arXiv subjects

E. Perez-Montero

Publications and source records attributed to E. Perez-Montero.

59 records · Page 4Linked to original sources

arXiv2007

Precision photometric redshift calibration for galaxy-galaxy weak lensing

Accurate photometric redshifts are among the key requirements for precision weak lensing measurements. Both the large size of the Sloan Digital Sky Survey (SDSS) and the existence of large spectroscopic redshift samples that are flux-limited beyond its depth have made it the optimal data source for developing methods to properly calibrate photometric redshifts for lensing. Here, we focus on galaxy-galaxy lensing in a survey with spectroscopic lens redshifts, as in the SDSS. We develop statistics that quantify the effect of source redshift errors on the lensing calibration and on the weighting scheme, and show how they can be used in the presence of redshift failure and sampling variance. We then demonstrate their use with 2838 source galaxies with spectroscopy from DEEP2 and zCOSMOS, evaluating several public photometric redshift algorithms, in two cases including a full p(z) for each object, and find lensing calibration biases as low as 1% (due to fortuitous cancellation of two types of bias) or as high as 20% for methods in active use (despite the small mean photoz bias of these algorithms). Our work demonstrates that lensing-specific statistics must be used to reliably calibrate the lensing signal, due to asymmetric effects of (frequently non-Gaussian) photoz errors. We also demonstrate that large-scale structure (LSS) can strongly impact the photoz calibration and its error estimation, due to a correlation between the LSS and the photoz errors, and argue that at least two independent degree-scale spectroscopic samples are needed to suppress its effects. Given the size of our spectroscopic sample, we can reduce the galaxy-galaxy lensing calibration error well below current SDSS statistical errors.

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arXiv2007

The interplay between ionized gas and massive stars in the HII galaxy IIZw70: integral field spectroscopy with PMAS

We performed an integral field spectroscopic study for the HII galaxy IIZw70 in order to investigate the interplay between its ionized interstellar medium (ISM) and the massive star formation (SF). Observations were taken in the optical spectral range (3700-6800 A) with the Potsdam Multi-Aperture Spectrophotometer (PMAS) attached to the 3.5 m telescope at CAHA. We created and analysed maps of spatially distributed emission-lines, continuum emission and properties of the ionized ISM (e.g. physical-chemical conditions, dust extinction, kinematics). We investigated the relation of these properties to the spatial distribution and evolutionary stage of the massive stars. For the first time we have detected the presence of Wolf-Rayet (WR) stars in this galaxy. The peak of the ionized gas emission coincides with the location of the WR bump. The region of the galaxy with lower dust extinction corresponds to the region that shows the lowest values of velocity dispersion and radial velocity. The overall picture suggests that the ISM of this region is being disrupted via photoionization and stellar winds, leading to a spatial decoupling between gas+stars and dust clouds. The bulk of dust appears to be located at the boundaries of the region occupied by the probable ionizing cluster. We also found that this region is associated to the nebular emission in HeII4686 and to the intensity maximum of most emission lines. This indicates that the hard ionizing radiation responsible for the HeII4686 nebular emission can be related to the youngest stars. Within $\sim$ 0.4 x 0.3 kpc^2 in the central burst, we derived O/H using direct determinations of Te[OIII]. We found abundances in the range 12+log(O/H)=7.65-8.05, yielding an error-weighted mean of 12+log(O/H)=7.86 $\pm$0.05.

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arXiv2006

A Spectroscopic Study of the Near-IR [SIII] Lines in a Sample of HII Galaxies: chemical abundances

A detailed spectroscopic study, from lambda 3700 A to 1 um, was performed for a sample of 34 HII galaxies in order to derive fundamental parameters for their HII regions and ionizing sources, as well as gaseous metal abundances. All the spectra included the nebular [SIII]9069,9532 A lines, given their importance in the derivation of the S/H abundance and relevant ionization diagnostics. A systematic method was followed to correct the near-IR [SIII] line fluxes for the effects of the atmospheric transmission.A comparative analysis of the predictions of the empirical abundance indicators R23 and S23 has been performed. The relative hardness of their ionizing sources was studied using the eta parameter, and exploring the role played by metallicity. For 22 galaxies of the sample a direct value of te[SIII] was derived, along with their ionic and total S/H abundances. Their ionic and total O/H abundances were derived using direct determinations of te[OIII].For the rest of the objects, the total S/H abundance was derived using S23. The abundance range covered by our sample goes from 1/20 solar up to solar metallicity. The mean S/O ratio derived is log (S/O)=-1.68+/-0.20 dex, 1 sigma below the solar S/O value. The S/O abundance ratio shows no significant trend with O/H over the range of abundance covered in this work, in agreement with previous findings.There is a trend for HII galaxies with lower gaseous metallicity to present harder ionizing spectra. We compared the distribution of the ionic ratios O+/O++ vs. S+/S++ derived for our sample with the predictions of a grid of photoionization models performed for different stellar effective temperatures. This analysis indicates that a large fraction of galaxies in our sample seem to be ionized by extremely hard spectra.

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arXiv2002

Empirical diagnostics of HII regions based on sulphur emission lines

Spectrophotometry constitutes a unique way to obtain the whole diagnostics (density, temperature, ionic abundances) of ionized gas nebulae, thus providing invaluable information about the objects where they reside. If such nebulae are in the low excitation regime, the diagnostics have to relie on the observation of the more intense emission lines. We have compiled data for a sample of HII regions, GEHR and HII galaxies and compared them with results derived from photoionizacion models whose parameters cover the physical conditions of the nebulae. Our results confirm a lower uncertainty for the diagnostics when using empirical methods based on the strong lines of [SII] and [SIII] replacing and complementing those based on the [OII] and [OIII] lines.

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arXiv1999

An empirical calibration of nebular abundances based on the sulphur emission lines

We present an empirical calibration of nebular abundances based on the strong emission lines of [SII] and [SIII] in the red part of the spectrum through the definition of a sulphur abundance parameter S23. This calibration presents two important advantages against the commonly used one based on the optical oxygen lines: it remains single-valued up to abundances close to solar and is rather independent of the degree of ionization of the nebula.

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