arXiv subjects

D. Paraficz

Publications and source records attributed to D. Paraficz.

6 recordsLinked to original sources

arXiv2017

ALMA view of RX J1131-1231: Sub-kpc CO (2-1) mapping of a molecular disk in a lensed star-forming quasar host galaxy

We present ALMA 2-mm continuum and CO (2-1) spectral line imaging of the gravitationally lensed z=0.654 star-forming/quasar composite RX J1131-1231 at 240-400 mas angular resolution. The continuum emission is found to be compact and coincident with the optical emission, whereas the molecular gas forms a complete Einstein ring, which shows strong differential magnification. The de-lensed source structure is determined on 400-pc resolution using a visibility-fitting lens modelling technique. The reconstructed molecular gas velocity-field is consistent with a rotating disk with a maximum rotational velocity of 280 km/s. From dynamical model fitting we find an enclosed mass M(r<5 kpc)=(1.46+/-0.31)*10^11 M_sol. The molecular gas distribution is highly structured, with clumps that are co-incident with higher gas velocity dispersion regions 40-50 km/s and with the intensity peaks in the optical emission, which are associated with sites of on-going turbulent star-formation. The peak in the CO (2-1) distribution is not co-incident with the AGN, where there is a paucity of molecular gas emission, possibly due to radiative feedback from the central engine. The intrinsic molecular gas luminosity is L'_CO=(1.2+/-0.3)*10^10 K km/s pc^2 and the inferred gas mass is M(H2)=(8.3+/-3.0)*10^10 M_sol, which given its dynamical mass is consistent with a CO-H2 conversion factor of alpha = 5.5+/-2.0 M_solar(K km/s pc^2)^-1. This suggests that the star-formation efficiency is dependent on the host galaxy morphology as opposed to the nature of the AGN. The far-infrared continuum spectral energy distribution shows evidence for heated dust, equivalent to an obscured star-formation rate of SFR=69^(+41)_(-25)*(7.3/u_IR)M_sol/yr, which demonstrates the composite star-forming/AGN nature of this system. RX J1131-1231

astro-ph.GA↗

arXiv2016

ASTErIsM - Application of topometric clustering algorithms in automatic galaxy detection and classification

We present a study on galaxy detection and shape classification using topometric clustering algorithms. We first use the DBSCAN algorithm to extract, from CCD frames, groups of adjacent pixels with significant fluxes and we then apply the DENCLUE algorithm to separate the contributions of overlapping sources. The DENCLUE separation is based on the localization of pattern of local maxima, through an iterative algorithm which associates each pixel to the closest local maximum. Our main classification goal is to take apart elliptical from spiral galaxies. We introduce new sets of features derived from the computation of geometrical invariant moments of the pixel group shape and from the statistics of the spatial distribution of the DENCLUE local maxima patterns. Ellipticals are characterized by a single group of local maxima, related to the galaxy core, while spiral galaxies have additional ones related to segments of spiral arms. We use two different supervised ensemble classification algorithms, Random Forest, and Gradient Boosting. Using a sample of ~ 24000 galaxies taken from the Galaxy Zoo 2 main sample with spectroscopic redshifts, and we test our classification against the Galaxy Zoo 2 catalog. We find that features extracted from our pipeline give on average an accuracy of ~ 93%, when testing on a test set with a size of 20% of our full data set, with features deriving from the angular distribution of density attractor ranking at the top of the discrimination power.

astro-ph.IM↗

arXiv2016

The PCA Lens-Finder: application to CFHTLS

We present the results of a new search for galaxy-scale strong lensing systems in CFHTLS Wide. Our lens-finding technique involves a preselection of potential lens galaxies, applying simple cuts in size and magnitude. We then perform a Principal Component Analysis of the galaxy images, ensuring a clean removal of the light profile. Lensed features are searched for in the residual images using the clustering topometric algorithm DBSCAN. We find 1098 lens candidates that we inspect visually, leading to a cleaned sample of 109 new lens candidates. Using realistic image simulations we estimate the completeness of our sample and show that it is independent of source surface brightness, Einstein ring size (image separation) or lens redshift. We compare the properties of our sample to previous lens searches in CFHTLS. Including the present search, the total number of lenses found in CFHTLS amounts to 678, which corresponds to ~4 lenses per square degree down to i=24.8. This is equivalent to ~ 60.000 lenses in total in a survey as wide as Euclid, but at the CFHTLS resolution and depth.

