity related to the local shape (at the given mass scale) of the power spectrum. This implies, for a given shape of the power spectrum, a redshift dependence of the mass function, which is quite important for a cold dark matter power spectrum. Our results are in good agreement with numerical simulations.

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arXiv2006

Understanding the Cosmic Mass Function High Mass Behaviour

We claim that the discrepancy found between theoretical predictions for the cosmic mass function and those found in numerical simulations is due to the fact that in deriving the former all mass elements are assumed to be at the center of the object they belong to (the all-mass-at-center problem). By an appropriate treatment of this problem, using the spherical collapse model (which is not a bad approximation in the high mass limit), we obtain both the high mass behaviour found in simulations and the true assymptotic behaviour of the mass function (for arbitrarily high masses). Therefore, we conclude that by combining ellipsoidal dynamics with a suitable treatment of the all-mass-at-center problem (that we will show in a follow up work) a theoretical prediction for the cosmic mass function in full agreement with simulations may be obtained.

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