arXiv subjects

Ana I. Ennis

Publications and source records attributed to Ana I. Ennis.

5 recordsLinked to original sources

arXiv2026

The contribution of the color space in LSST-like photometry for the selection of extragalactic globular cluster candidates

Globular clusters (GCs) are excellent tracers of their host galaxies' evolutionary histories. Traditional methods for identifying GCs in galaxies rely on cuts over photometric catalogs and can yield source lists with high levels of contamination from compact background galaxies and foreground stars. In an era when large-scale sky surveys produce photometry for millions of sources, it is essential to employ flexible and scalable tools to reliably identify GCs in external galaxies. To prepare for surveys like Rubin/LSST, we need to explore practical methodological improvements and quantify the limitations inherent in the datasets. This paper investigates the selection of point-like extragalactic GCs exclusively in the $ugrizY$ color space. We use archival data to assemble an LSST-like photometric catalog for the Fornax Cluster containing labeled confirmed GCs, galaxies, and stars. From this catalog, using principal component analysis and non-linear auto-encoders (AEs), we construct inputs to random forest and multi-layer perceptron classifiers. We show that selecting GCs using all the 15 available colors can lead to a minimum contamination rate of ~30%, whereas the use of color-color diagrams may double such rate. If only the first 4 principal components of the colors are used instead, the same minimum contamination rate is achieved without increasing incompleteness. The AEs did not improve GC identification. To further reduce contamination and extract the full potential of LSST for star cluster studies, we argue for the need to augment photometric information with ancillary data (morphology from space-based missions and near-infrared photometry) before attempting to leverage more complex models.

astro-ph.GA↗

arXiv2022

J-PLUS: A catalogue of globular cluster candidates around the M81/M82/NGC3077 triplet of galaxies

Globular clusters (GCs) are proxies of the formation assemblies of their host galaxies. However, few studies exist targeting GC systems of spiral galaxies up to several effective radii. Through 12-band Javalambre Photometric Local Universe Survey (J-PLUS) imaging, we study the point sources around the M81/M82/NGC3077 triplet in search of new GC candidates. We develop a tailored classification scheme to search for GC candidates based on their similarity to known GCs via a principal components analysis (PCA) projection. Our method accounts for missing data and photometric errors. We report 642 new GC candidates in a region of 3.5 deg$^2$ around the triplet, ranked according to their Gaia astrometric proper motions when available. We find tantalising evidence for an overdensity of GC candidate sources forming a bridge connecting M81 and M82. Finally, the spatial distribution of the GC candidates $(g-i)$ colours is consistent with halo/intra-cluster GCs, i.e. it gets bluer as they get further from the closest galaxy in the field. We further employ a regression-tree based model to estimate the metallicity distribution of the GC candidates based on their J-PLUS bands. The metallicity distribution of the sample candidates is broad and displays a bump towards the metal-rich end. Our list increases the population of GC candidates around the triplet by 3-fold, stresses the usefulness of multi-band surveys in finding these objects, and provides a testbed for further studies analysing their spatial distribution around nearby (spirals) galaxies.

astro-ph.GA↗

arXiv2022

Scaling relations for globular cluster systems in early-type galaxies. II. Is there an environmental dependence?

The current properties of globular cluster systems (GCSs) are the result of the evolution experienced by their host galaxies, which shape the richness of the GCS as well as its spatial distribution, among other features. We carry out an analysis of the projected radial distribution of globular clusters for a sample of almost 30 early-type galaxies (ETGs) of intermediate and low luminosity, located in cluster environments (Virgo, Fornax and Coma). We also include in the study six ETGs, for which the parameters of their GCS radial profiles are publicly available. The final analysis is performed on an enlarged sample (~ 100 GCSs), by adding the GCSs of ETGs from our previous paper (Paper I). Scaling relations involving different parameters of the GCSs are obtained for the whole sample and complement those obtained in Paper I. Several of such relations point to a second-order dependence on the environmental density. Finally, the results are analysed in the literature context.

astro-ph.GA↗

arXiv2020

A Gemini/GMOS study of the bright elliptical galaxy NGC 3613 and its globular cluster system

We present the first photometric study of the globular cluster system (GCS) of the E galaxy NGC 3613 (Mv = -21.5, d = 30.1 Mpc), as well as the surface photometry of the host galaxy, based on Gemini/GMOS images. Being considered the central galaxy of a group, NGC 3613 inhabits a low-density environment although its intrinsic brightness is similar to the expected one for galaxies in the centre of clusters. The following characteristics are obtained for this GCS. The colour distribution is bimodal, with metal-poor globular clusters (GCs) getting slightly bluer with increasing radius. The radial and azimuthal projected distributions show that metal-rich GCs are more concentrated towards the host galaxy and trace its light distribution very precisely, while metal-poor GCs present a more extended and uniform distribution. The GC luminosity function helps validate the adopted distance. The estimated total GC population of Ntot= 2075 +/- 130 leads to a specific frequency Sn=5.2 +/- 0.7, a value within the expected range for GCSs with host galaxies of similar luminosity. The surface photometry of NGC 3613 reveals a three-component profile and a noticeable substructure. Finally, a small sample of ultra-compact dwarf (UCD) candidates are identified in the surroundings of the host galaxy.

astro-ph.GA↗

arXiv2019

Scaling relations for globular cluster systems in early-type galaxies

The formation and growth of globular cluster systems (GCSs) is closely related to the evolutionary processes experienced by their host galaxies. In particular, their radial distributions scale with several properties of the galaxies and their halos. We performed a photometric study, by means of HST/ACS archival data of several intermediate luminosity galaxies located in low density environments. It was supplemented with available photometric data of GCSs from the Virgo and Fornax clusters, resulting in a sample of almost 30 GCSs for which we fitted their radial profiles. The resulting overall properties agree with those from previous studies, as we found that the effective radius, extension and concentration of the GCS radial profiles correlate with the stellar mass, effective radius and number of globular clusters, presenting in some cases a bilinear relation. The extension also correlates with the central velocity dispersion for central galaxies, but not for satellites. From a statistical comparison with numerical simulations we obtained good agreement between the effective radius and extension of the GCS scale with the effective and virial radius of the halos, respectively. Finally, we analysed these results in the literature context.

astro-ph.GA↗