astro-ph.GA↗

arXiv2012

The Bullet cluster at its best: weighing stars, gas and dark matter

We present a new strong lensing mass reconstruction of the Bullet cluster (1E 0657-56) at z=0.296, based on WFC3 and ACS HST imaging and VLT/FORS2 spectroscopy. The strong lensing constraints underwent substantial revision compared to previously published analysis, there are now 14 (six new and eight previously known) multiply-imaged systems, of which three have spectroscopically confirmed redshifts (including one newly measured from this work). The reconstructed mass distribution explicitly included the combination of three mass components: i) the intra-cluster gas mass derived from X-ray observation, ii) the cluster galaxies modeled by their fundamental plane scaling relations and iii) dark matter. The model that includes the intra-cluster gas is the one with the best Bayesian evidence. This model has a total RMS value of 0.158" between the predicted and measured image positions for the 14 multiple images considered. The proximity of the total RMS to resolution of HST/WFC3 and ACS (0.07-0.15" FWHM) demonstrates the excellent precision of our mass model. The derived mass model confirms the spatial offset between the X-ray gas and dark matter peaks. The fraction of the galaxy halos mass to total mass is found to be f_s=11+/-5% for a total mass of 2.5+/-0.1 x 10^14 solar mass within a 250 kpc radial aperture.

astro-ph.CO↗

arXiv2007

The Afterglows of Swift-era Gamma-Ray Bursts. I. Comparing pre-Swift and Swift era Long/Soft (Type II) GRB Optical Afterglows

We have gathered optical photometry data from the literature on a large sample of Swift-era gamma-ray burst (GRB) afterglows including GRBs up to September 2009, for a total of 76 GRBs, and present an additional three pre-Swift GRBs not included in an earlier sample. Furthermore, we publish 840 additional new photometry data points on a total of 42 GRB afterglows, including large data sets for GRBs 050319, 050408, 050802, 050820A, 050922C, 060418, 080413A and 080810. We analyzed the light curves of all GRBs in the sample and derived spectral energy distributions for the sample with the best data quality, allowing us to estimate the host galaxy extinction. We transformed the afterglow light curves into an extinction-corrected z=1 system and compared their luminosities with a sample of pre-Swift afterglows. The results of a former study, which showed that GRB afterglows clustered and exhibited a bimodal distribution in luminosity space, is weakened by the larger sample. We found that the luminosity distribution of the two afterglow samples (Swift-era and pre-Swift) are very similar, and that a subsample for which we were not able to estimate the extinction, which is fainter than the main sample, can be explained by assuming a moderate amount of line-of-sight host extinction. We derived bolometric isotropic energies for all GRBs in our sample, and found only a tentative correlation between the prompt energy release and the optical afterglow luminosity at one day after the GRB in the z=1 system. A comparative study of the optical luminosities of GRB afterglows with echelle spectra (which show a high number of foreground absorbing systems) and those without reveals no indication that the former are statistically significantly more luminous. (abridged)

astro-ph↗

arXiv2006

Microlensing variability in time-delay quasars

We have searched for microlensing variability in the light curves of five gravitationally lensed quasars with well-determined time delays: SBS 1520+530, FBQ 0951+2635, RX J0911+0551, B1600+434 and HE 2149-2745. By comparing the light curve of the leading image with a suitably time offset light curve of a trailing image we find that two (SBS 1520+530 and FBQ 0951+2635) out of the five quasars have significant long-term (years) and short-term (100 days) brightness variations that may be attributed to microlensing.The short-term variations may be due to nanolenses, relativistic hot or cold spots in the quasar accretion disks, or coherent microlensing at large optical depth.

astro-ph↗